The effect of infection and lag screw fixation on the union of membranous bone grafts in a rabbit model.

Science.gov (United States)

Fialkov, J A; Phillips, J H; Walmsley, S L

1994-03-01

Infection complicating craniofacial procedures contributes significantly to patient morbidity and health care costs. The role of fixation materials in this setting remains unclear. As foreign material, does fixation hardware increase patients' susceptibility to developing postoperative infection? Furthermore, once infection is established, should fixation hardware be removed? To answer these questions, we performed an onlay membranous bone grafting procedure to the mandible in 94 New Zealand White rabbits, applied lag-screw fixation in half the animals, and inoculated the wounds with different bacterial doses. We quantified the differential rates of infection and rates of graft union in the presence of infection. The infection rates for the rigidly fixated group were not significantly different from the rates for the nonfixated group for a range of bacterial inoculum doses. There was no significant difference in the rates of resolution of infection and sepsis between the two groups. Gross and histologic assessments revealed a significantly lower union rate for infected grafts when compared with uninfected grafts. Furthermore, grafts rigidly fixated with a lag screw showed a higher rate of union when compared with nonfixated grafts in the presence of infection. In the absence of infection, the union rates for fixated and nonfixated groups did not differ significantly. While fixation hardware has been cited as a risk factor for postoperative infection, we were unable to show that lag-screw fixation contributes to this risk. Although infection impaired the union of membranous bone grafts to the recipient mandible, fixation of the grafts with a lag screw significantly decreased this deleterious effect of infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Lag screw stabilization of a cervical vertebral fracture by use of computed tomography in a horse

International Nuclear Information System (INIS)

Barnes, H.G.; Tucker, R.L.; Grant, B.D.; Roberts, G.D.; Prades, M.

1995-01-01

A traumatic fracture of C2 was diagnosed radiographically in a 1-year-old German Warm-blood stallion. Fracture configuration was difficult to see on survey radiographs. Computed tomography yielded a more accurate assessment of the fracture and facilitated fracture repair with cortical lag screws. Precise screw placement, to avoid spinal cord damage, was obtained by use of computed tomography. Follow-up radiography revealed normal bone healing, and the horse was in dressage schooling 24 months after surgery

Salter-Harris type II metacarpal and metatarsal fracture in three foals. Treatment by minimally-invasive lag screw osteosynthesis combined with external coaptation.

Science.gov (United States)

Klopfenstein Bregger, Micaël D; Fürst, Anton E; Kircher, Patrick R; Kluge, Katharina; Kummer, Martin

2016-05-18

To describe minimally-invasive lag screw osteosynthesis combined with external coaptation for the treatment of Salter-Harris type II third metacarpal and third metatarsal bone fractures. Three foals aged two weeks to four months with a Salter-Harris type II third metacarpal or third metatarsal fracture. Surgery was carried out under general anaesthesia in lateral recumbency. After fracture reduction, the metaphyseal fragment was stabilized with two cortical screws placed in lag fashion under fluoroscopic control. A cast was applied for at least two weeks. All foals had a good outcome with complete fracture healing and return to complete soundness without any angular limb deformity. All foals had moderate transient digital hyperextension after cast removal. Internal fixation of Salter-Harris type II third metacarpal or third metatarsal fractures with two cortical screws in lag fashion, combined with external coaptation provided good stabilization and preserved the longitudinal growth potential of the injured physis.

A lateral approach for screw repair in lag fashion of spiral third metacarpal and metatarsal medial condylar fractures in horses.

Science.gov (United States)

Smith, Lewis C R; Greet, Timothy R C; Bathe, Andrew P

2009-08-01

To describe a lateral approach for screw fixation in lag fashion of simple spiral medial condylar fractures of the third metacarpus/metatarsus (MC3/MT3). Case series. Thoroughbred racehorses (n=9). Nondisplaced medial MC3/MT3 condylar fractures (3 thoracic, 6 pelvic limbs), with mean length 126 mm (range, 91-151 mm) were repaired by internal fixation, under general anesthesia, using multiple 4.5 mm cortical screws inserted in lag fashion from the lateral aspect of the limb, using radiographic or fluoroscopic guidance. Horses were recovered from anesthesia in half-limb casts; 7 unassisted and 2 using a rope-recovery system. Horses had 2 months box rest, 1 month in-hand walking, and follow-up radiographic examination at 3 months. Horses recovered uneventfully from anesthesia. Five horses raced; 1 returned to training, was persistently lame, and was retired to stud; 2 were retired directly to stud; and 1 horse was lost to follow-up. MC3/MT3 medial condylar fractures were successfully repaired by screws inserted n lag fashion form the lateral aspect. Use of a lateral approach to medial condylar MC3/MT3 fractures allows screw insertion perpendicular to the fracture plane without interference with palmar/plantar soft tissue structures or from the splint bones. Although repair was performed under general anesthesia, the technique should be adaptable to application in standing horses.

Dual head screw hip nailing for trochanteric fractures

Science.gov (United States)

Mavrogenis, Andreas F.; Igoumenou, Vasilios G.; Megaloikonomos, Panayiotis D.; Panagopoulos, George N.; Galanopoulos, Ioannis P.; Vottis, Christos Th.; Karamanis, Eirinaios; Koulouvaris, Panayiotis; Papagelopoulos, Panayiotis J.

2017-01-01

Introduction: There are limited information and inconclusive results for dual head screw intramedullary hip nails for trochanteric fractures. Therefore, we performed a prospective study to evaluate the healing of fractures, and survival, function, and complications of patients operated with this implant. Methods: We prospectively studied 79 patients (61 women and 18 men; mean age: 84.7 years; range: 65–96 years) with a low-energy trochanteric fracture, treated with a dual head screw intramedullary hip nail from 2013 to 2016. The mean follow-up was 2.1 years (range: 1–3 years); seven patients were lost to follow up. This left 72 patients for further analysis. We evaluated the healing of fractures, and survival, function, and complications of patients. Results: Fracture healing was evident in 70 patients (97.2%) at 2–3 months postoperatively. One patient experienced cut-out and z-effect phenomenon of the head screws. Another patient experienced a periprosthetic femoral diaphysis fracture at the distal tip of the nail. A third patient experienced an acute postoperative superficial skin infection that was treated successfully with wound dressing changes and a course of antibiotics. Sixteen patients (22.2%) deceased within 12 months postoperatively. In the remaining patients, the Harris Hip Score (HHS) at 12 months postoperatively was excellent in 16 (28.6%), good in 23 (41.1%), fair in 10 (17.8%), and poor in 7 patients (12.5%). The function declined after the patients’ fracture. Fair and poor results were related to age > 85 years, poor pre-fracture level of function, and AO/OTA-31-A3 fracture types. Conclusion: The dual head screw intramedullary hip nail is associated with high healing and low complication rates for intertrochanteric fractures. The function of the patients is good or excellent in most cases; however, it declines, especially for those patients with age > 85 years, poor pre-fracture level of function, and AO/OTA-31-A3 fracture types

Dual head screw hip nailing for trochanteric fractures

Directory of Open Access Journals (Sweden)

Mavrogenis Andreas F.

2017-01-01

Full Text Available Introduction: There are limited information and inconclusive results for dual head screw intramedullary hip nails for trochanteric fractures. Therefore, we performed a prospective study to evaluate the healing of fractures, and survival, function, and complications of patients operated with this implant. Methods: We prospectively studied 79 patients (61 women and 18 men; mean age: 84.7 years; range: 65–96 years with a low-energy trochanteric fracture, treated with a dual head screw intramedullary hip nail from 2013 to 2016. The mean follow-up was 2.1 years (range: 1–3 years; seven patients were lost to follow up. This left 72 patients for further analysis. We evaluated the healing of fractures, and survival, function, and complications of patients. Results: Fracture healing was evident in 70 patients (97.2% at 2–3 months postoperatively. One patient experienced cut-out and z-effect phenomenon of the head screws. Another patient experienced a periprosthetic femoral diaphysis fracture at the distal tip of the nail. A third patient experienced an acute postoperative superficial skin infection that was treated successfully with wound dressing changes and a course of antibiotics. Sixteen patients (22.2% deceased within 12 months postoperatively. In the remaining patients, the Harris Hip Score (HHS at 12 months postoperatively was excellent in 16 (28.6%, good in 23 (41.1%, fair in 10 (17.8%, and poor in 7 patients (12.5%. The function declined after the patients’ fracture. Fair and poor results were related to age > 85 years, poor pre-fracture level of function, and AO/OTA-31-A3 fracture types. Conclusion: The dual head screw intramedullary hip nail is associated with high healing and low complication rates for intertrochanteric fractures. The function of the patients is good or excellent in most cases; however, it declines, especially for those patients with age > 85 years, poor pre-fracture level of function, and AO/OTA-31-A3

[A clinical study on the relationship of the tail femur distance and the lag screw migration or cutting-out after the third generation of Gamma nail fixation of intertrochanteric fracture].

Science.gov (United States)

Hou, Yu; Yao, Qi; Zhang, Gen'ai; Ding, Lixiang

2018-01-01

To confirm the association between tail femur distance (TFD) and lag screw migration or cutting-out in the treatment of intertrochanteric fracture with the third generation of Gamma nail (TGN). The clinical data of 124 cases of intertrochanteric fracture treated with TGN internal fixation and followed up more than 18 months between January 2012 and December 2015 were reviewed and analyzed. There were 52 males and 72 females, with an age of 46-93 years (mean, 78.5 years). According to AO/Association for the Study of Internal Fixation (AO/ASIF) classification, 43 cases were type 31-A1, 69 cases were type 31-A2, and 12 cases were type 31-A3. The time from injury to operation was 1-10 days (mean, 2.9 days). According to the fracture healing of the patients, the patients were divided into the healing group and failure group. The age, gender, height, bone mineral density (BMD), fracture AO/ASIF classification, the time from injury to operation, and the TFD value at 1 day after operation were recorded and compared. The risk factors for the migration or cutting-out of lag screw were analyzed by logistic regression. There were 111 cases in healing group, the healing time was 80-110 days (mean, 95.5 days). There were 13 cases in failure group, including 2 cases of lag screw cutting-out and 11 cases of significant migration. Except for the TFD value at 1 day after operation in failure group was significantly higher than that in the healing group( t =5.14, P =0.00), there was no significant difference in gender, age, height, BMD, fracture of AO/ASIF classification, and the time from injury to operation ( P >0.05) between 2 groups. logistic regression analysis showed that TFD value was a risk factor for the migration or cutting-out of lag screw (B=1.22, standardized coefficient=0.32, Wald χ 2 =14.66, P =0.00, OR=3.37). The patients with higher TFD value had higher risk of postoperative lag screw migration or cutting-out. This result indicates that the appropriate length of the

Dual small fragment plating improves screw-to-screw load sharing for mid-diaphyseal humeral fracture fixation: a finite element study.

Science.gov (United States)

Kosmopoulos, Victor; Luedke, Colten; Nana, Arvind D

2015-01-01

A smaller humerus in some patients makes the use of a large fragment fixation plate difficult. Dual small fragment plate constructs have been suggested as an alternative. This study compares the biomechanical performance of three single and one dual plate construct for mid-diaphyseal humeral fracture fixation. Five humeral shaft finite element models (1 intact and 4 fixation) were loaded in torsion, compression, posterior-anterior (PA) bending, and lateral-medial (LM) bending. A comminuted fracture was simulated by a 1-cm gap. Fracture fixation was modelled by: (A) 4.5-mm 9-hole large fragment plate (wide), (B) 4.5-mm 9-hole large fragment plate (narrow), (C) 3.5-mm 9-hole small fragment plate, and (D) one 3.5-mm 9-hole small fragment plate and one 3.5-mm 7-hole small fragment plate. Model A showed the best outcomes in torsion and PA bending, whereas Model D outperformed the others in compression and LM bending. Stress concentrations were located near and around the unused screw holes for each of the single plate models and at the neck of the screws just below the plates for all the models studied. Other than in PA bending, Model D showed the best overall screw-to-screw load sharing characteristics. The results support using a dual small fragment locking plate construct as an alternative in cases where crutch weight-bearing (compression) tolerance may be important and where anatomy limits the size of the humerus bone segment available for large fragment plate fixation.

Biomechanical evaluation of bending strength of spinal pedicle screws, including cylindrical, conical, dual core and double dual core designs using numerical simulations and mechanical tests.

Science.gov (United States)

Amaritsakul, Yongyut; Chao, Ching-Kong; Lin, Jinn

2014-09-01

Pedicle screws are used for treating several types of spinal injuries. Although several commercial versions are presently available, they are mostly either fully cylindrical or fully conical. In this study, the bending strengths of seven types of commercial pedicle screws and a newly designed double dual core screw were evaluated by finite element analyses and biomechanical tests. All the screws had an outer diameter of 7 mm, and the biomechanical test consisted of a cantilever bending test in which a vertical point load was applied using a level arm of 45 mm. The boundary and loading conditions of the biomechanical tests were applied to the model used for the finite element analyses. The results showed that only the conical screws with fixed outer diameter and the new double dual core screw could withstand 1,000,000 cycles of a 50-500 N cyclic load. The new screw, however, exhibited lower stiffness than the conical screw, indicating that it could afford patients more flexible movements. Moreover, the new screw produced a level of stability comparable to that of the conical screw, and it was also significantly stronger than the other screws. The finite element analysis further revealed that the point of maximum tensile stress in the screw model was comparable to the point at which fracture occurred during the fatigue test. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.

Definition of a safe zone for antegrade lag screw fixation of fracture of posterior column of the acetabulum by 3D technology.

Science.gov (United States)

Feng, Xiaoreng; Zhang, Sheng; Luo, Qiang; Fang, Jintao; Lin, Chaowen; Leung, Frankie; Chen, Bin

2016-03-01

The objective of this study was to define a safe zone for antegrade lag screw fixation of fracture of posterior column of the acetabulum using a novel 3D technology. Pelvic CT data of 59 human subjects were obtained to reconstruct three-dimensional (3D) models. The transparency of 3D models was then downgraded along the axial perspective (the view perpendicular to the cross section of the posterior column axis) to find the largest translucent area. The outline of the largest translucent area was drawn on the iliac fossa. The line segments of OA, AB, OC, CD, the angles of OAB and OCD that delineate the safe zone (ABDC) were precisely measured. The resultant line segments OA, AB, OC, CD, and angles OAB and OCD were 28.46mm(13.15-44.97mm), 45.89mm (34.21-62.85mm), 36.34mm (18.68-55.56mm), 53.08mm (38.72-75.79mm), 37.44° (24.32-54.96°) and 55.78° (43.97-79.35°) respectively. This study demonstrates that computer-assisted 3D modelling techniques can aid in the precise definition of the safe zone for antegrade insertion of posterior column lag screws. A full-length lag screw can be inserted into the zone (ABDC), permitting a larger operational error. Copyright © 2016 Elsevier Ltd. All rights reserved.

Post wall fixation by lag screw only in associated both column fractures with posterior wall involvement.

Science.gov (United States)

Wang, Hu; Utku, Kandemir; Zhuang, Yan; Zhang, Kun; Fu, Ya-Hui; Wei, Xing; Wang, Peng-Fei; Cong, Yu-Xuan; Lei, Jin-Lai; Zhang, Bin-Fei

2017-07-01

To evaluate the quality of reduction, clinical outcomes and complications of associated both column acetabular fractures with posterior wall involvement that are treated through single ilioinguinal approach and fixation of posterior wall by lag screws only. We conducted a retrospective review involving ninety-nine consecutive patients with associated both column fractures of acetabulum treated through single ilioinguinal approach. Patients were divided into two groups. The first group consisted of 35 patients presented with both column fractures with posterior wall involvement that fixation performed with lag screws. This group was compared to a second group of 64 patients with both column fractures without posterior wall involvement. The quality of reduction was assessed using criteria described by Matta. The size of posterior wall fragment was measured. Functional outcome was evaluated using Modified Postel Merle D'Aubigne score. Radiographs at the latest follow up were analyzed for arthritis (Kellgren-Lawrence classification), and femoral head avascular necrosis (Ficat/Arlet classification). The study showed no significant differences in all preoperative variables (P>0.05). While intraoperative blood loss and operative time in group 1 were increased compared to group 2, the difference was not statistically significant (P>0.05). The height, relative depth and peripheral length of posterior wall respectively were 27.8±2.5mm (range: 24-35mm), 71.5±5.4% (range: 65-88%), 23.0±2.3mm (range: 17-28mm). The mean posterior wall fracture displacement is 5.0±3.2mm (range: 0-11mm). There was no difference regarding the quality of reduction between the two groups (P>0.05). The excellent to good clinical outcome was around 71.4% in the group 1 versus 73.4% in the group 2 at the final follow-up, this difference was not statistically significant (P>0.05). There was no difference in rate of complications between the two groups (P>0.05). Lag screws fixation of posterior wall

Outcome of lag-screw treatment of incomplete fractures of the frontal plane of the radial facet of the third carpal bone in horses.

Science.gov (United States)

Rutherford, D J; Bladon, B; Rogers, C W

2007-04-01

To describe outcomes for horses diagnosed with incomplete, non-displaced fractures of the frontal plane of the radial facet (INFR) of the third carpal bone (C3) treated by placement of a lag screw across the fracture under arthroscopic guidance. Horses (n=13) diagnosed with INFR and treated between December 1999 and January 2005 using a lag screw placed over the fracture were studied. For each case, five horses matched for sire, age and sex which were not known to have INFR were sought for comparison. Racing performance data were collected from a commercial online database. The racing performance of cases pre- and post-operatively, and of cases and matched horses in the post-operative period was compared. Sixteen INFR were found in the 13 horses. Radiographic evidence of healed fracture lines 2-4 months after surgery was seen in 11/16 (69%) fractures; 11/13 (85%) cases raced again after a median recovery period of 292 (range 149-681) days. Treatment was considered successful in 9/13 (69%) cases, which were still in training or had been retired for reasons other than lameness localised to the middle carpal joint at the end of the study period. Just 6/13 (46%) cases had raced prior to injury. The racing ability pre- and post-operatively of five cases was compared, three (60%) of which performed better post-operatively than they had before. There was no significant difference in racing longevity or ability post-operatively between patients and matched (control) horses. Post-operatively, there was little difference in the racing performance between horses diagnosed with INFR which had a lag screw placed across the fracture line and horses matched for sire, age and sex which were not known to have INFR. Horses which were diagnosed with INFR of C3 and had a lag screw placed across the fracture had a good prognosis for future racing performance.

A Biomechanical Analysis of 2 Constructs for Metacarpal Spiral Fracture Fixation in a Cadaver Model: 2 Large Screws Versus 3 Small Screws.

Science.gov (United States)

Eu-Jin Cheah, Andre; Behn, Anthony W; Comer, Garet; Yao, Jeffrey

2017-12-01

Surgeons confronted with a long spiral metacarpal fracture may choose to fix it solely with lagged screws. A biomechanical analysis of a metacarpal spiral fracture model was performed to determine whether 3 1.5-mm screws or 2 2.0-mm screws provided more stability during bending and torsional loading. Second and third metacarpals were harvested from 12 matched pairs of fresh-frozen cadaveric hands and spiral fractures were created. One specimen from each matched pair was fixed with 2 2.0-mm lagged screws whereas the other was fixed with 3 1.5-mm lagged screws. Nine pairs underwent combined cyclic cantilever bending and axial compressive loading followed by loading to failure. Nine additional pairs were subjected to cyclic external rotation while under a constant axial compressive load and were subsequently externally rotated to failure under a constant axial compressive load. Paired t tests were used to compare cyclic creep, stiffness, displacement, rotation, and peak load levels. Average failure torque for all specimens was 7.2 ± 1.7 Nm. In cyclic torsional testing, the group with 2 screws exhibited significantly less rotational creep than the one with 3 screws. A single specimen in the group with 2 screws failed before cyclic bending tests were completed. No other significant differences were found between test groups during torsional or bending tests. Both constructs were biomechanically similar except that the construct with 2 screws displayed significantly less loosening during torsional cyclic loading, although the difference was small and may not be clinically meaningful. Because we found no obvious biomechanical advantage to using 3 1.5-mm lagged screws to fix long spiral metacarpal fractures, the time efficiency and decreased implant costs of using 2-2.0 mm lagged screws may be preferred. Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

The effect of infection and lag screw fixation on revascularization and new bone deposition in membranous bone grafts in a rabbit model.

Science.gov (United States)

Fialkov, J A; Phillips, J H; Walmsley, S L; Morava-Protzner, I

1996-08-01

We have suggested that rigid fixation of membranous bone grafts in the presence of infection may improve graft-recipient bone union by facilitating graft revascularzation. To test this hypothesis, we grafted autogenous membranous bone grafts to the mandibles of 94 New Zealand White rabbits. Lag screw fixation was applied in half the animals. The wounds were inoculated with a range of Staphylococcus aureus doses. Infected and noninfected rabbits were injected weekly over a 5-week course with fluorescein bone markers and with a marker of vascular endothelium (procion red) just prior to sacrifice. Revascularization and new bone deposition in the grafts were then quantified histologically for the 75 rabbits available for data collection. Infection decreased the amount of graft revascularized and the amount of new bone deposited for both rigidly fixated and nonfixated grafts. Grafts fixated with a lag screw showed a greater amount of revascularization and new bone deposition in the presence and absence of infection when compared with nonfixated grafts, supporting the hypothesis that rigid fixation of membranous bone grafts in the presence of infection may promote graft survival and union by improving revascularization and osteogenesis within the graft.

Cerclage wire and lag screw fixation of the lateral malleolus in supination and external rotation fractures of the ankle.

Science.gov (United States)

Bajwa, Amarjit S; Gantz, D E

2005-01-01

Wound dehiscence and exposed lateral hardware can occur after open reduction internal fixation of lateral malleolus. The bulk of a lateral plate and the minimum soft tissue over the lateral malleolus may contribute to this situation. The objective of this study was to evaluate a series of patients with lateral malleolar fractures treated with operative reduction using minimal hardware. We wanted to observe whether there was any loss of reduction and whether there were any incidences of soft tissue disruption. Fifty-two patients with long spiral fracture of the lateral malleolus in a supination-external rotation injury were treated with two or three 3.5-mm lag screws inserted 1 cm apart and 1 or 2 circlage wires. Less rigid fixation was supplemented with a below-the-knee plaster cast. All patients were followed up until clinical and radiological evidence of fracture healing at 6, 10, and 14 weeks postoperatively. By 10 weeks, all patients were full weight bearing, although most patients still limped. At 14 weeks' follow-up, there were no infections or wound dehiscences. All patients were able to return to their activities of daily living. All the fractures had united without loss of original position. Two fractures of the posterior bone spikes seen during surgery united uneventfully. Long spiral fractures of the lateral malleolus of the ankle can be treated successfully with 2 or 3 lag screws and circlage wires without compromising the outcome of the fracture healing.

Accurate guide wire of lag screw placement in the intertrochanteric fractures: a technical note.

Science.gov (United States)

Li, Jiang; Wang, Liao; Li, Xiaodong; Feng, Kai; Tang, Jian; Wang, Xiaoqing

2017-09-01

Cephalomedullary fixations are commonly used in the treatment of intertrochanteric fractures. In clinical practice, one of the difficulties is when we exit the guide wire in a wrong position of femoral neck and insert near the hole again, the guide wire often flow into the previous track. This study develops a surgical technique to direct the guide wire to slip away the previous track and slip into a right position. When guide wire is exited to the cortex of femoral, we let the wire in and out at the cortical layer for several times to enlarge the entry hole. After that, electric drill is inverted, rubbed and entered slowly at a right angle. When guide wire encountered new resistance, the electric drill is turned back instantly. This technique can help trauma and orthopedic surgeons to obtain precision placement of the lag screw after the first try is failed.

Biomechanical comparison of 3.0 mm headless compression screw and 3.5 mm cortical bone screw in a canine humeral condylar fracture model.

Science.gov (United States)

Gonsalves, Mishka N; Jankovits, Daniel A; Huber, Michael L; Strom, Adam M; Garcia, Tanya C; Stover, Susan M

2016-09-20

To compare the biomechanical properties of simulated humeral condylar fractures reduced with one of two screw fixation methods: 3.0 mm headless compression screw (HCS) or 3.5 mm cortical bone screw (CBS) placed in lag fashion. Bilateral humeri were collected from nine canine cadavers. Standardized osteotomies were stabilized with 3.0 mm HCS in one limb and 3.5 mm CBS in the contralateral limb. Condylar fragments were loaded to walk, trot, and failure loads while measuring construct properties and condylar fragment motion. The 3.5 mm CBS-stabilized constructs were 36% stiffer than 3.0 mm HCS-stabilized constructs, but differences were not apparent in quality of fracture reduction nor in yield loads, which exceeded expected physiological loads during rehabilitation. Small residual fragment displacements were not different between CBS and HCS screws. Small fragment rotation was not significantly different between screws, but was weakly correlated with moment arm length (R² = 0.25). A CBS screw placed in lag fashion provides stiffer fixation than an HCS screw, although both screws provide similar anatomical reduction and yield strength to condylar fracture fixation in adult canine humeri.

Generalized viscothermoelasticity theory of dual-phase-lagging model for damping analysis in circular micro-plate resonators

Science.gov (United States)

Grover, D.; Seth, R. K.

2018-05-01

Analysis and numerical results are presented for the thermoelastic dissipation of a homogeneous isotropic, thermally conducting, Kelvin-Voigt type circular micro-plate based on Kirchhoff's Love plate theory utilizing generalized viscothermoelasticity theory of dual-phase-lagging model. The analytical expressions for thermoelastic damping of vibration and frequency shift are obtained for generalized dual-phase-lagging model and coupled viscothermoelastic plates. The scaled thermoelastic damping has been illustrated in case of circular plate and axisymmetric circular plate for fixed aspect ratio for clamped and simply supported boundary conditions. It is observed that the damping of vibrations significantly depend on time delay and mechanical relaxation times in addition to thermo-mechanical coupling in circular plate under resonance conditions and plate dimensions.

Avulsion Fracture of the Calcaneus Treated With a Soft Anchor Bridge and Lag Screw Technique: A Report of Two Cases.

Science.gov (United States)

Yoshida, Kazushige; Kasama, Kentaro; Akahane, Tsutomu

2016-01-01

The displaced extra-articular avulsion fracture of the calcaneus has been classified as a Böhler type 1c calcaneal fracture, and most cases will require surgical repair. In the present report, we describe 2 patients in whom we performed the soft anchor bridge technique using single loaded suture anchors with lag screws for the repair of Böhler type 1c avulsion fractures of the calcaneus. In one of these patients, clinically relevant osteoporosis complicated the injury. In both cases, bone union was achieved, and by 1.5 months after surgery satisfactory recovery was observed. To our knowledge, the soft anchor bridge technique was first used for the treatment of rotator cuff tears, and the greatest merit of this technique is the ability to generate vertical compression force to the pulled out rotator cuff through the use of knotting sutures. In recent years, the soft anchor bridge technique using 4 suture anchors has also been used for fractures of the greater tuberosity of the humerus, an injury that poses operative difficulties similar to those encountered with an avulsion fracture of the calcaneus owing to the traction force of the rotator cuff and relative weakness of adjacent bone. The outcomes of our patients suggest that the soft anchor bridge technique combined with adjunct lag screws is useful in the fixation of avulsion fractures of the calcaneus. In addition, the result in the elderly patient indicates the possibility of using this technique for patients with osteoporosis. Copyright © 2016 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

A numerical study on dual-phase-lag model of bio-heat transfer during hyperthermia treatment.

Science.gov (United States)

Kumar, P; Kumar, Dinesh; Rai, K N

2015-01-01

The success of hyperthermia in the treatment of cancer depends on the precise prediction and control of temperature. It was absolutely a necessity for hyperthermia treatment planning to understand the temperature distribution within living biological tissues. In this paper, dual-phase-lag model of bio-heat transfer has been studied using Gaussian distribution source term under most generalized boundary condition during hyperthermia treatment. An approximate analytical solution of the present problem has been done by Finite element wavelet Galerkin method which uses Legendre wavelet as a basis function. Multi-resolution analysis of Legendre wavelet in the present case localizes small scale variations of solution and fast switching of functional bases. The whole analysis is presented in dimensionless form. The dual-phase-lag model of bio-heat transfer has compared with Pennes and Thermal wave model of bio-heat transfer and it has been found that large differences in the temperature at the hyperthermia position and time to achieve the hyperthermia temperature exist, when we increase the value of τT. Particular cases when surface subjected to boundary condition of 1st, 2nd and 3rd kind are discussed in detail. The use of dual-phase-lag model of bio-heat transfer and finite element wavelet Galerkin method as a solution method helps in precise prediction of temperature. Gaussian distribution source term helps in control of temperature during hyperthermia treatment. So, it makes this study more useful for clinical applications. Copyright © 2015 Elsevier Ltd. All rights reserved.

Surgical repair of propagating condylar fractures of the third metacarpal/metatarsal bones with cortical screws placed in lag fashion in 26 racehorses (2007-2015).

Science.gov (United States)

Moulin, N; François, I; Coté, N; Alford, C; Cleary, O; Desjardins, M R

2018-01-19

Despite the recommendation of plate fixation for propagating condylar fractures of the third metacarpal (McIII) or third metatarsal bone (MtIII), lag screw fixation can be a viable surgical option. To evaluate short-term outcome and long-term racing performance of horses that underwent lag screw fixation of long condylar fractures of the McIII/MtIII. Retrospective case series. Medical records, post-surgical racing performance and outcome of 26 horses with propagating fractures of the medial and/or lateral condyle of McIII/MtIII were reviewed. Medical information included were age, breed, sex, physical examination at admission, circumstances of fracture, radiographic evaluation, anaesthesia and recovery records, surgical and post-operative management, as well as complications. Outcome included racing data and information from telephone interviews. Twenty-six horses (9 Standardbreds and 17 Thoroughbreds) were admitted with a long condylar fracture of the McIII/MtIII. Fore- and hindlimbs were equally represented with the left hindlimb being more frequently involved. Most of the fractures had a spiralling component (76%) and four (15%) were comminuted. Fifteen (58%) horses raced post-surgery including nine Standardbreds (100%) and six Thoroughbreds (35%). Twelve of them were placed in at least one race and 11 won at least once. One horse sustained a severe complication in recovery. No significant difference was observed in the racing performances before and after surgery. Follow-up method and duration were not standardised and there is a low number of cases with six surgeons. Long condylar fractures can be repaired using lag fashion technique combined with a half-limb or full-limb tight cast for recovery as a good surgical alternative. Similar results to plate fixation can be expected, with a return to racing of more than 50%, and the prognosis being even better for pacers. © 2018 EVJ Ltd.

Effects of Print Publication Lag in Dual Format Journals on Scientometric Indicators

Science.gov (United States)

Heneberg, Petr

2013-01-01

Background Publication lag between manuscript submission and its final publication is considered as an important factor affecting the decision to submit, the timeliness of presented data, and the scientometric measures of the particular journal. Dual-format peer-reviewed journals (publishing both print and online editions of their content) adopted a broadly accepted strategy to shorten the publication lag: to publish the accepted manuscripts online ahead of their print editions, which may follow days, but also years later. Effects of this widespread habit on the immediacy index (average number of times an article is cited in the year it is published) calculation were never analyzed. Methodology/Principal Findings Scopus database (which contains nearly up-to-date documents in press, but does not reveal citations by these documents until they are finalized) was searched for the journals with the highest total counts of articles in press, or highest counts of articles in press appearing online in 2010–2011. Number of citations received by the articles in press available online was found to be nearly equal to citations received within the year when the document was assigned to a journal issue. Thus, online publication of in press articles affects severely the calculation of immediacy index of their source titles, and disadvantages online-only and print-only journals when evaluating them according to the immediacy index and probably also according to the impact factor and similar measures. Conclusions/Significance Caution should be taken when evaluating dual-format journals supporting long publication lag. Further research should answer the question, on whether the immediacy index should be replaced by an indicator based on the date of first publication (online or in print, whichever comes first) to eliminate the problems analyzed in this report. Information value of immediacy index is further questioned by very high ratio of authors’ self-citations among the

Computer-assisted surgery for screw insertion into the distal sesamoid bone in horses: an in vitro study.

Science.gov (United States)

Gygax, Diego; Lischer, Christoph; Auer, Joerg A

2006-10-01

To compare the precision of computer-assisted surgery with a conventional technique (CV) using a special guiding device for screw insertion into the distal sesamoid bone in horses. In vitro experimental study. Cadaveric forelimb specimens. Insertion of a 3.5 mm cortex screw in lag fashion along the longitudinal axis of intact (non-fractured) distal sesamoid bones was evaluated in 2 groups (8 limbs each): CV and computer-assisted surgery (CAS). For CV, the screw was inserted using a special guiding device and fluoroscopy, whereas for CAS, the screw was inserted using computer-assisted navigation. The accuracy of screw placement was verified by radiography, computed tomography, and specimen dissection. Surgical precision was better in CAS compared with CV. CAS improves the accuracy of lateromedial screw insertion, in lag fashion, into the distal sesamoid bone. The CAS technique should be considered for improved accuracy of screw insertion in fractures of the distal sesamoid bone.

Two-temperature theory in magneto-thermoelasticity with fractional order dual-phase-lag heat transfer

Energy Technology Data Exchange (ETDEWEB)

Ezzat, Magdy A., E-mail: maezzat2000@yahoo.com [Department of Mathematics, Faculty of Sciences and Letters in Al Bukayriyyah, Al-Qassim University, Al-Qassim (Saudi Arabia); El-Karamany, Ahmed S., E-mail: qaramani@gmail.com [Department of Mathematical and Physical Sciences, Nizwa University, P.O. Box 1357, Nizwa 611 (Oman); Ezzat, Shereen M. [Department of Mathematics, Faculty of Sciences and Letters in Al Bukayriyyah, Al-Qassim University, Al-Qassim (Saudi Arabia)

2012-11-15

Highlights: Black-Right-Pointing-Pointer We model fractional order dual-phase-lag heat conduction law. Black-Right-Pointing-Pointer We applied the model on a perfect conducting half-space of elastic material. Black-Right-Pointing-Pointer Some theories of generalized thermoelasticity follow as limit cases. Black-Right-Pointing-Pointer State space approach is adopted for the solution of one-dimensional problems. Black-Right-Pointing-Pointer The model will improve the efficiency of thermoelectric material. - Abstract: A new mathematical model of two-temperature magneto-thermoelasticity is constructed where the fractional order dual-phase-lag heat conduction law is considered. The state space approach developed in Ezzat (2008) is adopted for the solution of one-dimensional application for a perfect conducting half-space of elastic material, which is thermally shocked in the presence of a transverse magnetic field. The Laplace transform technique is used. A numerical method is employed for the inversion of the Laplace transforms. According to the numerical results and its graphs, conclusion about the new theory has been constructed. Some theories of generalized thermoelasticity follow as limit cases. Some comparisons have been shown in figures to estimate effects of temperature discrepancy and fractional order parameter on all the studied fields.

Suppression of surface-originated gate lag by a dual-channel AlN/GaN high electron mobility transistor architecture

Science.gov (United States)

Deen, David A.; Storm, David F.; Scott Katzer, D.; Bass, R.; Meyer, David J.

2016-08-01

A dual-channel AlN/GaN high electron mobility transistor (HEMT) architecture is demonstrated that leverages ultra-thin epitaxial layers to suppress surface-related gate lag. Two high-density two-dimensional electron gas (2DEG) channels are utilized in an AlN/GaN/AlN/GaN heterostructure wherein the top 2DEG serves as a quasi-equipotential that screens potential fluctuations resulting from distributed surface and interface states. The bottom channel serves as the transistor's modulated channel. Dual-channel AlN/GaN heterostructures were grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. HEMTs fabricated with 300 nm long recessed gates demonstrated a gate lag ratio (GLR) of 0.88 with no degradation in drain current after bias stressed in subthreshold. These structures additionally achieved small signal metrics ft/fmax of 27/46 GHz. These performance results are contrasted with the non-recessed gate dual-channel HEMT with a GLR of 0.74 and 82 mA/mm current collapse with ft/fmax of 48/60 GHz.

Percutaneous Intramedullary Screw Fixation of Distal Fibula Fractures: A Case Series and Systematic Review

NARCIS (Netherlands)

Loukachov, Vladimir V.; Birnie, Merel F. N.; Dingemans, Siem A.; de Jong, Vincent M.; Schepers, Tim

2017-01-01

The current reference standard for unstable ankle fractures is open reduction and internal fixation using a plate and lag screws. This approach requires extensive dissection and wound complications are not uncommon. The use of intramedullary screw fixation might overcome these issues. The aim of our

Suppression of surface-originated gate lag by a dual-channel AlN/GaN high electron mobility transistor architecture

International Nuclear Information System (INIS)

Deen, David A.; Storm, David F.; Scott Katzer, D.; Bass, R.; Meyer, David J.

2016-01-01

A dual-channel AlN/GaN high electron mobility transistor (HEMT) architecture is demonstrated that leverages ultra-thin epitaxial layers to suppress surface-related gate lag. Two high-density two-dimensional electron gas (2DEG) channels are utilized in an AlN/GaN/AlN/GaN heterostructure wherein the top 2DEG serves as a quasi-equipotential that screens potential fluctuations resulting from distributed surface and interface states. The bottom channel serves as the transistor's modulated channel. Dual-channel AlN/GaN heterostructures were grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. HEMTs fabricated with 300 nm long recessed gates demonstrated a gate lag ratio (GLR) of 0.88 with no degradation in drain current after bias stressed in subthreshold. These structures additionally achieved small signal metrics f_t/f_m_a_x of 27/46 GHz. These performance results are contrasted with the non-recessed gate dual-channel HEMT with a GLR of 0.74 and 82 mA/mm current collapse with f_t/f_m_a_x of 48/60 GHz.

Suppression of surface-originated gate lag by a dual-channel AlN/GaN high electron mobility transistor architecture

Energy Technology Data Exchange (ETDEWEB)

Deen, David A., E-mail: david.deen@alumni.nd.edu; Storm, David F.; Scott Katzer, D.; Bass, R.; Meyer, David J. [Naval Research Laboratory, Electronics Science and Technology Division, Washington, DC 20375 (United States)

2016-08-08

A dual-channel AlN/GaN high electron mobility transistor (HEMT) architecture is demonstrated that leverages ultra-thin epitaxial layers to suppress surface-related gate lag. Two high-density two-dimensional electron gas (2DEG) channels are utilized in an AlN/GaN/AlN/GaN heterostructure wherein the top 2DEG serves as a quasi-equipotential that screens potential fluctuations resulting from distributed surface and interface states. The bottom channel serves as the transistor's modulated channel. Dual-channel AlN/GaN heterostructures were grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. HEMTs fabricated with 300 nm long recessed gates demonstrated a gate lag ratio (GLR) of 0.88 with no degradation in drain current after bias stressed in subthreshold. These structures additionally achieved small signal metrics f{sub t}/f{sub max} of 27/46 GHz. These performance results are contrasted with the non-recessed gate dual-channel HEMT with a GLR of 0.74 and 82 mA/mm current collapse with f{sub t}/f{sub max} of 48/60 GHz.

Retrograde lag screw placement in anterior acetabular column with regard to the anterior pelvic plane and midsagittal plane -- virtual mapping of 260 three-dimensional hemipelvises for quantitative anatomic analysis.

Science.gov (United States)

Ochs, Bjoern Gunnar; Stuby, Fabian Maria; Ateschrang, Atesch; Stoeckle, Ulrich; Gonser, Christoph Emanuel

2014-10-01

Percutaneous screw placement can be used for minimally invasive treatment of none or minimally displaced fractures of the anterior column. The complex pelvic geometry can pose a major challenge even for experienced surgeons. The present study examined the preformed bone stock of the anterior column in 260 hemipelvises (130 male and 130 female). Screws were virtually implanted using iPlan(®) CMF (BrainLAB AG, Feldkirchen, Germany); the maximal implant length and the maximal implant diameter were assessed. The study showed, that 6.5mm can generally be used in men; in women however individual planning is essential in regard to the maximal implant diameter since we found that in 15.4% of women, screws with a diameter less than 6.5mm were necessary. The virtual analysis of the preformed bone stock corridor of the anterior column showed two constrictions of crucial clinical importance. These can be found after 18% and 55% (men) respectively 16% and 55% (women) measured from the entry point along the axis of the implant. The entry point of the retrograde anterior column screw in our collective was located lateral of tuberculum pubicum at the level of the superior-medial margin of foramen obturatum. In female patients, the entry point was located significantly more lateral of symphysis and closer to the cranial margin of ramus superior ossis pubis. The mean angle between the screw trajectory and the anterior pelvic plane in sagittal section was 31.6 ± 5.5°, the mean angle between the screw trajectory and the midsagittal plane in axial section was 55.9 ± 4.6° and the mean angle between the screw trajectory and the midsagittal plane in coronal section was 42.1 ± 3.9° with no significant deviation between both sexes. The individual angles formed by the screw trajectory and the anterior pelvic and midsagittal plane are independent from anthropometric parameters sex, age, body length and weight. Therefore, they can be used for orientation in lag screw placement keeping

Soft tissue freezing process. Identification of the dual-phase lag model parameters using the evolutionary algorithm

Science.gov (United States)

Mochnacki, Bohdan; Majchrzak, Ewa; Paruch, Marek

2018-01-01

In the paper the soft tissue freezing process is considered. The tissue sub-domain is subjected to the action of cylindrical cryoprobe. Thermal processes proceeding in the domain considered are described using the dual-phase lag equation (DPLE) supplemented by the appropriate boundary and initial conditions. DPLE results from the generalization of the Fourier law in which two lag times are introduced (relaxation and thermalization times). The aim of research is the identification of these parameters on the basis of measured cooling curves at the set of points selected from the tissue domain. To solve the problem the evolutionary algorithms are used. The paper contains the mathematical model of the tissue freezing process, the very short information concerning the numerical solution of the basic problem, the description of the inverse problem solution and the results of computations.

Robust lag synchronization between two different chaotic systems via dual-stage impulsive control

International Nuclear Information System (INIS)

Hua-Guang, Zhang; Tie-Dong, Ma; Jie, Fu; Shao-Cheng, Tong

2009-01-01

In this paper, an improved impulsive lag synchronization scheme for different chaotic systems with parametric uncertainties is proposed. Based on the new definition of synchronization with error bound and a novel impulsive control scheme (the so-called dual-stage impulsive control), some new and less conservative sufficient conditions are established to guarantee that the error dynamics can converge to a predetermined level, which is more reasonable and rigorous than the existing results. In particular, some simpler and more convenient conditions are derived by taking the same impulsive distances and control gains. Finally, some numerical simulations for the Lorenz system and the Chen system are given to demonstrate the effectiveness and feasibility of the proposed method

Effect of Cortical Screw Diameter on Reduction and Stabilization of Type III Distal Phalanx Fractures: An Equine Cadaveric Study.

Science.gov (United States)

Kay, Alastair T; Durgam, Sushmitha; Stewart, Matthew; Joslyn, Stephen; Schaeffer, David J; Horn, Gavin; Kesler, Richard; Chew, Peter

2016-11-01

To compare reduction of type III distal phalangeal fractures using 4.5 and 5.5 mm cortical screws placed in lag fashion and an intact hoof capsule model. Cadaveric experimental study. Hooves from 12 adult horses (n=24). Sagittal fractures were created in pairs of distal phalanges after distal interphalangeal joint disarticulation and were reduced with either 4.5 or 5.5 mm cortical screws placed in lag fashion. Contralateral phalanges served as non-reduced controls. Fracture reduction following screw placement was assessed by comparing pre-reduction and post-reduction fracture gap measurements from radiographs using paired t-tests. Effects of incremental loading (0, 135, 270, 540, 800, 1070, and 1335 kg) on fracture gaps in 6 phalanges reduced with 4.5 mm screws and 5 phalanges reduced with 5.5 mm screws were measured from fluoroscopic images and assessed by 2-way ANOVA. Significance was set at Pfractures were reliably created. Only 5.5 mm cortical screws, not 4.5 mm screws, significantly reduced fracture gaps and constrained fracture gap expansion 3 cm distal to the articular surface. Compressive loading closed the fracture gaps at the articular surface in both non-reduced control groups and those reduced with either 5.5 or 4.5 mm screws. The 5.5 mm cortical screws were more effective than 4.5 mm screws in reducing type III distal phalanx fractures and restricting distal fracture gap expansion under load. © Copyright 2016 by The American College of Veterinary Surgeons.

Quantitative dual-energy CT for phantomless evaluation of cancellous bone mineral density of the vertebral pedicle: correlation with pedicle screw pull-out strength

Energy Technology Data Exchange (ETDEWEB)

Wichmann, Julian L.; Booz, Christian; Bauer, Ralf W.; Kerl, J.M.; Fischer, Sebastian; Lehnert, Thomas; Vogl, Thomas J.; Khan, M.F. [University Hospital Frankfurt, Department of Diagnostic and Interventional Radiology, Frankfurt am Main (Germany); Wesarg, Stefan [Fraunhofer IGD, Cognitive Computing and Medical Imaging, Darmstadt (Germany); Kafchitsas, Konstantinos [Spine Center, Asklepios Klinik Lindenlohe, Schwandorf (Germany)

2015-06-01

To evaluate quantitative dual-energy computed tomography (DECT) for phantomless analysis of cancellous bone mineral density (BMD) of vertebral pedicles and to assess the correlation with pedicle screw pull-out strength. Twenty-nine thoracic and lumbar vertebrae from cadaver specimens were examined with DECT. Using dedicated post-processing software, a pedicle screw vector was mapped (R1, intrapedicular segment of the pedicle vector; R2, intermediate segment; R3, intracorporal segment; global, all segments) and BMD was calculated. To invasively evaluate pedicle stability, pedicle screws were drilled through both pedicles and left pedicle screw pull-out strength was measured. Resulting values were correlated using the paired t test and Pearson's linear correlation. Average pedicle screw vector BMD (R1, 0.232 g/cm{sup 3}; R2, 0.166 g/cm{sup 3}; R3, 0.173 g/cm{sup 3}; global, 0.236 g/cm{sup 3}) showed significant differences between R1-R2 (P < 0.002) and R1-R3 (P < 0.034) segments while comparison of R2-R3 did not reach significance (P > 0.668). Average screw pull-out strength (639.2 N) showed a far stronger correlation with R1 (r = 0.80; P < 0.0001) than global BMD (r = 0.42; P = 0.025), R2 (r = 0.37; P = 0.048) and R3 (r = -0.33; P = 0.078) segments. Quantitative DECT allows for phantomless BMD assessment of the vertebral pedicle. BMD of the intrapedicular segment shows a significantly stronger correlation with pedicle screw pull-out strength than other segments. (orig.)

Analysis of dual-phase-lag thermal behaviour in layered films with temperature-dependent interface thermal resistance

International Nuclear Information System (INIS)

Liu, K-C

2005-01-01

This work analyses theoretically the dual-phase-lag thermal behaviour in two-layered thin films with an interface thermal resistance, which is predicted by the radiation boundary condition model. The effect of the interface thermal resistance on the transmission-reflection phenomenon, induced by a pulsed volumetric source adjacent to the exterior surface of one layer, is investigated. Due to the difference between the two layers in the relaxation times, τ q and τ T , and the nonlinearity of the interfacial boundary condition, complexity is introduced and some mathematical difficulties are involved in solving the present problem. A hybrid application of the Laplace transform method and a control-volume formulation are used along with the linearization technique. The results show that the effect of the thermophysical properties on the behaviour of the energy passing across the interface gradually reduces with increasing interface thermal resistance. The lagging thermal behaviour depends on the magnitude of τ T and τ q more than on the ratio of τ T /τ q

Slab fractures of the third tarsal bone: Minimally invasive repair using a single 3.5 mm cortex screw placed in lag fashion in 17 Thoroughbred racehorses.

Science.gov (United States)

Barker, W H J; Wright, I M

2017-03-01

A technique for minimally invasive repair of slab fractures of the third tarsal bone has not previously been reported. Results of third tarsal bone slab fracture repair in Thoroughbred racehorses are lacking. To report the outcomes of repair of uniplanar frontal slab factures of the third tarsal bone using a single 3.5 mm cortex screw in lag fashion. Retrospective case series. Case records of horses that had undergone this procedure were reviewed. Seventeen horses underwent surgery. Eighteen percent of cases had wedge shaped third tarsal bones. A point midway between the long and lateral digital extensor tendons and centrodistal and tarsometatarsal joints created a suitable entry site for implants. The fracture location, configuration and curvature of the third tarsal bone and associated joints requires a dorsolateral proximal-plantaromedial distal trajectory for the screw, which was determined by preplaced needles. There were no complications and fractures healed in all cases at 4-6 months post surgery. Seventy-nine percent of horses returned to racing and, at the time of reporting, 3 are in post operative rehabilitation programmes. The technique reported provides a safe, appropriate and repeatable means of repairing slab fractures of the third tarsal bone. Surgical repair is a viable alternative to conservative management. © 2016 EVJ Ltd.

Tapping insertional torque allows prediction for better pedicle screw fixation and optimal screw size selection.

Science.gov (United States)

Helgeson, Melvin D; Kang, Daniel G; Lehman, Ronald A; Dmitriev, Anton E; Luhmann, Scott J

2013-08-01

There is currently no reliable technique for intraoperative assessment of pedicle screw fixation strength and optimal screw size. Several studies have evaluated pedicle screw insertional torque (IT) and its direct correlation with pullout strength. However, there is limited clinical application with pedicle screw IT as it must be measured during screw placement and rarely causes the spine surgeon to change screw size. To date, no study has evaluated tapping IT, which precedes screw insertion, and its ability to predict pedicle screw pullout strength. The objective of this study was to investigate tapping IT and its ability to predict pedicle screw pullout strength and optimal screw size. In vitro human cadaveric biomechanical analysis. Twenty fresh-frozen human cadaveric thoracic vertebral levels were prepared and dual-energy radiographic absorptiometry scanned for bone mineral density (BMD). All specimens were osteoporotic with a mean BMD of 0.60 ± 0.07 g/cm(2). Five specimens (n=10) were used to perform a pilot study, as there were no previously established values for optimal tapping IT. Each pedicle during the pilot study was measured using a digital caliper as well as computed tomography measurements, and the optimal screw size was determined to be equal to or the first size smaller than the pedicle diameter. The optimal tap size was then selected as the tap diameter 1 mm smaller than the optimal screw size. During optimal tap size insertion, all peak tapping IT values were found to be between 2 in-lbs and 3 in-lbs. Therefore, the threshold tapping IT value for optimal pedicle screw and tap size was determined to be 2.5 in-lbs, and a comparison tapping IT value of 1.5 in-lbs was selected. Next, 15 test specimens (n=30) were measured with digital calipers, probed, tapped, and instrumented using a paired comparison between the two threshold tapping IT values (Group 1: 1.5 in-lbs; Group 2: 2.5 in-lbs), randomly assigned to the left or right pedicle on each

Biopolymer augmentation of the lag screw in the treatment of femoral neck fractures - a biomechanical in-vitro study

Directory of Open Access Journals (Sweden)

Paech A

2010-04-01

Full Text Available Abstract The cut-out of the sliding screw is one of the most common complications in the treatment of intertrochanteric fractures. The reasons for the cut-out are: a suboptimal position of the hip-screw in the femoral head, the type of fracture and poor bone quality. The aim of this study was to reproduce the cut-out event biomechanically and to evaluate the possible prevention of this event by the use of a biopolymer augmentation of the hip screw. Concerning the density and compression force of osteoporotic femoral bone polyurethane foam according to the terms of the Association for Standard Testing Material (ASTMF 1839-97 was used as test material. The polyurethane foam Lumoltan 200 with a compression force of 3.3 Mpa and a density of 0.192 g/cm3 was used to reproduce the osteoporotic bone of the femoral fragment (density 12 lbm/ft3. A cylinder of 50 mm of length and 50 mm of width was produced by a rotary splint raising procedure with planar contact. The axial load of the system was performed by a hydraulic force cylinder of a universal test machine type Zwick 1455, Ulm, Germany. The CCD-angle of the used TGN-System was preset at 130 degrees. The migration pattern of the hip screw in the polyurethane foam was measured and expressed as a curve of the distance in millimeter [mm] against the applied load in Newton [N] up to the cut-out point. During the tests the implants reached a critical changing point from stable to unstable with an increased load progression of steps of 50 Newton. This unstable point was characterized by an increased migration speed in millimeters and higher descending gradient in the migration curve. This peak of the migration curve served as an indicator for the change of the hip screw position in the simulated bone material. The applied load in the non-augmented implant showed that in this group for a density degree of 12 (0,192 g/cm3 the mean force at the failure point was 1431 Newton (± 52 Newton. In the augmented

Numerical solution of non-linear dual-phase-lag bioheat transfer equation within skin tissues.

Science.gov (United States)

Kumar, Dinesh; Kumar, P; Rai, K N

2017-11-01

This paper deals with numerical modeling and simulation of heat transfer in skin tissues using non-linear dual-phase-lag (DPL) bioheat transfer model under periodic heat flux boundary condition. The blood perfusion is assumed temperature-dependent which results in non-linear DPL bioheat transfer model in order to predict more accurate results. A numerical method of line which is based on finite difference and Runge-Kutta (4,5) schemes, is used to solve the present non-linear problem. Under specific case, the exact solution has been obtained and compared with the present numerical scheme, and we found that those are in good agreement. A comparison based on model selection criterion (AIC) has been made among non-linear DPL models when the variation of blood perfusion rate with temperature is of constant, linear and exponential type with the experimental data and it has been found that non-linear DPL model with exponential variation of blood perfusion rate is closest to the experimental data. In addition, it is found that due to absence of phase-lag phenomena in Pennes bioheat transfer model, it achieves steady state more quickly and always predict higher temperature than thermal and DPL non-linear models. The effect of coefficient of blood perfusion rate, dimensionless heating frequency and Kirchoff number on dimensionless temperature distribution has also been analyzed. The whole analysis is presented in dimensionless form. Copyright © 2017 Elsevier Inc. All rights reserved.

Osteosynthesis of the first phalanx fractures in horses by means of lag screws

International Nuclear Information System (INIS)

Bereznowski, A.; Janicki, A.M.; Sterna, J.

1996-01-01

Fractures of the first phalanx belong to the most frequent in horses. Three cases of surgical treatment of first phalanx fractures in horses have been presented. The cases differed by the period of time between the accident and surgical treatment. In all cases osteosynthesis by means of orthopedic screws was applied. In all horses fracture repair was successful, however, not all horses recovered fully enough to return to work. (author)

Estimation of dual phase lag model parameters using the evolutionary algorithms

Directory of Open Access Journals (Sweden)

B. Mochnacki

2011-07-01

Full Text Available Generalization of Fourier law, in particular the introduction of two ‘delay times’ (relaxation time q and thermalization time T leads to thenew form of energy equation called the dual-phase-lag model (DPLM. This equation should be applied in a case of microscale heat transfermodeling. In particular, DPLM constitutes a good approximation of thermal processes which are characterized by extremely short duration(e.g. ultrafast laser pulse, extreme temperature gradients and geometrical features of domain considered (e.g. thin metal film. The aim ofconsiderations presented in this paper is the identification of two above mentioned positive constants q, T. They correspond to the relaxationtime, which is the mean time for electrons to change their energy states and the thermalization time, which is the mean time required forc(TTl G(TT electrons and lattice to reach equilibrium. In this paper the DPlLMlequation ise appllied for analysis of thermal processes proceeding in a thint metal film subjected to a laser beam. At the stage of computations connected with the identification problem solution the evolutionaryalgorithms are used. To solve the problem the additional information concerning the transient temperature distribution on a metal film surface is assumed to be known.

Removal torque of nail interlocking screws is related to screw proximity to the fracture and screw breakage.

Science.gov (United States)

White, Alexander A; Kubacki, Meghan R; Samona, Jason; Telehowski, Paul; Atkinson, Patrick J

2016-06-01

Studies have shown that titanium implants can be challenging to explant due to the material's excellent biocompatibility and resulting osseointegration. Clinically, titanium alloy nail interlocking screws may require removal to dynamize a construct or revise the nail due to nonunion, infection, pain, or periprosthetic fracture. This study was designed to determine what variables influence the removal torque for titanium alloy interlocking screws. An intramedullary nail with four interlocking screws was used to stabilize a 1-cm segmental femoral defect in a canine model for 16 weeks. The animals were observed to be active following a several-day recovery after surgery. In six animals, the femora and implanted nail/screws were first tested to failure in torsion to simulate periprosthetic fracture of an implant after which the screws were then removed. In four additional animals, the screws were removed without mechanical testing. Both intraoperative insertional and extraction torques were recorded for all screws. Mechanical testing to failure broke 10/24 screws. On average, the intact screws required 70% of the insertional torque during removal while broken screws only required 16% of the insertional torque (p torque than the outboard distal screw (p torque was ∼80°. The peak axial load did not significantly correlate with the torque required to remove the screws. On average, the removal torque was lower than at the time of insertion, and less torque was required to remove broken screws and screws remote to the fracture. However, broken screws will require additional time to retrieve the remaining screw fragment. This study suggests that broken screws and screws in prematurely active patients will require less torque to remove. © IMechE 2016.

Ball Screw Actuator Including a Compliant Ball Screw Stop

Science.gov (United States)

Wingett, Paul T. (Inventor); Hanlon, Casey (Inventor)

2017-01-01

An actuator includes a ball nut, a ball screw, and a ball screw stop. The ball nut is adapted to receive an input torque and in response rotates and supplies a drive force. The ball screw extends through the ball nut and has a first end and a second end. The ball screw receives the drive force from the ball nut and in response selectively translates between a retract position and a extend position. The ball screw stop is mounted on the ball screw proximate the first end to translate therewith. The ball screw stop engages the ball nut when the ball screw is in the extend position, translates, with compliance, a predetermined distance toward the first end upon engaging the ball nut, and prevents further rotation of the ball screw upon translating the predetermined distance.

Screw-vector bond graphs for kinetic-static modelling and analysis of mechanisms

International Nuclear Information System (INIS)

Bidard, Catherine

1994-01-01

This dissertation deals with the kinetic-static modelling and analysis of spatial mechanisms used in robotics systems. A framework is proposed, which embodies a geometrical and a network approach for kinetic-static modelling. For this purpose we use screw theory and bond graphs. A new form of bond graphs is introduced: the screw-vector bond graph, whose power variables are defined to be wrenches and twists expressed as intrinsic screw-vectors. The mechanism is then identified as a network, whose components are kinematic pairs and whose topology is described by a directed graph. A screw-vector Simple Junction Structure represents the topological constraints. Kinematic pairs are represented by one-port elements, defined by two reciprocal screw-vector spaces. Using dual bases of screw-vectors, a generic decomposition of kinematic pair elements is given. The reduction of kinetic-static models of series and parallel kinematic chains is used in order to derive kinetic-static functional models in geometric form. Thereupon, the computational causality assignment is adapted for the graphical analysis of the mobility and the functioning of spatial mechanisms, based on completely or incompletely specified models. (author) [fr

Pullout strength of misplaced pedicle screws in the thoracic and lumbar vertebrae - A cadaveric study

Directory of Open Access Journals (Sweden)

Shyam K Saraf

2013-01-01

Full Text Available Background: The objective of this cadaveric study was to analyze the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of lower thoracic and lumbar pedicle screws. We also investigated the effect of bone mineral density (BMD, diameter of pedicle screws, and the region of spine on the pullout strength of pedicle screws. Materials and Methods: Sixty fresh human cadaveric vertebrae (D10-L2 were harvested. Dual-energy X-ray absorptiometry (DEXA scan of vertebrae was done for BMD. Titanium pedicle screws of different diameters (5.2 and 6.2 mm were inserted in the thoracic and lumbar segments after dividing the specimens into three groups: a standard pedicle screw (no cortical perforation; b screw with medial cortical perforation; and c screw with lateral cortical perforation. Finally, pullout load of pedicle screws was recorded using INSTRON Universal Testing Machine. Results: Compared with standard placement, medially misplaced screws had 9.4% greater mean pullout strength and laterally misplaced screws had 47.3% lesser mean pullout strength. The pullout strength of the 6.2 mm pedicle screws was 33% greater than that of the 5.2 mm pedicle screws. The pullout load of pedicle screws in lumbar vertebra was 13.9% greater than that in the thoracic vertebra ( P = 0.105, but it was not statistically significant. There was no significant difference between pullout loads of vertebra with different BMD ( P = 0.901. Conclusion: The mean pullout strength was less with lateral misplaced pedicle screws while medial misplaced pedicle screw had more pullout strength. The pullout load of 6.2 mm screws was greater than that of 5.2 mm pedicle screws. No significant correlation was found between bone mineral densities and the pullout strength of vertebra. Similarly, the pullout load of screw placed in thoracic and lumbar vertebrae was not significantly different.

