Immediate percutaneous sacroiliac screw insertion for unstable pelvic fractures: is it safe enough?

Science.gov (United States)

Acker, A; Perry, Z H; Blum, S; Shaked, G; Korngreen, A

2018-04-01

The purpose of this study was to compare the results of immediate and delayed percutaneous sacroiliac screws surgery for unstable pelvic fractures, regarding technical results and complication rate. Retrospective study. The study was conducted at the Soroka University Medical center, Beer Sheva, Israel, which is a level 1 trauma Center. 108 patients with unstable pelvic injuries were operated by the orthopedic department at the Soroka University Medical Center between the years 1999-2010. A retrospective analysis found 50 patients with immediate surgery and 58 patients with delayed surgery. Preoperative and postoperative imaging were analyzed and data was collected regarding complications. All patients were operated on by using the same technique-percutaneous fixation of sacroiliac joint with cannulated screws. The study's primary outcome measure was the safety and quality of the early operation in comparison with the late operation. A total of 156 sacroiliac screws were inserted. No differences were found between the immediate and delayed treatment groups regarding technical outcome measures (P value = 0.44) and complication rate (P value = 0.42). The current study demonstrated that immediate percutaneous sacroiliac screw insertion for unstable pelvic fractures produced equally good technical results, in comparison with the conventional delayed operation, without additional complications.

An in vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: an axial positioned dynamic compression plate and two abaxial transarticular cortical screws inserted in lag fashion versus three parallel transarticular cortical screws inserted in lag fashion.

Science.gov (United States)

Sod, Gary A; Riggs, Laura M; Mitchell, Colin F; Hubert, Jeremy D; Martin, George S

2010-01-01

To compare in vitro monotonic biomechanical properties of an axial 3-hole, 4.5 mm narrow dynamic compression plate (DCP) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion (DCP-TLS) with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion (3-TLS) for the equine proximal interphalangeal (PIP) joint arthrodesis. Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Cadaveric adult equine forelimbs (n=15 pairs). For each forelimb pair, 1 PIP joint was stabilized with an axial 3-hole narrow DCP (4.5 mm) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion and 1 with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion. Five matching pairs of constructs were tested in single cycle to failure under axial compression, 5 construct pairs were tested for cyclic fatigue under axial compression, and 5 construct pairs were tested in single cycle to failure under torsional loading. Mean values for each fixation method were compared using a paired t-test within each group with statistical significance set at Pcycle to failure, of the DCP-TLS fixation were significantly greater than those of the 3-TLS fixation. Mean cycles to failure in axial compression of the DCP-TLS fixation was significantly greater than that of the 3-TLS fixation. The DCP-TLS was superior to the 3-TLS in resisting the static overload forces and in resisting cyclic fatigue. The results of this in vitro study may provide information to aid in the selection of a treatment modality for arthrodesis of the equine PIP joint.

Anterior transarticular C1-C2 fixation with contralateral screw insertion: a report of two cases and technical note.

Science.gov (United States)

Lvov, Ivan; Grin, Andrey; Kaykov, Aleksandr; Smirnov, Vladimir; Krylov, Vladimir

2017-08-08

Anterior transarticular fixation of the C1-C2 vertebrae is a well-known technique that involves screw insertion through the body of the C2 vertebra into the lateral masses of the atlas through an anterior transcervical approach. Meanwhile, contralateral screw insertion has been previously described only in anatomical studies. We describe two case reports of the clinical application of this new technique. In Case 1, the patient was diagnosed with an unstable C1 fracture. The clinical features of the case did not allow for any type of posterior atlantoaxial fusion, Halo immobilization, or routine anterior fixation using the Reindl and Koller techniques. The possible manner of screw insertion into the anterior third of the right lateral mass was via a contralateral trajectory, which was performed in this case. Case 2 involved a patient with neglected posteriorly dislocated dens fracture who could not lie in the prone position due to concomitant cardiac pathology. Reduction of atlantoaxial dislocation was insufficient, even after scar tissue resection at the fracture, while transdental fusion was not possible. Considering the success of the previous case, atlantoaxial fixation was performed through the small approach, using the Reindl technique and contralateral screw insertion. These two cases demonstrate the potential of anterior transarticular fixation of C1-C2 vertebrae in cases where posterior atlantoaxial fusion is not achievable. This type of fixation can be performed through a single approach if one screw is inserted using the Reindl technique and another is inserted via a contralateral trajectory.

Use of palatally inserted mini-screw for upper molar distalization: A case series

Directory of Open Access Journals (Sweden)

Valliollah Arash

2015-09-01

Full Text Available  Abstract Reports have shown that molars can be distalized successfully with virtually no orthodontic anchorage loss with an intraosseous anchorage, even with fully erupted second molars. The purpose of this study was evaluating the effects of mini-screws as skeletal anchorage for upper molar distalization. In this case series, three patients needing maxillary first molar distalization, were selected. mini-screw was inserted in the anterior part of the palate. The screws were anchored to the first premolars by transpalatal arch and immediately loaded (150-160 g by 0.018-inch arch-wire and steel open-coil spring to distalize maxillary molars. The skeletal and dental changes were measured on cephalograms obtained before and after distalization. The amount of first molar distalization in the patients was 4 mm with 2°of tipping, 4 mm with 5°of tipping, and 3.5 mm with 2°of tipping respectively. Upper incisors and first premolars were stable during distalization.       

The feasibility of inserting a C1 pedicle screw in patients with ponticulus posticus: a retrospective analysis of eleven patients.

Science.gov (United States)

Zhang, Xin-Liang; Huang, Da-Geng; Wang, Xiao-Dong; Zhu, Jin-Wen; Li, Yi-Bing; He, Bao-Rong; Hao, Ding-Jun

2017-04-01

Ponticulus posticus is a common anatomic variation that can be mistaken for a broad posterior arch during C1 pedicle screw placement. When the atlas lateral mass screws are placed via the posterior arch, injury to the vertebral artery may result. To our knowledge, there are few clinical studies that have analyzed the feasibility of C1 pedicle screw fixation in patients with ponticulus posticus, in clinical practice. To evaluate the feasibility of inserting a C1 pedicle screw in patients with ponticulus posticus. Between January 2008 and January 2012, 11 consecutive patients with atlantoaxial instability, and with a ponticulus posticus at C1, underwent posterior fusion surgery in our institution. According to preoperative computed tomography (CT) reconstruction, a complete ponticulus posticus was found unilaterally in nine patients and bilaterally in two. Postoperative CT reconstructive imaging was performed to assess whether C1 pedicle screw placement was successful. Patients were followed up at regular intervals and evaluated for symptoms of ponticulus posticus syndrome. Thirteen C1 pedicles (atlas vertebral artery groove), each with a complete ponticulus posticus, were successfully inserted with thirteen 3.5- or 4.0-mm diameter pedicle screws, without resection of the bony anomaly. No intraoperative complications (venous plexus, vertebral artery, or spinal cord injury) occurred. The mean follow-up period was 21 (range 14-30) months. Postoperative CT reconstructive images showed that all 13 pedicle screws were inserted in the C1 pedicles without destruction of the atlas pedicle cortical bone. In the follow-up period, none of the patients demonstrated clinical symptoms of ponticulus posticus syndrome or developed bone fusion. Three-dimensional CT imaging should be considered prior to C1 pedicle screw fixation in patients with ponticulus posticus, to avoid mistaking the ponticulus posticus for a widened dorsal arch of the atlas. If there is no ponticulus posticus

[Comparison of screw' inserting angle through the 11th and 12th rib anterior approaches for L1 burst fracture].

Science.gov (United States)

Ma, Li-Tai; Liu, Hao; Li, Tao; Song, Yue-Ming; Pei, Fu-Xing; Liu, Li-Min; Gong, Quan; Zeng, Jian-Cheng; Feng, Gan-Jun; Zhou, Zhong-Jie

2012-12-01

To compare screw's inserting angle through the 11th and 12th rib in treating L1 burst fracture, explore effects on inserting screw and postoperative angle. From October 2007 to October 2010, 108 patients with L1 brust fracture treated through anterior approach were analyzed,including 68 males and 40 females, aged from 21 to 64 years (mean 38.22 years). All patients were divided into the 11th (A, 51 cases) and 12th (B, 57 cases) approach. The data of operation time,blood loss, duration of incision pain, JOA score, Oswestry score, VAS score, quality of life (SF-36), recovery of nervous function, coronal Cobb angle, included angle between screw and plate were observed. All patients were followed up for 9 to 37 months, mean 23 months. The operation time, blood loss, duration of incision pain, in group A were lower than group B (P0.05). There were no differences in Cobb angle before operation, but had significance after operation (P=0.000). There were statistically significance between two group in angle between screw and plate (P=0.000, P=0.003). The 11th rib approach for the treatment of L1 burst fracture has less effects on screw, less trauma and less angle between screw and plate.

Training Distal Locking Screw Insertion Skills to Novice Trainees: A Comparison Between Fluoroscopic- and Electromagnetic-Guided Techniques.

Science.gov (United States)

Leroux, Timothy; Khoshbin, Amir; Nousiainen, Markku T

2015-10-01

To compare the effect fluoroscopy or electromagnetic (EM) guidance has on the learning of locking screw insertion in tibial nails in surgical novices. A randomized, prospective, controlled trial was conducted involving 18 surgical trainees with no prior experience inserting locking screws in intramedullary nails. After a training session using fluoroscopy, participants underwent a pretest using fluoroscopic guidance. Participants were then randomized into either the fluoroscopy or EM group and were further trained using their respective technique. Post, retention, and transfer tests were conducted. Outcomes included task completion, drill attempts, screw changes, and radiation time. Intragroup comparisons revealed that the EM group used significantly less drill attempts during the post and retention tests compared with the pretest (P = 0.016 and P = 0.016, respectively). Intergroup comparisons revealed that the EM group was (1) more likely to complete the task during the retention test (P = 0.043) and (2) had significantly less radiation time during the post and retention tests (P = 0.002 and P = 0.003, respectively). Radiation time in the EM group during the transfer test increased to a level equal to what the fluoroscopy group used during the post and retention tests (P = 0.71 and P = 0.92, respectively). No other significant between-group differences occurred. EM guidance may be safely used to assist in the training of surgical novices in the skill of distal locking screw insertion. Not only does this technology significantly improve the ability to complete the task and decrease radiation use but also it does so without compromising skill acquisition. Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

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.

Comparative Analysis of Effect of Density, Insertion Angle and Reinsertion on Pull-Out Strength of Single and Two Pedicle Screw Constructs Using Synthetic Bone Model

OpenAIRE

Krishnan, Venkatesh; Varghese, Vicky; Kumar, Gurunathan Saravana

2016-01-01

Study Design Biomechanical study. Purpose To determine the effect of density, insertion angle and reinsertion on pull-out strength of pedicle screw in single and two screw-rod configurations. Overview of Literature Pedicle screw pull-out studies have involved single screw construct, whereas two screws and rod constructs are always used in spine fusions. Extrapolation of results using the single screw construct may lead to using expensive implants or increasing the fusion levels specifically i...

Are computer numerical control (CNC)-manufactured patient-specific metal templates available for posterior thoracic pedicle screw insertion? Feasibility and accuracy evaluation.

Science.gov (United States)

Kong, Xiangxue; Tang, Lei; Ye, Qiang; Huang, Wenhua; Li, Jianyi

2017-11-01

Accurate and safe posterior thoracic pedicle insertion (PTPI) remains a challenge. Patient-specific drill templates (PDTs) created by rapid prototyping (RP) can assist in posterior thoracic pedicle insertion, but pose biocompatibility risks. The aims of this study were to develop alternative PDTs with computer numerical control (CNC) and assess their feasibility and accuracy in assisting PTPI. Preoperative CT images of 31 cadaveric thoracic vertebras were obtained and then the optimal pedicle screw trajectories were planned. The PDTs with optimal screw trajectories were randomly assigned to be designed and manufactured by CNC or RP in each vertebra. With the guide of the CNC- or RP-manufactured PDTs, the appropriate screws were inserted into the pedicles. Postoperative CT scans were performed to analyze any deviations at entry point and midpoint of the pedicles. The CNC group was found to be significant manufacture-time-shortening, and cost-decreasing, when compared with the RP group (P  0.05). The screw positions were grade 0 in 90.3% and grade 1 in 9.7% of the cases in the CNC group and grade 0 in 93.5% and grade 1 in 6.5% of the cases in the RP group (P = 0.641). CNC-manufactured PDTs are viable for assisting in PTPI with good feasibility and accuracy.

CT-based morphometric analysis of the occipital condyle: focus on occipital condyle screw insertion.

Science.gov (United States)

Zhou, Jinsong; Espinoza Orías, Alejandro A; Kang, Xia; He, Jade; Zhang, Zhihai; Inoue, Nozomu; An, Howard S

2016-11-01

OBJECTIVE The segmental occipital condyle screw (OCS) is an alternative fixation technique in occipitocervical fusion. A thorough morphological study of the occipital condyle (OC) is critical for OCS placement. The authors set out to introduce a more precise CT-based method for morphometric analysis of the OC as it pertains to the placement of the segmental OCS, and they describe a novel preoperative simulation method for screw placement. Two new clinically relevant parameters, the height available for the OCS and the warning depth, are proposed. METHODS CT data sets from 27 fresh-frozen human cadaveric occipitocervical spines were used. All measurements were performed using a commercially available 3D reconstruction software package. The length, width, and sagittal angle of the condyle were measured in the axial plane at the base of the OC. The height of the OC and the height available for the segmental OCS were measured in the reconstructed oblique sagittal plane, fitting the ideal trajectory of the OCS recommended in the literature. The placement of a 3.5-mm-diameter screw that had the longest length of bicortical purchase was simulated into the OC in the oblique sagittal plane, with the screw path not being blocked by the occiput and not violating the hypoglossal canal cranially or the atlantooccipital joint caudally. The length of the simulated screw was recorded. The warning depth was measured as the shortest distance from the entry point of the screw to the posterior border of the hypoglossal canal. RESULTS The mean length and width of the OC were found to be larger in males: 22.2 ± 1.7 mm and 12.1 ± 1.0 mm, respectively, overall (p < 0.0001 for both). The mean sagittal angle was 28.0° ± 4.9°. The height available for the OCS was significantly less than the height of the OC (6.2 ± 1.3 mm vs 9.4 ± 1.5 mm, p < 0.0001). The mean screw length (19.3 ± 1.9 mm) also presented significant sex-related differences: male greater than female (p = 0.0002). The

[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

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...

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)

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)

Feasibility of Modified Anterior Odontoid Screw Fixation: Analysis of a New Trajectory Using 3-Dimensional Simulation Software.

Science.gov (United States)

Zhang, Li-Lian; Chen, Qi; Wang, Hao-Li; Xu, Hua-Zi; Tian, Nai-Feng

2018-05-03

Anterior odontoid screw fixation (AOSF) has been suggested as the optimal treatment for type II and some shallow type III odontoid fractures. However, only the classical surgical trajectory is available; no newer entry points or trajectories have been reported. We evaluated the anatomic feasibility of a new trajectory for AOSF using 3-dimensional (3D) screw insertion simulation software (Mimics). Computed tomography (CT) scans of patients (65 males and 59 females) with normal cervical structures were obtained consecutively, and the axes were reconstructed in 3 dimensions by Mimics software. Then simulated operations were performed using 2 new entry points below the superior articular process using bilateral screws of different diameters (group 1: 4 mm and 4 mm; group 2: 4 mm and 3.5 mm; group 3: 3.5 mm and 3.5 mm). The success rates and the required screw lengths were recorded and analyzed. The success rates were 79.03% for group 1, 95.16% for group 2, and 98.39% for group 3. The success rates for groups 2 and 3 did not differ significantly, and both were significantly better than the rate for group 1. The success rate was much higher in males than in females in group 1, but the success rate was similar in males and females in the other 2 groups. Screw lengths did not differ significantly among the 3 groups, but an effect of sex was apparent. Our modified trajectory is anatomically feasible for fixation of anterior odontoid fractures, but further anatomic experiments and clinical research are needed. Copyright © 2018 Elsevier Inc. All rights reserved.

Numerical studies on the heat transfer and friction characteristics of the first wall inserted with the screw blade for water cooled ceramic breeder blanket of CFETR

International Nuclear Information System (INIS)

Jiang, Kecheng; Ma, Xuebin; Cheng, Xiaoman; Liu, Songlin

2016-01-01

Highlights: • Enhanced heat transfer and friction characteristics of the FW inserted with screw blade is investigated. • The screw blade structure optimization was done on the screw pitch and diameter. • Decreasing screw pitch and increasing screw diameter could further enhance heat transfer accompanied with increasing flow resistance. • Evaluate the overall enhanced heat performance by using the PEC value. - Abstract: The Water Cooled Ceramic Breeder (WCCB) blanket based on Pressurized Water Reactor (PWR) condition is one of the blanket candidates for Chinese Fusion Engineering Test Reactor (CFETR). The first wall (FW) which plays an important part in the blanket design must remove the high heat flux radiated from plasma and nuclear heat deposition on the structure in any operating conditions. In this paper, the characteristics of enhanced heat transfer and friction for the FW with the inserted screw blade are studied by the numerical method. After the comparison between the numerical and experimental results, the standard k–ε turbulent model is selected to do the numerical calculation. The numerical results show that the peak temperature of RAFM steel could be reduced by decreasing screw pitch or increasing screw diameter, while accompanied with ascending flow resistance. Besides, among all of the chosen calculation cases compared with the smooth channel, the maximum value of temperature reduction is 10 °C under the conditions of heat flux of 0.5 MW/m"2 as well as screw pitch of 18 mm and screw diameter of 6 mm. The maximum increment ratio of the friction factor is 257% under the conditions of screw pitch of 10 mm and screw diameter of 4 mm. Furthermore, screw blade of 74 mm pitch and 4 mm diameter presents the highest overall performance evaluation criterion (PEC) value of 0.93 under Reynolds number of 270 000 conditions, and shows the best overall heat transfer enhancement performance.

Numerical studies on the heat transfer and friction characteristics of the first wall inserted with the screw blade for water cooled ceramic breeder blanket of CFETR

Energy Technology Data Exchange (ETDEWEB)

Jiang, Kecheng [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); University of Science and Technology of China, Hefei, Anhui 230037 (China); Ma, Xuebin; Cheng, Xiaoman [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Liu, Songlin, E-mail: slliu@ipp.ac.cn [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031 (China)

2016-03-15

Highlights: • Enhanced heat transfer and friction characteristics of the FW inserted with screw blade is investigated. • The screw blade structure optimization was done on the screw pitch and diameter. • Decreasing screw pitch and increasing screw diameter could further enhance heat transfer accompanied with increasing flow resistance. • Evaluate the overall enhanced heat performance by using the PEC value. - Abstract: The Water Cooled Ceramic Breeder (WCCB) blanket based on Pressurized Water Reactor (PWR) condition is one of the blanket candidates for Chinese Fusion Engineering Test Reactor (CFETR). The first wall (FW) which plays an important part in the blanket design must remove the high heat flux radiated from plasma and nuclear heat deposition on the structure in any operating conditions. In this paper, the characteristics of enhanced heat transfer and friction for the FW with the inserted screw blade are studied by the numerical method. After the comparison between the numerical and experimental results, the standard k–ε turbulent model is selected to do the numerical calculation. The numerical results show that the peak temperature of RAFM steel could be reduced by decreasing screw pitch or increasing screw diameter, while accompanied with ascending flow resistance. Besides, among all of the chosen calculation cases compared with the smooth channel, the maximum value of temperature reduction is 10 °C under the conditions of heat flux of 0.5 MW/m{sup 2} as well as screw pitch of 18 mm and screw diameter of 6 mm. The maximum increment ratio of the friction factor is 257% under the conditions of screw pitch of 10 mm and screw diameter of 4 mm. Furthermore, screw blade of 74 mm pitch and 4 mm diameter presents the highest overall performance evaluation criterion (PEC) value of 0.93 under Reynolds number of 270 000 conditions, and shows the best overall heat transfer enhancement performance.

Compressive forces achieved in simulated equine third metacarpal bone lateral condylar fractures of varying fragment thickness with Acutrak Plus screw and 4.5 mm AO cortical screws.

Science.gov (United States)

Lewis, Andrew J; Sod, Gary A; Burba, Daniel J; Mitchell, Colin F

2010-01-01

To compare compression pressure (CP) of 6.5 mm Acutrak Plus (AP) and 4.5 mm AO cortical screws (AO) when inserted in simulated lateral condylar fractures of equine 3rd metacarpal (MC3) bones. Paired in vitro biomechanical testing. Cadaveric equine MC3 bones (n=12 pair). Complete lateral condylar osteotomies were created parallel to the midsagittal ridge at 20, 12, and 8 mm axial to the epicondylar fossa on different specimens grouped accordingly. Interfragmentary compression was measured using a pressure sensor placed in the fracture plane before screw placement for fracture fixation. CP was acquired and mean values of CP for each fixation method were compared between the 6.5 mm (AP) and 4.5 mm (AO) for each group using a paired t-test within each fracture fragment thickness group with statistical significance set at Pfractures, especially complete fractures. Because interfragmentary compression plays a factor in the overall stability of a repair, it is recommended for use only in patients with thin lateral condyle fracture fragments, as the compression tends to decrease with an increase in thickness.

Radiostrontium clearance and bone formation in response to simulated internal screw fixation

International Nuclear Information System (INIS)

Daum, W.J.; Simmons, D.J.; Fenster, R.; Shively, R.A.

1987-01-01

Changes in radiostrontium clearance (SrC) and bone formation (tetracycline labeling) were observed in the femurs of skeletally mature dogs following the various operative steps involved in bone screw fixation. Drilling, but not periosteal stripping, produced a small but statistically significant increase in SrC and endosteal bone formation in the distal third of the bone. Strontium clearance values equivalent to those produced by drilling alone were recorded after screw fixation at low or high torque (5 versus 20 inch pounds), as well as by the insertion of loosely fitting stainless steel implants. Bone formation (equals the percentage tetracycline-labeled trabecular bone surfaces) was increased by 30% when SrC values exceeded 3.5 ml/100 g bone/min, and the relationship was linear when SrC values ranged between 1.0 and 7.0 ml/100 g bone/min. The changes in SrC and bone formation one-week after bone screw application are primarily those associated with a response to local trauma caused by drilling

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)

Numerical Simulation and Performance Analysis of Twin Screw Air Compressors

Directory of Open Access Journals (Sweden)

W. S. Lee

2001-01-01

Full Text Available A theoretical model is proposed in this paper in order to study the performance of oil-less and oil-injected twin screw air compressors. Based on this model, a computer simulation program is developed and the effects of different design parameters including rotor profile, geometric clearance, oil-injected angle, oil temperature, oil flow rate, built-in volume ratio and other operation conditions on the performance of twin screw air compressors are investigated. The simulation program gives us output variables such as specific power, compression ratio, compression efficiency, volumetric efficiency, and discharge temperature. Some of the above results are then compared with experimentally measured data and good agreement is found between the simulation results and the measured data.

Advantages of Direct Insertion of a Straight Probe Without a Guide Tube During Anterior Odontoid Screw Fixation of Odontoid Fractures.