Simple New Screw Insertion Technique without Extraction for Broken Pedicle Screws.

Science.gov (United States)

Kil, Jin-Sang; Park, Jong-Tae

2018-05-01

Spinal transpedicular screw fixation is widely performed. Broken pedicle screw rates range from 3%-7.1%. Several techniques have been described for extraction of broken pedicle screws. However, most of these techniques require special instruments. We describe a simple, modified technique for management of broken pedicle screws without extraction. No special instruments or drilling in an adjacent pedicle are required. We used a high-speed air drill with a round burr. With C-arm fluoroscopy guidance, the distal fragment of a broken pedicle screw was palpated using free-hand technique through the screw entry hole. A high-speed air drill with a round burr (not a diamond burr) was inserted through the hole. Drilling began slowly and continued until enough space was obtained for new screw insertion. Using this space, we performed new pedicle screw fixation medially alongside the distal fragment of the broken pedicle screw. We performed the insertion with a previously used entry hole and pathway in the pedicle. The same size pedicle screw was used. Three patients were treated with this modified technique. New screw insertion was successful in all cases after partial drilling of the distal broken pedicle screw fragment. There were no complications, such as screw loosening, dural tears, or root injury. We describe a simple, modified technique for management of broken pedicle screws without extraction. This technique is recommended in patients who require insertion of a new screw. Copyright © 2017. Published by Elsevier Inc.

Numerical simulation of time fractional dual-phase-lag model of heat transfer within skin tissue during thermal therapy.

Science.gov (United States)

Kumar, Dinesh; Rai, K N

2017-07-01

In this paper, we investigated the thermal behavior in living biological tissues using time fractional dual-phase-lag bioheat transfer (DPLBHT) model subjected to Dirichelt boundary condition in presence of metabolic and electromagnetic heat sources during thermal therapy. We solved this bioheat transfer model using finite element Legendre wavelet Galerkin method (FELWGM) with help of block pulse function in sense of Caputo fractional order derivative. We compared the obtained results from FELWGM and exact method in a specific case, and found a high accuracy. Results are interpreted in the form of standard and anomalous cases for taking different order of time fractional DPLBHT model. The time to achieve hyperthermia position is discussed in both cases as standard and time fractional order derivative. The success of thermal therapy in the treatment of metastatic cancerous cell depends on time fractional order derivative to precise prediction and control of temperature. The effect of variability of parameters such as time fractional derivative, lagging times, blood perfusion coefficient, metabolic heat source and transmitted power on dimensionless temperature distribution in skin tissue is discussed in detail. The physiological parameters has been estimated, corresponding to the value of fractional order derivative for hyperthermia treatment therapy. Copyright © 2017 Elsevier Ltd. All rights reserved.

Hybrid magnetorheological fluid–elastomeric lag dampers for helicopter stability augmentation

International Nuclear Information System (INIS)

Hu Wei; Wereley, Norman M

2008-01-01

A laboratory demonstration of a hybrid magnetorheological fluid–elastomeric (MRFE) damper is investigated for adjustable or programmable lag mode damping in helicopters, so that damping requirements can be varied as a function of different flight conditions. The laboratory demonstration of this hybrid MRFE lag damper consists of a double lap shear elastomeric damper in parallel with two magnetorheological (MR) flow mode dampers. This is compared to a damper where only elastomeric materials are implemented, i.e., a double lap shear specimen. The relationship between the output force and the quasi-steady harmonic displacement input to a flow mode MR damper is exploited, where the output force can be adjusted as a function of applied magnetic field. Equivalent viscous damping is used to compare the damping characteristics of the hybrid damper to a conventional elastomeric damper under steady-state sinusoidal displacement excitation. To demonstrate feasibility, a hybrid MRFE damper test setup is designed, and single frequency (lag frequency or rotor in-plane bending frequency) and dual frequency (lag frequency and rotor frequency) tests are conducted under different magnetic fields. The hybrid MRFE damper exhibits amplitude-dependent damping behavior. However, with application of a magnetic field, the damping level is controlled to a specific damping level objective as a function of displacement amplitude. Similarly, under dual frequency conditions, damping degradation at the lag frequency, because of lag motion at the rotor frequency, can also be recovered by increasing magnetic field. A time-domain analysis is developed to study the nonlinear dynamic behavior of the hybrid MRFE damper. Using rate-dependent elasto-slides, the amplitude-dependent behavior of the hybrid MRFE damper is accurately reconstructed using both constant and current-dependent (i.e. controllable) parameters. The analysis is physically motivated and can be applied to the elastomer and MR fluid

Pedicle screw anchorage of carbon fiber-reinforced PEEK screws under cyclic loading.

Science.gov (United States)

Lindtner, Richard A; Schmid, Rene; Nydegger, Thomas; Konschake, Marko; Schmoelz, Werner

2018-03-01

Pedicle screw loosening is a common and significant complication after posterior spinal instrumentation, particularly in osteoporosis. Radiolucent carbon fiber-reinforced polyetheretherketone (CF/PEEK) pedicle screws have been developed recently to overcome drawbacks of conventional metallic screws, such as metal-induced imaging artifacts and interference with postoperative radiotherapy. Beyond radiolucency, CF/PEEK may also be advantageous over standard titanium in terms of pedicle screw loosening due to its unique material properties. However, screw anchorage and loosening of CF/PEEK pedicle screws have not been evaluated yet. The aim of this biomechanical study therefore was to evaluate whether the use of this alternative nonmetallic pedicle screw material affects screw loosening. The hypotheses tested were that (1) nonmetallic CF/PEEK pedicle screws resist an equal or higher number of load cycles until loosening than standard titanium screws and that (2) PMMA cement augmentation further increases the number of load cycles until loosening of CF/PEEK screws. In the first part of the study, left and right pedicles of ten cadaveric lumbar vertebrae (BMD 70.8 mg/cm 3  ± 14.5) were randomly instrumented with either CF/PEEK or standard titanium pedicle screws. In the second part, left and right pedicles of ten vertebrae (BMD 56.3 mg/cm 3  ± 15.8) were randomly instrumented with either PMMA-augmented or nonaugmented CF/PEEK pedicle screws. Each pedicle screw was subjected to cyclic cranio-caudal loading (initial load ranging from - 50 N to + 50 N) with stepwise increasing compressive loads (5 N every 100 cycles) until loosening or a maximum of 10,000 cycles. Angular screw motion ("screw toggling") within the vertebra was measured with a 3D motion analysis system every 100 cycles and by stress fluoroscopy every 500 cycles. The nonmetallic CF/PEEK pedicle screws resisted a similar number of load cycles until loosening as the contralateral standard

EFFECT OF PILOT HOLE TAPPING ON PULLOUT STRENGTH AND INSERTION TORQUE OF DUAL CORE PEDICLE SCREWS.

Science.gov (United States)

Rosa, Rodrigo César; Silva, Patrícia; Falcai, Maurício José; Shimano, Antônio Carlos; Defino, Helton Luiz Aparecido

2010-01-01

To evaluate the influence of pilot hole tapping on pullout resistance and insertion torque of pedicle screws with a conical core. Mechanical tests using a universal testing machine were performed on pedicle screws with a conical core that were inserted into pedicles in the fifth lumbar vertebra of calves. The insertion torque was measured using a torque meter with a capacity of 10 Nm, which was considered to be the highest torque value. The pilot holes were prepared using a probe of external diameter 3.8 mm and tapping of the same dimensions and thread characteristics as the screw. Decreased insertion torque and pullout resistance were observed in the group with prior tapping of the pilot hole. Pilot hole tapping reduced the insertion torque and pullout resistance of pedicle screws with a conical core that had been inserted into the pedicle of the fifth lumbar vertebra of calves.

Fixation of femoral capital physeal fractures with 7.0 mm cannulated screws in five bulls

International Nuclear Information System (INIS)

Wilson, D.G.; Crawford, W.H.; Stone, W.C.; Frampton, J.W.

1991-01-01

Salter-Harris type I fractures of the femoral capital physis were repaired in five Holstein bulls with three 7.0 mm cannulated screws placed in lag fashion. Radiographically at months 7 to 10, the fractures were healed and there was periarticular bone production on the femoral necks and the dorsal acetabular rims. Four bulls had normal gaits, and one bull had muscle atrophy and barely detectable lameness

Central tarsal bone fractures in horses not used for racing: Computed tomographic configuration and long-term outcome of lag screw fixation.

Science.gov (United States)

Gunst, S; Del Chicca, F; Fürst, A E; Kuemmerle, J M

2016-09-01

There are no reports on the configuration of equine central tarsal bone fractures based on cross-sectional imaging and clinical and radiographic long-term outcome after internal fixation. To report clinical, radiographic and computed tomographic findings of equine central tarsal bone fractures and to evaluate the long-term outcome of internal fixation. Retrospective case series. All horses diagnosed with a central tarsal bone fracture at our institution in 2009-2013 were included. Computed tomography and internal fixation using lag screw technique was performed in all patients. Medical records and diagnostic images were reviewed retrospectively. A clinical and radiographic follow-up examination was performed at least 1 year post operatively. A central tarsal bone fracture was diagnosed in 6 horses. Five were Warmbloods used for showjumping and one was a Quarter Horse used for reining. All horses had sagittal slab fractures that began dorsally, ran in a plantar or plantaromedial direction and exited the plantar cortex at the plantar or plantaromedial indentation of the central tarsal bone. Marked sclerosis of the central tarsal bone was diagnosed in all patients. At long-term follow-up, 5/6 horses were sound and used as intended although mild osteophyte formation at the distal intertarsal joint was commonly observed. Central tarsal bone fractures in nonracehorses had a distinct configuration but radiographically subtle additional fracture lines can occur. A chronic stress related aetiology seems likely. Internal fixation of these fractures based on an accurate diagnosis of the individual fracture configuration resulted in a very good prognosis. © 2015 EVJ Ltd.

Percutaneous Intramedullary Screw Fixation of Distal Fibula Fractures: A Case Series and Systematic Review.

Science.gov (United States)

Loukachov, Vladimir V; Birnie, Merel F N; Dingemans, Siem A; de Jong, Vincent M; Schepers, Tim

The current reference standard for unstable ankle fractures is open reduction and internal fixation using a plate and lag screws. This approach requires extensive dissection and wound complications are not uncommon. The use of intramedullary screw fixation might overcome these issues. The aim of our study was to provide an overview of the published data regarding intramedullary screw fixation of fibula fractures combined with a small consecutive case series. We performed a search of published studies to identify the studies in which fibula fractures were treated with percutaneous intramedullary screw fixation. Additionally, all consecutive patients treated for an unstable ankle fracture in a level 1 trauma center using an intramedullary screw were retrospectively included. The literature search identified 6 studies with a total of 180 patients. Wound infection was seen in 1 patient (0.6%), anatomic reduction was achieved in 168 patients (93.3%), and a loss of reduction was seen in 2 patients (1.1%). Implant removal was deemed necessary in 3 patients (1.7%) and nonunion was seen is 2 patients (1.1%). A total of 11 patients, in whom no wound complications occurred, were included in our study. The follow-up duration was a minimum of 12 months. A secondary dislocation was seen in 1 patient, and delayed union was observed after 7.5 months in 1 other patient. In conclusion, intramedullary screw fixation is a safe and adequate method to use for fibula fractures, with a low risk of wound complications. Additional research regarding functional outcome is warranted. Copyright © 2017 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Effects of Screw Configuration on the Preload Force of Implant-Abutment Screws.

Science.gov (United States)

Zipprich, Holger; Rathe, Florian; Pinz, Sören; Schlotmann, Luca; Lauer, Hans-Christoph; Ratka, Christoph

The aim of this study was to investigate the effects of tightening torque, screw head angle, and thread number on the preload force of abutment screws. The test specimens consisted of three self-manufactured components (ie, a thread sleeve serving as an implant analog, an abutment analog, and an abutment screw). The abutment screws were fabricated with metric M1.6 external threads. The thread number varied between one and seven threads. The screw head angles were produced in eight varying angles (30 to 180 degrees). A sensor unit simultaneously measured the preload force of the screw and the torsion moment inside the screw shank. The tightening of the screw with the torque wrench was performed in five steps (15 to 35 Ncm). The torque wrench was calibrated before each step. Only the tightening torque and screw head angle affected the resulting preload force of the implant-abutment connection. The thread number had no effect. There was an approximately linear correlation between tightening torque and preload force. The tightening torque and screw head angle were the only study parameters that affected the resulting preload force of the abutment screw. The results obtained from this experiment are valid only for a single torque condition. Further investigations are needed that analyze other parameters that affect preload force. Once these parameters are known, it will add value for a strong, but detachable connection between the implant and abutment. Short implants and flat-to-flat connections especially will benefit significantly from this knowledge.

Abnormal Ventral and Dorsal Attention Network Activity During Single and Dual Target Detection in Schizophrenia

Directory of Open Access Journals (Sweden)

Amy M. Jimenez

2016-03-01

Full Text Available Early visual perception and attention are impaired in schizophrenia, and these deficits can be observed on target detection tasks. These tasks activate distinct ventral and dorsal brain networks which support stimulus-driven and goal-directed attention, respectively. We used single and dual target rapid serial visual presentation (RSVP tasks during fMRI with an ROI approach to examine regions within these networks associated with target detection and the attentional blink (AB in 21 schizophrenia outpatients and 25 healthy controls. In both tasks, letters were targets and numbers were distractors. For the dual target task, the second target (T2 was presented at 3 different lags after the first target (T1 (lag1=100ms, lag3=300ms, lag7=700ms. For both single and dual target tasks, patients identified fewer targets than controls. For the dual target task, both groups showed the expected AB effect with poorer performance at lag 3 than at lags 1 or 7, and there was no group by lag interaction. During the single target task, patients showed abnormally increased deactivation of the temporo-parietal junction (TPJ, a key region of the ventral network. When attention demands were increased during the dual target task, patients showed overactivation of the posterior intraparietal cortex, a key dorsal network region, along with failure to deactivate TPJ. Results suggest inefficient and faulty suppression of salience-oriented processing regions, resulting in increased sensitivity to stimuli in general, and difficulty distinguishing targets from non-targets.

Positioning device for screwing or unscrewing screw nut

International Nuclear Information System (INIS)

Sevelinge, G.

1987-01-01

This automatic positioning device for screwing or unscrewing a screw nut on a closure stud has a drawed socket and means for axially centre and angularly by wedge the socket on the closure stud and generate a continuous spiral between the socket and the closure stud [fr

Management of simple (types A and B) closed tibial shaft fractures using percutaneous lag-screw fixation and Ilizarov external fixation in adults.

Science.gov (United States)

El-Sayed, Mohamed; Atef, Ashraf

2012-10-01

Although intramedullary fixation of closed simple (type A or B) diaphyseal tibial fractures in adults is well tolerated by patients, providing lower morbidity rates and better mobility, it is associated with some complications. This study evaluated the results of managing these fractures using percutaneous minimal internal fixation using one or more lag screws, and Ilizarov external fixation. This method was tested to evaluate its efficacy in immediate weight bearing, fracture healing and prevention of any post-immobilisation stiffness of the ankle and knee joints. This randomised blinded study was performed at a referral, academically supervised, level III trauma centre. Three hundred and twenty-four of the initial 351 patients completed this study and were followed up for a minimum of 12 (12-88) months. Patient ages ranged from 20 to 51 years, with a mean of 39 years. Ankle and knee movements and full weight bearing were encouraged immediately postoperatively. Solid union was assessed clinically and radiographically. Active and passive ankle and knee ranges of motion were measured and compared with the normal side using the Wilcoxon signed rank test for matched pairs. Subjective Olerud and Molander Ankle Score was used to detect any ankle joint symptoms at the final follow-up. No patient showed delayed or nonunion. All fractures healed within 95-129 days. Based on final clinical and radiographic outcomes, this technique proves to be adequate for managing simple diaphyseal tibial fractures. On the other hand, it is relatively expensive, technically demanding, necessitates exposure to radiation and patients are expected to be frame friendly.

Hollow Abutment Screw Design for Easy Retrieval in Case of Screw Fracture in Dental Implant System.

Science.gov (United States)

Sim, Bo Kyun; Kim, Bongju; Kim, Min Jeong; Jeong, Guk Hyun; Ju, Kyung Won; Shin, Yoo Jin; Kim, Man Yong; Lee, Jong-Ho

2017-01-01

The prosthetic component of dental implant is attached on the abutment which is connected to the fixture with an abutment screw. The abutment screw fracture is not frequent; however, the retrieval of the fractured screw is not easy, and it poses complications. A retrieval kit was developed which utilizes screw removal drills to make a hole on the fractured screw that provides an engaging drill to unscrew it. To minimize this process, the abutment screw is modified with a prefabricated access hole for easy retrieval. This study aimed to introduce this modified design of the abutment screw, the concept of easy retrieval, and to compare the mechanical strengths of the conventional and hollow abutment screws by finite element analysis (FEA) and mechanical test. In the FEA results, both types of abutment screws showed similar stress distribution in the single artificial tooth system. A maximum load difference of about 2% occurred in the vertical load by a mechanical test. This study showed that the hollow abutment screw may be an alternative to the conventional abutment screws because this is designed for easy retrieval and that both abutment screws showed no significant difference in the mechanical tests and in the FEA.

[Fracture of implant abutment screws and removal of a remaining screw piece

NARCIS (Netherlands)

Broeke, S.M. van den; Baat, C. de

2008-01-01

Fracture of the implant abutment screws is a complication which can render an implant useless. The prevalence of abutment screw fracture does not exceed 2.5% after 10 years. Causes are loosening of implant abutment screw, too few, too short or too narrow implants, implants not inserted perpendicular

Effect of Repeated Screw Joint Closing and Opening Cycles and Cyclic Loading on Abutment Screw Removal Torque and Screw Thread Morphology: Scanning Electron Microscopy Evaluation.

Science.gov (United States)

Arshad, Mahnaz; Mahgoli, Hosseinali; Payaminia, Leila

To evaluate the effect of repeated screw joint closing and opening cycles and cyclic loading on abutment screw removal torque and screw thread morphology using scanning electron microscopy (SEM). Three groups (n = 10 in each group) of implant-abutment-abutment screw assemblies were created. There were also 10 extra abutment screws as new screws in group 3. The abutment screws were tightened to 12 Ncm with an electronic torque meter; then they were removed and removal torque values were recorded. This sequence was repeated 5 times for group 1 and 15 times for groups 2 and 3. The same screws in groups 1 and 2 and the new screws in group 3 were then tightened to 12 Ncm; this was also followed by screw tightening to 30 Ncm and retightening to 30 Ncm 15 minutes later. Removal torque measurements were performed after screws were subjected to cyclic loading (0.5 × 10⁶ cycles; 1 Hz; 75 N). Moreover, the surface topography of one screw from each group before and after cyclic loading was evaluated with SEM and compared with an unused screw. All groups exhibited reduced removal torque values in comparison to insertion torque in each cycle. However, there was a steady trend of torque loss in each group. A comparison of the last cycle of the groups before loading showed significantly greater torque loss value in the 15th cycle of groups 2 and 3 compared with the fifth cycle of group 1 (P abutment is definitively placed.

Hollow Abutment Screw Design for Easy Retrieval in Case of Screw Fracture in Dental Implant System

Directory of Open Access Journals (Sweden)

Bo Kyun Sim

2017-01-01

Full Text Available The prosthetic component of dental implant is attached on the abutment which is connected to the fixture with an abutment screw. The abutment screw fracture is not frequent; however, the retrieval of the fractured screw is not easy, and it poses complications. A retrieval kit was developed which utilizes screw removal drills to make a hole on the fractured screw that provides an engaging drill to unscrew it. To minimize this process, the abutment screw is modified with a prefabricated access hole for easy retrieval. This study aimed to introduce this modified design of the abutment screw, the concept of easy retrieval, and to compare the mechanical strengths of the conventional and hollow abutment screws by finite element analysis (FEA and mechanical test. In the FEA results, both types of abutment screws showed similar stress distribution in the single artificial tooth system. A maximum load difference of about 2% occurred in the vertical load by a mechanical test. This study showed that the hollow abutment screw may be an alternative to the conventional abutment screws because this is designed for easy retrieval and that both abutment screws showed no significant difference in the mechanical tests and in the FEA.

Hollow Abutment Screw Design for Easy Retrieval in Case of Screw Fracture in Dental Implant System

Science.gov (United States)

Kim, Bongju; Shin, Yoo Jin

2017-01-01

The prosthetic component of dental implant is attached on the abutment which is connected to the fixture with an abutment screw. The abutment screw fracture is not frequent; however, the retrieval of the fractured screw is not easy, and it poses complications. A retrieval kit was developed which utilizes screw removal drills to make a hole on the fractured screw that provides an engaging drill to unscrew it. To minimize this process, the abutment screw is modified with a prefabricated access hole for easy retrieval. This study aimed to introduce this modified design of the abutment screw, the concept of easy retrieval, and to compare the mechanical strengths of the conventional and hollow abutment screws by finite element analysis (FEA) and mechanical test. In the FEA results, both types of abutment screws showed similar stress distribution in the single artificial tooth system. A maximum load difference of about 2% occurred in the vertical load by a mechanical test. This study showed that the hollow abutment screw may be an alternative to the conventional abutment screws because this is designed for easy retrieval and that both abutment screws showed no significant difference in the mechanical tests and in the FEA. PMID:29065610

Hollow Abutment Screw Design for Easy Retrieval in Case of Screw Fracture in Dental Implant System

OpenAIRE

Sim, Bo Kyun; Kim, Bongju; Kim, Min Jeong; Jeong, Guk Hyun; Ju, Kyung Won; Shin, Yoo Jin; Kim, Man Yong; Lee, Jong-Ho

2017-01-01

The prosthetic component of dental implant is attached on the abutment which is connected to the fixture with an abutment screw. The abutment screw fracture is not frequent; however, the retrieval of the fractured screw is not easy, and it poses complications. A retrieval kit was developed which utilizes screw removal drills to make a hole on the fractured screw that provides an engaging drill to unscrew it. To minimize this process, the abutment screw is modified with a prefabricated access ...

Extraction of sunflower oil by twin screw extruder: screw configuration and operating condition effects

Energy Technology Data Exchange (ETDEWEB)

Kartika, I.A. [FATETA-IPB, Bogor (Indonesia). Department of Agroindustrial Technology; Pontalier, P.Y.; Rigal, L. [Laboratoire de Chimie Agro-Industrielle, UMR 1010 INRA/INP-ENSIACET, Toulouse (France)

2006-12-15

The objective of this study was to investigate the screw configuration allowing oil extraction from sunflower seeds with a twin-screw extruder. Experiments were conducted using a co-rotating twin-screw extruder. Five screw profiles were examined to define the best performance (oil extraction yield, specific mechanical energy and oil quality) by studying the influence of operating conditions, barrel temperature, screw speed and feed rate. Generally, the position and spacing between two reversed screw elements affected oil extraction yield. An increase of oil extraction yield was observed as the reversed screw elements were moved with increased spacing between two elements and with smaller pitch elements. In addition, oil extraction yield increased as barrel temperature, screw speed and feed rate were decreased. Highest oil extraction yield (85%) with best cake meal quality (residual oil content lower than 13%) was obtained under operating conditions of 120 {sup o}C, 75 rpm and 19 kg/h. Furthermore, the operating parameters influenced energy input. A decrease in barrel temperature and feed rate followed by an increase in screw speed increased energy input, particularly specific mechanical energy input. Effect of the operating parameters on oil quality was less important. In all experiments tested, the oil quality was very good. The acid value was below 2 mg of KOH/g of oil and total phosphorus content was low, below 100 mg/kg. (author)

The pullout performance of pedicle screws

CERN Document Server

Demir, Teyfik

2015-01-01

This brief book systematically discusses all subjects that affect the pullout strength of pedicle screws. These screws are used in spinal surgeries to stabilize the spine. The holding strength of the pedicle screw is vital since loosening of the pedicle screws can cause revision surgeries. Once the pedicle screw is pulled out, it is harder to obtain same stabilization for the fused vertebrae. The book reviews the effect of screw designs, application techniques, cement augmentation, coating of the screw and test conditions on the pullout strength. The studies with finite element analysis were also included.

Aerial Triangulation Close-range Images with Dual Quaternion

Directory of Open Access Journals (Sweden)

SHENG Qinghong

2015-05-01

Full Text Available A new method for the aerial triangulation of close-range images based on dual quaternion is presented. Using dual quaternion to represent the spiral screw motion of the beam in the space, the real part of dual quaternion represents the angular elements of all the beams in the close-range area networks, the real part and the dual part of dual quaternion represents the line elements corporately. Finally, an aerial triangulation adjustment model based on dual quaternion is established, and the elements of interior orientation and exterior orientation and the object coordinates of the ground points are calculated. Real images and large attitude angle simulated images are selected to run the experiments of aerial triangulation. The experimental results show that the new method for the aerial triangulation of close-range images based on dual quaternion can obtain higher accuracy.

Development of load calculation techniques on screw and screw press energy consumption

OpenAIRE

Татарьянц, Максим Сергеевич; Завинский, Сергей Иванович; Трошин, Алексей Георгиевич

2015-01-01

The process of pressing of wood chips in screw machines is researched. It is defined processes taking place in different parts of the screw, formulas allowing to calculate the loads acting on the screw flights, as well as to determine the power required for compression. The unit costs of energy consumption and raw materials in the degree of heat pressing are determined

Dual Phase Lag Model of Melting Process in Domain of Metal Film Subjected to an External Heat Flux

Directory of Open Access Journals (Sweden)

Mochnacki B.

2016-12-01

Full Text Available Heating process in the domain of thin metal film subjected to a strong laser pulse are discussed. The mathematical model of the process considered is based on the dual-phase-lag equation (DPLE which results from the generalized form of the Fourier law. This approach is, first of all, used in the case of micro-scale heat transfer problems (the extremely short duration, extreme temperature gradients and very small geometrical dimensions of the domain considered. The external heating (a laser action is substituted by the introduction of internal heat source to the DPLE. To model the melting process in domain of pure metal (chromium the approach basing on the artificial mushy zone introduction is used and the main goal of investigation is the verification of influence of the artificial mushy zone ‘width’ on the results of melting modeling. At the stage of numerical modeling the author’s version of the Control Volume Method is used. In the final part of the paper the examples of computations and conclusions are presented.

2D and 3D assessment of sustentaculum tali screw fixation with or without Screw Targeting Clamp.

Science.gov (United States)

De Boer, A Siebe; Van Lieshout, Esther M M; Vellekoop, Leonie; Knops, Simon P; Kleinrensink, Gert-Jan; Verhofstad, Michael H J

2017-12-01

Precise placement of sustentaculum tali screw(s) is essential for restoring anatomy and biomechanical stability of the calcaneus. This can be challenging due to the small target area and presence of neurovascular structures on the medial side. The aim was to evaluate the precision of positioning of the subchondral posterior facet screw and processus anterior calcanei screw with or without a Screw Targeting Clamp. The secondary aim was to evaluate the added value of peroperative 3D imaging over 2D radiographs alone. Twenty Anubifix™ embalmed, human anatomic lower limb specimens were used. A subchondral posterior facet screw and a processus anterior calcanei screw were placed using an extended lateral approach. A senior orthopedic trauma surgeon experienced in calcaneal fracture surgery and a senior resident with limited experience in calcaneal surgery performed screw fixation in five specimens with and in five specimens without the clamp. 2D lateral and axial radiographs and a 3D recording were obtained postoperatively. Anatomical dissection was performed postoperatively as a diagnostic golden standard in order to obtain the factual screw positions. Blinded assessment of quality of fixation was performed by two surgeons. In 2D, eight screws were considered malpositioned when placed with the targeting device versus nine placed freehand. In 3D recordings, two additional screws were malpositioned in each group as compared to the golden standard. As opposed to the senior surgeon, the senior resident seemed to get the best results using the Screw Targeting Clamp (number of malpositioned screws using freehand was eight, and using the targeting clamp five). In nine out of 20 specimens 3D images provided additional information concerning target area and intra-articular placement. Based on the 3D assessment, five additional screws would have required repositioning. Except for one, all screw positions were rated equally after dissection when compared with 3D examinations

Frictional performance of ball screw

International Nuclear Information System (INIS)

Nakashima, Katuhiro; Takafuji, Kazuki

1985-01-01

As feed screws, ball screws have become to be adopted in place of trapezoidal threads. The structure of ball screws is complex, but those are the indispensable component of NC machine tools and machining centers, and are frequently used for industrial robots. As the problems in the operation of ball screws, there are damage, life and the performance related to friction. As to the damage and life, though there is the problem of the load distribution on balls, the results of the research on rolling bearings are applied. The friction of ball screws consists of the friction of balls and a spiral groove, the friction of a ball and a ball, the friction in a ball-circulating mechanism and the viscous friction of lubricating oil. It was decided to synthetically examine the frictional performance of ball screws, such as driving torque, the variation of driving torque, efficiency, the formation of oil film and so on, under the working condition of wide range, using the screws with different accuracy and the nuts of various circuit number. The experimental setup and the processing of the experimental data, the driving performance of ball screws and so on are reported. (Kako, I.)

Kinematics of Planetary Roller Screw Mechanism considering Helical Directions of Screw and Roller Threads

Directory of Open Access Journals (Sweden)

Shangjun Ma

2015-01-01

Full Text Available Based on the differential principle of thread transmission, an analytical model considering helical directions between screw and roller threads in planetary roller screw mechanism (PRSM is presented in this work. The model is critical for the design of PRSM with a smaller lead and a bigger pitch to realize a higher transmission accuracy. The kinematic principle of planetary transmission is employed to analyze the PRSM with different screw thread and roller thread directions. In order to investigate the differences with different screw thread and roller thread directions, the numerical model is developed by using the software Adams to validate the analytical solutions calculated by the presented model. The results indicate, when the helical direction of screw thread is identical with the direction of roller thread, that the lead of PRSM is unaffected regardless of whether sliding between screw and rollers occurs or not. Only when the direction of screw thread is reverse to the direction of roller thread, the design of PRSM with a smaller lead can be realized under a bigger pitch. The presented models and numerical simulation method can be used to research the transmission accuracy of PRSM.

Loosening torque of Universal Abutment screws after cyclic loading: influence of tightening technique and screw coating.

Science.gov (United States)

Bacchi, Atais; Regalin, Alexandre; Bhering, Claudia Lopes Brilhante; Alessandretti, Rodrigo; Spazzin, Aloisio Oro

2015-10-01

The purpose of this study was to evaluate the influence of tightening technique and the screw coating on the loosening torque of screws used for Universal Abutment fixation after cyclic loading. Forty implants (Titamax Ti Cortical, HE, Neodent) (n=10) were submerged in acrylic resin and four tightening techniques for Universal Abutment fixation were evaluated: A - torque with 32 Ncm (control); B - torque with 32 Ncm holding the torque meter for 20 seconds; C - torque with 32 Ncm and retorque after 10 minutes; D - torque (32 Ncm) holding the torque meter for 20 seconds and retorque after 10 minutes as initially. Samples were divided into subgroups according to the screw used: conventional titanium screw or diamond like carbon-coated (DLC) screw. Metallic crowns were fabricated for each abutment. Samples were submitted to cyclic loading at 10(6) cycles and 130 N of force. Data were analyzed by two-way ANOVA and Tukey's test (5%). The tightening technique did not show significant influence on the loosening torque of screws (P=.509). Conventional titanium screws showed significant higher loosening torque values than DLC (P=.000). The use of conventional titanium screw is more important than the tightening techniques employed in this study to provide long-term stability to Universal Abutment screws.

Sacroiliac Screw Fixation

NARCIS (Netherlands)

E.W. van den Bosch

2003-01-01

textabstractThe aim of this thesis is to evaluate three major aspects of the use of sacroiliac screws in patients with unstable pelvic ring fractures: the optimal technique for sacroiliac screw fixation, the reliability of peroperative fluoroscopy and the late results. We focused on the questions

Complications of syndesmotic screw removal

NARCIS (Netherlands)

Schepers, Tim; van Lieshout, Esther M. M.; de Vries, Mark R.; van der Elst, Maarten

2011-01-01

Currently, the metallic syndesmotic screw is the gold standard in the treatment of syndesmotic disruption. Whether or not this screw needs to be removed remains debatable. The aim of the current study was to determine the complications which occur following routine removal of the syndesmotic screw

Transpedicular screw fixation in the thoracic and lumbar spine with a novel cannulated polyaxial screw system

Directory of Open Access Journals (Sweden)

Lutz Weise

2008-10-01

Full Text Available Lutz Weise, Olaf Suess, Thomas Picht, Theodoros KombosNeurochirurgische Klinik, Charité – Universitätsmedizin Berlin, Berlin, GermanyObjective: Transpedicular screws are commonly and successfully used for posterior fixation in spinal instability, but their insertion remains challenging. Even using navigation techniques, there is a misplacement rate of up to 11%. The aim of this study was to assess the accuracy of a novel pedicle screw system.Methods: Thoracic and lumbar fusions were performed on 67 consecutive patients for tumor, trauma, degenerative disease or infection. A total of 326 pedicular screws were placed using a novel wire-guided, cannulated, polyaxial screw system (XIA Precision®, Stryker. The accuracy of placement was assessed post operatively by CT scan, and the patients were followed-up clinically for a mean of 16 months.Results: The total medio-caudal pedicle wall perforation rate was 9.2% (30/326. In 19 of these 30 cases a cortical breakthrough of less than 2 mm occurred. The misplacement rate (defined as a perforation of 2 mm or more was 3.37% (11/326. Three of these 11 screws needed surgical revision due to neurological symptoms or CSF leakage. There have been no screw breakages or dislocations over the follow up-period.Conclusion: We conclude that the use of this cannulated screw system for the placement of pedicle screws in the thoracic and lumbar spine is accurate and safe. The advantages of this technique include easy handling without a time-consuming set up. Considering the incidence of long-term screw breakage, further investigation with a longer follow-up period is necessary.Keywords: spinal instrumentation, pedicle screws, misplacement, pedicle wall perforation

Scaphoid Fracture Fixation with an Acutrak? Screw

OpenAIRE

Loving, Vilert A.; Richardson, Michael L.

2015-01-01

We report a case of fixation of a scaphoid fracture using an Acutrak? screw. This screw is cannulated and headless, which allows it to be implanted below the surface of the bone. It uses the same concept of variable thread pitch as the Herbert screw, but unlike the Herbert screw, is fully threaded, with continuously varying pitch along its length. This variable pitch creates constant compression across a fracture as the screw is advanced, and gives the screw its unique appearance. This featur...

In vitro evaluation of force-expansion characteristics in a newly designed orthodontic expansion screw compared to conventional screws

Directory of Open Access Journals (Sweden)

Oshagh Morteza

2009-01-01

Full Text Available Objective : Expansion screws like Hyrax, Haas and other types, produce heavy interrupted forces which are unfavorable for dental movement and could be harmful to the tooth and periodontium. The other disadvantage of these screws is the need for patient cooperation for their regular activation. The purpose of this study was to design a screw and compare its force- expansion curve with other types. Materials and Methods : A new screw was designed and fabricated in the same dimension, with conventional types, with the ability of 8 mm expansion (Free wire length: 12 mm, initial compression: 4.5 mm, spring wire diameter: 0.4 mm, spring diameter: 3 mm, number of the coils: n0 ine, material: s0 tainless steel. In this in vitro study, the new screw was placed in an acrylic orthodontic appliance, and after mounting on a stone cast, the force-expansion curve was evaluated by a compression test machine and compared to other screws. Results : Force-expansion curve of designed screw had a flatter inclination compared to other screws. Generally it produced a light continuous force (two to 3.5 pounds for every 4 mm of expansion. Conclusion : In comparison with heavy and interrupted forces of other screws, the newly designed screw created light and continuous forces.

Geothermal ORC Systems Using Large Screw Expanders

OpenAIRE

Biederman, Tim R.; Brasz, Joost J.

2014-01-01

Geothermal ORC Systems using Large Screw Expanders Tim Biederman Cyrq Energy Abstract This paper describes a low-temperature Organic Rankine Cycle Power Recovery system with a screw expander a derivative of developed of Kaishan's line of screw compressors, as its power unit. The screw expander design is a modified version of its existing refrigeration compressor used on water-cooled chillers. Starting the ORC development program with existing refrigeration screw compre...

The applicability of PEEK-based abutment screws.

Science.gov (United States)

Schwitalla, Andreas Dominik; Abou-Emara, Mohamed; Zimmermann, Tycho; Spintig, Tobias; Beuer, Florian; Lackmann, Justus; Müller, Wolf-Dieter

2016-10-01

The high-performance polymer PEEK (poly-ether-ether-ketone) is more and more being used in the field of dentistry, mainly for removable and fixed prostheses. In cases of screw-retained implant-supported reconstructions of PEEK, an abutment screw made of PEEK might be advantageous over a conventional metal screw due to its similar elasticity. Also in case of abutment screw fracture, a screw of PEEK could be removed more easily. M1.6-abutment screws of four different PEEK compounds were subjected to tensile tests to set their maximum tensile strengths in relation to an equivalent stress of 186MPa, which is aused by a tightening torque of 15Ncm. Two screw types were manufactured via injection molding and contained 15% short carbon fibers (sCF-15) and 40% (sCF-40), respectively. Two screw types were manufactured via milling and contained 20% TiO2 powder (TiO2-20) and >50% parallel orientated, continuous carbon fibers (cCF-50). A conventional abutments screw of Ti6Al4V (Ti; CAMLOG(®) abutment screw, CAMLOG, Wimsheim, Germany) served as control. The maximum tensile strength was 76.08±5.50MPa for TiO2-20, 152.67±15.83MPa for sCF-15, 157.29±20.11MPa for sCF-40 and 191.69±36.33MPa for cCF-50. The maximum tensile strength of the Ti-screws amounted 1196.29±21.4MPa. The results of the TiO2-20 and the Ti screws were significantly different from the results of the other samples, respectively. For the manufacturing of PEEK abutment screws, PEEK reinforced by >50% continuous carbon fibers would be the material of choice. Copyright © 2016 Elsevier Ltd. All rights reserved.

Undertapping of Lumbar Pedicle Screws Can Result in Tapping With a Pitch That Differs From That of the Screw, Which Decreases Screw Pullout Force.

Science.gov (United States)

Bohl, Daniel D; Basques, Bryce A; Golinvaux, Nicholas S; Toy, Jason O; Matheis, Erika A; Bucklen, Brandon S; Grauer, Jonathan N

2015-06-15

Survey of spine surgeons and biomechanical comparison of screw pullout forces. To investigate what may be a suboptimal practice regularly occurring in spine surgery. In order for a tap to function in its intended manner, the pitch of the tap should be the same as the pitch of the screw. Undertapping has been shown to increase the pullout force of pedicle screws compared with line-to-line tapping. However, given the way current commercial lumbar pedicle screw systems are designed, undertapping may result in a tap being used that has a different pitch from that of the screw (incongruent pitch). A survey asked participants questions to estimate the proportion of cases each participant performed in the prior year using various hole preparation techniques. Participant responses were interpreted in the context of manufacturing specifications of specific instrumentation systems. Screw pullout forces were compared between undertapping with incongruent pitch and undertapping with congruent pitch using 0.16 g/cm polyurethane foam block and 6.5-mm screws. Of the 3679 cases in which participants reported tapping, participants reported line-to-line tapping in 209 cases (5%), undertapping with incongruent pitch in 1156 cases (32%), and undertapping with congruent pitch in 2314 cases (63%). The mean pullout force for undertapping with incongruent pitch was 56 N (8%) less than the mean pullout force for undertapping with congruent pitch. This is equivalent to 13 lb. This study estimates that for about 1 out of every 3 surgical cases with tapping of lumbar pedicle screws in the United States, hole preparation is being performed by undertapping with incongruent pitch. This study also shows that undertapping with incongruent pitch results in a decrease in pullout force by 8% compared with undertapping with congruent pitch. Steps should be taken to correct this suboptimal practice. 3.

Adaptive lag synchronization and parameters adaptive lag identification of chaotic systems

Energy Technology Data Exchange (ETDEWEB)

Xu Yuhua, E-mail: yuhuaxu2004@163.co [College of Information Science and Technology, Donghua University, Shanghai 201620 (China) and Department of Mathematics, Yunyang Teachers' College, Hubei, Shiyan 442000 (China); Zhou Wuneng, E-mail: wnzhou@163.co [College of Information Science and Technology, Donghua University, Shanghai 201620 (China) and Key Laboratory of Wireless Sensor Network and Communication, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Fang Jian' an, E-mail: jafang@dhu.edu.c [College of Information Science and Technology, Donghua University, Shanghai 201620 (China); Sun Wen, E-mail: sunwen_2201@163.co [School of Mathematics and Information, Yangtze University, Hubei, Jingzhou 434023 (China)

2010-07-26

This Letter investigates the problem of adaptive lag synchronization and parameters adaptive lag identification of chaotic systems. In comparison with those of existing parameters identification schemes, the unknown parameters are identified by adaptive lag laws, and the delay time is also identified in this Letter. Numerical simulations are also given to show the effectiveness of the proposed method.

Comparison of effectiveness between cork-screw and peg-screw electrodes for transcranial motor evoked potential monitoring using the finite element method.

Science.gov (United States)

Tomio, Ryosuke; Akiyama, Takenori; Ohira, Takayuki; Yoshida, Kazunari

2016-01-01

Intraoperative monitoring of motor evoked potentials by transcranial electric stimulation is popular in neurosurgery for monitoring motor function preservation. Some authors have reported that the peg-screw electrodes screwed into the skull can more effectively conduct current to the brain compared to subdermal cork-screw electrodes screwed into the skin. The aim of this study was to investigate the influence of electrode design on transcranial motor evoked potential monitoring. We estimated differences in effectiveness between the cork-screw electrode, peg-screw electrode, and cortical electrode to produce electric fields in the brain. We used the finite element method to visualize electric fields in the brain generated by transcranial electric stimulation using realistic three-dimensional head models developed from T1-weighted images. Surfaces from five layers of the head were separated as accurately as possible. We created the "cork-screws model," "1 peg-screw model," "peg-screws model," and "cortical electrode model". Electric fields in the brain radially diffused from the brain surface at a maximum just below the electrodes in coronal sections. The coronal sections and surface views of the brain showed higher electric field distributions under the peg-screw compared to the cork-screw. An extremely high electric field was observed under cortical electrodes. Our main finding was that the intensity of electric fields in the brain are higher in the peg-screw model than the cork-screw model.

Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study

Directory of Open Access Journals (Sweden)

Herrera Antonio

2010-06-01

Full Text Available Abstract Background Primary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces. A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied. Methods The tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed. Results The mean loads to failure for each group were 295,44 N (Group 1; 9 × 23 screw, 564,05 N (Group 2; 9 × 28, 614,95 N (Group 3; 9 × 35, 651,14 N (Group 4; 10 × 28 and 664,99 (Group 5; 10 × 35. No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P Conclusions Longer and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm do not achieve optimal fixation and should be implanted only with special requirements.

Percutaneous anterior C1/2 transarticular screw fixation: salvage of failed percutaneous odontoid screw fixation for odontoid fracture

OpenAIRE

Wu, Ai-Min; Jin, Hai-Ming; Lin, Zhong-Ke; Chi, Yong-Long; Wang, Xiang-Yang

2017-01-01

Background The objective of this study is to investigate the outcomes and safety of using percutaneous anterior C1/2 transarticular screw fixation as a salvage technique for odontoid fracture if percutaneous odontoid screw fixation fails. Methods Fifteen in 108 odontoid fracture patients (planned to be treated by percutaneous anterior odontoid screw fixation) were failed to introduce satisfactory odontoid screw trajectory. To salvage this problem, we chose the percutaneous anterior C1/2 trans...

Evaluation of the Effect of Fixation Angle between Polyaxial Pedicle Screw Head and Rod on the Failure of Screw-Rod Connection

Directory of Open Access Journals (Sweden)

Engin Çetin

2015-01-01

Full Text Available Introduction. Polyaxial screws had been only tested according to the ASTM standards (when they were perpendicularly positioned to the rod. In this study, effects of the pedicle screws angled fixation to the rod on the mechanical properties of fixation were investigated. Materials and Method. 30 vertically fixed screws and 30 screws fixed with angle were used in the study. Screws were used in three different diameters which were 6.5 mm, 7.0 mm, and 7.5 mm, in equal numbers. Axial pull-out and flexion moment tests were performed. Test results compared with each other using appropriate statistical methods. Results. In pull-out test, vertically fixed screws, in 6.5 mm and 7.0 mm diameter, had significantly higher maximum load values than angled fixed screws with the same diameters (P<0.01. Additionally, vertically fixed screws, in all diameters, had significantly greater stiffness according to corresponding size fixed with angle (P<0.005. Conclusion. Fixing the pedicle screw to the rod with angle significantly decreased the pull-out stiffness in all diameters. Similarly, pedicle screw instrumentation fixed with angle decreased the minimum sagittal angle between the rod and the screw in all diameters for flexion moment test but the differences were not significant.

Standard Waste Box Lid Screw Removal Option Testing

International Nuclear Information System (INIS)

Anast, Kurt Roy

2016-01-01

This report provides results from test work conducted to resolve the removal of screws securing the standard waste box (SWB) lids that hold the remediated nitrate salt (RNS) drums. The test work evaluated equipment and process alternatives for removing the 42 screws that hold the SWB lid in place. The screws were secured with a red Loctite thread locker that makes removal very difficult because the rivets that the screw threads into would slip before the screw could be freed from the rivet, making it impossible to remove the screw and therefore the SWB lid.

Standard Waste Box Lid Screw Removal Option Testing

Energy Technology Data Exchange (ETDEWEB)

Anast, Kurt Roy [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2016-03-11

This report provides results from test work conducted to resolve the removal of screws securing the standard waste box (SWB) lids that hold the remediated nitrate salt (RNS) drums. The test work evaluated equipment and process alternatives for removing the 42 screws that hold the SWB lid in place. The screws were secured with a red Loctite thread locker that makes removal very difficult because the rivets that the screw threads into would slip before the screw could be freed from the rivet, making it impossible to remove the screw and therefore the SWB lid.

Misplaced Cervical Screws Requiring Reoperation.

Science.gov (United States)

Peterson, Jeremy C; Arnold, Paul M; Smith, Zachary A; Hsu, Wellington K; Fehlings, Michael G; Hart, Robert A; Hilibrand, Alan S; Nassr, Ahmad; Rahman, Ra'Kerry K; Tannoury, Chadi A; Tannoury, Tony; Mroz, Thomas E; Currier, Bradford L; De Giacomo, Anthony F; Fogelson, Jeremy L; Jobse, Bruce C; Massicotte, Eric M; Riew, K Daniel

2017-04-01

A multicenter, retrospective case series. In the past several years, screw fixation of the cervical spine has become commonplace. For the most part, this is a safe, low-risk procedure. While rare, screw backout or misplaced screws can lead to morbidity and increased costs. We report our experiences with this uncommon complication. A multicenter, retrospective case series was undertaken at 23 institutions in the United States. Patients were included who underwent cervical spine surgery from January 1, 2005, to December 31, 2011, and had misplacement of screws requiring reoperation. Institutional review board approval was obtained at all participating institutions, and detailed records were sent to a central data center. A total of 12 903 patients met the inclusion criteria and were analyzed. There were 11 instances of screw backout requiring reoperation, for an incidence of 0.085%. There were 7 posterior procedures. Importantly, there were no changes in the health-related quality-of-life metrics due to this complication. There were no new neurologic deficits; a patient most often presented with pain, and misplacement was diagnosed on plain X-ray or computed tomography scan. The most common location for screw backout was C6 (36%). This study represents the largest series to tabulate the incidence of misplacement of screws following cervical spine surgery, which led to revision procedures. The data suggest this is a rare event, despite the widespread use of cervical fixation. Patients suffering this complication can require revision, but do not usually suffer neurologic sequelae. These patients have increased cost of care. Meticulous technique and thorough knowledge of the relevant anatomy are the best means of preventing this complication.

Are We Underestimating the Significance of Pedicle Screw Misplacement?

Science.gov (United States)

Sarwahi, Vishal; Wendolowski, Stephen F; Gecelter, Rachel C; Amaral, Terry; Lo, Yungtai; Wollowick, Adam L; Thornhill, Beverly

2016-05-01

A retrospective review of charts, x-rays (XRs) and computed tomography (CT) scans was performed. To evaluate the accuracy of pedicle screw placement using a novel classification system to determine potentially significant screw misplacement. The accuracy rate of pedicle screw (PS) placement varies from 85% to 95% in the literature. This demonstrates technical ability but does not represent the impact of screw misplacement on individual patients. This study quantifies the rate of screw misplacement on a per-patient basis to highlight its effect on potential morbidity. A retrospective review of charts, XRs and low-dose CT scans of 127 patients who underwent spinal fusion with pedicle screws for spinal deformity was performed. Screws were divided into four categories: screws at risk (SAR), indeterminate misplacements (IMP), benign misplacements (BMP), accurately placed (AP). A total of 2724 screws were placed in 127 patients. A total of 2396 screws were placed accurately (87.96%). A total of 247 screws (9.07%) were BMP, 52 (1.91%) were IMP, and 29 (1.06%) were considered SAR. Per-patient analysis showed 23 (18.11%) of patients had all screws AP. Thirty-five (27.56%) had IMP and 18 (14.17%) had SAR. Risk factor analysis showed smaller Cobb angles increased likelihood of all screws being AP. Sub-analysis of adolescent idiopathic scoliotic patients showed no curve or patient characteristic that correlated with IMP or SAR. Over 40% of patients had screws with either some/major concern. Overall reported screw misplacement is low, but it does not reflect the potential impact on patient morbidity. Per-patient analysis reveals more concerning numbers toward screw misplacement. With increasing pedicle screw usage, the number of patients with misplaced screws will likely increase proportionally. Better strategies need to be devised for evaluation of screw placement, including establishment of a national database of deformity surgery, use of intra-operative image guidance, and

Tricortical cervical inter-body screw fixation.

Directory of Open Access Journals (Sweden)

Goel A

1997-01-01

Full Text Available A new tricortical method of screw implantation for anterior cervical interbody plate fixation is described. The screws are placed obliquely such that they engage the anterior cortex of the body and traverse through the cortices adjoining the disc space. By this method the screws not only hold the plate firmly with a tricortical purchase, but by virtue of their course stabilize the two adjoining vertebral bodies by themselves. Sixteen patients were treated by this method. In three of these cases only tricortical screws without the metal plate were used for fixation. The advantages of the technique are discussed.

Accuracy of computer-assisted cervicle pedicle screw installation

International Nuclear Information System (INIS)

Zhang Honglei; Zhou Dongsheng; Jang Zhensong

2009-01-01

Objective: To investigate the accuracy of computer-assisted cervical pedicle screw installation and the reason of screw malposition. Methods: A total of 172 cervical pedicle screws were installed by computer-assisted navigation for 30 patients with lower cervical spinal diseases. All the patients were examined by X-ray and CT after operation. Screw's position and direction were measured on the sagittal and transectional images of intraoperative navigation and post-operative CT. Then linear regression analysis was taken between navigational and post-operative CT's images. Results: Two screws perforated the upper pedicle wall, 3 perforated the lateral pedicle wall.There was a positive linear correlation between navigational and post-operative CT's images. Conclusion: Computer-assisted navigation can provide the high accuracy of cervical pedicle screw installation and excursion phenomenon is reason of screw malposition. (authors)

Photothermal waves for two temperature with a semiconducting medium under using a dual-phase-lag model and hydrostatic initial stress

Science.gov (United States)

Lotfy, Kh.

2017-07-01

The dual-phase-lag (DPL) model with two different time translations and Lord-Shulman (LS) theory with one relaxation time are applied to study the effect of hydrostatic initial stress on medium under the influence of two temperature parameter(a new model will be introduced using two temperature theory) and photothermal theory. We solved the thermal loading at the free surface in the semi-infinite semiconducting medium-coupled plasma waves with the effect of mechanical force during a photothermal process. The exact expressions of the considered variables are obtained using normal mode analysis also the two temperature coefficient ratios were obtained analytically. Numerical results for the field quantities are given in the physical domain and illustrated graphically under the effects of several parameters. Comparisons are made between the results of the two different models with and without two temperature parameter, and for two different values of the hydrostatic initial stress. A comparison is carried out between the considered variables as calculated from the generalized thermoelasticity based on the DPL model and the LS theory in the absence and presence of the thermoelastic and thermoelectric coupling parameters.

Comparison of Expansive Pedicle Screw and Polymethylmethacrylate-Augmented Pedicle Screw in Osteoporotic Sheep Lumbar Vertebrae: Biomechanical and Interfacial Evaluations

OpenAIRE

Liu, Da; Zhang, Yi; Zhang, Bo; Xie, Qing-yun; Wang, Cai-ru; Liu, Jin-biao; Liao, Dong-fa; Jiang, Kai; Lei, Wei; Pan, Xian-ming

2013-01-01

BACKGROUND: It was reported that expansive pedicle screw (EPS) and polymethylmethacrylate-augmented pedicle screw (PMMA-PS) could be used to increase screw stability in osteoporosis. However, there are no studies comparing the two kinds of screws in vivo. Thus, we aimed to compare biomechanical and interfacial performances of EPS and PMMA-PS in osteoporotic sheep spine. METHODOLOGY/PRINCIPAL FINDINGS: After successful induction of osteoporotic sheep, lumbar vertebrae in each sheep were random...

Simple Technique for Removing Broken Pedicular Screws

Directory of Open Access Journals (Sweden)

A Agrawal

2014-03-01

Full Text Available The procedure for removing a broken pedicle screw should ideally be technically easy and minimally invasive, as any damage to the pedicle, during removal of the broken screw, may weaken the pedicle, thus compromising on the success of re-instrumentation. We describe the case of a 32-year old man who had undergone surgery for traumatic third lumbar vertebral body fracture three years prior to current admission and had developed the complication of pedicle screw breakage within the vertebral body. The patient underwent re-exploration and removal of the distal screws. Through a paravertebral incision and muscle separation, the screws and rods were exposed and the implants were removed.

The effect of different screw-rod design on the anti-rotational torque: a biomechanical comparison of three conventional screw-rod constructs.

Science.gov (United States)

Huang, Zifang; Wang, Chongwen; Fan, Hengwei; Sui, Wenyuan; Li, Xueshi; Wang, Qifei; Yang, Junlin

2017-07-28

Screw-rod constructs have been widely used to correct spinal deformities, but the effects of different screw-rod systems on anti-rotational torque have not been determined. This study aimed to analyze the biomechanical effect of different rod-screw constructs on anti-rotational torque. Three conventional spinal screw-rod systems (Legacy, RF-F-10 and USSII) were used to test the anti-rotational torque in the material test machine. ANOVA was performed to evaluate the anti-rotational capacity of different pedicle screws-rod constructs. The anti-rotational torque of Legacy group, RF-F-10 group and USSII group were 12.3 ± 1.9 Nm, 6.8 ± 0.4 Nm, and 3.9 ± 0.8 Nm, with a P value lower than 0.05. This results indicated that the Legacy screws-rod construct could provide a highest anti-rotation capacity, which is 68% and 210% greater than RF-F-10 screw-rod construct and USSII screw-rod respectively. The anti-rotational torque may be mainly affected by screw cap and groove design. Our result showed the anti-rotational torque are: Legacy system > RF-F-10 system > USSII system, suggesting that appropriate rod-screw constructs selection in surgery may be vital for anti-rotational torque improvement and preventing derotation correction loss.

Screw piles for cold climate foundations

Energy Technology Data Exchange (ETDEWEB)

Schmidt, R.; Sakr, M. [Almita Manufacturing Ltd., Edmonton, AB (Canada)

2008-07-01

Almita Manufacturing is an Alberta-based company that designs and builds screw piles with its own installation teams. It also engineers and supplies piles to numerous other companies and independent installers. The company services industries such as oil and gas; power transmission and distribution; and commercial construction. This presentation discussed the design and technical aspects of screw piles. A screw pile was defined as a steel pipe shaft with a 45 degree cut at the bottom and a formed helical plate welded to the outside of the pipe near the base and at a selected point on the shaft. The pile is screwed into the ground with a planetary drive head of suitable torque rating. The helical plate or helix helps facilitate the installation of the pile and gives the screw pile increased bearing capacity and pull-out resistance over a traditional straight-shaft pile. Screw piles were compared against cast in place concrete piles and steel driven piles. Screw piles were reported to have no tailings; no concrete curing time; no rebar, anchor belts, and no liners; and no dewatering. Screw piles can also be installed in all types of weather. Rhe Cree Burn Camp case study near Fort McMurray, Alberta was also presented. This residential camp and recreation complex consists of pre-fabricated units that make up three storey housing buildings and a single floor multi-use building. The case study provided information on soil; design parameter inputs; load testing program and pile configuration; geotechnical and structural design results; compression load test arrangement; pile test setup; and test results. The presentation also discussed fabrication as well as installation equipment. Various applications were also presented through a series of project pictures. Last, the presentation provided a simple cost analysis. tabs., figs.

A biomechanical comparison of headless tapered variable pitch and AO cortical bone screws for fixation of a simulated slab fracture in equine third carpal bones.

Science.gov (United States)

Bueno, Aloisio C D; Galuppo, Larry D; Taylor, Kenneth T; Jensen, David G; Stover, Susan M

2003-01-01

To compare the mechanical shear strengths and stiffnesses obtained from in vitro testing of a simulated complete third carpal bone (C3) frontal plane radial facet slab fracture (osteotomy) stabilized with either a 4/5 Acutrak (AT) compression screw or a 4.5-mm AO cortical bone (AO) screw inserted in lag fashion. Drilling, tapping, and screw insertion torques, forces, and times also were compared between AT and AO implants. In vitro biomechanical assessment of site preparation, screw insertion, and shear failure test variables of bone screw stabilized simulated C3 slab fracture in paired cadaveric equine carpi. Eight pairs of cadaveric equine C3 without orthopedic abnormalities. Standardized simulated C3 slab fractures were repaired with either AO or AT screws (AO/C3 and AT/C3 groups, respectively). Drilling, tapping, and screw insertion torques, forces, and times were measured with a materials testing machine for each screw type. Repaired specimens were tested in axially oriented shear until failure. Paired Students t-tests were used to assess differences between site preparation, screw insertion, and shear testing variables. Significance was set at P bone fragment measurements of the standardized simulated C3 slab fractures created for AO or AT screws. There were no significant differences for mean and maximum drilling torques; however, the tapered AT drill had greater maximum drilling force compared with the 3.2-mm and 4.5-mm AO drill bits. Mean insertion torque and force measured from the self-tapping AT screw were not significantly different compared with the 4.5-mm AO tap. There were no significant differences in maximum screw torque among constructs. Total procedure time was significantly longer for the AT group (5.8 +/- 1.6 minutes) compared with the AO group (2.9 +/- 1.1 minutes; P =.001). AT stabilized specimens had significantly greater mean +/- SD initial shear stiffness (3.64 +/- 1.08 kN/mm) than AO specimens (1.64 +/- 0.73 kN/mm; P =.005). All other

Complications of syndesmotic screw removal

NARCIS (Netherlands)

T. Schepers (Tim); E.M.M. van Lieshout (Esther); M.R. de Vries (Mark); M. van der Elst (Maarten)

2011-01-01

textabstractBackground: Currently, the metallic syndesmotic screw is the gold standard in the treatment of syndesmotic disruption. Whether or not this screw needs to be removed remains debatable. The aim of the current study was to determine the complications which occur following routine removal of

Vertical-Screw-Auger Conveyer Feeder

Science.gov (United States)

Walton, Otis (Inventor); Vollmer, Hubert J. (Inventor)

2016-01-01

A conical feeder is attached to a vertically conveying screw auger. The feeder is equipped with scoops and rotated from the surface to force-feed regolith the auger. Additional scoops are possible by adding a cylindrical section above the conical funnel section. Such then allows the unit to collect material from swaths larger in diameter than the enclosing casing pipe of the screw auger. A third element includes a flexible screw auger. All three can be used in combination in microgravity and zero atmosphere environments to drill and recover a wide area of subsurface regolith and entrained volatiles through a single access point on the surface.

Calculating Characteristics of the Screws with Constant And Variable Step

Directory of Open Access Journals (Sweden)

B. N. Zotov

2015-01-01

Full Text Available This work is devoted to creating a technique for calculating power characteristics of the screws with constant and variable step for the centrifugal pumps. The technique feature is that the reverse currents, which are observed in screws working at low flow, are numerically taken into account. The paper presents a diagram of the stream in the screw with flow to the network Q=0, and the static pressure of the screw in this mode is computed according to reverse current parameters. Maximum flow of screw is determined from the known formulas. When calculating the power characteristics and computing the overall efficiency of the screw, for the first time a volumetric efficiency of the screw is introduced. It is defined as a ratio between the flow into the network and the sum of the reverse current flows and a flow into the network. This approach allowed us to determine the efficiency of the screw over the entire range of flows.A comparison of experimental characteristics of the constant step screw with those of calculated by the proposed technique shows their good agreement.The technique is also used in calculating characteristics of the variable step screws. The variable step screw is considered as a screw consisting of two screws with a smooth transition of the blades from the inlet to the outlet. Screws in which the step at the inlet is less than that of at the outlet as well as screws with the step at the inlet being more than that of at the outlet were investigated. It is shown that a pressure of the screw with zero step and the value of the reverse currents depend only on the parameters of the input section of the screw, and the maximum flow, if the step at the inlet is more than the step at the outlet, is determined by the parameters of the output part of the screw. Otherwise, the maximum flow is determined a little bit differently.The paper compares experimental characteristics with characteristics calculated by the technique for variable step

A Novel Pedicle Screw with Mobile Connection: A Pilot Study

Directory of Open Access Journals (Sweden)

Yasuaki Tokuhashi

2014-01-01

Full Text Available To prevent adjacent disc problems after spinal fusion, a pedicle screw with a mobile junction between the head and threaded shaft was newly developed. The threaded shaft of the screw has 10 degrees mobility in all directions, but its structure is to prevent abnormal translation and tilting. This screw was evaluated as follows: (1 endurance test: 106 times rotational stress was applied; (2 biological reactions: novel screws with a mobile head and conventional screws with a fixed head were inserted into the bilateral pedicles of the L3, L4, and L5 in two mini pigs with combination. Eight months after surgery, vertebral units with the screw rod constructs were collected. After CT scan, the soft and bony tissues around the screws were examined grossly and histologically. As a result, none of the screws broke during the endurance test stressing. The mean amount of abrasion wear was 0.0338 g. In the resected mini pig section, though zygapophyseal joints between fixed-head screws showed bony union, the amount of callus in the zygapophyseal joints connected with mobile-head screws was small, and joint space was confirmed by CT. No metalloses were noted around any of the screws. Novel screws were suggested to be highly durable and histologically safe.

A biomechanical comparison of headless tapered variable pitch compression and ao cortical bone screws for fixation of a simulated midbody transverse fracture of the proximal sesamoid bone in horses.

Science.gov (United States)

Eddy, Alison L; Galuppo, Larry D; Stover, Susan M; Taylor, Kenneth T; Jensen, David G

2004-01-01

To compare mechanical properties and failure characteristics of 2 methods of fixation for repair of a transverse, midbody fracture of the proximal sesamoid bone (PSB): 4.5-mm AO cortical bone screw (AO) placed in lag fashion and 4/5-mm Acutrak (AT) self-compressing screw. An in vitro biomechanical evaluation of intact forelimb preparations and forelimb preparations with a simulated midbody PSB fracture stabilized by a bone screw. Sixteen paired and 8 unilateral cadaveric equine forelimbs. A midbody transverse osteotomy was created in the medial PSB of bilateral forelimbs of 8 equine cadavers. The osteotomized PSB in 1 forelimb from each cadaver was repaired with an AO screw. The osteotomized PSB in each contralateral limb was repaired with an AT screw. Eight unilateral intact control limbs were also studied. Mechanical properties were determined from axial compression, single cycle to failure, load-deformation curves. Failure characteristics were determined by evaluation of video images and radiographs. No statistically significant differences were found between repair groups. Both AO and AT groups had significantly lower mechanical properties than intact limbs except for stiffness. AO and AT constructs were mechanically comparable when used to stabilize a simulated midbody fracture of the medial PSB. Both constructs were mechanically inferior to intact limbs. Clinical Relevance- The AT screw should be considered for clinical use because of the potential for less soft tissue impingement and superior biocompatibility compared with the stainless-steel AO screw. However, postoperative external coaptation is necessary to augment initial fracture stability for either fixation method, and to maintain a standing metacarpophalangeal joint dorsiflexion angle between 150 degrees and 155 degrees.

Minimally Invasive Technique for PMMA Augmentation of Fenestrated Screws

Directory of Open Access Journals (Sweden)

Jan-Helge Klingler

2015-01-01

Full Text Available Purpose. To describe the minimally invasive technique for cement augmentation of cannulated and fenestrated screws using an injection cannula as well as to report its safety and efficacy. Methods. A total of 157 cannulated and fenestrated pedicle screws had been cement-augmented during minimally invasive posterior screw-rod spondylodesis in 35 patients from January to December 2012. Retrospective evaluation of cement extravasation and screw loosening was carried out in postoperative plain radiographs and thin-sliced triplanar computed tomography scans. Results. Twenty-seven, largely prevertebral cement extravasations were detected in 157 screws (17.2%. None of the cement extravasations was causing a clinical sequela like a new neurological deficit. One screw loosening was noted (0.6% after a mean follow-up of 12.8 months. We observed no cementation-associated complication like pulmonary embolism or hemodynamic insufficiency. Conclusions. The presented minimally invasive cement augmentation technique using an injection cannula facilitates convenient and safe cement delivery through polyaxial cannulated and fenestrated screws during minimally invasive screw-rod spondylodesis. Nevertheless, the optimal injection technique and design of fenestrated screws have yet to be identified. This trial is registered with German Clinical Trials DRKS00006726.

Insertion profiles of 4 headless compression screws.

Science.gov (United States)

Hart, Adam; Harvey, Edward J; Lefebvre, Louis-Philippe; Barthelat, Francois; Rabiei, Reza; Martineau, Paul A

2013-09-01

In practice, the surgeon must rely on screw position (insertion depth) and tactile feedback from the screwdriver (insertion torque) to gauge compression. In this study, we identified the relationship between interfragmentary compression and these 2 factors. The Acutrak Standard, Acutrak Mini, Synthes 3.0, and Herbert-Whipple implants were tested using a polyurethane foam scaphoid model. A specialized testing jig simultaneously measured compression force, insertion torque, and insertion depth at half-screw-turn intervals until failure occurred. The peak compression occurs at an insertion depth of -3.1 mm, -2.8 mm, 0.9 mm, and 1.5 mm for the Acutrak Mini, Acutrak Standard, Herbert-Whipple, and Synthes screws respectively (insertion depth is positive when the screw is proud above the bone and negative when buried). The compression and insertion torque at a depth of -2 mm were found to be 113 ± 18 N and 0.348 ± 0.052 Nm for the Acutrak Standard, 104 ± 15 N and 0.175 ± 0.008 Nm for the Acutrak Mini, 78 ± 9 N and 0.245 ± 0.006 Nm for the Herbert-Whipple, and 67 ± 2N, 0.233 ± 0.010 Nm for the Synthes headless compression screws. All 4 screws generated a sizable amount of compression (> 60 N) over a wide range of insertion depths. The compression at the commonly recommended insertion depth of -2 mm was not significantly different between screws; thus, implant selection should not be based on compression profile alone. Conically shaped screws (Acutrak) generated their peak compression when they were fully buried in the foam whereas the shanked screws (Synthes and Herbert-Whipple) reached peak compression before they were fully inserted. Because insertion torque correlated poorly with compression, surgeons should avoid using tactile judgment of torque as a proxy for compression. Knowledge of the insertion profile may improve our understanding of the implants, provide a better basis for comparing screws, and enable the surgeon to optimize compression. Copyright �

Ball Screw Actuator Including a Stop with an Integral Guide

Science.gov (United States)

Wingett, Paul T. (Inventor); Perek, John (Inventor); Geck, Kellan (Inventor)

2015-01-01

An actuator includes a housing assembly, a ball nut, a ball screw, and a ball screw stop. The ball nut is rotationally mounted in the housing assembly, is adapted to receive an input torque, and is configured, upon receipt thereof, to rotate and supply a drive force. The ball screw is mounted within the housing assembly and extends through the ball nut. The ball screw has a first end and a second end, and is coupled to receive the drive force from the ball nut. The ball screw is configured, upon receipt of the drive force, to selectively translate between a stow position and a deploy position. The ball screw stop is mounted on the ball screw to translate therewith and is configured to at selectively engage the housing assembly while the ball screw is translating, and engage the ball nut when the ball screw is in the deploy position.

Ball Screw Actuator Including an Axial Soft Stop

Science.gov (United States)

Wingett, Paul T. (Inventor); Forrest, Steven Talbert (Inventor); Abel, Steve (Inventor); Woessner, George (Inventor); Hanlon, Casey (Inventor)

2016-01-01

An actuator includes an actuator housing, a ball screw, and an axial soft stop assembly. The ball screw extends through the actuator housing and has a first end and a second end. The ball screw is coupled to receive a drive force and is configured, upon receipt of the drive force, to selectively move in a retract direction and an extend direction. The axial soft stop assembly is disposed within the actuator housing. The axial soft stop assembly is configured to be selectively engaged by the ball screw and, upon being engaged thereby, to translate, with compliance, a predetermined distance in the extend direction, and to prevent further movement of the ball screw upon translating the predetermined distance.

Time lags in biological models

CERN Document Server

MacDonald, Norman

1978-01-01

In many biological models it is necessary to allow the rates of change of the variables to depend on the past history, rather than only the current values, of the variables. The models may require discrete lags, with the use of delay-differential equations, or distributed lags, with the use of integro-differential equations. In these lecture notes I discuss the reasons for including lags, especially distributed lags, in biological models. These reasons may be inherent in the system studied, or may be the result of simplifying assumptions made in the model used. I examine some of the techniques available for studying the solution of the equations. A large proportion of the material presented relates to a special method that can be applied to a particular class of distributed lags. This method uses an extended set of ordinary differential equations. I examine the local stability of equilibrium points, and the existence and frequency of periodic solutions. I discuss the qualitative effects of lags, and how these...

Hydraulic screw fastening devices - design, maintenance, operational experience

International Nuclear Information System (INIS)

Lachner.

1976-01-01

With hydraulic screw fastening devices, pretension values with a maximum deviation of +-2.5% from the rated value can be achieved. This high degree of pretension accuracy is of considerable importance with regard to the safety factor required for the screw connection between reactor vessel head and reactor vessel. The operating rhythm of a nuclear power station with its refuelling art regular intervals makes further demands on the screw fastening device, in particular in connection with the transport of screws and for nuts. The necessary installations extend the screw fastening device into a combination of a high-pressure hydraulic cylinder system with an electrical or pneumoelectrical driving unit and an electrical control unit. Maintenance work is complicated by the large number of identical, highly stressed structural elements in connection with an unfavourable relation operating time/outage time. The problems have been perpetually reduced by close cooperation between the manufacturers and users of screw fastening devices. (orig./AK) [de

Stress corrosion cracking lifetime prediction of spring screw

International Nuclear Information System (INIS)

Koh, S. K.; Ryu, C. H.

2004-01-01

A lifetime prediction of holddown spring screw in nuclear fuel assembly was performed using fracture mechanics approach. The spring screw was designed such that it was capable of sustaining the loads imposed by the initial tensile preload and operational loads. In order to investigate the cause of failure and to predict the stress corrosion cracking life of the screw, a stress analysis of the top nozzle spring assembly was done using finite element analysis. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Normalized stress intensity factors for PWSCC life prediction was proposed. Primary water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of the Scott model and resulted in 1.78 years, which was fairly close to the actual service life of the holddown spring screw

Magnesium Alloys as a Biomaterial for Degradable Craniofacial Screws

Science.gov (United States)

Henderson, Sarah E.; Verdelis, Konstantinos; Maiti, Spandan; Pal, Siladitya; Chung, William L.; Chou, Da-Tren; Kumta, Prashant N.; Almarza, Alejandro J.

2014-01-01

Recently, magnesium (Mg) alloys have received significant attention as a potential biomaterial for degradable implants, and this study was directed at evaluating the suitability of Mg for craniofacial bone screws. The objective was to implant screws fabricated from commercially available Mg-alloys (pure Mg and AZ31) in-vivo in a rabbit mandible. First, Mg-alloy screws were compared to stainless steel screws in an in-vitro pull-out test and determined to have a similar holding strength (~40N). A finite element model of the screw was created using the pull-out test data, and the model can be used for future Mg-alloy screw design. Then, Mg-alloy screws were implanted for 4, 8, and 12 weeks, with two controls of an osteotomy site (hole) with no implant and a stainless steel screw implanted for 12 weeks. MicroCT (computed tomography) was used to assess bone remodeling and Mg-alloy degradation, both visually and qualitatively through volume fraction measurements for all time points. Histologic analysis was also completed for the Mg-alloys at 12 weeks. The results showed that craniofacial bone remodeling occurred around both Mg-alloy screw types. Pure Mg had a different degradation profile than AZ31, however bone growth occurred around both screw types. The degradation rate of both Mg-alloy screw types in the bone marrow space and the muscle were faster than in the cortical bone space at 12 weeks. Furthermore, it was shown that by alloying Mg, the degradation profile could be changed. These results indicate the promise of using Mg-alloys for craniofacial applications. PMID:24384125

Tightening techniques for the retaining screws of universal abutment

Directory of Open Access Journals (Sweden)

Alexandre Wittcinski REGALIN

Full Text Available Abstract Purpose This study evaluated the torque maintenance of universal abutment retaining screws using different tightening techniques, and coated or uncoated screws. Material and method The screws were tightened to implants as following: Control – 32 Ncm torque; H20 – holding 32 Ncm torque for 20 s; R – 32 Ncm torque, repeated after 10 min (retorque; and H20+R – combining the two tightening techniques. Titanium and coated screws were also evaluated. Result Statistical analysis showed higher maintained torque for titanium screws (p<0.001. The H20+R technique showed the highest maintained torque (p=0.003, but the H20 technique’s maintained torque was similar. Conclusion Titanium screws associating the two tightening techniques can improve maintained torque.

Do screws and screw holes affect osteolysis in cementless cups using highly crosslinked polyethylene? A 7 to 10-year follow-up case-control study.

Science.gov (United States)

Taniguchi, N; Jinno, T; Takada, R; Koga, D; Ando, T; Okawa, A; Haro, H

2018-05-01

The use of screws and the presence of screw holes may cause acetabular osteolysis and implant loosening in cementless total hip arthroplasty (THA) using conventional polyethylene. In contrast, this issue is not fully understood using highly crosslinked polyethylene (HXLPE), particularly in large comparative study. Therefore, we performed a case-control study to assess the influence of screw usage and screw holes on: (1) implant fixation and osteolysis and (2) polyethylene steady-state wear rate, using cases with HXLPE liners followed up for 7-10 years postoperatively. The screw usage and screw holes adversely affect the implant fixation and incidence of wear-related osteolysis in THA with HXLPE. We reviewed 209 primary cementless THAs performed with 26-mm cobalt-chromium heads on HXLPE liners. To compare the effects of the use of screws and the presence of screw holes, the following groups were established: (1) with-screw (n=140); (2) without-screw (n=69); (3) no-hole (n=27) and (4) group in which a cup with screw holes, but no screw was used (n=42). Two adjunct groups (no-hole cups excluded) were established to compare the differences in the two types of HXLPE: (5) remelted group (n=100) and (6) annealed group (n=82). Implant stability and osteolysis were evaluated by plain radiography and computed tomography. The wear rate from 1 year to the final evaluation was measured using plain X-rays and PolyWare Digital software. All cups and stems achieved bony fixation. On CT-scan, no acetabular osteolysis was found, but there were 3 cases with a small area of femoral osteolysis. The mean steady-state wear rate of each group was (1) 0.031±0.022, (2) 0.033±0.035, (3) 0.031±0.024, (4) 0.029±0.018, (5) 0.030±0.018 and (6) 0.034±0.023mm/year, respectively. A comparison of the effects of screw usage or screw holes found no significant between-group differences in the implant stability, prevalence of osteolysis [no acetabular osteolysis and 3/209 at femoral side (1

A geometrical introduction to screw theory

International Nuclear Information System (INIS)

Minguzzi, E

2013-01-01

This work introduces screw theory, a venerable but little known theory aimed at describing rigid body dynamics. This formulation of mechanics unifies in the concept of screw the translational and rotational degrees of freedom of the body. It captures a remarkable mathematical analogy between mechanical momenta and linear velocities, and between forces and angular velocities. For instance, it clarifies that angular velocities should be treated as applied vectors and that, under the composition of motions, they sum with the same rules of applied forces. This work provides a short and rigorous introduction to screw theory intended for an undergraduate and general readership. (paper)

Twin screw wet granulation: Binder delivery.

Science.gov (United States)

Saleh, Mohammed F; Dhenge, Ranjit M; Cartwright, James J; Hounslow, Michael J; Salman, Agba D

2015-06-20

The effects of three ways of binder delivery into the twin screw granulator (TSG) on the residence time, torque, properties of granules (size, shape, strength) and binder distribution were studied. The binder distribution was visualised through the transparent barrel using high speed imaging as well as quantified using offline technique. Furthermore, the effect of binder delivery and the change of screw configuration (conveying elements only and conveying elements with kneading elements) on the surface velocity of granules across the screw channel were investigated using particle image velocimetry (PIV). The binder was delivered in three ways; all solid binder incorporated with powder mixture, 50% of solid binder mixed with powder mixture and 50% mixed with water, all the solid binder dissolved in water. Incorporation of all solid binder with powder mixture resulted in the relatively longer residence time and higher torque, narrower granule size distribution, more spherical granules, weaker big-sized granules, stronger small-sized granules and better binder distribution compared to that in other two ways. The surface velocity of granules showed variation from one screw to another as a result of uneven liquid distribution as well as shown a reduction while introducing the kneading elements into the screw configuration. Copyright © 2015. Published by Elsevier B.V.

Development of structural schemes of parallel structure manipulators using screw calculus

Science.gov (United States)

Rashoyan, G. V.; Shalyukhin, K. A.; Gaponenko, EV

2018-03-01

The paper considers the approach to the structural analysis and synthesis of parallel structure robots based on the mathematical apparatus of groups of screws and on a concept of reciprocity of screws. The results are depicted of synthesis of parallel structure robots with different numbers of degrees of freedom, corresponding to the different groups of screws. Power screws are applied with this aim, based on the principle of static-kinematic analogy; the power screws are similar to the orts of axes of not driven kinematic pairs of a corresponding connecting chain. Accordingly, kinematic screws of the outlet chain of a robot are simultaneously determined which are reciprocal to power screws of kinematic sub-chains. Solution of certain synthesis problems is illustrated with practical applications. Closed groups of screws can have eight types. The three-membered groups of screws are of greatest significance, as well as four-membered screw groups [1] and six-membered screw groups. Three-membered screw groups correspond to progressively guiding mechanisms, to spherical mechanisms, and to planar mechanisms. The four-membered group corresponds to the motion of the SCARA robot. The six-membered group includes all possible motions. From the works of A.P. Kotelnikov, F.M. Dimentberg, it is known that closed fifth-order screw groups do not exist. The article presents examples of the mechanisms corresponding to the given groups.

CT provides precise size assessment of implanted titanium alloy pedicle screws.

Science.gov (United States)

Elliott, Michael J; Slakey, Joseph B

2014-05-01

After performing instrumented spinal fusion with pedicle screws, postoperative imaging using CT to assess screw position may be necessary. Stainless steel implants produce significant metal artifact on CT, and the degree of distortion is at least partially dependent on the cross-sectional area of the implanted device. If the same effect occurs with titanium alloy implants, ability to precisely measure proximity of screws to adjacent structures may be adversely affected as screw size increases. We therefore asked whether (1) CT provides precise measurements of true screw widths; and (2) precision degrades based on the size of the titanium implant imaged. CT scans performed on 20 patients after instrumented spinal fusion for scoliosis were reviewed. The sizes of 151 titanium alloy pedicle screws were measured and compared with known screw size. The amount of metal bloom artifact was determined for each of the four screw sizes. ANOVA with Tukey's post hoc test were performed to evaluate differences in scatter, and Spearman's rho coefficient was used to measure relationship between screw size and scatter. All screws measured larger than their known size, but even with larger 7-mm screws the size differential was less than 1 mm. The four different screw sizes produced scatter amounts that were different from each other (p titanium alloy pedicle screws produces minimal artifact, thus making this the preferred imaging modality to assess screw position after surgery. Although the amount of artifact increases with the volume of titanium present, the degree of distortion is minimal and is usually less than 1 mm.

Fate of the syndesmotic screw--Search for a prudent solution.

Science.gov (United States)

Kaftandziev, Igor; Spasov, Marko; Trpeski, Simon; Zafirova-Ivanovska, Beti; Bakota, Bore

2015-11-01

Ankle fractures are common injuries. Since the recognition of the importance of syndesmotic injury in ankle fractures, much of the scientific work has been focused on concomitant syndesmotic injury. Despite the invention of novel devices for restoration and maintenance of the congruent syndesmosis following syndesmotic injury, the metallic syndesmotic screw is still considered to be the "gold standard". The aim of this study was to compare the clinical results in patients who retained the syndesmosis screw with those in whom the screw was removed following open reduction and internal fixation of the malleolar fracture associated with syndesmosis disruption. This was a retrospective study of 82 patients. Minimum follow-up was 12 months. Clinical evaluation included American Orthopaedic Foot and Ankle Society (AOFAS) score and Visual Analogue Scale (VAS) for patient general satisfaction. The condition of the screw (removed, intact or broken), presence of radiolucency around the syndesmotic screw and the tibiofibular clear space were recorded using final follow-up radiographs. Three cortices were engaged in 66 patients (80%) and quadricortical fixation was performed in the remaining 16 patients (20%). The number of engaged cortices did not correlate with the clinical outcome and screw fracture. A single syndesmotic screw was used in 71 patients (86%. The mean AOFAS score in the group with intact screw (I) was 83; the scores in the group with broken screw (B) and removed screw (R) were 92.5 and 85.5, respectively. There was a statistically significant difference between the three groups: this was due to the difference between groups I and B; the difference between groups I and R and groups B and R were not statistically significant. There were no statistically significant differences in VAS results. There were no statistically significant differences in clinical outcome between the group with the screw retained and the group in which the screw was removed; however, the

Economics of water injected air screw compressor systems

Science.gov (United States)

Venu Madhav, K.; Kovačević, A.

2015-08-01

There is a growing need for compressed air free of entrained oil to be used in industry. In many cases it can be supplied by oil flooded screw compressors with multi stage filtration systems, or by oil free screw compressors. However, if water injected screw compressors can be made to operate reliably, they could be more efficient and therefore cheaper to operate. Unfortunately, to date, such machines have proved to be insufficiently reliable and not cost effective. This paper describes an investigation carried out to determine the current limitations of water injected screw compressor systems and how these could be overcome in the 15-315 kW power range and delivery pressures of 6-10 bar. Modern rotor profiles and approach to sealing and cooling allow reasonably inexpensive air end design. The prototype of the water injected screw compressor air system was built and tested for performance and reliability. The water injected compressor system was compared with the oil injected and oil free compressor systems of the equivalent size including the economic analysis based on the lifecycle costs. Based on the obtained results, it was concluded that water injected screw compressor systems could be designed to deliver clean air free of oil contamination with a better user value proposition than the oil injected or oil free screw compressor systems over the considered range of operations.

SPECTRAL LAGS AND THE LAG-LUMINOSITY RELATION: AN INVESTIGATION WITH SWIFT BAT GAMMA-RAY BURSTS

International Nuclear Information System (INIS)

Ukwatta, T. N.; Dhuga, K. S.; Eskandarian, A.; Maximon, L. C.; Parke, W. C.; Stamatikos, M.; Sakamoto, T.; Barthelmy, S. D.; Gehrels, N.; Norris, J. P.

2010-01-01

Spectral lag, the time difference between the arrival of high-energy and low-energy photons, is a common feature in gamma-ray bursts (GRBs). Norris et al. reported a correlation between the spectral lag and the isotropic peak luminosity of GRBs based on a limited sample. More recently, a number of authors have provided further support for this correlation using arbitrary energy bands of various instruments. In this paper, we report on a systematic extraction of spectral lags based on the largest Swift sample to date of 31 GRBs with measured redshifts. We extracted the spectral lags for all combinations of the standard Swift hard X-ray energy bands: 15-25 keV, 25-50 keV, 50-100 keV, and 100-200 keV and plotted the time dilation corrected lag as a function of isotropic peak luminosity. The mean value of the correlation coefficient for various channel combinations is -0.68 with a chance probability of ∼0.7 x 10 -3 . In addition, the mean value of the power-law index is 1.4 ± 0.3. Hence, our study lends support to the existence of a lag-luminosity correlation, albeit with large scatter.

Osteosynthesis of the first phalanx fractures in horses by means of lag screws; Osteosynteza zlaman kosci pecinowej u koni z zastosowaniem srub ciagnacych

Energy Technology Data Exchange (ETDEWEB)

Bereznowski, A.; Janicki, A.M.; Sterna, J. [Katedra Chirurgii Zwierzat, Wydzial Weterynarii, SGGW-AR, Warsaw (Poland)

1996-12-31

Fractures of the first phalanx belong to the most frequent in horses. Three cases of surgical treatment of first phalanx fractures in horses have been presented. The cases differed by the period of time between the accident and surgical treatment. In all cases osteosynthesis by means of orthopedic screws was applied. In all horses fracture repair was successful, however, not all horses recovered fully enough to return to work. (author). 6 refs, 5 figs.

Screw-worm eradication in the Americas - Overview

International Nuclear Information System (INIS)

Wyss, John H.

2000-01-01

Screw-worms (Cochliomyia hominivorax, Coquerel) are found only in the Americas, and are known, therefore, as the New World Screw-worm (NWS). The larval stages of the fly feed on the living flesh of their host. A screw-worm infestation can kill an adult animal in 7-10 days if not treated. All warm-blooded animals are affected including man. Although screw-worms had long been recognised as a severe pest of animals in the southwestern United States, they had never been detected east of the Mississippi River before 1933. In July 1933, screw-worms were transported on infested cattle to Georgia and became established east of the Mississippi River. Screw-worms spread quickly in the southeastern United States and were able to overwinter in southern Florida. Being new to the region, they were quickly recognised as a severe pest with a tremendous economic impact on livestock production. The livestock owners in the southeastern United States immediately noticed an increase in the number of animal deaths and increased costs of insecticides, veterinary medicines, veterinary services, inspection and handling. At the same time, they observed a decrease in animal weights and in milk production. Due to these observations, the livestock industry in the southeastern United States requested help in controlling screw-worms. Because of these requests, the research community became interested in control and eradication measures for this pest. Early work by Crushing and Patton in 1933 recognised that C. hominivorax was an obligatory animal parasite and different from the secondary blowfly, Cochliomyia macellaria. In 1934, the US Department of Agriculture (USDA), Agricultural Research Service (ARS) opened a research station in Valdosa, Georgia, and E.W. Laake and E.F. Knipling were assigned to work there. In September 1935, R.C. Bushland was hired by ARS to do research related to screw-worms at an ARS Research Laboratory in Dallas, Texas. Melvin and Bushland in 1936 developed artificial

The accuracy and safety of fluoroscopically guided percutaneous pedicle screws in the lumbosacral junction and the lumbar spine: a review of 880 screws.

Science.gov (United States)

Chiu, C K; Kwan, M K; Chan, C Y W; Schaefer, C; Hansen-Algenstaedt, N

2015-08-01

We undertook a retrospective study investigating the accuracy and safety of percutaneous pedicle screws placed under fluoroscopic guidance in the lumbosacral junction and lumbar spine. The CT scans of patients were chosen from two centres: European patients from University Medical Center Hamburg-Eppendorf, Germany, and Asian patients from the University of Malaya, Malaysia. Screw perforations were classified into grades 0, 1, 2 and 3. A total of 880 percutaneous pedicle screws from 203 patients were analysed: 614 screws from 144 European patients and 266 screws from 59 Asian patients. The mean age of the patients was 58.8 years (16 to 91) and there were 103 men and 100 women. The total rate of perforation was 9.9% (87 screws) with 7.4% grade 1, 2.0% grade 2 and 0.5% grade 3 perforations. The rate of perforation in Europeans was 10.4% and in Asians was 8.6%, with no significant difference between the two (p = 0.42). The rate of perforation was the highest in S1 (19.4%) followed by L5 (14.9%). The accuracy and safety of percutaneous pedicle screw placement are comparable to those cited in the literature for the open method of pedicle screw placement. Greater caution must be taken during the insertion of L5 and S1 percutaneous pedicle screws owing to their more angulated pedicles, the anatomical variations in their vertebral bodies and the morphology of the spinal canal at this location. ©2015 The British Editorial Society of Bone & Joint Surgery.

Conceptual design of ball-screw type control element drive mechanism

Energy Technology Data Exchange (ETDEWEB)

Kim, Ji Ho; Kim, Jong In; Huh, Hyung [Korea Atomic Energy Research Institute, Taejon (Korea)

1999-10-01

In this report, the design features of ball-screw type CEDM with fine-step movement capability are described. The contents of this report are as follows: -Review of Design Requirements for Ball-screw type CEDM -System Description for Ball-screw type CEDM -Design of Ball Bearing and Ball-screw Assembly -Detail Design of Rotary Step Motor -Detail Design of Angular Position Indicator -Materials. The Ball-screw type CEDM described in this report is to be utilized as the starting point for design development of CEDM for SMART. 11 refs., 43 figs., 3 tabs. (Author)

Passage of an Anterior Odontoid Screw through Gastrointestinal Tract.

Science.gov (United States)

Leitner, L; Brückmann, C I; Gilg, M M; Bratschitsch, G; Sadoghi, P; Leithner, A; Radl, R

2017-01-01

Purpose . Anterior screw fixation has become a popular surgical treatment method for instable odontoid fractures. Screw loosening and migration are a rare, severe complication following anterior odontoid fixation, which can lead to esophagus perforation and requires revision operation. Methods . We report a case of screw loosening and migration after anterior odontoid fixation, which perforated the esophagus and was excreted without complications in a 78-year-old male patient. Results . A ventral dislocated anterior screw perforated through the esophagus after eight years after implantation and was excreted through the gastrointestinal (GI) tract. At a 6-month follow-up after the event the patient was asymptomatic. Conclusion . Extrusion via the GI tract is not safe enough to be considered as a treatment option for loosened screws. Some improvements could be implemented to prevent such an incident. Furthermore, this case is a fine example that recent preoperative imaging is mandatory before revision surgery for screw loosening.

Passage of an Anterior Odontoid Screw through Gastrointestinal Tract

Directory of Open Access Journals (Sweden)

L. Leitner

2017-01-01

Full Text Available Purpose. Anterior screw fixation has become a popular surgical treatment method for instable odontoid fractures. Screw loosening and migration are a rare, severe complication following anterior odontoid fixation, which can lead to esophagus perforation and requires revision operation. Methods. We report a case of screw loosening and migration after anterior odontoid fixation, which perforated the esophagus and was excreted without complications in a 78-year-old male patient. Results. A ventral dislocated anterior screw perforated through the esophagus after eight years after implantation and was excreted through the gastrointestinal (GI tract. At a 6-month follow-up after the event the patient was asymptomatic. Conclusion. Extrusion via the GI tract is not safe enough to be considered as a treatment option for loosened screws. Some improvements could be implemented to prevent such an incident. Furthermore, this case is a fine example that recent preoperative imaging is mandatory before revision surgery for screw loosening.

Range of motion, sacral screw and rod strain in long posterior spinal constructs: a biomechanical comparison between S2 alar iliac screws with traditional fixation strategies.

Science.gov (United States)

Sutterlin, Chester E; Field, Antony; Ferrara, Lisa A; Freeman, Andrew L; Phan, Kevin

2016-12-01

S1 screw failure and L5/S1 non-union are issues with long fusions to S1. Improved construct stiffness and S1 screw offloading can help avoid this. S2AI screws have shown to provide similar stiffness to iliac screws when added to L3-S1 constructs. We sought to examine and compare the biomechanical effects on an L2-S1 pedicle screw construct of adding S2AI screws, AxiaLIF, L5-S1 interbody support via transforaminal lumbar interbody fusion (TLIF), and to examine the effect of the addition of cross connectors to each of these constructs. Two S1 screws and one rod with strain gauges (at L5/S1) were used in L2-S1 screw-rod constructs in 7 L1-pelvis specimens (two with low BMD). ROM, S1 screw and rod strain were assessed using a pure-moment flexibility testing protocol. Specimens were tested intact, and then in five instrumentation states consisting of: (I) Pedicle screws (PS) L2-S1; (II) PS + S2AI screws; (III) PS + TLIF L5/S1; (IV) PS + AxiaLIF L5/S1; (V) PS + S2AI + AxiaLIF L5/S1. The five instrumentation conditions were also tested with crosslinks at L2/3 and S1/2. Tests were conducted in flexion-extension, lateral bending and axial torsion with no compressive preload. S2A1 produces reduced S1 screw strain for flexion-extension, lateral bending and axial torsion, as well as reduced rod strain in lateral bending and axial torsion in comparison to AxiaLIF and interbody instrumentation, at the expense of increased rod flexion-extension strain. Cross-connectors may have a role in further reduction of S1 screw and rod strain. From a biomechanical standpoint, the use of the S2AI technique is at least equivalent to traditional iliac screws, but offers lower prominence and ease of assembly compared to conventional sacroiliac stabilization.

Experimental study of pedicle screw stability on low BMD vertebrae

International Nuclear Information System (INIS)

Li Qi; Yang Huilin; Tang Tiansi; Wu Yiwei; Wang Yijin

2005-01-01

Objective: To conduct biomechanical study of different pedicle screws stability on spinal specimen, discuss the relationship between design parameter of screw, insertion torgue and BMD, establish the theoretical foundation for application of pedicle screw on osteoporotic patients. Methods: Six fixed lumbar cadavers were collected, the effects of design parameter, insertion torque and etc on fixation stability were determined under various BMD by using biomechanical ways. Results: According to in vitro study: (1) There was a significant difference among pullout strength of all screws (P 2 >U 1 >SF 1 >SF 2 >RF. Conclusions: There is a close correlated between type of screw, BMD and stability. The U-type screw displays the best fixation effect on specimen of low BMD. (authors)

Safety and surgical techniques of C1 lateral mass screws

International Nuclear Information System (INIS)

Kubo, Shinichiro; Kuroki, Hiroshi; Hanado, Shoji; Hamanaka, Hideaki; Inomata, Naoki; Kuroki, Shuji; Chosa, Etsuo

2010-01-01

The objectives of this study were to evaluate the proper insertion techniques of C1 lateral mass screws. Eighteen consecutive patients were examined after upper cervical fusion using twenty-nine C1 lateral mass screws. Screws were placed by three different techniques; Goel's technique (4), Tan's technique (20), Notching technique (5). Pre and post-operative CT scans with multiplanar reconstruction were used to detect cortical breaches and direction of screws. No transverse foramen and vertebral groove violation was found in CT scans. Three had breached superior articular facet of the atlas. However, the range of motion (R.O.M) of atlanto-occipital joints had not changed postoperatively. Theses screws were inserted with Tan's technique and two of three were directed medially. It is feasible to safely insert C1 lateral mass screws when correct insertion point and direction are considered preoperatively. However, care should be taken because screws can violate the atlanto-occipital joint especially with Tan's technique. (author)

Accuracy of pedicle screw placement in patients with Marfan syndrome.

Science.gov (United States)

Qiao, Jun; Zhu, Feng; Xu, Leilei; Liu, Zhen; Sun, Xu; Qian, Bangping; Jiang, Qing; Zhu, Zezhang; Qiu, Yong

2017-03-21

There is no study concerning safety and accuracy of pedicle screw placement in Marfan syndrome. The objective of this study is to investigate accuracy and safety of pedicle screw placement in scoliosis associated with Marfan syndrome. CT scanning was performed to analyze accuracy of pedicle screw placement. Pedicle perforations were classified as medial, lateral or anterior and categorized to four grades: ≤ 2 mm as Grade 1, 2.1-4.0 mm as Grade 2, 4.1-6.0 mm as Grade 3, ≥6.1 mm as Grade 4. Fully contained screws or with medial wall perforation ≤ 2 mm or with lateral wall perforation ≤ 6 mm and without injury of visceral organs were considered acceptable, otherwise were unacceptable. 976 pedicle screws were placed, 713 screws (73.1%) were fully contained within the cortical boundaries of the pedicle. 924 (94.7%) screws were considered as acceptable, and 52 (5.3%) as unacceptable. The perforation rate was higher using free-hand technique than O-arm navigation technique (30.8% VS. 11.4%, P Marfan syndrome is accuracy and safe. O-arm navigation was an effective modality to ensure the safety and accuracy of screw placement. Special attention should be paid when screws were placed at the lumber spine and the concave side of spine deformity to avoid the higher rate of complications.

Process and remote device for unscrewing and extracting an assembly screw

International Nuclear Information System (INIS)

Lagarrigue, F.

1990-01-01

The device comprises a C-shaped frame, with two parallel arms and a joining section fixed at one end of a long support, an extraction screw engaged in a hole through one arm and having one end made of a centre punch directed towards the inside of the frame and a remote mean for screwed or unscrewed the extraction screw. A supporting and centering piece can also be fixed to the second branch of the frame. The screw is extracted by exerting a moment about the axis of the screw through the support and frame after tightening the extraction screw. This device can be used particularly for the unscrewing and the extraction of the screw of the springs of a nuclear fuel assembly [fr

Stress and stability of plate-screw fixation and screw fixation in the treatment of Schatzker type IV medial tibial plateau fracture: a comparative finite element study.

Science.gov (United States)

Huang, Xiaowei; Zhi, Zhongzheng; Yu, Baoqing; Chen, Fancheng

2015-11-25

The purpose of this study is to compare the stress and stability of plate-screw fixation and screw fixation in the treatment of Schatzker type IV medial tibial plateau fracture. A three-dimensional (3D) finite element model of the medial tibial plateau fracture (Schatzker type IV fracture) was created. An axial force of 2500 N with a distribution of 60% to the medial compartment was applied to simulate the axial compressive load on an adult knee during single-limb stance. The equivalent von Mises stress, displacement of the model relative to the distal tibia, and displacement of the implants were used as the output measures. The mean stress value of the plate-screw fixation system was 18.78 MPa, which was significantly (P stress value of the triangular fragment in the plate-screw fixation system model was 42.04 MPa, which was higher than that in the screw fixation model (24.18 MPa). But the mean stress of the triangular fractured fragment in the screw fixation model was significantly higher in terms of equivalent von Mises stress (EVMS), x-axis, and z-axis (P < 0.001). This study demonstrated that the load transmission mechanism between plate-screw fixation system and screw fixation system was different and the stability provided by the plate-screw fixation system was superior to the screw fixation system.

Medial Malleolar Fractures: An Anatomic Survey Determining the ...

African Journals Online (AJOL)

However, the literature lacks a defined method for selecting lag screw length, relying more ... Aim: The aim of this study is to help define the ideal lag screw length for medial melleolar fracture fixation. .... Biometrics 1977;33:159‑74. 8. Ricci WM ...

BIOMECHANICAL EVALUATION OF THE INFLUENCE OF CERVICAL SCREWS TAPPING AND DESIGN.

Science.gov (United States)

Silva, Patricia; Rosa, Rodrigo César; Shimano, Antonio Carlos; Albuquerque de Paula, Francisco José; Volpon, José Batista; Aparecido Defino, Helton Luiz

2009-01-01

To assess if the screw design (self-drilling/self-tapping) and the pilot hole tapping could affect the insertion torque and screw pullout strength of the screw used in anterior fixation of the cervical spine. Forty self-tapping screws and 20 self-drilling screws were inserted into 10 models of artificial bone and 10 cervical vertebrae of sheep. The studied parameters were the insertion torque and pullout strength. The following groups were created: Group I-self-tapping screw insertion after pilot hole drilling and tapping; Group II-self-tapping screw insertion after pilot hole drilling without tapping; Group III-self-drilling screw insertion without drilling and tapping. In Groups I and II, the pilot hole had 14.0 mm in depth and was made with a 3mmn drill, while tapping was made with a 4mm tap. The insertion torque was measured and the pullout test was performed. The comparison between groups was made considering the mean insertion torque and the maximum mean pullout strength with the variance analysis (ANOVA; p≤ 0.05). Previous drilling and tapping of pilot hole significantly decreased the insertion torque and the pullout strength. The insertion torque and pullout strength of self-drilling screws were significantly higher when compared to self-tapping screws inserted after pilot hole tapping.

Posterior cervical spine arthrodesis with laminar screws. A report of two cases

International Nuclear Information System (INIS)

Nakanishi, Kazuo; Tanaka, Masato; Sugimoto, Yoshihisa; Ozaki, Toshifumi

2007-01-01

We performed fixation using laminar screws in 2 patients in whom lateral mass screws, pedicle screws or transarticular screws could not be inserted. One was a 56-year-old woman who had anterior atlantoaxial subluxation (AAS). When a guide wire was inserted using an imaging guide, the hole bled massively. We thought the re-insertion of a guide wire or screw would thus increase the risk of vascular injury, so we used laminar screws. The other case was an 18-year-old man who had a hangman fracture. Preoperative magnetic resonance angiography showed occlusion of the left vertebral artery. A laminar screw was inserted into the patent side (i.e., the right side of C2). Cervical pedicle screws are the most biomechanically stable screws. However, their use carries a high risk of neurovascular complications during screw insertion, because the cervical pedicle is small and is adjacent laterally to the vertebral artery, medially to the spinal cord, and vertically to the nerve roots. Lateral mass screws are also reported to involve a risk of neurovascular injuries. The laminar screw method was thus thought to be useful, since arterial injuries could thus be avoided and it could also be used as a salvage modality for the previous misinsertion. (author)

Modeling and Analyzing the Slipping of the Ball Screw

Directory of Open Access Journals (Sweden)

Nannan Xu

Full Text Available AbstractThis paper aims to set up the ball systematic slipping model and analyze the slipping characteristics caused by different factors for a ball screw operating at high speeds. To investigate the ball screw slipping mechanism, transformed coordinate system should be established firstly. Then it is used to set up mathematical modeling for the ball slipping caused by the three main reasons and the speed of slipping can be calculated. Later, the influence of the contact angle, helix angle and screw diameter for ball screw slipping will be analyzed according to the ball slipping model and slipping speeds equation and the slipping analysis will be obtained. Finally, curve of slipping analysis and that of mechanical efficiency of the ball screw analysis by Lin are compared, which will indirectly verify the correctness of the slipping model. The slipping model and the curve of slipping analysis established in this paper will provide theory basis for reducing slipping and improving the mechanical efficiency of a ball screw operating at high speeds.

Comparative effect of implant-abutment connections, abutment angulations, and screw lengths on preloaded abutment screw using three-dimensional finite element analysis: An in vitro study.

Science.gov (United States)

Kanneganti, Krishna Chaitanya; Vinnakota, Dileep Nag; Pottem, Srinivas Rao; Pulagam, Mahesh

2018-01-01

The purpose of this study is to compare the effect of implant-abutment connections, abutment angulations, and screw lengths on screw loosening (SL) of preloaded abutment using three dimensional (3D) finite element analysis. 3D models of implants (conical connection with hex/trilobed connections), abutments (straight/angulated), abutment screws (short/long), and crown and bone were designed using software Parametric Technology Corporation Creo and assembled to form 8 simulations. After discretization, the contact stresses developed for 150 N vertical and 100 N oblique load applications were analyzed, using ABAQUS. By assessing damage initiation and shortest fatigue load on screw threads, the SL for 2.5, 5, and 10 lakh cyclic loads were estimated, using fe-safe program. The obtained values were compared for influence of connection design, abutment angulation, and screw length. In straight abutment models, conical connection showed more damage (14.3%-72.3%) when compared to trilobe (10.1%-65.73%) at 2.5, 5, and 10 lakh cycles for both vertical and oblique loads, whereas in angulated abutments, trilobe (16.1%-76.9%) demonstrated more damage compared to conical (13.5%-70%). Irrespective of the connection type and abutment angulation, short screws showed more percentage of damage compared to long screws. The present study suggests selecting appropriate implant-abutment connection based on the abutment angulation, as well as preferring long screws with more number of threads for effective preload retention by the screws.

A four lumen screwing device for multiparametric brain monitoring.

Science.gov (United States)

Feuerstein, T H; Langemann, H; Gratzl, O; Mendelowitsch, A

2000-01-01

We describe multiparametric monitoring in severe head trauma using a new screwing device. Our aim was to create a screw which would make the implantation of the probes and thus multiparametric monitoring easier. The new screw allows us to implant 3 probes (microdialysis, Paratrend and an intracranial pressure device) through one burr hole. The screw has four channels, the fourth being for ventricular drainage. We monitored 13 patients with severe head trauma (GCS = 3-8) for up to 7 days. Brain tissue pO2, pCO2, pH, and temperature were measured on-line with the Paratrend 7 machine. The microdialytic parameters glucose, lactate, pyruvate and glutamate were determined semi on-line with a CMA 600 enzymatic analyser. There were no complications in any of the patients that could be ascribed to the screw.

Experiments on screw-pinch plasmas with elongated cross section

International Nuclear Information System (INIS)

Lassing, H.W.

1989-01-01

In this thesis experiments are described carried out with SPICA II, a toroidal screw-pinch plasma device. this device is the last one in a series of plasma machines of the toroidal screw-pinch differing from its predecessor in its race-track shaped section. In devices of the type toroidal screw-pinch stable confinement is possible of plasmas with larger β values than in a tokamak discharge. In a pinch the plasma is screwed up, during the formation, in such a way that in a relatively small volume a plasma is formated with a high pressure. During the screwing up the plasma is heated by shock heating as well as adiabatic compression. With the modified snowplow model the density and temperature after the formation can be calculated, starting from the initial conditions. When all ions arrive into the plasma column, the density in the column is determined by the volume compression. First purpose of the experiments was to find a stable discharge. Subsequently discharges have been made with a high as possible β in order to investigate at which maximum β it is possible to confine screw-pinch plasmas stably. When these had been found, the nature and importance could be investigated of the processes following which the screw-pinch plasma looses its energy. (author), 75 res.; 95 figs.; 8 tabs

Determination of Screw and Nail Withdrawal Resistance of Some Important Wood Species

Directory of Open Access Journals (Sweden)

Alper Aytekin

2008-04-01

Full Text Available In this study, screw and nail withdrawal resistance of fir (Abies nordmanniana, oak (Quercus robur L. black pine (Pinus nigra Arnold and Stone pine (Pinus pinea L. wood were determined and compared. The data represent the testing of withdrawal resistance of three types of screws as smart, serrated and conventional and common nails. The specimens were prepared according to TS 6094 standards. The dimensions of the specimens were 5x5x15cm and for all of the directions. Moreover, the specimens were conditioned at ambient room temperature and 65±2% relative humidity. The screws and nails were installed according to ASTM-D 1761 standards. Nail dimensions were 2.5mm diameter and 50 mm length, conventional screws were 4x50mm, serrated screws were 4x45mm and smart screws were 4x50mm. Results show that the maximum screw withdrawal resistance value was found in Stone pine for the serrated screw. There were no significant differences between Stone pine and oak regarding screw withdrawal resistance values. Conventional screw yielded the maximum screw withdrawal resistance value in oak, followed by Stone pine, black pine and fir. Oak wood showed the maximum screw withdrawal resistance value for the smart screw, followed by Stone pine, black pine, and fir. Oak wood showed higher nail withdrawal resistances than softwood species. It was also determined that oak shows the maximum nail withdrawal resistance in all types. The nail withdrawal resistances at the longitudinal direction are lower with respect to radial and tangential directions.

Enhancement of Orthodontic Anchor Screw Stability Under Immediate Loading by Ultraviolet Photofunctionalization Technology.

Science.gov (United States)

Takahashi, Maiko; Motoyoshi, Mitsuru; Inaba, Mizuki; Hagiwara, Yoshiyuki; Shimizu, Noriyoshi

Ultraviolet (UV)-mediated photofunctionalization technology is intended to enhance the osseointegration capability of titanium implants. There are concerns about orthodontic anchor screws loosening under immediate loading protocols in adolescent orthodontic treatment. The purpose of this in vivo study was to evaluate the effects of photofunctionalization on the intrabony stability of orthodontic titanium anchor screws and bone-anchor screw contact under immediate loading in growing rats. Custom-made titanium anchor screws (1.4 mm in diameter and 4.0 mm in length) with or without photofunctionalization pretreatment were placed on the proximal epiphysis of the tibial bone in 6-week-old male Sprague-Dawley rats and were loaded immediately after placement. After 2 weeks of loading, the stability of the anchor screws was evaluated using a Periotest device, and the bone-anchor screw contact ratio (BSC) was assessed by a histomorphometric analysis using field-emission scanning electron microscopy. In the unloaded group, Periotest values (PTVs) were ~25 for UV-untreated screws and 13 for UVtreated screws (P < .01), while in the immediate-loading group, PTVs were 28 for UV-untreated screws and 16 for UV-treated screws (P < .05). Significantly less screw mobility was observed in both UV-treated groups regardless of the loading protocol. The BSC was increased ~1.8 fold for UV-treated screws, compared with UV-untreated screws, regardless of the loading protocol. Photofunctionalization enhanced the intrabony stability of orthodontic anchor screws under immediate loading in growing rats by increasing bone-anchor screw contact.

Probing and Tapping: Are We Inserting Pedicle Screws Correctly?

Science.gov (United States)

Prasad, Vishal; Mesfin, Addisu; Lee, Robert; Reigrut, Julie; Schmidt, John

2016-11-01

Although there are a significant number of research publications on the topic of bone morphology and the strength of bone, the clinical significance of a failed pedicle screw is often revision surgery and the potential for further postoperative complications; especially in elderly patients with osteoporotic bone. The purpose of this report is to quantify the mechanical strength of the foam-screw interface by assessing probe/pilot hole diameter and tap sizes using statistically relevant sample sizes under highly controlled test conditions. The study consisted of two experiments and used up to three different densities of reference-grade polyurethane foam (ASTM 1839), including 0.16, 0.24, and 0.32 g/cm 3 . All screws and rods were provided by K2M Inc. and screws were inserted to a depth of 25 mm. A series of pilot holes, 1.5, 2.2, 2.7, 3.2, 3.7, 4.2, 5.0, and 6.0 mm in diameter were drilled through the entire depth of the material. A 6.5 × 45-mm pedicle screw was inserted and axially pulled from the material (n = 720). A 3.0-mm pilot hole was drilled and tapped with: no tap, 3.5-, 4.5-, 5.5-, and 6.5-mm taps. A 6.5 × 45-mm pedicle screw was inserted and axially pulled from the material (n = 300). The size of the probe/pilot hole had a nonlinear, parabolic effect on pullout strength. This shape suggests an optimum-sized probe hole for a given size pedicle screw. Too large or too small of a probe hole causes a rapid falloff in pullout strength. The tap data demonstrated that not tapping and undertapping by two or three sizes did not significantly alter the pullout strength of the screws. The data showed an exponential falloff of pullout strength when as tap size increased to the diameter of the screw. In the current study, the data show that an ideal pilot hole size half the diameter of the screw is a starting point. Also, that if tapping was necessary, to use a tap two sizes smaller than the screw being implanted. A similar optimum pilot hole or tap size may be

Economics of water injected air screw compressor systems

OpenAIRE

Madhav, K. V.; Kovacevic, A.

2015-01-01

There is a growing need for compressed air free of entrained oil to be used in industry. In many cases it can be supplied by oil flooded screw compressors with multi stage filtration systems, or by oil free screw compressors. However, if water injected screw compressors can be made to operate reliably, they could be more efficient and therefore cheaper to operate. Unfortunately, to date, such machines have proved to be insufficiently reliable and not cost effective. This paper describes an in...

Adjacent-segment disease after thoracic pedicle screw fixation.

Science.gov (United States)

Agarwal, Nitin; Heary, Robert F; Agarwal, Prateek

2018-03-01

OBJECTIVE Pedicle screw fixation is a technique widely used to treat conditions ranging from spine deformity to fracture stabilization. Pedicle screws have been used traditionally in the lumbar spine; however, they are now being used with increasing frequency in the thoracic spine as a more favorable alternative to hooks, wires, or cables. Although safety concerns, such as the incidence of adjacent-segment disease (ASD) after cervical and lumbar fusions, have been reported, such issues in the thoracic spine have yet to be addressed thoroughly. Here, the authors review the literature on ASD after thoracic pedicle screw fixation and report their own experience specifically involving the use of pedicle screws in the thoracic spine. METHODS Select references from online databases, such as PubMed (provided by the US National Library of Medicine at the National Institutes of Health), were used to survey the literature concerning ASD after thoracic pedicle screw fixation. To include the authors' experience at Rutgers New Jersey Medical School, a retrospective review of a prospectively maintained database was performed to determine the incidence of complications over a 13-year period in 123 consecutive adult patients who underwent thoracic pedicle screw fixation. Children, pregnant or lactating women, and prisoners were excluded from the review. By comparing preoperative and postoperative radiographic images, the occurrence of thoracic ASD and disease within the surgical construct was determined. RESULTS Definitive radiographic fusion was detected in 115 (93.5%) patients. Seven incidences of instrumentation failure and 8 lucencies surrounding the screws were observed. One patient was observed to have ASD of the thoracic spine. The mean follow-up duration was 50 months. CONCLUSIONS This long-term radiographic evaluation revealed the use of pedicle screws for thoracic fixation to be an effective stabilization modality. In particular, ASD seems to be less of a problem in the

Positioning of pedicle screws in adolescent idiopathic scoliosis using electromyography

Directory of Open Access Journals (Sweden)

Bruno Moreira Gavassi

2015-06-01

Full Text Available OBJECTIVE: To analyze the occurrence of poor positioning of pedicle screws inserted with the aid of intraoperative electromyographic stimulation in the treatment of Adolescent Idiopathic Scoliosis (AIS.METHODS: This is a prospective observational study including all patients undergoing surgical treatment for AIS, between March and December 2013 at a single institution. All procedures were monitored by electromyography of the inserted pedicle screws. The position of the screws was evaluated by assessment of postoperative CT and classified according to the specific AIS classification system.RESULTS: Sixteen patients were included in the study, totalizing 281 instrumented pedicles (17.5 per patient. No patient had any neurological deficit or complaint after surgery. In the axial plane, 195 screws were found in ideal position (69.4% while in the sagittal plane, 226 screws were found in ideal position (80.4%. Considering both the axial and the sagittal planes, it was observed that 59.1% (166/281 of the screws did not violate any cortical wall.CONCLUSION: The use of pedicle screws proved to be a safe technique without causing neurological damage in AIS surgeries, even with the occurrence of poor positioning of some implants.

Preoperative CT planning of screw length in arthroscopic Latarjet.

Science.gov (United States)

Hardy, Alexandre; Gerometta, Antoine; Granger, Benjamin; Massein, Audrey; Casabianca, Laurent; Pascal-Moussellard, Hugues; Loriaut, Philippe

2018-01-01

The Latarjet procedure has shown its efficiency for the treatment of anterior shoulder dislocation. The success of this technique depends on the correct positioning and fusion of the bone block. The length of the screws that fix the bone block can be a problem. They can increase the risk of non-union if too short or be the cause of nerve lesion or soft tissue discomfort if too long. Suprascapular nerve injuries have been reported during shoulder stabilisation surgery up to 6 % of the case. Bone block non-union depending on the series is found around 20 % of the cases. The purpose of this study was to evaluate the efficiency of this CT preoperative planning to predict optimal screws length. The clinical importance of this study lies in the observation that it is the first study to evaluate the efficiency of CT planning to predict screw length. Inclusion criteria were patients with chronic anterior instability of the shoulder with an ISIS superior to 4. Exclusion criteria were patients with multidirectional instability or any previous surgery on this shoulder. Thirty patients were included prospectively, 11 of them went threw a CT planning, before their arthroscopic Latarjet. Optimal length of both screws was calculated, adding the size of the coracoid at 5 and 15 mm from the tip to the glenoid. Thirty-two-mm screws were used for patients without planning. On a post-operative CT scan with 3D reconstruction, the distance between the screw tip and the posterior cortex was measured. A one-sample Wilcoxon test was used to compare the distance from the tip of the screw to an acceptable positioning of ±2 mm from the posterior cortex. In the group without planning, screw 1 tended to differ from the acceptable positioning: mean 3.44 mm ± 3.13, med 2.9 mm, q1; q3 [0.6; 4.75] p = 0.1118, and screw 2 differed significantly from the acceptable position: mean 4.83 mm ± 4.11, med 3.7 mm, q1; q3 [1.7; 5.45] p = 0.0045. In the group with planning, position of

Study on pedicle screw fixation of cervical spine assisted CT-based navigation system compared with the individual cervical peddle screws placement technique

International Nuclear Information System (INIS)

He Xishun; Yang Huilin; Zhu Ruofu; Tan Xiangqi; Wang Genlin; Tang Tiansi

2008-01-01

Objective: To explore a safe and effective method for placing the cervical pedicle screws. Methods: There were ten adult cadaver specimens of cervica spine (C 1 -C 7 ) with intact structures including ligament and perivertebral muscles. The spiral computed tomography scan (Elscint CT Twin flash) at the section of 1 mm and three-dimensional reconstruction of all 10 cervical specimens were taken. By CT scan, the parameters of the cervical pedicles were measure,Then taking randomly 5 cervical specimens, according to the CT measurements, an appropriate screw was inserted into pedicle individually. In the other 5 human cadaver cervical vertebraes, Φ3.5 mm screws were inserted into the C 2 -C 7 pedicles by assisted by CT-based navigation system. Cortical integrity of every sample was examined by anatomic dissection, the spiral computed tomography scan and arrows,and coronal reconstruction. Results: Sixty screws was inserted into pedicle individually, and the achievement ratio was 90%, the perfectness ratio was 75%, 60 screws was placed into pedicle assisted by CT-based navigation system, and the achievement ratio was 96.6%, the perfectness ratio was 90%. By chi-square test for statistical analysis, there were no statistical significance between the accuracy rate of two methods(P>0.05). However there was statistical significance between the perfectness ratio between two methods(P<0.05). Conclusion: Compared with the individual cervical peddle screws placement technique, the perfectness ratio of pedicle screw fixation of cervical spine assisted by CT-based navigation system is higher, but there are no significant difference in accuracy. (authors)

[Clinical efficacy of unilateral percutaneous transfacet screws combined with contralateral pedicle screw versus bilateral pedicle screws fixation in the treatment of the degenerative lumbar disease].

Science.gov (United States)

Hao, Rong-Xue; Zhou, Hui; Pan, Hao; Yue, Jun; Chen, Hui-Guo; Yang, He-Jie; Jia, Gao-Yong; Wang, Dong; Lin, Yan; Xu, Hua-Zi

2017-09-25

To investigate the surgical outcome of unilateral pedicle screw(UPS) after TLIF technique combined with contralateral percutaneous transfacet screw(PTS) fixation vs bilateral pedicle screws(BPS) fixation in treatment of degenerative lumbar disease. From January 2009 to June 2012, 46 patients with degenerative lumbar diseases, including 30 males and 16 females with an average age of 51.5 years old, who were divided into two groups according to different fixation methods. Twenty-two cases underwent UPS after TLIF technique combined with contralateral PTS fixation (group A), while the others underwent BPS fixation(group B). The relative data were analyzed, such as blood loss volume, operative time, fusion rate, ODI score, JOA score and so on. All the patients were followed up for 1 to 3 years with an average of 22 months. Except one case of each group was uncertainty fusion, the rest have obtained bony fusion, and the fusion rates in group A and B were 95.5% and 95.8%, respectively. No displacement and breakage of screw were found during follow-up. Operative time and blood loss volume in group A were better than of group B( P 0.05). Two approaches had similar clinical outcomes for degenerative lumbar disease with no severe instability. Compared with BPS fixation, the UPS after TLIF technique and contralateral PTS fixation has the advantages of less trauma, shorter operative time and less blood loss, and it is a safe and feasible surgical technique.