Science.gov (United States)

Park, Jin Hoon; Kang, Dong-Ho; Lee, Moon Kyu; Yoo, Byoungwoo; Jung, Sang Ku; Hwang, Soo-Hyun; Kim, Jeoung Hee; Oh, Sunkyu; Lee, Eun Jung; Jeon, Sang Ryong; Roh, Sung Woo; Rhim, Seung Chul

2016-05-01

A retrospective cohort study. The aim of this study was to compare the anterior odontoid screw fixation (AOSF) with a guide tube or with a straight probe. AOSF associates with several complications, including malpositioning, fixation loss, and screw breakage. Screw pull-out from the C2 body is the most common complication. All consecutive patients with type II or rostral shallow type III odontoid fractures who underwent AOSFs during the study period were enrolled retrospectively. The guide-tube AOSF method followed the standard published method except C3 body and C2-3 disc annulus rimming was omitted to prevent disc injury; instead, the guide tube was anchored at the anterior inferior C2 vertebra corner. After 2 screw pull-outs, the guide-tube cohort was analyzed to identify the cause of instrument failure. Thereafter, the straight-probe method was developed. A guide tube was not used. A small pilot hole was made on the most anterior side of the inferior endplate, followed by insertion of a 2.5 mm straight probe through the C2 body. Non-union and instrument failure rates and screw-direction angles of the guide-tube and straight-probe groups were recorded. The guide-tube group (n = 13) had 2 screw pull-outs and 1 non-union. The straight-probe group (n = 8) had no complications and significantly larger screw-direction angles than the guide-tube group (60.5 ± 4.63 vs. 54.8 ± 3.82 degrees; P = 0.047). Straight-probe AOSF yielded larger direction angles without injuring bone and disc. Complications were absent. The procedure was easier than guide-tube AOSF and assured sufficient engagement, even in horizontal fracture orientation cases. 3.

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.

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.

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)

Z-2 Threaded Insert Design and Testing

Science.gov (United States)

Ross, Amy; Rhodes, Richard; Jones, Robert J.; Graziosi, David; Ferl, Jinny; Sweeny, Mitch; Scarborough, Stephen

2016-01-01

NASA's Z-2 prototype space suit contains several components fabricated from an advanced hybrid composite laminate consisting of IM10 carbon fiber and fiber glass. One requirement was to have removable, replaceable helicoil inserts to which other suit components would be fastened. An approach utilizing bonded in inserts with helicoils inside of them was implemented. During initial assembly, cracking sounds were heard followed by the lifting of one of the blind inserts out of its hole when the screws were torqued. A failure investigation was initiated to understand the mechanism of the failure. Ultimately, it was determined that the pre-tension caused by torqueing the fasteners is a much larger force than induced from the pressure loads of the suit which was not considered in the insert design. Bolt tension is determined by dividing the torque on the screw by a k value multiplied by the thread diameter of the bolt. The k value is a factor that accounts for friction in the system. A common value used for k for a non-lubricated screw is 0.2. The k value can go down by as much as 0.1 if the screw is lubricated which means for the same torque, a much larger tension could be placed on the bolt and insert. This paper summarizes the failure investigation that was performed to identify the root cause of the suit failure and details how the insert design was modified to resist a higher pull out tension.

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.

Influence of Screw Length and Bone Thickness on the Stability of Temporary Implants

Directory of Open Access Journals (Sweden)

Daniel Jogaib Fernandes

2015-09-01

Full Text Available The purpose of this work was to study the influence of screw length and bone thickness on the stability of temporary implants. A total of 96 self-drilling temporary screws with two different lengths were inserted into polyurethane blocks (n = 66, bovine femurs (n = 18 and rabbit tibia (n = 12 with different cortical thicknesses (1 to 8 mm. Screws insertion in polyurethane blocks was assisted by a universal testing machine, torque peaks were collected by a digital torquemeter and bone thickness was monitored by micro-CT. The results showed that the insertion torque was significantly increased with the thickness of cortical bone from polyurethane (p < 0.0001, bovine (p = 0.0035 and rabbit (p < 0.05 sources. Cancellous bone improved significantly the mechanical implant stability. Insertion torque and insertion strength was successfully moduled by equations, based on the cortical/cancellous bone behavior. Based on the results, insertion torque and bone strength can be estimate in order to prevent failure of the cortical layer during temporary screw placement. The stability provided by a cortical thickness of 2 or 1 mm coupled to cancellous bone was deemed sufficient for temporary implants stability.

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.

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.

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.

Insertion torques influenced by bone density and surface roughness of HA–TiO{sub 2} coatings

Energy Technology Data Exchange (ETDEWEB)

Cheng, T.; Chen, Y.; Nie, X., E-mail: xnie@uwindsor.ca

2013-12-31

Bio-ceramic TiO{sub 2} coatings containing calcium (Ca) and phosphorous (P) were deposited onto Ti–6Al–4V alloy screws using plasma electrolytic oxidation (PEO) processes in an alkaline electrolyte with hydroxyapatite (HA) suspension. Coating on each screw had different surface roughness and morphology. Insertion torque (IT) of the coated screws in low (10 pcf, pounds per cubic feet), medium–high (20 pcf), and high (40 pcf) density of artificial bones was measured in comparison with that of the uncoated and sandblasted screws having similar surface roughness. Higher insertion torques and final seating torques were obtained in the coated screws which may result in less micro-movement during the primary implantation stage and thus lower the risk of implant failure. Scanning electron microscopy (SEM) analysis indicated that all coatings still adhesively remained on the screw surfaces after inserted into the bones with different densities. The relationship between coefficient of friction and surface roughness was also addressed to better understand the results of insertion torque. It was found that a lower density bone (similar to aged bone) would need a surface-rougher coated screw to achieve a high torque while a high density bone can have a wide range of selections for surface roughness of the screw. - Highlights: • The insertion torque of PEO-coated screws is higher than machined and sandblasting implants. • Lower density bone needs a rougher coated implant to increase the insertion torque. • The composite HA–TiO{sub 2} coating could benefit dental implants in both primary and secondary stability stages.

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.

[Odontoid bending stiffness after anterior fixation with a single lag screw: biomechanical study].

Science.gov (United States)

Buchvald, P; Čapek, L; Barsa, P

2015-01-01

PURPOSE OF THE STUDY The aim of the experiment was to compare the bending stiffness of an intact odontoid process with bending stiffness after its simulated type II fracture was fixed with a single lag screw. The experiment was done with a desire to answer the question of whether a single osteosynthetic screw is sufficient for good fixation of a type II odontoid fracture. MATERIAL AND METHODS The C2 vertebrae of six cadavers were used. With simultaneous measurement of odontoid bending stiffness, the occurrence of a fracture (type IIA, Grauer's modification of the Anderson- D'Alonzo classification) was simulated using action exerted by a tearing machine in the direction perpendicular to the odontoid axis. Each odontoid fracture was subsequently treated by direct osteosynthesis with a single lag screw inserted in the axial direction by a standard surgical procedure in order to provide conditions similar to those achieved by routine surgical management. The treated odontoid process was subsequently subjected to the same tearing machine loading as applied to it at the start of the experiment. The bending stiffness measured was then compared with that found before the fracture occurred. The results were statistically evaluated by the t-test for paired samples at the level of significance α = 0.05. RESULTS The average value of bending stiffness for odontoid processes of intact vertebrae at the moment of fracture occurrence was 318.3 N/mm. After single axial lag screw fixation of the fracture, the average bending stiffness for the odontoid processes treated was 331.3 N/mm. DISCUSSION Higher values of bending stiffness after screw fixation were found in all specimens and, in comparison with the values recorded before simulated fractures, the increase was statistically significant. CONCLUSIONS The results of our measurements suggest that the single lag screw fixation of a type IIA odontoid fracture will provide better stability for the fracture fragment-C2 body complex on

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

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)

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

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.

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.

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.

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

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.

Torque de inserção e resistência ao arrancamento dos parafusos vertebrais com alma cilíndrica e cônica Insertion torque and pullout strength of vertebral screws with cylindrical and conic core

Directory of Open Access Journals (Sweden)

Ariane Zamarioli

2008-10-01

para fixação anterior da coluna vertebral são influenciados pela densidade do corpo de prova, desenho da rosca do parafuso e diâmetro do orifício-piloto.OBJECTIVE: To evaluate insertion torque and pullout strength of three different screws used in the anterior fixation of the spine, considering the influence of the diameter of the pilot hole (DOP, the test specimen density (CDP, and the screw thread design. METHODS: The authors used polyurethane test specimens with two densities: 0.16 and 0.32 g/cm³, and three types of screws (USS I, USS II posterior, and USS II anterior. In the first stage, the pilot hole was made with a 3.8 mm probe for all screws; in the second stage, with a probe smaller than the inner diameter of the screws (3.5 mm for screws USS I; 3.4 mm for USS II posterior screws, and 3.0 mm for USS II anterior screws. 12 experimental groups were formed with ten specimen tests in each group, according to the polyurethane density, DOP, and the type of screw used. Torque was measured during insertion of the screws and the pullout strength by a mechanical assay in a universal test machine. RESULTS: The maximum insertion torque presented a decreasing value in test specimens of 0.16 g/cm³ and 0.32 g/cm³ and in all pilot hole diameters. Maximum pullout strength in test specimens of 0.16 g/cm³ and 3.8 mm of perforation diameter was greater in USS II posterior screws than in USS I screws. With the perforation diameter smaller than the inner screw diameter, USS II posterior and anterior screws presented higher values than the USS I screw. In test specimens with 0.32 g/cm³ of density and perforation diameter of 3.8 mm, the pullout strength of USS II posterior and USS I screws was greater than that of USS II anterior screws. With the smaller perforation diameter than the inner diameter, the values were decreasing between the USS II posterior screw, then the USS II anterior screw, and then the USS I screw. CONCLUSION: Insertion torque and pullout strength of the

Pull out Strength of Dual Outer Diameter Pedicle Screws Compared to Uncemented and Cemented Standard Pedicle Screws: A Biomechanical in vitro Study.

Science.gov (United States)

Lorenz, Andrea; Leichtle, Carmen I; Frantz, Sandra; Bumann, Marte; Tsiflikas, Ilias; Shiozawa, Thomas; Leichtle, Ulf G

2017-05-01

To analyze the potential of the dual outer diameter screw and systematically evaluate the pull-out force of the dual outer diameter screw compared to the uncemented and cemented standard pedicle screws with special regard to the pedicle diameter and the vertebra level. Sixty vertebrae of five human spines (T 6 -L 5 ) were sorted into three study groups for pairwise comparison of the uncemented dual outer diameter screw, the uncemented standard screw, and the cemented standard screw, and randomized with respect to bone mineral density (BMD) and vertebra level. The vertebrae were instrumented, insertion torque was determined, and pull-out testing was performed using a material testing machine. Failure load was evaluated in pairwise comparison within each study group. The screw-to-pedicle diameter ratio was determined and the uncemented dual outer diameter and standard screws were compared for different ratios as well as vertebra levels. Significantly increased pull-out forces were measured for the cemented standard screw compared to the uncemented standard screw (+689 N, P dual outer diameter screw (+403 N, P dual outer diameter screw to the uncemented standard screw in the total study group, a distinct but not significant increase was measured (+149 N, P = 0.114). Further analysis of these two screws, however, revealed a significant increase of pull-out force for the dual outer diameter screw in the lumbar region (+247 N, P = 0.040), as well as for a screw-to-pedicle diameter ratio between 0.6 and 1 (+ 488 N, P = 0.028). For clinical application, cement augmentation remains the gold standard for increasing screw stability. According to our results, the use of a dual outer diameter screw is an interesting option to increase screw stability in the lumbar region without cement augmentation. For the thoracic region, however, the screw-to-pedicle diameter should be checked and attention should be paid to screw cut out, if the dual outer diameter screw is considered. �

The glide of screw dislocations in bcc Fe: Atomistic static and dynamic simulations

International Nuclear Information System (INIS)

Chaussidon, Julien; Fivel, Marc; Rodney, David

2006-01-01

We present atomic-scale simulations of screw dislocation glide in bcc iron. Using two interatomic potentials that, respectively, predict degenerate and non-degenerate core structures, we compute the static 0 K dependence of the screw dislocation Peierls stress on crystal orientation and show strong boundary condition effects related to the generation of non-glide stress components. At finite temperatures we show that, with a non-degenerate core, glide by nucleation/propagation of kink-pairs in a {1 1 0} glide plane is obtained at low temperatures. A transition in the twinning region, towards an average {1 1 2} glide plane, with the formation of debris loops is observed at higher temperatures

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.

Effect of modifying the screw access channels of zirconia implant abutment on the cement flow pattern and retention of zirconia restorations.

Science.gov (United States)

Wadhwani, Chandur; Chung, Kwok-Hung

2014-07-01

The effect of managing the screw access channels of zirconia implant abutments in the esthetic zone has not been extensively evaluated. The purpose of this study was to determine the effect of an insert placed within the screw access channel of an anterior zirconia implant abutment on the amount of cement retained within the restoration-abutment system and on the dislodging force. Thirty-six paired zirconia abutments and restorations were fabricated by computer-aided design and computer-aided manufacturing and were divided into 3 groups: open abutment, with the screw access channel unfilled; closed abutment, with the screw access channel sealed; and insert abutment, with a thin, tubular metal insert projection continuous with the screw head and placed into the abutment screw access channel. The restorations were cemented to the abutments with preweighed eugenol-free zinc oxide cement (TempBond NE). Excess cement was removed, and the weight of the cement that remained in the restoration-abutment system was measured. Vertical tensile dislodging forces were recorded at a crosshead speed of 5 mm/min after incubation in a 37°C water bath for 24 hours. The specimens were examined for the cement flow pattern into the screw access channel after dislodgement. Data were analyzed with ANOVA, followed by multiple comparisons by using the Tukey honestly significant difference test (α = .05). The mean (standard deviation) of retentive force values ranged from 108.1 ± 29.9 N to 148.3 ± 21.0 N. The retentive force values differed significantly between the insert abutment and both the open abutment (P abutment groups (P abutment and insert abutment being greater than closed abutment (P abutment with a metal insert significantly affected both the cement retained within the abutment itself and the retention capabilities of the zirconia restoration cemented with TempBond NE cement. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier

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.

Clinical results of free-hand pedicle screw placement by the palpation of lateral wall of pedicle (PLP) method for scoliosis surgery

International Nuclear Information System (INIS)

Oyama, Motohiko; Shimizu, Takachika; Fueki, Keisuke; Ino, Masatake; Toda, Naofumi; Tanouti, Tetu; Tatara, Yasunori; Manabe, Nodoka

2011-01-01

The purpose of this study was to evaluate the accuracy of thoracic pedicle screw (TPS) placement by the palpation of the lateral wall of the pedicle (PLP) method. The subjects of this study were 45 scoliosis patients. The accuracy of TPS placement was evaluated by postoperative CT. Of the 348 TPSs inserted, 26 (7.5%) breached the pedicle wall. Of the 26 misplaced screws, 20 were inserted on the wrong trajectory, and 6 were inserted at the wrong insertion point. The preoperative major Cobb angle averaged 70.4 deg in the group with pedicle perforation by the TPS, and 54.1 deg in the group with correct placement of the TPS (p=0.006). No intra- or post-operative complications developed as a result of the pedicle perforation. The PLP method is useful in deciding on the correct insertion point, but it is of no assistance in inserting screws along the correct trajectory. This, it will be necessary to improve the technique of determining the correct trajectory for the TPS. (author)

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.

Development of a nasogastric tube insertion simulator: a collaborative interdisciplinary effort.

Science.gov (United States)

Summer, Lindsay; Gonzalez, Laura; Jimeno, Miguel; Christensen, Ken

2009-01-01

The nursing faculty shortage has created the need for more innovative and effective ways to better stimulate nursing students. Simulation technology is one way to increase the effectiveness of teaching faculty. In this article, a collaborative project between the College of Nursing and College of Engineering at the University of South Florida to develop and evaluate a PC-based software simulator based on videogame technologies for nursing skill acquisition is discussed. A software simulator for teaching and assessing mastery of the procedure for nasogastric tube insertion is described. The purpose of the simulator is to complement the standard training of nasogastric tube insertion that uses static mannequins and instruction/assessment by nursing instructors. The simulator was used in a fundamentals of nursing class at the University of South Florida, with 75 students enrolled. Evaluation showed that the simulator significantly increased the confidence of the students in their ability to perform nasogastric tube insertion.

Automatic insertion of simulated microcalcification clusters in a software breast phantom

Science.gov (United States)

Shankla, Varsha; Pokrajac, David D.; Weinstein, Susan P.; DeLeo, Michael; Tuite, Catherine; Roth, Robyn; Conant, Emily F.; Maidment, Andrew D.; Bakic, Predrag R.

2014-03-01

An automated method has been developed to insert realistic clusters of simulated microcalcifications (MCs) into computer models of breast anatomy. This algorithm has been developed as part of a virtual clinical trial (VCT) software pipeline, which includes the simulation of breast anatomy, mechanical compression, image acquisition, image processing, display and interpretation. An automated insertion method has value in VCTs involving large numbers of images. The insertion method was designed to support various insertion placement strategies, governed by probability distribution functions (pdf). The pdf can be predicated on histological or biological models of tumor growth, or estimated from the locations of actual calcification clusters. To validate the automated insertion method, a 2-AFC observer study was designed to compare two placement strategies, undirected and directed. The undirected strategy could place a MC cluster anywhere within the phantom volume. The directed strategy placed MC clusters within fibroglandular tissue on the assumption that calcifications originate from epithelial breast tissue. Three radiologists were asked to select between two simulated phantom images, one from each placement strategy. Furthermore, questions were posed to probe the rationale behind the observer's selection. The radiologists found the resulting cluster placement to be realistic in 92% of cases, validating the automated insertion method. There was a significant preference for the cluster to be positioned on a background of adipose or mixed adipose/fibroglandular tissues. Based upon these results, this automated lesion placement method will be included in our VCT simulation pipeline.

Field simulation of axisymmetric plasma screw pinches by alternating-direction-implicit methods

International Nuclear Information System (INIS)

Lambert, M.A.

1996-06-01

An axisymmetric plasma screw pinch is an axisymmetric column of ionized gaseous plasma radially confined by forces from axial and azimuthal currents driven in the plasma and its surroundings. This dissertation is a contribution to detailed, high resolution computer simulation of dynamic plasma screw pinches in 2-d rz-coordinates. The simulation algorithm combines electron fluid and particle-in-cell (PIC) ion models to represent the plasma in a hybrid fashion. The plasma is assumed to be quasineutral; along with the Darwin approximation to the Maxwell equations, this implies application of Ampere's law without displacement current. Electron inertia is assumed negligible so that advective terms in the electron momentum equation are ignored. Electrons and ions have separate scalar temperatures, and a scalar plasma electrical resistivity is assumed. Altemating-direction-implicit (ADI) methods are used to advance the electron fluid drift velocity and the magnetic fields in the simulation. The ADI methods allow time steps larger than allowed by explicit methods. Spatial regions where vacuum field equations have validity are determined by a cutoff density that invokes the quasineutral vacuum Maxwell equations (Darwin approximation). In this dissertation, the algorithm was first checked against ideal MM stability theory, and agreement was nicely demonstrated. However, such agreement is not a new contribution to the research field. Contributions to the research field include new treatments of the fields in vacuum regions of the pinch simulation. The new treatments predict a level of magnetohydrodynamic turbulence near the bulk plasma surface that is higher than predicted by other methods

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.

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.

In Vivo Evaluation of Immediately Loaded Stainless Steel and Titanium Orthodontic Screws in a Growing Bone

OpenAIRE

Gritsch, Kerstin; Laroche, Norbert; Bonnet, Jeanne-Marie; Exbrayat, Patrick; Morgon, Laurent; Rabilloud, Muriel; Grosgogeat, Brigitte

2013-01-01

The present work intends to evaluate the use of immediate loaded orthodontic screws in a growing model, and to study the specific bone response. Thirty-two screws (half of stainless steel and half of titanium) were inserted in the alveolar bone of 8 growing pigs. The devices were immediately loaded with a 100 g orthodontic force. Two loading periods were assessed: 4 and 12 weeks. Both systems of screws were clinically assessed. Histological observations and histomorphometric analysis evaluate...

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.

Evaluation of the use of intra-operative radiology for open placement of lag screws for the stabilization of sacroiliac luxation in cats.

Science.gov (United States)

Silveira, Francisco; Quinn, Robert J; Adrian, Anna M; Owen, Martin R; Bush, Mark A

2017-01-16

To assess the effect of intra-operative radiology on the quality of lag screw insertion for the management of sacroiliac joint luxations in cats. In this retrospective single-centre study, the surgical, anaesthetic and imaging records of 40 screws (32 cats) placed with lag effect for management of sacroiliac luxation were reviewed. Postoperative radiographs were assessed for sacroiliac joint reduction, screw position, and sacral width purchased by each screw. Cases were divided into two groups according to the use of (IOR) or the absence of intra-operative radiology (NIOR). A total of 23 lag screws were placed with the aid of intra-operative radiology and 17 without. Three of the 23 screws placed in the IOR group exited the sacrum as opposed to eight of 17 screws in the NIOR group (p = 0.03). Mean sacral width purchased by the screws in the IOR group (70.8%) was also significantly higher (p = 0.002) than in the NIOR group (54.6%). Mean general anaesthetic times for unilateral and bilateral screw placement for the IOR group and NIOR group were not significantly different. The use of intra-operative radiology can significantly improve the quality of lag screw insertion for the stabilization of sacroiliac luxations in cats, which should lead to a reduced incidence of postoperative screw loosening.

Flow Field Simulation and Noise Control of a Twin-Screw Engine-Driven Supercharger

Directory of Open Access Journals (Sweden)

Tao Wang

2016-01-01

Full Text Available With the advantages of good low-speed torque capability and excellent instant response performance, twin-screw superchargers have great potential in the automobile market, but the noise of these superchargers is the main factor that discourages their use. Therefore, it is important to study their noise mechanism and methods of reducing it. This study included a transient numerical simulation of a twin-screw supercharger flow field with computational fluid dynamics software and an analysis of the pressure field of the running rotor. The results showed that overcompression was significant in the compression end stage of the supercharger, resulting in a surge in airflow to a supersonic speed and the production of shock waves that resulted in loud noise. On the basis of these findings, optimization of the supercharger is proposed, including expansion of the supercharger exhaust orifice and creation of a slot along the direction of the rotor spiral normal line at the exhaust port, so as to reduce the compression end pressure, improve the exhaust flow channel, and weaken the source of the noise. Experimental results showed that the noise level value of the improved twin-screw supercharger was significantly lower at the same speed than the original model, with an average decrease of about 5 dB (A.

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

Modelica-based modeling and simulation of a twin screw compressor for heat pump applications

International Nuclear Information System (INIS)

Chamoun, Marwan; Rulliere, Romuald; Haberschill, Philippe; Peureux, Jean-Louis

2013-01-01

A new twin screw compressor has been developed by SRM (Svenska Rotor Maskiner) for use in a new high temperature heat pump using water as refrigerant. This article presents a mathematical model of the thermodynamic process of compression in twin screw compressors. Using a special discretization method, a transient twin screw compressor model has been developed using Modelica in order to study the dry compression cycle of this machine at high temperature levels. The pressure and enthalpy evolution in the control volumes of the model are calculated as a function of the rotational angle of the male rotor using energy and continuity equations. In addition, associated processes encountered in real machines such as variable fluid leakages, water injection and heat losses are modeled and implemented in the main compressor model. A comparison is performed using the model developed, demonstrating the behavior of the compressor and the evolution of its different parameters in different configurations with and without water injection. This comparison shows the need for water injection to avoid compressor failure and improve its efficiency. -- Highlights: • Difficulties related to the compressor limit the development of a high temperature heat pump using water as refrigerant. • A new water vapor double screw compressor has been developed to overcome compression problems. • A dynamic model of this compressor has been developed and simulated using Modelica. • The behavior of the compressor has been identified all along the compression cycle and efficiencies have been calculated

Augmented reality fluoroscopy simulation of the guide-wire insertion in DHS surgery: A proof of concept study.