Multiaxial pedicle screw designs: static and dynamic mechanical testing.

Science.gov (United States)

Stanford, Ralph Edward; Loefler, Andreas Herman; Stanford, Philip Mark; Walsh, William R

2004-02-15

Randomized investigation of multiaxial pedicle screw mechanical properties. Measure static yield and ultimate strengths, yield stiffness, and fatigue resistance according to an established model. Compare these measured properties with expected loads in vivo. Multiaxial pedicle screws provide surgical versatility, but the complexity of their design may reduce their strength and fatigue resistance. There is no published data on the mechanical properties of such screws. Screws were assembled according to a vertebrectomy model for destructive mechanical testing. Groups of five assemblies were tested in static tension and compression and subject to three cyclical loads. Modes of failure, yield, and ultimate strength, yield stiffness, and cycles to failure were determined for six designs of screw. Static compression yield loads ranged from 217.1 to 388.0 N and yield stiffness from 23.7 to 38.0 N/mm. Cycles to failure ranged from 42 x 10(3) to 4,719 x 10(3) at 75% of static ultimate load. There were significant differences between designs in all modes of testing. Failure occurred at the multiaxial link in static and cyclical compression. Bending yield strengths just exceeded loads expected in vivo. Multiaxial designs had lower static bending yield strength than fixed screw designs. Five out of six multiaxial screw designs achieved one million cycles at 200 N in compression bending. "Ball-in-cup" multiaxial locking mechanisms were vulnerable to fatigue failure. Smooth surfaces and thicker material appeared to be protective against fatigue failure.

On Helical Projection and Its Application in Screw Modeling

Directory of Open Access Journals (Sweden)

Riliang Liu

2014-04-01

Full Text Available As helical surfaces, in their many and varied forms, are finding more and more applications in engineering, new approaches to their efficient design and manufacture are desired. To that end, the helical projection method that uses curvilinear projection lines to map a space object to a plane is examined in this paper, focusing on its mathematical model and characteristics in terms of graphical representation of helical objects. A number of interesting projective properties are identified in regard to straight lines, curves, and planes, and then the method is further investigated with respect to screws. The result shows that the helical projection of a cylindrical screw turns out to be a Jordan curve, which is determined by the screw's axial profile and number of flights. Based on the projection theory, a practical approach to the modeling of screws and helical surfaces is proposed and illustrated with examples, and its possible application in screw manufacturing is discussed.

Accuracy of S2 Alar-Iliac Screw Placement Under Robotic Guidance.

Science.gov (United States)

Laratta, Joseph L; Shillingford, Jamal N; Lombardi, Joseph M; Alrabaa, Rami G; Benkli, Barlas; Fischer, Charla; Lenke, Lawrence G; Lehman, Ronald A

Case series. To determine the safety and feasibility of S2 alar-iliac (S2AI) screw placement under robotic guidance. Similar to standard iliac fixation, S2AI screws aid in achieving fixation across the sacropelvic junction and decreasing S1 screw strain. Fortunately, the S2AI technique minimizes prominent instrumentation and the need for offset connectors to the fusion construct. Herein, we present an analysis of the largest series of robotic-guided S2AI screws in the literature without any significant author conflicts of interest with the robotics industry. Twenty-three consecutive patients who underwent spinopelvic fixation with 46 S2AI screws under robotic guidance were analyzed from 2015 to 2016. Screws were placed by two senior spine surgeons, along with various fellow or resident surgical assistants, using a proprietary robotic guidance system (Renaissance; Mazor Robotics Ltd., Caesara, Israel). Screw position and accuracy was assessed on intraoperative CT O-arm scans and analyzed using three-dimensional interactive viewing and manipulation of the images. The average caudal angle in the sagittal plane was 31.0° ± 10.0°. The average horizontal angle in the axial plane using the posterior superior iliac spine as a reference was 42.8° ± 6.6°. The average S1 screw to S2AI screw angle was 11.3° ± 9.9°. Two violations of the iliac cortex were noted, with an average breach distance of 7.9 ± 4.8 mm. One breach was posterior (2.2%) and one was anterior (2.2%). The overall robotic S2AI screw accuracy rate was 95.7%. There were no intraoperative neurologic, vascular, or visceral complications related to the placement of the S2AI screws. Spinopelvic fixation achieved using a bone-mounted miniature robotic-guided S2AI screw insertion technique is safe and reliable. Despite two breaches, no complications related to the placement of the S2AI screws occurred in this series. Level IV, therapeutic. Copyright © 2017 Scoliosis Research Society. Published by Elsevier

Development and Testing of X-Ray Imaging-Enhanced Poly-L-Lactide Bone Screws.

Directory of Open Access Journals (Sweden)

Wei-Jen Chang

Full Text Available Nanosized iron oxide particles exhibit osteogenic and radiopaque properties. Thus, iron oxide (Fe3O4 nanoparticles were incorporated into a biodegradable polymer (poly-L-lactic acid, PLLA to fabricate a composite bone screw. This multifunctional, 3D printable bone screw was detectable on X-ray examination. In this study, mechanical tests including three-point bending and ultimate tensile strength were conducted to evaluate the optimal ratio of iron oxide nanoparticles in the PLLA composite. Both injection molding and 3D printing techniques were used to fabricate the PLLA bone screws with and without the iron oxide nanoparticles. The fabricated screws were implanted into the femoral condyles of New Zealand White rabbits. Bone blocks containing the PLLA screws were resected 2 and 4 weeks after surgery. Histologic examination of the surrounding bone and the radiopacity of the iron-oxide-containing PLLA screws were evaluated. Our results indicated that addition of iron oxide nanoparticles at 30% significantly decreased the ultimate tensile stress properties of the PLLA screws. The screws with 20% iron oxide exhibited strong radiopacity compared to the screws fabricated without the iron oxide nanoparticles. Four weeks after surgery, the average bone volume of the iron oxide PLLA composite screws was significantly greater than that of PLLA screws without iron oxide. These findings suggested that biodegradable and X-ray detectable PLLA bone screws can be produced by incorporation of 20% iron oxide nanoparticles. Furthermore, these screws had significantly greater osteogenic capability than the PLLA screws without iron oxide.

Biomechanical properties of a novel biodegradable magnesium-based interference screw

Directory of Open Access Journals (Sweden)

Marco Ezechieli

2016-06-01

Full Text Available Magnesium-based interference screws may be an alternative in anterior/posterior cruciate ligament reconstruction. The well-known osteoconductive effects of biodegradable magnesium alloys may be useful. It was the purpose of this study to evaluate the biomechanical properties of a magnesium based interference screw and compare it to a standard implant. A MgYREZr-alloy interference screw and a standard implant (Milagro®; De Puy Mitek, Raynham, MA, USA were used for graft fixation. Specimens were placed into a tensile loading fixation of a servohydraulic testing machine. Biomechanical analysis included pretensioning of the constructs at 20 N for 1 min following cyclic pretensioning of 20 cycles between 20 and 60 N. Biomechanical elongation was evaluated with cyclic loading of 1000 cycles between 50 and 200 N at 0.5 Hz. Maximum load to failure was 511.3±66.5 N for the Milagro® screw and 529.0±63.3 N for magnesium-based screw (ns, P=0.57. Elongations after preload, during cyclical loading and during failure load were not different between the groups (ns, P>0.05. Stiffness was 121.1±13.8 N/mm for the magnesiumbased screw and 144.1±18.4 for the Milagro® screw (ns, P=0.32. MgYREZr alloy interference screws show comparable results in biomechanical testing to standard implants and may be an alternative for anterior cruciate reconstruction in the future.

Pose and Motion Estimation Using Dual Quaternion-Based Extended Kalman Filtering

Energy Technology Data Exchange (ETDEWEB)

Goddard, J.S.; Abidi, M.A.

1998-06-01

A solution to the remote three-dimensional (3-D) measurement problem is presented for a dynamic system given a sequence of two-dimensional (2-D) intensity images of a moving object. The 3-D transformation is modeled as a nonlinear stochastic system with the state estimate providing the six-degree-of-freedom motion and position values as well as structure. The stochastic model uses the iterated extended Kalman filter (IEKF) as a nonlinear estimator and a screw representation of the 3-D transformation based on dual quaternions. Dual quaternions, whose elements are dual numbers, provide a means to represent both rotation and translation in a unified notation. Linear object features, represented as dual vectors, are transformed using the dual quaternion transformation and are then projected to linear features in the image plane. The method has been implemented and tested with both simulated and actual experimental data. Simulation results are provided, along with comparisons to a point-based IEKF method using rotation and translation, to show the relative advantages of this method. Experimental results from testing using a camera mounted on the end effector of a robot arm are also given.

Robust Short-Lag Spatial Coherence Imaging.

Science.gov (United States)

Nair, Arun Asokan; Tran, Trac Duy; Bell, Muyinatu A Lediju

2018-03-01

Short-lag spatial coherence (SLSC) imaging displays the spatial coherence between backscattered ultrasound echoes instead of their signal amplitudes and is more robust to noise and clutter artifacts when compared with traditional delay-and-sum (DAS) B-mode imaging. However, SLSC imaging does not consider the content of images formed with different lags, and thus does not exploit the differences in tissue texture at each short-lag value. Our proposed method improves SLSC imaging by weighting the addition of lag values (i.e., M-weighting) and by applying robust principal component analysis (RPCA) to search for a low-dimensional subspace for projecting coherence images created with different lag values. The RPCA-based projections are considered to be denoised versions of the originals that are then weighted and added across lags to yield a final robust SLSC (R-SLSC) image. Our approach was tested on simulation, phantom, and in vivo liver data. Relative to DAS B-mode images, the mean contrast, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) improvements with R-SLSC images are 21.22 dB, 2.54, and 2.36, respectively, when averaged over simulated, phantom, and in vivo data and over all lags considered, which corresponds to mean improvements of 96.4%, 121.2%, and 120.5%, respectively. When compared with SLSC images, the corresponding mean improvements with R-SLSC images were 7.38 dB, 1.52, and 1.30, respectively (i.e., mean improvements of 14.5%, 50.5%, and 43.2%, respectively). Results show great promise for smoothing out the tissue texture of SLSC images and enhancing anechoic or hypoechoic target visibility at higher lag values, which could be useful in clinical tasks such as breast cyst visualization, liver vessel tracking, and obese patient imaging.

Effects on Subtalar Joint Stress Distribution After Cannulated Screw Insertion at Different Positions and Directions.

Science.gov (United States)

Yuan, Cheng-song; Chen, Wan; Chen, Chen; Yang, Guang-hua; Hu, Chao; Tang, Kang-lai

2015-01-01

We investigated the effects on subtalar joint stress distribution after cannulated screw insertion at different positions and directions. After establishing a 3-dimensional geometric model of a normal subtalar joint, we analyzed the most ideal cannulated screw insertion position and approach for subtalar joint stress distribution and compared the differences in loading stress, antirotary strength, and anti-inversion/eversion strength among lateral-medial antiparallel screw insertion, traditional screw insertion, and ideal cannulated screw insertion. The screw insertion approach allowing the most uniform subtalar joint loading stress distribution was lateral screw insertion near the border of the talar neck plus medial screw insertion close to the ankle joint. For stress distribution uniformity, antirotary strength, and anti-inversion/eversion strength, lateral-medial antiparallel screw insertion was superior to traditional double-screw insertion. Compared with ideal cannulated screw insertion, slightly poorer stress distribution uniformity and better antirotary strength and anti-inversion/eversion strength were observed for lateral-medial antiparallel screw insertion. Traditional single-screw insertion was better than double-screw insertion for stress distribution uniformity but worse for anti-rotary strength and anti-inversion/eversion strength. Lateral-medial antiparallel screw insertion was slightly worse for stress distribution uniformity than was ideal cannulated screw insertion but superior to traditional screw insertion. It was better than both ideal cannulated screw insertion and traditional screw insertion for anti-rotary strength and anti-inversion/eversion strength. Lateral-medial antiparallel screw insertion is an approach with simple localization, convenient operation, and good safety. Copyright © 2015 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Electromagnetic Lead Screw for Potential Wave Energy Application

DEFF Research Database (Denmark)

Lu, Kaiyuan; Wu, Weimin

2014-01-01

This paper presents a new type electromagnetic lead screw (EMLS) intended for wave energy application. Similar to the mechanical lead screw, this electromagnetic version can transfer slow linear motion to high-rotational motion, offering gearing effects. Compared with the existing pure magnetic...

Bioresorbable screws reinforced with phosphate glass fibre: manufacturing and mechanical property characterisation.

Science.gov (United States)

Felfel, R M; Ahmed, I; Parsons, A J; Rudd, C D

2013-01-01

Use of bioresorbable screws could eliminate disadvantages associated with metals such as removal operations, corrosion, MRI interference and stress shielding. Mechanical properties of bioresorbable polymers alone are insufficient for load bearing applications application as screws. Thus, reinforcement is necessary to try and match or surpass the mechanical properties of cortical bone. Phosphate based glass fibres were used to reinforce polylactic acid (PLA) in order to produce unidirectionally aligned (UD) and unidirectionally plus randomly distributed (UD/RM) composite screws (P40 UD and P40 UD/RM). The maximum flexural and push-out properties for the composite screws (P40 UD and P40 UD/RM) increased by almost 100% in comparison with the PLA screws. While the pull-out strength and stiffness of the headless composite screws were ∼80% (strength) and ∼130% (stiffness) higher than for PLA, those with heads exhibited properties lower than those for PLA alone as a result of failure at the heads. An increase in the maximum shear load and stiffness for the composite screws (∼30% and ∼40%) in comparison to the PLA screws was also seen. Maximum torque for the PLA screws was ∼1000 mN m, while that for the composite screws were slightly lower. The SEM micrographs for P40 UD and P40 UD/RM screws revealed small gaps around the fibres, which were suggested to be due to buckling of the UD fibres during the manufacturing process. Copyright © 2012 Elsevier Ltd. All rights reserved.

Process and apparatus for optimizing screwing position for closure stud

International Nuclear Information System (INIS)

Bourdonne, J.C.; Briand, A.

1987-01-01

The stud is fixed to a screwing and unscrewing device. The vertical position and alignment of the stud with the axis of the threated hole is checking. The stud is descended into the hole and rotated in the unscrewing direction. After detection of the point of engagement, the stud is rotated in the screwing direction. When a gamming is detected the descent is stopped and the screwing device is positioned in a new position. When the screwing couple returns below the disconnection couple, the stud is rotated with a reduced speed and then with a normal speed until the end [fr

Grid deformation strategies for CFD analysis of screw compressors

OpenAIRE

Rane, S.; Kovacevic, A.; Stosic, N.; Kethidi, M.

2013-01-01

Customized grid generation of twin screw machines for CFD analysis is widely used by the refrigeration and air-conditioning industry today, but is currently not suitable for topologies such as those of single screw, variable pitch or tri screw rotors. This paper investigates a technique called key-frame re-meshing that supplies pre-generated unstructured grids to the CFD solver at different time steps. To evaluate its accuracy, the results of an isentropic compression-expansion process in a r...

Locking screw apparatus and method for underwater remote replacement

International Nuclear Information System (INIS)

Balog, L.J.

1987-01-01

A method is described for locking in place a screw which secures together first and second structures in the internal region of a nuclear reactor core. The first structure has a screw bore with a counterbore portion formed in an outer surface. The method comprises the steps of: forming a lateral recess in the counterbore portion and spaced from the outer surface, providing an elongated screw having an enlarged shoulder flange and an angular drive head with a lateral width substantially less than that of the counterbore portion, disposing the screw through the screw bore in threaded engagement with the second structure and with the shoulder rotatably seated in the counterbore portion. This provides a locking member having an angular opening and disposing it in the counterbore portion against the flange with the drive head received in the opening for engagement with the locking member to prevent rotation. This deforms a portion of the locking member into the recess for engagement to prevent movement of the locking member with respect to the first structure

Tests for the dynamic behavior of insulation valve screws

International Nuclear Information System (INIS)

Tulke, K.D.; Stoppler, W.; Stern, G.

1994-01-01

Thermal tensile tests were performed at a temperature of 270 C, with two new original insulation valve conical screws M30-Tx92,5 mm (material: 21 CrMo V 5 7)and two prestrained ones during the event on 27.12.92. In order to assure the results obtained with regard to the dynamic load on the insulation valve during ''quick opening'', in addition tensile impact tests were performed at 270 C with six original insulation valve conical screws. Impact velocity reached 13,5 m/s at four screws and 6 m/s at two screws. Test conditions regarding collision damping and mass distribution were adapted, by means of parameter studies, to the situation of the insulation valve. During thermal tensile tests, strength and deformation values, such as stress at flow start, tensile strength, fracture prolongation and strain, necking at fracture as well as energy absorption up to maximum force and up to rupture, were determined. During tensile impact tests, deformation values, such as elongation, strain and necking, and energy absorption by the screw, were determined. (orig.) [de

Correction Capability in the 3 Anatomic Planes of Different Pedicle Screw Designs in Scoliosis Instrumentation.

Science.gov (United States)

Wang, Xiaoyu; Aubin, Carl-Eric; Coleman, John; Rawlinson, Jeremy

2017-05-01

Computer simulations to compare the correction capabilities of different pedicle screws in adolescent idiopathic scoliosis (AIS) instrumentations. To compare the correction and resulting bone-screw forces associated with different pedicle screws in scoliosis instrumentations. Pedicle screw fixation is widely used in surgical instrumentation for spinal deformity treatment. Screw design, correction philosophies, and surgical techniques are constantly evolving to achieve better control of the vertebrae and correction of the spinal deformity. Yet, there remains a lack of biomechanical studies that quantify the effects and advantages of different screw designs in terms of correction kinematics. The correction capabilities of fixed-angle, multiaxial, uniaxial, and saddle axial screws were kinematically analyzed, simulated, and compared. These simulations were based on the screw patterns and correction techniques proposed by 2 experienced surgeons for 2 AIS cases. Additional instrumentations were assessed to compare the correction and resulting bone-screw forces associated with each type of screw. The fixed-angle, uniaxial and saddle axial screws had similar kinematic behavior and performed better than multiaxial screws in the coronal and transverse planes (8% and 30% greater simulated corrections, respectively). Uniaxial and multiaxial screws were less effective than fixed-angle and saddle axial screws in transmitting compression/distraction to the anterior spine because of their sagittal plane mobility between the screw head and shank. Only the saddle axial screws allow vertebra angle in the sagittal plane to be independently adjusted. Pedicle screws of different designs performed differently for deformity corrections or for compensating screw placement variations in different anatomic planes. For a given AIS case, screw types should be determined based on the particular instrumentation objectives, the deformity's stiffness and characteristics so as to make the best of

High effective inverse dynamics modelling for dual-arm robot

Science.gov (United States)

Shen, Haoyu; Liu, Yanli; Wu, Hongtao

2018-05-01

To deal with the problem of inverse dynamics modelling for dual arm robot, a recursive inverse dynamics modelling method based on decoupled natural orthogonal complement is presented. In this model, the concepts and methods of Decoupled Natural Orthogonal Complement matrices are used to eliminate the constraint forces in the Newton-Euler kinematic equations, and the screws is used to express the kinematic and dynamics variables. On this basis, the paper has developed a special simulation program with symbol software of Mathematica and conducted a simulation research on the a dual-arm robot. Simulation results show that the proposed method based on decoupled natural orthogonal complement can save an enormous amount of CPU time that was spent in computing compared with the recursive Newton-Euler kinematic equations and the results is correct and reasonable, which can verify the reliability and efficiency of the method.

The improvement of screw compressor performance using a newly developed rotor profile

International Nuclear Information System (INIS)

Kishi, Takayuki; Nishio, Toshio; Matsui, Akira; Ino, Nobumi

1994-01-01

An oil-compression phenomenon occurs at two portions of a conventional oil injected screw compressor that degrades the isothermal efficiency of the screw compressor. Hence a new screw rotor profile and lubricant have been developed in order to avoid the above oil-compression phenomena. Mycom and Fermi National Accelerator Laboratory have measured the performance of a new Mycom compound type screw compressor 2016C using the new profile rotors and the new lubricant. In the experiments, a 33% enhancement rate in the isothermal efficiency of the new screw compressor installed in Fermilab was achieved

Numerical study of internal flow in twin screw extruder and its mixing performance analysis

International Nuclear Information System (INIS)

Kim, Nak Soo; Kim, Hong Bum; Lee, Jae Wook

2006-01-01

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder

The biomechanical consequences of rod reduction on pedicle screws: should it be avoided?

Science.gov (United States)

Paik, Haines; Kang, Daniel G; Lehman, Ronald A; Gaume, Rachel E; Ambati, Divya V; Dmitriev, Anton E

2013-11-01

Rod contouring is frequently required to allow for appropriate alignment of pedicle screw-rod constructs. When residual mismatch is still present, a rod persuasion device is often used to achieve further rod reduction. Despite its popularity and widespread use, the biomechanical consequences of this technique have not been evaluated. To evaluate the biomechanical fixation strength of pedicle screws after attempted reduction of a rod-pedicle screw mismatch using a rod persuasion device. Fifteen 3-level, human cadaveric thoracic specimens were prepared and scanned for bone mineral density. Osteoporotic (n=6) and normal (n=9) specimens were instrumented with 5.0-mm-diameter pedicle screws; for each pair of comparison level tested, the bilateral screws were equal in length, and the screw length was determined by the thoracic level and size of the vertebra (35 to 45 mm). Titanium 5.5-mm rods were contoured and secured to the pedicle screws at the proximal and distal levels. For the middle segment, the rod on the right side was intentionally contoured to create a 5-mm residual gap between the inner bushing of the pedicle screw and the rod. A rod persuasion device was then used to engage the setscrew. The left side served as a control with perfect screw/rod alignment. After 30 minutes, constructs were disassembled and vertebrae individually potted. The implants were pulled in-line with the screw axis with peak pullout strength (POS) measured in Newton (N). For the proximal and distal segments, pedicle screws on the right side were taken out and reinserted through the same trajectory to simulate screw depth adjustment as an alternative to rod reduction. Pedicle screws reduced to the rod generated a 48% lower mean POS (495±379 N) relative to the controls (954±237 N) (p.05). In circumstances where a rod is not fully seated within the pedicle screw, the use of a rod persuasion device decreases the overall POS and work energy to failure of the screw or results in outright

Intermaxillary Fixation Screw Morbidity in Treatment of Mandibular Fractures

DEFF Research Database (Denmark)

Florescu, Vlad-Andrei; Kofod, Thomas; Pinholt, Else Marie

2016-01-01

Purpose The aim of the present retrospective study was to investigate the morbidity of screws used for intermaxillary fixation (IMF) in the treatment of mandibular fractures. A review of the published data was also performed for a comparison of outcomes. Our hypothesis was that the use of screws...... for IMF of mandibular fractures would result in minimal morbidity. Materials and Methods Patients treated for mandibular fractures from 2007 to 2013, using screws for IMF, using the international diagnosis code for mandibular fracture, DS026, were anonymously selected (Department of Oral and Maxillofacial...... Surgery, Rigshospitalet, University Hospital of Copenhagen, Copenhagen, Denmark). The fracture type, radiographic findings, treatment modality, screw type and number, and root damage were recorded. For the outcome comparison, a review of the published data regarding iatrogenic dental root damage caused...

The Analysis of Soil Resistance During Screw Displacement Pile Installation

Science.gov (United States)

Krasinski, Adam

2015-02-01

The application of screw displacement piles (SDP) is still increasing due to their high efficiency and many advantages. However, one technological problem is a serious disadvantage of those piles. It relates to the generation of very high soil resistance during screw auger penetration, especially when piles are installed in non-cohesive soils. In many situations this problem causes difficulties in creating piles of designed length and diameter. It is necessary to find a proper method for prediction of soil resistance during screw pile installation. The analysis of screw resistances based on model and field tests is presented in the paper. The investigations were carried out as part of research project, financed by the Polish Ministry of Science and Higher Education. As a result of tests and analyses the empirical method for prediction of rotation resistance (torque) during screw auger penetration in non-cohesive subsoil based on CPT is proposed.

Repetition and lag effects in movement recognition.

Science.gov (United States)

Hall, C R; Buckolz, E

1982-03-01

Whether repetition and lag improve the recognition of movement patterns was investigated. Recognition memory was tested for one repetition, two-repetitions massed, and two-repetitions distributed with movement patterns at lags of 3, 5, 7, and 13. Recognition performance was examined both immediately afterwards and following a 48 hour delay. Both repetition and lag effects failed to be demonstrated, providing some support for the claim that memory is unaffected by repetition at a constant level of processing (Craik & Lockhart, 1972). There was, as expected, a significant decrease in recognition memory following the retention interval, but this appeared unrelated to repetition or lag.

Process and device for the ultrasonic testing of slotted screws screwed into a head of a nuclear reactor fuel element for cracks

International Nuclear Information System (INIS)

Scharpenberg, R.

1986-01-01

To achieve correct echo signals, a test head is set separately on each area limited by a slot of the top of the slotted screw and the screw head is ultrasonically sounded in the direction of the suspected cracks. (orig./HP) [de

Effect of diameter of the drill hole on torque of screw insertion and pushout strength for headless tapered compression screws in simulated fractures of the lateral condyle of the equine third metacarpal bone.

Science.gov (United States)

Carpenter, Ryan S; Galuppo, Larry D; Stover, Susan M

2006-05-01

To compare variables for screw insertion, pushout strength, and failure modes for a headless tapered compression screw inserted in standard and oversize holes in a simulated lateral condylar fracture model. 6 pairs of third metacarpal bones from horse cadavers. Simulated lateral condylar fractures were created, reduced, and stabilized with a headless tapered compression screw by use of a standard or oversize hole. Torque, work, and time for drilling, tapping, and screw insertion were measured during site preparation and screw implantation. Axial load and displacement were measured during screw pushout. Effects of drill hole size on variables for screw insertion and screw pushout were assessed by use of Wilcoxon tests. Drill time was 59% greater for oversize holes than for standard holes. Variables for tapping (mean maximum torque, total work, positive work, and time) were 42%, 70%, 73%, and 58% less, respectively, for oversize holes, compared with standard holes. Variables for screw pushout testing (mean yield load, failure load, failure displacement, and failure energy) were 40%, 40%, 47%, and 71% less, respectively, for oversize holes, compared with standard holes. Screws could not be completely inserted in 1 standard and 2 oversize holes. Enlarging the diameter of the drill hole facilitated tapping but decreased overall holding strength of screws. Therefore, holes with a standard diameter are recommended for implantation of variable pitch screws whenever possible. During implantation, care should be taken to ensure that screw threads follow tapped bone threads.

Dual-energy X-ray absorptiometry and force-plate analysis of gait in dogs with healed femora after leg-lengthening plate fixation

International Nuclear Information System (INIS)

Muir, P.; Markel, M.D.; Bogdanske, J.J.; Johnson, K.A.

1995-01-01

Dual-energy x-ray absorptiometry was used to measure bone mineral density of four regions in healed femora of nine dogs after fracture fixation with a leg-lengthening plate. Six to 85 months (mean, 46 months) after surgery, the bone mineral density of healed femora was not significantly different from the contralateral uninjured femora (P > .05; power = 0.8 at delta = 15%). Radiolucencies around the proximal screws, apparently associated with screw loosening, were seen on radiographic views of the healed femora of three dogs. In one of these dogs, one screw in the proximal metaphysis had broken. Force-plate analysis of gait was also performed on dogs at the time of bone mineral density measurement. Peak vertical force was decreased in the pelvic limb with the healed fracture compared with the contralateral unoperated limb (P < 0.05). Clinically apparent lameness in three dogs did not appear to be associated with altered bone mineral density and may have been caused by hip osteoarthritis, a nondisplaced hairline diaphyseal fracture, and screw loosening in conjunction with extensive post-traumatic soft tissue injury

The Analysis of Soil Resistance During Screw Displacement Pile Installation

Directory of Open Access Journals (Sweden)

Krasinski Adam

2015-02-01

Full Text Available The application of screw displacement piles (SDP is still increasing due to their high efficiency and many advantages. However, one technological problem is a serious disadvantage of those piles. It relates to the generation of very high soil resistance during screw auger penetration, especially when piles are installed in non-cohesive soils. In many situations this problem causes difficulties in creating piles of designed length and diameter. It is necessary to find a proper method for prediction of soil resistance during screw pile installation. The analysis of screw resistances based on model and field tests is presented in the paper. The investigations were carried out as part of research project, financed by the Polish Ministry of Science and Higher Education. As a result of tests and analyses the empirical method for prediction of rotation resistance (torque during screw auger penetration in non-cohesive subsoil based on CPT is proposed.

Biomechanical evaluation of the locking titanium cable in the fixture of distal tibiofibular syndesmosis injury

Directory of Open Access Journals (Sweden)

Shu-zhi YAO

2016-08-01

Full Text Available Objective 　The article aims at evaluating the biological properties of tibiofibular titanium cable fixation device in terms of both anti-separation and stress shielding by comparison to the interior fixation with lag screw based on experimental observation. Methods 　Six corpse ankle specimens were first tested of pressure-separation and stress measurement, the data from which were compared to the normal group, and then a syndesmosis injury model was established. All the samples are randomly divided into 2 groups of 3 specimens each, which were treated with tibiofibula locked titanium cable and lag screw fixation respectively for syndesmosis injury. Then, the samples were tested for pressure-separation and stress measurement. The biomechanical properties as anti-separation ability and stress shielding were analyzed and compared between the two fixation method. Results 　Both tibiofibula locked titanium cables and lag screws were able to provide enough strong lateral anti-separation ability, but strong fixation screws were inferior to tibiofibular titanium cable fixation device in fibular longitudinal stress transduction. Conclusion 　Tibiofibular titanium cable fixation device not only provide sufficient lateral anti-separation, but also reduces the tibial and fibular longitudinal stress shielding, thus being superior to the traditional lag screw in biomechanical properties. DOI: 10.11855/j.issn.0577-7402.2016.07.09

Preload, Coefficient of Friction, and Thread Friction in an Implant-Abutment-Screw Complex.

Science.gov (United States)

Wentaschek, Stefan; Tomalla, Sven; Schmidtmann, Irene; Lehmann, Karl Martin

To examine the screw preload, coefficient of friction (COF), and tightening torque needed to overcome the thread friction of an implant-abutment-screw complex. In a customized load frame, 25 new implant-abutment-screw complexes including uncoated titanium alloy screws were torqued and untorqued 10 times each, applying 25 Ncm. Mean preload values decreased significantly from 209.8 N to 129.5 N according to the number of repetitions. The overall COF increased correspondingly. There was no comparable trend for the thread friction component. These results suggest that the application of a used implant-abutment-screw complex may be unfavorable for obtaining optimal screw preload.

Translaminar screw fixation in the lumbar spine: technique, indications, results

OpenAIRE

Grob, D.; Humke, T.

1998-01-01

Translaminar screw fixation of the lumbar spine represents a simple and effective technique for short segment fusion in the degenerative spine. Clinical experience with 173 patients who underwent translaminar screw fixation revealed a fusion rate of 94%. The indications for translaminar screw fixation as a primary fixation procedure are: segmental dysfunction, lumbar spinal stenosis with painful degenerative changes, segmental revision surgery after discectomies, and painful disc-related synd...

Inspection and replacement of baffle assembly screws inside American reactor vessels

International Nuclear Information System (INIS)

Neal, K.; Chaumont, J.C.

1999-01-01

The baffle assembly inside the vessel of a 900 MWe reactor designed by Framatome, is made up of 44 plates fixed on 8 horizontal supports by a system of about 1000 screws. These plates undergo high neutron flux and the problem of screw cracking appeared at the end of the eighties in the first-generation reactors. The first operation on a large scale concerning the screws of a Westinghouse type reactor, was performed on the Tihange-1 power plant where Framatome controlled 960 screws and replaced 91. In 1997 as a consequence of the Belgian and French feedback experience, American plant operators launched a vast program of preventive actions: material analysis, inspection of baffle plate screws and replacement of defective screws. This program was held in cooperation with EPRI (electric power research institute) and under the control of NRC (nuclear regulatory commission). Framatome Technologies Inc (FTI) was in charge of the in-situ inspection and replacement of the screws. FTI designed special tools and equipment adapted to the 2-loop American reactors but the basis ideas were those applied on the Tihange reactor. The successful experience of FTI has allowed the firm to be commissioned for 6 2-loops American reactors. (A.C.)

Fracture resistance of abutment screws made of titanium, polyetheretherketone, and carbon fiber-reinforced polyetheretherketone

Directory of Open Access Journals (Sweden)

Eduardo Aloisio Fleck NEUMANN

2014-08-01

Full Text Available Fractured abutment screws may be replaced; however, sometimes, the screw cannot be removed and the entire implant must be surgically removed and replaced. The aim of this study was to compare the fracture resistance of abutment retention screws made of titanium, polyetheretherketone (PEEK and 30% carbon fiber-reinforced PEEK, using an external hexagonal implant/UCLA-type abutment interface assembly. UCLA-type abutments were fixed to implants using titanium screws (Group 1, polyetheretherketone (PEEK screws (Group 2, and 30% carbon fiber-reinforced PEEK screws (Group 3. The assemblies were placed on a stainless steel holding apparatus to allow for loading at 45o off-axis, in a universal testing machine. A 200 N load (static load was applied at the central point of the abutment extremity, at a crosshead speed of 5 mm/minute, until failure. Data was analyzed by ANOVA and Tukey’s range test. The titanium screws had higher fracture resistance, compared with PEEK and 30% carbon fiber-reinforced PEEK screws (p 0.05. Finally, visual analysis of the fractions revealed that 100% of them occurred at the neck of the abutment screw, suggesting that this is the weakest point of this unit. PEEK abutment screws have lower fracture resistance, in comparison with titanium abutment screws.

Fracture resistance of abutment screws made of titanium, polyetheretherketone, and carbon fiber-reinforced polyetheretherketone.

Science.gov (United States)

Neumann, Eduardo Aloisio Fleck; Villar, Cristina Cunha; França, Fabiana Mantovani Gomes

2014-01-01

Fractured abutment screws may be replaced; however, sometimes, the screw cannot be removed and the entire implant must be surgically removed and replaced. The aim of this study was to compare the fracture resistance of abutment retention screws made of titanium, polyetheretherketone (PEEK) and 30% carbon fiber-reinforced PEEK, using an external hexagonal implant/UCLA-type abutment interface assembly. UCLA-type abutments were fixed to implants using titanium screws (Group 1), polyetheretherketone (PEEK) screws (Group 2), and 30% carbon fiber-reinforced PEEK screws (Group 3). The assemblies were placed on a stainless steel holding apparatus to allow for loading at 45o off-axis, in a universal testing machine. A 200 N load (static load) was applied at the central point of the abutment extremity, at a crosshead speed of 5 mm/minute, until failure. Data was analyzed by ANOVA and Tukey's range test. The titanium screws had higher fracture resistance, compared with PEEK and 30% carbon fiber-reinforced PEEK screws (p 0.05). Finally, visual analysis of the fractions revealed that 100% of them occurred at the neck of the abutment screw, suggesting that this is the weakest point of this unit. PEEK abutment screws have lower fracture resistance, in comparison with titanium abutment screws.

Strength evaluation of top nozzle holddown spring screw for nuclear fuel assembly

International Nuclear Information System (INIS)

Koh, S. K.; Won, S. Y.; Ryu, C. H.; Kim, Y. J.; Lee, K. S.; Jeon, K. L.

2002-01-01

Holddown springs are required to maintain the nuclear fuel assembly in contact with lower core plate and permit thermal and irradiation-induced length changes. Therefore, the holddown spring screw must be designed such that it is capable of sustaining the loads imposed by the initial tensile preload and operational loads. Prior to assessing the structural integrity of the spring screw in the corrosive and irradiating environment throughout the design lifetime of the fuel assembly, the strength evaluation of screw was made in this paper using the mechanics of materials and finite element methods. Calculations based on the mechanics of materials, showed that the preloaded screw with an operating holddown force had a quite large margin of safety in strength. However, the elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Preloading on the screw applied for tightening had beneficial effects on the screw strength by reducing the stress level at the critical regions, compared to the screw without preload. Calculated spring deflection using the finite element analysis was in close agreement with the experimentally measured deflection

Comparative effect of implant-abutment connections, abutment angulations, and screw lengths on preloaded abutment screw using three-dimensional finite element analysis: An in vitro study

OpenAIRE

Krishna Chaitanya Kanneganti; Dileep Nag Vinnakota; Srinivas Rao Pottem; Mahesh Pulagam

2018-01-01

Purpose: The purpose of this study is to compare the effect of implant-abutment connections, abutment angulations, and screw lengths on screw loosening (SL) of preloaded abutment using three dimensional (3D) finite element analysis. Materials and Methods: 3D models of implants (conical connection with hex/trilobed connections), abutments (straight/angulated), abutment screws (short/long), and crown and bone were designed using software Parametric Technology Corporation Creo and assembled t...

Screw expander for light duty diesel engines

Science.gov (United States)

1983-01-01

Preliminary selection and sizing of a positive displacement screw compressor-expander subsystem for a light-duty adiabatic diesel engine; development of a mathematical model to describe overall efficiencies for the screw compressor and expander; simulation of operation to establish overall efficiency for a range of design parameters and at given engine operating points; simulation to establish potential net power output at light-duty diesel operating points; analytical determination of mass moments of inertia for the rotors and inertia of the compressor-expander subsystem; and preparation of engineering layout drawings of the compressor and expander are discussed. As a result of this work, it was concluded that the screw compressor and expander designed for light-duty diesel engine applications are viable alternatives to turbo-compound systems, with acceptable efficiencies for both units, and only a moderate effect on the transient response.

Control of influence of a thread on a bending of screws

International Nuclear Information System (INIS)

Proskuriakov, N E; Lopa, I V; Trapeznikov, E V

2017-01-01

The influence of the threads and the bending of screw on their moments of inertia of the cross section considered. This problem is actual since existing methods exclude from calculations the influence of supporting the thread, using as the basic geometrical parameter such as the internal diameter of the thread (diameter of cavities). Fundamental difference of a bend of the screw from a bend of a smooth rod consists that moment of inertia of the screw is a variable. It is shown that the change in cross-section moment of inertia along the length of the screw are essential and have periodic character. Analytical interrelation of the bending of the screw and the decreasing of moment of inertia of its cross section is established and equation describing this phenomenon is suggested. The greatest decrease of the moment of inertia occurs in the middle of the screw length, and the lowest - at its ends. Function and approximate coefficients for the main types of thread are proposed, which take into account this change. (paper)

Bioabsorbable metal screws in traumatology: A promising innovation

Directory of Open Access Journals (Sweden)

Roland Biber

2017-04-01

Full Text Available MAGNEZIX® CS (Syntellix AG, Hanover, Germany is a bioabsorbable compression screw made of a magnesium alloy (MgYREZr. Currently there are only two clinical studies reporting on a limited number of elective patients who received this screw in a hallux valgus operation. We applied MAGNEZIX® CS for fixation of distal fibular fracture in a trauma patient who had sustained a bimalleolar fracture type AO 44-B2.3. Clinical course was uneventful, fracture healing occurred within three months. Follow-up X-rays showed a radiolucent area around the implant for some months, yet this radiolucent area had disappeared in the 17-months follow-up X-ray. Keywords: Magnesium, Bioabsorbable, Compression screw, Osteosynthesis, Ankle fracture

History of Retractor Technologies for Percutaneous Pedicle Screw Fixation Systems.

Science.gov (United States)

Mobbs, Ralph J; Phan, Kevin

2016-02-01

Minimally invasive techniques aimed at minimizing surgery-associated risk and morbidity of spinal surgery have increased in popularity in recent years. Their potential advantages include reduced length of hospital stay, blood loss, and requirement for post-operative analgesia and earlier return to work. One such minimally invasive technique is the use of percutaneous pedicle screw fixation, which is paramount for promoting rigid and stable constructs and fusion in the context of trauma, tumors, deformity and degenerative disease. Percutaneous pedicle screw insertion can be an intimidating prospect for surgeons who have only been trained in open techniques. One of the ongoing challenges of this percutaneous system is to provide the surgeon with adequate access to the pedicle entry anatomy and adequate tactile or visual feedback concerning the position and anatomy of the rod and set-screw construct. This review article discusses the history and evolution of percutaneous pedicle screw retractor technologies and outlines the advances over the last decade in the rapidly expanding field of minimal access surgery for posterior pedicle screw based spinal stabilization. As indications for percutaneous pedicle screw techniques expand, the nuances of the minimally invasive surgery techniques and associated technologies will also multiply. It is important that experienced surgeons have access to tools that can improve access with a greater degree of ease, simplicity and safety. We here discuss the technical challenges of percutaneous pedicle screw retractor technologies and a variety of systems with a focus on the pros and cons of various retractor systems. © 2016 Chinese Orthopaedic Association and John Wiley & Sons Australia, Ltd.

The Improvement of Bone-Tendon Fixation by Porous Titanium Interference Screw: A Rabbit Animal Model.

Science.gov (United States)

Tsai, Pei-I; Chen, Chih-Yu; Huang, Shu-Wei; Yang, Kuo-Yi; Lin, Tzu-Hung; Chen, San-Yuan; Sun, Jui-Sheng

2018-05-04

The interference screw is a widely used fixation device in the anterior cruciate ligament (ACL) reconstruction surgeries. Despite the generally satisfactory results, problems of using interference screws were reported. By using additive manufacturing (AM) technology, we developed an innovative titanium alloy (Ti 6 Al 4 V) interference screw with rough surface and inter-connected porous structure designs to improve the bone-tendon fixation. An innovative Ti 6 Al 4 V interference screws were manufactured by AM technology. In vitro mechanical tests were performed to validate its mechanical properties. Twenty-seven New Zealand white rabbits were randomly divided into control and AM screw groups for biomechanical analyses and histological analysis at 4, 8 and 12 weeks postoperatively; while micro-CT analysis was performed at 12 weeks postoperatively. The biomechanical tests showed that the ultimate failure load in the AM interference screw group was significantly higher than that in the control group at all tested periods. These results were also compatible with the findings of micro-CT and histological analyses. In micro-CT analysis, the bone-screw gap was larger in the control group; while for the additive manufactured screw, the screw and bone growth was in close contact. In histological study, the bone-screw gaps were wider in the control group and were almost invisible in the AM screw group. The innovative AM interference screws with surface roughness and inter-connected porous architectures demonstrated better bone-tendon-implant integration, and resulted in stronger biomechanical characteristics when compared to traditional screws. These advantages can be transferred to future interference screw designs to improve their clinical performance. The AM interference screw could improve graft fixation and eventually result in better biomechanical performance of the bone-tendon-screw construct. The innovative AM interference screws can be transferred to future

Failure analysis of top nozzle holddown spring screw for nuclear fuel assembly

International Nuclear Information System (INIS)

Koh, S. K.; Ryu, C. H.; Na, E. G.; Baek, T. H.; Jeon, K. L.

2003-01-01

A failure analysis of holddown spring screw was performed using fracture mechanics approach. The spring screw was designed such that it was capable of sustaining the loads imposed by the initial tensile preload and operational loads. In order to investigate the cause of failure, a stress analysis of the top nozzle spring assembly was done using finite element analysis and a life prediction of the screw was made using a fracture mechanics approach. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Primary water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of the Scott model and resulted in 1.42 years, which was fairly close to the actual service life of the holddown spring screw

The Study of Vibration Processes in Oil Flooded Screw Compressors

Directory of Open Access Journals (Sweden)

I. V. Filippov

2014-01-01

Full Text Available Vibration processes that accompany most of machines and mechanisms are of interest to the researcher, as a source of information about the technical condition and the nature of the business processes flow. Vibration-based diagnostics of oil flooded screw compressors allows us to estimate the deviation of their operation from the main mode in accordance with changing the settings of vibration processes.The oil flooded screw compressor transition from the main mode of operation to the abnormal one is accompanied by complex gas-dynamic phenomena i.e. the initial gaps and their decays. This leads to changes in the nature of vibration processes, prompting suggestions that there is a relationship to a change of vibration parameters and mode of compressor operation.Studies were conducted by combined method using an analytical calculation of the decay parameters of the initial discontinuity and an experimental one based on the measurement of acceleration on the body of the real oil flooded screw compressor. A virtually adequate reaction of the decay parameters of the initial gap and the peak values of vibration acceleration to the change of operation mode of oil flooded screw compressor has been received. The peak value of the vibration acceleration was selected by the method of Gating being time-coinciding with the beginning discharge phase of the oil flooded screw compressor, and therefore, with the decay time of the initial discontinuity.This indicates a large degree of hypothesis likelihood on an existing initial break in oil flooded screw compressor when operating in abnormal conditions. This work contains the study results of vibration processes and their relationship to the operating mode of the oil flooded screw compressor, which distinguish it from the other works studied vibration processes in reciprocating compressors. The vibration parameters control of operating oil flooded screw compressor allows us to create an automatic capacity control

Analysis of Material Flow in Screw Extrusion of Aluminum

International Nuclear Information System (INIS)

Haugen, Bjoern; Oernskar, Magnus; Welo, Torgeir; Wideroee, Fredrik

2010-01-01

Screw extrusion of aluminum is a new process for production of aluminum profiles. The commercial potential could be large. Little experimental and numerical work has been done with respect to this process.The material flow of hot aluminum in a screw extruder has been analyzed using finite element formulations for the non-Newtonian Navier-Stokes equations. Aluminum material properties are modeled using the Zener-Holloman material model. Effects of stick-slip conditions are investigated with respect to pressure build up and mixing quality of the extrusion process.The numerical results are compared with physical experiments using an experimental screw extruder.

Decrease in Hydrogen Embrittlement Susceptibility of 10B21 Screws by Bake Aging

Directory of Open Access Journals (Sweden)

Kuan-Jen Chen

2016-08-01

Full Text Available The effects of baking on the mechanical properties and fracture characteristics of low-carbon boron (10B21 steel screws were investigated. Fracture torque tests and hydrogen content analysis were performed on baked screws to evaluate hydrogen embrittlement (HE susceptibility. The diffusible hydrogen content within 10B21 steel dominated the fracture behavior of the screws. The fracture torque of 10B21 screws baked for a long duration was affected by released hydrogen. Secondary ion mass spectroscopy (SIMS result showed that hydrogen content decreased with increasing baking duration, and thus the HE susceptibility of 10B21 screws improved. Diffusible hydrogen promoted crack propagation in high-stress region. The HE of 10B21 screws can be prevented by long-duration baking.

Jet lag prevention

Science.gov (United States)

... lose time. Symptoms of jet lag include: Trouble falling asleep or waking up Tiredness during the day ... at your destination. For longer trips, before you leave, try to adapt to the time schedule of ...

The movement of screw dislocations in tungsten

International Nuclear Information System (INIS)

Tian Xiaogeng; Woo Chungho

2004-01-01

Using Acland potential for tungsten, the movement of 1/2a screw dislocation under shear stress was investigated by molecular dynamics simulation. Equilibrated core structure was obtained by relaxation of screw dislocation with proper boundary conditions. We found that the equilibrium dislocation core has three-fold symmetry and spread out in three direction on {1 1 0} planes. The screw dislocation core could not keep the original shape when the shear stress applied. The dislocation could not move until the shear stress became large enough. The dislocation moved in zigzag when the shear stress neared the Peierls stress. When the shear stress became larger, the dislocation moved in zigzag at the beginning and than moved almost in straight line in [2-bar11] direction. The large shear stress applied, the long distance moved before the dislocation stilled in z-direction and the large velocity in y-direction

Screw Remaining Life Prediction Based on Quantum Genetic Algorithm and Support Vector Machine

Directory of Open Access Journals (Sweden)

Xiaochen Zhang

2017-01-01

Full Text Available To predict the remaining life of ball screw, a screw remaining life prediction method based on quantum genetic algorithm (QGA and support vector machine (SVM is proposed. A screw accelerated test bench is introduced. Accelerometers are installed to monitor the performance degradation of ball screw. Combined with wavelet packet decomposition and isometric mapping (Isomap, the sensitive feature vectors are obtained and stored in database. Meanwhile, the sensitive feature vectors are randomly chosen from the database and constitute training samples and testing samples. Then the optimal kernel function parameter and penalty factor of SVM are searched with the method of QGA. Finally, the training samples are used to train optimized SVM while testing samples are adopted to test the prediction accuracy of the trained SVM so the screw remaining life prediction model can be got. The experiment results show that the screw remaining life prediction model could effectively predict screw remaining life.

Ball Nut Preload Diagnosis of the Hollow Ball Screw through Support Vector Machine

Directory of Open Access Journals (Sweden)

Yi-Cheng Huang

2018-01-01

Full Text Available This paper studies the diagnostic results of hollow ball screws with different ball nut preload through the support vector machine (SVM process. The method is testified by considering the use of ball screw pretension and different ball nut preload. SVM was used to discriminate the hollow ball screw preload status through the vibration signals and servo motor current signals. Maximum dynamic preloads of 2%, 4%, and 6% ball screws were predesigned, manufactured, and conducted experimentally. Signal patterns with different preload features are separatedby SVM. The irregularity development of the ball screw driving motion current and rolling balls vibration of the ball screw can be discriminated via SVM based on complexity perception. The experimental results successfully show that the prognostic status of ball nut preload can be envisaged by the proposed methodology. The smart reasoning for the health of the ball screw is available based on classification of SVM. This diagnostic method satisfies the purposes of prognostic effectiveness on knowing the ball nut preload status

Locking screw-plate interface stability in carbon-fibre reinforced polyetheretherketone proximal humerus plates.

Science.gov (United States)

Hak, David J; Fader, Ryan; Baldini, Todd; Chadayammuri, Vivek B S

2017-09-01

Carbon-fibre reinforced polyetheretherketone (CFR-PEEK) plates have recently been introduced for proximal humerus fracture treatment. The purpose of this study was to compare the locking screw-plate interface stability in CFR-PEEK versus stainless steel (SS) proximal humerus plates. Locking screw mechanical stability was evaluated independently in proximal and shaft plate holes. Stiffness and load to failure were tested for three conditions: (1) on-axis locking screw insertion in CFR-PEEK versus SS plates, (2) on-axis locking screw insertion, removal, and reinsertion in CFR-PEEK plates, and (3) 10-degree off-axis locking screw insertion in CFR-PEEK plates. Cantilever bending at a rate of 1 mm/minute was produced by an Instron machine and load-displacement data recorded. Shaft locking screw load to failure was significantly greater in CFR-PEEK plates compared to SS plates (746.4 ± 89.7 N versus 596.5 ± 32.6 N, p PEEK plates (p PEEK plates. The mechanical stability of locking screws in CFR-PEEK plates is comparable or superior to locking screws in SS plates.

Kinematic analysis of parallel manipulators by algebraic screw theory

CERN Document Server

Gallardo-Alvarado, Jaime

2016-01-01

This book reviews the fundamentals of screw theory concerned with velocity analysis of rigid-bodies, confirmed with detailed and explicit proofs. The author additionally investigates acceleration, jerk, and hyper-jerk analyses of rigid-bodies following the trend of the velocity analysis. With the material provided in this book, readers can extend the theory of screws into the kinematics of optional order of rigid-bodies. Illustrative examples and exercises to reinforce learning are provided. Of particular note, the kinematics of emblematic parallel manipulators, such as the Delta robot as well as the original Gough and Stewart platforms are revisited applying, in addition to the theory of screws, new methods devoted to simplify the corresponding forward-displacement analysis, a challenging task for most parallel manipulators. Stands as the only book devoted to the acceleration, jerk and hyper-jerk (snap) analyses of rigid-body by means of screw theory; Provides new strategies to simplify the forward kinematic...

A rationale method for evaluating unscrewing torque values of prosthetic screws in dental implants

Directory of Open Access Journals (Sweden)

Felipe Miguel Saliba

2011-02-01

Full Text Available OBJECTIVES: Previous studies that evaluated the torque needed for removing dental implant screws have not considered the manner of transfer of the occlusal loads in clinical settings. Instead, the torque used for removal was applied directly to the screw, and most of them omitted the possibility that the hexagon could limit the action of the occlusal load in the loosening of the screws. The present study proposes a method for evaluating the screw removal torque in an anti-rotational device independent way, creating an unscrewing load transfer to the entire assembly, not only to the screw. MATERIAL AND METHODS: Twenty hexagonal abutments without the hexagon in their bases were fixed with a screw to 20 dental implants. They were divided into two groups: Group 1 used titanium screws and Group 2 used titanium screws covered with a solid lubricant. A torque of 32 Ncm was applied to the screw and then a custom-made wrench was used for rotating the abutment counterclockwise, to loosen the screw. A digital torque meter recorded the torque required to loosen the abutment. RESULTS: There was a significant difference between the means of Group 1 (38.62±6.43 Ncm and Group 2 (48.47±5.04 Ncm, with p=0.001. CONCLUSION: This methodology was effective in comparing unscrewing torque values of the implant-abutment junction even with a limited sample size. It confirmed a previously shown significant difference between two types of screws.

[Development of polyaxial locking plate screw system of sacroiliac joint].

Science.gov (United States)

Fan, Weijie; Xie, Xuesong; Zhou, Shuping; Zhang, Yonghu

2014-09-01

To develop an instrument for sacroiliac joint fixation with less injury and less complications. Firstly, 18 adult pelvic specimens (8 males and 10 females) were used to measure the anatomical data related to the locking plates and locking screws on the sacrum and ilium, and the polyaxial locking plate screw system of the sacroiliac joint was designed according to the anatomic data. This system was made of medical titanium alloy. Then 4 adult male plevic specimens were harvested and the experiment was divided into 3 groups: group A (normal pelvic), group B (the dislocated sacroiliac joint fixed with sacroiliac screws), and group C (the dislocated sacroiliac joint fixed with polyaxial locking plate screw system). The vertical displacement of sacroiliac joint under the condition of 0-700 N vertical load and the horizontal displacement on angle under the condition of 0-12 N·m torsional load were compared among the 3 groups by using the biological material test system. Finally, the simulated application test was performed on 1 adult male cadaveric specimen to observe soft tissue injury and the position of the locking plate and screw by X-ray films. According to the anatomic data of the sacrum and ilium, the polyaxial locking plate screw system of the sacroiliac joint was designed. The biomechanical results showed that the vertical displacement of the sacroiliac joint under the condition of 0-700 N vertical load in group A was significantly bigger than that in group B and group C (P 0.05). The horizontal displacement on angle under the condition of 0-12 N·m torsional load in group A was significantly less than that in group B and group C (P 0.05). The test of simulating application showed that the specimen suffered less soft tissue injury, and this instrument could be implanted precisely and safely. The polyaxial locking plate screw system of the sacroiliac joint has the advantages of smaller volume and less injury; polyaxial fixation enables flexible adjustment screw

Lag synchronization of hyperchaos with application to secure communications

International Nuclear Information System (INIS)

Li Chuandong; Liao Xiaofeng; Wong Kwokwo

2005-01-01

In this paper, hyperchaotic lag synchronization is restated as a nonlinear and lag-in-time observer design issue. This approach leads to a systematic tool, which guarantees the lag synchronization of a wide class of chaotic or hyperchaotic systems via a scalar signal. By exploiting this result, we propose a hyperchaos-based cryptosystem scheme that combines the conventional cryptographic methods and the lag synchronization of chaotic circuits. The computer simulation results show that the lag synchronization scheme and the cryptosystem proposed in this paper are both feasible

Lag profile inversion method for EISCAT data analysis

Directory of Open Access Journals (Sweden)

I. I. Virtanen

2008-03-01

Full Text Available The present standard EISCAT incoherent scatter experiments are based on alternating codes that are decoded in power domain by simple summation and subtraction operations. The signal is first digitised and then different lagged products are calculated and decoded in real time. Only the decoded lagged products are saved for further analysis so that both the original data samples and the undecoded lagged products are lost. A fit of plasma parameters can be later performed using the recorded lagged products. In this paper we describe a different analysis method, which makes use of statistical inversion in removing range ambiguities from the lag profiles. An analysis program carrying out both the lag profile inversion and the fit of the plasma parameters has been constructed. Because recording the received signal itself instead of the lagged products allows very flexible data analysis, the program is constructed to use raw data, i.e. IQ-sampled signal recorded from an IF stage of the radar. The program is now capable of analysing standard alternating-coded EISCAT experiments as well as experiments with any other kind of radar modulation if raw data is available. The program calculates the ambiguous lag profiles and is capable of inverting them as such but, for analysis in real time, time integration is needed before inversion. We demonstrate the method using alternating code experiments in the EISCAT UHF radar and specific hardware connected to the second IF stage of the receiver. This method produces a data stream of complex samples, which are stored for later processing. The raw data is analysed with lag profile inversion and the results are compared to those given by the standard method.

Outcomes of osteoporotic trochanteric fractures treated with cement-augmented dynamic hip screw

Science.gov (United States)

Gupta, Rakesh Kumar; Gupta, Vinay; Gupta, Navdeep

2012-01-01

Background: Dynamic hip screw (DHS) has been the standard treatment for stable trochanteric fracture patterns, but complications of lag screw cut out from a superior aspect, due to inadequate bone anchorage, occur frequently in elderly osteoporotic patients. Polymethylmethacrylate (PMMA) has been used as an augmentation tool to facilitate fixation stability in cadaveric femora for biomechanical studies and in pathological fractures. However, there are very few reports on the utilization of PMMA cement to prevent these complications in fresh intertrochanteric fractures. A prospective study was conducted to evaluate the outcome and efficacy of PMMA augmented DHS in elderly osteoporotic patients with intertrochanteric fractures. Materials and Methods: The study included 64 patients (AO type31-A2.1 in eight, A2.2 in 29, A2.3 in 17 patients, and 31-A3.1 in five, A3.2 in three, and A3.3 in two patients) with an average age of 72 years (60 – 94 years) of which 60 were available for final followup. PMMA augmentation of DHS was performed in all cases by injecting PMMA cement into the femoral head with a custommade gun designed by the authors. The clinical outcome was rated as per the Salvati and Wilson scoring system at the time of final followup of one year. Results were graded as excellent (score > 31), good (score 24 – 31), fair (score 16 – 23), and poor (score < 16). Results: Fracture united in all patients and the average time to union was 13.8 weeks (range 12 – 16 weeks). At an average followup of 18 months (range 12 – 24 months), no incidence of varus collapse or superior screw cut out was observed in any of the patients in spite of weightbearing ambulation from the early postoperative period. There was no incidence of avascular necrosis (AVN) or cement penetration into the joint in our series. Most of the patients were able to regain their prefracture mobility status with a mean hip pain score of 8.6. Conclusion: Cement augmentation of DHS appears to be an

Outcomes of osteoporotic trochanteric fractures treated with cement-augmented dynamic hip screw

Directory of Open Access Journals (Sweden)

Rakesh Kumar Gupta

2012-01-01

Full Text Available Background: Dynamic hip screw (DHS has been the standard treatment for stable trochanteric fracture patterns, but complications of lag screw cut out from a superior aspect, due to inadequate bone anchorage, occur frequently in elderly osteoporotic patients. Polymethylmethacrylate (PMMA has been used as an augmentation tool to facilitate fixation stability in cadaveric femora for biomechanical studies and in pathological fractures. However, there are very few reports on the utilization of PMMA cement to prevent these complications in fresh intertrochanteric fractures. A prospective study was conducted to evaluate the outcome and efficacy of PMMA augmented DHS in elderly osteoporotic patients with intertrochanteric fractures. Materials and Methods: The study included 64 patients (AO type31-A2.1 in eight, A2.2 in 29, A2.3 in 17 patients, and 31-A3.1 in five, A3.2 in three, and A3.3 in two patients with an average age of 72 years (60 − 94 years of which 60 were available for final followup. PMMA augmentation of DHS was performed in all cases by injecting PMMA cement into the femoral head with a custommade gun designed by the authors. The clinical outcome was rated as per the Salvati and Wilson scoring system at the time of final followup of one year. Results were graded as excellent (score > 31, good (score 24 − 31, fair (score 16 − 23, and poor (score < 16. Results: Fracture united in all patients and the average time to union was 13.8 weeks (range 12 − 16 weeks. At an average followup of 18 months (range 12 − 24 months, no incidence of varus collapse or superior screw cut out was observed in any of the patients in spite of weightbearing ambulation from the early postoperative period. There was no incidence of avascular necrosis (AVN or cement penetration into the joint in our series. Most of the patients were able to regain their prefracture mobility status with a mean hip pain score of 8.6. Conclusion: Cement augmentation of DHS appears

Current trends in pedicle screw stimulation techniques: lumbosacral, thoracic, and cervical levels.

Science.gov (United States)

Isley, Michael R; Zhang, Xiao-Feng; Balzer, Jeffrey R; Leppanen, Ronald E

2012-06-01

Unequivocally, pedicle screw instrumentation has evolved as a primary construct for the treatment of both common and complex spinal disorders. However an inevitable and potentially major complication associated with this type of surgery is misplacement of a pedicle screw(s) which may result in neural and vascular complications, as well as impair the biomechanical stability of the spinal instrumentation resulting in loss of fixation. In light of these potential surgical complications, critical reviews of outcome data for treatment of chronic, low-back pain using pedicle screw instrumentation concluded that "pedicle screw fixation improves radiographically demonstrated fusion rates;" however the expense and complication rates for such constructs are considerable in light of the clinical benefit (Resnick et al. 2005a). Currently, neuromonitoring using free-run and evoked (triggered) electromyography (EMG) is widely used and advocated for safer and more accurate placement of pedicle screws during open instrumentation procedures, and more recently, guiding percutaneous placement (minimally invasive) where the pedicle cannot be easily inspected visually. The latter technique, evoked or triggered EMG when applied to pedicle screw instrumentation surgeries, has been referred to as the pedicle screw stimulation technique. As concluded in the Position Statement by the American Society of Neurophysiological Monitoring (ASNM), multimodality neuromonitoring using free-run EMG and the pedicle screw stimulation technique was considered a practice option and not yet a standard of care (Leppanen 2005). Subsequently, the American Association of Neurological Surgeons/Congress of Neurological Surgeons (AANS/CNS) Joint Section on Disorders of the Spine and Peripheral Nerves published their "Guidelines for the Performance of Fusion Procedures for Degenerative Disease of the Lumbar Spine" (Heary 2005, Resnick et al. 2005a, Resnick et al. 2005b). It was concluded that the "primary

Comparing lagged linear correlation, lagged regression, Granger causality, and vector autoregression for uncovering associations in EHR data.

Science.gov (United States)

Levine, Matthew E; Albers, David J; Hripcsak, George

2016-01-01

Time series analysis methods have been shown to reveal clinical and biological associations in data collected in the electronic health record. We wish to develop reliable high-throughput methods for identifying adverse drug effects that are easy to implement and produce readily interpretable results. To move toward this goal, we used univariate and multivariate lagged regression models to investigate associations between twenty pairs of drug orders and laboratory measurements. Multivariate lagged regression models exhibited higher sensitivity and specificity than univariate lagged regression in the 20 examples, and incorporating autoregressive terms for labs and drugs produced more robust signals in cases of known associations among the 20 example pairings. Moreover, including inpatient admission terms in the model attenuated the signals for some cases of unlikely associations, demonstrating how multivariate lagged regression models' explicit handling of context-based variables can provide a simple way to probe for health-care processes that confound analyses of EHR data.

In vivo Study of the Accuracy of Dual-arch Impressions.

Science.gov (United States)

de Lima, Luciana Martinelli Santayana; Borges, Gilberto Antonio; Junior, Luiz Henrique Burnett; Spohr, Ana Maria

2014-06-01

This study evaluated in vivo the accuracy of metal (Smart®) and plastic (Triple Tray®) dual-arch trays used with vinyl polysiloxane (Flexitime®), in the putty/wash viscosity, as well as polyether (Impregum Soft®) in the regular viscosity. In one patient, an implant-level transfer was screwed on an implant in the mandibular right first molar, serving as a pattern. Ten impressions were made with each tray and impression material. The impressions were poured with Type IV gypsum. The width and height of the pattern and casts were measured in a profile projector (Nikon). The results were submitted to Student's t-test for one sample (α = 0.05). For the width distance, the plastic dual-arch trays with vinyl polysiloxane (4.513 mm) and with polyether (4.531 mm) were statistically wider than the pattern (4.489 mm). The metal dual-arch tray with vinyl polysiloxane (4.504 mm) and with polyether (4.500 mm) did not differ statistically from the pattern. For the height distance, only the metal dual-arch tray with polyether (2.253 mm) differed statistically from the pattern (2.310 mm). The metal dual-arch tray with vinyl polysiloxane, in the putty/wash viscosities, reproduced casts with less distortion in comparison with the same technique with the plastic dual-arch tray. The plastic or metal dual-arch trays with polyether reproduced cast with greater distortion. How to cite the article: Santayana de Lima LM, Borges GA, Burnett LH Jr, Spohr AM. In vivo study of the accuracy of dual-arch impressions. J Int Oral Health 2014;6(3):50-5.

Comparative effect of implant-abutment connections, abutment angulations, and screw lengths on preloaded abutment screw using three-dimensional finite element analysis: An in vitro study

Directory of Open Access Journals (Sweden)

Krishna Chaitanya Kanneganti

2018-01-01

Conclusions: The present study suggests selecting appropriate implant-abutment connection based on the abutment angulation, as well as preferring long screws with more number of threads for effective preload retention by the screws.

Statistical time lags in ac discharges

International Nuclear Information System (INIS)

Sobota, A; Kanters, J H M; Van Veldhuizen, E M; Haverlag, M; Manders, F

2011-01-01

The paper presents statistical time lags measured for breakdown events in near-atmospheric pressure argon and xenon. Ac voltage at 100, 400 and 800 kHz was used to drive the breakdown processes, and the voltage amplitude slope was varied between 10 and 1280 V ms -1 . The values obtained for the statistical time lags are roughly between 1 and 150 ms. It is shown that the statistical time lags in ac-driven discharges follow the same general trends as the discharges driven by voltage of monotonic slope. In addition, the validity of the Cobine-Easton expression is tested at an alternating voltage form.

Statistical time lags in ac discharges

Energy Technology Data Exchange (ETDEWEB)

Sobota, A; Kanters, J H M; Van Veldhuizen, E M; Haverlag, M [Eindhoven University of Technology, Department of Applied Physics, Postbus 513, 5600MB Eindhoven (Netherlands); Manders, F, E-mail: a.sobota@tue.nl [Philips Lighting, LightLabs, Mathildelaan 1, 5600JM Eindhoven (Netherlands)

2011-04-06

The paper presents statistical time lags measured for breakdown events in near-atmospheric pressure argon and xenon. Ac voltage at 100, 400 and 800 kHz was used to drive the breakdown processes, and the voltage amplitude slope was varied between 10 and 1280 V ms{sup -1}. The values obtained for the statistical time lags are roughly between 1 and 150 ms. It is shown that the statistical time lags in ac-driven discharges follow the same general trends as the discharges driven by voltage of monotonic slope. In addition, the validity of the Cobine-Easton expression is tested at an alternating voltage form.

Accelerated Tooth Movement with Orthodontic Mini-Screws

Directory of Open Access Journals (Sweden)

S. Aksakalli

2017-01-01

Full Text Available This case report outlines the possibility of accelerated tooth movement with the combination of microosteoperforation and mini-screws. A 14-year-old male patient presented Class II malocclusion with maxillary incisor protrusion. Upper first premolars were extracted, and after leveling, accelerated canine distalization started. For pre- and postdistalization times, amount of distalization, periodontal health, and root resorption were assessed. Within the limitations of this case report, micro-osteoperforations with mini-screw have a potential for shortening the treatment time.

Experimental study of the density distribution of the particles of the material in screw installation

Directory of Open Access Journals (Sweden)

Demidov S. F.

2017-02-01

Full Text Available the experimental studies of density distribution of the particles of a mixture of wheat, oats, rye to feed pigs by infrared heating at the time of stay and temperature at the exit of the installation. The purpose of the work is to study the quality of treatment of the product with the settings with the screw and the screw with installed round jumper on the pen of the screw. Screw installations with infrared emitters of selected wavelength give the opportunity for intense and continuous heat treatment process. The authors used the optimal parameters of the process with the screw and the screw with installed round jumper on the pen of the screw. The parameters of screw installation during the study were the following: the number of revolutions of the screw was 10 rpm, density of heat flux was 12 kW/m2, output capacity – 250 kg/h.

Oral mucosa tissue response to titanium cover screws.

Science.gov (United States)

Olmedo, Daniel G; Paparella, María L; Spielberg, Martín; Brandizzi, Daniel; Guglielmotti, María B; Cabrini, Rómulo L

2012-08-01

Titanium is the most widely used metal in dental implantology. The release of particles from metal structures into the biologic milieu may be the result of electrochemical processes (corrosion) and/or mechanical disruption during insertion, abutment connection, or removal of failing implants. The aim of the present study is to evaluate tissue response of human oral mucosa adjacent to titanium cover screws. One hundred fifty-three biopsies of the supra-implant oral mucosa adjacent to the cover screw of submerged dental implants were analyzed. Histologic studies were performed to analyze epithelial and connective tissue as well as the presence of metal particles, which were identified using microchemical analysis. Langerhans cells, macrophages, and T lymphocytes were studied using immunohistochemical techniques. The surface of the cover screws was evaluated by scanning electron microscopy (SEM). Forty-one percent of mucosa biopsies exhibited metal particles in different layers of the section thickness. Particle number and size varied greatly among specimens. Immunohistochemical study confirmed the presence of macrophages and T lymphocytes associated with the metal particles. Microchemical analysis revealed the presence of titanium in the particles. On SEM analysis, the surface of the screws exhibited depressions and irregularities. The biologic effects seen in the mucosa in contact with the cover screws might be associated with the presence of titanium or other elements, such as aluminum or vanadium. The potential long-term biologic effects of particles on soft tissues adjacent to metallic devices should be further investigated because these effects might affect the clinical outcome of the implant.

Effectiveness of screw surface coating on the stability of zirconia abutments after cyclic loading.

Science.gov (United States)

Basílio, Mariana de Almeida; Butignon, Luis Eduardo; Arioli Filho, João Neudenir

2012-01-01

Different surface treatments have been developed in attempts to prevent the loosening of abutment screws. The aim of the current study was to compare the effectiveness of titanium alloy screws with tungsten-doped diamond-like carbon (W-DLC) coating and uncoated screws in providing stability to zirconia (ZrO2) ceramic abutments after cyclic loading. Twenty prefabricated ZrO2 ceramic abutments on their respective external-hex implants were divided into two groups of equal size according to the type of screw used: uncoated titanium alloy screw (Ti) or titanium alloy screw with W-DLC coating (W-DLC/Ti). The removal torque value (preload) of the abutment screw was measured before and after loading. Cyclic loading between 11 and 211 N was applied at an angle of 30 degrees to the long axis of the implants at a frequency of 15 Hz. A target of 0.5 X 106 cycles was defined. Group means were calculated and compared using analysis of variance and the F test (α = .05). Before cyclic loading, the preload for Ti screws was significantly higher than that for W-DLC/Ti screws (P = .021). After cyclic loading, there was no significant difference between them (P = .499). Under the studied conditions, it can be concluded that, after cyclic loading, both abutment screws presented a significant reduction in the mean retained preload and similar effectiveness in maintaining preload.

Mechanical comparison between lengthened and short sacroiliac screws in sacral fracture fixation: a finite element analysis.

Science.gov (United States)

Zhao, Y; Zhang, S; Sun, T; Wang, D; Lian, W; Tan, J; Zou, D; Zhao, Y

2013-09-01

To compare the stability of lengthened sacroiliac screw and standard sacroiliac screw for the treatment of unilateral vertical sacral fractures; to provide reference for clinical applications. A finite element model of Tile type C pelvic ring injury (unilateral Denis type II fracture of the sacrum) was produced. The unilateral sacral fractures were fixed with lengthened sacroiliac screw and sacroiliac screw in six different types of models respectively. The translation and angle displacement of the superior surface of the sacrum (in standing position on both feet) were measured and compared. The stability of one lengthened sacroiliac screw fixation in S1 or S2 segment is superior to that of one sacroiliac screw fixation in the same sacral segment. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one sacroiliac screw fixation in S1 and S2 segments respectively. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one lengthened sacroiliac screw fixation in S1 or S2 segment. The stability of one sacroiliac screw fixation in S1 and S2 segments respectively is markedly superior to that of one sacroiliac screw fixation in S1 or S2 segment. The vertical and rotational stability of lengthened sacroiliac screw fixation and sacroiliac screw fixation in S2 is superior to that of S1. In a finite element model of type C pelvic ring disruption, S1 and S2 lengthened sacroiliac screws should be utilized for the fixation as regularly as possible and the most stable fixation is the combination of the lengthened sacroiliac screws of S1 and S2 segments. Even if lengthened sacroiliac screws cannot be systematically used due to specific conditions, one sacroiliac screw fixation in S1 and S2 segments respectively is recommended. No matter which kind of sacroiliac screw is used, if only one screw can be implanted, the fixation in S2 segment is more recommended

Correlation between classification and secondary screw penetration in proximal humeral fractures.

Directory of Open Access Journals (Sweden)

Qiuke Wang

Full Text Available In this study, we investigated the correlation between fracture classification and secondary screw penetration.We retrospectively identified 189 patients with displaced proximal humeral fractures treated by ORIF at our hospital between June 2006 and June 2013. All fractures were classified radiographically before surgery and follow-up for least 2 years after surgery was recommended. At each follow-up, radiographs were taken in three orthogonal views to evaluate secondary screw penetration.The study population consisted of 189 patients. Of these, 70 were male and 119 female, with a mean age of 59.1 years; the mean follow-up time was 28.5 months. Secondary screw penetration occurred in 26 patients. The risk of developing secondary screw penetration was 11.3-fold higher in four-part fractures than two-part fractures (P 0.05.Patients with four-part fractures, type C fractures and medial hinges disruption are vulnerable to secondary screw penetration. This allows additional precautions to be instituted and measures to be taken as needed.

Percutaneous Iliac Screws for Minimally Invasive Spinal Deformity Surgery

Directory of Open Access Journals (Sweden)

Michael Y. Wang

2012-01-01

Full Text Available Introduction. Adult spinal deformity (ASD surgeries carry significant morbidity, and this has led many surgeons to apply minimally invasive surgery (MIS techniques to reduce the blood loss, infections, and other peri-operative complications. A spectrum of techniques for MIS correction of ASD has thus evolved, most recently the application of percutaneous iliac screws. Methods. Over an 18 months 10 patients with thoracolumbar scoliosis underwent MIS surgery. The mean age was 73 years (70% females. Patients were treated with multi-level facet osteotomies and interbody fusion using expandable cages followed by percutaneous screw fixation. Percutaneous iliac screws were placed bilaterally using the obturator outlet view to target the ischial body. Results. All patients were successfully instrumented without conversion to an open technique. Mean operative time was 302 minutes and the mean blood loss was 480 cc, with no intraoperative complications. A total of 20 screws were placed successfully as judged by CT scanning to confirm no bony violations. Complications included: two asymptomatic medial breaches at T10 and L5, and one patient requiring delayed epidural hematoma evacuation. Conclusions. Percutaneous iliac screws can be placed safely in patients with ASD. This MIS technique allows for successful caudal anchoring to stress-shield the sacrum and L5-S1 fusion site in long-segment constructs.

Theoretical investigation of flash vaporisation in a screw expander

Science.gov (United States)

Vasuthevan, Hanushan; Brümmer, Andreas

2017-08-01

In the present study flash vaporisation of liquid injection in a twin screw expander for a Trilateral Flash Cycle (TFC) is examined theoretically. The TFC process comprises a pressure increase in the working fluid, followed by heating the liquid close to boiling point. The hot liquid is injected into the working chamber of a screw expander. During this process the pressure of the liquid drops below the saturation pressure, while the temperature of the liquid remains virtually constant. Hence the liquid is superheated and in a metastable state. The liquid jet seeks to achieve a stable state in thermodynamic equilibrium and is therefore partially vaporised. This effect is referred to as flash vaporisation. Accordingly, a two-phase mixture, consisting of vapour and liquid, exists in the working chamber. Thermodynamic simulations were carried out using water as the working fluid for representative screw expander geometry. The simulations presented are performed from two different aspects during the filling process of a screw expander. The first case is the vaporisation of the injected liquid in a state of thermodynamic equilibrium, whereby the two-phase mixture is treated entirely as a compressible and homogeneous gas. The second case considers flashing efficiency. It describes the quantity of flashed vapour and consists of a liquid and vapour domain. Both models are compared and analysed with respect to the operational behaviour of a screw expander.

Sacroiliac secure corridor: analysis for safe insertion of iliosacral screws

Directory of Open Access Journals (Sweden)

Henrique Alves Cruz

2013-08-01

Full Text Available OBJECTIVE: Posterior pelvic lesions, especially of the sacral-iliac joint, have high mortality and morbidity risks. Definitive fixation is necessary for the joint stabilization, and one option is the sacral percutaneous pinning with screws. Proximity to important structures to this region brings risks to the fixation procedure; therefore, it is important to know the tridimensional anatomy of the pelvis posterior region. Deviations of the surgeon's hand of four degrees may target the screws to those structures; dimorphisms of the upper sacrum and a poor lesion reduction may redound in a screw malpositioning. This study is aimed to evaluate the dimensions of a safe surgical corridor for safe sacroiliac screw insertion and relations with age and sex of the patients. METHOD: One hundred randomly selected pelvis CTs of patients with no pelvic diseases, seen at a tertiary care teaching Hospital. Measurements were made by computer and the safest area for screw insertion was calculated by two methods. The results were expressed in mm (not in degrees, in order to be a further surgical reference. RESULTS: There was a significant size difference in the analyzed sacral vertebra, differing on a wider size in men than in women. There was no significant statistical difference between vertebral size and age. By both methods, a safe area for screw insertion could be defined. CONCLUSION: Age does not influence the width of the surgical corridor. The surgeon has a safe corridor considered narrower when inserting screws in a female pelvis than when in a male one. However, as the smallest vertebra found (feminine was considered for statics, it was concluded that this corridor is 20 mm wide in any direction, taking as a reference the centrum of the vertebra.

Dorsal bridge plating or transarticular screws for Lisfranc fracture dislocations.

Science.gov (United States)

Kirzner, N; Zotov, P; Goldbloom, D; Curry, H; Bedi, H

2018-04-01

Aims The aim of this retrospective study was to compare the functional and radiological outcomes of bridge plating, screw fixation, and a combination of both methods for the treatment of Lisfranc fracture dislocations. Patients and Methods A total of 108 patients were treated for a Lisfranc fracture dislocation over a period of nine years. Of these, 38 underwent transarticular screw fixation, 45 dorsal bridge plating, and 25 a combination technique. Injuries were assessed preoperatively according to the Myerson classification system. The outcome measures included the American Orthopaedic Foot and Ankle Society (AOFAS) score, the validated Manchester Oxford Foot Questionnaire (MOXFQ) functional tool, and the radiological Wilppula classification of anatomical reduction. Results Significantly better functional outcomes were seen in the bridge plate group. These patients had a mean AOFAS score of 82.5 points, compared with 71.0 for the screw group and 63.3 for the combination group (p bridge plate group, 38.1 in the screw group, and 45.5 in the combination group (p bridge plating have better functional and radiological outcomes than those treated with transarticular screws or a combination technique. Cite this article: Bone Joint J 2018;100-B:468-74.

Studies on positive conveying in helically channeled single screw extruders

Directory of Open Access Journals (Sweden)

L. Pan

2012-07-01

Full Text Available A solids conveying theory called double-flight driving theory was proposed for helically channeled single screw extruders. In the extruder, screw channel rotates against static barrel channel, which behaves as cooperative embedded twin-screws for the positive conveying. They turn as two parallel arc plates, between which an arc-plate solid-plug was assumed. By analyzing the forces on the solid-plug in the barrel channel and screw channel, the boundary conditions when the solid-plug is waived of being cut off on barrel wall, were found to have the capacity of the positive conveying. Experimental data were obtained using a specially designed extruder with a helically channeled barrel in the feeding zone and a pressure-adjustable die. The effects of the barrel channel geometry and friction coefficients on the conveying mechanism were presented and compared with the experimental results. The simulations showed that the positive conveying could be achieved after optimizing extruder designs. Compared with the traditional design with the friction-drag conveying, the throughput is higher while screw torque and energy consumption are decreased. Besides, the design criteria of the barrel channel were also discussed.

Individualized 3D printing navigation template for pedicle screw fixation in upper cervical spine.

Directory of Open Access Journals (Sweden)

Fei Guo

Full Text Available Pedicle screw fixation in the upper cervical spine is a difficult and high-risk procedure. The screw is difficult to place rapidly and accurately, and can lead to serious injury of spinal cord or vertebral artery. The aim of this study was to design an individualized 3D printing navigation template for pedicle screw fixation in the upper cervical spine.Using CT thin slices data, we employed computer software to design the navigation template for pedicle screw fixation in the upper cervical spine (atlas and axis. The upper cervical spine models and navigation templates were produced by 3D printer with equal proportion, two sets for each case. In one set (Test group, pedicle screws fixation were guided by the navigation template; in the second set (Control group, the screws were fixed under fluoroscopy. According to the degree of pedicle cortex perforation and whether the screw needed to be refitted, the fixation effects were divided into 3 types: Type I, screw is fully located within the vertebral pedicle; Type II, degree of pedicle cortex perforation is 1 mm or with the poor internal fixation stability and in need of renovation. Type I and Type II were acceptable placements; Type III placements were unacceptable.A total of 19 upper cervical spine and 19 navigation templates were printed, and 37 pedicle screws were fixed in each group. Type I screw-placements in the test group totaled 32; Type II totaled 3; and Type III totaled 2; with an acceptable rate of 94.60%. Type I screw placements in the control group totaled 23; Type II totaled 3; and Type III totaled 11, with an acceptable rate of 70.27%. The acceptability rate in test group was higher than the rate in control group. The operation time and fluoroscopic frequency for each screw were decreased, compared with control group.The individualized 3D printing navigation template for pedicle screw fixation is easy and safe, with a high success rate in the upper cervical spine surgery.

Noninvasive method for retrieval of broken dental implant abutment screw

Directory of Open Access Journals (Sweden)

Jagadish Reddy Gooty

2014-01-01

Full Text Available Dental implants made of titanium for replacement of missing teeth are widely used because of ease of technical procedure and high success rate, but are not free of complications and may fail. Fracturing of the prosthetic screw continues to be a problem in restorative practice and great challenge to remove the fractured screw conservatively. This case report describes and demonstrates the technique of using an ultrasonic scaler in the removal of the fracture screw fragment as a noninvasive method without damaging the hex of implants.

Design of platform for removing screws from LCD display shields

Science.gov (United States)

Tu, Zimei; Qin, Qin; Dou, Jianfang; Zhu, Dongdong

2017-11-01

Removing the screws on the sides of a shield is a necessary process in disassembling a computer LCD display. To solve this issue, a platform has been designed for removing the screws on display shields. This platform uses virtual instrument technology with LabVIEW as the development environment to design the mechanical structure with the technologies of motion control, human-computer interaction and target recognition. This platform removes the screws from the sides of the shield of an LCD display mechanically thus to guarantee follow-up separation and recycle.

[Three-dimensional computed tomography analysis and clinical application of sacroiliac screw placement].

Science.gov (United States)

Yin, Y C; Zhang, R P; Li, S L; Hou, Z Y; Chen, W; Zhang, Y Z

2018-03-01

Objective: To evaluate the possibility of transverse sacroiliac screw placement in different segments of the sacrum. Methods: Data of 80 pelvic CT scans (slice thickness ≤1.0 mm) archived in CT department of the Third Hospital of Hebei Medical University from September 2016 to October 2017 were retrospectively collected. Mimics software was used to rebuild the pelvis three-dimensional model. According to whether the sacral 1(S(1)) segment could place the transverse sacroiliac screws or not, all the sacrums were divided into normal group ( n =55) and dysmorphic group ( n =25). Simulation the S(1), sacral 2(S(2)) transverse sacroiliac screw placement in 3-Matic software. Analysis whether there was any difference in maximum diameter and length of S(2) transverse sacroiliac screw between the normal group and the dysmorphic group. The pelvic CT data of the dysmorphic group were measured, and the optimal tilt angle and length of the oblique S(1) screw were obtained. The feasibility of transverse sacroiliac screw insertion in sacral 3(S(3)) segment was evaluated. t -test, rank sum test, and χ(2) test was used to analyze data, respectively. Results: In the dysmorphic group, the largest diameter of the S(1) transverse screw was (4.9±1.6)mm, and the normal group was (13.6±3.6)mm ( t =-15.07, P =0.00). In the dysmorphic group, the largest diameter of S(2) transverse screw was (13.8±3.0)mm, and was (12.4±2.2)mm in the normal group( t =2.11, P =0.04). There was no significant difference in the length of S(2) transverse sacroiliac screw between the two groups ( t =0.47, P =0.64). In the dysmorphic group, the anterior vertebral height of S(1) was (23.1±4.0)mm, which was significantly higher than that of the normal group ((14.1±4.2)mm)( t =9.01, P =0.00). The angle of S(1)S(2) in the dysmorphic group was 10.9°(3.8°, 17.6°), which was significantly larger than that of the normal group (2.0°(1.0°, 2.0°) ( Z =-4.03, P =0.00). In the dysmorphic group, the incline angle

Micro-CT evaluation and histological analysis of screw-bone interface of expansive pedicle screw in osteoporotic sheep.

Science.gov (United States)

Wan, Shi-yong; Lei, Wei; Wu, Zi-xiang; Lv, Rong; Wang, Jun; Fu, Suo-chao; Li, Bo; Zhan, Ce

2008-04-01

To investigate the properties of screw-bone interface of expansive pedicle screw (EPS) in osteoporotic sheep by micro-CT and histological observation. Six female sheep with bilateral ovariectomy-induced osteoporosis were employed in this experiment. After EPS insertion in each femoral condyle, the sheep were randomly divided into two groups: 3 sheep were bred for 3 months (Group A), while the other 3 were bred for 6 months (Group B). After the animals being killed, the femoral condyles with EPS were obtained, which were three-dimensionally-imaged and reconstructed by micro-CT. Histological evaluation was made thereafter. The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within the spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT with the same thresholds. The three-dimensional (3-D) parameters, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), were significantly better in expansive sections than non-expansive sections (P less than 0.05). Histologically, newly-formed bony trabeculae crawled along the expansive fissures and into the center of EPS. The newly-formed bones, as well as the bones at the bone-screw interface, closely contacted with the EPS and constructed four compartments. The findings of the current study, based on micro-CT and histological evaluation, suggest that EPS can significantly provide stabilization in osteoporotic cancellous bones.

Stress corrosion cracking life estimation of hold-down spring screw for nuclear fuel assembly

International Nuclear Information System (INIS)

Koh, S.K.

2005-01-01

Hold-down spring screw fractures due to primary water stress corrosion cracking were observed in nuclear fuel assemblies. The screw fastens hold-down springs that are required to maintain the nuclear fuel assembly in contact with upper core plate and permit thermal and irradiation-induced length changes. In order to investigate the primary causes of the screw fractures, the finite element stress analysis and fracture mechanics analysis were performed on the hold-down spring assembly. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded the yield strength of the screw material, resulting in local plastic deformation. Preloading on the screw applied for tightening had beneficial effects on the screw strength by reducing the stress level at the critical regions, compared to the screw without preload. Calculated deflections and strains at the hold-down springs using the finite element analysis were in very close agreements with the experimentally measured deflections and strains. Primary water stress corrosion cracking (PWSCC) life of the Inconel 600 screw was predicted by integrating the Scott's model and resulted in a life of 1.42 years, which was fairly close to the field experience. Cracks were expected to originate at the threaded region of the screw and propagated to the opposite side of the spring, which was confirmed by the fractographic analysis of the fractured screws. (orig.)

Biomechanical Comparison of External Fixation and Compression Screws for Transverse Tarsal Joint Arthrodesis.

Science.gov (United States)

Latt, L Daniel; Glisson, Richard R; Adams, Samuel B; Schuh, Reinhard; Narron, John A; Easley, Mark E

2015-10-01

Transverse tarsal joint arthrodesis is commonly performed in the operative treatment of hindfoot arthritis and acquired flatfoot deformity. While fixation is typically achieved using screws, failure to obtain and maintain joint compression sometimes occurs, potentially leading to nonunion. External fixation is an alternate method of achieving arthrodesis site compression and has the advantage of allowing postoperative compression adjustment when necessary. However, its performance relative to standard screw fixation has not been quantified in this application. We hypothesized that external fixation could provide transverse tarsal joint compression exceeding that possible with screw fixation. Transverse tarsal joint fixation was performed sequentially, first with a circular external fixator and then with compression screws, on 9 fresh-frozen cadaveric legs. The external fixator was attached in abutting rings fixed to the tibia and the hindfoot and a third anterior ring parallel to the hindfoot ring using transverse wires and half-pins in the tibial diaphysis, calcaneus, and metatarsals. Screw fixation comprised two 4.3 mm headless compression screws traversing the talonavicular joint and 1 across the calcaneocuboid joint. Compressive forces generated during incremental fixator foot ring displacement to 20 mm and incremental screw tightening were measured using a custom-fabricated instrumented miniature external fixator spanning the transverse tarsal joint. The maximum compressive force generated by the external fixator averaged 186% of that produced by the screws (range, 104%-391%). Fixator compression surpassed that obtainable with screws at 12 mm of ring displacement and decreased when the tibial ring was detached. No correlation was found between bone density and the compressive force achievable by either fusion method. The compression across the transverse tarsal joint that can be obtained with a circular external fixator including a tibial ring exceeds that

Mini-Fragment Fixation Is Equivalent to Bicortical Screw Fixation for Horizontal Medial Malleolus Fractures.

Science.gov (United States)

Wegner, Adam M; Wolinsky, Philip R; Robbins, Michael A; Garcia, Tanya C; Amanatullah, Derek F

2018-05-01

Horizontal fractures of the medial malleolus occur through application of valgus or abduction force through the ankle that creates a tension failure of the medial malleolus. The authors hypothesize that mini-fragment T-plates may offer improved fixation, but the optimal fixation construct for these fractures remains unclear. Forty synthetic distal tibiae with identical osteotomies were randomized into 4 fixation constructs: (1) two parallel unicortical cancellous screws; (2) two parallel bicortical cortical screws; (3) a contoured mini-fragment T-plate with 2 unicortical screws in the fragment and 2 bicortical screws in the shaft; and (4) a contoured mini-fragment T-plate with 2 bicortical screws in the fragment and 2 unicortical screws in the shaft. Specimens were subjected to offset axial tension loading on a servohydraulic testing system and tracked using high-resolution video. Failure was defined as 2 mm of articular displacement. Analysis of variance followed by a Tukey-Kramer post hoc test was used to assess for differences between groups, with significance defined as Pfragment T-plate constructs (239±83 N/mm and 190±37 N/mm) and the bicortical screw construct (240±17 N/mm) were not statistically different. The mean stiffness values of both mini-fragment T-plate constructs and the bicortical screw construct were higher than that of a parallel unicortical screw construct (102±20 N/mm). Contoured T-plate constructs provide stiffer initial fixation than a unicortical cancellous screw construct. The T-plate is biomechanically equivalent to a bicortical screw construct, but may be superior in capturing small fragments of bone. [Orthopedics. 2018; 41(3):e395-e399.]. Copyright 2018, SLACK Incorporated.

Repair of microdamage in osteonal cortical bone adjacent to bone screw.

Directory of Open Access Journals (Sweden)

Lei Wang

Full Text Available Up to date, little is known about the repair mode of microdamage in osteonal cortical bone resulting from bone screw implantation. In this study, self-tapping titanium cortical bone screws were inserted into the tibial diaphyses of 24 adult male rabbits. The animals were sacrificed at 1 day, 2 weeks, 1 month and 2 months after surgery. Histomorphometric measurement and confocal microscopy were performed on basic fuchsin stained bone sections to examine the morphological characteristics of microdamage, bone resorption activity and spatial relationship between microdamage and bone resorption. Diffuse and linear cracks were coexisted in peri-screw bone. Intracortical bone resorption was significantly increased 2 weeks after screw installation and reach to the maximum at 1 month. There was no significant difference in bone resorption between 1-month and 2-months groups. Microdamage was significantly decreased within 1 month after surgery. Bone resorption was predisposed to occur in the region of <100 µm from the bone-screw interface, where had extensive diffuse damage mixed with linear cracks. Different patterns of resorption cavities appeared in peri-screw bone. These data suggest that 1 the complex microdamage composed of diffuse damage and linear cracks is a strong stimulator for initiating targeted bone remodeling; 2 bone resorption activities taking place on the surfaces of differently oriented Haversian and Volkmann canals work in a team for the repair of extensive microdamage; 3 targeted bone remodeling is a short-term reaction to microdamage and thereby it may not be able to remove all microdamage resulting from bone screw insertion.

TIP APEX DISTANCE OF INTRAMEDULLARY DEVICES AS A PREDICTOR OF CUT-OUT FAILURE IN TREATMENT OF PERITROCHANTERIC ELDERLY HIP FRACTURES

Directory of Open Access Journals (Sweden)

Purushotham K

2017-02-01

Full Text Available BACKGROUND A Tip-Apex Distance (TAD of greater than 25 mm has been shown to be an accurate predictor of lag screw cut-out when Sliding Hip Screws (SHS are used to treat Peritrochanteric (PT fractures. The purpose of this study was to determine, which factors, including TAD correlated with successful clinical outcomes of PT hip fractures surgically treated with intramedullary devices. MATERIALS AND METHODS A total of 72 patients were included in this retrospective study. TAD values were radiographically analysed at a mean follow up of 13 months. This was correlated with limited functional status and rate of revision for implant failure or inability to achieve fracture union. Only 62 patients had adequate follow up to fracture union or definitive failure. RESULTS There were 36 intertrochanteric fractures and 26 subtrochanteric fractures. Overall, 5 patients (9.8% went on to experience lag screw cut out. The average TAD of patients who did not cut-out was 18 mm compared to 38 mm for those who did (p=0.012. All patients who cut-out had IT fractures. CONCLUSION The percentage of cut-outs correlated clinically to both the severity of IT fractures and the TAD. Using a cut-off of 25 mm, there was a statistically significant difference in the incidence of lag screw cut-out (p<0.001. As in sliding hip screw, surgeons should strive for a TAD less than 25 mm when using IM devices in the treatment of PT hip fractures to help avoid lag screw cut-out.

Surgical repair of mid-body proximal sesamoid bone fractures in 25 horses.

Science.gov (United States)

Busschers, Evita; Richardson, Dean W; Hogan, Patricia M; Leitch, Midge

2008-12-01

To describe the characteristics of unilateral mid-body proximal sesamoid bone (PSB) fractures, to determine factors associated with the outcome of horses after surgical repair, and to describe a technique for arthroscopically assisted screw fixation in lag fashion. Retrospective case series. Horses (n=25) with unilateral mid-body PSB fracture. Medical records (1996-2006), radiographs, and arthroscopic videos of horses with surgically repaired unilateral mid-body PSB fractures were reviewed. Retrieved data included signalment, affected limb and PSB, fracture characteristics, and surgical technique. Outcome was established by radiographic assessment of healing and race records; categorical data were analyzed using Fisher's Exact test. Medial forelimb PSBs were most commonly affected (80%). Surgical technique and degree of reduction were significantly associated with outcome; 44% of horses with screw repair and none of the horses with wire fixation raced (P=.047). Factors that may have influenced this outcome were differences in fracture reduction (improved reduction in 22% wire repairs and 88% screw repairs, P=.002) and use of external coaptation (22% wire repair and 88% lag screw repair, P=.002). None of the horses with unimproved reduction raced after surgery. Only 28% of horses with mid-body PSB fractures raced after surgery. Compared with wire fixation, screw fixation in lag fashion resulted in good reduction and is seemingly a superior repair technique. For mid-body PSB fractures, arthroscopically assisted screw fixation in lag fashion and external coaptation for anesthesia recovery and initial support provides the best likelihood of return to athletic use.

Behavioral Processes in Long-Lag Intervention Studies.

Science.gov (United States)

Miller, Dale T; Dannals, Jennifer E; Zlatev, Julian J

2017-05-01

We argue that psychologists who conduct experiments with long lags between the manipulation and the outcome measure should pay more attention to behavioral processes that intervene between the manipulation and the outcome measure. Neglect of such processes, we contend, stems from psychology's long tradition of short-lag lab experiments where there is little scope for intervening behavioral processes. Studying process in the lab invariably involves studying psychological processes, but in long-lag field experiments it is important to study causally relevant behavioral processes as well as psychological ones. To illustrate the roles that behavioral processes can play in long-lag experiments we examine field experiments motivated by three policy-relevant goals: prejudice reduction, health promotion, and educational achievement. In each of the experiments discussed we identify various behavioral pathways through which the manipulated psychological state could have produced the observed outcome. We argue that if psychologists conducting long-lag interventions posited a theory of change that linked manipulated psychological states to outcomes via behavioral pathways, the result would be richer theory and more practically useful research. Movement in this direction would also permit more opportunities for productive collaborations between psychologists and other social scientists interested in similar social problems.

The use of blocking screws with internal lengthening nail and reverse rule of thumb for blocking screws in limb lengthening and deformity correction surgery

Directory of Open Access Journals (Sweden)

Saravanaraja Muthusamy

2016-09-01

Full Text Available Abstract Internal lengthening nail (ILN is a recent development in limb lengthening and deformity correction specialty. The ILN has the distinct advantage of combining acute deformity correction with gradual lengthening of bone. While using ILN, the short metaphyseal bone fragment may develop a deformity at the time of osteotomy and nail insertion or during bone lengthening because of the wide medullary canal. These deformities are typically predictable, and blocking screws (Poller screws are helpful in these situations. This manuscript describes the common deformities that occur in femur and tibia with osteotomies at different locations while using ILN in antegrade and retrograde nailing technique. Also, a systematic approach to the appropriate use of blocking screws in these deformities is described. In addition, the “reverse rule of thumb” is introduced as a quick reference to determine the ideal location(s and number of blocking screws. These principles are applicable to limb lengthening and deformity correction as well as fracture fixation using intramedullary nails.

The use of blocking screws with internal lengthening nail and reverse rule of thumb for blocking screws in limb lengthening and deformity correction surgery.

Science.gov (United States)

Muthusamy, Saravanaraja; Rozbruch, S Robert; Fragomen, Austin T

2016-11-01

Internal lengthening nail (ILN) is a recent development in limb lengthening and deformity correction specialty. The ILN has the distinct advantage of combining acute deformity correction with gradual lengthening of bone. While using ILN, the short metaphyseal bone fragment may develop a deformity at the time of osteotomy and nail insertion or during bone lengthening because of the wide medullary canal. These deformities are typically predictable, and blocking screws (Poller screws) are helpful in these situations. This manuscript describes the common deformities that occur in femur and tibia with osteotomies at different locations while using ILN in antegrade and retrograde nailing technique. Also, a systematic approach to the appropriate use of blocking screws in these deformities is described. In addition, the "reverse rule of thumb" is introduced as a quick reference to determine the ideal location(s) and number of blocking screws. These principles are applicable to limb lengthening and deformity correction as well as fracture fixation using intramedullary nails.

X-ray time lags in PG 1211+143

Science.gov (United States)

Lobban, A. P.; Vaughan, S.; Pounds, K.; Reeves, J. N.

2018-05-01

We investigate the X-ray time lags of a recent ˜630 ks XMM-Newton observation of PG 1211+143. We find well-correlated variations across the XMM-Newton EPIC bandpass, with the first detection of a hard lag in this source with a mean time delay of up to ˜3 ks at the lowest frequencies. We find that the energy-dependence of the low-frequency hard lag scales approximately linearly with log(E) when averaged over all orbits, consistent with the propagating fluctuations model. However, we find that the low-frequency lag behaviour becomes more complex on time-scales longer than a single orbit, suggestive of additional modes of variability. We also detect a high-frequency soft lag at ˜10-4 Hz with the magnitude of the delay peaking at ≲ 0.8 ks, consistent with previous observations, which we discuss in terms of small-scale reverberation.

Research on energy conversion mechanism of a screw centrifugal pump under the water

International Nuclear Information System (INIS)

Quan, H; Li, R N; Han, W; Cheng, X R; Shen, Z J; Su, Q M

2013-01-01

In order to research screw centrifugal pump impeller power capability and energy conversion mechanism, we used Navier-Stokes equation and standard k-ε equation turbulence model on the basis of the Euler equations to carry out screw centrifugal pump internal flow numerical simulation. This was explored by simulating specific design conditions; the medium is water, variation of speed and pressure of flow filed under the action of the impeller, and the screw centrifugal impeller shroud line and wheel line segment take monitoring sites. The monitoring points are between dynamic head and static head change to analyze the energy conversion capability along the impeller corners of screw centrifugal pump. The results show that the energy of fluid of the screw centrifugal pump is provided by spiral segment, the spiral segment in front of the impeller has played a multi-level role, it has significant reference value to research the energy conversion mechanism of screw centrifugal pump under solid-liquid two phase

Posterior pelvic ring fractures: Closed reduction and percutaneous CT-guided sacroiliac screw fixation

International Nuclear Information System (INIS)

Jacob, Augustinus Ludwig; Messmer, Peter; Stock, Klaus-Wilhelm; Suhm, Norbert; Baumann, Bernard; Regazzoni, Pietro; Steinbrich, Wolfgang

1997-01-01

Purpose. To assess the midterm results of closed reduction and percutaneous fixation (CRPF) with computed tomography (CT)-guided sacroiliac screw fixation in longitudinal posterior pelvic ring fractures. Methods. Thirteen patients with 15 fractures were treated. Eleven patients received a unilateral, two a bilateral, screw fixation. Twenty-seven screws were implanted. Continuous on-table traction was used in six cases. Mean radiological follow-up was 13 months. Results. Twenty-five (93%) screws were placed correctly. There was no impingement of screws on neurovascular structures. Union occurred in 12 (80%), delayed union in 2 (13%), and nonunion in 1 of 15 (7%) fractures. There was one screw breakage and two axial dislocations. Conclusion. Sacroiliac CRPF of longitudinal fractures of the posterior pelvic ring is technically simple, minimally invasive, well localized, and stable. It should be done by an interventional/surgical team. CT is an excellent guiding modality. Closed reduction may be a problem and succeeds best when performed as early as possible

The Peierls stress of the moving [Formula: see text] screw dislocation in Ta.

Science.gov (United States)

Liu, Ruiping; Wang, Shaofeng; Wu, Xiaozhi

2009-08-26

The Peierls stress of the moving [Formula: see text] screw dislocation with a planar and non-dissociated core structure in Ta has been calculated. The elastic strain energy which is associated with the discrete effect of the lattice and ignored in classical Peierls-Nabarro (P-N) theory has been taken into account in calculating the Peierls stress, and it can make the Peierls stress become smaller. The Peierls stress we obtain is very close to the experimental data. As shown in the numerical calculations and atomistic simulations, the core structure of the screw dislocation undergoes significant changes under the explicit stress before the screw dislocation moves. Moreover, the mechanism of the screw dislocation is revealed by our results and the experimental data that the screw dislocation retracts its extension in three {110} planes and transforms its dissociated core structure into a planar configuration. Therefore, the core structure of the moving [Formula: see text] screw dislocation in Ta is proposed to be planar.

The Peierls stress of the moving 1/2{110} screw dislocation in Ta

International Nuclear Information System (INIS)

Liu Ruiping; Wang Shaofeng; Wu Xiaozhi

2009-01-01

The Peierls stress of the moving 1/2 {110} screw dislocation with a planar and non-dissociated core structure in Ta has been calculated. The elastic strain energy which is associated with the discrete effect of the lattice and ignored in classical Peierls-Nabarro (P-N) theory has been taken into account in calculating the Peierls stress, and it can make the Peierls stress become smaller. The Peierls stress we obtain is very close to the experimental data. As shown in the numerical calculations and atomistic simulations, the core structure of the screw dislocation undergoes significant changes under the explicit stress before the screw dislocation moves. Moreover, the mechanism of the screw dislocation is revealed by our results and the experimental data that the screw dislocation retracts its extension in three {110} planes and transforms its dissociated core structure into a planar configuration. Therefore, the core structure of the moving 1/2 {110} screw dislocation in Ta is proposed to be planar.

Individualized 3D printing navigation template for pedicle screw fixation in upper cervical spine.

Science.gov (United States)

Guo, Fei; Dai, Jianhao; Zhang, Junxiang; Ma, Yichuan; Zhu, Guanghui; Shen, Junjie; Niu, Guoqi

2017-01-01

Pedicle screw fixation in the upper cervical spine is a difficult and high-risk procedure. The screw is difficult to place rapidly and accurately, and can lead to serious injury of spinal cord or vertebral artery. The aim of this study was to design an individualized 3D printing navigation template for pedicle screw fixation in the upper cervical spine. Using CT thin slices data, we employed computer software to design the navigation template for pedicle screw fixation in the upper cervical spine (atlas and axis). The upper cervical spine models and navigation templates were produced by 3D printer with equal proportion, two sets for each case. In one set (Test group), pedicle screws fixation were guided by the navigation template; in the second set (Control group), the screws were fixed under fluoroscopy. According to the degree of pedicle cortex perforation and whether the screw needed to be refitted, the fixation effects were divided into 3 types: Type I, screw is fully located within the vertebral pedicle; Type II, degree of pedicle cortex perforation is stability and no need to renovate; Type III, degree of pedicle cortex perforation is >1 mm or with the poor internal fixation stability and in need of renovation. Type I and Type II were acceptable placements; Type III placements were unacceptable. A total of 19 upper cervical spine and 19 navigation templates were printed, and 37 pedicle screws were fixed in each group. Type I screw-placements in the test group totaled 32; Type II totaled 3; and Type III totaled 2; with an acceptable rate of 94.60%. Type I screw placements in the control group totaled 23; Type II totaled 3; and Type III totaled 11, with an acceptable rate of 70.27%. The acceptability rate in test group was higher than the rate in control group. The operation time and fluoroscopic frequency for each screw were decreased, compared with control group. The individualized 3D printing navigation template for pedicle screw fixation is easy and safe

Comparison of the Pullout Strength of Different Pedicle Screw Designs and Augmentation Techniques in an Osteoporotic Bone Model.

Science.gov (United States)

Kiyak, Gorkem; Balikci, Tevfik; Heydar, Ahmed Majid; Bezer, Murat

2018-02-01

Mechanical study. To compare the pullout strength of different screw designs and augmentation techniques in an osteoporotic bone model. Adequate bone screw pullout strength is a common problem among osteoporotic patients. Various screw designs and augmentation techniques have been developed to improve the biomechanical characteristics of the bone-screw interface. Polyurethane blocks were used to mimic human osteoporotic cancellous bone, and six different screw designs were tested. Five standard and expandable screws without augmentation, eight expandable screws with polymethylmethacrylate (PMMA) or calcium phosphate augmentation, and distal cannulated screws with PMMA and calcium phosphate augmentation were tested. Mechanical tests were performed on 10 unused new screws of each group. Screws with or without augmentation were inserted in a block that was held in a fixture frame, and a longitudinal extraction force was applied to the screw head at a loading rate of 5 mm/min. Maximum load was recorded in a load displacement curve. The peak pullout force of all tested screws with or without augmentation was significantly greater than that of the standard pedicle screw. The greatest pullout force was observed with 40-mm expandable pedicle screws with four fins and PMMA augmentation. Augmented distal cannulated screws did not have a greater peak pullout force than nonaugmented expandable screws. PMMA augmentation provided a greater peak pullout force than calcium phosphate augmentation. Expandable pedicle screws had greater peak pullout forces than standard pedicle screws and had the advantage of augmentation with either PMMA or calcium phosphate cement. Although calcium phosphate cement is biodegradable, osteoconductive, and nonexothermic, PMMA provided a significantly greater peak pullout force. PMMA-augmented expandable 40-mm four-fin pedicle screws had the greatest peak pullout force.

Electromyogram synergy control of a dexterous artificial hand to unscrew and screw objects.

Science.gov (United States)

Kent, Benjamin A; Karnati, Nareen; Engeberg, Erik D

2014-03-21

Due to their limited dexterity, it is currently not possible to use a commercially available prosthetic hand to unscrew or screw objects without using elbow and shoulder movements. For these tasks, prosthetic hands function like a wrench, which is unnatural and limits their use in tight working environments. Results from timed rotational tasks with human subjects demonstrate the clinical need for increased dexterity of prosthetic hands, and a clinically viable solution to this problem is presented for an anthropomorphic artificial hand. Initially, a human hand motion analysis was performed during a rotational task. From these data, human hand synergies were derived and mapped to an anthropomorphic artificial hand. The synergy for the artificial hand is controlled using conventional dual site electromyogram (EMG) signals. These EMG signals were mapped to the developed synergy to control four joints of the dexterous artificial hand simultaneously.Five limb absent and ten able-bodied test subjects participated in a comparison study to complete a timed rotational task as quickly as possible with their natural hands (except for one subject with a bilateral hand absence), eight commercially available prosthetic hands, and the proposed synergy controller. Each test subject used two to four different artificial hands. With the able-bodied subjects, the developed synergy controller reduced task completion time by 177% on average. The limb absent subjects completed the task faster on average than with their own prostheses by 46%. There was a statistically significant improvement in task completion time with the synergy controller for three of the four limb absent participants with integrated prostheses, and was not statistically different for the fourth. The proposed synergy controller reduced average task completion time compared to commercially available prostheses. Additionally, the synergy controller is able to function in a small workspace and requires less physical

Cement Augmentation in Sacroiliac Screw Fixation Offers Modest Biomechanical Advantages in a Cadaver Model.

Science.gov (United States)

Osterhoff, Georg; Dodd, Andrew E; Unno, Florence; Wong, Angus; Amiri, Shahram; Lefaivre, Kelly A; Guy, Pierre

2016-11-01

Sacroiliac screw fixation in elderly patients with pelvic fractures is prone to failure owing to impaired bone quality. Cement augmentation has been proposed as a possible solution, because in other anatomic areas this has been shown to reduce screw loosening. However, to our knowledge, this has not been evaluated for sacroiliac screws. We investigated the potential biomechanical benefit of cement augmentation of sacroiliac screw fixation in a cadaver model of osteoporotic bone, specifically with respect to screw loosening, construct survival, and fracture-site motion. Standardized complete sacral ala fractures with intact posterior ligaments in combination with ipsilateral upper and lower pubic rami fractures were created in osteoporotic cadaver pelves and stabilized by three fixation techniques: sacroiliac (n = 5) with sacroiliac screws in S1 and S2, cemented (n = 5) with addition of cement augmentation, and transsacral (n = 5) with a single transsacral screw in S1. A cyclic loading protocol was applied with torque (1.5 Nm) and increasing axial force (250-750 N). Screw loosening, construct survival, and sacral fracture-site motion were measured by optoelectric motion tracking. A sample-size calculation revealed five samples per group to be required to achieve a power of 0.80 to detect 50% reduction in screw loosening. Screw motion in relation to the sacrum during loading with 250 N/1.5 Nm was not different among the three groups (sacroiliac: 1.2 mm, range, 0.6-1.9; cemented: 0.7 mm, range, 0.5-1.3; transsacral: 1.1 mm, range, 0.6-2.3) (p = 0.940). Screw subsidence was less in the cemented group (3.0 mm, range, 1.2-3.7) compared with the sacroiliac (5.7 mm, range, 4.7-10.4) or transsacral group (5.6 mm, range, 3.8-10.5) (p = 0.031). There was no difference with the numbers available in the median number of cycles needed until failure; this was 2921 cycles (range, 2586-5450) in the cemented group, 2570 cycles (range, 2500-5107) for the sacroiliac specimens, and

Evaluation of two styles of slotted, flat-head screws

International Nuclear Information System (INIS)

Reeves, C.A. Jr.; Johnson, W.B.

1979-01-01

A series of torque tests were performed to evaluate the relative merits of two different flat-head screws fabricated from a uranium--6% niobium alloy. The screws tested were machined with both normal, straight-through slots in the head and with slots having radiused bottoms. Test results indicate that both designs easily surpass the required 20-inch-pound-proof torque

Covering the screw-access holes of implant restorations in the esthetic zone: a clinical report.

Directory of Open Access Journals (Sweden)

Abolfazl Saboury

2014-12-01

Full Text Available Screw-retained implant restorations have an advantage of predictable retention as well as retrievability, and obviate the risk of excessive sub-gingival cement commonly associated with cement retained implant restorations. Screw-retained restorations generally have screw access holes, which can compromise esthetics and weaken the porcelain around the holes. The purpose of this study is to describe the use of a separate overcasting crown design to cover the screw access hole of implant screw-retained prosthesis for improved esthetics.

Screw-System-Based Mobility Analysis of a Family of Fully Translational Parallel Manipulators

Directory of Open Access Journals (Sweden)

Ernesto Rodriguez-Leal

2013-01-01

Full Text Available This paper investigates the mobility of a family of fully translational parallel manipulators based on screw system analysis by identifying the common constraint and redundant constraints, providing a case study of this approach. The paper presents the branch motion-screws for the 3-RP̲C-Y parallel manipulator, the 3-RCC-Y (or 3-RP̲RC-Y parallel manipulator, and a newly proposed 3-RP̲C-T parallel manipulator. Then the paper determines the sets of platform constraint-screws for each of these three manipulators. The constraints exerted on the platforms of the 3-RP̲C architectures and the 3-RCC-Y manipulators are analyzed using the screw system approach and have been identified as couples. A similarity has been identified with the axes of couples: they are perpendicular to the R joint axes, but in the former the axes are coplanar with the base and in the latter the axes are perpendicular to the limb. The remaining couples act about the axis that is normal to the base. The motion-screw system and constraint-screw system analysis leads to the insightful understanding of the mobility of the platform that is then obtained by determining the reciprocal screws to the platform constraint screw sets, resulting in three independent instantaneous translational degrees-of-freedom. To validate the mobility analysis of the three parallel manipulators, the paper includes motion simulations which use a commercially available kinematics software.

Intraoperative insertion torque of lumbar pedicle screw and postoperative radiographic evaluation. Short-term observation

International Nuclear Information System (INIS)

Mizuno, Koichi; Shinomiya, Kenichi; Otani, Kazuyuki

2005-01-01

The correlation between the insertion torque of a lumbar pedicle screw and the mechanical stability of the screw in the bone has been mentioned in in vitro studies. The purpose of this study was to confirm the factors affecting the insertion torque of such screws in vivo. Also, the contribution of insertion torque to the initial stability of the fusion area was to be analyzed in vivo. A series of 23 cases representing 50 lumbar vertebrae were included in this study, in which we examined bone mineral density using quantitative computed tomography (CT) prior to operation. Two screw shapes were utilized, with the insertion torque for each screw measured at two points in time. The correlation between insertion torque and mineral density was investigated. Screw positions were confirmed on postoperative CT scans, and the effect of the screw thread cutting into the cortex bone was investigated. Radiographic changes at three points during a period of 3 months were also measured, and we then evaluated the interrelations between these changes and insertion torque. Furthermore, the relation between insertion torque and instability at 3 months was investigated. Correlations of insertion torque and bone mineral density depended on screw shape. There was no correlation found with mineral density in the case of cylindrical screws. Insertion torque was not affected by the screw thread cutting into the cortex of bone. As for postoperative alignment changes, no definitive trends could be ascertained, and no interrelations with torque and alignment changes were observed. There is a possibility that insertion torque was related to early-stage stability, but no statistical relation could be determined. (author)

Twin Screw Mixer/Fine Grind Facility

Data.gov (United States)

Federal Laboratory Consortium — The 40-mm Twin-Screw Mixer/Extruder (TSE) pilot plant is a continuous, remotely operated, flexible facility that can significantly enhance safety and environmental...

[Measurement of screw length through drilling technique in osteosynthesis of the proximal humerus fractures].

Science.gov (United States)

Avcı, Cem Coşkun; Gülabi, Deniz; Sağlam, Necdet; Kurtulmuş, Tuhan; Saka, Gürsel

2013-01-01

This study aims to investigate the efficacy of screw length measurement through drilling technique on the reduction of intraarticular screw penetration and fluoroscopy time in osteosynthesis of proximal humerus fractures. Between January 2008 and June 2012, 98 patients (34 males, 64 females; mean age 64.4 years; range 35 to 81 years) who underwent osteosynthesis using locking anatomical proximal humerus plates (PHILOS) in our clinic with the diagnosis of Neer type 2, 3 or 4 were included. Two different surgical techniques were used to measure proximal screw length in the plate and patients were divided into two groups based on the technique used. In group 1, screw length was determined by a 3 mm blunt tipped Kirschner wire without fluoroscopic control. In group 2, bilateral fluoroscopic images for each screw at least were obtained. Intraarticular screw penetration was detected in five patients (10.6%) in group 1, and in 19 patients (37.3%) in group 2. The mean fluoroscopic imaging time was 10.6 seconds in group 1 and 24.8 seconds in group 2, indicating a statistically significant difference. Screw length measurement through the drilling technique significantly reduces the intraarticular screw penetration and fluoroscopy time in osteosynthesis of proximal humerus fractures using PHILOS plates.

Biomechanical evaluation of a second generation headless compression screw for ankle arthrodesis in a cadaver model.

Science.gov (United States)

Somberg, Andrew Max; Whiteside, William K; Nilssen, Erik; Murawski, Daniel; Liu, Wei

2016-03-01

Many types of screws, plates, and strut grafts have been utilized for ankle arthrodesis. Biomechanical testing has shown that these constructs can have variable stiffness. More recently, headless compression screws have emerged as an evolving method of achieving compression in various applications but there is limited literature regarding ankle arthrodesis. The aim of this study was to determine the biomechanical stability provided by a second generation fully threaded headless compression screw compared to a standard headed, partially threaded cancellous screw in a cadaveric ankle arthrodesis model. Twenty fresh frozen human cadaver specimens were subjected to simulated ankle arthrodesis with either three standard cancellous-bone screws (InFix 7.3mm) or with three headless compression screws (Acumed Acutrak 2 7.5mm). The specimens were subjected to cyclic loading and unloading at a rate of 1Hz, compression of 525 Newtons (N) and distraction of 20N for a total of 500 cycles using an electromechanical load frame (Instron). The amount of maximum distraction was recorded as well as the amount of motion that occurred through 1, 10, 50, 100, and 500 cycles. No significant difference (p=0.412) was seen in the amount of distraction that occurred across the fusion site for either screw. The average maximum distraction after 500 cycles was 201.9μm for the Acutrak 2 screw and 235.4μm for the InFix screw. No difference was seen throughout each cycle over time for the Acutrak 2 screw (p-value=0.988) or the InFix screw (p-value=0.991). Both the traditional InFix type screw and the second generation Acumed Acutrak headless compression screws provide adequate fixation during ankle arthrodesis under submaximal loads. There is no demonstrable difference between traditional cannulated partially threaded screws and headless compression screws studied in this model. Copyright © 2015 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.

Pedicle Screw Insertion Accuracy Using O-Arm, Robotic Guidance, or Freehand Technique: A Comparative Study.

Science.gov (United States)

Laudato, Pietro Aniello; Pierzchala, Katarzyna; Schizas, Constantin

2018-03-15

A retrospective radiological study. The aim of this study was to evaluate the accuracy of pedicle screw insertion using O-Arm navigation, robotic assistance, or a freehand fluoroscopic technique. Pedicle screw insertion using either "O-Arm" navigation or robotic devices is gaining popularity. Although several studies are available evaluating each of those techniques separately, no direct comparison has been attempted. Eighty-four patients undergoing implantation of 569 lumbar and thoracic screws were divided into three groups. Eleven patients (64 screws) had screws inserted using robotic assistance, 25 patients (191 screws) using the O-arm, while 48 patients (314 screws) had screws inserted using lateral fluoroscopy in a freehand technique. A single experienced spine surgeon assisted by a spinal fellow performed all procedures. Screw placement accuracy was assessed by two independent observers on postoperative computed tomography (CTs) according to the A to D Rampersaud criteria. No statistically significant difference was noted between the three groups. About 70.4% of screws in the freehand group, 69.6% in the O arm group, and 78.8% in the robotic group were placed completely within the pedicle margins (grade A) (P > 0.05). About 6.4% of screws were considered misplaced (grades C&D) in the freehand group, 4.2% in the O-arm group, and 4.7% in the robotic group (P > 0.05). The spinal fellow inserted screws with the same accuracy as the senior surgeon (P > 0.05). The advent of new technologies does not appear to alter accuracy of screw placement in our setting. Under supervision, spinal fellows might perform equally well to experienced surgeons using new tools. The lack of difference in accuracy does not imply that the above-mentioned techniques have no added advantages. Other issues, such as surgeon/patient radiation, fiddle factor, teaching suitability, etc., outside the scope of our present study, need further assessment. 3.