Science.gov (United States)

van Duren, B H; Sugand, K; Wescott, R; Carrington, R; Hart, A

2018-05-01

Hip fractures contribute to a significant clinical burden globally with over 1.6 million cases per annum and up to 30% mortality rate within the first year. Insertion of a dynamic hip screw (DHS) is a frequently performed procedure to treat extracapsular neck of femur fractures. Poorly performed DHS fixation of extracapsular neck of femur fractures can result in poor mobilisation, chronic pain, and increased cut-out rate requiring revision surgery. A realistic, affordable, and portable fluoroscopic simulation system can improve performance metrics in trainees, including the tip-apex distance (the only clinically validated outcome), and improve outcomes. We developed a digital fluoroscopic imaging simulator using orthogonal cameras to track coloured markers attached to the guide-wire which created a virtual overlay on fluoroscopic images of the hip. To test the accuracy with which the augmented reality system could track a guide-wire, a standard workshop femur was used to calibrate the system with a positional marker fixed to indicate the apex; this allowed for comparison between guide-wire tip-apex distance (TAD) calculated by the system to be compared to that physically measured. Tests were undertaken to determine: (1) how well the apex could be targeted; (2) the accuracy of the calculated TAD. (3) The number of iterations through the algorithm giving the optimal accuracy-time relationship. The calculated TAD was found to have an average root mean square error of 4.2 mm. The accuracy of the algorithm was shown to increase with the number of iterations up to 20 beyond which the error asymptotically converged to an error of 2 mm. This work demonstrates a novel augmented reality simulation of guide-wire insertion in DHS surgery. To our knowledge this has not been previously achieved. In contrast to virtual reality, augmented reality is able to simulate fluoroscopy while allowing the trainee to interact with real instrumentation and performing the procedure on

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.

Occam paradox? A variation of tapia syndrome and an unreported complication of guidewire-assisted pedicle screw insertion.

Science.gov (United States)

Emohare, Osa; Peterson, Erik; Slinkard, Nathaniel; Janus, Seth; Morgan, Robert

2013-10-01

Study Design Case report. Clinical Question The clinical aim is to report on a previously unknown association between guidewire-assisted pedicle screw insertion and neuropraxia of the recurrent laryngeal nerve (RLN), and how this may overlap with the signs of Tapia syndrome; we also report our approach to the clinical management of this patient. Methods A 17-year-old male patient with idiopathic scoliosis experienced Tapia syndrome after posterior instrumentation and arthrodesis at the level of T1-L1. After extubation, the patient had a hoarse voice and difficulty in swallowing. Imaging showed a breach in the cortex of the anterior body of T1 corresponding to the RLN on the right. Results Otolaryngological examination noted right vocal fold immobility, decreased sensation of the endolarynx, and pooling of secretions on flexible laryngoscopy that indicated right-sided cranial nerve X injury and left-sided tongue deviation. Aspiration during a modified barium swallow prompted insertion of a percutaneous endoscopic gastrostomy tube before the patient was sent home. On postoperative day 20, a barium swallow demonstrated reduced aspiration, and the patient reported complete resolution of symptoms. The feeding tube was removed, and the patient resumed a normal diet 1 month later. Tapia syndrome, or persistent unilateral laryngeal and hypoglossal paralysis, is an uncommon neuropraxia, which has previously not been observed in association with a breached vertebral body at T1 along the course of the RLN. Conclusion Tapia syndrome should be a differential diagnostic consideration whenever these symptoms persist postoperatively and spine surgeons should be aware of this as a potential complication of guidewires in spinal 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

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.

[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

Optimization of spinal implant screw for lower vertebra through finite element studies.

Science.gov (United States)

Biswas, Jayanta; Karmakar, Santanu; Majumder, Santanu; Banerjee, Partha Sarathi; Saha, Subrata; Roychowdhury, Amit

2014-01-01

The increasing older population is suffering from an increase in age-related spinal degeneration that causes tremendous pain. Spine injury is mostly indicated at the lumbar spine (L3-L5) and corresponding intervertebral disks. Finite element analysis (FEA) is now one of the most efficient and accepted tools used to simulate these pathological conditions in computer-assisted design (CAD) models. In this study, L3-L5 spines were modeled, and FEA was performed to formulate optimal remedial measures. Three different loads (420, 490.5, and 588.6 N) based on three body weights (70, 90, and 120 kg) were applied at the top surface of the L3 vertebra, while the lower surface of the L5 vertebra remained fixed. Models of implants using stainless steel and titanium alloy (Ti6Al4V) pedicle screws and rods with three different diameters (4, 5, and 6 mm) were inserted into the spine models. The relative strengths of bone (very weak, weak, standard, strong, and very strong) were considered to determine the patient-specific effect. A total of 90 models were simulated, and von Mises stress and strain, shear stress, and strain intensity contour at the bone-implant interface were analyzed. Results of these analyses indicate that the 6-mm pedicle screw diameter is optimal for most cases. Experimental and clinical validation are needed to confirm these theoretical results.

Cervical pedicle screw fixation at C6 and C7 A cadaveric study

Directory of Open Access Journals (Sweden)

Ye Li

2015-01-01

Conclusion: The intersection of the horizontal line through the midpoint of the transverse process root and vertical line through the intersection of the posterolateral and posterior planes of the isthmus can be used as an entry point for C6 and C7 pedicle screw fixation. The screws should be inserted at 60 or 90° with the posterolateral isthmus in the horizontal plane and at 75° with the posterior isthmus in the sagittal plane. The LSC should not exceed 30 mm.

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.

Percutaneous Sacroiliac Screw Placement: A Prospective Randomized Comparison of Robot-assisted Navigation Procedures with a Conventional Technique

Science.gov (United States)

Wang, Jun-Qiang; Wang, Yu; Feng, Yun; Han, Wei; Su, Yong-Gang; Liu, Wen-Yong; Zhang, Wei-Jun; Wu, Xin-Bao; Wang, Man-Yi; Fan, Yu-Bo

2017-01-01

Background: Sacroiliac (SI) screw fixation is a demanding technique, with a high rate of screw malposition due to the complex pelvic anatomy. TiRobot™ is an orthopedic surgery robot which can be used for SI screw fixation. This study aimed to evaluate the accuracy of robot-assisted placement of SI screws compared with a freehand technique. Methods: Thirty patients requiring posterior pelvic ring stabilization were randomized to receive freehand or robot-assisted SI screw fixation, between January 2016 and June 2016 at Beijing Jishuitan Hospital. Forty-five screws were placed at levels S1 and S2. In both methods, the primary end point screw position was assessed and classified using postoperative computed tomography. Fisher's exact probability test was used to analyze the screws’ positions. Secondary end points, such as duration of trajectory planning, surgical time after reduction of the pelvis, insertion time for guide wire, number of guide wire attempts, and radiation exposure without pelvic reduction, were also assessed. Results: Twenty-three screws were placed in the robot-assisted group and 22 screws in the freehand group; no postoperative complications or revisions were reported. The excellent and good rate of screw placement was 100% in the robot-assisted group and 95% in the freehand group. The P value (0.009) showed the same superiority in screw distribution. The fluoroscopy time after pelvic reduction in the robot-assisted group was significantly shorter than that in the freehand group (median [Q1, Q3]: 6.0 [6.0, 9.0] s vs. median [Q1, Q3]: 36.0 [21.5, 48.0] s; χ2 = 13.590, respectively, P < 0.001); no difference in operation time after reduction of the pelvis was noted (χ2 = 1.990, P = 0.158). Time for guide wire insertion was significantly shorter for the robot-assisted group than that for the freehand group (median [Q1, Q3]: 2.0 [2.0, 2.7] min vs. median [Q1, Q3]: 19.0 [15.5, 45.0] min; χ2 = 20.952, respectively, P < 0.001). The number of guide

Periodontal ligament formation around different types of dental titanium implants. I. The self-tapping screw type implant system

DEFF Research Database (Denmark)

Warrer, K; Karring, T; Gotfredsen, K

1993-01-01

The aim of this study was to determine if a periodontal ligament can form around self-tapping, screw type titanium dental implants. Implants were inserted in contact with the periodontal ligament of root tips retained in the mandibular jaws of 7 monkeys. In each side of the mandible, 1 premolar......, a periodontal ligament can form on self-tapping, screw type titanium dental implants in areas where a void is present between the surrounding bone and the implant at the time of insertion....... and 2 molars were removed in such a manner that in approximately half the cases, the root tips were retained. Following healing, the experimental areas were examined on radiographs, and sites were selected for the insertion of the implants, so that every second implant would have a close contact...

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.

Comparative endurance testing of the Biomet Matthews Nail and the Dynamic Compression Screw, in simulated condylar and supracondylar femoral fractures

Directory of Open Access Journals (Sweden)

Davies Benjamin M

2008-01-01

Full Text Available Abstract Background The dynamic compression screw is a plate and screws implant used to treat fractures of the distal femur. The Biomet Matthews Nail is a new retrograde intramedullary nail designed as an alternative surgical option to treat these fractures. The objective of this study was to assess the comparative endurance of both devices. Method The dynamic compression screw (DCS and Biomet Matthews Nail (BMN were implanted into composite femurs, which were subsequently cyclically loaded using a materials testing machine. Simulated fractures were applied to each femur prior to the application of load. Either a Y type fracture or a transverse osteotomy was prepared on each composite femur using a jig to enable consistent positioning of cuts. Results The Biomet Matthews Nail demonstrated a greater endurance limit load over the dynamic compression screw in both fracture configurations. Conclusion The distal locking screws pass through the Biomet Matthews Nail in a unique "cruciate" orientation. This allows for greater purchase in the bone of the femoral condyle and potentially improves the stability of the fracture fixation. As these fractures are usually in weak osteoporotic bone, the Biomet Matthews Nail represents a favourable surgical option in these patients.

Conservative treatment of a mandibular condyle fracture: Comparing intermaxillary fixation with screws or arch bar. A randomised clinical trial.

Science.gov (United States)

van den Bergh, B; Blankestijn, J; van der Ploeg, T; Tuinzing, D B; Forouzanfar, T

2015-06-01

A mandibular condyle fracture can be treated conservatively by intermaxillary fixation (IMF) or by open reposition and internal fixation (ORIF). Many IMF-modalities can be chosen, including IMF-screws (IMFS). This prospective multi-centre randomised clinical trial compared the use of IMFS with the use of arch bars in the treatment of mandibular condyle fractures. The study population consisted of 50 patients (mean age: 31.8 years). Twenty-four (48%) patients were allocated in the IMFS group. Twenty-six (52%) patients were assigned to the arch bars group. In total 188 IMF-screws were used (5-12 screws per patient, mean 7.83 screws per patient). All pain scores were lower in the IMFS group. Three patients developed a malocclusion (IFMS-group: one patient, arch bars-group: two patients). Mean surgical time was significantly shorter in the IMFS group (59 vs. 126 min; pfractured on insertion (0.53%), one (0.53%) screw was inserted into a root. Six (3.2%) screws loosened spontaneously in four patients. Mucosal disturbances were seen in 22 patients, equally divided over both groups. Considering the advantages and the disadvantages of IMFS, and observing the results of this study, the authors conclude that IMFS provide a superior method for IMF. IMFS are safer for the patients and surgeons. Copyright © 2015 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

[SCREW-BASED INTERMAXILLARY TRACTION COMBINED WITH OCCLUSAL SPLINT FOR TREATMENT OF PEDIATRIC MANDIBULAR CONDYLAR FRACTURE].

Science.gov (United States)

Wu, Yang; Long, Xing; Deng, Mohong; Cai, Hengxing; Meng, Qinggong; Li, Bo

2015-04-01

To evaluate the effectiveness of the screw-based intermaxillary traction combined with occlusal splint in the treatment of pediatric mandibular condylar fracture. Between June 2005 and December 2013, 35 pediatric patients with 49 mandibular condylar fractures were treated, and the clinical data were retrospectively reviewed. There were 25 boys and 10 girls, aged 3-13 years (mean, 7.3 years). The injury causes included falling (18 cases), traffic accident (14 cases), and violence (3 cases). The time between injury and treatment was 2-30 days (mean, 6.8 days). Restricted mouth opening was observed, and the maximal mouth opening was (22.74 +/- 7.22) mm except 3 patients who were too young to measure. Condylar fractures were located at the left (12 cases), at the right (9 cases), at bilateral (14 cases) based on the sites; and fractures were classified as intracapsular (35 fractures), neck (10 fractures), and subcondylar (4 fractures) based on the fracture line. Four self-drilling titanium screws were inserted into the alveolar bone of both maxilla and mandible. After screw inserting, an occlusal splint with a fulcrum was used on the affected side and elastic band was put to perform anterior intermaxillary traction. After 1 month, the screws and splint were removed. Follow-up examinations were carried out on schedule. All the patients were followed up from 6 months to 8 years and 10 months (median, 71 months). No screw-related complication occurred in the others except one case of screw loosening. The postoperative maximal mouth opening was (38.82 +/- 2.02) nim. Mild joint noise was found in 4 cases and opening deviation occurred in 6 cases. Radiographic results demonstrated complete condyle remodeling was achieved in 24 cases (32 fractures), and moderate remodeling in 11 cases (17 fractures) at last follow-up. The screw-based intermaxillary traction combined with occlusal splint might be an effective method for pediatric mandibular condylar fracture. The screw

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.

Does intraoperative navigation improve the accuracy of pedicle screw placement in the apical region of dystrophic scoliosis secondary to neurofibromatosis type I: comparison between O-arm navigation and free-hand technique.

Science.gov (United States)

Jin, Mengran; Liu, Zhen; Liu, Xingyong; Yan, Huang; Han, Xiao; Qiu, Yong; Zhu, Zezhang

2016-06-01

To assess the accuracy of O-arm-navigation-based pedicle screw insertion in dystrophic scoliosis secondary to NF-1 and compare it with free-hand pedicle screw insertion technique. 32 patients with dystrophic NF-1-associated scoliosis were divided into two groups. A total of 92 pedicle screws were implanted in apical region (two vertebrae above and below the apex each) in 13 patients using O-arm-based navigation (O-arm group), and 121 screws were implanted in 19 patients using free-hand technique (free-hand group). The postoperative CT images were reviewed and analyzed for pedicle violation. The screw penetration was divided into four grades: grade 0 (ideal placement), grade 1 (penetration 4 mm). The accuracy rate of pedicle screw placement (grade 0, 1) was significantly higher in the O-arm group (79 %, 73/92) compared to 67 % (81/121) of the free-hand group (P = 0.045). Meanwhile, a significantly lower prevalence of grade 2-3 perforation was observed in the O-arm group (21 vs. 33 %, P arm navigation compared to free-hand technique (2 vs. 15 %, P arm navigation (58 vs. 42 %, P arm-based pedicle screw placement in dystrophic NF-1-associated scoliosis. O-arm navigation system does facilitate pedicle screw insertion in dystrophic NF-1-associated scoliosis, demonstrating superiorities in the safety and accuracy of pedicle screw placement in comparison with free-hand technique.

External jig in the placement of distal interlocking screws | Ikem ...

African Journals Online (AJOL)

Retrograde (52.2%) was the commonest surgical approach used for femur. The main indication for SIGN interlocking surgery was recent fracture 77.8%. Open reduction 97.8% was the commonest method of reduction used. The mean±SD bone union time was 3.58±0.56 months and range 3-5 months. Distal screw insertion ...

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.

不安定性骨盤骨折に対する各種 iliosacral screw の三点曲げ強度試験

OpenAIRE

野阪, 善雅; 稲田, 有史; 川西, 弘一; 前田, 裕仁; 三野, 浩也; 宮本, 誠司

1999-01-01

It is generally accepted that internal fixation using iliosacral screws for unstable pelvic fractures is effective. However, the placement of iliosacral screws is technically demanding and it has been reported that screws can be damaged by the load from the early part of the postoperative stage. We have reported that the dull insertion method of placement of iliosacral screws and combination of motor-evoked potential monitoring can reduce complications, whereas the strength of the iliosacral ...

Influence of implantoplasty on stress distribution of exposed implants at different bone insertion levels

Directory of Open Access Journals (Sweden)

João Paulo Mendes TRIBST

2017-12-01

Full Text Available Abstract This study evaluated the effect of implantoplasty on different bone insertion levels of exposed implants. A model of the Bone Level Tapered implant (Straumann Institute, Waldenburg, Switzerland was created through the Rhinoceros software (version 5.0 SR8, McNeel North America, Seattle, WA, USA. The abutment was fixed to the implant through a retention screw and a monolithic crown was modeled over a cementation line. Six models were created with increasing portions of the implant threads exposed: C1 (1 mm, C2 (2 mm, C3 (3 mm, C4 (4 mm, C5 (5 mm and C6 (6 mm. The models were made in duplicates and one of each pair was used to simulate implantoplasty, by removing the threads (I1, I2, I3, I4, I5 and I6. The final geometry was exported in STEP format to ANSYS (ANSYS 15.0, ANSYS Inc., Houston, USA and all materials were considered homogeneous, isotropic and linearly elastic. To assess distribution of stress forces, an axial load (300 N was applied on the cusp. For the periodontal insert, the strains increased in the peri-implant region according to the size of the exposed portion and independent of the threads’ presence. The difference between groups with and without implantoplasty was less than 10%. Critical values were found when the inserted portion was smaller than the exposed portion. In the exposed implants, the stress generated on the implant and retention screw was higher in the models that received implantoplasty. For the bone tissue, exposure of the implant’s thread was a damaging factor, independent of implantoplasty. Implantoplasty treatment can be safely used to control peri-implantitis if at least half of the implant is still inserted in bone.

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.

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

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.

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

[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

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

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.

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

Mapping occipital bone thickness using computed tomography for safe screw placement.

Science.gov (United States)

Morita, Tomonori; Takebayashi, Tsuneo; Takashima, Hiroyuki; Yoshimoto, Mitsunori; Ida, Kazunori; Tanimoto, Katsumasa; Ohnishi, Hirofumi; Fujiwara, Hiroyoshi; Nagae, Masateru; Yamashita, Toshihiko

2015-08-01

OBJECT Safe and effective insertion of occipital bone screws requires morphological analysis of the occipital bone, which is poorly documented in the literature. The authors of this study present morphological data for determining the area of screw placement for optimal internal fixation. METHODS The subjects of this institutional review board-approved retrospective study were 105 individuals without head and neck disease who underwent CT imaging at the authors' hospital. There were 55 males and 50 females, with a mean age of 57.1 years (range 20-91 years). Measurements using CT were taken according to a matrix of 55 points following a grid with 1-cm spacing based on the external occipital protuberance (EOP). RESULTS The maximum thickness of the occipital bone was at the level of the EOP at 16.4 mm. Areas with thicknesses > 8 mm were more frequent at the EOP and up to 2 cm in all directions, as well as up to 1 cm in all directions at a height of 1 cm inferiorly, and up to 3 cm from the EOP inferiorly. The male group tended to have a thicker occipital bone than the female group, and the differences were significant around the EOP. The ratio of the trabecular bone to the occipital bone thickness was > 30% in the central region. At positions more than 2 cm laterally, the ratio was < 15%, and the ratio gradually decreased further laterally. CONCLUSIONS Screws that are 8 mm long can be placed in the area extending 2 cm laterally from the EOP at the level of the superior nuchal line and approximately 3 cm inferior to the center. These results suggest that it may be possible to effectively insert a screw over a wider area than the conventional reference range.

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.

Comparison of migration behavior between single and dual lag screw implants for intertrochanteric fracture fixation

Directory of Open Access Journals (Sweden)

Katonis Pavlos G

2009-05-01

Full Text Available Abstract Background Lag screw cut-out failure following fixation of unstable intertrochanteric fractures in osteoporotic bone remains an unsolved challenge. This study tested if resistance to cut-out failure can be improved by using a dual lag screw implant in place of a single lag screw implant. Migration behavior and cut-out resistance of a single and a dual lag screw implant were comparatively evaluated in surrogate specimens using an established laboratory model of hip screw cut-out failure. Methods Five dual lag screw implants (Endovis, Citieffe and five single lag screw implants (DHS, Synthes were tested in the Hip Implant Performance Simulator (HIPS of the Legacy Biomechanics Laboratory. This model simulated osteoporotic bone, an unstable fracture, and biaxial rocking motion representative of hip loading during normal gait. All constructs were loaded up to 20,000 cycles of 1.45 kN peak magnitude under biaxial rocking motion. The migration kinematics was continuously monitored with 6-degrees of freedom motion tracking system and the number of cycles to implant cut-out was recorded. Results The dual lag screw implant exhibited significantly less migration and sustained more loading cycles in comparison to the DHS single lag screw. All DHS constructs failed before 20,000 cycles, on average at 6,638 ± 2,837 cycles either by cut-out or permanent screw bending. At failure, DHS constructs exhibited 10.8 ± 2.3° varus collapse and 15.5 ± 9.5° rotation around the lag screw axis. Four out of five dual screws constructs sustained 20,000 loading cycles. One dual screw specimens sustained cut-out by medial migration of the distal screw after 10,054 cycles. At test end, varus collapse and neck rotation in dual screws implants advanced to 3.7 ± 1.7° and 1.6 ± 1.0°, respectively. Conclusion The single and double lag screw implants demonstrated a significantly different migration resistance in surrogate specimens under gait loading simulation with

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.

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)

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.)

Activated states for cross-slip at screw dislocation intersections in face-centered cubic nickel and copper via atomistic simulation

International Nuclear Information System (INIS)

Rao, S.I.; Dimiduk, D.M.; El-Awady, J.A.; Parthasarathy, T.A.; Uchic, M.D.; Woodward, C.

2010-01-01

We extend our recent simulation studies where a screw dislocation in face-centered cubic (fcc) Ni was found to spontaneously attain a low energy partially cross-slipped configuration upon intersecting a forest dislocation. Using atomistic (molecular statics) simulations with embedded atom potentials, we evaluated the activation barrier for a dislocation to transform from fully residing on the glide plane to fully residing on a cross-slip plane intersecting a forest dislocation in both Ni and Cu. The activation energies were obtained by determining equilibrium configurations (energies) when variable pure tensile or compressive stresses were applied along the [1 1 1] direction on the partially cross-slipped state. We show that the activation energy is a factor of 2-5 lower than that for cross-slip in isolation via the Escaig process. The cross-slip activation energies obtained at the intersection in Cu were in reasonable accord with the experimentally determined cross-slip activation energy for Cu. Further, the activation barrier for cross-slip at these intersections was shown to be linearly proportional to (d/b)[ln(√(3)d/b)] 1/2 , as in the Escaig process, where d is the Shockley partial dislocation spacing and b is the Burgers vector of the screw dislocation. These results suggest that cross-slip should be preferentially observed at selected screw dislocation intersections in fcc materials.

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.

The FADE mass-stat: A technique for inserting or deleting particles in molecular dynamics simulations

Energy Technology Data Exchange (ETDEWEB)

Borg, Matthew K., E-mail: matthew.borg@strath.ac.uk [Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom); Lockerby, Duncan A., E-mail: duncan.lockerby@warwick.ac.uk [School of Engineering, University of Warwick, Coventry CV4 7AL (United Kingdom); Reese, Jason M., E-mail: jason.reese@ed.ac.uk [School of Engineering, University of Edinburgh, Edinburgh EH9 3JL (United Kingdom)

2014-02-21

The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually “fades-in” (inserts) or “fades-out” (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C{sub 60} Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.

The FADE mass-stat: A technique for inserting or deleting particles in molecular dynamics simulations

International Nuclear Information System (INIS)

Borg, Matthew K.; Lockerby, Duncan A.; Reese, Jason M.

2014-01-01

The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually “fades-in” (inserts) or “fades-out” (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C 60 Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors

[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 evaluation of immediate loading of electroeroded screw-retained titanium fixed prostheses supported by tilted implant: a multicenter retrospective study.

Science.gov (United States)

Acocella, Alessandro; Ercoli, Carlo; Geminiani, Alessandro; Feng, Changyong; Billi, Mauro; Acocella, Gabriele; Giannini, Domenico; Sacco, Roberto

2012-05-01

Immediate occlusal loading of dental implants in the edentulous mandible has proven to be an effective, reliable, and predictable treatment protocol. However, there is limited long-term data available in the literature, when an electroeroded definitive cast-titanium fixed prosthesis is used for this treatment protocol. The aim of this study was to evaluate the clinical effectiveness of dental implants (Astra Tech Dental, Mölndal, Sweden) in the edentulous mandible immediately loaded with an electroeroded cast-titanium screw-retained fixed prosthesis. Forty-five patients received five implants each in the interforaminal area. All the implants were inserted with torque up to 40 Ncm and the distal implants were distally tilted approximately 20 to 30 degrees to minimize the length of posterior cantilevers. Implants were loaded within 48 hours of placement with an acrylic resin-titanium screw-retained prosthesis fabricated by electroerosion. Two of the 225 inserted implants failed after 3 and 16 months of healing, respectively, with a cumulative survival rate of 99.1% and a prosthetic survival rate of 97.8%. Immediate loading of tilted dental implants inserted in the edentulous mandible with a screw-retained titanium definitive prosthesis fabricated with electrical discharge machining provide reliable and predictable results. © 2011 Wiley Periodicals, Inc.