A technique for the management of screw access opening in cement-retained implant restorations

Directory of Open Access Journals (Sweden)

Hamid Kermanshah

2014-01-01

Full Text Available Introduction: Abutment screw loosening has been considered as a common complication of implant-supported dental prostheses. This problem is more important in cement-retained implant restorations due to their invisible position of the screw access opening. Case Report: This report describes a modified retrievability method for cement-retained implant restorations in the event of abutment screw loosening. The screw access opening was marked with ceramic stain and its porcelain surface was treated using hydrofluoric acid (HF, silane, and adhesive to bond to composite resin. Discussion: The present modified technique facilitates screw access opening and improves the bond between the porcelain and composite resin.

Novel free-hand T1 pedicle screw method: Review of 44 consecutive cases

Directory of Open Access Journals (Sweden)

Mark A Rivkin

2014-01-01

Full Text Available Summary of Background Data: Multilevel posterior cervical instrumented fusions are becoming more prevalent in current practice. Biomechanical characteristics of the cervicothoracic junction may necessitate extending the construct to upper thoracic segments. However, fixation in upper thoracic spine can be technically demanding owing to transitional anatomy while suboptimal placement facilitates vascular and neurologic complications. Thoracic instrumentation methods include free-hand, fluoroscopic guidance, and CT-based image guidance. However, fluoroscopy of upper thoracic spine is challenging secondary to vertebral geometry and patient positioning, while image-guided systems present substantial financial commitment and are not readily available at most centers. Additionally, imaging modalities increase radiation exposure to the patient and surgeon while potentially lengthening surgical time. Materials and Methods: Retrospective review of 44 consecutive patients undergoing a cervicothoracic fusion by a single surgeon using the novel free-hand T1 pedicle screw technique between June 2009 and November 2012. A starting point medial and cephalad to classic entry as well as new trajectory were utilized. No imaging modalities were employed during screw insertion. Postoperative CT scans were obtained on day 1. Screw accuracy was independently evaluated according to the Heary classification. Results: In total, 87 pedicle screws placed were at T1. Grade 1 placement occurred in 72 (82.8% screws, Grade 2 in 4 (4.6% screws and Grade 3 in 9 (10.3% screws. All Grade 2 and 3 breaches were <2 mm except one Grade 3 screw breaching 2-4 mm laterally. Only two screws (2.3% were noted to be Grade 4, both breaching medially by less than 2 mm. No new neurological deficits or returns to operating room took place postoperatively. Conclusions: This modification of the traditional starting point and trajectory at T1 is safe and effective. It attenuates additional bone

Hopf bifurcation and chaos in macroeconomic models with policy lag

International Nuclear Information System (INIS)

Liao Xiaofeng; Li Chuandong; Zhou Shangbo

2005-01-01

In this paper, we consider the macroeconomic models with policy lag, and study how lags in policy response affect the macroeconomic stability. The local stability of the nonzero equilibrium of this equation is investigated by analyzing the corresponding transcendental characteristic equation of its linearized equation. Some general stability criteria involving the policy lag and the system parameter are derived. By choosing the policy lag as a bifurcation parameter, the model is found to undergo a sequence of Hopf bifurcation. The direction and stability of the bifurcating periodic solutions are determined by using the normal form theory and the center manifold theorem. Moreover, we show that the government can stabilize the intrinsically unstable economy if the policy lag is sufficiently short, but the system become locally unstable when the policy lag is too long. We also find the chaotic behavior in some range of the policy lag

Treatment for Trochanteric Fracture of the Femur with Short Femoral Nail: A Comparison between the Asian Intramedullary Hip Screw (IMHS) and the Conventional IMHS.

Science.gov (United States)

Kawaji, Hidemi; Uematsu, Takuya; Oba, Ryosuke; Satake, Yoshihiko; Hoshikawa, Naoya; Takai, Shinro

2016-01-01

We usually use short femoral nails for the treatment of trochanteric fracture of the femur. In this retrospective study, we investigated and compared the clinical results of the conventional intramedullary hip screw (IMHS) and the Asian IMHS, which is a redesigned version of the former. The subjects were 42 patients; 21 treated with the Asian IMHS and 21 were treated with the conventional IMHS. From the clinical records, we retrospectively investigated the patients' age, sex, in-hospital waiting period for operation, operating time, intraoperative blood loss, walking ability before fracture and at discharge, and complication pertaining to the operation. The 21 patients (4 men and 17 women) receiving the Asian IMHS and the 21 patients (5 men and 16 women) receiving the conventional IMHS did not differ significantly in mean age, sex ratio, preoperative waiting period, mean postoperative hospital stay, mean operation time, or mean intraoperative blood loss. Among patients receiving the Asian IMHS, the complications of intraoperative fractures of the femur developed in 3 patients and breakage of the implant occurred in 1 patient. No complications occurred in patients receiving the conventional IMHS. Compared with the conventional IMHS, the Asian IMHS is smaller, has increased variations in the shaft/neck angle of the lag screw, and has a titanium-alloy construction, allowing magnetic resonance imaging. The intraoperative fracture may have occurred because of the configuration of the distal interlocking screw in the Asian IMHS. Breakage of the implant likely occurred because the nail was too small in diameter, and too short in length for the unstable AO 31-A3 fracture. If careful attention is paid to the configuration of its distal interlocking screw intraoperatively and a nail of appropriate size is selected, the Asian IMHS is better suited than the conventional IMHS for treating Japanese patients, who generally have a small physique, because of its many variations in

Exposure-lag-response in Longitudinal Studies: Application of Distributed Lag Non-linear Models in an Occupational Cohort.

Science.gov (United States)

Neophytou, Andreas M; Picciotto, Sally; Brown, Daniel M; Gallagher, Lisa E; Checkoway, Harvey; Eisen, Ellen A; Costello, Sadie

2018-02-13

Prolonged exposures can have complex relationships with health outcomes, as timing, duration, and intensity of exposure are all potentially relevant. Summary measures such as cumulative exposure or average intensity of exposure may not fully capture these relationships. We applied penalized and unpenalized distributed lag non-linear models (DLNMs) with flexible exposure-response and lag-response functions in order to examine the association between crystalline silica exposure and mortality from lung cancer and non-malignant respiratory disease in a cohort study of 2,342 California diatomaceous earth workers, followed 1942-2011. We also assessed associations using simple measures of cumulative exposure assuming linear exposure-response and constant lag-response. Measures of association from DLNMs were generally higher than from simpler models. Rate ratios from penalized DLNMs corresponding to average daily exposures of 0.4 mg/m3 during lag years 31-50 prior to the age of observed cases were 1.47 (95% confidence interval (CI) 0.92, 2.35) for lung cancer and 1.80 (95% CI: 1.14, 2.85) for non-malignant respiratory disease. Rate ratios from the simpler models for the same exposure scenario were 1.15 (95% CI: 0.89-1.48) and 1.23 (95% CI: 1.03-1.46) respectively. Longitudinal cohort studies of prolonged exposures and chronic health outcomes should explore methods allowing for flexibility and non-linearities in the exposure-lag-response. © The Author(s) 2018. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health.

Corporate Governance and Audit Report Lag in Malaysia

OpenAIRE

Mohamad Naimi Mohamad-Nor; ; Rohami Shafie; Wan Nordin Wan-Hussin

2010-01-01

This paper examines audit report lag in Malaysian public listed companies, following the implementation of the Malaysian Code on Corporate Governance in 2001. It departs from the standard audit report lag studies by incorporating characteristics of the board of directors and the audit committee. Multivariate analysis using 628 annual reports for the year ended 2002 indicates that active and larger audit committees shorten audit lag. However, we fail to find evidence that audit committee indep...

Trochanteric fracture-implant motion during healing - A radiostereometry (RSA) study.

Science.gov (United States)

Bojan, Alicja J; Jönsson, Anders; Granhed, Hans; Ekholm, Carl; Kärrholm, Johan

2018-03-01

Cut-out complication remains a major unsolved problem in the treatment of trochanteric hip fractures. A better understanding of the three-dimensional fracture-implant motions is needed to enable further development of clinical strategies and countermeasures. The aim of this clinical study was to characterise and quantify three-dimensional motions between the implant and the bone and between the lag screw and nail of the Gamma nail. Radiostereometry Analysis (RSA) analysis was applied in 20 patients with trochanteric hip fractures treated with an intramedullary nail. The following three-dimensional motions were measured postoperatively, at 1 week, 3, 6 and 12 months: translations of the tip of the lag screw in the femoral head, motions of the lag screw in the nail, femoral head motions relative to the nail and nail movements in the femoral shaft. Cranial migration of the tip of the lag screw dominated over the other two translation components in the femoral head. In all fractures the lag screw slid laterally in the nail and the femoral head moved both laterally and inferiorly towards the nail. All femoral heads translated posteriorly relative to the nail, and rotations occurred in both directions with median values close to zero. The nail tended to retrovert in the femoral shaft. Adverse fracture-implant motions were detected in stable trochanteric hip fractures treated with intramedullary nails with high resolution. Therefore, RSA method can be used to evaluate new implant designs and clinical strategies, which aim to reduce cut-out complications. Future RSA studies should aim at more unstable fractures as these are more likely to fail with cut-out. Copyright © 2018 Elsevier Ltd. All rights reserved.

[Clinical application of atlas translaminar screws fixation in treatment of atlatoaxial instability].

Science.gov (United States)

Wang, Guoyou; Fu, Shijie; Shen, Huarui; Guan, Taiyuan; Xu, Ping

2013-10-01

To explore the effectiveness of fixation of atlas translaminar screws in the treatment of atlatoaxial instability. A retrospective analysis was made on the clinical data of 32 patients with atlatoaxial instability treated with atlantoaxial trans-pedicle screws between March 2007 and August 2009. Of them, 7 patients underwent atlas translaminar screws combined with axis transpedicle screws fixation because of fracture types, anatomic variation, and intraoperative reason, including 5 males and 2 females with an average age of 48.2 years (range, 35-69 years). A total of 9 translaminar screws were inserted. Injury was caused by traffic accident in 4 cases, falling from height in 2 cases, and crushing in 1 case. Two cases had simple odontoid fracture (Anderson type II), and 5 cases had odontoid fracture combined with other injuries (massa lateralis atlantis fracture in 2, atlantoaxial dislocation in 1, and Hangman fracture in 2). The interval between injury and operation was 4-9 days (mean, 6 days). The preoperative Japanese Orthopaedic Association (JOA) score was 8.29 +/- 1.60. The X-ray films showed good position of the screws. Healing of incision by first intention was obtained, and no patient had injuries of the spinal cord injury, nerve root, and vertebral artery. Seven cases were followed up 9-26 months (mean, 14 months). Good bone fusion was observed at 8 months on average (range, 6-11 months). No loosening, displacement, and breakage of internal fixation, re-dislocation and instability of atlantoaxial joint, or penetrating of pedicle screw into the spinal canal and the spinal cord occurred. The JOA score was significantly improved to 15.29 +/- 1.38 at 6 months after operation (t = 32.078, P = 0.000). Atlas translaminar screws fixation has the advantages of firm fixation, simple operating techniques, and relative safety, so it may be a remedial measure of atlatoaxial instability.

Clinical accuracy of three-dimensional fluoroscopy (IsoC-3D)-assisted upper thoracic pedicle screw insertion

International Nuclear Information System (INIS)

Sugimoto, Yoshihisa; Ito, Yasuo; Shimokawa, Tetsuya; Shiozaki, Yasuyuki; Mazaki, Tetsuro; Tomioka, Masao; Tanaka, Masato

2010-01-01

Correct screw placement is especially difficult in the upper thoracic vertebrae. At the cervicothoracic junction (C7-T2), problems can arise because of the narrowness of the pedicle and the difficulty of using a lateral image intensifier there. Other upper thoracic vertebrae (T3-6) pose a problem for screw insertion also because of the narrower pedicle. We inserted 154 pedicle screws into 78 vertebrae (C7 to T6) in 38 patients. Screws were placed using intraoperative data acquisition by an isocentric C-arm fluoroscope (Siremobile Iso-C3D) and computer navigation. Out of 90 pedicle screws inserted into 45 vertebrae between C7 and T2, 87 of the 90 (96.7%) screws were classified as grade 1 (no perforation). Of 64 pedicle screws inserted into 33 vertebrae between T3 and T6, 61 of 64 (95.3%) screws were classified as grade 1. In this study, we reduced pedicle screw misplacement at the level of the C7 and upper thoracic (T1-6) vertebrae using the three-dimensional fluoroscopy navigation system. (author)

Pedicle Screw Fixation Study in Immature Porcine Spines to Improve Pullout Resistance during Animal Testing.

Directory of Open Access Journals (Sweden)

Sophie Le Cann

Full Text Available The porcine model is frequently used during development and validation of new spinal devices, because of its likeness to the human spine. These spinal devices are frequently composed of pedicle screws with a reputation for stable fixation but which can suffer pullouts during preclinical implantation on young animals, leading to high morbidity. With a view to identifying the best choices to optimize pedicle screw fixation in the porcine model, this study evaluates ex vivo the impact of weight (age of the animal, the level of the vertebrae (lumbar or thoracic and the type of screw anchorage (mono- or bi-cortical on pedicle screw pullouts. Among the 80 pig vertebrae (90- and 140-day-old tested in this study, the average screw pullout forces ranged between 419.9N and 1341.2N. In addition, statistical differences were found between test groups, pointing out the influence of the three parameters stated above. We found that the the more caudally the screws are positioned (lumbar level, the greater their pullout resistance is, moreover, screw stability increases with the age, and finally, the screws implanted with a mono-cortical anchorage sustained lower pullout forces than those implanted with a bi-cortical anchorage. We conclude that the best anchorage can be obtained with older animals, using a lumbar fixation and long screws traversing the vertebra and inducing bi-cortical anchorage. In very young animals, pedicle screw fixations need to be bi-cortical and more numerous to prevent pullout.

Pedicle Screw Fixation Study in Immature Porcine Spines to Improve Pullout Resistance during Animal Testing.

Science.gov (United States)

Le Cann, Sophie; Cachon, Thibaut; Viguier, Eric; Miladi, Lotfi; Odent, Thierry; Rossi, Jean-Marie; Chabrand, Patrick

2015-01-01

The porcine model is frequently used during development and validation of new spinal devices, because of its likeness to the human spine. These spinal devices are frequently composed of pedicle screws with a reputation for stable fixation but which can suffer pullouts during preclinical implantation on young animals, leading to high morbidity. With a view to identifying the best choices to optimize pedicle screw fixation in the porcine model, this study evaluates ex vivo the impact of weight (age) of the animal, the level of the vertebrae (lumbar or thoracic) and the type of screw anchorage (mono- or bi-cortical) on pedicle screw pullouts. Among the 80 pig vertebrae (90- and 140-day-old) tested in this study, the average screw pullout forces ranged between 419.9N and 1341.2N. In addition, statistical differences were found between test groups, pointing out the influence of the three parameters stated above. We found that the the more caudally the screws are positioned (lumbar level), the greater their pullout resistance is, moreover, screw stability increases with the age, and finally, the screws implanted with a mono-cortical anchorage sustained lower pullout forces than those implanted with a bi-cortical anchorage. We conclude that the best anchorage can be obtained with older animals, using a lumbar fixation and long screws traversing the vertebra and inducing bi-cortical anchorage. In very young animals, pedicle screw fixations need to be bi-cortical and more numerous to prevent pullout.

An electromagnetic screw and nut system for operating vertical motions along an axis

International Nuclear Information System (INIS)

Fehr, Henri.

1975-01-01

This invention concerns a magnetic screw and nut system for operating control rods, designed for vertical mounting and having no mobile or slide contacts. It makes it possible to rotate a screw located inside a sealed tubular containment that can have a very thick wall. All the electromagnetic components entering into the operation are outside this containment. The magnetic screw has a constant air gap. The tube, manufactured of a non-magnetic material, includes two added annular pole pieces forming part of its wall and whose internal surfaces have a thread corresponding to that of the screw. The two annular pole pieces are spaced axially from each other by an amount equal to an integral number of thread pitches. An external winding and magnetic armature associated to these pole pieces form the fixed magnetic nut. A multiphase non-synchronous motor is placed around the tube and near the nut, the stator is external, the rotor is the screw. An appliance for fixing the degree of axial displacement freedom of the screw can be provided [fr

Influence of abutment screw preload on stress distribution in marginal bone.

Science.gov (United States)

Khraisat, Ameen

2012-01-01

Changes in an implant assembly after abutment connection might possibly cause deformation in the implant/abutment joint and even in the marginal bone. The aim of this study was to evaluate the influence of abutment screw preload through the implant collar on marginal bone stress without external load application. Models of three implant parts made of titanium (implant, abutment, and abutment screw) and cortical bone were built and positioned with computer-aided design software. Meshing and generation of boundary conditions, loads, and interactions were performed. Each part was meshed independently. The sole load applied to the model was a torque of 32 Ncm on the abutment screw about its axis of rotation. The implant collar was deformed axially after the screw was tightened (3 μm). This deformation resulted in 60 MPa of stress in the marginal bone. Moreover, pressure on the marginal bone in a radial direction was observed. It can be concluded that, without any external load application, abutment screw preload exerts stresses on the implant collar and the marginal bone. These findings should help guide the development of new implant/abutment joint designs that exert less stress on the marginal bone.

Deterministic Properties of Serially Connected Distributed Lag Models

Directory of Open Access Journals (Sweden)

Piotr Nowak

2013-01-01

Full Text Available Distributed lag models are an important tool in modeling dynamic systems in economics. In the analysis of composite forms of such models, the component models are ordered in parallel (with the same independent variable and/or in series (where the independent variable is also the dependent variable in the preceding model. This paper presents an analysis of certain deterministic properties of composite distributed lag models composed of component distributed lag models arranged in sequence, and their asymptotic properties in particular. The models considered are in discrete form. Even though the paper focuses on deterministic properties of distributed lag models, the derivations are based on analytical tools commonly used in probability theory such as probability distributions and the central limit theorem. (original abstract

Performance Characteristics of a 4 × 6 Oil-Free Twin-Screw Compressor

Directory of Open Access Journals (Sweden)

Sun-Seok Byeon

2017-07-01

Full Text Available The screw compressor in the early stage of development is generally known as the oil-injection type. However, escalating environmental problems and advances in electronic components have spurred continuous R & D to minimize the oil content in compressed air. The oil-free twin-screw compressor is continuously compressed by inner volumetric change between rotors and casing. For this reason, in order to predict the overall performance of the screw compressor at the early stage of the design process, industry still relies on the empirical method. However, it is difficult using the existing empirical method to gain more information of the inner fluid flow of the twin-screw compressor. Flow simulation techniques using CFD are required. This study presents applications of a recently proposed overset grid method to the solution of the flow around a moving boundary. In order to analyze the performance of a 4 × 6 oil-free screw compressor, the 3-D, unsteady and compressible flow fields were numerically calculated with a shear stress transport (SST turbulence model, and implemented by the commercial software, Star-CCM+. The pressure distributions were calculated and graphically depicted. Results also showed that the volumetric and adiabatic efficiencies of the screw compressor measured by the experiments were 78% and 71%, respectively.

Bioresorbable composite screws manufactured via forging process: pull-out, shear, flexural and degradation characteristics.

Science.gov (United States)

Felfel, R M; Ahmed, I; Parsons, A J; Rudd, C D

2013-02-01

Bioresorbable screws have the potential to overcome some of the complications associated with metallic screws currently in use. Removal of metallic screws after bone has healed is a serious issue which can lead to refracture due to the presence of screw holes. Poly lactic acid (PLA), fully 40 mol% P(2)O(5) containing phosphate unidirectional (P40UD) and a mixture of UD and short chopped strand random fibre mats (P40 70%UD/30%RM) composite screws were prepared via forging composite bars. Water uptake and mass loss for the composite screws manufactured increased significantly to ∼1.25% (P=0.0002) and ∼1.1% (P<0.0001), respectively, after 42 days of immersion in PBS at 37 °C. The initial maximum flexural load for P40 UD/RM and P40 UD composite screws was ∼60% (P=0.0047) and ∼100% (P=0.0037) higher than for the PLA screws (∼190 N), whilst the shear load was slightly higher in comparison to PLA (∼2.2 kN). The initial pull-out strengths for the P40 UD/RM and PLA screws were similar whereas that for P40 UD screws was ∼75% higher (P=0.022). Mechanical properties for the composite screws decreased initially after 3 days of immersion and this reduction was ascribed to the degradation of the fibre/matrix interface. After 3 days interval the mechanical properties (flexural, shear and pull-out) maintained their integrity for the duration of the study (at 42 days). This property retention was attributed to the chemical durability of the fibres used and stability of the matrix properties during the degradation process. It was also deemed necessary to enhance the fibre/matrix interface via use of a coupling agent in order to maintain the initial mechanical properties acquired for the required period of time. Lastly, it is also suggested that the degrading reinforcement fibres may have the potential to buffer any acidic products released from the PLA matrix. Copyright © 2012 Elsevier Ltd. All rights reserved.

Numerical simulation of a twin screw expander for performance prediction

Science.gov (United States)

Papes, Iva; Degroote, Joris; Vierendeels, Jan

2015-08-01

With the increasing use of twin screw expanders in waste heat recovery applications, the performance prediction of these machines plays an important role. This paper presents a mathematical model for calculating the performance of a twin screw expander. From the mass and energy conservation laws, differential equations are derived which are then solved together with the appropriate Equation of State in the instantaneous control volumes. Different flow processes that occur inside the screw expander such as filling (accompanied by a substantial pressure loss) and leakage flows through the clearances are accounted for in the model. The mathematical model employs all geometrical parameters such as chamber volume, suction and leakage areas. With R245fa as working fluid, the Aungier Redlich-Kwong Equation of State has been used in order to include real gas effects. To calculate the mass flow rates through the leakage paths formed inside the screw expander, flow coefficients are considered as constant and they are derived from 3D Computational Fluid Dynamic calculations at given working conditions and applied to all other working conditions. The outcome of the mathematical model is the P-V indicator diagram which is compared to CFD results of the same twin screw expander. Since CFD calculations require significant computational time, developed mathematical model can be used for the faster performance prediction.

New concept single screw compressors and their manufacture technology

Science.gov (United States)

Feng, Q.; Liu, F.; Chang, L.; Feng, C.; Peng, C.; Xie, J.; van den Broek, M.

2017-08-01

Single screw compressors were generally acknowledged as one of the nearly perfect machines by compressor researchers and manufacturers. However the rapid wear of the star-wheel in a single screw compressor during operation is a key reason why it hasn’t previously joined the main current compressors’ market. After more than ten years of effective work, the authors of this paper have proposed a new concept single screw compressor whose mesh-couple profile is enveloped with multi-column. Also a new design method and manufacture equipment for this kind of compressor have been developed and are described in this paper. A lot of prototype tests and a long period of industrial operations under full loading conditions have shown that the mesh-couple profiles of the new concept single compressors have excellent anti-wearness.

Screw engine used as an expander in ORC for low-potential heat utilization

Science.gov (United States)

Richter, Lukáš

2017-09-01

This paper deals with a screw motor that is used as an expander in an ORC (Organic Rankin Cycle) system, whose organic working substance allows the transformation of low-potential heat (waste heat, solar and geothermal energy) into electrical energy. The article describes the specific properties of an organic substance and a screw motor that must be considered when designing and assembling a complete power unit. Screw machines are not commonly used as expansion devices, so it is necessary to perform an analysis that makes it possible to adapt the screw machine to the expansion process in terms of profiling and design.

The Research of Screw Thread Parameter Measurement Based on Position Sensitive Detector and Laser

International Nuclear Information System (INIS)

Tong, Q B; Ding, Z L; Chen, J C; Ai, L L; Yuan, F

2006-01-01

A technique and system of measuring screw thread parameter based on the theory of laser measurement is presented in this paper, which can be carried out the automated measurement of screw thread parameter. An inspection instrument was designed and produced, which included exterior imaging system of optical path, transverse displacement measurement system, axial displacement measurement system, and a module to deal with, control and assess the data in the upper system. The inspection and estimate of the screw thread contour curve were completed by using position sensitive device (PSD) as photoelectric detector to measure the coordinate data of the screw thread contour curve in the transverse section, and using precise raster to measure the axial displacement of the precision worktable under the screw thread test criterion., computer can gives a measured result according to coordinate data of the screw thread obtained by PSD. The relation between measured spot and image is established, and optimum design of the system organization are introduced, including the image length of receiving lens focal length optical system and the choice of PSD , and some main factor affected measuring precision are analyzed. The experimental results show that the measurement uncertainty of screw thread minor diameter can reach 0. 5μm, which can meet most requests for the measurement of screw thread parameter

Parametric analysis and design of a screw extruder for slightly non-Newtonian (pseudoplastic materials

Directory of Open Access Journals (Sweden)

J.I. Orisaleye

2018-04-01

Full Text Available Extruders have found application in the food, polymer and pharmaceutical industries. Rheological characteristics of materials are important in the specification of design parameters of screw extruders. Biopolymers, which consist of proteins, nucleic acids and polysaccharides, are shear-thinning (pseudoplastic within normal operating ranges. However, analytical models to predict and design screw extruders for non-Newtonian pseudoplastic materials are rare. In this study, an analytical model suitable to design a screw extruder for slightly non-Newtonian materials was developed. The model was used to predict the performance of the screw extruder while processing materials with power law indices slightly deviating from unity (the Newtonian case. Using non-dimensional analysis, the effects of design and operational parameters were investigated. Expressions to determine the optimum channel depth and helix angle were also derived. The model is capable of predicting the performance of the screw extruder within the range of power law indices considered (1/2⩽n⩽1. The power law index influences the choice of optimum channel depth and helix angle of the screw extruder. Keywords: Screw extruder, Slightly non-Newtonian, Shear-thinning, Pseudoplastic, Biopolymer, Power law

Dynamic modelling and PID loop control of an oil-injected screw compressor package

Science.gov (United States)

Poli, G. W.; Milligan, W. J.; McKenna, P.

2017-08-01

A significant amount of time is spent tuning the PID (Proportional, Integral and Derivative) control loops of a screw compressor package due to the unique characteristics of the system. Common mistakes incurred during the tuning of a PID control loop include improper PID algorithm selection and unsuitable tuning parameters of the system resulting in erratic and inefficient operation. This paper details the design and development of software that aims to dynamically model the operation of a single stage oil injected screw compressor package deployed in upstream oil and gas applications. The developed software will be used to assess and accurately tune PID control loops present on the screw compressor package employed in controlling the oil pressures, temperatures and gas pressures, in a bid to improve control of the operation of the screw compressor package. Other applications of the modelling software will include its use as an evaluation tool that can estimate compressor package performance during start up, shutdown and emergency shutdown processes. The paper first details the study into the fundamental operational characteristics of each of the components present on the API 619 screw compressor package and then discusses the creation of a dynamic screw compressor model within the MATLAB/Simulink software suite. The paper concludes by verifying and assessing the accuracy of the created compressor model using data collected from physical screw compressor packages.

Factors influencing success of cement versus screw-retained implant restorations: a clinical review

Directory of Open Access Journals (Sweden)

Ahmad Manawar

2012-10-01

Full Text Available Aim: As more and more dental practitioners are focusing on implant-supported fixed restorations, some clinicians favor the use of cement retained restorations while others consider screw retained prosthesis to be the best choice. Discussion: In screw-retained restorations, the fastening screw provides a solid joint between the restoration and the implant abutment, while in cement-retained prostheses the restorative screw is eliminated to enhance esthetics, occlusal stability, and passive fit of the restorations. The factors that influence the type of fixation of the prostheses to the implants like passivity of the framework, ease of fabrication, occlusion, esthetics, accessibility, retention and retrievability are discussed in this article with scientific studies demonstrating superior outcomes of one technique over another. Screwretained implant restorations have an advantage of predictable retention, retrievability and lack of potentially retained subgingival cement. However, a few disadvantages exist such as precise placement of the implant for optimal and esthetic location of the screw access hole and obtaining passive fit. On the other hand, cement retained restorations eliminate unesthetic screw access holes, have passive fit of castings, reduced complexity of clinical and lab procedures, enhanced esthetics, reduced cost factors and non disrupted morphology of the occlusal table. Conclusion: This article compares the advantages, potential disadvantages and limitations of screw and cement retained restorations and their specific implications in the most common clinical situation.

Low lag luminescent phosphors

International Nuclear Information System (INIS)

1976-01-01

The addition of potassium or rubidium salts to europium-activated fluorohalide phosphors produces X-ray screens with low lag, even at very low europium concentrations. The chemical preparation and afterglow test results are described

Metal Artifacts Reduction of Pedicle Screws on Spine Computed Tomography Images Using Variable Thresholding Technique

International Nuclear Information System (INIS)

Kaewlek, T.; Koolpiruck, D.; Thongvigitmanee, S.; Mongkolsuk, M.; Chiewvit, P.; Thammakittiphan, S.

2012-01-01

Metal artifacts are one of significant problems in computed tomography (CT). The streak lines and air gaps arise from metal implants of orthopedic patients, such as prosthesis, dental bucket, and pedicle screws that cause incorrect diagnosis and local treatment planning. A common technique to suppressed artifacts is by adjusting windows, but those artifacts still remain on the images. To improve the detail of spine CT images, the variable thresholding technique is proposed in this paper. Three medical cases of spine CT images categorized by the severity of artifacts (screws head, one full screw, and two full screws) were investigated. Metal regions were segmented by k-mean clustering, then transformed into a sinogram domain. The metal sinogram was identified by the variable thresholding method, and then replaced the new estimated values by linear interpolation. The modified sinogram was reconstructed by the filtered back- projection algorithm, and added the metal region back to the modified reconstructed image in order to reproduce the final image. The image quality of the proposed technique, the automatic thresholding (Kalender) technique, and window adjustment technique was compared in term of noise and signal to noise ratio (SNR). The propose method can reduce metal artifacts between pedicle screws. After processing by our proposed technique, noise in the modified images is reduced (screws head 121.15 to73.83, one full screw 160.88 to 94.04, and two full screws 199.73 to 110.05 from the initial image) and SNR is increased (screws head 0.87 to 1.88, one full screw 1.54 to 2.82, and two full screws 0.32 to 0.41 from the initial image). The variable thresholding technique can identify the suitable boundary for restoring the missing data. The efficiency of the metal artifacts reduction is indicated on the case of partial and full pedicle screws. Our technique can improve the detail of spine CT images better than automatic thresholding (Kalender) technique, and

To retain or remove the syndesmotic screw: a review of literature

NARCIS (Netherlands)

T. Schepers (Tim)

2011-01-01

textabstractIntroduction: Syndesmotic positioning screws are frequently placed in unstable ankle fractures. Many facets of adequate placement techniques have been the subject of various studies. Whether or not the syndesmosis screw should be removed prior to weight-bearing is still debated. In this

Atomistic simulations of cross-slip of jogged screw dislocations in copper

DEFF Research Database (Denmark)

Vegge, T.; Rasmussen, T.; Leffers, T.

2001-01-01

We have performed atomic-scare simulations of cross-slip processes of screw dislocations in copper, simulating jog-free dislocations as well as different types of jogged screw dislocations. Minimum-energy paths and corresponding transition state energies are obtained using the nudged-elastic...

Surgical strategies to improve fixation in the osteoporotic spine: the effects of tapping, cement augmentation, and screw trajectory.

Science.gov (United States)

Kuhns, Craig A; Reiter, Michael; Pfeiffer, Ferris; Choma, Theodore J

2014-02-01

Study Design Biomechanical study of pedicle screw fixation in osteoporotic bone. Objective To investigate whether it is better to tap or not tap osteoporotic bone prior to placing a cement-augmented pedicle screw. Methods Initially, we evaluated load to failure of screws placed in cancellous bone blocks with or without prior tapping as well as after varying the depths of tapping prior to screw insertion. Then we evaluated load to failure of screws placed in bone block models with a straight-ahead screw trajectory as well as with screws having a 23-degree cephalad trajectory (toward the end plate). These techniques were tested with nonaugmented (NA) screws as well as with bioactive cement (BioC) augmentation prior to screw insertion. Results In the NA group, pretapping decreased fixation strength in a dose-dependent fashion. In the BioC group, the tapped screws had significantly greater loads to failure (p tapping prior to cement augmentation will substantially improve fixation when compared with not tapping. Angulating screws more cephalad also seems to enhance aging spine fixation.

Performance Characteristics of a 4 × 6 Oil-Free Twin-Screw Compressor

OpenAIRE

Sun-Seok Byeon; Jae-Young Lee; Youn-Jea Kim

2017-01-01

The screw compressor in the early stage of development is generally known as the oil-injection type. However, escalating environmental problems and advances in electronic components have spurred continuous R & D to minimize the oil content in compressed air. The oil-free twin-screw compressor is continuously compressed by inner volumetric change between rotors and casing. For this reason, in order to predict the overall performance of the screw compressor at the early stage of the design ...

A power recirculating test rig for ball screw endurance tests

Directory of Open Access Journals (Sweden)

Giberti Hermes

2016-01-01

Full Text Available A conceptual design of an innovative test rig for endurance tests of ball screws is presented in this paper. The test rig layout is based on the power recirculating principle and it also allows to overtake the main critical issues of the ball screw endurance tests. Among these there are the high power required to make the test, the lengthy duration of the same and the high loads between the screw and the frame that holds it. The article describes the test rig designed scheme, the kinematic expedients to be adopted in order to obtain the required performance and functionality and the sizing procedure to choose the actuation system.

Drag and Torque on Locked Screw Propeller

Directory of Open Access Journals (Sweden)

Tomasz Tabaczek

2014-09-01

Full Text Available Few data on drag and torque on locked propeller towed in water are available in literature. Those data refer to propellers of specific geometry (number of blades, blade area, pitch and skew of blades. The estimation of drag and torque of an arbitrary propeller considered in analysis of ship resistance or propulsion is laborious. The authors collected and reviewed test data available in the literature. Based on collected data there were developed the empirical formulae for estimation of hydrodynamic drag and torque acting on locked screw propeller. Supplementary CFD computations were carried out in order to prove the applicability of the formulae to modern moderately skewed screw propellers.

The best location for proximal locking screw for femur interlocking nailing: A biomechanical study

Directory of Open Access Journals (Sweden)

Ahmet A Karaarslan

2016-01-01

Conclusion: According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels. To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.

The improvement of the edge screw connection in OSB and conventional particleboard

Directory of Open Access Journals (Sweden)

Popović Mlađan

2006-01-01

Full Text Available This work presents the method for improvement of direct screw connection performance in conventional particleboard (PB and oriented strand board (OSB. It is conceived on adhesive insertion into the pilot hole prior to embedment of the screw. The tests were carried out on the PB and OSB, both presenting interior boards and with the same nominal thickness of 18 mm. Particleboard screws of the 5 mm in diameter were inserted in the edge of the board. Pilot hole diameters were 2,5 mm and 3,0 mm and the depth of embedment was 30 mm for all tests. The chosen PVAc adhesive (type 3 with the addition of wood flour as consolidator in the range from 3-10% was inserted into pilot-hole. Tests were also obtained after consequent reassembly of the screw connection in order to examine the ratio of loss in withdrawal forces in such case. It was found that the insertion of PVAc adhesive into the pilot hole and the addition of wood flour have the positive effects on the screw withdrawal force in the tested boards.

Design of three-dimensional visualization based on the posterior lumbar pedicle screw fixation

Directory of Open Access Journals (Sweden)

Kai XU

2011-09-01

Full Text Available Objective To establish a three-dimensional visualization model of posterior lumbar pedicle screw fixation.Methods A patient with lumbar intervertebral disc hernia and another patient with compression fracture of lumbar vertebra were involved in the present study.Both patients underwent multi-slice spiral CT scan before and after lumbar pedicle screw fixation.The degree of preoperative vertebral compression,vertebral morphology before and after surgery,postoperative pedicle screw position,and decompression effects were observed.The original data of the multi-slice spiral CT were inputted into the computer.The three-dimensional reconstructed images of the lumbar and implanted screws were obtained using the software Amira 4.1 to show the three-dimensional shape of the lumbar vertebrae before and after surgery and the location of the implanted screws.Results The morphology and structure of the lumbar vertebrae before and after surgery and of the implanted screws were reconstructed using the digital navigation platform.The reconstructed 3D images could be displayed in multicolor,transparent,or arbitrary combinations.In the 3D surface reconstruction images,the location and structure of the implanted screws could be clearly observed,and the decompression of the spinal cord or nerve roots and the severity of the fracture and the compression of lumbar vertebrae could be fully evaluated.The reconstructed images before operation revealed the position of the vertebral pedicles and provided reference for intraoperative localization.Conclusions The three-dimensional computerized reconstructions of lumbar pedicle screw fixation may be valuable in basic research,clinical experiment,and surgical planning.The software Amira is one of the bases of three-dimensional reconstruction.

A computational study on the effect of fracture intrusion distance in three- and four-part trochanteric fractures treated with Gamma nail and sliding hip screw.

Science.gov (United States)

Goffin, Jérôme M; Pankaj, Pankaj; Simpson, A Hamish

2014-01-01

Using finite element analysis, the behaviors of the Gamma nail and the sliding hip screw (SHS) were compared in an osteoporotic bone model for the fixation of three- and four-part trochanteric fractures (31-A2 in the AO classification, types IV and V in Evans' classification). The size of the medial fragment was varied based on clinical data, and the case of a fractured greater trochanter was also considered. Our results showed that for Evans' type V stabilized with a Gamma nail and for Evans' types IV and V with the SHS, cancellous bone around the lag screw is susceptible to yielding, thus indicating a risk of cut-out. The volume of bone susceptible to yielding increases with an increase in size of the medial fragment. Conversely, Evans' type IV with a Gamma nail was not predicted to cut out. Our findings suggest that future clinical trials investigating fixation of unstable proximal fractures should include the size of the medial fragment and the integrity of the greater trochanter as covariables and be powered to evaluate whether intramedullary devices are superior to SHSs for Evans' type IV fractures and inferior/equivalent for type V. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Bone anchors or interference screws? A biomechanical evaluation for autograft ankle stabilization.

Science.gov (United States)

Jeys, Lee; Korrosis, Sotiris; Stewart, Todd; Harris, Nicholas J

2004-01-01

Autograft stabilization uses free semitendinosus tendon grafts to anatomically reconstruct the anterior talofibular ligament. Study aims were to evaluate the biomechanical properties of Mitek GII anchors compared with the Arthrex Bio-Tenodesis Screw for free tendon reconstruction of the anterior talofibular ligament. There are no differences in load to failure and percentage specimen elongation at failure between the 2 methods. Controlled laboratory study using porcine models. Sixty porcine tendon constructs were failure tested. Re-creating the pull of the anterior talofibular ligament, loads were applied at 70 degrees to the bones. Thirty-six tendons were fixed to porcine tali and tested using a single pull to failure; 10 were secured with anchors and No. 2 Ethibond, 10 with anchors and FiberWire, 10 with screws and Fiberwire, and 6 with partially gripped screws. Cyclic preloading was conducted on 6 tendons fixed by anchors and on 6 tendons fixed by screws before failure testing. Two groups of 6 components fixed to the fibula were also tested. The talus single-pull anchor group produced a mean load of 114 N and elongation of 37% at failure. The talus single-pull screw group produced a mean load of 227 N and elongation of 22% at failure (P anchors. The improved biomechanics of interference screws suggests that these may be more suited to in vivo reconstruction of the anterior talofibular ligament than are bone anchors.

To retain or remove the syndesmotic screw: a review of literature

NARCIS (Netherlands)

Schepers, T.

2011-01-01

Syndesmotic positioning screws are frequently placed in unstable ankle fractures. Many facets of adequate placement techniques have been the subject of various studies. Whether or not the syndesmosis screw should be removed prior to weight-bearing is still debated. In this study, the recent

Intra-operative computer navigation guided cervical pedicle screw insertion in thirty-three complex cervical spine deformities

Directory of Open Access Journals (Sweden)

S Rajasekaran

2010-01-01

Full Text Available Background: Cervical pedicle screw fixation is challenging due to the small osseous morphometrics and the close proximity of neurovascular elements. Computer navigation has been reported to improve the accuracy of pedicle screw placement. There are very few studies assessing its efficacy in the presence of deformity. Also cervical pedicle screw insertion in children has not been described before. We evaluated the safety and accuracy of Iso-C 3D-navigated pedicle screws in the deformed cervical spine. Materials and Methods: Thirty-three patients including 15 children formed the study group. One hundred and forty-five cervical pedicle screws were inserted using Iso-C 3D-based computer navigation in patients undergoing cervical spine stabilization for craniovertebral junction anomalies, cervico-thoracic deformities and cervical instabilities due to trauma, post-surgery and degenerative disorders. The accuracy and containment of screw placement was assessed from postoperative computerized tomography scans. Results: One hundred and thirty (89.7% screws were well contained inside the pedicles. Nine (6.1% Type A and six (4.2% Type B pedicle breaches were observed. In 136 levels, the screws were inserted in the classical description of pedicle screw application and in nine deformed vertebra, the screws were inserted in a non-classical fashion, taking purchase of the best bone stock. None of them had a critical breach. No patient had any neurovascular complications. Conclusion: Iso-C navigation improves the safety and accuracy of pedicle screw insertion and is not only successful in achieving secure pedicle fixation but also in identifying the best available bone stock for three-column bone fixation in altered anatomy. The advantages conferred by cervical pedicle screws can be extended to the pediatric population also.

Ball tip method for thoracic pedicle screw placement in patients with adolescent idiopathic scoliosis

International Nuclear Information System (INIS)

Watanabe, Kota; Matsumoto, Morio; Iizuka, Shingo

2008-01-01

The purpose of this study was to evaluate the efficacy of ball tip method for thoracic pedicle screw placements in idiopathic scoliosis patients. 24 patients with adolescent idiopathic scoliosis were included in this study. Conventional method was performed in 12 patients. Ball tip method was performed in 12 patients. Accuracy of the pedicle screw placement was evaluated based on the postoperative CT. In the ball tip method, a probe which was consisted of ball tip with flexible shaft was used. After removing of cortical bone at a starting point, the probe was inserted manually or sometimes with gently tapping by hammer. During the maneuver, the probe will gradually progress into cancellous bone in the pedicle, without perforating cortical bone in the pedicle. Following expansion of the hole by a rigid gear shift probe, screw was placed in the pedicle. 65.1% of screws were located within pedicle in the conventional group and 86.5% in the ball tip group. 5.3% of screws were located out of pedicle within 2 mm in the conventional group and 8.2% in the ball tip group. 15.8% of screws were located out of pedicle beyond 2 mm and 1.8% in the ball tip group. The ball tip method enhanced the accuracy of thoracic pedicle screw placements in adolescent idiopathic scoliosis patients. The ball tip method may be effective for accurate pedicle screw placement in patients with adolescent idiopathic scoliosis. (author)

Do subjective symptoms predict our perception of jet-lag?

Science.gov (United States)

Waterhouse, J; Edwards, B; Nevill, A; Atkinson, G; Reilly, T; Davies, P; Godfrey, R

2000-10-01

A total of 39 subjects were studied after a flight from the UK to either Sydney or Brisbane (10 time-zones to the east). Subjects varied widely in their age, their athletic ability, whether or not they were taking melatonin, and in their objectives when in Australia. For the first 6 days after arrival, subjects scored their jet-lag five times per day and other subjective variables up to five times per day, using visual analogue scales. For jet-lag, the scale was labelled 0 = no jet-lag to 10 = very bad jet-lag; the extremes of the other scales were labelled - 5 and + 5, indicating marked changes compared with normal, and the centrepoint was labelled 0 indicating 'normal'. Mean daily values for jet-lag and fatigue were initially high (+ 3.65 +/- 0.35 and + 1.55 +/- 0.22 on day 1, respectively) and fell progressively on subsequent days, but were still raised significantly (p concentration and motivation, and rises in irritability and nocturnal wakings, had recovered by day 4 or earlier, and bowel activity was less frequent, with harder stools, on days 1 and 2 only. Also, on day 1, there was a decrease in the ease of getting to sleep (- 1.33 +/- 0.55), but this changed to an increase from day 2 onwards (for example, + 0.75 +/- 0.25 on day 6). Stepwise regression analysis was used to investigate predictors of jet-lag. The severity of jet-lag at all the times that were measured was strongly predicted by fatigue ratings made at the same time. Its severity at 08:00 h was predicted by an earlier time of waking, by feeling less alert 30 min after waking and, marginally, by the number of waking episodes. Jet-lag at 12:00 and 16:00 h was strongly predicted by a fall of concentration at these times; jet-lag at mealtimes (12:00, 16:00 and 20:00 h) was predicted by the amount of feeling bloated. Such results complicate an exact interpretation that can be placed on an assessment of a global term such as jet-lag, particularly if the assessment is made only once per day.

Recent trends for drug lag in clinical development of oncology drugs in Japan: does the oncology drug lag still exist in Japan?

Science.gov (United States)

Maeda, Hideki; Kurokawa, Tatsuo

2015-12-01

This study exhaustively and historically investigated the status of drug lag for oncology drugs approved in Japan. We comprehensively investigated oncology drugs approved in Japan between April 2001 and July 2014, using publicly available information. We also examined changes in the status of drug lag between Japan and the United States, as well as factors influencing drug lag. This study included 120 applications for approval of oncology drugs in Japan. The median difference over a 13-year period in the approval date between the United States and Japan was 875 days (29.2 months). This figure peaked in 2002, and showed a tendency to decline gradually each year thereafter. In 2014, the median approval lag was 281 days (9.4 months). Multiple regression analysis identified the following potential factors that reduce drug lag: "Japan's participation in global clinical trials"; "bridging strategies"; "designation of priority review in Japan"; and "molecularly targeted drugs". From 2001 to 2014, molecularly targeted drugs emerged as the predominant oncology drug, and the method of development has changed from full development in Japan or bridging strategy to global simultaneous development by Japan's taking part in global clinical trials. In line with these changes, the drug lag between the United States and Japan has significantly reduced to less than 1 year.

Computed tomography fluoroscopy-guided placement of iliosacral screws in patients with unstable posterior pelvic fractures

International Nuclear Information System (INIS)

Iguchi, Toshihiro; Ogawa, Ken-Ichi; Doi, Takeshi; Munetomo, Kazuo; Miyasho, Koji; Hiraki, Takao; Kanazawa, Susumu; Ozaki, Toshifumi

2010-01-01

The purpose of this study was to evaluate retrospectively the safety and effectiveness of the computed tomography (CT) fluoroscopy-guided placement of iliosacral screws in patients with unstable posterior pelvic fractures. Six patients (four women and two men; mean age 55.8 years; range 35-77 years) with unstable posterior pelvic fractures underwent iliosacral screw placement under CT fluoroscopy guidance between November 2007 and August 2008. Unstable pelvic ring injury (AO types B and C) was the indication for this procedure. In all the six patients except one, CT fluoroscopy-guided placement had been technically successful. In one patient, a second screw had been inserted, with a tilt to the caudal site, and slightly advanced into the extrasacral body; afterward, it could be exchanged safely for a shorter screw. Five patients and one patient underwent placement of two screws and one screw, respectively. The mean duration of the procedure was 15.0 min (range 9-30 min) per screw; the duration was 12.3 min and 18.2 min for the first and second screws, respectively. No complications requiring treatment occurred during or after the procedure. The mean clinical and radiologic follow-up period was 14 months (range 6-21 months). All pelvic injuries had healed satisfactorily, without complication, and all patients are now doing well clinically and can walk. CT fluoroscopy-guided placement of iliosacral screws is a safe and effective treatment in patients with unstable posterior pelvic fractures. (orig.)

Virtual surgery simulation versus traditional approaches in training of residents in cervical pedicle screw placement.

Science.gov (United States)

Hou, Yang; Shi, Jiangang; Lin, Yanping; Chen, Huajiang; Yuan, Wen

2018-06-01

The cervical screw placement is one of the most difficult procedures in spine surgery, which often needs a long period of repeated practices and could cause screw placement-related complications. We performed this cadaver study to investigate the effectiveness of virtual surgical training system (VSTS) on cervical pedicle screw instrumentation for residents. A total of ten novice residents were randomly assigned to two groups: the simulation training (ST) group (n = 5) and control group (n = 5). The ST group received a surgical training of cervical pedicle screw placement on VSTS and the control group was given an introductory teaching session before cadaver test. Ten fresh adult spine specimens including 6 males and 4 females were collected, and were randomly allocated to the two groups. The bilateral C3-C6 pedicle screw instrumentation was performed in the specimens of the two groups, respectively. After instrumentation, screw positions of the two groups were evaluated by image examinations. There was significantly statistical difference in screw penetration rates between the ST (10%) and control group (62.5%, P VSTS as an advanced training tool exhibited promising effects on improving performance of novice residents in cervical pedicle screw placement compared with the traditional teaching methods.

On the phase lag of turbulent dissipation in rotating tidal flows

Science.gov (United States)

Zhang, Qianjiang; Wu, Jiaxue

2018-03-01

Field observations of rotating tidal flows in a shallow tidally swept sea reveal that a notable phase lag of both shear production and turbulent dissipation increases with height above the seafloor. These vertical delays of turbulent quantities are approximately equivalent in magnitude to that of squared mean shear. The shear production approximately equals turbulent dissipation over the phase-lag column, and thus a main mechanism of phase lag of dissipation is mean shear, rather than vertical diffusion of turbulent kinetic energy. By relating the phase lag of dissipation to that of the mean shear, a simple formulation with constant eddy viscosity is developed to describe the phase lag in rotating tidal flows. An analytical solution indicates that the phase lag increases linearly with height subjected to a combined effect of tidal frequency, Coriolis parameter and eddy viscosity. The vertical diffusion of momentum associated with eddy viscosity produces the phase lag of squared mean shear, and resultant delay of turbulent quantities. Its magnitude is inhibited by Earth's rotation. Furthermore, a theoretical formulation of the phase lag with a parabolic eddy viscosity profile can be constructed. A first-order approximation of this formulation is still a linear function of height, and its magnitude is approximately 0.8 times that with constant viscosity. Finally, the theoretical solutions of phase lag with realistic viscosity can be satisfactorily justified by realistic phase lags of dissipation.

Experimental results of single screw mechanical tests: a follow-up to SAND2005-6036.

Energy Technology Data Exchange (ETDEWEB)

Lee, Sandwook; Lee, Kenneth L.; Korellis, John S.; McFadden, Sam X.

2006-08-01

The work reported here was conducted to address issues raised regarding mechanical testing of attachment screws described in SAND2005-6036, as well as to increase the understanding of screw behavior through additional testing. Efforts were made to evaluate fixture modifications and address issues of interest, including: fabrication of 45{sup o} test fixtures, measurement of the frictional load from the angled fixture guide, employment of electromechanical displacement transducers, development of a single-shear test, and study the affect of thread start orientation on single-shear behavior. A286 and 302HQ, No.10-32 socket-head cap screws were tested having orientations with respect to the primary loading axis of 0{sup 0}, 45{sup o}, 60{sup o}, 75{sup o} and 90{sup o} at stroke speeds 0,001 and 10 in/sec. The frictional load resulting from the angled screw fixture guide was insignificant. Load-displacement curves of A286 screws did not show a minimum value in displacement to failure (DTF) for 60{sup o} shear tests. Tests of 302HQ screws did not produce a consistent trend in DTF with load angle. The effect of displacement rate on DTF became larger as shear angle increased for both A286 and 302HQ screws.

[Open double-row rotator cuff repair using the LASA-DR screw].

Science.gov (United States)

Schoch, C; Geyer, S; Geyer, M

2016-02-01

Safe and cost-effective rotator-cuff repair. All types of rotator cuff lesions. Frozen shoulder, rotator cuff mass defect, defect arthropathy. Extensive four-point fixation on the bony footprint is performed using the double-row lateral augmentation screw anchor (LASA-DR) with high biomechanical stability. Following mobilization of the tendons, these are refixed in the desired configuration first medially and then laterally. To this end, two drilling channels (footprint and lateral tubercle) are created for each screw. Using the shuttle technique, a suture anchor screw is reinforced with up to four pairs of threads. The medial row is then pierced and tied, and the sutures that have been left long are tied laterally around the screw heads (double row). 4 Weeks abduction pillow, resulting in passive physiotherapy, followed by initiation of active assisted physiotherapy. Full weight-bearing after 4-6 months. Prospective analysis of 35 consecutive Bateman-III lesions with excellent results and low rerupture rate (6%).

Deformations of the spin currents by topological screw dislocation and cosmic dispiration

International Nuclear Information System (INIS)

Wang, Jianhua; Ma, Kai; Li, Kang; Fan, Huawei

2015-01-01

We study the spin currents induced by topological screw dislocation and cosmic dispiration. By using the extended Drude model, we find that the spin dependent forces are modified by the nontrivial geometry. For the topological screw dislocation, only the direction of spin current is bent by deforming the spin polarization vector. In contrast, the force induced by cosmic dispiration could affect both the direction and magnitude of the spin current. As a consequence, the spin-Hall conductivity does not receive corrections from screw dislocation.

Deformations of the spin currents by topological screw dislocation and cosmic dispiration

Energy Technology Data Exchange (ETDEWEB)

Wang, Jianhua [School of Physics Science, Shaanxi University of Technology, Hanzhong 723000, Shaanxi (China); Ma, Kai, E-mail: makainca@gmail.com [School of Physics Science, Shaanxi University of Technology, Hanzhong 723000, Shaanxi (China); Li, Kang [Department of Physics, Hangzhou Normal University, Hangzhou 310036, Zhejiang (China); Fan, Huawei [School of Physics and Information Technology, Shaanxi Normal University, Xian 710000, Shaanxi (China)

2015-11-15

We study the spin currents induced by topological screw dislocation and cosmic dispiration. By using the extended Drude model, we find that the spin dependent forces are modified by the nontrivial geometry. For the topological screw dislocation, only the direction of spin current is bent by deforming the spin polarization vector. In contrast, the force induced by cosmic dispiration could affect both the direction and magnitude of the spin current. As a consequence, the spin-Hall conductivity does not receive corrections from screw dislocation.

Parameters Affecting the Extraction Process of Jatropha curcas Oil Using a Single Screw Extruder

Directory of Open Access Journals (Sweden)

Ali Nurrakhmad Siregar

2015-07-01

Full Text Available The most commonly used technique to separate oil and cake from J. curcas seeds is mechanical extraction. It uses simple tools such as a piston and a screw extruder to produce high pressure, driven by hand or by engine. A single screw extruder has one screw rotating inside the barrel and materials simultaneously flow from the feed to the die zone. The highest oil yield can be obtained by a well-designed oil press as well as finding the optimum conditions for all parameters involved during the extraction process. The influence of the parameters in a single screw extruder was studied using finite element analysis and computational fluid dynamics simulation with ANSYS POLYFLOW. The research focused on predicting the velocity, pressure and shear rate in the metering section that influenced the screw rotational speed and mass flow rate. The obtained results revealed that increasing the screw rotational speed will increase the pressure, velocity and shear rate. Meanwhile, increasing the mass flow rate results in decreasing the pressure while the velocity and shear rate remain constant.

Kinetic analysis of elastomeric lag damper for helicopter rotors

Science.gov (United States)

Liu, Yafang; Wang, Jidong; Tong, Yan

2018-02-01

The elastomeric lag dampers suppress the ground resonance and air resonance that play a significant role in the stability of the helicopter. In this paper, elastomeric lag damper which is made from silicone rubber is built. And a series of experiments are conducted on this elastomeric lag damper. The stress-strain curves of elastomeric lag dampers employed shear forces at different frequency are obtained. And a finite element model is established based on Burgers model. The result of simulation and tests shows that the simple, linear model will yield good predictions of damper energy dissipation and it is adequate for predicting the stress-strain hysteresis loop within the operating frequency and a small-amplitude oscillation.

Influence of bacterial colonization of the healing screws on peri-implant tissue

Directory of Open Access Journals (Sweden)

Simonetta D'Ercole

2013-06-01

Conclusion: The healing screws left in situ for a period of 90 days caused a peri-implant inflammation and the presence of periodontal pathogenic bacteria in the peri-implant sulcus, due to the plaque accumulation on screw surfaces.

GHRH excess and blockade in X-LAG syndrome.

Science.gov (United States)

Daly, Adrian F; Lysy, Philippe A; Desfilles, Céline; Rostomyan, Liliya; Mohamed, Amira; Caberg, Jean-Hubert; Raverot, Veronique; Castermans, Emilie; Marbaix, Etienne; Maiter, Dominique; Brunelle, Chloe; Trivellin, Giampaolo; Stratakis, Constantine A; Bours, Vincent; Raftopoulos, Christian; Beauloye, Veronique; Barlier, Anne; Beckers, Albert

2016-03-01

X-linked acrogigantism (X-LAG) syndrome is a newly described form of inheritable pituitary gigantism that begins in early childhood and is usually associated with markedly elevated GH and prolactin secretion by mixed pituitary adenomas/hyperplasia. Microduplications on chromosome Xq26.3 including the GPR101 gene cause X-LAG syndrome. In individual cases random GHRH levels have been elevated. We performed a series of hormonal profiles in a young female sporadic X-LAG syndrome patient and subsequently undertook in vitro studies of primary pituitary tumor culture following neurosurgical resection. The patient demonstrated consistently elevated circulating GHRH levels throughout preoperative testing, which was accompanied by marked GH and prolactin hypersecretion; GH demonstrated a paradoxical increase following TRH administration. In vitro, the pituitary cells showed baseline GH and prolactin release that was further stimulated by GHRH administration. Co-incubation with GHRH and the GHRH receptor antagonist, acetyl-(d-Arg(2))-GHRH (1-29) amide, blocked the GHRH-induced GH stimulation; the GHRH receptor antagonist alone significantly reduced GH release. Pasireotide, but not octreotide, inhibited GH secretion. A ghrelin receptor agonist and an inverse agonist led to modest, statistically significant increases and decreases in GH secretion, respectively. GHRH hypersecretion can accompany the pituitary abnormalities seen in X-LAG syndrome. These data suggest that the pathology of X-LAG syndrome may include hypothalamic dysregulation of GHRH secretion, which is in keeping with localization of GPR101 in the hypothalamus. Therapeutic blockade of GHRH secretion could represent a way to target the marked hormonal hypersecretion and overgrowth that characterizes X-LAG syndrome. © 2016 Society for Endocrinology.

THE DESIGN, FABRICATION AND PRELIMINARY TESTING OF AN INDIGENOUS SINGLE SCREW EXTRUDER

Directory of Open Access Journals (Sweden)

FOLASAYO T. FAYOSE

2017-10-01

Full Text Available Developing countries including Nigeria have become dumping grounds of unserviceable and broken down imported machineries because of poor adaptation. Detailed study and design of machines to suit local conditions will prevent poor adaptation of imported machines and high initial costs. In this study, a single screw starch extruder was designed, fabricated and tested using locally available materials. The extruder is the dry type and it has 27.12 kg/s capacity, a compression ratio of 4.5: 1 and is powered by a 5.5 kW electric motor. It consists of a hopper, feeding screw, extruder screw rotating in a barrel and variable die, all made of stainless steel. A unit of the machine costs N 470, 390.00.00 as at April 2015. When used to process cassava flour, a maximum temperature of 114°C was attained through viscous dissipation, up to an actual screw speed of 98.96 rpm (1.65 Hz and extruder efficiency of 64%. Barrel temperature varied directly with extrusion time in a polynomial trend while actual extruder screw speed and efficiency varied inversely with extrusion time and it is best fitted with a polynomial trend.

Using three-dimensional rapid prototyping in the design and development of orthopaedic screws in standardised pull-out tests.

Science.gov (United States)

Leslie, Laura Jane; Connolly, Ashley; Swadener, John G; Junaid, Sarah; Theivendran, Kanthan; Deshmukh, Subodh C

2018-05-01

The majority of orthopaedic screws are designed, tested and manufactured by existing orthopaedics companies and are predominantly developed with healthy bone in mind. The timescales and costs involved in the development of a new screw design, for example, for osteoporotic bone, are high. In this study, standard wood screws were used to analyse the concept of using three-dimensional printing, or rapid prototyping, as a viable stage of development in the design of a new bone screw. Six wood screws were reverse engineered and printed in polymeric material using stereolithography. Three of the designs were also printed in Ti6Al4V using direct metal laser sintering; however, these were not of sufficient quality to test further. Both the original metal screws (metal) and polymeric rapid prototyping screws were then tested using standard pull-out tests from low-density polyurethane blocks (Sawbones). Results showed the highest pull-out strengths for screws with the longest thread length and the smallest inner diameter. Of the six screw designs tested, five showed no more than a 17% variance between the metal and rapid prototyping results. A similar pattern of results was shown between the screw designs for both the metal and rapid prototyping screws in five of the six cases. While not producing fully comparable pull-out results to orthopaedic screws, the results from this study do provide evidence of the potential usefulness and cost-effectiveness of rapid prototyping in the early stages of design and testing of orthopaedic screws.

Complications and fixation techniques of trochanteric fractures with the TARGON(®) PF.

Science.gov (United States)

Takigawa, Naohide; Moriuchi, Hiromitsu; Abe, Muneki; Yasui, Kenji; Eshiro, Hisako; Kinoshita, Mitsuo

2014-01-01

The purpose of this study was to analyse clinical results of elderly patients with trochanteric fractures that were treated with use of TARGON(®) PF nail. Overall, 494 patients (113 males) were available for this study. On the basis of Jensen classification, there were 76 cases in type I, 164 cases in type II, 70 in type III, 129 in type IV and 55 in type V. (1) Sliding amount of lag screw in relation to the Jensen classification, (2) sliding amount of lag screw according to the Ikuta's classification that categorises the reduction in lateral view in three, Subtype A, Subtype N and Subtype P, (3) sliding amount of lag screw in correlation between Jensen classification and Ikuta's classification and (4) postoperative complications (9 cases; 1.7%) were assessed. Cut-out and back-out cases were seen in 6 cases (1.1%), and these severe complications were evaluated in details. In correlation between Jensen classification and Ikuta's classification, the excessive sliding of lag screw was prominent with the Subtype P, which was preoperatively in Jensen type III or V. Cut-out or back-out cases were caused either from (1) Subtype P that were preoperatively Jensen types III or V, or from (2) the fracture where there was bony defect anteriorly. Therefore, special care must be taken for these types. Copyright © 2013 Elsevier Ltd. All rights reserved.

Development of a high speed extrusion concept using a floating screw sleeve for solid-melt-separation

Science.gov (United States)

Karrenberg, Gregor; Wortberg, Johannes

2015-05-01

The High-Speed-S-Truder with floating screw sleeve is an alternative extrusion concept with solid-melt-separation. A fairly conventional 35 mm screw with a length of 21 D, which is accelerated by a 75 kW gearless, water cooled synchronous drive, conveys the resin into a 60 mm screw sleeve with a length of 10 D. Inside the sleeve the material is plasticizied and discharged into the outer screw channel of the sleeve through radial bores. Only the solid bed remains inside. The development of a melt pool - and thus a decrease of the plasticizing capacity - is avoided. The sleeve is rotated by drag forces only (approximately 10 - 15 % of the screw speed). Due to the low speed of the screw sleeve molten material is conveyed to a 4 D Dynamic Mixing Ring in a gentle manner. The DMRs floating ring and the screw sleeve are directly coupled. The granules in the screw channel are stopped by a barrier on the screw in front of the mixing device. So nearly no unmelted material can pass the system. For temperature management in the plastification and mixing zone a 3-zone heating/air-cooling system is used. Various kinds of experiments with the High-Speed S-Truder were conducted. Reachable throughputs with different types of material (LDPE, LLDPE, PP, PS) have been tested. Also three screw geometries, which are mainly varying in the channel depth, were compared. Experimental results and theoretical background will be described in this paper.

Increase of operational reliability and durability of square sectoral working bodies of flexible screw conveyors

Directory of Open Access Journals (Sweden)

O.L. Lyashuk

2017-12-01

Full Text Available The construction of the device for guiding screw sectional working bodies of increased operational reliability and durability and the method of determination of the force of guiding the design parameters are given. Two main methods of manufacturing screw mechanisms of machines of various service purposes were investigated and it was established that twisted screws, in terms of their strength and performance, considerably exceed rolling stock. The design of the device for manufacturing screw working bodies of conveyors by means of cutting by periodic and continuous methods, as the most reliable in operation, is developed. The specifics of their work are due to various operations of technological processes, as well as physical and mechanical properties of goods, determine the nomenclature and design parameters of screw mechanisms (SM. In studying the processes of forming screw spirals, the basic precision characteristics of the methods of drilling and rolling are established. A comparative study of two main methods in terms of their operational and durable capabilities has been carried out. An important factor determining the reliability and durability of a screw is the difference in the thickness of the inner and outer edges.

Investigation of a Ball Screw Feed Drive System Based on Dynamic Modeling for Motion Control

Directory of Open Access Journals (Sweden)

Yi-Cheng Huang

2017-06-01

Full Text Available This paper examines the frequency response relationship between the ball screw nut preload, ball screw torsional stiffness variations and table mass effect for a single-axis feed drive system. Identification for the frequency response of an industrial ball screw drive system is very important for the precision motion when the vibration modes of the system are critical for controller design. In this study, there is translation and rotation modes of a ball screw feed drive system when positioning table is actuated by a servo motor. A lumped dynamic model to study the ball nut preload variation and torsional stiffness of the ball screw drive system is derived first. The mathematical modeling and numerical simulation provide the information of peak frequency response as the different levels of ball nut preload, ball screw torsional stiffness and table mass. The trend of increasing preload will indicate the abrupt peak change in frequency response spectrum analysis in some mode shapes. This study provides an approach to investigate the dynamic frequency response of a ball screw drive system, which provides significant information for better control performance when precise motion control is concerned.

Clinical efficacy of bone cement injectable pedicle screw system combined with intervertebral fusion in treatment of lumbar spondylolysis and osteoporosis

Directory of Open Access Journals (Sweden)

Peng-yi DAI

2016-10-01

Full Text Available Objective 　To observe the therapeutic effect of bone cement injectable pedicle screw system combined with intervertebral fusion for lumbar spondylolysis and osteoporosis. Methods 　The clinical data were analyzed retrospectively of 21 patients with lumbar spondylolysis and osteoporosis who received treatment of bone cement injectable pedicle screw system and intervertebral fusion from Aug. 2013 to Nov. 2015. The 21 patients (9 males and 12 females aged from 60 to 80 years (mean 64 years old; 6 of them presented degenerative spondylolysis, 15 with isthmic spondylolisthesis; 2 cases had I degree slippage, 13 had Ⅱdegree slippage, 6 had Ⅲdegree slippage, and all the cases were unisegmental slippage including 9 cases in L4 and 12 cases in L5. Bone mineral density of lumbar vertebrae (L2-L5 was measured with dual-energy X-ray absorptiometry, and T values conforming to the diagnostic criteria of osteoporosis were less than or equal to -2.5; All patients were operated with whole lamina resection for decompression, bone cement injectable pedicle screws system implantation, propped open reduction and fixation intervertebral fusion. The clinical outcomes were determined by the radiographic evaluation including intervertebral height, height of intervertebral foramen, slip distance, slip rate and slip angle, and Oswestry disability index (ODI on preoperative, 3 months after operation and the end of the time, and the interbody fusion were followed up. Results 　Cerebrospinal fluid leakage of incision was observed in two cases after operation, compression and dressing to incision, Trendelenburg position, dehydration and other treatments were taken, and the stitches of incisions were taken out on schedule. Slips in the 21 patients were reset to different extent, and lumbar physiological curvatures were recovered. The intervertebral height and height of intervertebral foramen were obviously higher 3 months after operation than that before operation (P0

Non-symmetric approach to single-screw expander and compressor modeling

Science.gov (United States)

Ziviani, Davide; Groll, Eckhard A.; Braun, James E.; Horton, W. Travis; De Paepe, M.; van den Broek, M.

2017-08-01

Single-screw type volumetric machines are employed both as compressors in refrigeration systems and, more recently, as expanders in organic Rankine cycle (ORC) applications. The single-screw machine is characterized by having a central grooved rotor and two mating toothed starwheels that isolate the working chambers. One of the main features of such machine is related to the simultaneous occurrence of the compression or expansion processes on both sides of the main rotor which results in a more balanced loading on the main shaft bearings with respect to twin-screw machines. However, the meshing between starwheels and main rotor is a critical aspect as it heavily affects the volumetric performance of the machine. To allow flow interactions between the two sides of the rotor, a non-symmetric modelling approach has been established to obtain a more comprehensive model of the single-screw machine. The resulting mechanistic model includes in-chamber governing equations, leakage flow models, heat transfer mechanisms, viscous and mechanical losses. Forces and moments balances are used to estimate the loads on the main shaft bearings as well as on the starwheel bearings. An 11 kWe single-screw expander (SSE) adapted from an air compressor operating with R245fa as working fluid is used to validate the model. A total of 60 steady-steady points at four different rotational speeds have been collected to characterize the performance of the machine. The maximum electrical power output and overall isentropic efficiency measured were 7.31 kW and 51.91%, respectively.

Lags in the response of mountain plant communities to climate change

DEFF Research Database (Denmark)

Alexander, Jake M; Chalmandrier, Loïc; Lenoir, Jonathan

2018-01-01

Rapid climatic changes and increasing human influence at high elevations around the world will have profound impacts on mountain biodiversity. However, forecasts from statistical models (e.g. species distribution models) rarely consider that plant community changes could substantially lag behind...... plant species' spread along elevational gradients, "establishment lags" following their arrival in recipient communities, and "extinction lags" of resident species. Variation in lags is explained by variation among species in physiological and demographic responses, by effects of altered biotic...... turnover in future communities might lag behind simple expectations based on species' range shifts with unlimited dispersal. The model shows a combined contribution of altered biotic interactions and dispersal lags to plant community turnover along an elevational gradient following climate warming. Our...

[Basic laws of blood screw motion in human common carotid arteries].

Science.gov (United States)

Kulikov, V P; Kirsanov, R I

2008-08-01

The basic laws of blood screw motion in common carotid arteries in people were determined by means of modern ultrasound techniques for the first time. 92 healthy adults, aged 18-30, were examined. The blood flow in the middle one-third of common carotid arteries was registered by means of Color Doppler Imaging and impulse Doppler with the help of ultrasound Medison 8000EX scanner by linear transducer of 5-9 MHz. The steady registration of blood screw motion in both common carotid arteries in Color Doppler Imaging regimen was observed in 54.3 % of cases. The direction of screw stream rotation in most cases (54%) was multi-directed: in the right common carotid artery it was right, in the left common carotid artery--left (48%), and in 6% of cases it was reverse. For 46% of cases blood rotation in both common carotid arteries was one-directed (26%--right, 20%--left). The velocity parameters of rotation component of blood motion were determined, maximum velocity being 19.68 +/- 5.84 cm/sec, minimum--4.57 +/- 2.89 cm/sec, average--7.48 +/- 2.49 cm/sec, angular--10.7 +/- 2.49 sec(-1). The rated velocity of blood cells motion in screw motion with regard of screw current lines to the vessel vertical axis makes up from 158.67 +/- 32.79 to 224.39 +/- 46.37 cm/sec.

Comparison of 3D displacements of screw-retained zirconia implant crowns into implants with different internal connections with respect to screw tightening.

Science.gov (United States)

Rebeeah, Hanadi A; Yilmaz, Burak; Seidt, Jeremy D; McGlumphy, Edwin; Clelland, Nancy; Brantley, William

2018-01-01

Internal conical implant-abutment connections without horizontal platforms may lead to crown displacement during screw tightening and torque application. This displacement may affect the proximal contacts and occlusion of the definitive prosthesis. The purpose of this in vitro study was to evaluate the displacement of custom screw-retained zirconia single crowns into a recently introduced internal conical seal implant-abutment connection in 3D during hand and torque driver screw tightening. Stereolithic acrylic resin models were printed using computed tomography data from a patient missing the maxillary right central incisor. Two different internal connection implant systems (both ∼11.5 mm) were placed in the edentulous site in each model using a surgical guide. Five screw-retained single zirconia computer-aided design and computer-aided manufacturing (CAD-CAM) crowns were fabricated for each system. A pair of high-resolution digital cameras was used to record the relationship of the crown to the model. The crowns were tightened according to the manufacturers' specifications using a torque driver, and the cameras recorded their relative position again. Three-dimensional image correlation was used to measure and compare crown positions, first hand tightened and then torque driven. The displacement test was repeated 3 times for each crown. Commercial image correlation software was used to extract the data and compare the amount of displacement vertically, mesiodistally, and buccolingually. Repeated-measures ANOVA calculated the relative displacements for all 5 specimens for each implant for both crown screw hand tightening and after applied torque. A Student t test with Bonferroni correction was used for pairwise comparison of interest to determine statistical differences between the 2 implants (α=.05). The mean vertical displacements were statistically higher than the mean displacements in the mesiodistal and buccolingual directions for both implants

Screw compressor analysis from a vibration point-of-view

Science.gov (United States)

Hübel, D.; Žitek, P.

2017-09-01

Vibrations are a very typical feature of all compressors and are given great attention in the industry. The reason for this interest is primarily the negative influence that it can have on both the operating staff and the entire machine's service life. The purpose of this work is to describe the methodology of screw compressor analysis from a vibration point-of-view. This analysis is an essential part of the design of vibro-diagnostics of screw compressors with regard to their service life.

Research on the performance of water-injection twin screw compressor

International Nuclear Information System (INIS)

Li Jianfeng; Wu Huagen; Wang Bingming; Xing Ziwen; Shu Pengcheng

2009-01-01

Due to the development of the automotive fuel cell systems, the study on water-injection twin screw compressor has been aroused again. Twin screw compressors with water injection can be used to supply the clean compressed air for the Proton Exchange Membrane (PEM) fuel cell systems. In this research, a thermodynamic model of the working process of water-injection twin screw compressor was established based on the equations of conservation of mass and energy. The effects of internal leakage and air-water heat transfer were taken into account simultaneously in the present mathematical model. The experiments of the performance of a prototype compressor operating under various conditions were conducted to verify the model. The results show that the predictions of the model are in reasonable agreement with the experimental data.

Internally Heated Screw Pyrolysis Reactor (IHSPR) heat transfer performance study

Science.gov (United States)

Teo, S. H.; Gan, H. L.; Alias, A.; Gan, L. M.

2018-04-01

1.5 billion end-of-life tyres (ELT) were discarded globally each year and pyrolysis is considered the best solution to convert the ELT into valuable high energy-density products. Among all pyrolysis technologies, screw reactor is favourable. However, conventional screw reactor risks plugging issue due to its lacklustre heat transfer performance. An internally heated screw pyrolysis reactor (IHSPR) was developed by local renewable energy industry, which serves as the research subject for heat transfer performance study of this particular paper. Zero-load heating test (ZLHT) was first carried out to obtain the operational parameters of the reactor, followed by the one dimensional steady-state heat transfer analysis carried out using SolidWorks Flow Simulation 2016. Experiments with feed rate manipulations and pyrolysis products analyses were conducted last to conclude the study.

Lags in the response of mountain plant communities to climate change.

Science.gov (United States)

Alexander, Jake M; Chalmandrier, Loïc; Lenoir, Jonathan; Burgess, Treena I; Essl, Franz; Haider, Sylvia; Kueffer, Christoph; McDougall, Keith; Milbau, Ann; Nuñez, Martin A; Pauchard, Aníbal; Rabitsch, Wolfgang; Rew, Lisa J; Sanders, Nathan J; Pellissier, Loïc

2018-02-01

Rapid climatic changes and increasing human influence at high elevations around the world will have profound impacts on mountain biodiversity. However, forecasts from statistical models (e.g. species distribution models) rarely consider that plant community changes could substantially lag behind climatic changes, hindering our ability to make temporally realistic projections for the coming century. Indeed, the magnitudes of lags, and the relative importance of the different factors giving rise to them, remain poorly understood. We review evidence for three types of lag: "dispersal lags" affecting plant species' spread along elevational gradients, "establishment lags" following their arrival in recipient communities, and "extinction lags" of resident species. Variation in lags is explained by variation among species in physiological and demographic responses, by effects of altered biotic interactions, and by aspects of the physical environment. Of these, altered biotic interactions could contribute substantially to establishment and extinction lags, yet impacts of biotic interactions on range dynamics are poorly understood. We develop a mechanistic community model to illustrate how species turnover in future communities might lag behind simple expectations based on species' range shifts with unlimited dispersal. The model shows a combined contribution of altered biotic interactions and dispersal lags to plant community turnover along an elevational gradient following climate warming. Our review and simulation support the view that accounting for disequilibrium range dynamics will be essential for realistic forecasts of patterns of biodiversity under climate change, with implications for the conservation of mountain species and the ecosystem functions they provide. © 2017 John Wiley & Sons Ltd.

Biomechanical comparison of force levels in spinal instrumentation using monoaxial versus multi degree of freedom postloading pedicle screws.

Science.gov (United States)

Wang, Xiaoyu; Aubin, Carl-Eric; Crandall, Dennis; Labelle, Hubert

2011-01-15

biomechanical analysis and simulations of correction mechanisms and force levels during scoliosis instrumentation using two types of pedicle screws and primary correction maneuvers. to biomechanically analyze implant-vertebra and inter-vertebral forces during scoliosis correction, to address the hypothesis that multi degree of freedom (MDOF) postloading screws with a direct incremental segmental translation (DIST) correction technique significantly reduce the loads as compared with monoaxial (MA) tulip-top design screws with a rod derotation technique (RDT). MA screw is widely used for spinal instrumentation. The MDOF screw was introduced as a refinement of the correction philosophy based on multiaxial screws. The kinematics of the MDOF construct is fundamentally different and offers more degrees of freedom than that of the MA construct; however, a systematic comparison of their biomechanics has not been done so far. a biomechanical model was developed to simulate the instrumentation of six scoliotic patients, first with the MDOF screws and DIST. Then, the instrumentation with MA screws and RDT was simulated using the same cases. Thirty more simulations were done to study the force-level sensitivity to small implant placement variation. there was a small average difference of 7°, 5°, and 4° between the two simulated systems for the computed main thoracic Cobb angle, kyphosis, and apical axial rotation, respectively. On average, the mean, standard deviation (SD), and maximum values of the implant-vertebra forces for MDOF screws were 56%, 59%, and 59%, respectively, lower than those for the MA screws, while the intervertebral forces for the MDOF screws were 31%, 37%, and 36% lower, respectively. Under the same set of random small implant placement changes, the mean, SD, and maximum values of implant-vertebra force magnitude changes for MDOF screws were 93%, 92%, and 95%, respectively, lower than those for MA screws. with MDOF screws and DIST, it is possible for

Scapula fracture incidence in reverse total shoulder arthroplasty using screws above or below metaglene central cage: clinical and biomechanical outcomes.

Science.gov (United States)

Kennon, Justin C; Lu, Caroline; McGee-Lawrence, Meghan E; Crosby, Lynn A

2017-06-01

Reverse total shoulder arthroplasty (RTSA) is a viable treatment option for rotator cuff tear arthropathy but carries a complication risk of scapular fracture. We hypothesized that using screws above the central glenoid axis for metaglene fixation creates a stress riser contributing to increased scapula fracture incidence. Clinical type III scapular fracture incidence was determined with screw placement correlation: superior screw vs. screws placed exclusively below the glenoid midpoint. Cadaveric RTSA biomechanical modeling was employed to analyze scapular fractures. We reviewed 318 single-surgeon single-implant RTSAs with screw correlation to identify type III scapular fractures. Seventeen cadaveric scapula specimens were matched for bone mineral density, metaglenes implanted, and fixation with 2 screw configurations: inferior screws alone (group 1 INF ) vs. inferior screws with one additional superior screw (group 2 SUP ). Biomechanical load to failure was analyzed. Of 206 patients, 9 (4.4%) from the superior screw group experienced scapula fractures (type III); 0 fractures (0/112; 0%) were identified in the inferior screw group. Biomechanically, superior screw constructs (group 2 SUP ) demonstrated significantly (P < .05) lower load to failure (1077 N vs. 1970 N) compared with constructs with no superior screws (group 1 INF ). There was no significant age or bone mineral density discrepancy. Clinical scapular fracture incidence significantly decreased (P < .05) for patients with no screws placed above the central cage compared with patients with superior metaglene screws. Biomechanical modeling demonstrates significant construct compromise when screws are used above the central cage, fracturing at nearly half the ultimate load of the inferior screw constructs. We recommend use of inferior screws, all positioned below the central glenoid axis, unless necessary to stabilize the metaglene construct. Copyright © 2016 Journal of Shoulder and Elbow Surgery

Accuracy of navigated pedicle screw insertion by a junior spine surgeon without spinal surgery experience

International Nuclear Information System (INIS)

Yamazaki, Hironori; Kotani, Toshiaki; Motegi, Hiroyuki; Nemoto, Tetsuharu; Koshi, Takana; Nagahara, Ken; Minami, Syohei

2010-01-01

The purpose of this study was to investigate pedicle screw placement accuracy during navigated surgery by a junior spine surgeon who had no spinal surgery experience. A junior spine surgeon with no spinal surgery experience implanted a total of 137 pedicle screws by using a navigation system. Postoperative computerized tomography was performed to evaluate screw placement, and the pedicle perforation rate was 2.2%. There were no neurologic or vascular complications related to the pedicle screws. The results demonstrated that pedicle screws can be placed safely and effectively by a junior spine surgeon who has no spinal surgery experience when instructed by a senior spine surgeon. The results of this study suggest that navigation can be used as a surgical training tool for junior spine surgeons. (author)

Enhanced biocompatibility and osseointegration of calcium titanate coating on titanium screws in rabbit femur.

Science.gov (United States)

Wang, Zi-Li; He, Rong-Zhen; Tu, Bin; Cao, Xu; He, Jin-Shen; Xia, Han-Song; Liang, Chi; Zou, Min; Wu, Song; Wu, Zhen-Jun; Xiong, Kun

2017-06-01

This study aimed to examine the biocompatibility of calcium titanate (CaTiO 3 ) coating prepared by a simplified technique in an attempt to assess the potential of CaTiO 3 coating as an alternative to current implant coating materials. CaTiO 3 -coated titanium screws were implanted with hydroxyapatite (HA)-coated or uncoated titanium screws into medial and lateral femoral condyles of 48 New Zealand white rabbits. Imaging, histomorphometric and biomechanical analyses were employed to evaluate the osseointegration and biocompatibility 12 weeks after the implantation. Histology and scanning electron microscopy revealed that bone tissues surrounding the screws coated with CaTiO 3 were fully regenerated and they were also well integrated with the screws. An interfacial fibrous membrane layer, which was found in the HA coating group, was not noticeable between the bone tissues and CaTiO 3 -coated screws. X-ray imaging analysis showed in the CaTiO 3 coating group, there was a dense and tight binding between implants and the bone tissues; no radiation translucent zone was found surrounding the implants as well as no detachment of the coating and femoral condyle fracture. In contrast, uncoated screws exhibited a fibrous membrane layer, as evidenced by the detection of a radiation translucent zone between the implants and the bone tissues. Additionally, biomechanical testing revealed that the binding strength of CaTiO 3 coating with bone tissues was significantly higher than that of uncoated titanium screws, and was comparable to that of HA coating. The study demonstrated that CaTiO 3 coating in situ to titanium screws possesses great biocompatibility and osseointegration comparable to HA coating.

Edge screw withdrawal resistance in conventional particleboard and OSB: Influence of the particles type

Directory of Open Access Journals (Sweden)

Miljković Jovan

2007-01-01

Full Text Available This research was based on presumption that the changes in size and shape of wood particles are expected to have certain impact on the particleboard quality in general. Since the conventional particleboard (PB and oriented strand board (OSB were built of the quite diverse wood particles, they present interesting specimens in the comparison tests. In this work, the influence of the wood particles type on the edge screw holding performance of conventional particleboard and OSB was investigated. Those tests were obtained with the screw diameters of 4.0 mm, 4.5 mm and 5 mm. Depth of embedment was 30 mm for all tests and with the pilot-hole diameter kept in the range of 80-90% in respect of the screw root diameter. Additional tests of the thickness density profile and tensile strength perpendicular to the surface of the board were conducted. Since the middle layer structure of the particleboard embeds the screw body, both mentioned parameters are considered important in the aspect of the quality of the edge screw holding performance. In order to have further insight into the conformation of the middle layer the image survey was obtained on the split board section presenting the surface of the middle layer. Significant differences in the SWR performance of OSB and PB was recorded at all screw diameters. For the screw withdrawal tests parameters OSB samples showed 56-73% superior mean values then conventional PB. On the other hand, the OSB showed wider dispersions of measured withdrawal forces at all screw diameters, which might present some of the problems in certain engineering and project calculations.

Spectral evolution of GRBs with negative spectral lag using Fermi GBM observations

Science.gov (United States)

Chakrabarti, Arundhati; Chaudhury, Kishor; Sarkar, Samir K.; Bhadra, Arunava

2018-06-01

The positive spectral lag of Gamma Ray Bursts (GRBs) is often explained in terms of hard-to-soft spectral evolution of GRB pulses. While positive lags of GRBs is very common, there are few GRB pulses that exhibits negative spectral lags. In the present work we examine whether negative lags of GRBs also can be interpreted in terms of spectral evolution of GRB pulses or not. Using Fermi-GBM data, we identify two GRBs, GRB 090426C and GRB 150213A, with clean pulses that exhibit negative spectral lag. An indication of soft to hard transition has been noticed for the negative spectral lag events from the spectral evolution study. The implication of the present findings on the models of GRB spectral lags are discussed.

Percutaneous Cement-Augmented Screws Fixation in the Fractures of the Aging Spine: Is It the Solution?

Directory of Open Access Journals (Sweden)

Sébastien Pesenti

2014-01-01

Full Text Available Introduction. Management of elderly patients with thoracolumbar fractures is still challenging due to frequent osteoporosis and risk of screws pull-out. The aim of this study was to evaluate results of a percutaneous-only procedure to treat these fragile patients using cement-augmented screws. Methods. 12 patients diagnosed with a thoracolumbar fracture associated with an important loss of bone stock were included in this prospective study. Surgical procedure included systematically a percutaneous osteosynthesis using cemented fenestrated screws. When necessary, additional anterior support was performed using a kyphoplasty procedure. Clinical and radiographic evaluations were performed using CT scan. Results. On the whole series, 15 fractures were diagnosed and 96 cemented screws were inserted. The difference between the pre- and postoperative vertebral kyphosis was statistically significant (12.9° versus 4.4°, P=0.0006. No extrapedicular screw was reported and one patient was diagnosed with a cement-related pulmonary embolism. During follow-up period, no infectious complications, implant failures, or pull-out screws were noticed. Discussion. Aging spine is becoming an increasing public health issue. Management of these patients requires specific attention due to the augmented risk of complications. Using percutaneous-only screws fixation with cemented screw provides satisfactory results. A rigorous technique is mandatory in order to achieve best outcomes.

Design of Cold-Formed Steel Screw Connections with Gypsum Sheathing at Ambient and Elevated Temperatures

Directory of Open Access Journals (Sweden)

Wei Chen

2016-09-01

Full Text Available Load-bearing cold-formed steel (CFS walls sheathed with double layers of gypsum plasterboard on both sides have demonstrated good fire resistance and attracted increasing interest for use in mid-rise CFS structures. As the main connection method, screw connections between CFS and gypsum sheathing play an important role in both the structural design and fire resistance of this wall system. However, studies on the mechanical behavior of screw connections with double-layer gypsum sheathing are still limited. In this study, 200 monotonic tests of screw connections with single- or double-layer gypsum sheathing at both ambient and elevated temperatures were conducted. The failure of screw connections with double-layer gypsum sheathing in shear was different from that of single-layer gypsum sheathing connections at ambient temperature, and it could be described as the breaking of the loaded sheathing edge combined with significant screw tilting and the loaded sheathing edge flexing fracture. However, the screw tilting and flexing fracture of the loaded sheathing edge gradually disappear at elevated temperatures. In addition, the influence of the loaded edge distance, double-layer sheathing and elevated temperatures is discussed in detail with clear conclusions. A unified design formula for the shear strength of screw connections with gypsum sheathing is proposed for ambient and elevated temperatures with adequate accuracy. A simplified load–displacement model with the post-peak branch is developed to evaluate the load–displacement response of screw connections with gypsum sheathing at ambient and elevated temperatures.

In vivo degradation of a new concept of magnesium-based rivet-screws in the minipig mandibular bone

Energy Technology Data Exchange (ETDEWEB)

Schaller, Benoit [Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern (Switzerland); National Dental Centre Singapore, 168938 (Singapore); Saulacic, Nikola [Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern (Switzerland); Beck, Stefan, E-mail: SBECK2@its.jnj.com [Synthes Biomaterials, Eimattstr. 3, CH-4436 Oberdorf (Switzerland); Imwinkelried, Thomas [RMS Foundation, Bischmattstr. 12, CH-2544 Bettlach (Switzerland); Goh, Bee Tin [National Dental Centre Singapore, 168938 (Singapore); Nakahara, Ken [Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern (Switzerland); Hofstetter, Willy [Department of Clinical Research, University of Bern, CH-3010 Bern (Switzerland); Iizuka, Tateyuki [Department of Cranio-Maxillofacial Surgery, Inselspital, Bern University Hospital and University of Bern, CH-3010 Bern (Switzerland)

2016-12-01

Self-tapping of magnesium screws in hard bone may be a challenge due to the limited torsional strength of magnesium alloys in comparison with titanium. To avoid screw failure upon implantation, the new concept of a rivet-screw was applied to a WE43 magnesium alloy. Hollow cylinders with threads on the outside were expanded inside drill holes of minipig mandibles. During the expansion with a hexagonal mandrel, the threads engaged the surrounding bone and the inside of the screw transformed into a hexagonal screw drive to allow further screwing in or out of the implant. The in vivo degradation of the magnesium implants and the performance of the used coating were studied in a human standard-sized animal model. Four magnesium alloy rivet-screws were implanted in each mandible of 12 minipigs. Six animals received the plasmaelectrolytically coated magnesium alloy implants; another six received the uncoated magnesium alloy rivet-screws. Two further animals received one titanium rivet-screw each as control. In vivo radiologic examination was performed at one, four, and eight weeks. Euthanasia was performed for one group of seven animals (three animals with coated, three with uncoated magnesium alloy implants and one with titanium implant) at 12 weeks and for the remaining seven animals at 24 weeks. After euthanasia, micro-computed tomography and histological examination with histomorphometry were performed. Significantly less void formation as well as higher bone volume density (BV/TV) and bone-implant contact area (BIC) were measured around the coated implants compared to the uncoated ones. The surface coating was effective in delaying degradation despite plastic deformation. The results showed potential for further development of magnesium hollow coated screws for bone fixation. - Highlights: • A new concept of rivet screws as an alternative to classical screws is presented • The rivet screw concept was tested in vivo in a mini-pig pilot study • Un-coated and

In vivo degradation of a new concept of magnesium-based rivet-screws in the minipig mandibular bone

International Nuclear Information System (INIS)

Schaller, Benoit; Saulacic, Nikola; Beck, Stefan; Imwinkelried, Thomas; Goh, Bee Tin; Nakahara, Ken; Hofstetter, Willy; Iizuka, Tateyuki

2016-01-01

Self-tapping of magnesium screws in hard bone may be a challenge due to the limited torsional strength of magnesium alloys in comparison with titanium. To avoid screw failure upon implantation, the new concept of a rivet-screw was applied to a WE43 magnesium alloy. Hollow cylinders with threads on the outside were expanded inside drill holes of minipig mandibles. During the expansion with a hexagonal mandrel, the threads engaged the surrounding bone and the inside of the screw transformed into a hexagonal screw drive to allow further screwing in or out of the implant. The in vivo degradation of the magnesium implants and the performance of the used coating were studied in a human standard-sized animal model. Four magnesium alloy rivet-screws were implanted in each mandible of 12 minipigs. Six animals received the plasmaelectrolytically coated magnesium alloy implants; another six received the uncoated magnesium alloy rivet-screws. Two further animals received one titanium rivet-screw each as control. In vivo radiologic examination was performed at one, four, and eight weeks. Euthanasia was performed for one group of seven animals (three animals with coated, three with uncoated magnesium alloy implants and one with titanium implant) at 12 weeks and for the remaining seven animals at 24 weeks. After euthanasia, micro-computed tomography and histological examination with histomorphometry were performed. Significantly less void formation as well as higher bone volume density (BV/TV) and bone-implant contact area (BIC) were measured around the coated implants compared to the uncoated ones. The surface coating was effective in delaying degradation despite plastic deformation. The results showed potential for further development of magnesium hollow coated screws for bone fixation. - Highlights: • A new concept of rivet screws as an alternative to classical screws is presented • The rivet screw concept was tested in vivo in a mini-pig pilot study • Un-coated and

Screwing or unscrewing device for studs or bolls of big dimension

International Nuclear Information System (INIS)

Sevelinge, G.; Bourdonne, J.C.

1988-01-01

The device for screwing or unscrewing large studs or bolts has a system determining the optimun screwing position and orientation of the bolt, a variable speed bidirectional drive a pin holding the bolt axially and system compensating the weight of the bolt with an hydraulic jack with a pressure detector to which the drive is slaved [fr

On damping of screw dislocation bending vibrations in dissipative crystal: limiting cases

Science.gov (United States)

Dezhin, V. V.

2018-03-01

The expression for the generalized susceptibility of the dislocation obtained earlier was used. The electronic drag mechanism of dislocations is considered. The study of small dislocation oscillations was limited. The contribution of the attenuation of low-frequency bending screw dislocation vibrations to the overall coefficient of dynamic dislocation drag in the long-wave and short-wave limits is calculated. The damping of short-wave bending screw dislocation vibrations caused by an external action of an arbitrary frequency has been investigated. The contribution of long-wave bending screw dislocation vibrations damping in the total drag coefficient at an arbitrary frequency is found.

Chirality-controlled crystallization via screw dislocations.

Science.gov (United States)

Sung, Baeckkyoung; de la Cotte, Alexis; Grelet, Eric

2018-04-11

Chirality plays an important role in science from enantiomeric separation in chemistry to chiral plasmonics in nanotechnology. However, the understanding of chirality amplification from chiral building blocks to ordered helical superstructures remains a challenge. Here, we demonstrate that topological defects, such as screw dislocations, can drive the chirality transfer from particle to supramolecular structure level during the crystallization process. By using a model system of chiral particles, which enables direct imaging of single particle incorporation into growing crystals, we show that the crystallization kinetic pathway is the key parameter for monitoring, via the defects, the chirality amplification of the crystalline structures from racemic to predominantly homohelical. We provide an explanation based on the interplay between geometrical frustration, racemization induced by thermal fluctuations, and particle chirality. Our results demonstrate that screw dislocations not only promote the growth, but also control the chiral morphology and therefore the functionality of crystalline states.

Thermodynamic performance of multi-stage gradational lead screw vacuum pump

Science.gov (United States)

Zhao, Fan; Zhang, Shiwei; Sun, Kun; Zhang, Zhijun

2018-02-01

As a kind of dry mechanical vacuum pump, the twin-screw vacuum pump has an outstanding pumping performance during operation, widely used in the semiconductor industry. Compared with the constant lead screw (CLS) vacuum pump, the gradational lead screw (GLS) vacuum pump is more popularly applied in recent years. Nevertheless, not many comparative studies on the thermodynamic performance of GLS vacuum pump can be found in the literature. Our study focuses on one type of GLS vacuum pump, the multi-stage gradational lead screw (MGLS) vacuum pump, gives a detailed description of its construction and illustrates it with the drawing. Based on the structural analysis, the thermodynamic procedure is divided into four distinctive processes, including sucking process, transferring (compressing) process, backlashing process and exhausting process. The internal mechanism of each process is qualitatively illustrated and the mathematical expressions of seven thermodynamic parameters are given under the ideal situation. The performance curves of MGLS vacuum pump are plotted by MATLAB software and compared with those of the CLS vacuum pump in the same case. The results can well explain why the MGLS vacuum pump has more favorable pumping performance than the CLS vacuum pump in saving energy, reducing noise and heat dissipation.

A modified transcondylar screw to accommodate anatomical skull base variations.

Science.gov (United States)

Ghaly, R F; Lissounov, A

2017-01-01

Occipitocervical instability may be attributed to congenital, bony/ligamentous abnormalities, trauma, neoplasm, degenerative bone disease, and failed atlantoaxial fixation. Indications for occipitocervical fixation include the prevention of disabling pain, cranial nerve dysfunction, paralysis, or even sudden death. The screw trajectory for the modified transcondylar screw (mTCS) is optimally planned utilizing a three-dimensional skull reconstructed image. The modified mTCS technique is helpful where there is a loss of bone, such as after prior suboccipital craniotomy and/or an inadequate occipital condyle. The new proposed technique is similar to the classical transcondylar screw placement but follows a deeper course along the bony lip of foramen magnum toward clivus from a dorsolateral approach. The modified mTCS technique allows for direct visualization and, therefore, helps to avoid damage to the hypoglossal nerve and lateral aspect of brain stem.

The value of 18F-fluoride PET/CT in the assessment of screw loosening in patients after intervertebral fusion stabilization

International Nuclear Information System (INIS)

Seifen, Tanja; Rodrigues, Margarida; Rettenbacher, Lukas; Holzmannhofer, Johannes; Pirich, Christian; Piotrowski, Wolfgang; Mc Coy, Mark

2015-01-01

We evaluated 18 F-fluoride PET/CT for the diagnosis of screw loosening after intervertebral fusion stabilization and compared the results with those from functional radiography. A group of 59 patients with pain in the region of previous intervertebral fusion stabilization and suspicion of implant instability due to screw loosening were investigated with 18 F-fluoride PET/CT and functional radiography, 30.1 ± 3.4 and 29.3 ± 3.2 months, respectively, after surgery. The criterion for loosening was increased focal uptake surrounding the screw entry point and shaft. SUV max and SUV mean were measured in a region of interest (ROI) drawn around each screw (334 screws analysed). The final diagnosis was established by surgical exploration in 27 patients and clinical follow-up after intervertebral fusion stabilization in 32 patients. Of the 59 patients, 20 were proven positive for implant failure due to screw loosening and 39 were confirmed negative. The sensitivity, specificity and accuracy of 18 F-fluoride PET/CT were 75 %, 97.4 % and 89.8 % in the patient-based analysis, and 45.6 %, 100 % and 80 % in the screw-based analysis, respectively. The positive and negative predictive values were 93.8 % and 100 % in the patient-based analysis, and 88.4 and 76 % in the screw-based analysis, respectively. CT signs in PET/CT allowed screw breakage to be detected in three patients. SUV max , SUV mean and SUV max /SUV mean ratios in screw ROIs and respective values in reference regions were all found to be significantly different between screws positive for loosening (58 screws) and screws negative for loosening (276 screws). The ratio between SUV max in screw ROIs and the values in reference regions was the most significant parameter for distinguishing screws positive and screws negative for loosening. 18 F-Fluoride PET/CT imaging is useful for the diagnosis of screw loosening in patients with persistent symptoms after intervertebral fusion stabilization. (orig.)

Ipsilateral proximal femur and shaft fractures treated with hip screws and a reamed retrograde intramedullary nail.

Science.gov (United States)

Ostrum, Robert F; Tornetta, Paul; Watson, J Tracy; Christiano, Anthony; Vafek, Emily

2014-09-01

Although not common, proximal femoral fractures associated with ipsilateral shaft fractures present a difficult management problem. A variety of surgical options have been employed with varying results. We investigated the use of hip screws and a reamed retrograde intramedullary (IM) nail for the treatment of this combined fracture pattern in terms of postoperative alignment (malunion), nonunion, and complications. Between May 2002 and October 2011, a total of 95 proximal femoral fractures with associated shaft fractures were treated at three participating Level 1 trauma centers; all were treated with hip screw fixation (cannulated screws or sliding hip screws) and retrograde reamed IM nails. The medical records of these patients were reviewed retrospectively for alignment, malunion, nonunion, and complications. Followup was available on 92 of 95 (97%) of the patients treated with hip screws and a retrograde nail. Forty were treated with a sliding hip screw, and 52 were treated with cannulated screws. There were five proximal malunions in this series (5%). The union rate was 98% (90 of 92) for the femoral neck fractures and 91.3% (84 of 92) for the femoral shaft fractures after the initial surgery. There were two nonunions of comminuted femoral neck fractures after cannulated screw fixation. There was no difference in femoral neck union or alignment when comparing cannulated screws to a sliding hip screw. Four open comminuted femoral shaft fractures went on to nonunion and required secondary surgery to obtain union, and one patient developed symptomatic avascular necrosis. The treatment of ipsilateral proximal femoral neck and shaft fractures with hip screw fixation and a reamed retrograde nail demonstrated a high likelihood of union for the femoral neck fractures and a low risk of malunion. Comminution and initial displacement of the proximal femoral fracture may still lead to a small incidence of malunion or nonunion, and open comminuted femoral shaft fractures

Screw-in forces during instrumentation by various file systems.

Science.gov (United States)

Ha, Jung-Hong; Kwak, Sang Won; Kim, Sung-Kyo; Kim, Hyeon-Cheol

2016-11-01

The purpose of this study was to compare the maximum screw-in forces generated during the movement of various Nickel-Titanium (NiTi) file systems. Forty simulated canals in resin blocks were randomly divided into 4 groups for the following instruments: Mtwo size 25/0.07 (MTW, VDW GmbH), Reciproc R25 (RPR, VDW GmbH), ProTaper Universal F2 (PTU, Dentsply Maillefer), and ProTaper Next X2 (PTN, Dentsply Maillefer, n = 10). All the artificial canals were prepared to obtain a standardized lumen by using ProTaper Universal F1. Screw-in forces were measured using a custom-made experimental device (AEndoS- k , DMJ system) during instrumentation with each NiTi file system using the designated movement. The rotation speed was set at 350 rpm with an automatic 4 mm pecking motion at a speed of 1 mm/sec. The pecking depth was increased by 1 mm for each pecking motion until the file reach the working length. Forces were recorded during file movement, and the maximum force was extracted from the data. Maximum screw-in forces were analyzed by one-way ANOVA and Tukey's post hoc comparison at a significance level of 95%. Reciproc and ProTaper Universal files generated the highest maximum screw-in forces among all the instruments while M-two and ProTaper Next showed the lowest ( p files with smaller cross-sectional area for higher flexibility is recommended.

Hollow Mill for Extraction of Stripped Titanium Screws: An Easy, Quick, and Safe Technique

OpenAIRE

Gupta, Ravi; Singh, Harpreet; Singh, Amit; Garg, Sudhir

2014-01-01

Removal of jammed titanium screws can be difficult due to the problem of stripping of the hexagonal heads of the screws. We present a technique of extraction of stripped screws with the use of a standard 4.5 mm stainless steel hollow mill in a patient of peri-implant fracture of the radius fixed with a titanium locking plate 2 years back. The technique is quick, safe, and cost effective.

Radiographic study of the fifth metatarsal for optimal intramedullary screw fixation of Jones fracture.

Science.gov (United States)

Ochenjele, George; Ho, Bryant; Switaj, Paul J; Fuchs, Daniel; Goyal, Nitin; Kadakia, Anish R

2015-03-01

Jones fractures occur in the relatively avascular metadiaphyseal junction of the fifth metatarsal (MT), which predisposes these fractures to delayed union and nonunion. Operative treatment with intramedullary (IM) screw fixation is recommended in certain cases. Incorrect screw selection can lead to refractures, nonunion, and cortical blowout fractures. A better understanding of the anatomy of the fifth MT could aid in preoperative planning, guide screw size selection, and minimize complications. We retrospectively identified foot computed tomographic (CT) scans of 119 patients that met inclusion criteria. Using interactive 3-dimensional (3-D) models, the following measurements were calculated: MT length, "straight segment length" (distance from the base of the MT to the shaft curvature), and canal diameter. The diaphysis had a lateroplantar curvature where the medullary canal began to taper. The average straight segment length was 52 mm, and corresponded to 68% of the overall length of the MT from its proximal end. The medullary canal cross-section was elliptical rather than circular, with widest width in the sagittal plane and narrowest in coronal plane. The average coronal canal diameter at the isthmus was 5.0 mm. A coronal diameter greater than 4.5 mm at the isthmus was present in 81% of males and 74% of females. To our knowledge, this is the first anatomic description of the fifth metatarsal based on 3-D imaging. Excessive screw length could be avoided by keeping screw length less than 68% of the length of the fifth metatarsal. A greater than 4.5 mm diameter screw might be needed to provide adequate fixation for most study patients since the isthmus of the medullary canal for most were greater than 4.5 mm. Our results provide an improved understanding of the fifth metatarsal anatomy to guide screw diameter and length selection to maximize screw fixation and minimize complications. © The Author(s) 2014.

Idealized Compression Ratio for a Screw Briquetting Press

Directory of Open Access Journals (Sweden)

Peter Biath

2012-01-01

Full Text Available This paper deals with issues in determining the ideal compression ratio for a screw briquetting press. First, the principles of operation and a basic description of the main parts of a screw briquetting press are introduced. The next section describes the pressing space by means of 3D software. The pressing space was created using a Boolean subtract function. The final section of the paper measures the partial volumes of the pressing chamber in CATIA V5 by function of measuring. The measured values are substituted into the formula for the compression ratio, and the resulting evaluations are presented in the diagram in the conclusion of this paper.

Usefulness and radiological evaluation of accuracy of innovative "Smart" hand technique for pedicle screw placement: an anatomical study.

Science.gov (United States)

Comert, Ayhan; Dogan, İhsan; Çaglar, Y Sukru

2017-11-01

The aim of this study is to use a smartphone application during pedicle screw placement navigation and examine the accuracy of this application on anatomical dry vertebrae model. 76 dry vertebrae were used for this study and pedicle entry points, projections of pedicle screw trajectory lines in lateral and superior aspect of vertebral body were identified and drawn for each vertebra bilaterally. In each position, all angulations were measured directly before the procedure manually. 152 pedicle screws were inserted as a simulation of screw placement with the guidance of angle-meter smart app. Accuracy of the method was tested according to the occurrence of bone penetration and angular deviation of the inserted screws was evaluated in computed tomography images. Mean deviation of pedicle screws of 76 pedicle screws in right side in horizontal plane was measured 2.30°±1.78°; in sagittal plane 2.17°±1.57° and in left side in horizontal plane 3.01°±1.83°; in sagittal plane 2.38°±1.68°. No bone penetration was occurred during 152 pedicle screw placements. According to the t-test results, there were significant differences between two groups in craniocaudal direction of the right side pedicle screws and in craniocaudal direction of left side pedicle screws. The free smartphone application presented here as angle-meter can be interpreted as a safe digital device for spinal instrumentation procedures. As a prototype of future pedicle screw fixation systems, it should be improved in terms of its feasibility and compatibility with screw probes. This may lead to apply mobile digital angle meter in spinal procedure.

Risks to the Superior Gluteal Neurovascular Bundle During Iliosacral and Transsacral Screw Fixation: A Computed Tomogram Arteriography Study.

Science.gov (United States)

Maslow, Jed; Collinge, Cory A

2017-12-01

Iliosacral (IS) and transsacral (TS) screws are popular techniques to repair complicated injuries to the pelvis. The anatomy of the superior gluteal neurovasculature (SG NV bundle) is well described as running along the posterior ilium, providing innervation and perfusion to important abductor muscles. The method of pelvis fixation least likely to injure the SG NV bundle is unknown. Twenty uninjured patients with a contrasted computed tomogram of the pelvis and lower extremities (CTA) were evaluated. Starting points for an S1 IS screw and S1 and S2 TS screws were estimated on the "ghost" lateral CTA image for those pelvi with safe corridors (>9 mm diameter). The distance from the projected screw to the SG artery was measured. A distance of <3.65 mm (half of a 7.3-mm screw's diameter) was considered likely for NV bundle injury. Of 40 pelvi CTAs (single sides), 10 pelvi (25%) were determined to be inappropriate for an S1 TS screw. The average distances from the screw starting point and the artery were 25.3 mm (±9.2) for S1 IS, 12.4 mm (±9.0) for S1 TS, and 23.5 mm (±10.7) for S2 TS screws, respectively. Ten S1 TS screws (25%) and no S1 IS or S2 TS screws were projected to have caused injury to the SG NV bundle (P < 0.001). Inserting S1 IS and S2 TS screws put the SG NV anatomy at significantly less risk than S1 TS screws. This information may aid in choosing the "best" fixation option for patients with pelvic ring trauma requiring surgery.

Chitosan-coated Stainless Steel Screws for Fixation in Contaminated Fractures

OpenAIRE

Greene, Alex H.; Bumgardner, Joel D.; Yang, Yunzhi; Moseley, Jon; Haggard, Warren O.

2008-01-01

Stainless steel screws and other internal fixation devices are used routinely to stabilize bacteria-contaminated bone fractures from multiple injury mechanisms. In this preliminary study, we hypothesize that a chitosan coating either unloaded or loaded with an antibiotic, gentamicin, could lessen or prevent these devices from becoming an initial nidus for infection. The questions investigated for this hypothesis were: (1) how much of the sterilized coating remains on the screw with simulated ...

Energy saving screw compressor technology; Energiebesparende schroefcompressortechnologie

Energy Technology Data Exchange (ETDEWEB)

Moeller, A. [RefComp, Lonigo (Italy); Neus, M. [Delta Technics Engineering, Breda (Netherlands)

2011-03-15

Smart solutions to reduce the energy consumption are continuously part of investigation in the refrigeration technology. This article subscribed the technology on which way energy can be saved at the operation of screw compressors which are used in air conditioners and refrigerating machinery. The combination of frequency control and Vi-control (intrinsic volumetric ratio) such as researched in the laboratory of RefComp is for the user attractive because the energy efficiency during part load operation is much better. Smart uses of thermodynamics, electric technology and electronic control are the basics of these applications. According to the manufacturer's information it is possible with these new generation screw compressors to save approx. 26% energy in comparison with the standard screw compressor. [Dutch] In dit artikel wordt de technologie omschreven waarmee veel energie bespaard kan worden bij schroefcompressoren die worden gebruikt in airconditioningsystemen en koel- en vriesinstallaties. De combinatie van frequentieregeling en Vi- regeling (Vi is de intrinsieke volumetrische verhouding) zoals onderzocht in het laboratorium van RefComp biedt de gebruiker veel voordelen doordat de energie-efficintie van de compressor tijdens deellast enorm wordt verbeterd. Slim gebruik van thermodynamika, elektrotechniek en elektronica vormen de basis van deze toepassing. Volgens de fabrikant kan met deze nieuwe generatie schroefcompressoren circa 26 procent op het energiegebruik tijdens deellast worden bespaard in vergelijking met de standaard serie schroefcompressoren.

d = 2 transverse-field Ising model under the screw-boundary condition: an optimization of the screw pitch

International Nuclear Information System (INIS)

Nishiyama, Yoshihiro

2011-01-01

A length-N spin chain with the √N(=v)th neighbor interaction is identical to a two-dimensional (d = 2) model under the screw-boundary (SB) condition. The SB condition provides a flexible scheme to construct a d ≥ 2 cluster from an arbitrary number of spins; the numerical diagonalization combined with the SB condition admits a potential applicability to a class of systems intractable with the quantum Monte Carlo method due to the negative-sign problem. However, the simulation results suffer from characteristic finite-size corrections inherent in SB. In order to suppress these corrections, we adjust the screw pitch v(N) so as to minimize the excitation gap for each N. This idea is adapted to the transverse-field Ising model on the triangular lattice with N ≤ 32 spins. As a demonstration, the correlation-length critical exponent ν is analyzed in some detail

Perturbation effects of the carbon fiber-PEEK screws on radiotherapy dose distribution.

Science.gov (United States)

Nevelsky, Alexander; Borzov, Egor; Daniel, Shahar; Bar-Deroma, Raquel

2017-03-01

Radiation therapy, in conjunction with surgical implant fixation, is a common combined treatment in cases of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon-Fiber Reinforced Polyetheretherketone (CFR-PEEK) material has been recently introduced for production of intramedullary nails and plates. The purpose of this work was to investigate the perturbation effects of the new CFR-PEEK screws on radiotherapy dose distributions and to evaluate these effects in comparison with traditional titanium screws. The investigation was performed by means of Monte Carlo (MC) simulations for a 6 MV photon beam. The project consisted of two main stages. First, a comparison of measured and MC calculated doses was performed to verify the validity of the MC simulation results for different materials. For this purpose, stainless steel, titanium, and CFR-PEEK plates of various thicknesses were used for attenuation and backscatter measurements in a solid water phantom. For the same setup, MC dose calculations were performed. Next, MC dose calculations for titanium, CFR-PEEK screws, and CFR-PEEK screws with ultrathin titanium coating were performed. For the plates, the results of our MC calculations for all materials were found to be in good agreement with the measurements. This indicates that the MC model can be used for calculation of dose perturbation effects caused by the screws. For the CFR-PEEK screws, the maximum dose perturbation was less than 5%, compared to more than 30% perturbation for the titanium screws. Ultrathin titanium coating had a negligible effect on the dose distribution. CFR-PEEK implants have good prospects for use in radiotherapy because of minimal dose alteration and the potential for more accurate treatment planning. This could favorably influence treatment efficiency and decrease possible over- and underdose of adjacent tissues. The use of such implants has potential clinical advantages

Mechanisms of zero-lag synchronization in cortical motifs.

Directory of Open Access Journals (Sweden)

Leonardo L Gollo

2014-04-01

Full Text Available Zero-lag synchronization between distant cortical areas has been observed in a diversity of experimental data sets and between many different regions of the brain. Several computational mechanisms have been proposed to account for such isochronous synchronization in the presence of long conduction delays: Of these, the phenomenon of "dynamical relaying"--a mechanism that relies on a specific network motif--has proven to be the most robust with respect to parameter mismatch and system noise. Surprisingly, despite a contrary belief in the community, the common driving motif is an unreliable means of establishing zero-lag synchrony. Although dynamical relaying has been validated in empirical and computational studies, the deeper dynamical mechanisms and comparison to dynamics on other motifs is lacking. By systematically comparing synchronization on a variety of small motifs, we establish that the presence of a single reciprocally connected pair--a "resonance pair"--plays a crucial role in disambiguating those motifs that foster zero-lag synchrony in the presence of conduction delays (such as dynamical relaying from those that do not (such as the common driving triad. Remarkably, minor structural changes to the common driving motif that incorporate a reciprocal pair recover robust zero-lag synchrony. The findings are observed in computational models of spiking neurons, populations of spiking neurons and neural mass models, and arise whether the oscillatory systems are periodic, chaotic, noise-free or driven by stochastic inputs. The influence of the resonance pair is also robust to parameter mismatch and asymmetrical time delays amongst the elements of the motif. We call this manner of facilitating zero-lag synchrony resonance-induced synchronization, outline the conditions for its occurrence, and propose that it may be a general mechanism to promote zero-lag synchrony in the brain.

Accuracy of percutaneous pedicle screws for thoracic and lumbar spine fractures compared with open technique.

Science.gov (United States)

Paredes, Igor; Panero, Irene; Cepeda, Santiago; Castaño-Leon, Ana M; Jimenez-Roldan, Luis; Perez-Nuñez, Ángel; Alén, Jose A; Lagares, Alfonso

2018-06-14

This study aimed to compare the accuracy of screw placement between open pedicle screw fixation and percutaneous pedicle screw fixation (MIS) for the treatment of thoracolumbar spine fractures (TSF). Forty-nine patients with acute TSF who were treated with transpedicular screw fixation from January 2013 to December 2016 were retrospectively reviewed. The patients were divided into Open and MIS groups. Laminectomy was performed in either group if needed. The accuracy of the screw placement, the evolution of the Cobb sagital angle postoperatively and at 12-month follow up and the neurological status were recorded. AO type of fracture and TLICS score were also recorded. Mean age was 42 years old. Mean TLICS score was 6,29 and 5,96 for open and MIS groups respectively. Twenty five MIS and 24 open surgeries were performed, and 350 (175 in each group) screws were inserted (7,14 per patient). Twenty-four and 13 screws were considered ̈out ̈ in the open and MIS groups respectively (Odds ratio 1,98. 0,97-4,03 p=0,056). The Cobb sagittal angle went from 13,3o to 4,5o and from 14,9o to 8,2o in the Open and MIS groups respectively (both popen and MIS groups respectively. No neurological worsening was observed. For the treatment of acute thoracolumbar fractures, the MIS technique seems to achieve similar results to the open technique in relation to neurological improvement and deformity correction, while placing the screws more accurately.

Monthly ENSO Forecast Skill and Lagged Ensemble Size

Science.gov (United States)

Trenary, L.; DelSole, T.; Tippett, M. K.; Pegion, K.

2018-04-01

The mean square error (MSE) of a lagged ensemble of monthly forecasts of the Niño 3.4 index from the Climate Forecast System (CFSv2) is examined with respect to ensemble size and configuration. Although the real-time forecast is initialized 4 times per day, it is possible to infer the MSE for arbitrary initialization frequency and for burst ensembles by fitting error covariances to a parametric model and then extrapolating to arbitrary ensemble size and initialization frequency. Applying this method to real-time forecasts, we find that the MSE consistently reaches a minimum for a lagged ensemble size between one and eight days, when four initializations per day are included. This ensemble size is consistent with the 8-10 day lagged ensemble configuration used operationally. Interestingly, the skill of both ensemble configurations is close to the estimated skill of the infinite ensemble. The skill of the weighted, lagged, and burst ensembles are found to be comparable. Certain unphysical features of the estimated error growth were tracked down to problems with the climatology and data discontinuities.

Thermal Analysis of Ball screw Systems by Explicit Finite Difference Method

Energy Technology Data Exchange (ETDEWEB)

Min, Bog Ki [Hanyang Univ., Seoul (Korea, Republic of); Park, Chun Hong; Chung, Sung Chong [KIMM, Daejeon (Korea, Republic of)

2016-01-15

Friction generated from balls and grooves incurs temperature rise in the ball screw system. Thermal deformation due to the heat degrades positioning accuracy of the feed drive system. To compensate for the thermal error, accurate prediction of the temperature distribution is required first. In this paper, to predict the temperature distribution according to the rotational speed, solid and hollow cylinders are applied for analysis of the ball screw shaft and nut, respectively. Boundary conditions such as the convective heat transfer coefficient, friction torque, and thermal contact conductance (TCC) between balls and grooves are formulated according to operating and fabrication conditions of the ball screw. Explicit FDM (finite difference method) is studied for development of a temperature prediction simulator. Its effectiveness is verified through numerical analysis.

Thermal homogeneity of plastication processes in single-screw extruders

Science.gov (United States)

Bu, L. X.; Agbessi, Y.; Béreaux, Y.; Charmeau, J.-Y.

2018-05-01

Single-screw plastication, used in extrusion and in injection moulding, is a major way of processing commodity thermoplastics. During the plastication phase, the polymeric material is melted by the combined effects of shear-induced self-heating (viscous dissipation) and heat conduction coming from the barrel. In injection moulding, a high level of reliability is usually achieved that makes this process ideally suited to mass market production. Nonetheless, process fluctuations still appear that make moulded part quality control an everyday issue. In this work, we used a combined modelling of plastication, throughput calculation and laminar dispersion, to investigate if, and how, thermal fluctuations could propagate along the screw length and affect the melt homogeneity at the end of the metering section. To do this, we used plastication models to relate changes in processing parameters to changes in the plastication length. Moreover, a simple model of throughput calculation is used to relate the screw geometry, the polymer rheology and the processing parameters to get a good estimate of the mass flow rate. Hence, we found that the typical residence time in a single screw is around one tenth of the thermal diffusion time scale. This residence time is too short for the dispersion coefficient to reach a steady state, but too long to be able to neglect radial thermal diffusion and resort to a purely convective solution. Therefore, a full diffusion/convection problem has to be solved with a base flow described by the classic pressure and drag velocity field. Preliminary results already show the major importance of the processing parameters in the breakthrough curve of an arbitrary temperature fluctuation at the end of the metering section of injection moulding screw. When the flow back-pressure is high, the temperature fluctuation is spread more evenly with time, whereas a pressure drop in the flow will results in a breakthrough curve which presents a larger peak of

Feasibility of translaminar screw placement in Korean population: morphometric analysis of cervical spine.