Heat Transfer Enhancement Studies in a Circular Tube Fitted with Right-Left Helical Inserts with Spacer

OpenAIRE

P. K. Nagarajan; P. Sivashanmugam

2011-01-01

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with 300 right-left helical screw inserts with 100 mm spacer of different twist ratio has been presented for laminar and turbulent flow.. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer coefficient enhancement for 300 RL inserts with 100 mm spacer is quite comparable with for 300 R-L inserts. Performance evalu...

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.

Modeling, simulation, and optimal initiation planning for needle insertion into the liver.

Science.gov (United States)

Sharifi Sedeh, R; Ahmadian, M T; Janabi-Sharifi, F

2010-04-01

Needle insertion simulation and planning systems (SPSs) will play an important role in diminishing inappropriate insertions into soft tissues and resultant complications. Difficulties in SPS development are due in large part to the computational requirements of the extensive calculations in finite element (FE) models of tissue. For clinical feasibility, the computational speed of SPSs must be improved. At the same time, a realistic model of tissue properties that reflects large and velocity-dependent deformations must be employed. The purpose of this study is to address the aforementioned difficulties by presenting a cost-effective SPS platform for needle insertions into the liver. The study was constrained to planar (2D) cases, but can be extended to 3D insertions. To accommodate large and velocity-dependent deformations, a hyperviscoelastic model was devised to produce an FE model of liver tissue. Material constants were identified by a genetic algorithm applied to the experimental results of unconfined compressions of bovine liver. The approach for SPS involves B-spline interpolations of sample data generated from the FE model of liver. Two interpolation-based models are introduced to approximate puncture times and to approximate the coordinates of FE model nodes interacting with the needle tip as a function of the needle initiation pose; the latter was also a function of postpuncture time. A real-time simulation framework is provided, and its computational benefit is highlighted by comparing its performance with the FE method. A planning algorithm for optimal needle initiation was designed, and its effectiveness was evaluated by analyzing its accuracy in reaching a random set of targets at different resolutions of sampled data using the FE model. The proposed simulation framework can easily surpass haptic rates (>500 Hz), even with a high pose resolution level ( approximately 30). The computational time required to update the coordinates of the node at the

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.

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

CUDA accelerated simulation of needle insertions in deformable tissue

International Nuclear Information System (INIS)

Patriciu, Alexandru

2012-01-01

This paper presents a stiff needle-deformable tissue interaction model. The model uses a mesh-less discretization of continuum; avoiding thus the expensive remeshing required by the finite element models. The proposed model can accommodate both linear and nonlinear material characteristics. The needle-deformable tissue interaction is modeled through fundamental boundaries. The forces applied by the needle on the tissue are divided in tangent forces and constraint forces. The constraint forces are adaptively computed such that the material is properly constrained by the needle. The implementation is accelerated using NVidia CUDA. We present detailed analysis of the execution timing in both serial and parallel case. The proposed needle insertion model was integrated in a custom software that loads DICOM images, generate the deformable model, and can simulate different insertion strategies.

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.

Analysis on Accuracy of Bias, Linearity and Stability of Measurement System in Ball screw Processes by Simulation

Directory of Open Access Journals (Sweden)

Fan-Yun Pai

2015-11-01

Full Text Available To consistently produce high quality products, a quality management system, such as the ISO9001, 2000 or TS 16949 must be practically implemented. One core instrument of the TS16949 MSA (Measurement System Analysis is to rank the capability of a measurement system and ensure the quality characteristics of the product would likely be transformed through the whole manufacturing process. It is important to reduce the risk of Type I errors (acceptable goods are misjudged as defective parts and Type II errors (defective parts are misjudged as good parts. An ideal measuring system would have the statistical characteristic of zero error, but such a system could hardly exist. Hence, to maintain better control of the variance that might occur in the manufacturing process, MSA is necessary for better quality control. Ball screws, which are a key component in precision machines, have significant attributes with respect to positioning and transmitting. Failures of lead accuracy and axial-gap of a ball screw can cause negative and expensive effects in machine positioning accuracy. Consequently, a functional measurement system can incur great savings by detecting Type I and Type II errors. If the measurement system fails with respect to specification of the product, it will likely misjudge Type I and Type II errors. Inspectors normally follow the MSA regulations for accuracy measurement, but the choice of measuring system does not merely depend on some simple indices. In this paper, we examine the stability of a measuring system by using a Monte Carlo simulation to establish bias, linearity variance of the normal distribution, and the probability density function. Further, we forecast the possible area distribution in the real case. After the simulation, the measurement capability will be improved, which helps the user classify the measurement system and establish measurement regulations for better performance and monitoring of the precision of the ball screw.

Effect of screw position on single cycle to failure in bending and torsion of a locking plate-rod construct in a synthetic feline femoral gap model.

Science.gov (United States)

Niederhäuser, Simone K; Tepic, Slobodan; Weber, Urs T

2015-05-01

To evaluate the effect of screw position on strength and stiffness of a combination locking plate-rod construct in a synthetic feline femoral gap model. 30 synthetic long-bone models derived from beechwood and balsa wood. 3 constructs (2 locking plate-rod constructs and 1 locking plate construct; 10 specimens/construct) were tested in a diaphyseal bridge plating configuration by use of 4-point bending and torsion. Variables included screw position (near the fracture gap and far from the fracture gap) and application of an intramedullary pin. Constructs were tested to failure in each loading mode to determine strength and stiffness. Failure was defined as plastic deformation of the plate or breakage of the bone model or plate. Strength, yield angle, and stiffness were compared by use of a Wilcoxon test. Placement of screws near the fracture gap did not increase bending or torsional stiffness in the locking plate-rod constructs, assuming the plate was placed on the tension side of the bone. Addition of an intramedullary pin resulted in a significant increase in bending strength of the construct. Screw positioning did not have a significant effect on any torsion variables. Results of this study suggested that, in the investigated plate-rod construct, screw insertion adjacent to the fracture lacked mechanical advantages over screw insertion at the plate ends. For surgeons attempting to minimize soft tissue dissection, the decision to make additional incisions for screw placement should be considered with even more caution.

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.

Migração de parafuso em artroplastia total do joelho: relato clínico Screw migration in total knee arthroplasty: case report

Directory of Open Access Journals (Sweden)

Fernando Fonseca

2010-01-01

Full Text Available As complicações das artroplastias totais do joelho devidas ao material implantado são raras, exceto o desgaste do polietileno. O relato de migração de parafusos dentro da articulação do joelho é muito raro. Os autores relatam a migração intra-articular de um parafuso de segurança do polietileno numa artroplastia total do joelho com sacrifício do ligamento cruzado posterior (ATJ tipo Performance; Biomet, Warsaw, IN que obrigou a nova cirurgia para remoção do parafuso, substituição do componente de polietileno e aplicação de novo parafuso de fixação.Complications in total knee arthroplasty directly related to the implanted material are rare, with the exception of polyethylene wear. Descriptions of screw migration into the joint cavity are very rare. The authors report an intra-articular migration of a polyethylene safety screw in a total knee arthroplasty, with sacrifice of the posterior cruciate ligament (ATJ Performance type; Biomet, Warsaw, IN requiring a new surgery to remove the screw, replace the polyethylene insert and insert a new fixation screw.

Navigation of Pedicle Screws in the Thoracic Spine with a New Electromagnetic Navigation System: A Human Cadaver Study

Directory of Open Access Journals (Sweden)

Patrick Hahn

2015-01-01

Full Text Available Introduction. Posterior stabilization of the spine is a standard procedure in spinal surgery. In addition to the standard techniques, several new techniques have been developed. The objective of this cadaveric study was to examine the accuracy of a new electromagnetic navigation system for instrumentation of pedicle screws in the spine. Material and Method. Forty-eight pedicle screws were inserted in the thoracic spine of human cadavers using EMF navigation and instruments developed especially for electromagnetic navigation. The screw position was assessed postoperatively by a CT scan. Results. The screws were classified into 3 groups: grade 1 = ideal position; grade 2 = cortical penetration <2 mm; grade 3 = cortical penetration ≥2 mm. The initial evaluation of the system showed satisfied positioning for the thoracic spine; 37 of 48 screws (77.1%, 95% confidence interval [62.7%, 88%] were classified as group 1 or 2. Discussion. The screw placement was satisfactory. The initial results show that there is room for improvement with some changes needed. The ease of use and short setup times should be pointed out. Instrumentation is achieved without restricting the operator’s mobility during navigation. Conclusion. The results indicate a good placement technique for pedicle screws. Big advantages are the easy handling of the system.

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.

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

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

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

Biomechanical comparative study of the stability of injectable pedicle screws with different lateral holes augmented with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae.

Science.gov (United States)

Liu, Da; Sheng, Jun; Luo, Yang; Huang, Chen; Wu, Hong-Hua; Zhou, Jiang-Jun; Zhang, Xiao-Jun; Zheng, Wei

2018-03-19

Polymethylmethacrylate (PMMA) is widely used for pedicle screw augmentation in osteoporosis. Until now, there had been no studies of the relationship between screw stability and the distribution and volume of PMMA. The objective of this study was to analyze the relationship between screw stability and the distribution pattern and injected volume of PMMA. This is a biomechanical comparison of injectable pedicle screws with different lateral holes augmented with different volumes of PMMA in cadaveric osteoporotic lumbar vertebrae. Forty-eight osteoporotic lumbar vertebrae were randomly divided into Groups A, B, and C with different pedicle screws (16 vertebrae in each group), and then each group was randomly divided into Subgroups 0, 1, 2, and 3 with different volumes of PMMA (four vertebra with eight pedicles in each subgroup). A pilot hole was prepared in advance using the same method in all samples. Type A and type B pedicle screws were directly inserted into vertebrae in Groups A and B, respectively, and then different volumes of PMMA (0, 1.0, 1.5, and 2.0 mL) were injected through the screws and into vertebrae in Subgroups 0, 1, 2, and 3. The pilot holes were filled with different volumes of PMMA (0, 1.0, 1.5, and 2.0 mL), and then the screws were inserted in Groups C0, C1, C2, and C3. Screw position and distribution of PMMA were evaluated radiographically, and axial pullout tests were performed to measure maximum axial pullout strength (F max ). Polymethylmethacrylate surrounded the anterior one-third of screws in the vertebral body in Groups A1, A2, and A3; the middle one-third of screws in the junction area of the vertebral body and the pedicle in Groups B1, B2, and B3; and the full length of screws evenly in both the vertebral body and the pedicle in Groups C1, C2, and C3. There was no malpositioning of screws or leakage of PMMA in any sample. Two-way analysis of variance revealed that two factors-distribution and volume of PMMA-significantly influenced

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.

Percutaneous Sacroiliac Screw Placement: A Prospective Randomized Comparison of Robot-assisted Navigation Procedures with a Conventional Technique

Directory of Open Access Journals (Sweden)

Jun-Qiang Wang

2017-01-01

Conclusions: Accuracy of the robot-assisted technique was superior to that of the freehand technique. Robot-assisted navigation is safe for unstable posterior pelvic ring stabilization, especially in S1, but also in S2. SI screw insertion with robot-assisted navigation is clinically feasible.

Percutaneous cannulated screw fixation of sacral fractures and sacroiliac joint disruptions with CT-controlled guidewires performed by interventionalists: Single center experience in treating posterior pelvic instability

International Nuclear Information System (INIS)

Fischer, Sebastian; Vogl, Thomas J.; Marzi, Ingo; Zangos, Stephan; Wichmann, Julian L.; Scholtz, Jan-Erik; Mack, Martin G.; Schmidt, Sven; Eichler, Katrin

2015-01-01

Highlights: • Minimally invasive sacroiliac screw fixation can be performed under CT-imaging. • Guidewires help in precise placement of cannulated sacroiliac screw. • Only a diminishing rate of misplacements can be seen. • The method appears to be a safe and very accurate procedure. - Abstract: Objective: The purpose of our study was to evaluate minimally invasive sacroiliac screw fixation for treatment of posterior pelvic instability with the help of CT controlled guidewires, assess its accuracy, safety and effectiveness, and discuss potential pitfalls. Methods: 100 guidewires and hollow titan screws were inserted in 38 patients (49.6 ± 19.5 years) suffering from 35 sacral fractures and/or 16 sacroiliac joint disruptions due to 33 (poly-)traumatic, 2 osteoporotic and 1 post-infectious conditions. The guidewire and screw positions were analyzed in multiplanar reconstructions. Results: The mean minimal distance between guidewire and adjacent neural foramina was 4.5 ± 2.01 mm, with a distinctly higher precision in S1 than S2. Eight guidewires showed cortical contacts, resulting in a total of 2% mismatched screws with subsequent wall violation. The fracture gaps were reduced from 3.6 ± 0.53 mm to 1.2 ± 0.54 mm. During follow-up 3 cases of minor iatrogenic sacral impaction (<5 mm) due to the bolting and 2 cases of screw loosening were observed. Interventional time was 84.0 min with a mean of 2.63 screws per patient whilst acquiring a mean of 93.7 interventional CT-images (DLP 336.7 mGy cm). Conclusions: The treatment of posterior pelvic instability with a guidewire-based screw insertion technique under CT-imaging results in a very high accuracy and efficacy with a low complication rate. Careful attention should be drawn to radiation levels

Percutaneous cannulated screw fixation of sacral fractures and sacroiliac joint disruptions with CT-controlled guidewires performed by interventionalists: Single center experience in treating posterior pelvic instability

Energy Technology Data Exchange (ETDEWEB)

Fischer, Sebastian, E-mail: sebastian.fischer@kgu.de [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt (Germany); Vogl, Thomas J. [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt (Germany); Marzi, Ingo [Department of Trauma, Hand and Reconstructive Surgery, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt (Germany); Zangos, Stephan; Wichmann, Julian L.; Scholtz, Jan-Erik; Mack, Martin G. [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt (Germany); Schmidt, Sven [Orthopaedic University Hospital Friedrichsheim, Marienburgstraße, 260528 Frankfurt (Germany); Eichler, Katrin [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590 Frankfurt (Germany)

2015-02-15

Highlights: • Minimally invasive sacroiliac screw fixation can be performed under CT-imaging. • Guidewires help in precise placement of cannulated sacroiliac screw. • Only a diminishing rate of misplacements can be seen. • The method appears to be a safe and very accurate procedure. - Abstract: Objective: The purpose of our study was to evaluate minimally invasive sacroiliac screw fixation for treatment of posterior pelvic instability with the help of CT controlled guidewires, assess its accuracy, safety and effectiveness, and discuss potential pitfalls. Methods: 100 guidewires and hollow titan screws were inserted in 38 patients (49.6 ± 19.5 years) suffering from 35 sacral fractures and/or 16 sacroiliac joint disruptions due to 33 (poly-)traumatic, 2 osteoporotic and 1 post-infectious conditions. The guidewire and screw positions were analyzed in multiplanar reconstructions. Results: The mean minimal distance between guidewire and adjacent neural foramina was 4.5 ± 2.01 mm, with a distinctly higher precision in S1 than S2. Eight guidewires showed cortical contacts, resulting in a total of 2% mismatched screws with subsequent wall violation. The fracture gaps were reduced from 3.6 ± 0.53 mm to 1.2 ± 0.54 mm. During follow-up 3 cases of minor iatrogenic sacral impaction (<5 mm) due to the bolting and 2 cases of screw loosening were observed. Interventional time was 84.0 min with a mean of 2.63 screws per patient whilst acquiring a mean of 93.7 interventional CT-images (DLP 336.7 mGy cm). Conclusions: The treatment of posterior pelvic instability with a guidewire-based screw insertion technique under CT-imaging results in a very high accuracy and efficacy with a low complication rate. Careful attention should be drawn to radiation levels.

Simulations of the atomic structure, energetics, and cross slip of screw dislocations in copper

DEFF Research Database (Denmark)

Rasmussen, Torben; Jacobsen, Karsten Wedel; Leffers, Torben

1997-01-01

Using nanoscale atomistic simulations it has been possible to address the problem of cross slip of a dissociated screw dislocation in an fee metal (Cu) by a method not suffering from the limitations imposed by elasticity theory. The focus has been on different dislocation configurations relevant...... linear-elasticity theory showing recombination or repulsion of the partials near the free surface. Such recombination at the free surface might be important in the context of cross slip because it allows the creation of the above-mentioned energetically favorable constriction alone. In addition we...... to monitor the annihilation process, thereby determining the detailed dislocation reactions during annihilation....

Percutaneous cannulated screw fixation of sacral fractures and sacroiliac joint disruptions with CT-controlled guidewires performed by interventionalists: single center experience in treating posterior pelvic instability.

Science.gov (United States)

Fischer, Sebastian; Vogl, Thomas J; Marzi, Ingo; Zangos, Stephan; Wichmann, Julian L; Scholtz, Jan-Erik; Mack, Martin G; Schmidt, Sven; Eichler, Katrin

2015-02-01

The purpose of our study was to evaluate minimally invasive sacroiliac screw fixation for treatment of posterior pelvic instability with the help of CT controlled guidewires, assess its accuracy, safety and effectiveness, and discuss potential pitfalls. 100 guidewires and hollow titan screws were inserted in 38 patients (49.6±19.5 years) suffering from 35 sacral fractures and/or 16 sacroiliac joint disruptions due to 33 (poly-)traumatic, 2 osteoporotic and 1 post-infectious conditions. The guidewire and screw positions were analyzed in multiplanar reconstructions. The mean minimal distance between guidewire and adjacent neural foramina was 4.5±2.01mm, with a distinctly higher precision in S1 than S2. Eight guidewires showed cortical contacts, resulting in a total of 2% mismatched screws with subsequent wall violation. The fracture gaps were reduced from 3.6±0.53mm to 1.2±0.54mm. During follow-up 3 cases of minor iatrogenic sacral impaction (<5mm) due to the bolting and 2 cases of screw loosening were observed. Interventional time was 84.0min with a mean of 2.63 screws per patient whilst acquiring a mean of 93.7 interventional CT-images (DLP 336.7mGycm). The treatment of posterior pelvic instability with a guidewire-based screw insertion technique under CT-imaging results in a very high accuracy and efficacy with a low complication rate. Careful attention should be drawn to radiation levels. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

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 ...

[Anterior odontoid screw fixation using intra-operative cone-beam computed tomography and navigation].

Science.gov (United States)

Castro-Castro, Julián

2014-01-01

The purpose of this study was to asses the value of intraoperative cone-beam CT (O-arm) and stereotactic navigation for the insertion of anterior odontoid screws. this was a retrospective review of patients receiving surgical treatment for traumatic odontoid fractures during a period of 18 months. Procedures were guided with O-arm assistance in all cases. The screw position was verified with an intraoperative CT scan. Intraoperative and clinical parameters were evaluated. Odontoid fracture fusion was assessed on postoperative CT scans obtained at 3 and 6 months' follow-up Five patients were included in this series; 4 patients (80%) were male. Mean age was 63.6 years (range 35-83 years). All fractures were acute type ii odontoid fractures. The mean operative time was 116minutes (range 60-160minutes). Successful screw placement, judged by intraoperative computed tomography, was attained in all 5 patients (100%). The average preoperative and postoperative times were 8.6 (range 2-22 days) and 4.2 days (range 3-7 days) respectively. No neurological deterioration occurred after surgery. The rate of bone fusion was 80% (4/5). Although this initial study evaluated a small number of patients, anterior odontoid screw fixation utilizing the O-arm appears to be safe and accurate. This system allows immediate CT imaging in the operating room to verify screw position. Copyright © 2014 Sociedad Española de Neurocirugía. Published by Elsevier España. All rights reserved.

Gas flow through the clearances of screw spindle vacuum pumps; Gasspaltstroemungen in Schraubenspindel-Vakuumpumpen

Energy Technology Data Exchange (ETDEWEB)

Kauder, K.; Wenderott, D. [Dortmund Univ. (Germany). FG Fluidenergiemaschinen

1998-12-31

The documentation `Schraubenmaschinen` deals with the subject `screw spindle vacuum pump` for the first time. Therefore, this paper presents the type of maschine `screw spindle vacuum pump`, fixes its limits to the better known screw type compressor and finally classifies it in the crossover of vacuum-technology, characteristic geometry and the numerical simulation. The suggested reflections to choose a proper model of flow are based on the geometry of the screw spindle vacuum pump and fundamentals concerning the vacuum-technology and the state of flow. (orig.) [Deutsch] Die Schriftenreihe `Schraubenmaschinen` behandelt erstmals das Thema `Schraubenspindel-Vakuumpumpe`. Aus diesem Grund stellt der vorliegende Beitrag den Maschinentyp Schraubenspindel-Vakuumpumpe vor, grenzt ihn zur bekannteren Schraubenmaschine ab und ordnet ihn in der Schnittmenge aus Vakuumtechnik, charakteristischer Maschinengeometrie und der Simulation ein. Auf den vakuumtechnischen und stroemungstechnischen Grundlagen sowie geometrischen Betrachtungen basieren die genannten Ueberlegungen zur Auswahl geeigneter Stroemungsmodelle. (orig.)

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.

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

Ab-Initio Simulation of a/2 Screw Dislocations Gamma-TiAl

National Research Council Canada - National Science Library

Woodward, C; Rao, S. I

2004-01-01

...The equilibrium core structure of an isolated a/2screw dislocations is calculated using a first-principles pseudopotential-planewave method within the Local Density Approximation of Density Functional Theory...

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.

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)

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.

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.

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

Safety screw fixation technique in a case of coracoid base fracture with acromioclavicular dislocation and coracoid base cross-sectional size data from a computed axial tomography study.

Science.gov (United States)

Kawasaki, Yoshiteru; Hirano, Tetsuya; Miyatake, Katsutoshi; Fujii, Koji; Takeda, Yoshitsugu

2014-07-01

Coracoid base fracture accompanied by acromioclavicular joint dislocation with intact coracoclavicular ligaments is a rare injury. Generally, an open reduction with screw fixation is the first treatment choice, as it protects the important structures around the coracoid process. This report presents a new technique of screw fixation for coracoid base fracture and provides anatomic information on cross-sectional size of the coracoid base obtained by computed tomography (CT). An axial image of the coracoid base was visualized over the neck of the scapula, and a guidewire was inserted into this circle under fluoroscopic guidance. The wire was inserted easily into the neck of scapula across the coracoid base fracture with imaging in only 1 plane. In addition, 25 measurements of the coracoid base were made in 25 subjects on axial CT images. Average length of the long and short axes at the thinnest part of the coracoid base was 13.9 ± 2.0 mm (range 10.6-17.0) and 10.5 ± 2.2 mm (6.6-15.1), respectively. This new screw fixation technique and measurement data on the coracoid base may be beneficial for safety screw fixation of coracoid base fracture.

Foundations for computer simulation of a low pressure oil flooded single screw air compressor

Science.gov (United States)

Bein, T. W.

1981-12-01

The necessary logic to construct a computer model to predict the performance of an oil flooded, single screw air compressor is developed. The geometric variables and relationships used to describe the general single screw mechanism are developed. The governing equations to describe the processes are developed from their primary relationships. The assumptions used in the development are also defined and justified. The computer model predicts the internal pressure, temperature, and flowrates through the leakage paths throughout the compression cycle of the single screw compressor. The model uses empirical external values as the basis for the internal predictions. The computer values are compared to the empirical values, and conclusions are drawn based on the results. Recommendations are made for future efforts to improve the computer model and to verify some of the conclusions that are drawn.

Linear motion device and method for inserting and withdrawing control rods

International Nuclear Information System (INIS)

Smith, J. E.

1984-01-01

A linear motion device, more specifically a control rod drive mechanism (CRDM) for inserting and withdrawing control rods into a reactor core, is capable of independently and sequentially positioning two sets of control rods with a single motor stator and rotor. The CRDM disclosed can control more than one control rod lead screw without incurring a substantial increase in the size of the mechanism

Determination of the most appropriate stress distribution by Finite Element Analysis in fixation with resorbable screws after Bilateral Sagittal Split Ramus Osteotomy surgery

Directory of Open Access Journals (Sweden)

Sarkarat F.

2009-12-01

Full Text Available "nBackground and Aim: Due to the complications associated with fixation by Titanium screws and plates in Bilateral Sagittal Split Ramus Osteotomy (BSSRO surgery, the use of resorbable polymers has been increasingly recommended. Since there are not enough studies on this issue, this study aimed to assess the most appropriate stress distribution in fixation with resorbable screws after BSSRO surgery by Fnite Element Analysis (FEA."nMaterials and Methods: This experimental study was performed on simulated human mandible using Ansys and Catia softwares. The osteotomy line was applied to the simulated model and experimental loads of 75, 135 and 600 N were respectively exerted according to the natural direction of occlusal force. The distribution pattern of stress was assessed and compared for fixation with one resorbable screw, two resorbable screws in vertical pattern, two resorbable screws in horizontal pattern, three resorbable screws in L pattern and three resorbable screws in inverted backward L pattern using Ansys software."nResults: Among the four simulated fixations, L pattern showed the highest primary stability. Two screws in vertical pattern were also associated with sufficient primary stability and less trauma and cost for patients. One screw did not provide enough stability under 600 N."nConclusion: Polymer-based resorbable screws (polyglycolic acid and D, L polylactide acid provided satisfactory primary stability in BSSRO surgery.

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.)

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.

Biomechanical analysis of titanium fixation plates and screws in ...

African Journals Online (AJOL)

hole Y plates with monocortical screws. 150 N incisal occlusal loads were simulated on the models. The commercial ANSYS software was utilized to calculate the Von Mises stresses on fixative appliances. Results: The highest Von Mises stress ...

Coating dental implant abutment screws with diamondlike carbon doped with diamond nanoparticles: the effect on maintaining torque after mechanical cycling.

Science.gov (United States)

Lepesqueur, Laura Soares; de Figueiredo, Viviane Maria Gonçalves; Ferreira, Leandro Lameirão; Sobrinho, Argemiro Soares da Silva; Massi, Marcos; Bottino, Marco Antônio; Nogueira Junior, Lafayette

2015-01-01

To determine the effect of maintaining torque after mechanical cycling of abutment screws that are coated with diamondlike carbon and coated with diamondlike carbon doped with diamond nanoparticles, with external and internal hex connections. Sixty implants were divided into six groups according to the type of connection (external or internal hex) and the type of abutment screw (uncoated, coated with diamondlike carbon, and coated with diamondlike carbon doped with diamond nanoparticles). The implants were inserted into polyurethane resin and crowns of nickel chrome were cemented on the implants. The crowns had a hole for access to the screw. The initial torque and the torque after mechanical cycling were measured. The torque values maintained (in percentages) were evaluated. Statistical analysis was performed using one-way analysis of variance and the Tukey test, with a significance level of 5%. The largest torque value was maintained in uncoated screws with external hex connections, a finding that was statistically significant (P = .0001). No statistically significant differences were seen between the groups with and without coating in maintaining torque for screws with internal hex connections (P = .5476). After mechanical cycling, the diamondlike carbon with and without diamond doping on the abutment screws showed no improvement in maintaining torque in external and internal hex connections.

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.

Development of a DIPG Orthotopic Model in Mice Using an Implantable Guide-Screw System.

Directory of Open Access Journals (Sweden)

Miguel Marigil

Full Text Available In this work we set to develop and to validate a new in vivo frameless orthotopic Diffuse Intrinsic Pontine Glioma (DIPG model based in the implantation of a guide-screw system.It consisted of a guide-screw also called bolt, a Hamilton syringe with a 26-gauge needle and an insulin-like 15-gauge needle. The guide screw is 2.6 mm in length and harbors a 0.5 mm central hole which accepts the needle of the Hamilton syringe avoiding a theoretical displacement during insertion. The guide-screw is fixed on the mouse skull according to the coordinates: 1mm right to and 0.8 mm posterior to lambda. To reach the pons the Hamilton syringe is adjusted to a 6.5 mm depth using a cuff that serves as a stopper. This system allows delivering not only cells but also any kind of intratumoral chemotherapy, antibodies or gene/viral therapies.The guide-screw was successfully implanted in 10 immunodeficient mice and the animals were inoculated with DIPG human cell lines during the same anesthetic period. All the mice developed severe neurologic symptoms and had a median overall survival of 95 days ranging the time of death from 81 to 116 days. Histopathological analysis confirmed tumor into the pons in all animals confirming the validity of this model.Here we presented a reproducible and frameless DIPG model that allows for rapid evaluation of tumorigenicity and efficacy of chemotherapeutic or gene therapy products delivered intratumorally to the pons.

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.

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

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

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.

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.

Atomistic simulations of screw dislocation cross slip in copper and nickel

DEFF Research Database (Denmark)

Vegge, Tejs

2001-01-01

This paper presents calculations of screw dislocation cross slip in copper and nickel systems, using the nudged elastic band method and interatomic potentials based on the effective-medium theory. The validity of recent attempts to predict cross slip activation energies by ‘elastic scaling’ between...

CT morphometric analysis to determine the anatomical basis for the use of transpedicular screws during reconstruction and fixations of anterior cervical vertebrae.

Directory of Open Access Journals (Sweden)

Chun Chen

Full Text Available BACKGROUND: Accurate placement of pedicle screw during Anterior Transpedicular Screw fixation (ATPS in cervical spine depends on accurate anatomical knowledge of the vertebrae. However, little is known of the morphometric characteristics of cervical vertebrae in Chinese population. METHODS: Three-dimensional reconstructions of CT images were performed for 80 cases. The anatomic data and screw fixation parameters for ATPS fixation were measured using the Mimics software. FINDINGS: The overall mean OPW, OPH and PAL ranged from 5.81 to 7.49 mm, 7.77 to 8.69 mm, and 33.40 to 31.13 mm separately, and SPA was 93.54 to 109.36 degrees from C3 to C6, 104.99 degrees at C7, whereas, 49.00 to 32.26 degrees from C4 to C7, 46.79 degrees at C3 (TPA. Dl/rSIP had an increasing trend away from upper endplate with mean value from 1.87 to 5.83 mm. Dl/rTIP was located at the lateral portion of the anterior cortex of vertebrae for C3 to C5 and ipsilateral for C6 to C7 with mean value from -2.70 to -3.00 mm, and 0.17 to 3.18 mm. The entrance points for pedicular screw insertion for C3 to C5 and C6 to C7 were recommended -2∼-3 mm and 0-4 mm from the median sagittal plane, respectively, 1-4 mm and 5-6 mm from the upper endplate, with TPA being 46.79-49.00 degrees and 40.89-32.26 degrees, respectively, and SPA being 93.54-106.69 degrees and 109.36-104.99 degrees, respectively. The pedicle screw insertion diameter was recommended 3.5 mm (C3 and C4, 4.0 mm (C5 to C7, and the pedicle axial length was 21-24 mm for C3 to C7 for both genders. However, the ATPS insertion in C3 should be individualized given its relatively small anatomical dimensions. CONCLUSIONS: The data provided a morphometric basis for the ATPS fixation technique in lower cervical fixation. It will help in preoperative planning and execution of this surgery.

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

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

Linear motion device and method for inserting and withdrawing control rods

Science.gov (United States)

Smith, J.E.

Disclosed is a linear motion device and more specifically a control rod drive mechanism (CRDM) for inserting and withdrawing control rods into a reactor core. The CRDM and method disclosed is capable of independently and sequentially positioning two sets of control rods with a single motor stator and rotor. The CRDM disclosed can control more than one control rod lead screw without incurring a substantial increase in the size of the mechanism.

Treatment of unicameral calcaneal bone cysts in children: review of literature and results using a cannulated screw for continuous decompression of the cyst.

Science.gov (United States)

Saraph, Vinay; Zwick, Ernst-Bernhard; Maizen, Claudia; Schneider, Frank; Linhart, Wolfgang E

2004-01-01

Nine unicameral bone cysts of the calcaneus in children were managed surgically using the technique of continuous decompression with titanium cannulated cancellous screws. The average age of the patients at surgery was 12.8 years. At follow-up a minimum of 2 years after surgery, eight cysts showed complete healing; one patient showed healing with residuals. Irritation at the screw insertion site necessitated early removal of the screw in one patient; implant-related problems were not observed in the other patients. Patients were allowed to bear weight after surgery. Implant extraction was performed after full consolidation of the cyst and was uneventful in all patients. A review of the literature and the different treatment modalities used for managing calcaneal cysts is also presented.

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.

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

A Simulation-Based Blended Curriculum for Short Peripheral Intravenous Catheter Insertion: An Industry-Practice Collaboration.

Science.gov (United States)

Glover, Kevin R; Stahl, Brian R; Murray, Connie; LeClair, Matthew; Gallucci, Susan; King, Mary Anne; Labrozzi, Laura J; Schuster, Catherine; Keleekai, Nowai L

2017-09-01

Despite peripheral intravenous catheter (PIVC) insertion being a commonly performed skill, practicing nurses may receive little substantive education, training, or opportunities to practice this skill at a competent level. This article describes a collaboration between private industry and a hospital to modify, implement, and evaluate a simulation-based blended PIVC insertion continuing education program for staff nurses. Included is an overview of the practical and theoretical rationale for the initial development of the curriculum to address an identified PIVC insertion education gap, the collaborative modification and implementation of the program, and an evaluation of the program. The curriculum combined self-paced e-learning and classroom-based deliberate practice with simulation tools of varying fidelity in a peer-to-peer learning environment. Given the mutual challenges of resource allocation in industry training and clinical nursing education departments, interprofessional partnerships may be an effective option for sharing instructional knowledge and resources to promote innovation and improve patient care. J Contin Educ Nurs. 2017;48(9):397-406. Copyright 2017, SLACK Incorporated.

[Fusion of reconstructed titanic plate, vertebral pedical screws and autogenous granulated cancellous bone graft in posterior occipitocervical region].

Science.gov (United States)

Zhong, Dejun; Song, Yueming

2006-08-01

To explore the technique of fusing the reconstructed titanic plate, the C2 pedical screws, and the autogenous granulated cancellous bone graft in the occipitocervical region. From April 2002 to January 2005, 19 patients aged 31-67 years with occipitocervical instability underwent the occipitocervical fusion using the reconstructed plate, C2 pedical screws, and autogenous granulated cancellous bone graft. Of the patients, 8 had complex occipitocervical deformity, 8 had old atlantoaxial fracture and dislocation, 2 had rheumatoid arthritis and anterior dislocation of the atlantoaxial joint, and 1 had cancer of the deltoid process of the axis. No complication occurred during and after operation. The follow-up for an average of 16 months in 19 patients showed that all the patients achieved solid bony fusion in the occipitocervical region. There was no broken plate, broken screw, looseness of the internal fixation or neurovascular injury. The fixation of the C2 pedical screws with the reconstructed titanic plate is reliable, the insertion is easy, and the autogenous granulated cancellous bone graft has a high fusion rate, thus resulting in a satisfactory effect in the occipitocervical fusion.

Morphometric Evaluation of Occipital Condyles: Defining Optimal Trajectories and Safe Screw Lengths for Occipital Condyle-Based Occipitocervical Fixation in Indian Population.

Science.gov (United States)

Bosco, Aju; Venugopal, Prakash; Shetty, Ajoy Prasad; Shanmuganathan, Rajasekaran; Kanna, Rishi Mugesh

2018-04-01

Computed tomographic (CT) morphometric analysis. To assess the feasibility and safety of occipital condyle (OC)-based occipitocervical fixation (OCF) in Indians and to define anatomical zones and screw lengths for safe screw placement. Limitations of occipital squama-based OCF has led to development of two novel OC-based OCF techniques. Morphometric analysis was performed on the OCs of 70 Indian adults. The feasibility of placing a 3.5-mm-diameter screw into OCs was investigated. Safe trajectories and screw lengths for OC screws and C0-C1 transarticular screws without hypoglossal canal or atlantooccipital joint compromise were estimated. The average screw length and safe sagittal and medial angulations for OC screws were 19.9±2.3 mm, ≤6.4°±2.4° cranially, and 31.1°±3° medially, respectively. An OC screw could not be accommodated by 27% of the population. The safe sagittal angles and screw lengths for C0-C1 transarticular screw insertion (48.9°±5.7° cranial, 26.7±2.9 mm for junctional entry technique; 36.7°±4.6° cranial, 31.6±2.7 mm for caudal C1 arch entry technique, respectively) were significantly different than those in other populations. The risk of vertebral artery injury was high for the caudal C1 arch entry technique. Screw placement was uncertain in 48% of Indians due to the presence of aberrant anatomy. There were significant differences in the metrics of OC-based OCF between Indian and other populations. Because of the smaller occipital squama dimensions in Indians, OC-based OCF techniques may have a higher application rate and could be a viable alternative/salvage option in selected cases. Preoperative CT, including three-dimensional-CT-angiography (to delineate vertebral artery course), is imperative to avoid complications resulting from aberrant bony and vascular anatomy. Our data can serve as a valuable reference guide in placing these screws safely under fluoroscopic guidance.

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...

Strain measurements of the tibial insert of a knee prosthesis using a knee motion simulator.

Science.gov (United States)

Sera, Toshihiro; Iwai, Yuya; Yamazaki, Takaharu; Tomita, Tetsuya; Yoshikawa, Hideki; Naito, Hisahi; Matsumoto, Takeshi; Tanaka, Masao

2017-12-01

The longevity of a knee prosthesis is influenced by the wear of the tibial insert due to its posture and movement. In this study, we assumed that the strain on the tibial insert is one of the main reasons for its wear and investigated the influence of the knee varus-valgus angles on the mechanical stress of the tibial insert. Knee prosthesis motion was simulated using a knee motion simulator based on a parallel-link six degrees-of-freedom actuator and the principal strain and pressure distribution of the tibial insert were measured. In particular, the early stance phase obtained from in vivo X-ray images was examined because the knee is applied to the largest load during extension/flexion movement. The knee varus-valgus angles were 0° (neutral alignment), 3°, and 5° malalignment. Under a neutral orientation, the pressure was higher at the middle and posterior condyles. The first and second principal strains were larger at the high and low pressure areas, respectively. Even for a 3° malalignment, the load was concentrated at one condyle and the positive first principal strain increased dramatically at the high pressure area. The negative second principal strain was large at the low pressure area on the other condyle. The maximum equivalent strain was 1.3-2.1 times larger at the high pressure area. For a 5° malalignment, the maximum equivalent strain increased slightly. These strain and pressure measurements can provide the mechanical stress of the tibial insert in detail for determining the longevity of an artificial knee joint.

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.

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...

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.

Surgical technique of percutaneous iliosacral screw fixation in S3 level in unstable pelvic fracture with closed degloving injury and morrell lavallee lesion: Two case reports

Directory of Open Access Journals (Sweden)

Ismail H. Dilogo

2017-01-01

Conclusions: Percutaneous screw fixation at the level of S3 is feasible and can be inserted in S3 level by sacroiliac type and sacral type with minimal soft tissue intervention and good functional outcome.

Effectiveness of the Thoracic Pedicle Screw Placement Using the Virtual Surgical Training System: A Cadaver Study.

Science.gov (United States)

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

2018-03-14

The virtual simulation surgery has initially exhibited its promising potentials in neurosurgery training. To evaluate effectiveness of the Virtual Surgical Training System (VSTS) on novice residents placing thoracic pedicle screws in a cadaver study. A total of 10 inexperienced residents participated in this study and were randomly assigned to 2 groups. The group using VSTS to learn thoracic pedicle screw fixation was the simulation training (ST) group and the group receiving an introductory teaching session was the control group. Ten fresh adult spine specimens including 6 males and 4 females with a mean age of 58.5 yr (range: 33-72) were collected and randomly allocated to the 2 groups. After exposing anatomic structures of thoracic spine, the bilateral pedicle screw placement of T6-T12 was performed on each cadaver specimen. The postoperative computed tomography scan was performed on each spine specimen, and experienced observers independently reviewed the placement of the pedicle screws to assess the incidence of pedicle breach. The screw penetration rates of the ST group (7.14%) was significantly lower in comparison to the control group (30%, P < .05). Statistically significant difference in acceptable rates of screws also occurred between the ST (100%) and control (92.86%) group (P < .05). In addition, the average screw penetration distance in control group (2.37 mm ± 0.23 mm) was significantly greater than ST group (1.23 mm ± 0.56 mm, P < .05). The virtual reality surgical training of thoracic pedicle screw instrumentation effectively improves surgical performance of novice residents compared to those with traditional teaching method, and can help new beginners to master the surgical technique within shortest period of time.

Posterior Surgery for Adolescent Idiopathic Scoliosis With Pedicle Screws and Ultrahigh-Molecular Weight Polyethylene Tape: Achieving the Ideal Thoracic Kyphosis.

Science.gov (United States)

Imagama, Shiro; Ito, Zenya; Wakao, Norimitsu; Ando, Kei; Hirano, Kenichi; Tauchi, Ryoji; Muramoto, Akio; Matsui, Hiroki; Matsumoto, Tomohiro; Sakai, Yoshihito; Katayama, Yoshito; Matsuyama, Yukihiro; Ishiguro, Naoki

2016-10-01

Prospective clinical case series. To describe our surgical procedure and results for posterior correction and fusion with a hybrid approach using pedicle screws, hooks, and ultrahigh-molecular weight polyethylene tape with direct vertebral rotation (DVR) (the PSTH-DVR procedure) for treatment of adolescent idiopathic scoliosis (AIS) with satisfactory correction in the coronal and sagittal planes. Introduction of segmental pedicle screws in posterior surgery for AIS has facilitated good correction and fusion. However, procedures using only pedicle screws have risks during screw insertion, higher costs, and decreased postoperative thoracic kyphosis. We have obtained good outcomes compared with segmental pedicle screw fixation in surgery for AIS using a relatively simple operative procedure (PSTH-DVR) that uses fewer pedicle screws. The subjects were 30 consecutive patients with AIS who underwent the PSTH-DVR procedure and were followed for a minimum of 2 years. Preoperative flexibility, preoperative and postoperative Cobb angles, correction rates, loss of correction, thoracic kyphotic angles (T5-T12), coronal balance, sagittal balance, and shoulder balance were measured on plain radiographs. Rib hump, operation time, estimated blood loss, spinal cord monitoring findings, complications, and scoliosis research society (SRS)-22 scores were also examined. The mean preoperative curve of 58.0 degrees (range, 40-96 degrees) was corrected to a mean of 9.9 degrees postoperatively, and the correction rate was 83.6%. Fusion was obtained in all patients without loss of correction. In 10 cases with preoperative kyphosis angles (T5-T12) correction of deformity with PSTH-DVR is equivalent to that of all-pedicle screw constructs. The procedure gives favorable correction, is advantageous for kyphosis compared with segmental screw fixation, and uses the minimum number of pedicle screws. Therefore, the PSTH-DVR procedure may be useful for treatment of idiopathic scoliosis.

[Evaluation of the risk of mediastinal or retroperitoneal injuries caused by dorso-lumbar pedicle screws].

Science.gov (United States)

Hernigou, P; Germany, W

1998-09-01

Within an anatomical and a clinical study, the authors employed computerized tomographic scans to evaluate the risks of anterior surrounding tissues injuries during screw insertion. CT scans of 20 patients suffering from cardiac disease were reviewed retrospectively. Scans through the thoracic and lumbar spine were obtained using 6 mm slice thickness. These examinations were performed with intravenous contrast medium. Measurements of vessel diameters and distance of the soft tissues situated directly anterior to the spine were done. A retrospective study of 61 pedicle screws implanted for spine fractures evaluated the penetration of the anterior vertebral cordex with X rays and CT scans. Computerized tomographic scans of the thoracic and lumbar spine of the 20 patients in the control group confirmed proximity of the posterior mediastinal structures to the anterior vertebral cortex. Many structures of the posterior mediastinum were within five millimeters of the anterior vertebral cortex and thus were at risk: aorta, azygos vein, vena cava, parietal pleura and lungs. The theoretical risk of unrecognized screw penetrations evaluated on geometric shape of the anterior vertebral body is as high as 21 per cent when screw position is only seen with an antero posterior and a lateral X Ray. In the other group, computerized tomographic scans showed that 30 per cent of the implanted screws were outside the boundaries of the anterior thoracic spine. Two orthogonal incidences do not enable determination of whether the extremity of the screw is slightly outside the anterior cortex of the vertebral body. However the geometric shape of the anterior vertebral body enables peroperative definition of a safety zone on two orthogonal incidences. Even if a breach of a few millimeters of the anterior cortical boundaries of the vertebral body may not initially damage the adjacent soft-tissue structures, chronic irritation may result in late damages of these structures. The use of

Evaluation of osseous integration of titanium orthopedic screws with novel SLA treatment in porcine model.

Directory of Open Access Journals (Sweden)

Tzu-Hsiang Lin

Full Text Available The success of many endosseous implants in orthopaedic and dental applications depends on the surface characteristics, as they affect osseous integration. Previous investigations indicated that a novel large-grit sand-blasted and acid-etched (SLA titanium (denoted as SLAffinity-Ti implant had better bone integration than that of a comparably shaped implant with a plasma-sprayed titanium surface. The purpose of the present investigation was to create a SLAffinity surface on pedicle screws and trauma screws and to compare it with the surfaces of a sand-blasted-only implant and commercial implants in terms of bone integration. The cortical bone and spine of twelve minipigs were implanted with 3 and 4 implants, respectively, and the bone integration was evaluated using micro-computed tomography (micro-CT, mechanical tests (pull-out strength and stripping torque, and histological analysis (toluidine blue and hematoxylin and eosin staining one and three months after implantation. The micro-CT images showed that the gap between the bone and implant was consistently higher in the sand-blasted-only and commercial groups compared to that in the SLAffinity group 1 and 3 months after implantation. Moreover, the bone volume of implant inserted into bone and the percentage of implant inside bone tissue were greater in the SLAffinity screws 1 and 3 months after implantation, as compared to the sand-blasted and commercial screws. In the mechanical tests, the removal torque and pull-out strength (p < 0.05 were higher in the SLAffinity group at 1 and 3 months. The histological results were consistent with mechanical testing, showing that the SLAffinity group had the most mineralized matrix, the most bone formation around the screws, and the most bone cells in bone tissue. These findings indicate that a SLAffinity surface can effectively enhance the holding strength and integration of pedicle screws and cortical screws, promoting early healing and improving

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...

3D printing-based minimally invasive cannulated screw treatment of unstable pelvic fracture.

Science.gov (United States)

Cai, Leyi; Zhang, Yingying; Chen, Chunhui; Lou, Yiting; Guo, Xiaoshan; Wang, Jianshun

2018-04-04

Open reduction and internal fixation of pelvic fractures could restore the stability of the pelvic ring, but there were several problems. Minimally invasive closed reduction cannulated screw treatment of pelvic fractures has lots advantages. However, how to insert the cannulated screw safely and effectively to achieve a reliable fixation were still hard for orthopedist. Our aim was to explore the significance of 3D printing technology as a new method for minimally invasive cannulated screw treatment of unstable pelvic fracture. One hundred thirty-seven patients with unstable pelvic fractures from 2014 to 2016 were retrospectively analyzed. Based on the usage of 3D printing technology for preoperative simulation surgery, they were assigned to 3D printing group (n = 65) and control group (n = 72), respectively. These two groups were assessed in terms of operative time, intraoperative fluoroscopy, postoperative reduction effect, fracture healing time, and follow-up function. The effect of 3D printing technology was evaluated through minimally invasive cannulated screw treatment. There was no significant difference in these two groups with respect to general conditions, such as age, gender, fracture type, time from injury to operation, injury cause, and combined injury. Length of surgery and average number of fluoroscopies were statistically different for 3D printing group and the control group (p 3D printing group, versus 22/72 cases (30.6%) scored as excellent and 36/72 cases (50%) as good for the control group. On the other hand, using the Majeed functional scoring criteria, there were 27/65 (41.5%) excellent and 26/65 (40%) good cases for the 3D printing group in comparison to 30/72 (41.7%) and 28/72 (38.9%) cases for the control group, respectively. This suggests no significant difference between these two groups about the function outcomes. Full reduction and proper fixation of the pelvic ring and reconstruction of anatomical morphology are of great

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.