Science.gov (United States)

Ji, Gyu Yeul; Oh, Chang Hyun; Park, Sang Hyuk; Kurniawan, Ferry; Lee, Junho; Jeon, Jae Kyun; Shin, Dong Ah; Kim, Keung Nyun

2015-01-01

To analyze the feasibility of unilateral and bilateral translaminar screw placement in Koran population, and compare the acceptance rate using previously reported data in American population. The translaminar lengths, thickness, heights, and sagittal-diagonal measurements were performed. The feasibility analysis was performed using unilateral and bilateral 3.5 mm cervical screw placement on the CT scans within 0.5 mm of safety margin. We also performed radiographic analysis of the morphometric dimensions and the feasibility of unilateral and bilateral translaminar screw placement at C3-C7. Korean population had similar or significantly shorter translaminar lengths and thickness (lengths and thickness in C7 among males; lengths in C6-C7 and thickness in C4 among females) than American population, but had similar or significantly longer translaminar heights and sagittal-diagonal measurements (heights in C3-C7 and sagittal-diagonal measurements in C3-C6 among males; heights in C7 and sagittal-diagonal measurements in C3-C7 among females). Unilaterally, translaminar screw acceptance rates in C3-C7 were similar between Korean and American male population, but the rates in C4-C6 were significantly smaller between Korean and American female population. Bilaterally, translaminar screw acceptance rates in C3 and C5-C6 were significantly larger between Korean and American male population, but the rates in C3-C7 were similar between Korean and American female population. The feasibility of unilateral and bilateral translaminar screw placement is different depending on different ethnics. Subaxial cervical unilateral translaminar screw placement among Korean male population and bilateral placement at C4-C7 among Korean female population are more acceptable than American population.

Comparison of multiple linear regression and artificial neural network in developing the objective functions of the orthopaedic screws.

Science.gov (United States)

Hsu, Ching-Chi; Lin, Jinn; Chao, Ching-Kong

2011-12-01

Optimizing the orthopaedic screws can greatly improve their biomechanical performances. However, a methodical design optimization approach requires a long time to search the best design. Thus, the surrogate objective functions of the orthopaedic screws should be accurately developed. To our knowledge, there is no study to evaluate the strengths and limitations of the surrogate methods in developing the objective functions of the orthopaedic screws. Three-dimensional finite element models for both the tibial locking screws and the spinal pedicle screws were constructed and analyzed. Then, the learning data were prepared according to the arrangement of the Taguchi orthogonal array, and the verification data were selected with use of a randomized selection. Finally, the surrogate objective functions were developed by using either the multiple linear regression or the artificial neural network. The applicability and accuracy of those surrogate methods were evaluated and discussed. The multiple linear regression method could successfully construct the objective function of the tibial locking screws, but it failed to develop the objective function of the spinal pedicle screws. The artificial neural network method showed a greater capacity of prediction in developing the objective functions for the tibial locking screws and the spinal pedicle screws than the multiple linear regression method. The artificial neural network method may be a useful option for developing the objective functions of the orthopaedic screws with a greater structural complexity. The surrogate objective functions of the orthopaedic screws could effectively decrease the time and effort required for the design optimization process. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.

Assessment of Different Metal Screw Joint Parameters by Using Multiple Criteria Analysis Methods

Directory of Open Access Journals (Sweden)

Audrius Čereška

2018-05-01

Full Text Available This study compares screw joints made of different materials, including screws of different diameters. For that purpose, 8, 10, 12, 14, 16 mm diameter steel screws and various parts made of aluminum (Al, steel (Stl, bronze (Brz, cast iron (CI, copper (Cu and brass (Br are considered. Multiple criteria decision making (MCDM methods such as evaluation based on distance from average solution (EDAS, simple additive weighting (SAW, technique for order of preference by similarity to ideal solution (TOPSIS and complex proportional assessment (COPRAS are utilized to assess reliability of screw joints also considering cost issues. The entropy, criterion impact loss (CILOS and integrated determination of objective criteria weights (IDOCRIW methods are utilized to assess weights of decision criteria and find the best design alternative. Numerical results confirm the validity of the proposed approach.

Analysis of Modeling Parameters on Threaded Screws.

Energy Technology Data Exchange (ETDEWEB)

Vigil, Miquela S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Brake, Matthew Robert [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Vangoethem, Douglas [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2015-06-01

Assembled mechanical systems often contain a large number of bolted connections. These bolted connections (joints) are integral aspects of the load path for structural dynamics, and, consequently, are paramount for calculating a structure's stiffness and energy dissipation prop- erties. However, analysts have not found the optimal method to model appropriately these bolted joints. The complexity of the screw geometry cause issues when generating a mesh of the model. This paper will explore different approaches to model a screw-substrate connec- tion. Model parameters such as mesh continuity, node alignment, wedge angles, and thread to body element size ratios are examined. The results of this study will give analysts a better understanding of the influences of these parameters and will aide in finding the optimal method to model bolted connections.

Computer simulation of migration atomic mechanism and substitutional impurity interaction with screw dislocation core in bcc lattice

International Nuclear Information System (INIS)

Klyavin, O.V.; Likhodedov, N.P.; Orlov, A.N.

1986-01-01

Distribution and migration of substitutional impurity atoms (He and C) in the screw dislocation core of the 1/2 type is studied in α-Fe. The atomic mechanism of impurity atom diffusion over screw dislocation core, consisting in the fact that impurity migration proceeds in a screw trajectory, is discovered and analyzed. It is shown that tubular He diffusion over screw dislocation may proceed at T <= 300 K

Treating Simple Tibia Fractures with Poly-DL-Lactic Acid Screw as a ...

African Journals Online (AJOL)

Purpose: To investigate the curative effect of poly-DL-lactic acid (PDLLA) absorbable screw as a locked intramedullary nail for simple tibia fractures. Methods: In this study, 35 patients treated with the PDLLA screw were observed, and another 35 patients treated with a traditional locking intramedullary nail were treated as ...

Clinical results and functional outcomes after direct intralaminar screw repair of spondylolysis.

Science.gov (United States)

Menga, Emmanuel N; Kebaish, Khaled M; Jain, Amit; Carrino, John A; Sponseller, Paul D

2014-01-01

Prospective analysis. Our objective was to analyze clinical and functional results of patients with spondylolysis treated via direct intralaminar screw fixation and autograft, a minimally invasive and motion-preserving surgery. Spondylolysis is usually treated nonoperatively; multiple surgical techniques are available when nonoperative measures fail. No studies evaluate the clinical and functional outcomes and their correlation with pars defect size and disc morphology on magnetic resonance imaging. We reviewed patients with spondylolysis treated with intralaminar screw fixation and bone grafting from 2000 through 2010. Of the 31 patients (mean age, 16 yr; range, 10-37 yr), 25 (81%) were competitive athletes. Preoperative computed tomographic scans were used to measure the pars defect size, and preoperative magnetic resonance images were graded using Pfirrmann classification for correlation with postoperative outcomes. Student t test was used for analysis (significance, P spondylolysis repair for persistent pain starting 18 months after intralaminar screw fixation, 2 patients sustained unilateral intralaminar screw fractures at L5, and 1 patient required irrigation and debridement for a superficial postoperative infection. There was no correlation among preoperative magnetic resonance imaging disc morphology, defect size on computed tomography, patient age, and clinical outcomes. Direct repair of spondylolysis with intralaminar screws offers a low profile, reliable treatment with good functional outcome and a low complication rate in active patients. 4.

Axial loading screw fixation for chevron type osteotomies of the distal first metatarsal: a retrospective outcomes analysis.

Science.gov (United States)

Murphy, Ryan M; Fallat, Lawrence M; Kish, John P

2014-01-01

The distal chevron osteotomy is a widely accepted technique for the treatment of hallux abductovalgus deformity. Although the osteotomy is considered to be stable, displacements of the capital fragment has been described. We propose a new method for fixation of the osteotomy involving the axial loading screw (ALS) used in addition to single screw fixation. We believe this method will provide a more mechanically stable construct. We reviewed the charts of 46 patients in whom 52 feet underwent a distal chevron osteotomy that was fixated with either 1 screw or 2 screws that included the ALS. We hypothesized that the ALS group would have fewer displacements and would heal more quickly than the single screw fixation group. We found that the group with ALS fixation had healed at a mean of 6.5 weeks and that the group with single screw fixation had healed at 9.53 weeks (p = .001). Also, 8 cases occurred of displacement of the capital fragment in the single screw, control group compared with 2 cases of displacement in the ALS group. However, this finding was not statistically significant. The addition of the ALS to single screw fixation allowed the patients to heal approximately 3 weeks earlier than single screw fixation alone. The ALS is a fixation option for the surgeon to consider when osseous correction of hallux abducto valgus is performed. Copyright © 2014 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Biomechanical in vitro assessment of screw augmentation in locked plating of proximal humerus fractures.

Science.gov (United States)

Röderer, Götz; Scola, Alexander; Schmölz, Werner; Gebhard, Florian; Windolf, Markus; Hofmann-Fliri, Ladina

2013-10-01

Proximal humerus fracture fixation can be difficult because of osteoporosis making it difficult to achieve stable implant anchorage in the weak bone stock even when using locking plates. This may cause implant failure requiring revision surgery. Cement augmentation has, in principle, been shown to improve stability. The aim of this study was to investigate whether augmentation of particular screws of a locking plate aimed at a region of low bone quality is effective in improving stability in a proximal humerus fracture model. Twelve paired human humerus specimens were included. Quantitative computed tomography was performed to determine bone mineral density (BMD). Local bone quality in the direction of the six proximal screws of a standard locking plate (PHILOS, Synthes) was assessed using mechanical means (DensiProbe™). A three-part fracture model with a metaphyseal defect was simulated and fixed with the plate. Within each pair of humeri the two screws aimed at the region of the lowest bone quality according to the DensiProbe™ were augmented in a randomised manner. For augmentation, 0.5 ml of bone cement was injected in a screw with multiple outlets at its tip under fluoroscopic control. A cyclic varus-bending test with increasing upper load magnitude was performed until failure of the screw-bone fixation. The augmented group withstood significantly more load cycles. The correlation of BMD with load cycles until failure and BMD with paired difference in load cycles to failure showed that augmentation could compensate for a low BMD. The results demonstrate that augmentation of screws in locked plating in a proximal humerus fracture model is effective in improving primary stability in a cyclic varus-bending test. The augmentation of two particular screws aimed at a region of low bone quality within the humeral head was almost as effective as four screws with twice the amount of bone cement. Screw augmentation combined with a knowledge of the local bone quality

Biomechanical Analysis of Suture Anchor vs Tenodesis Screw for FHL Transfer.

Science.gov (United States)

Drakos, Mark C; Gott, Michael; Karnovsky, Sydney C; Murphy, Conor I; DeSandis, Bridget A; Chinitz, Noah; Grande, Daniel; Chahine, Nadeen

2017-07-01

Chronic Achilles injury is often treated with flexor hallucis longus (FHL) tendon transfer to the calcaneus using 1 or 2 incisions. A single incision avoids the risks of extended dissections yet yields smaller grafts, which may limit fixation options. We investigated the required length of FHL autograft and biomechanical profiles for suture anchor and biotenodesis screw fixation. Single-incision FHL transfer with suture anchor or biotenodesis screw fixation to the calcaneus was performed on 20 fresh cadaveric specimens. Specimens were cyclically loaded until maximal load to failure. Length of FHL tendon harvest, ultimate load, stiffness, and mode of failure were recorded. Tendon harvest length needed for suture anchor fixation was 16.8 ± 2.1 mm vs 29.6 ± 2.4 mm for biotenodesis screw ( P = .002). Ultimate load to failure was not significantly different between groups. A significant inverse correlation existed between failure load and donor age when all specimens were pooled (ρ = -0.49, P Anchor failure occurred mostly by suture breakage (n = 8). Adequate FHL tendon length could be harvested through a single posterior incision for fixation to the calcaneus with either fixation option, but suture anchor required significantly less graft length. Stiffness, fixation strength, and load to failure were comparable between groups. An inverse correlation existed between failure load and donor age. Younger specimens with screw fixation demonstrated significantly greater failure loads. Adequate harvest length for FHL transfer could be achieved with a single posterior incision. There was no difference in strength of fixation between suture anchor and biotenodesis screw.

Clinical Outcomes of Posterior C1 and C2 Screw-Rod Fixation for Atlantoaxial Instability.

Science.gov (United States)

Işik, Hasan Serdar; Sandal, Evren; Çağli, Sedat

2017-06-14

In this study, we aimed at sharing our experiences and contributing to the literature by making a retrospective analysis of the patients we operated with screw-rod system for atlantoaxial instability in our clinic. Archive files of adult patients, who were operated for posterior C1-C2 stabilization with screw and rod in our clinic between January 2006 and January 2016, were analyzed. 28 patients, who had pre and post-operative images, follow-up forms and who were followed for at least one year, were analyzed. Preoperative clinical and radiological records, preoperative observations, postoperative complications, and clinical responses were evaluated. The average age of 28 patients (F:13 M:19) was 44.7 (21-73). Fixation was performed with C1-C2 screw-rod system on the basis of the following diagnoses; type 2 odontoid fracture (16), basilar invagination (5), C1-C2 instability (5), and atlantoaxial subluxation secondary to rheumatoid arthritis (2). Lateral mass screws were inserted at C1 segment. C2 screws inserted were bilateral pedicle in 12 cases, bilateral pars in 4, bilateral laminar in 8 and one side pars, one side laminar in 4 cases. There was no screw malposition. Neither implant failure nor recurrent instability was observed during follow-up. Significant clinical improvement was reported according to the assessments done with JOA and VAS scores. C1-C2 screw fixation is regarded as a more successful and safe method than other fixation methods in surgical treatment of atlantoaxial instability considering complications, success in reduction, fusion and fixation strength. C2 laminar screw technique is as successful as the other alternatives in fixation and fusion.

Use of a life-size three-dimensional-printed spine model for pedicle screw instrumentation training.

Science.gov (United States)

Park, Hyun Jin; Wang, Chenyu; Choi, Kyung Ho; Kim, Hyong Nyun

2018-04-16

Training beginners of the pedicle screw instrumentation technique in the operating room is limited because of issues related to patient safety and surgical efficiency. Three-dimensional (3D) printing enables training or simulation surgery on a real-size replica of deformed spine, which is difficult to perform in the usual cadaver or surrogate plastic models. The purpose of this study was to evaluate the educational effect of using a real-size 3D-printed spine model for training beginners of the free-hand pedicle screw instrumentation technique. We asked whether the use of a 3D spine model can improve (1) screw instrumentation accuracy and (2) length of procedure. Twenty life-size 3D-printed lumbar spine models were made from 10 volunteers (two models for each volunteer). Two novice surgeons who had no experience of free-hand pedicle screw instrumentation technique were instructed by an experienced surgeon, and each surgeon inserted 10 pedicle screws for each lumbar spine model. Computed tomography scans of the spine models were obtained to evaluate screw instrumentation accuracy. The length of time in completing the procedure was recorded. The results of the latter 10 spine models were compared with those of the former 10 models to evaluate learning effect. A total of 37/200 screws (18.5%) perforated the pedicle cortex with a mean of 1.7 mm (range, 1.2-3.3 mm). However, the latter half of the models had significantly less violation than the former half (10/100 vs. 27/100, p 3D-printed spine model can be an excellent tool for training beginners of the free-hand pedicle screw instrumentation.

Unconventional fixation Thoracolumbar fractures using round hole boneplates and transpedicular screws

International Nuclear Information System (INIS)

Behairy, Yaser M.

2001-01-01

In an attempt to contain the high cost of commercially available pediclescrew systems, several authors have used unconventional alternatives such aslocally made plates or dynamic compression plates (DCP) along with cancellousscrews for transpedicular fixation of the thoracolumbar spine. These plates,however, allow for a wide range of motion at the plate-screw interphase andthe construct does not provide stability in the sagittal plane. Round holebone plates, on the other hand, allow much less mobility at the plate-screwinterphase and the final construct offers better stability in the sagittalplane. Our objective was to determine the clinical, radiologic and functionalstatus of patients who underwent posterior fracture fixation using round holebone plates and cancellous screws and evaluate the construct's ability tomaintain reduction of the fracture. This was a postoperative follow-up ofpatients with fractures around the thoracolumbar junction fixed using roundhole bone plates and cancellous transpedicular screws. Round hole bone platesalong with 6.5 mm transpedicular cancellous screws were used for posteriorspinal instrumentation in neurologically intact patients with isolatedunstable fractures of the last thoracic or first lumbar vertebra. Seventeenpatients were included in this study. There mean follow-up was 10 months(range 5 to 12). All had evidence of fusion at a mean of 5 months (range 4 to7). No patients had breakage or loosening of the screws and none had breakageof the plate. The mean kyphosis angle at the fracture site was 34 degreepreoperatively, -4 degree in the immediate postoperative period, and 3 degreeon final follow-up radiographs. The percentage loss of anterior vertebralbody height was 51% in the immediate postoperative period and 16% on finalfollow-up radiographs. The use of round hole bone plates along with 6.5 mmcancellous screws inserted into the pedicles provides an angle-stableconstruct that allows for better stability in the sagittal plane

[Polymethylmethacrylate augmentation of bone cement-injectable cannulated pedicle screws for the treatment of degenerative lumbar diseases with osteoporosis].

Science.gov (United States)

Sun, H L; Li, C D; Yang, Z C; Yi, X D; Liu, H; Lu, H L; Li, H; Wang, Y

2016-12-18

To describe the application of polymethylmethacrylate augmentation of bone cement-injectable cannulated pedicle screws for the treatment of degenerative lumbar diseases with osteoporosis. Observation group included 14 cases of degenerative lumbar diseases with osteoporosis received polymethylmethacrylate augmentation of bone cement-injectable cannulated pedicle screws from November 2014 to July 2015, control group included 12 cases of degenerative lumbar diseases with osteoporosis received polymethylmethacrylate augmentation with traditional pedicle screws.The operation time, blood loss, number of pedicle screws and number of augmented pedicle screws in the two groups were compared. The bone cement leakage and pulmonary bone cement embolism in the two groups were also compared. The fusion rate and pedicle screws loosening by lumbar X ray and dynamic X ray were evaluated. The clinical results were assessed by visual analog scale (VAS) of pain on lumbar and lower limbers, lumbar Japanese Orthopaedic Association scores (JOA), Prolo functional scores and Oswestry disability (ODI) scores. Differences of operation time and blood loss in the two groups were not statistically significant. The average number of pedicle screws was 9.9±4.7 and the average number of augmented pedicle screws was 5.9±2.6 in observation group while the average number of pedicle screws was 7.1±2.8 and the average number of augmented pedicle screws was 3.0±1.9 in control group. The ratio of augmented pedicle screws was higher in observation group than in control group (0.69±0.30 vs.0.47±0.30,Pdegenerative lumbar diseases with osteoporosis was effective, with simple working processes and lower risk of bone cement leakage. The short-term clinical result was good.

Bone properties of the humeral head and resistance to screw cutout

DEFF Research Database (Denmark)

Frich, L. H.; Jensen, N. C.

2014-01-01

Surgical treatment of fractures involving the proximal humeral head is hampered by complications. Screw cutout is the major pitfall seen in connection with rigid plating. We have exploited a bony explanation for this phenomenon. Materials and Methods: We examined the convex surface of the humeral...... sectioning technique. Results: The bone strength and bone density correlated well and revealed large regional variations across the humeral head. Bone strength and stiffness of the trabecular bone came to a maximum in the most medial anterior and central parts of the humeral head, where strong textural...... screw directions will predictably place screws in areas of the humeral head comprising low density and low strength cancellous bone. New concepts of plates and plating techniques for the surgical treatment of complex fractures of the proximal humerus should take bone distribution, strength...

Theoretical prediction of pullout strengths for dental and orthopaedic screws with conical profile and buttress threads.

Science.gov (United States)

Shih, Kao-Shang; Hou, Sheng-Mou; Lin, Shang-Chih

2017-12-01

The pullout strength of a screw is an indicator of how secure bone fragments are being held in place. Such bone-purchasing ability is sensitive to bone quality, thread design, and the pilot hole, and is often evaluated by experimental and numerical methods. Historically, there are some mathematical formulae to simulate the screw withdrawal from the synthetic bone. There are great variations in screw specifications. However, extensive investigation of the correlation between experimental and analytical results has not been reported in literature. Referring to the literature formulae, this study aims to evaluate the differences in the calculated pullout strengths. The pullout tests of the surgical screws are measured and the sawbone is used as the testing block. The absolute errors and correlation coefficients of the experimental and analytical results are calculated as the comparison baselines of the formulae. The absolute error of the dental, traumatic, and spinal groups are 21.7%, 95.5%, and 37.0%, respectively. For the screws with a conical profile and/or tiny threads, the calculated and measured results are not well correlated. The formulae are not accurate indicators of the pullout strengths of the screws where the design parameters are slightly varied. However, the experimental and numerical results are highly correlated for the cylindrical screws. The pullout strength of a conical screw is higher than that of its counterpart, but all formulae consistently predict the opposite results. In general, the bony purchase of the buttress threads is securer than that of the symmetric thread. An absolute error of up to 51.4% indicates the theoretical results cannot predict the actual value of the pullout strength. Only thread diameter, pitch, and depth are considered in the investigated formulae. The thread profile and shape should be formulated to modify the slippage mechanism at the bone-screw interfaces and simulate the strength change in the squeezed bones

Potential risks of using cement-augmented screws for spinal fusion in patients with low bone quality.

Science.gov (United States)

Martín-Fernández, M; López-Herradón, A; Piñera, A R; Tomé-Bermejo, F; Duart, J M; Vlad, M D; Rodríguez-Arguisjuela, M G; Alvarez-Galovich, L

2017-08-01

Dramatic increases in the average life expectancy have led to increases in the variety of degenerative changes and deformities observed in the aging spine. The elderly population can present challenges for spine surgeons, not only because of increased comorbidities, but also because of the quality of their bones. Pedicle screws are the implants used most commonly in spinal surgery for fixation, but their efficacy depends directly on bone quality. Although polymethyl methacrylate (PMMA)-augmented screws represent an alternative for patients with osteoporotic vertebrae, their use has raised some concerns because of the possible association between cement leakages (CLs) and other morbidities. To analyze potential complications related to the use of cement-augmented screws for spinal fusion and to investigate the effectiveness of using these screws in the treatment of patients with low bone quality. A retrospective single-center study. This study included 313 consecutive patients who underwent spinal fusion using a total of 1,780 cement-augmented screws. We analyzed potential complications related to the use of cement-augmented screws, including CL, vascular injury, infection, screw extraction problems, revision surgery, and instrument failure. There are no financial conflicts of interest to report. A total of 1,043 vertebrae were instrumented. Cement leakage was observed in 650 vertebrae (62.3%). There were no major clinical complications related to CL, but two patients (0.6%) had radicular pain related to CL at the S1 foramina. Of the 13 patients (4.1%) who developed deep infections requiring surgical debridement, two with chronic infections had possible spondylitis that required instrument removal. All patients responded well to antibiotic therapy. Revision surgery was performed in 56 patients (17.9%), most of whom had long construction. A total of 180 screws were removed as a result of revision. There were no problems with screw extraction. These results

Release of metal in vivo from stressed and nonstressed maxillofacial fracture plates and screws.

Science.gov (United States)

Matthew, I R; Frame, J W

2000-07-01

To analyze the release of metal into the adjacent tissues from stressed and nonstressed titanium and stainless steel miniplates and screws. Two miniplates were inserted into the cranial vaults of 12 beagle dogs while they were under general endotracheal anesthesia. One miniplate was shaped to fit the curvature of the skull (control). Another miniplate, made of the same material, was bent in a curve until the midpoint was raised 3 mm above the ends. Screws were inserted and tightened until the plate conformed to the skull curvature, creating stresses in the system. Four animals (2 each, having titanium or stainless steel plates and screws) were killed after 4, 12, and 24 weeks. Metallosis of adjacent soft tissues was assessed qualitatively. Miniplates and screws were removed, and adjacent soft tissue and bone was excised. Titanium, iron, chromium, nickel, and aluminum levels were assayed by ultraviolet/visible light and atomic absorption spectrophotometry. Nonparametric statistical methods were used for data analysis. There was no clear relationship between pigmentation of soft tissue adjacent to the miniplates and screws and the concentrations of metal present. The data did not demonstrate any consistent differences in the concentrations of metallic elements next to stressed and nonstressed (control) miniplates and screws of either material. Stresses arising through poor contouring of miniplates do not appear to influence the extent of release of metal into the adjacent tissues.

Cortical bone trajectory screw fixation versus traditional pedicle screw fixation for 2-level posterior lumbar interbody fusion: comparison of surgical outcomes for 2-level degenerative lumbar spondylolisthesis.

Science.gov (United States)

Sakaura, Hironobu; Miwa, Toshitada; Yamashita, Tomoya; Kuroda, Yusuke; Ohwada, Tetsuo

2018-01-01

OBJECTIVE The cortical bone trajectory (CBT) screw technique is a new nontraditional pedicle screw (PS) insertion method. However, the biomechanical behavior of multilevel CBT screw/rod fixation remains unclear, and surgical outcomes in patients after 2-level posterior lumbar interbody fusion (PLIF) using CBT screw fixation have not been reported. Thus, the purposes of this study were to examine the clinical and radiological outcomes after 2-level PLIF using CBT screw fixation for 2-level degenerative lumbar spondylolisthesis (DS) and to compare these outcomes with those after 2-level PLIF using traditional PS fixation. METHODS The study included 22 consecutively treated patients who underwent 2-level PLIF with CBT screw fixation for 2-level DS (CBT group, mean follow-up 39 months) and a historical control group of 20 consecutively treated patients who underwent 2-level PLIF using traditional PS fixation for 2-level DS (PS group, mean follow-up 35 months). Clinical symptoms were evaluated using the Japanese Orthopaedic Association (JOA) scoring system. Bony union was assessed by dynamic plain radiographs and CT images. Surgery-related complications, including symptomatic adjacent-segment disease (ASD), were examined. RESULTS The mean operative duration and intraoperative blood loss were 192 minutes and 495 ml in the CBT group and 218 minutes and 612 ml in the PS group, respectively (p 0.05, respectively). The mean JOA score improved significantly from 12.3 points before surgery to 21.1 points (mean recovery rate 54.4%) at the latest follow-up in the CBT group and from 12.8 points before surgery to 20.4 points (mean recovery rate 51.8%) at the latest follow-up in the PS group (p > 0.05). Solid bony union was achieved at 90.9% of segments in the CBT group and 95.0% of segments in the PS group (p > 0.05). Symptomatic ASD developed in 2 patients in the CBT group (9.1%) and 4 patients in the PS group (20.0%, p > 0.05). CONCLUSIONS Two-level PLIF with CBT screw fixation

Precision insertion of percutaneous sacroiliac screws using a novel augmented reality-based navigation system: a pilot study.

Science.gov (United States)

Wang, Huixiang; Wang, Fang; Leong, Anthony Peng Yew; Xu, Lu; Chen, Xiaojun; Wang, Qiugen

2016-09-01

Augmented reality (AR) enables superimposition of virtual images onto the real world. The aim of this study is to present a novel AR-based navigation system for sacroiliac screw insertion and to evaluate its feasibility and accuracy in cadaveric experiments. Six cadavers with intact pelvises were employed in our study. They were CT scanned and the pelvis and vessels were segmented into 3D models. The ideal trajectory of the sacroiliac screw was planned and represented visually as a cylinder. For the intervention, the head mounted display created a real-time AR environment by superimposing the virtual 3D models onto the surgeon's field of view. The screws were drilled into the pelvis as guided by the trajectory represented by the cylinder. Following the intervention, a repeat CT scan was performed to evaluate the accuracy of the system, by assessing the screw positions and the deviations between the planned trajectories and inserted screws. Post-operative CT images showed that all 12 screws were correctly placed with no perforation. The mean deviation between the planned trajectories and the inserted screws was 2.7 ± 1.2 mm at the bony entry point, 3.7 ± 1.1 mm at the screw tip, and the mean angular deviation between the two trajectories was 2.9° ± 1.1°. The mean deviation at the nerve root tunnels region on the sagittal plane was 3.6 ± 1.0 mm. This study suggests an intuitive approach for guiding screw placement by way of AR-based navigation. This approach was feasible and accurate. It may serve as a valuable tool for assisting percutaneous sacroiliac screw insertion in live surgery.

Optimization and Numerical Simulation of Outlet of Twin Screw Extruder

Directory of Open Access Journals (Sweden)

Zhang Yuan

2018-01-01

Full Text Available In view of the unreasonable design of non-intermeshing counter-rotating twin screw extruder die, the problem of productivity reduction was discussed. Firstly, the mathematical model of extruder productivity was established. The extruder die model was improved. Secondly, the force analysis of twin screw extruder physical model was carried out. Meanwhile, A combination of mechanical analysis and numerical simulation was adopted. The velocity field, pressure field and viscosity field were calculated by Mini-Element interpolation method, linear interpolation method and Picard iterative convergence method respectively. The influence of die model on the quantity of each field before and after improvement was analyzed. The results show that the improved model had increased the rheological parameters of the flow field, the leakage and reverse flow decreased. Through post-processing calculation, the productivity of the third dies extruder was 10% higher than before. The research results provide a theoretical basis for the design and optimization of die model of non intermeshing counter-rotating twin screw extruder.

Modelling of capital asset pricing by considering the lagged effects

Science.gov (United States)

Sukono; Hidayat, Y.; Bon, A. Talib bin; Supian, S.

2017-01-01

In this paper the problem of modelling the Capital Asset Pricing Model (CAPM) with the effect of the lagged is discussed. It is assumed that asset returns are analysed influenced by the market return and the return of risk-free assets. To analyse the relationship between asset returns, the market return, and the return of risk-free assets, it is conducted by using a regression equation of CAPM, and regression equation of lagged distributed CAPM. Associated with the regression equation lagged CAPM distributed, this paper also developed a regression equation of Koyck transformation CAPM. Results of development show that the regression equation of Koyck transformation CAPM has advantages, namely simple as it only requires three parameters, compared with regression equation of lagged distributed CAPM.

Recurrent Laryngeal Edema Imitating Angioedema Caused by Dislocated Screw after Anterior Spine Surgery

Directory of Open Access Journals (Sweden)

Piotr Wójtowicz

2015-01-01

Full Text Available The anterior cervical spine surgery is a common procedure to stabilize vertebrae damaged by various diseases. The plates and screws are usually used in the spine fixation. This kind of instrumentation may detach from the bones which is a rare but well-known complication. A 77-year-old male presented to the otorhinolaryngology department with throat pain, choking, and dysphagia. At first the angioedema was diagnosed and he was treated conservatively. The endoscopy revealed laryngeal edema, being more defined on the right side with right vocal fold paresis. CT scans showed the stabilizing plate with two screws attached tightly and the back-out of the third screw toward soft tissue of the neck. In the meantime, his condition deteriorated and he needed tracheotomy. In few days the surgical removal of the dislocated screw was performed successfully. Although two-month follow-up reported no obstruction of the larynx, the vocal folds paresis with gradual functional improvement was observed. Long-term complication of anterior spine surgery sometimes may suggest laryngeal angioedema at first. If the conservative treatment is ineffective and there is a history of anterior spine surgery, the clinicians should consider the displacement of the plate or screws in differential diagnosis.

Conceptual framework for model-based analysis of residence time distribution in twin-screw granulation

DEFF Research Database (Denmark)

Kumar, Ashish; Vercruysse, Jurgen; Vanhoorne, Valerie

2015-01-01

Twin-screw granulation is a promising continuous alternative for traditional batchwise wet granulation processes. The twin-screw granulator (TSG) screws consist of transport and kneading element modules. Therefore, the granulation to a large extent is governed by the residence time distribution...... within each module where different granulation rate processes dominate over others. Currently, experimental data is used to determine the residence time distributions. In this study, a conceptual model based on classical chemical engineering methods is proposed to better understand and simulate...... the residence time distribution in a TSG. The experimental data were compared with the proposed most suitable conceptual model to estimate the parameters of the model and to analyse and predict the effects of changes in number of kneading discs and their stagger angle, screw speed and powder feed rate...

A comparitive clinical study between self tapping and drill free screws as a source of rigid orthodontic anchorage.

Science.gov (United States)

Gupta, Nishant; Kotrashetti, S M; Naik, Vijay

2012-03-01

Self-tapping miniscrews are commonly being used as a temporary anchorage device for orthodontic purpose. A prerequisite for the insertion of these screws is the preparation of a pilot hole, which is time consuming and may result in damage to nerves, tooth root, drill bit breakage and thermal necrosis of bone. On the other hand the design of drill-free screws enables them to be inserted without drilling. The aim of this prospective study was to compare the stability and clinical response of the soft tissue around the self tapping and drill free screws when used for orthodontic anchorage for en mass retraction of maxillary anterior teeth. The study sample consisted of 20 patients requiring retraction of maxillary anterior teeth. The screws were placed in the alveolar bone between maxillary 2nd premolar and 1st molar bilaterally at the junction of attached gingiva and moveable mucosa. Pilot hole was drilled on the side which was selected for insertion of the self tapping screw under copious irrigation, after which it was inserted. Drill free screw was inserted on the contralateral side without predrilling. All screws were immediately loaded with 150-200 gm of retraction force. Patients were recalled for regular follow up for a period of 6 months. If the screws became mobile or showed any signs of inflammation during the course of the study, they were considered to be a failure. After a period of 6 months an overall success rate of 77.5% was noted. Four self tapping and five drill-free screws failed during the study. There was no statistically significant difference between the two types of screws with respect to success/failure. Mobility was found to be the major cause for the failure. Both self-tapping and the drill-free screws are effective anchorage units. But the latter have an edge over the conventional self-tapping screws because of decrease in operative time, little bone debris, less thermal damage, lower morbidity, and minimal patient discomfort as

Root contact with maxillomandibular fixation screws in orthognathic surgery: incidence and consequences.

Science.gov (United States)

Camargo, I B; Van Sickels, J E; Laureano Filho, J R; Cunningham, L L

2016-08-01

The use of maxillomandibular fixation (MMF) screws in orthognathic surgery has become common in recent years. The risk of injury to adjacent roots with their placement in this population has not been studied extensively. The aim of this study was to review the incidence and consequences of root contact/injury in patients undergoing orthognathic surgery. A retrospective analysis of the treatment and radiographic records of patients who underwent orthognathic surgery between January 2013 and September 2014 at a university in Kentucky, USA was performed. The mean number of screws used was correlated to the mean number of roots affected using Spearman's test, set to a level of significance of 5%. Of 125 patients who underwent orthognathic surgery, 15 (12%) had evidence of root contact. Subsequent radiographs showed resolution of the bone defects. There was no clinical evidence of pulpal necrosis or pain during follow-up. The average number of screws used was 3.14±0.35 per patient, with an average of 0.17±0.52 root contacts per patient. There was no correlation between the number of screws used and the number of roots injured (P=0.279). Based on these results, MMF screws can safely be used to establish interim fixation during orthognathic surgery. Caution should be taken during placement to avoid direct injury to the roots of teeth. Copyright © 2016 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

Lag-Lead Compensator for Shape Memory Alloy in Gripping Manipulation

Directory of Open Access Journals (Sweden)

Made Andik Setiawan

2010-12-01

Full Text Available Shape Memory Alloy (SMA is emerging actuator for micro and nano application, on the other hand the developing controller in such area needs much further considerations.This paper is to present the evaluation of close-loop controller responses of the TiNi SMA spring based gripper by introduced lag, lead and lag-lead compensator. A SMA spring has a diameter of 50 mm wire and 350 gram hanging mass. Driving the SMA actuator is used pulse width modulation (PWM signal and responses tested by varying frequencies and duty-cycles. The implemented frequencies in this study are 12, 25, 125, 250 and 1150 Hz. Lab-View and DAQ-Card is used as a controller, interfacer and data recorder of the system. The gripper fabricated consists of two fingers and the total angular displacement of the gripper is 300. The experimental result of the SMA open-loop response are presented and discussed. For advanced application, the close-loop controller is implemented and studied. The close-loop controllers employed are lag, lead and lag-lead compensator. The SMA response indicated that the rise-time and the steady-state error of the cloop-loop are shorter and lower than open-loop controller. The tuning, response and program of the lag, lead and lag-lead compensator are presented and discussed in this paper.

Acromioclavicular Joint Fixation Using an Acroplate Combined With a Coracoclavicular Screw

Science.gov (United States)

Tavakoli Darestani, Reza; Ghaffari, Arash; Hosseinpour, Mehrdad

2013-01-01

Background Appropriate treatment of acromioclavicular joint dislocation is controversial. Acroplate fixation is one of the most common treatment methods of acromioclavicular joint (ACJ) dislocation. Based on the risk of re-dislocation after Acroplate fixation, we assumed that combined fixation with an Acroplate and a coracoclavicular screw helps improve the outcome. Objectives The main purpose of the current study was to compare the outcome of ACJ dislocation treated with an Acroplate alone and in combination with coracoclavicular screw. Patients and Methods This study was carried out on 40 patients with ACJ dislocation types III to VI who were divided randomly into two equal groups: Acroplate group (P) and Acroplate in combination with coracoclavicular screw group (P + S). The screws were extracted 3-6 months postoperatively. The patients were followed for 1 year and Imatani’s score was calculated. Finally, the data were compared between the groups. Results The mean Imatani’s score was significantly higher in P + S group (83.4 ± 14.1) than P group (81.2 ± 10.3) (P < 0.001). The mean duration of surgery was the same in the two groups (59.8 ± 9.4 minutes in group P V.s 64.3 ± 10.9 minutes in group P + S; P = 0.169). There were no cases of re-dislocation, degenerative changes and ossification and all patients returned to their previous jobs or sporting activities. Conclusions Using a coracoclavicular screw combined with an Acroplate can improve the patients’ function after ACJ disruption without any significant increase in surgical duration. Authors recommend this technique in the fixation of ACJ dislocation. PMID:24396788

ADOLESCENT IDIOPATHIC SCOLIOSIS: EVALUATION ON THE EFFECT OF SCREW DENSITY IN THE CORRECTION

Directory of Open Access Journals (Sweden)

Enguer Beraldo Garcia

2016-03-01

Full Text Available ABSTRACT Objective: The objective was to investigate implant density or the number of screws correlated with the correction of the main curve in patients undergoing surgery for adolescent idiopathic scoliosis (AIS. Methods: We evaluated 112 medical records: 33 patients with screw density of up to 50%, and 79 patients with a density of 100%; all patients underwent surgical correction by posterior approach with transpedicular fixation. Results: In the group of patients with screw density of up to 50% the residual Cobb median was 10°; in the group with 100% density, the median was 7°. Conclusion: Biostatistical analysis showed that the group with up to 50% of screw density presented correction rate of 82.1% and the group with 100% density had correction of about 86.8%. It is therefore concluded that the difference is statistically significant in favor of the fixation with 100% density (p =0.010.

Parameters Affecting the Extraction Process of Jatropha Curcas Oil Using a Single Screw Extruder

OpenAIRE

Siregar, Ali Nurrakhmad; Ghani, Jaharah A; Che Haron, Che Hassan; Rizal, Muhammad

2015-01-01

The most commonly used technique to separate oil and cake from J. curcas seeds is mechanical extraction. It uses simple tools such as a piston and a screw extruder to produce high pressure, driven by hand or by engine. A single screw extruder has one screw rotating inside the barrel and materials simultaneously flow from the feed to the die zone. The highest oil yield can be obtained by a well-designed oil press as well as finding the optimum conditions for all parameters involved during the ...

Landau quantization, Aharonov–Bohm effect and two-dimensional pseudoharmonic quantum dot around a screw dislocation

International Nuclear Information System (INIS)

Filgueiras, Cleverson; Rojas, Moises; Aciole, Gilson; Silva, Edilberto O.

2016-01-01

Highlights: • We derive the Schrödinger equation for an electron around a screw dislocation in the presence of an external magnetic field. • We consider the electron confined on an interface. • Modifications due to the screw dislocation on the light interband absorption coefficient and absorption threshold frequency. - Abstract: We investigate the influence of a screw dislocation on the energy levels and the wavefunctions of an electron confined in a two-dimensional pseudoharmonic quantum dot under the influence of an external magnetic field inside a dot and Aharonov–Bohm field inside a pseudodot. The exact solutions for energy eigenvalues and wavefunctions are computed as functions of applied uniform magnetic field strength, Aharonov–Bohm flux, magnetic quantum number and the parameter characterizing the screw dislocation, the Burgers vector. We investigate the modifications due to the screw dislocation on the light interband absorption coefficient and absorption threshold frequency. Two scenarios are possible, depending on if singular effects either manifest or not. We found that as the Burgers vector increases, the curves of frequency are pushed up towards of the growth of it. One interesting aspect which we have observed is that the Aharonov–Bohm flux can be tuned in order to cancel the screw effect of the model.

Landau quantization, Aharonov–Bohm effect and two-dimensional pseudoharmonic quantum dot around a screw dislocation

Energy Technology Data Exchange (ETDEWEB)

Filgueiras, Cleverson, E-mail: cleverson.filgueiras@dfi.ufla.br [Departamento de Física, Universidade Federal de Lavras, Caixa Postal 3037, 37200-000, Lavras, MG (Brazil); Rojas, Moises, E-mail: moises.leyva@dfi.ufla.br [Departamento de Física, Universidade Federal de Lavras, Caixa Postal 3037, 37200-000, Lavras, MG (Brazil); Aciole, Gilson [Unidade Acadêmica de Física, Universidade Federal de Campina Grande, POB 10071, 58109-970, Campina Grande, PB (Brazil); Silva, Edilberto O., E-mail: edilberto.silva@ufma.br [Departamento de Física, Universidade Federal do Maranhão, 65085-580, São Luís, MA (Brazil)

2016-11-25

Highlights: • We derive the Schrödinger equation for an electron around a screw dislocation in the presence of an external magnetic field. • We consider the electron confined on an interface. • Modifications due to the screw dislocation on the light interband absorption coefficient and absorption threshold frequency. - Abstract: We investigate the influence of a screw dislocation on the energy levels and the wavefunctions of an electron confined in a two-dimensional pseudoharmonic quantum dot under the influence of an external magnetic field inside a dot and Aharonov–Bohm field inside a pseudodot. The exact solutions for energy eigenvalues and wavefunctions are computed as functions of applied uniform magnetic field strength, Aharonov–Bohm flux, magnetic quantum number and the parameter characterizing the screw dislocation, the Burgers vector. We investigate the modifications due to the screw dislocation on the light interband absorption coefficient and absorption threshold frequency. Two scenarios are possible, depending on if singular effects either manifest or not. We found that as the Burgers vector increases, the curves of frequency are pushed up towards of the growth of it. One interesting aspect which we have observed is that the Aharonov–Bohm flux can be tuned in order to cancel the screw effect of the model.

Pullout characteristics of percutaneous pedicle screws with different cement augmentation methods in elderly spines: An in vitro biomechanical study.

Science.gov (United States)

Charles, Y P; Pelletier, H; Hydier, P; Schuller, S; Garnon, J; Sauleau, E A; Steib, J-P; Clavert, P

2015-05-01

Vertebroplasty prefilling or fenestrated pedicle screw augmentation can be used to enhance pullout resistance in elderly patients. It is not clear which method offers the most reliable fixation strength if axial pullout and a bending moment is applied. The purpose of this study is to validate a new in vitro model aimed to reproduce a cut out mechanism of lumbar pedicle screws, to compare fixation strength in elderly spines with different cement augmentation techniques and to analyze factors that might influence the failure pattern. Six human specimens (82-100 years) were instrumented percutaneously at L2, L3 and L4 by non-augmented screws, vertebroplasty augmentation and fenestrated screws. Cement distribution (2 ml PMMA) was analyzed on CT. Vertebral endplates and the rod were oriented at 45° to the horizontal plane. The vertebral body was held by resin in a cylinder, linked to an unconstrained pivot, on which traction (10 N/s) was applied until rupture. Load-displacement curves were compared to simultaneous video recordings. Median pullout forces were 488.5 N (195-500) for non-augmented screws, 643.5 N (270-1050) for vertebroplasty augmentation and 943.5 N (750-1084) for fenestrated screws. Cement augmentation through fenestrated screws led to significantly higher rupture forces compared to non-augmented screws (P=0.0039). The pullout force after vertebroplasty was variable and linked to cement distribution. A cement bolus around the distal screw tip led to pullout forces similar to non-augmented screws. A proximal cement bolus, as it was observed in fenestrated screws, led to higher pullout resistance. This cement distribution led to vertebral body fractures prior to screw pullout. The experimental setup tended to reproduce a pullout mechanism observed on radiographs, combining axial pullout and a bending moment. Cement augmentation with fenestrated screws increased pullout resistance significantly, whereas the fixation strength with the vertebroplasty

MIS Single-position Lateral and Oblique Lateral Lumbar Interbody Fusion and Bilateral Pedicle Screw Fixation: Feasibility and Perioperative Results.

Science.gov (United States)

Blizzard, Daniel J; Thomas, J Alex

2018-03-15

Retrospective review of prospectively collected data of the first 72 consecutive patients treated with single-position one- or two-level lateral (LLIF) or oblique lateral interbody fusion (OLLIF) with bilateral percutaneous pedicle screw and rod fixation by a single spine surgeon. To evaluate the clinical feasibility, accuracy, and efficiency of a single-position technique for LLIF and OLLIF with bilateral pedicle screw and rod fixation. Minimally-invasive lateral interbody approaches are performed in the lateral decubitus position. Subsequent repositioning prone for bilateral pedicle screw and rod fixation requires significant time and resources and does not facilitate increased lumbar lordosis. The first 72 consecutive patients (300 screws) treated with single-position LLIF or OLLIF and bilateral pedicle screws by a single surgeon between December 2013 and August 2016 were included in the study. Screw accuracy and fusion were graded using computed tomography and several timing parameters were recorded including retractor, fluoroscopy, and screw placement time. Complications including reoperation, infection, and postoperative radicular pain and weakness were recorded. Average screw placement time was 5.9 min/screw (standard deviation, SD: 1.5 min; range: 3-9.5 min). Average total operative time (interbody cage and pedicle screw placement) was 87.9 minutes (SD: 25.1 min; range: 49-195 min). Average fluoroscopy time was 15.0 s/screw (SD: 4.7 s; range: 6-25 s). The pedicle screw breach rate was 5.1% with 10/13 breaches measured as < 2 mm in magnitude. Fusion rate at 6-months postoperative was 87.5%. Two (2.8%) patients underwent reoperation for malpositioned pedicle screws with subsequent resolution of symptoms. The single-position, all-lateral technique was found to be feasible with accuracy, fluoroscopy usage, and complication rates comparable with the published literature. This technique eliminates the time and staffing associated with

Effects of phase lag on the information rate of a bistable Duffing oscillator

International Nuclear Information System (INIS)

Perkins, Edmon; Balachandran, Balakumar

2015-01-01

To utilize noise for systems, which are transmitting or receiving information, the information rate is a necessary metric to consider. The phase lag, which is the difference between the sender (applied forcing) and receiver (the oscillator) phases, has a significant effect on the information rate. However, this phase lag is a nonlinear function of the noise level. Here, the effects of phase lag on the information rate for a Duffing oscillator are examined and comparative discussions are made with phase lag from linear response theory. The phase lag is shown to be an important variable in calculating the information rate. - Highlights: • Simulations and Fokker–Planck analysis for Duffing oscillator response are performed. • The phase lag is found to be a nonlinear function of the noise level. • The phase lag is shown to be important for calculating the information rate metric

Effects of phase lag on the information rate of a bistable Duffing oscillator

Energy Technology Data Exchange (ETDEWEB)

Perkins, Edmon, E-mail: edmon@umd.edu; Balachandran, Balakumar, E-mail: balab@umd.edu

2015-02-06

To utilize noise for systems, which are transmitting or receiving information, the information rate is a necessary metric to consider. The phase lag, which is the difference between the sender (applied forcing) and receiver (the oscillator) phases, has a significant effect on the information rate. However, this phase lag is a nonlinear function of the noise level. Here, the effects of phase lag on the information rate for a Duffing oscillator are examined and comparative discussions are made with phase lag from linear response theory. The phase lag is shown to be an important variable in calculating the information rate. - Highlights: • Simulations and Fokker–Planck analysis for Duffing oscillator response are performed. • The phase lag is found to be a nonlinear function of the noise level. • The phase lag is shown to be important for calculating the information rate metric.

CT-based bone density assessment for iliosacral screw trajectories

Directory of Open Access Journals (Sweden)

Andreas Schicho

2016-01-01

Full Text Available Introduction: Sacroiliac screw placement is one standard treatment option for stabilization of posterior pelvic ring injuries encountering high intra- and inter-individual variations of bone stock quality as well as a vast variety and prevalence of sacral dysmorphism. An individual, easy-to-use preoperative bone stock quality estimation would be of high value for the surgeon. Materials and Methods: We analyzed 36 standard computed tomography datasets with the uninjured pelvic ring. Using a two-plane cross-referencing technique, we assessed the Hounsfield unit (HU mean values as well as standard deviation and minimum/maximum values within selected region of interests (ROIs at five key areas: os ilium left and right, massa lateralis of os sacrum left and right, and central vertebral body on levels S1 and S2. Results: Results showed no difference in mean HU at any ROI when comparing male and female data. For all ROIs set on S1 and S2, there was an age-related decline of HU with a calculated slope significantly different from zero. There was no statistical difference of slopes when comparing S1- and S2-level with respect to any distinct ROI. Comparison of levels S1 and S2 revealed differences at the vertebral body and at the right os ilium. The right and left massa lateralis of os sacrum had lower bone density than the center of the vertebral body, the right, or left os ilium on S1; right and left massa lateralis density did not differ significantly. On level S2, results were comparable with no difference of massa lateralis density. Conclusion: With our easy-to-use preoperative assessment of bone density of five key areas of sacroiliac screw anchoring we were able to find the lowest bone density in both the left and right massa lateralis on levels S1 and S2 with high inter- and intra-individual variations. Significantly lower bone density was found in the center of the vertebral bodies S2 in comparison to S1, which both are crucial for iliosacral

Kinematics of a Hybrid Manipulator by Means of Screw Theory

International Nuclear Information System (INIS)

Gallardo-Alvarado, J

2005-01-01

In this work the kinematics of a hybrid manipulator, namely a fully parallel-serial manipulator, with a particular topology is approached by means of the theory of screws. Given the length of the six independent limbs, the forward position analysis of the mechanism under study, indeed the computation of the resulting pose, position and orientation, of the end-platform with respect to the fixed platform, is carried out in closed-form solution. Therefore conveniently this initial analysis avoids the use of a numerical technique such as the Newton-Raphson method. Writing in screw form the reduced acceleration state of the translational platform, with respect to the fixed platform, a simple expression for the computation of the acceleration of the translational platform is derived by taking advantage of the properties of reciprocal screws, via the Klein form, a bilinear symmetric form of the Lie algebra e(3). Following a similar procedure, a simple expression for the computation of the angular acceleration of the end-platform, with respect to the translational platform, is easily derived. Naturally, as an intermediate step, this contribution also provides the forward and inverse velocity analyses of the chosen parallel-serial manipulator. Finally, in order to prove the versatility of the expressions obtained via screw theory for solving the kinematics, up to the acceleration analysis, of the proposed spatial mechanism, a numerical example is solved with the help of commercial computer codes

Simultaneous live cell imaging using dual FRET sensors with a single excitation light.

Directory of Open Access Journals (Sweden)

Yusuke Niino

Full Text Available Fluorescence resonance energy transfer (FRET between fluorescent proteins is a powerful tool for visualization of signal transduction in living cells, and recently, some strategies for imaging of dual FRET pairs in a single cell have been reported. However, these necessitate alteration of excitation light between two different wavelengths to avoid the spectral overlap, resulting in sequential detection with a lag time. Thus, to follow fast signal dynamics or signal changes in highly motile cells, a single-excitation dual-FRET method should be required. Here we reported this by using four-color imaging with a single excitation light and subsequent linear unmixing to distinguish fluorescent proteins. We constructed new FRET sensors with Sapphire/RFP to combine with CFP/YFP, and accomplished simultaneous imaging of cAMP and cGMP in single cells. We confirmed that signal amplitude of our dual FRET measurement is comparable to of conventional single FRET measurement. Finally, we demonstrated to monitor both intracellular Ca(2+ and cAMP in highly motile cardiac myocytes. To cancel out artifacts caused by the movement of the cell, this method expands the applicability of the combined use of dual FRET sensors for cell samples with high motility.

Determination of Screw and Nail Withdrawal Strengths in Parallel and Perpendicular to Grain of some Hardwoods of Iran

Directory of Open Access Journals (Sweden)

Sadegh Maleki

2013-06-01

Full Text Available In this study, screw and nail withdrawal strengths parallel and perpendicular longitudinal to grain of some hardwoods; oak (Quercus castaneifolia, hornbeam (Carpinus betulus, beech (Fagus orientalis, Sycamore (Platanus oriantalis and poplar (Populus deltoids were investigated. The tests were conducted following ASTM D 1761 with specimen dimension of 15×5×5(T×R×L. Three kinds of screws namely sheet metal screw, wood screw and coarse drywall screw with diameter of 4 and 5 mm were used. Three different nails with nominal diameter of 2.5, 3.25 and 3.75 mm were also used. The highest screw withdrawal strengths parallel and perpendicular to grain were related to hornbeam, beech, oak, Sycamore and poplar respectively. Furthermore, the highest nail withdrawal strengths parallel and perpendicular to grain were related to hornbeam, oak, beech, Sycamore and poplar respectively for nails with 3.75 mm diameter. Higher density and shear strength of hornbeam compared to the other species accounts for its high screw and nail withdrawal strengths parallel and perpendicular to grain.

The effect of polyethylene creep on tibial insert locking screw loosening and back-out in prosthetic knee joints.

Science.gov (United States)

Sanders, Anthony P; Raeymaekers, Bart

2014-10-01

A prosthetic knee joint typically comprises a cobalt-chromium femoral component that articulates with a polyethylene tibial insert. A locking screw may be used to prevent micromotion and dislodgement of the tibial insert from the tibial tray. Screw loosening and back-out have been reported, but the mechanism that causes screw loosening is currently not well understood. In this paper, we experimentally evaluate the effect of polyethylene creep on the preload of the locking screw. We find that the preload decreases significantly as a result of polyethylene creep, which reduces the torque required to loosen the locking screw. The torque applied to the tibial insert due to internal/external rotation within the knee joint during gait could thus drive locking screw loosening and back-out. The results are very similar for different types of polyethylene. Copyright © 2014 Elsevier Ltd. All rights reserved.

When long-range zero-lag synchronization is feasible in cortical networks

Directory of Open Access Journals (Sweden)

Atthaphon eViriyopase

2012-07-01

Full Text Available Many studies have reported long-range synchronization of neuronal activity between brain areas, in particular in the gamma-band with frequencies in the range of 40-80 Hz. Several studies have reported synchrony with zero phase lag, which is remarkable considering the synaptic and conduction delays inherent in the connections between distant brain areas. This result has led to many speculations about the possible functional role of zero-lag synchrony, e.g., for neuronal communication in attention, memory and feature binding. However, recent studies using recordings of single-unit activity and local field potentials report that neuronal synchronization occurs with non-zero phase lags. This raises the questions whether zero-lag synchrony can occur in the brain and, if so, under which conditions.We used analytical methods and computer simulations to investigate which connectivity between neuronal populations allows or prohibits zero-lag synchrony. We did so for a model where two oscillators interact via a relay oscillator. Analytical results and computer simulations were obtained for both type I Mirollo-Strogatz neurons and type II Hodgkin-Huxley neurons. We have investigated the dynamics of the model for various types of synaptic coupling and importantly considered the potential impact of Spike-Timing Dependent Plasticity (STDP and its learning window. We confirm previous results that zero-lag synchrony can be achieved in this configuration. This is much easier to achieve with Hodgkin-Huxley neurons, which have a biphasic phase response curve, than for type I neurons. STDP facilitates zero-lag synchrony as it adjusts the synaptic strengths such that zero-lag synchrony is feasible for a much larger range of parameters than without STDP.

Stability of biodegradable metal (Mg-Ca-Zn alloy) screws compared with absorbable polymer and titanium screws for sagittal split ramus osteotomy of the mandible using the finite element analysis model.

Science.gov (United States)

Lee, Jee-Ho; Han, Hyung-Seop; Kim, Yu-Chan; Lee, Jin-Yong; Lee, Bu-Kyu

2017-10-01

Mg-Ca-Zn alloy has been suggested for the application of fixation materials during maxillofacial surgery. We investigated the stability of Mg-Ca-Zn alloy for clinical application during orthognathic surgery. The finite element model for the fixation of sagittal split ramus osteotomy was constructed. In the bicortical screw fixation of the mandible setback condition, the stress distributions of Mg-Ca-Za alloy, polylactic acid polymer, and titanium were evaluated using the virtual model with occlusal loading of 132 N. The deformations of the three different materials of fixation screw were observed according to masticatory force ranging from 132 to 1,000 N. When comparing the stress distribution placed on cortical bone between the polymer and magnesium alloy groups, the magnesium alloy screws could bear more stress, thereby decreasing the stress, which might be distributed to other biologic components, such as the condyle and cortical ramus of the mandible. Deformations of the screws according to functional load were minimal, and the deformation remained stability of sagittal split ramus osteotomy setback surgery. Copyright © 2017. Published by Elsevier Ltd.

A Race Against Time: Time Lags in Terrestrial-Aquatic Linkages

Science.gov (United States)

Basu, N. B.

2017-12-01

Unprecedented decreases in atmospheric nitrogen (N) deposition together with increases in agricultural N-use efficiency have led to decreases in net anthropogenic N inputs in many eastern U.S. and Canadian watersheds as well as in Europe. Despite such decreases, N concentrations in streams and rivers continue to increase, and problems of coastal eutrophication remain acute. Such a mismatch between N inputs and outputs can arise due to legacy N accumulation and subsequent lag times between implementation of conservation measures and improvements in water quality. In the present study, we quantified such lag times by pairing long-term N input trajectories with stream N concentration data in multiple watersheds in North America. Results show significant nonlinearity between N inputs and outputs, with a strong hysteresis effect indicative of decadal-scale lag times. Lag times were found to be negatively correlated with both tile drainage and watershed slope, with tile drainage being a dominant control in fall and watershed slope being significant during the spring snowmelt period. Quantification of such lags will be crucial to policy-makers as they struggle to set appropriate goals for water quality improvement in human-impacted watersheds.

A phenomenological study on twin screw extruders

NARCIS (Netherlands)

Janssen, L.P.B.M.

1976-01-01

Although more and more twin screw extruders are being used in the polymer industry, the theoretical background is relatively undeveloped. The literature abounds in contradictions and often informs the reader that all extrusion problems can be solved if a certain new design is considered. The

Improving the API dissolution rate during pharmaceutical hot-melt extrusion I: Effect of the API particle size, and the co-rotating, twin-screw extruder screw configuration on the API dissolution rate.

Science.gov (United States)

Li, Meng; Gogos, Costas G; Ioannidis, Nicolas

2015-01-15

The dissolution rate of the active pharmaceutical ingredients in pharmaceutical hot-melt extrusion is the most critical elementary step during the extrusion of amorphous solid solutions - total dissolution has to be achieved within the short residence time in the extruder. Dissolution and dissolution rates are affected by process, material and equipment variables. In this work, we examine the effect of one of the material variables and one of the equipment variables, namely, the API particle size and extruder screw configuration on the API dissolution rate, in a co-rotating, twin-screw extruder. By rapidly removing the extruder screws from the barrel after achieving a steady state, we collected samples along the length of the extruder screws that were characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) to determine the amount of undissolved API. Analyses of samples indicate that reduction of particle size of the API and appropriate selection of screw design can markedly improve the dissolution rate of the API during extrusion. In addition, angle of repose measurements and light microscopy images show that the reduction of particle size of the API can improve the flowability of the physical mixture feed and the adhesiveness between its components, respectively, through dry coating of the polymer particles by the API particles. Copyright © 2014. Published by Elsevier B.V.

Visualization and understanding of the granulation liquid mixing and distribution during continuous twin screw granulation using NIR chemical imaging.

Science.gov (United States)

Vercruysse, Jurgen; Toiviainen, Maunu; Fonteyne, Margot; Helkimo, Niko; Ketolainen, Jarkko; Juuti, Mikko; Delaet, Urbain; Van Assche, Ivo; Remon, Jean Paul; Vervaet, Chris; De Beer, Thomas

2014-04-01