Comparison of Neck Screw and Conventional Fixation Techniques in Mandibular Condyle Fractures Using 3-Dimensional Finite Element Analysis.

Science.gov (United States)

Conci, Ricardo Augusto; Tomazi, Flavio Henrique Silveira; Noritomi, Pedro Yoshito; da Silva, Jorge Vicente Lopes; Fritscher, Guilherme Genehr; Heitz, Claiton

2015-07-01

To compare the mechanical stress on the mandibular condyle after the reduction and fixation of mandibular condylar fractures using the neck screw and 2 other conventional techniques according to 3-dimensional finite element analysis. A 3-dimensional finite element model of a mandible was created and graphically simulated on a computer screen. The model was fixed with 3 different techniques: a 2.0-mm plate with 4 screws, 2 plates (1 1.5-mm plate and 1 2.0-mm plate) with 4 screws, and a neck screw. Loads were applied that simulated muscular action, with restrictions of the upper movements of the mandible, differentiation of the cortical and medullary bone, and the virtual "folds" of the plates and screws so that they could adjust to the condylar surface. Afterward, the data were exported for graphic visualization of the results and quantitative analysis was performed. The 2-plate technique exhibited better stability in regard to displacement of fractures, deformity of the synthesis materials, and minimum and maximum tension values. The results with the neck screw were satisfactory and were similar to those found when a miniplate was used. Although the study shows that 2 isolated plates yielded better results compared with the other groups using other fixation systems and methods, the neck screw could be an option for condylar fracture reduction. Copyright © 2015 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.

Open reduction and internal fixation: Screw injury - Retrospective study

Directory of Open Access Journals (Sweden)

Preetha Balaji

2017-01-01

Full Text Available Background/Aims: Open reduction and internal fixation (ORIF is a standard surgical procedure in jaw trauma and in orthognathic surgery. Insertion of screws is a significant risk for accidental tooth root injury with varying outcomes. Contrary evidences are found in literature due to a variety of study designs. This study was undertaken to address the lacunae and possibly estimate the difference in occurrence of tooth damage during or after ORIF between trauma and planned osteotomies. Materials and Methods: In this retrospective study, the data of ORIF in either trauma or orthognathic surgery fulfilling inclusion and exclusion criteria were collected and analyzed. Results: There were 1632 patients fulfilling the inclusion and exclusion criteria and formed the study group, of which 663 were in orthognathic surgery, of whom 210 had bimaxillary orthognathic surgery. In the trauma group, 358 patients had fractures involving both jaws whereas 272 had maxilla alone and 339 had mandibular fractures alone. On comparing the outcome, of the 9073 screws studied, 93.40% were not involved in any contact with the teeth, 6.3% were in category of potential hits (near apices or the root surfaces, and only 0.28% had evidence of root damage with the screws. It is observed that molar and premolar had a significant difference in terms of the type of surgery (P ≤ 0.05 whereas canine (P = 0.75 and incisor (P = 0.67 showed no statistical difference. Conclusion: ORIF when used as mentioned is a safe way for the management of fractures. The incidence of root injury is not uncommon but can be avoided with careful planning and execution.

Measurement of Tip Apex Distance and Migration of Lag Screws and Novel Blade Screw Used for the Fixation of Intertrochanteric Fractures.

Directory of Open Access Journals (Sweden)

Jesse Chieh-Szu Yang

Full Text Available Fixation with a dynamic hip screw (DHS is one of the most common methods for stabilizing intertrochanteric fractures, except for unstable and reverse oblique fracture types. However, failure is often observed in osteoporotic patients whereby the lag screw effectively 'cuts out' through the weak bone. Novel anti-migration blades have been developed to be used in combination with a lag screw ('Blade Screw' to improve the fixation strength in osteoporotic intertrochanteric fractures. An in-vitro biomechanical study and a retrospective clinical study were performed to evaluate lag screw migration when using the novel Blade Screw and a traditional threaded DHS. The biomechanical study showed both the Blade Screw and DHS displayed excessive migration (≥10 mm before reaching 20,000 loading cycles in mild osteoporotic bone, but overall migration of the Blade Screw was significantly less (p ≤ 0.03. Among the patients implanted with a Blade Screw in the clinical study, there was no significant variation in screw migration at 3-months follow-up (P = 0.12. However, the patient's implanted with a DHS did display significantly greater migration (P<0.001 than those implanted with the Blade Screw. In conclusion, the Blade Screw stabilizes the bone fragments during dynamic loading so as to provide significantly greater resistance to screw migration in patients with mild osteoporosis.

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.

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.

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.

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.

Comparison of open reduction versus minimally invasive surgical approaches on screw position in canine sacroiliac lag-screw fixation.

Science.gov (United States)

Déjardin, Loïc M; Marturello, Danielle M; Guiot, Laurent P; Guillou, Reunan P; DeCamp, Charles E

2016-07-19

To compare accuracy and consistency of sacral screw placement in canine pelves treated for sacroiliac luxation with open reduction and internal fixation (ORIF) or minimally invasive osteosynthesis (MIO) techniques. Unilateral sacroiliac luxations created experimentally in canine cadavers were stabilized with an iliosacral lag screw applied via ORIF or MIO techniques (n = 10/group). Dorsoventral and craniocaudal screw angles were measured using computed tomography multiplanar reconstructions in transverse and dorsal planes, respectively. Ratios between pilot hole length and sacral width (PL/SW-R) were obtained. Data between groups were compared statistically (p sacroiliac luxations provides more accurate and consistent sacral screw placement than ORIF. With proper techniques, iatrogenic neurological damage can be avoided with both techniques. The PL /SW-R, which relates to safe screw fixation, also demonstrates that screw penetration of at least 60% of the sacral width is achievable regardless of surgical approach. These findings, along with the limited dissection needed for accurate sacral screw placement, suggest that MIO of sacroiliac luxations is a valid alternative to ORIF.

Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out.

Science.gov (United States)

Pujari-Palmer, Michael; Robo, Celine; Persson, Cecilia; Procter, Philip; Engqvist, Håkan

2018-01-01

Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in fixation failure. While numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw pull-out force, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of high strength calcium phosphate cements (hsCPCs, specifically dicalcium phosphate) affected the corresponding orthopedic screw pull-out force in urethane foam models of "healthy" and "osteoporotic" synthetic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R 2 = 0.79) was weaker than correlation with total cement porosity (R 2 = 0.89). In open pore Sawbone that mimics "healthy" cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). High strength, low porosity cements also produced higher pull-out forces (50-190% increase) in "healthy" Sawbones with cortical fixation if the failure strength of the cortical material was similar to, or greater than (a metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell, thereby increasing the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5mL (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity calcium phosphate cement (CPC) may

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.

Blade number impact on pressure and performance of archimedes screw turbine using CFD

Science.gov (United States)

Maulana, Muhammad Ilham; Syuhada, Ahmad; Nawawi, Muhammad

2018-02-01

Many rivers in Indonesia can be used as source of mini/micro hydro power plant using low head turbine. The most suitable type of turbine used in fluid flow with low head is the Archimedes screw turbine. The Archimedes screw hydro turbine is a relative newcomer to the small-scale hydropower that can work efficiently on heads as low as 10 meter. In this study, the performance of Archimedes water turbines that has different blade numbers that are thoroughly evaluated to obtain proper blade configuration. For this purpose, numerical simulations are used to predict the pressure changes that occur along the turbine. The simulation results show that turbines with an amount of two blades have more sloping pressure distribution so that it has better stability.

Development of a virtual reality haptic Veress needle insertion simulator for surgical skills training.

Science.gov (United States)

Okrainec, A; Farcas, M; Henao, O; Choy, I; Green, J; Fotoohi, M; Leslie, R; Wight, D; Karam, P; Gonzalez, N; Apkarian, J

2009-01-01

The Veress needle is the most commonly used technique for creating the pneumoperitoneum at the start of a laparoscopic surgical procedure. Inserting the Veress needle correctly is crucial since errors can cause significant harm to patients. Unfortunately, this technique can be difficult to teach since surgeons rely heavily on tactile feedback while advancing the needle through the various layers of the abdominal wall. This critical step in laparoscopy, therefore, can be challenging for novice trainees to learn without adequate opportunities to practice in a safe environment with no risk of injury to patients. To address this issue, we have successfully developed a prototype of a virtual reality haptic needle insertion simulator using the tactile feedback of 22 surgeons to set realistic haptic parameters. A survey of these surgeons concluded that our device appeared and felt realistic, and could potentially be a useful tool for teaching the proper technique of Veress needle insertion.

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

Two-Finger Tightness: What Is It? Measuring Torque and Reproducibility in a Simulated Model.

Science.gov (United States)

Acker, William B; Tai, Bruce L; Belmont, Barry; Shih, Albert J; Irwin, Todd A; Holmes, James R

2016-05-01

Residents in training are often directed to insert screws using "two-finger tightness" to impart adequate torque but minimize the chance of a screw stripping in bone. This study seeks to quantify and describe two-finger tightness and to assess the variability of its application by residents in training. Cortical bone was simulated using a polyurethane foam block (30-pcf density) that was prepared with predrilled holes for tightening 3.5 × 14-mm long cortical screws and mounted to a custom-built apparatus on a load cell to capture torque data. Thirty-three residents in training, ranging from the first through fifth years of residency, along with 8 staff members, were directed to tighten 6 screws to two-finger tightness in the test block, and peak torque values were recorded. The participants were blinded to their torque values. Stripping torque (2.73 ± 0.56 N·m) was determined from 36 trials and served as a threshold for failed screw placement. The average torques varied substantially with regard to absolute torque values, thus poorly defining two-finger tightness. Junior residents less consistently reproduced torque compared with other groups (0.29 and 0.32, respectively). These data quantify absolute values of two-finger tightness but demonstrate considerable variability in absolute torque values, percentage of stripping torque, and ability to consistently reproduce given torque levels. Increased years in training are weakly correlated with reproducibility, but experience does not seem to affect absolute torque levels. These results question the usefulness of two-finger tightness as a teaching tool and highlight the need for improvement in resident motor skill training and development within a teaching curriculum. Torque measuring devices may be a useful simulation tools for this purpose.

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.

CFD Modelling in Screw Compressors With Complex Multi Rotor Configurations

OpenAIRE

Rane, Sham Ramchandra; Kovacevic, Ahmed; Kethidi, Madhulika

2012-01-01

Computational Fluid Dynamics (CFD) of screw compressors is challenging due to the positive displacement nature of the process, existence of very fine fluid leakage paths, coexistence of working fluid and lubricant or coolant, fluid injection and most importantly the lack of methodologies available to generate meshes required for the full three dimensional transient simulations. In this paper, currently available technology of grid remeshing has been used to demonstrate the CFD simulations of ...

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.

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)

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...

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.

Influence of abutment type and esthetic veneering on preload maintenance of abutment screw of implant-supported crowns.

Science.gov (United States)

Delben, Juliana Aparecida; Barão, Valentim Adelino Ricardo; Dos Santos, Paulo Henrique; Assunção, Wirley Gonçalves

2014-02-01

The effect of veneering materials on screw joint stability remains inconclusive. Thus, this study evaluated the preload maintenance of abutment screws of single crowns fabricated with different abutments and veneering materials. Sixty crowns were divided into five groups (n = 12): UCLA abutment in gold alloy with ceramic (group GC) and resin (group GR) veneering, UCLA abutment in titanium with ceramic (group TiC) and resin (group TiR) veneering, and zirconia abutment with ceramic veneering (group ZiC). Abutment screws made of gold were used with a 35 Ncm insertion torque. Detorque measurements were obtained initially and after mechanical cycling. Data were analyzed by ANOVA and Fisher's exact test at a significance level of 5%. For the initial detorque means (in Ncm), group TiC (21.4 ± 1.78) exhibited statistically lower torque maintenance than groups GC (23.9 ± 0.91), GR (24.1 ± 1.34), and TiR (23.2 ± 1.33) (p abutment type and veneering material. More irregular surfaces in the hexagon area of the castable abutments were observed. The superiority of any veneering material concerning preload maintenance was not established. © 2013 by the American College of Prosthodontists.

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.

Minimally invasive mini open split-muscular percutaneous pedicle screw fixation of the thoracolumbar spine

Directory of Open Access Journals (Sweden)

Murat Ulutaş

2015-03-01

Full Text Available We prospectively assessed the feasibility and safety of a new percutaneous pedicle screw (PPS fixation technique for instrumentation of the thoracic and lumbar spine in this study. All patients were operated in the prone position under general anesthesia. A 6 to 8 cm midline skin incision was made and wide sub-cutaneous dissection was performed. The paravertebral muscles were first dissected subperiosteally into the midline incision of the fascia for lumbar microdiscectomy with transforaminal lumbar interbody fusion cage implantation. After the secondary paramedian incisions on the fascia, the PPSs were inserted via cleavage of the multifidus muscles directly into the pedicles under fluoroscopy visualization. A total of 35 patients underwent surgery with this new surgical technique. The control group for operative time, blood loss and analgesic usage consisted of 35 randomly selected cases from our department. The control group underwent surgery via conventional pedicle screw instrumentation with paramedian fusion. All patients in the minimal invasive surgery series were ambulatory with minimal pain on the first postoperative day. The operation time and blood loss and the postoperative analgesic consumption were significantly less with this new technique. In conclusion, the minimal invasive mini open split-muscular percutaneous pedicle screw fixation technique is safe and feasible. It can be performed via a short midline skin incision and can also be combined with interbody fusion, causing minimal pain without severe muscle damage.

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

Screw Placement and Osteoplasty Under Computed Tomographic–Fluoroscopic Guidance in a Case of Advanced Metastatic Destruction of the Iliosacral Joint

International Nuclear Information System (INIS)

Trumm, Christoph Gregor; Rubenbauer, Bianca; Piltz, Stefan; Reiser, Maximilian F.; Hoffmann, Ralf-Thorsten

2011-01-01

We present a case of combined surgical screw placement and osteoplasty guided by computed tomography–fluoroscopy (CTF) in a 68-year-old man with unilateral osteolytic destruction and a pathological fracture of the iliosacral joint due to a metastasis from renal cell carcinoma. The patient experienced intractable lower back pain that was refractory to analgesia. After transarterial particle and coil embolization of the tumor-feeding vessels in the angiography unit, the procedure was performed under general anesthesia by an interdisciplinary team of interventional radiologists and trauma surgeons. Under intermittent single-shot CTF, two K wires were inserted into the left iliosacral joint from a lateral transiliac approach at the S1 level followed by two self-tapping surgical screws. Continuous CTF was used for monitoring of the subsequent polymethylmethacrylate injection through two vertebroplasty cannulas for further stabilization of the screw threads within the osteolytic sacral ala. Both the screw placement and cement injection were successful, with no complications occurring during or after the procedure. With additional nonsteroidal anti-inflammatory and opioid medication, the patient reported a marked decrease in his lower back pain and was able to move independently again at the 3-month follow-up assessment. In our patient with intolerable back pain due to tumor destruction and consequent pathological fracture of the iliosacral joint, CTF-guided iliosacral screw placement combined with osteoplasty was successful with respect to joint stabilization and a reduction in the need for analgesic therapy.

Continuous decompression of unicameral bone cyst with cannulated screws: a comparative study.

Science.gov (United States)

Brecelj, Janez; Suhodolcan, Lovro

2007-09-01

We determined the role of mechanical decompression in the resolution of unicameral bone cyst. A total of 69 children with unicameral bone cysts were treated either by (i) open curettage and bone grafting, (ii) steroid injection or (iii) cannulated screw insertion. During a mean follow-up of 69 months (range, 12-58), the cysts were evaluated by radiological criteria. The healing rates in the three groups were 25, 12 and 29% after the first treatment, and a further 50, 19 and 65% after the second. The study has demonstrated the advantages of the decompression technique for unicameral bone cysts over other treatment modalities studied.

Atomistic simulation of hydrogen dynamics near dislocations in vanadium hydrides

International Nuclear Information System (INIS)

Ogawa, Hiroshi

2015-01-01

Highlights: • Hydrogen–dislocation interaction was simulated by molecular dynamics method. • Different distribution of H atoms were observed at edge and screw dislocation. • Planner distribution of hydrogen may be caused by partialized edge dislocation. • Hydrogen diffusivity was reduced in both edge and screw dislocation models. • Pipe diffusion was observed for edge dislocation but not for screw dislocation. - Abstract: Kinetics of interstitial hydrogen atoms near dislocation cores were analyzed by atomistic simulation. Classical molecular dynamics method was applied to model structures of edge and screw dislocations in α-phase vanadium hydride. Simulation showed that hydrogen atoms aggregate near dislocation cores. The spatial distribution of hydrogen has a planner shape at edge dislocation due to dislocation partialization, and a cylindrical shape at screw dislocation. Simulated self-diffusion coefficients of hydrogen atoms in dislocation models were a half- to one-order lower than that of dislocation-free model. Arrhenius plot of self-diffusivity showed slightly different activation energies for edge and screw dislocations. Directional dependency of hydrogen diffusion near dislocation showed high and low diffusivity along edge and screw dislocation lines, respectively, hence so called ‘pipe diffusion’ possibly occur at edge dislocation but does not at screw dislocation

The Effect of Model Fidelity on Learning Outcomes of a Simulation-Based Education Program for Central Venous Catheter Insertion.

Science.gov (United States)

Diederich, Emily; Mahnken, Jonathan D; Rigler, Sally K; Williamson, Timothy L; Tarver, Stephen; Sharpe, Matthew R

2015-12-01

Simulation-based education for central venous catheter (CVC) insertion has been repeatedly documented to improve performance, but the impact of simulation model fidelity has not been described. The aim of this study was to examine the impact of the physical fidelity of the simulation model on learning outcomes for a simulation-based education program for CVC insertion. Forty consecutive residents rotating through the medical intensive care unit of an academic medical center completed a simulation-based education program for CVC insertion. The curriculum was designed in accordance with the principles of deliberate practice and mastery learning. Each resident underwent baseline skills testing and was then randomized to training on a commercially available CVC model with high physical fidelity (High-Fi group) or a simply constructed model with low physical fidelity (Low-Fi group) in a noninferiority trial. Upon completion of their medical intensive care unit rotation 4 weeks later, residents returned for repeat skills testing on the high-fidelity model using a 26-item checklist. The mean (SD) posttraining score on the 26-item checklist for the Low-Fi group was 23.8 (2.2) (91.5%) and was not inferior to the mean (SD) score for the High-Fi group of 22.5 (2.6) (86.5%) (P Simulation-based education using equipment with low physical fidelity can achieve learning outcomes comparable with those with high-fidelity equipment, as long as other aspects of fidelity are maintained and robust educational principles are applied during the design of the curriculum.

Three-dimensional navigation is more accurate than two-dimensional navigation or conventional fluoroscopy for percutaneous sacroiliac screw fixation in the dysmorphic sacrum: a randomized multicenter study.

Science.gov (United States)

Matityahu, Amir; Kahler, David; Krettek, Christian; Stöckle, Ulrich; Grutzner, Paul Alfred; Messmer, Peter; Ljungqvist, Jan; Gebhard, Florian

2014-12-01

To evaluate the accuracy of computer-assisted sacral screw fixation compared with conventional techniques in the dysmorphic versus normal sacrum. Review of a previous study database. Database of a multinational study with 9 participating trauma centers. The reviewed group included 130 patients, 72 from the navigated group and 58 from the conventional group. Of these, 109 were in the nondysmorphic group and 21 in the dysmorphic group. Placement of sacroiliac (SI) screws was performed using standard fluoroscopy for the conventional group and BrainLAB navigation software with either 2-dimensional or 3-dimensional (3D) navigation for the navigated group. Accuracy of SI screw placement by 2-dimensional and 3D navigation versus conventional fluoroscopy in dysmorphic and nondysmorphic patients, as evaluated by 6 observers using postoperative computerized tomography imaging at least 1 year after initial surgery. Intraobserver agreement was also evaluated. There were 11.9% (13/109) of patients with misplaced screws in the nondysmorphic group and 28.6% (6/21) of patients with misplaced screws in the dysmorphic group, none of which were in the 3D navigation group. Raw agreement between the 6 observers regarding misplaced screws was 32%. However, the percent overall agreement was 69.0% (kappa = 0.38, P dysmorphic proximal sacral segment. We recommend the use of 3D navigation, where available, for insertion of SI screws in patients with normal and dysmorphic proximal sacral segments. Therapeutic level I.

Comparison of the Mechanical Characteristics of a Universal Small Biplane Plating Technique Without Compression Screw and Single Anatomic Plate With Compression Screw.

Science.gov (United States)

Dayton, Paul; Ferguson, Joe; Hatch, Daniel; Santrock, Robert; Scanlan, Sean; Smith, Bret

2016-01-01

To better understand the mechanical characteristics of biplane locked plating in small bone fixation, the present study compared the stability under cyclic cantilever loading of a 2-plate locked biplane (BPP) construct without interfragmentary compression with that of a single-plate locked construct with an additional interfragmentary screw (SPS) using surrogate bone models simulating Lapidus arthrodesis. In static ultimate plantar bending, the BPP construct failed at significantly greater load than did the SPS construct (556.2 ± 37.1 N versus 241.6 ± 6.3 N, p = .007). For cyclic failure testing in plantar bending at a 180-N starting load, the BPP construct failed at a significantly greater number of cycles (158,322 ± 50,609 versus 13,718 ± 10,471 cycles) and failure load (242.5 ± 25.0 N versus 180.0 ± 0.0 N) than the SPS construct (p = .002). For cyclic failure testing in plantar bending at a 120-N starting load, the results were not significantly different between the BPP and SPS constructs for the number of cycles (207,646 ± 45,253 versus 159,334 ± 69,430) or failure load (205.0 ± 22.4 N versus 185.0 ± 33.5 N; p = .300). For cyclic testing with 90° offset loading (i.e., medial to lateral bending) at a 120-N starting load, all 5 BPP constructs (tension side) and 2 of the 5 SPS constructs reached 250,000 cycles without failure. Overall, the present study found the BPP construct to have superior or equivalent stability in multiplanar orientations of force application in both static and fatigue testing. Thus, the concept of biplane locked plating, using 2 low profile plates and unicortical screw insertion, shows promise in small bone fixation, because it provides consistent stability in multiplanar orientations, making it universally adaptable to many clinical situations. Copyright © 2016 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

Dual-worm screw compressors; Compresseurs bi-vis

Energy Technology Data Exchange (ETDEWEB)

Baleydier, J P [Bitzer France, 69 - Lyon (France)

1998-12-31

Low power worm-screw moto-compressors are used in any king of refrigerating machineries and more and more in air conditioning systems. This paper presents the principle of dual-screw moto-compressors: worm-screw technology, role of oil (lubrication, tightness, cooling), compression, internal pressure, power reduction, lubrication, economizer, operation, model selection and accessories. (J.S.)

Dual-worm screw compressors; Compresseurs bi-vis

Energy Technology Data Exchange (ETDEWEB)

Baleydier, J.P. [Bitzer France, 69 - Lyon (France)

1997-12-31

Low power worm-screw moto-compressors are used in any king of refrigerating machineries and more and more in air conditioning systems. This paper presents the principle of dual-screw moto-compressors: worm-screw technology, role of oil (lubrication, tightness, cooling), compression, internal pressure, power reduction, lubrication, economizer, operation, model selection and accessories. (J.S.)

Evaluation of a prototype correction algorithm to reduce metal artefacts in flat detector computed tomography of scaphoid fixation screws

Energy Technology Data Exchange (ETDEWEB)

Filli, Lukas; Finkenstaedt, Tim; Andreisek, Gustav; Guggenberger, Roman [University Hospital of Zurich, Department of Diagnostic and Interventional Radiology, Zurich (Switzerland); Marcon, Magda [University Hospital of Zurich, Department of Diagnostic and Interventional Radiology, Zurich (Switzerland); University of Udine, Institute of Diagnostic Radiology, Department of Medical and Biological Sciences, Udine (Italy); Scholz, Bernhard [Imaging and Therapy Division, Siemens AG, Healthcare Sector, Forchheim (Germany); Calcagni, Maurizio [University Hospital of Zurich, Division of Plastic Surgery and Hand Surgery, Zurich (Switzerland)

2014-12-15

The aim of this study was to evaluate a prototype correction algorithm to reduce metal artefacts in flat detector computed tomography (FDCT) of scaphoid fixation screws. FDCT has gained interest in imaging small anatomic structures of the appendicular skeleton. Angiographic C-arm systems with flat detectors allow fluoroscopy and FDCT imaging in a one-stop procedure emphasizing their role as an ideal intraoperative imaging tool. However, FDCT imaging can be significantly impaired by artefacts induced by fixation screws. Following ethical board approval, commercially available scaphoid fixation screws were inserted into six cadaveric specimens in order to fix artificially induced scaphoid fractures. FDCT images corrected with the algorithm were compared to uncorrected images both quantitatively and qualitatively by two independent radiologists in terms of artefacts, screw contour, fracture line visibility, bone visibility, and soft tissue definition. Normal distribution of variables was evaluated using the Kolmogorov-Smirnov test. In case of normal distribution, quantitative variables were compared using paired Student's t tests. The Wilcoxon signed-rank test was used for quantitative variables without normal distribution and all qualitative variables. A p value of < 0.05 was considered to indicate statistically significant differences. Metal artefacts were significantly reduced by the correction algorithm (p < 0.001), and the fracture line was more clearly defined (p < 0.01). The inter-observer reliability was ''almost perfect'' (intra-class correlation coefficient 0.85, p < 0.001). The prototype correction algorithm in FDCT for metal artefacts induced by scaphoid fixation screws may facilitate intra- and postoperative follow-up imaging. (orig.)

Evaluation of a prototype correction algorithm to reduce metal artefacts in flat detector computed tomography of scaphoid fixation screws

International Nuclear Information System (INIS)

Filli, Lukas; Finkenstaedt, Tim; Andreisek, Gustav; Guggenberger, Roman; Marcon, Magda; Scholz, Bernhard; Calcagni, Maurizio

2014-01-01

The aim of this study was to evaluate a prototype correction algorithm to reduce metal artefacts in flat detector computed tomography (FDCT) of scaphoid fixation screws. FDCT has gained interest in imaging small anatomic structures of the appendicular skeleton. Angiographic C-arm systems with flat detectors allow fluoroscopy and FDCT imaging in a one-stop procedure emphasizing their role as an ideal intraoperative imaging tool. However, FDCT imaging can be significantly impaired by artefacts induced by fixation screws. Following ethical board approval, commercially available scaphoid fixation screws were inserted into six cadaveric specimens in order to fix artificially induced scaphoid fractures. FDCT images corrected with the algorithm were compared to uncorrected images both quantitatively and qualitatively by two independent radiologists in terms of artefacts, screw contour, fracture line visibility, bone visibility, and soft tissue definition. Normal distribution of variables was evaluated using the Kolmogorov-Smirnov test. In case of normal distribution, quantitative variables were compared using paired Student's t tests. The Wilcoxon signed-rank test was used for quantitative variables without normal distribution and all qualitative variables. A p value of < 0.05 was considered to indicate statistically significant differences. Metal artefacts were significantly reduced by the correction algorithm (p < 0.001), and the fracture line was more clearly defined (p < 0.01). The inter-observer reliability was ''almost perfect'' (intra-class correlation coefficient 0.85, p < 0.001). The prototype correction algorithm in FDCT for metal artefacts induced by scaphoid fixation screws may facilitate intra- and postoperative follow-up imaging. (orig.)

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.

Mathematical modeling of the working cycle of oil injected rotary twin screw compressor

Energy Technology Data Exchange (ETDEWEB)

Seshaiah, N. [Cryogenics and Gas dynamics Laboratory, Department of Mechanical Engineering, National Institute of Technology, Sector-2, NIT Campus, Rourkela 769008, Orissa (India)]. E-mail: seshuet@yahoo.com; Ghosh, Subrata Kr. [Cryogenics and Gas dynamics Laboratory, Department of Mechanical Engineering, National Institute of Technology, Sector-2, NIT Campus, Rourkela 769008, Orissa (India); Sahoo, R.K. [Cryogenics and Gas dynamics Laboratory, Department of Mechanical Engineering, National Institute of Technology, Sector-2, NIT Campus, Rourkela 769008, Orissa (India); Sarangi, Sunil Kr. [Cryogenics and Gas dynamics Laboratory, Department of Mechanical Engineering, National Institute of Technology, Sector-2, NIT Campus, Rourkela 769008, Orissa (India)

2007-01-15

Oil injected twin-screw air and gas compressors are widely used for medium pressure applications in many industries. Low cost air compressors can be adopted for compression of helium and special gases, leading to significant cost saving. Mathematical analysis of oil injected twin-screw compressor is carried out on the basis of the laws of perfect gas and standard thermodynamic relations. Heat transfer coefficient required for computer simulation is experimentally obtained and used in performance prediction, when the working medium being air or helium. A mathematical model has been developed for calculating the compressor performance and for validating the results with experimental data. The flow coefficients required for numerical simulation to calculate leakage flow rates are obtained from efficiency verses clearance curves. Effect of some of the compressor operating and design parameters on power and volumetric efficiencies have been analyzed and presented.

Mathematical modeling of the working cycle of oil injected rotary twin screw compressor

International Nuclear Information System (INIS)

Seshaiah, N.; Ghosh, Subrata Kr.; Sahoo, R.K.; Sarangi, Sunil Kr.

2007-01-01

Oil injected twin-screw air and gas compressors are widely used for medium pressure applications in many industries. Low cost air compressors can be adopted for compression of helium and special gases, leading to significant cost saving. Mathematical analysis of oil injected twin-screw compressor is carried out on the basis of the laws of perfect gas and standard thermodynamic relations. Heat transfer coefficient required for computer simulation is experimentally obtained and used in performance prediction, when the working medium being air or helium. A mathematical model has been developed for calculating the compressor performance and for validating the results with experimental data. The flow coefficients required for numerical simulation to calculate leakage flow rates are obtained from efficiency verses clearance curves. Effect of some of the compressor operating and design parameters on power and volumetric efficiencies have been analyzed and presented

Evaluation of a prototype correction algorithm to reduce metal artefacts in flat detector computed tomography of scaphoid fixation screws.

Science.gov (United States)

Filli, Lukas; Marcon, Magda; Scholz, Bernhard; Calcagni, Maurizio; Finkenstädt, Tim; Andreisek, Gustav; Guggenberger, Roman

2014-12-01

The aim of this study was to evaluate a prototype correction algorithm to reduce metal artefacts in flat detector computed tomography (FDCT) of scaphoid fixation screws. FDCT has gained interest in imaging small anatomic structures of the appendicular skeleton. Angiographic C-arm systems with flat detectors allow fluoroscopy and FDCT imaging in a one-stop procedure emphasizing their role as an ideal intraoperative imaging tool. However, FDCT imaging can be significantly impaired by artefacts induced by fixation screws. Following ethical board approval, commercially available scaphoid fixation screws were inserted into six cadaveric specimens in order to fix artificially induced scaphoid fractures. FDCT images corrected with the algorithm were compared to uncorrected images both quantitatively and qualitatively by two independent radiologists in terms of artefacts, screw contour, fracture line visibility, bone visibility, and soft tissue definition. Normal distribution of variables was evaluated using the Kolmogorov-Smirnov test. In case of normal distribution, quantitative variables were compared using paired Student's t tests. The Wilcoxon signed-rank test was used for quantitative variables without normal distribution and all qualitative variables. A p value of < 0.05 was considered to indicate statistically significant differences. Metal artefacts were significantly reduced by the correction algorithm (p < 0.001), and the fracture line was more clearly defined (p < 0.01). The inter-observer reliability was "almost perfect" (intra-class correlation coefficient 0.85, p < 0.001). The prototype correction algorithm in FDCT for metal artefacts induced by scaphoid fixation screws may facilitate intra- and postoperative follow-up imaging. Flat detector computed tomography (FDCT) is a helpful imaging tool for scaphoid fixation. The correction algorithm significantly reduces artefacts in FDCT induced by scaphoid fixation screws. This may facilitate intra

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

The Hot-gas screw-type engine - Simulation as a basis for construction. Pt. 3; Die Heissgasschraubenmaschine - simulationsgestuetzte Auslegung. T. 3

Energy Technology Data Exchange (ETDEWEB)

Kauder, K.; Unwerth, T. von [Dortmund Univ. (Germany). FG Fluidenergiemaschinen

1998-12-31

In this paper new results of the research regarding the design of the first experimental plant for a hot-gas screw-type machine are reported. Target of the development is the verification of operating behaviour as well as the thermal and mechanical behaviour of the screw-type motor parts. The selection and dimensioning of the plant components is described with a main focus on the construction of the thermally high-loaded hot-gas screw-type engine. Its manufacturing tolerances are based on simulations, with which the mechanical deformations of the rotors and the casing respective the resulting clearance-heights can be calculated. With inclusion of an efficient cooling method for the motor parts, for the, in the article documented, projected nominal working condition with a material-depending limit for the entrance temperature at {theta}{sub E,} {sub M}=600 C, a pressure ratio {pi}=6 and a male rotor peripheral speed u{sub HR}=120 ms{sup -1}, each rotor should be decreased by 0.07 mm. (orig.) [Deutsch] Es wird ueber neue Forschungsergebnisse im Hinblick auf die konstruktive Realisierung der ersten Versuchsanlage einer Heissgasschraubenmaschine berichtet. Ziel der daran durchgefuehrten Untersuchungen ist die Verifikation des Betriebsverhaltens sowie des thermischen und mechanischen Bauteilverhaltens des Heissgasschraubenmotors. Nachzulesen ist die Auswahl und Dimensionierung der Anlagenkomponenten, wobei ein Hauptaugenmerk auf der Auslegung des thermisch hoch belasteten Schraubenmotors liegt. Dessen Dimensionierung liegen Simulationsrechnungen zugrunde, mit deren Hilfe die mechanischen Verformungen der Rotoren und des Gehaeuses respektive der daraus resultierenden Spalthoehen a priori angegeben werden koennen. Fuer den hier dokumentierten, angestrebten Nennbetriebszustand mit einer werkstoffbedingt begrenzten Motoreintrittstemperatur von {theta}{sub E,} {sub M}=600 C, einem Druckverhaeltnis von {pi}=6 und einer Hauptrotorumfangsgeschwindigkeit von u{sub HR}=120 ms

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.

Improving Nurses' Peripheral Intravenous Catheter Insertion Knowledge, Confidence, and Skills Using a Simulation-Based Blended Learning Program

Science.gov (United States)

Keleekai, Nowai L.; Schuster, Catherine A.; Murray, Connie L.; King, Mary Anne; Stahl, Brian R.; Labrozzi, Laura J.; Gallucci, Susan; LeClair, Matthew W.; Glover, Kevin R.

2016-01-01

Introduction Peripheral intravenous catheter (PIVC) insertion is one of the most common invasive procedures performed in a hospital, but most nurses receive little formal training in this area. Blended PIVC insertion training programs that incorporate deliberate simulated practice have the potential to improve clinical practice and patient care. Methods The study was a randomized, wait-list control group with crossover using nurses on three medical/surgical units. Baseline PIVC knowledge, confidence, and skills assessments were completed for both groups. The intervention group then received a 2-hour PIVC online course, followed by an 8-hour live training course using a synergistic mix of three simulation tools. Both groups were then reassessed. After crossover, the wait-list group received the same intervention and both groups were reassessed. Results At baseline, both groups were similar for knowledge, confidence, and skills. Compared with the wait-list group, the intervention group had significantly higher scores for knowledge, confidence, and skills upon completing the training program. After crossover, the wait-list group had similarly higher scores for knowledge, confidence, and skills than the intervention group. Between the immediate preintervention and postintervention periods, the intervention group improved scores for knowledge by 31%, skills by 24%, and decreased confidence by 0.5%, whereas the wait-list group improved scores for knowledge by 28%, confidence by 16%, and skills by 15%. Conclusions Results demonstrate significant improvements in nurses' knowledge, confidence, and skills with the use of a simulation-based blended learning program for PIVC insertion. Transferability of these findings from a simulated environment into clinical practice should be further explored. PMID:27504890

Comparison of revision strategies for failed C2-posterior cervical pedicle screws: a biomechanical study.

Science.gov (United States)

Mayer, Michael; Zenner, Juliane; Bogner, Robert; Hitzl, Wolfgang; Figl, Markus; von Keudell, Arvind; Stephan, Daniel; Penzkofer, Rainer; Augat, Peter; Korn, Gundobert; Resch, Herbert; Koller, Heiko

2013-01-01

With increasing usage within challenging biomechanical constructs, failures of C2 posterior cervical pedicle screws (C2-pCPSs) will occur. The purpose of the study was therefore to investigate the biomechanical characteristics of two revision techniques after the failure of C2-pCPSs. Twelve human C2 vertebrae were tested in vitro in a biomechanical study to compare two strategies for revision screws after failure of C2-pCPSs. C2 pedicles were instrumented using unicortical 3.5-mm CPS bilaterally (Synapse/Synthes, Switzerland). Insertion accuracy was verified by fluoroscopy. C2 vertebrae were potted and fixed in an electromechanical testing machine with the screw axis coaxial to the pullout direction. Pullout testing was conducted with load and displacement data taken continuously. The peak load to failure was measured in newtons (N) and is reported as the pullout resistance (POR). After pullout, two revision strategies were tested in each vertebra. In Group-1, revision was performed with 4.0-mm C2-pCPSs. In Group-2, revision was performed with C2-pedicle bone-plastic combined with the use of a 4-mm C2-pCPSs. For the statistical analysis, the POR between screws was compared using absolute values (N) and the POR of the revision techniques normalized to that of the primary procedures (%). The POR of primary 3.5-mm CPSs was 1,140.5 ± 539.6 N for Group-1 and 1,007.7 ± 362.5 N for Group-2; the difference was not significant. In the revision setting, the POR in Group-1 was 705.8 ± 449.1 N, representing a reduction of 38.1 ± 32.9 % compared with that of primary screw fixation. For Group-2, the POR was 875.3 ± 367.9 N, representing a reduction of 13.1 ± 23.4 %. A statistical analysis showed a significantly higher POR for Group-2 compared with Group-1 (p = 0.02). Although the statistics showed a significantly reduced POR for both revision strategies compared with primary fixation (p plastic, the POR can be significantly increased compared with the use of only an

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.

Numerical simulation on the screw pinch by 2-D MHD pinch code 'topics' including impurities and neutrals effects

International Nuclear Information System (INIS)

Nagata, A.; Ashida, H.; Okamoto, M.; Hirano, K.

1981-03-01

Two dimentional fluid simulation code ''TOPICS'' is developed for the STP-2, the shock heated screw pinch at Nagoya. It involves the effects of impurity ions and neutral atoms. In order to estimate the radiation losses, the impurity continuity equations with ionizations and recombinations are solved simultaneously with the plasma fluid equations. The results are compared with the coronal equilibrium model. It is found that the coronal equilibrium model underestimates the radiation losses from shock heated pinch plasmas in its initial dynamic phase. The present calculations including impurities and neutrals show the importance of the radiation losses from the plasma of the STP-2. Introducing the anomalous resistivity caused by the ion acoustic instability, the observed magnetic field penetration is explained fairly well. (author)

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.

The kinetics of porous insertion electrodes

Energy Technology Data Exchange (ETDEWEB)

Atlung, S; West, K [British Columbia Univ., Vancouver (Canada)

1989-05-01

The principles of porous electrodes are discussed as well as the discharge of the insertion compound, the working potential, transport in the electrolyte, the time dependence of the electrolyte concentration, and modeling of the porous electrode. The simulation of a TiS2 porous electrode and the composite insertion electrode are considered as well. The influence of electrode thickness and porosity in a typical porous TiS2 electrode is revealed. It is shown that the use of insertion compounds as battery electrodes is limited by the requirement that the inserted ion must be distributed in the interior of the insertion compound particle. 15 refs.

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.

Finite element analysis of the equivalent stress distribution in Schanz screws during the use of a femoral fracture distractor

Directory of Open Access Journals (Sweden)

Vincenzo Giordano

Full Text Available ABSTRACT To evaluate the mechanical stress and elastic deformation exercised in the thread/shaft transition of Schanz screws in assemblies with different screw anchorage distances in the entrance to the bone cortex, through the distribution and location of tension in the samples. An analysis of 3D finite elements was performed to evaluate the distribution of the equivalent stress (triple stress state in a Schanz screw fixed bicortically and orthogonally to a tubular bone, using two mounting patterns: (1 thread/shaft transition located 20 mm from the anchorage of the Schanz screws in the entrance to the bone cortex and (2 thread/shaft transition located 3 mm from the anchorage of the Schanz screws in entrance to the bone cortex. The simulations were performed maintaining the same direction of loading and the same distance from the force vector in relation to the center of the hypothetical bone. The load applied, its direction, and the distance to the center of the bone were constant during the simulations in order to maintain the moment of flexion equally constant. The present calculations demonstrated linear behavior during the experiment. It was found that the model with a distance of 20 mm between the Schanz screws anchorage in the entrance to the bone cortex and the thread/shaft transition reduces the risk of breakage or fatigue of the material during the application of constant static loads; in this model, the maximum forces observed were higher (350 MPa. The distance between the Schanz screws anchorage at the entrance to the bone cortex and the smooth thread/shaft transition of the screws used in a femoral distractor during acute distraction of a fracture must be farther from the entrance to the bone cortex, allowing greater degree of elastic deformation of the material, lower mechanical stress in the thread/shaft transition, and minimized breakage or fatigue. The suggested distance is 20 mm.

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

Wear resistance of thick diamond like carbon coatings against polymeric materials used in single screw plasticizing technology

Science.gov (United States)

Zitzenbacher, G.; Liu, K.; Forsich, C.; Heim, D.

2015-05-01

Wear on the screw and barrel surface accompany polymer single screw plasticizing technology from the beginning. In general, wear on screws can be reduced by using nitrided steel surfaces, fused armour alloys on the screw flights and coatings. However, DLC-coatings (Diamond Like Carbon) comprise a number of interesting properties such as a high hardness, a low coefficient of friction and an excellent corrosion resistance due to their amorphous structure. The wear resistance of about 50 µm thick DLC-coatings against polyamide 6.6, polybutylene terephthalate and polypropylene is investigated in this paper. The tribology in the solids conveying zone of a single screw extruder until the beginning of melting is evaluated using a pin on disc tribometer and a so called screw tribometer. The polymeric pins are pressed against coated metal samples using the pin on disc tribometer and the tests are carried out at a defined normal force and sliding velocity. The screw tribometer is used to perform tribological experiments between polymer pellets and rotating coated metal shafts simulating the extruder screw. Long term experiments were performed to evaluate the wear resistance of the DLC-coating. A reduction of the coefficient of friction can be observed after a frictional distance of about 20 kilometers using glass fibre reinforced polymeric materials. This reduction is independent on the polymer and accompanied by a black layer on the wear surface of the polymeric pins. The DLC-coated metal samples show an up to 16 µm deep wear track after the 100 kilometer test period against the glass fiber filled materials only.

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

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

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.

Atomistic simulations of screw dislocations in bcc tungsten: From core structures and static properties to interaction with vacancies

Energy Technology Data Exchange (ETDEWEB)

Xu, Ke [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, Beijing 100191 (China); Niu, Liang-Liang [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, Beijing 100191 (China); Department of Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, MI 48109 (United States); Jin, Shuo, E-mail: jinshuo@buaa.edu.cn [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, Beijing 100191 (China); Shu, Xiaolin [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, Beijing 100191 (China); Xie, Hongxian [School of Mechanical Engineering, Hebei University of Technology, Tianjin 300132 (China); Wang, Lifang; Lu, Guang-Hong [School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, Beijing 100191 (China)

2017-02-15

Atomistic simulations have been used to investigate the core structures, static properties of isolated 1/2 <1 1 1> screw dislocations, and their interaction with vacancies in bcc tungsten (W) based on three empirical interatomic potentials. Differential displacement maps show that only one embedded atom method potential is able to reproduce the compact non-degenerate core as evidenced by ab initio calculations. The obtained strain energy and stress distribution from atomistic simulations are, in general, consistent with elasticity theory predictions. In particular, one component of the calculated shear stress, which is not present according to elasticity theory, is non-negligible in the core region of our dislocation model. The differences between the results calculated from three interatomic potentials are in details, such as the specific value and the symmetry, but the trend of spatial distributions of static properties in the long range are close to each other. By calculating the binding energies between the dislocations and vacancies, we demonstrate that the dislocations act as vacancy sinks, which may be important for the nucleation and growth of hydrogen bubbles in W under irradiation.

Deformation Analysis of the Main Components in a Single Screw Compressor

Science.gov (United States)

Liu, Feilong; Liao, Xueli; Feng, Quanke; Van Den Broek, Martijn; De Paepe, Michel

2015-08-01

The single screw compressor is used in many fields such as air compression, chemical industry and refrigeration. During operation, different gas pressures and temperatures applied on the components can cause different degrees of deformation, which leads to a difference between the thermally induced clearance and the designed clearance. However, limited research about clearance design is reported. In this paper, a temperature measurement instrument and a convective heat transfer model were described and used to establish the temperature of a single screw air compressor's casing, screw rotor and star wheel. 3-D models of these three main components were built. The gas force deformation, thermal- structure deformation and thermal-force coupling deformation were carried out by using a finite element simulation method. Results show that the clearance between the bottom of the groove and the top of star wheel is reduced by 0.066 mm, the clearance between the side of groove and the star wheel is reduced by 0.015 mm, and the clearance between the cylinder and the rotor is reduced by 0.01 mm. It is suggested that these deformations should be taken into account during the design of these clearances.

Peripheral venous catheter insertion simulation training: A randomized controlled trial comparing performance after instructor-led teaching versus peer-assisted learning.

Science.gov (United States)

Pelloux, Sophie; Grégoire, Arnaud; Kirmizigul, Patrice; Maillot, Sandrine; Bui-Xuan, Bernard; Llorca, Guy; Boet, Sylvain; Lehot, Jean-Jacques; Rimmelé, Thomas

2017-12-01

Peripheral venous catheter insertion is a procedural skill that every medical student should master. Training is often limited to a small number of students and is poorly evaluated. The objective of this study was to evaluate the performance of peer-assisted learning in comparison to instructor-led teaching for peripheral venous catheter insertion training. Students were randomized to the control group attending a traditional instructor-led training session (slideshow and demonstration by an anesthetist instructor, followed by training on a procedural simulator) or to the test group attending a peer-assisted training session (slideshow and demonstration video-recorded by the same instructor, followed by training on a procedural simulator). The primary endpoint was the performance of peripheral venous catheter insertion, assessed on procedural simulator one week later by blinded experts using a standardized 20-item grid. Students self-evaluated their confidence levels using a numeric 10-point scale. Eighty-six students were included, 73 of whom attended the assessment session. The median performance score was 12/20 [8-15] in the instructor-led teaching group versus 13/20 [11-15] in the peer-assisted learning group (P=0.430). Confidence levels improved significantly after the assessment session and were significantly higher in the peer-assisted learning group (7.6/10 [7.0-8.0] versus 7.0/10 [5.0-8.0], P=0.026). Peer-assisted learning is effective for peripheral venous catheter insertion training and can be as effective as instructor-led teaching. Given the large number of students to train, this finding is important for optimizing the cost-effectiveness of peripheral venous catheter insertion training. Copyright © 2017 Société française d’anesthésie et de réanimation (Sfar). Published by Elsevier Masson SAS. All rights reserved.

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.

Peptide insertion, positioning, and stabilization in a membrane: insight from an all-atom molecular dynamics simulation.

Science.gov (United States)

Babakhani, Arneh; Gorfe, Alemayehu A; Gullingsrud, Justin; Kim, Judy E; Andrew McCammon, J

Peptide insertion, positioning, and stabilization in a model membrane are probed via an all-atom molecular dynamics (MD) simulation. One peptide (WL5) is simulated in each leaflet of a solvated dimyristoylglycero-3-phosphate (DMPC) membrane. Within the first 5 ns, the peptides spontaneously insert into the membrane and then stabilize during the remaining 70 ns of simulation time. In both leaflets, the peptides localize to the membrane interface, and this localization is attributed to the formation of peptide-lipid hydrogen bonds. We show that the single tryptophan residue in each peptide contributes significantly to these hydrogen bonds; specifically, the nitrogen heteroatom of the indole ring plays a critical role. The tilt angles of the indole rings relative to the membrane normal in the upper and lower leaflets are approximately 26 degrees and 54 degrees , respectively. The tilt angles of the entire peptide chain are 62 degrees and 74 degrees . The membrane induces conformations of the peptide that are characteristic of beta-sheets, and the peptide enhances the lipid ordering in the membrane. Finally, the diffusion rate of the peptides in the membrane plane is calculated (based on experimental peptide concentrations) to be approximately 6 A(2)/ns, thus suggesting a 500 ns time scale for intermolecular interactions.

[Finite element analysis of stress changes of posterior spinal pedicle screw infixation].

Science.gov (United States)

Yan, Jia-Zhi; Wu, Zhi-Hong; Xu, Ri-Xin; Wang, Xue-Song; Xing, Ze-Jun; Zhao, Yu; Zhang, Jian-Guo; Shen, Jian-Xiong; Wang, Yi-Peng; Qiu, Gui-Xing

2009-01-06

To evaluate the mechanical response of L3-L4 segment after posterior interfixation with a transpedicle screw system. Spiral CT machine was used to conduct continuous parallel scan on the L3-L4 section of a 40-year-old healthy male Chinese. The image data thus obtained were introduced into MIMICS software to reconstruct the 2-D data into volume data and obtain 3-D models of every element.. Pro/3-D model construction software system was used to simulate the 3-D entity of L3-L4 fixed by screw robs through spinal pedicle via posterior approach that was introduced into the finite element software ABAQUS to construct a 3-D finite element model. The stress changes on the vertebrae and screw under the axial pressure of 0.5 mPa was analyzed. Under the evenly distributed pressure the displacement of the L4 model was 0.00125815 mm, with an error of only 0.8167% from the datum displacement. The convergence of the model was good. The stress of the fixed vertebral body, intervertebral disc, and internal fixators changed significantly. The stress concentration zone of the intervertebral disc turned from the posterolateral side to anterolateral side. The stress produced by the fixed vertebral bodies decreased significantly. Obvious stress concentration existed in the upper and lower sides of the base of screw and the fixed screw at the upper vertebral body bore greater stress than the lower vertebral body. Integration of computer aided device and finite element analysis can successfully stimulate the internal fixation of L3-IA visa posterior approach and observe the mechanic changes in the vertebral column more directly.

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.

Torque Removal Evaluation of Screw in One-Piece and Two-Piece Abutments Tightened with a Handheld screwdriver

Directory of Open Access Journals (Sweden)

Jalil Ghanbarzadeh

2013-12-01

Full Text Available Introduction: Some clinicians use a handheld screw driver instead of a torque wrench to definitively tighten abutment screws. The aim of this study was to compare the removal torque of one-piece and two-piece abutments tightened with a handheld driver and a torque control ratchet. Methods: 40 ITI implants were placed in acrylic blocks and divided into 4 groups. In groups one and two, 10 ITI one-piece abutments (Solid® and in groups three and four, 10 ITI two-piece abutments (Synocta® were placed on the implants. In groups one and three abutments were tightened by 5 experienced males and 5 experienced females using a handheld driver. In groups two and four abutments were tightened using a torque wrench with torque values of 10, 20 and 35 N.cm. Insertion torque and removal torque values of the abutments were measured with a digital torque meter. Results: The insertion torque values (ITVs of males in both abutments were significantly higher than those of females. ITVs in both Solid® and Synocta® abutments tightened with a handheld screwdriver were similar to the torque of 20 N.cm in the torque wrench. Removal torque values (RTVs of solid® abutments were higher than those of synocta® abutments. Conclusion: The one- piece abutments (solid® showed higher RTVs than the two-piece abutments (synocta®. Hand driver does not produce sufficient preload force for the final tightening of the abutment

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

Does a trochanteric lag screw improve fixation of vertically oriented femoral neck fractures? A biomechanical analysis in cadaveric bone.

Science.gov (United States)

Hawks, Michael A; Kim, Hyunchul; Strauss, Joseph E; Oliphant, Bryant W; Golden, Robert D; Hsieh, Adam H; Nascone, Jason W; O'Toole, Robert V

2013-10-01

We assessed the biomechanical performances of a trochanteric lag screw construct and a traditional inverted triangle construct in the treatment of simulated Pauwels type 3 femoral neck fractures. An inverted triangle construct (three 7.3-mm cannulated screws placed in inverted triangle orientation) and a trochanteric lag screw construct (two 7.3-mm cannulated screws placed across the superior portion of the femoral neck and one 4.5-mm lag screw placed perpendicular to the fracture in superolateral to inferomedial orientation) were tested in nine matched pairs of non-osteoporotic human cadaveric femora. We used a previously described vertically oriented femoral neck fracture model and testing protocol that incrementally loaded the constructs along the mechanical axis of the femur to 1400 N. Specimens that survived incremental loading underwent cyclic loading. Apparent construct stiffness, force at 3mm of displacement, and survival of incremental loading were recorded. The trochanteric lag screw group had a 70% increase in stiffness (261 N/mm [29 standard deviation] versus 153 N/mm [16 standard deviation]; P=0.026) and a 43% increase in force required for displacement (620 N versus 435 N; P=0.018) compared with the inverted triangle group. One trochanteric lag screw and no inverted triangle specimen survived incremental loading. A trochanteric lag screw construct applied to vertically oriented femoral neck fractures provides marked improvement in mechanical performance compared with the inverted triangle construct. © 2013.

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.

First Metatarsophalangeal Joint Arthrodesis: A Retrospective Comparison of Crossed-screws, Locking and Non-Locking Plate Fixation with Lag Screw

Directory of Open Access Journals (Sweden)

Leif Claassen

2017-07-01

Full Text Available Background:Locking plate fixation is increasingly used for first metatarsophalangeal joint (MTP-I arthrodesis. Still there is few comparable clinical data regarding this procedure. Methods:We retrospectively evaluated 60 patients who received an arthrodesis of the MTP-I between January 2008 and June 2010. With 20 patients each we performed a locking plate fixation with lag screw, arthrodesis with crossed-screwsor with a nonlocking plate with lag screw. Results: There were four non-unions in crossed-screws patients and one nonunion in non-locked plate group. All the patients in locking plate group achieved union. 90% of the patients were completely or mildly satisfied in locking plate group, whereas this rate was 80% for patients in both crossed screws and non-locking plate groups. Conclusions: Use of dorsal plating for arthrodesis of MTP1 joint either locking or non-locking were associated with high union rate and acceptable and comparable functional outcome. Although nonunion rate was high using two crossed screws but functional outcome was not significantly different compare to dorsal plating. Level of evidence:Ш, retrospective comparative study

Use of a National Continuing Medical Education Meeting to Provide Simulation-Based Training in Temporary Hemodialysis Catheter Insertion Skills: A Pre-Test Post-Test Study

Directory of Open Access Journals (Sweden)

Edward G Clark

2014-10-01

Full Text Available Background: Simulation-based-mastery-learning (SBML is an effective method to train nephrology fellows to competently insert temporary, non-tunneled hemodialysis catheters (NTHCs. Previous studies of SBML for NTHC-insertion have been conducted at a local level. Objectives: Determine if SBML for NTHC-insertion can be effective when provided at a national continuing medical education (CME meeting. Describe the correlation of demographic factors, prior experience with NTHC-insertion and procedural self-confidence with simulated performance of the procedure. Design: Pre-test – post-test study. Setting: 2014 Canadian Society of Nephrology annual meeting. Participants: Nephrology fellows, internal medicine residents and medical students. Measurements: Participants were surveyed regarding demographics, prior NTHC-insertion experience, procedural self-confidence and attitudes regarding the training they received. NTHC-insertion skills were assessed using a 28-item checklist. Methods: Participants underwent a pre-test of their NTHC-insertion skills at the internal jugular site using a realistic patient simulator and ultrasound machine. Participants then had a training session that included a didactic presentation and 2 hours of deliberate practice using the simulator. On the following day, trainees completed a post-test of their NTHC-insertion skills. All participants were required to meet or exceed a minimum passing score (MPS previously set at 79%. Trainees who did not reach the MPS were required to perform more deliberate practice until the MPS was achieved. Results: Twenty-two individuals participated in SBML training. None met or exceeded the MPS at baseline with a median checklist score of 20 (IQR, 7.25 to 21. Seventeen of 22 participants (77% completed post-testing and improved their scores to a median of 27 (IQR, 26 to 28; p < 0.001. All met or exceeded the MPS on their first attempt. There were no significant correlations between demographics

Use of a national continuing medical education meeting to provide simulation-based training in temporary hemodialysis catheter insertion skills: a pre-test post-test study.

Science.gov (United States)

Clark, Edward G; Paparello, James J; Wayne, Diane B; Edwards, Cedric; Hoar, Stephanie; McQuillan, Rory; Schachter, Michael E; Barsuk, Jeffrey H

2014-01-01

Simulation-based-mastery-learning (SBML) is an effective method to train nephrology fellows to competently insert temporary, non-tunneled hemodialysis catheters (NTHCs). Previous studies of SBML for NTHC-insertion have been conducted at a local level. Determine if SBML for NTHC-insertion can be effective when provided at a national continuing medical education (CME) meeting. Describe the correlation of demographic factors, prior experience with NTHC-insertion and procedural self-confidence with simulated performance of the procedure. Pre-test - post-test study. 2014 Canadian Society of Nephrology annual meeting. Nephrology fellows, internal medicine residents and medical students. Participants were surveyed regarding demographics, prior NTHC-insertion experience, procedural self-confidence and attitudes regarding the training they received. NTHC-insertion skills were assessed using a 28-item checklist. Participants underwent a pre-test of their NTHC-insertion skills at the internal jugular site using a realistic patient simulator and ultrasound machine. Participants then had a training session that included a didactic presentation and 2 hours of deliberate practice using the simulator. On the following day, trainees completed a post-test of their NTHC-insertion skills. All participants were required to meet or exceed a minimum passing score (MPS) previously set at 79%. Trainees who did not reach the MPS were required to perform more deliberate practice until the MPS was achieved. Twenty-two individuals participated in SBML training. None met or exceeded the MPS at baseline with a median checklist score of 20 (IQR, 7.25 to 21). Seventeen of 22 participants (77%) completed post-testing and improved their scores to a median of 27 (IQR, 26 to 28; p < 0.001). All met or exceeded the MPS on their first attempt. There were no significant correlations between demographics, prior experience or procedural self-confidence with pre-test performance. Small sample-size and

Devolatilization Analysis in a Twin Screw Extruder by using the Flow Analysis Network (FAN) Method

Science.gov (United States)

Tomiyama, Hideki; Takamoto, Seiji; Shintani, Hiroaki; Inoue, Shigeki

We derived the theoretical formulas for three mechanisms of devolatilization in a twin screw extruder. These are flash, surface refreshment and forced expansion. The method for flash devolatilization is based on the equation of equilibrium concentration which shows that volatiles break off from polymer when they are relieved from high pressure condition. For surface refreshment devolatilization, we applied Latinen's model to allow estimation of polymer behavior in the unfilled screw conveying condition. Forced expansion devolatilization is based on the expansion theory in which foams are generated under reduced pressure and volatiles are diffused on the exposed surface layer after mixing with the injected devolatilization agent. Based on these models, we developed the simulation software of twin-screw extrusion by the FAN method and it allows us to quantitatively estimate volatile concentration and polymer temperature with a high accuracy in the actual multi-vent extrusion process for LDPE + n-hexane.

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

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.

Bite Reconstruction in the Aesthetic Zone Using One-Piece Bicortical Screw Implants

Directory of Open Access Journals (Sweden)

Stefan Ihde

2018-01-01

Full Text Available The aim of this article was to present the clinical application of a new, smooth surfaced one-piece bicortical screw implant with immediate loading protocol. An 18-year-old, healthy male patient with a history of total dislocation and replantation of teeth 11 and 21 in early childhood was admitted to the clinic. Teeth 11 and 21 were extracted, and two long one-piece implants were inserted at extraction sockets in one surgical session under local anesthesia. Temporary composite crowns were placed in the patient on the same day. After 3 months, the single-phase two-layer impression was made and the composite crowns were replaced with metal-ceramic crowns. After 12 months, satisfactory aesthetic and functional results were obtained.

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.

Adapted preparation technique for screw-type implants: explorative in vitro pilot study in a porcine bone model.

Science.gov (United States)

Beer, Andreas; Gahleitner, André; Holm, Anders; Birkfellner, Wolfgang; Homolka, Peter

2007-02-01

The aim of this study was to quantify the effect of adapted preparation on the insertion torque of self-tapping implants in cancellous bone. In adapted preparation, bone condensation - and thus, insertion torque - is controlled by changing the diameter of the drilling. After preparation of cancellous porcine vertebral bone with drills of 2.85, 3, 3.15 or 3.35 mm final diameters, Brånemark sytem Mk III implants (3.75 x 11.5 mm) were inserted in 141 sites. During implantation, the insertion torque was recorded. Prior to implant insertion, bone mineralization (bone mineral density (BMD)) was measured with dental quantative computed tomography. The BMD values measured at the implant position were correlated with insertion torque for varying bone condensation. Based on the average torque recorded during implant insertion into the pre-drilled canals with a diameter of 3 mm, torque increased by approximately 17% on reducing the diameter of the drill by 5% (to 2.85 mm). On increasing the diameter of the osteotomy to 3.15 mm (5%) or 3.35 mm (12%), torque values decreased by approximately 21% and 50%, respectively. The results demonstrate a correlation between primary stability (average insertion torque) and the diameter of the implant bed on using a screw-shaped implant. Thus, using an individualized bone mineralization-dependent drilling technique, optimized torque values could be achieved in all tested bone qualities with BMDs ranging from 330 to 500 mg/cm(3). The results indicate that using a bone-dependent drilling technique, higher torque values can also be achieved in poor bone using an individualized drilling resulting in higher bone condensation. As immediate function is dependent on primary stability (high insertion torque), this indicates that primary stability can be increased using a modified drilling technique in lesser mineralized bone.

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

Design-Based Comparison of Spine Surgery Simulators: Optimizing Educational Features of Surgical Simulators.

Science.gov (United States)

Ryu, Won Hyung A; Mostafa, Ahmed E; Dharampal, Navjit; Sharlin, Ehud; Kopp, Gail; Jacobs, W Bradley; Hurlbert, R John; Chan, Sonny; Sutherland, Garnette R

2017-10-01

Simulation-based education has made its entry into surgical residency training, particularly as an adjunct to hands-on clinical experience. However, one of the ongoing challenges to wide adoption is the capacity of simulators to incorporate educational features required for effective learning. The aim of this study was to identify strengths and limitations of spine simulators to characterize design elements that are essential in enhancing resident education. We performed a mixed qualitative and quantitative cohort study with a focused survey and interviews of stakeholders in spine surgery pertaining to their experiences on 3 spine simulators. Ten participants were recruited spanning all levels of training and expertise until qualitative analysis reached saturation of themes. Participants were asked to perform lumbar pedicle screw insertion on 3 simulators. Afterward, a 10-item survey was administrated and a focused interview was conducted to explore topics pertaining to the design features of the simulators. Overall impressions of the simulators were positive with regards to their educational benefit, but our qualitative analysis revealed differing strengths and limitations. Main design strengths of the computer-based simulators were incorporation of procedural guidance and provision of performance feedback. The synthetic model excelled in achieving more realistic haptic feedback and incorporating use of actual surgical tools. Stakeholders from trainees to experts acknowledge the growing role of simulation-based education in spine surgery. However, different simulation modalities have varying design elements that augment learning in distinct ways. Characterization of these design characteristics will allow for standardization of simulation curricula in spinal surgery, optimizing educational benefit. Copyright © 2017 Elsevier Inc. All rights reserved.

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 study of two materials for dynamic hip screw during fall and gait loading: titanium alloy and stainless steel.

Science.gov (United States)

Taheri, Nooshin S; Blicblau, Aaron S; Singh, Manmohan

2011-11-01

Internal fixation with dynamic hip screw is a choice of treatment for hip fractures to stabilize a femoral fracture. Choosing the proper implant and its material has a great effect on the healing process and failure prevention. The purpose of this analysis was to assess biomechanical behavior of dynamic hip screw with two different materials implanted in the femur during fall and gait. A 3D finite element model of an intact femur and a 3D implant within the same femur were developed. A finite element analysis was carried out to establish the effect of load conditions and implant material properties on biomechanical behavior of the dynamic hip screw after internal fixation. Two load configurations are chosen: one simulating the stance phase of the normal gait cycle, and the other replicating a low-energy fall. The implanted femur was investigated with two different materials for the dynamic hip screw: stainless steel and titanium alloy. During stance, more stress is placed on the implanted femur compared with the intact femur. During a fall, the implanted femur is in a greater state of stress, which mostly occurs inside the dynamic hip screw. Titanium alloy decreases stress levels by an average of 40% compared with stainless steel. However, deformation is slightly reduced with a stainless steel dynamic hip screw during both load cases. After internal fixation, dynamic hip screw generates greater stresses within the implanted femur compared with the intact femur under the same loading conditions. A titanium alloy implant appears to undergo less stress from a low-energy fall compared with stainless steel and can be considered the preferred implant material. The critical parts of the dynamic hip screw are the forth distal screw and the plate.

Comparison of computer assisted surgery with conventional technique for treatment of abaxial distal phalanx fractures in horses: an in vitro study.

Science.gov (United States)

Rossol, Melanie; Gygax, Diego; Andritzky-Waas, Juliane; Zheng, Guoyan; Lischer, Christoph J; Zhang, Xuan; Auer, Joerg A

2008-01-01

To (1) evaluate and compare computer-assisted surgery (CAS) with conventional screw insertion (conventional osteosynthesis [COS]) for treatment of equine abaxial distal phalanx fractures; (2) compare planned screw position with actual postoperative position; and (3) determine preferred screw insertion direction. Experimental study. Cadaveric equine limbs (n=32). In 8 specimens each, a 4.5 mm cortex bone screw was inserted in lag fashion in dorsopalmar (plantar) direction using CAS or COS. In 2 other groups of 8, the screws were inserted in opposite direction. Precision of CAS was determined by comparison of planned and actual screw position. Preferred screw direction was also assessed for CAS and COS. In 4 of 6 direct comparisons, screw positioning was significantly better with CAS. Results of precision analysis for screw position were similar to studies published in human medicine. None of evaluated criteria identified a preferred direction for screw insertion. For abaxial fractures of the distal phalanx, superior precision in screw position is achieved with CAS technique compared with COS technique. Abaxial fractures of the distal phalanx lend themselves to computer-assisted implantation of 1 screw in a dorsopalmar (plantar) direction. Because of the complex anatomic relationships, and our results, we discourage use of COS technique for repair of this fracture type.

Improving Nurses' Peripheral Intravenous Catheter Insertion Knowledge, Confidence, and Skills Using a Simulation-Based Blended Learning Program: A Randomized Trial.

Science.gov (United States)

Keleekai, Nowai L; Schuster, Catherine A; Murray, Connie L; King, Mary Anne; Stahl, Brian R; Labrozzi, Laura J; Gallucci, Susan; LeClair, Matthew W; Glover, Kevin R

2016-12-01

Peripheral intravenous catheter (PIVC) insertion is one of the most common invasive procedures performed in a hospital, but most nurses receive little formal training in this area. Blended PIVC insertion training programs that incorporate deliberate simulated practice have the potential to improve clinical practice and patient care. The study was a randomized, wait-list control group with crossover using nurses on three medical/surgical units. Baseline PIVC knowledge, confidence, and skills assessments were completed for both groups. The intervention group then received a 2-hour PIVC online course, followed by an 8-hour live training course using a synergistic mix of three simulation tools. Both groups were then reassessed. After crossover, the wait-list group received the same intervention and both groups were reassessed. At baseline, both groups were similar for knowledge, confidence, and skills. Compared with the wait-list group, the intervention group had significantly higher scores for knowledge, confidence, and skills upon completing the training program. After crossover, the wait-list group had similarly higher scores for knowledge, confidence, and skills than the intervention group. Between the immediate preintervention and postintervention periods, the intervention group improved scores for knowledge by 31%, skills by 24%, and decreased confidence by 0.5%, whereas the wait-list group improved scores for knowledge by 28%, confidence by 16%, and skills by 15%. Results demonstrate significant improvements in nurses' knowledge, confidence, and skills with the use of a simulation-based blended learning program for PIVC insertion. Transferability of these findings from a simulated environment into clinical practice should be further explored.

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.

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

A CFD study of Screw Compressor Motor Cooling Analysis

Science.gov (United States)

Branch, S.

2017-08-01

Screw compressors use electric motors to drive the male screw rotor. They are cooled by the suction refrigerant vapor that flows around the motor. The thermal conditions of the motor can dramatically influence the performance and reliability of the compressor. The more optimized this flow path is, the better the motor performance. For that reason it is important to understand the flow characteristics around the motor and the motor temperatures. Computational fluid dynamics (CFD) can be used to provide a detailed analysis of the refrigerant’s flow behavior and motor temperatures to identify the undesirable hot spots in the motor. CFD analysis can be used further to optimize the flow path and determine the reduction of hot spots and cooling effect. This study compares the CFD solutions of a motor cooling model to a motor installed with thermocouples measured in the lab. The compressor considered for this study is an R134a screw compressor. The CFD simulation of the motor consists of a detailed breakdown of the stator and rotor components. Orthotropic thermal conductivity material properties are used to represent the simplified motor geometry. In addition, the analysis includes the motor casings of the compressor to draw heat away from the motor by conduction. The study will look at different operating conditions and motor speeds. Finally, the CFD study will investigate the predicted motor temperature change by varying the vapor mass flow rates and motor speed. Recommendations for CFD modeling of such intricate heat transfer phenomenon have thus been proposed.

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

[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.

An atomic string model for a screw dislocation in iron: Implications for the development of interatomic potentials

International Nuclear Information System (INIS)

Gilbert, M.R.; Dudarev, S.L.; Chiesa, S.; Derlet, P.M.

2009-01-01

Thermally activated motion of screw dislocations is the rate-determining mechanism for plastic deformation and fracture of body centred cubic (bcc) metals and alloys. Recent experimental observations by S.G. Roberts' group at Oxford showed that ductile-brittle behaviour of bcc vanadium, tungsten, pure iron, and iron-chromium alloys is controlled by an Arrhenius process in which the energy for thermal activation is proportional to the formation energy for a double kink on a b= 1/2 screw dislocation, where b is the Burgers vector of the dislocation. Interpreting these experimental observations and extending the analysis to the case of irradiated materials requires developing a full quantitative treatment for perfect and kinked screw dislocations. Modelling screw dislocations also presents a challenge for the development of interatomic potentials. Recent density functional theory (DFT) calculations have revealed that the ground-state structure of the core of screw dislocations in all the bcc transition metals is non-degenerate and symmetric, whereas inter-atomic potentials used in molecular dynamics simulations for these metals often predict a degenerate, symmetry-broken core-structure. In this work we show how, by treating the structure of a screw dislocation within a multistring Frenkel-Kontorova model, we can develop a criterion that guarantees the correct symmetric core of the dislocation. Extending this treatment, we find a systematic recipe for constructing Finnis-Sinclair-type potentials that are able, as a matter of routine, produce non-degenerate core structures of 1/2 screw dislocations. Modelling thermally activated mobility of screw dislocations also requires that the transition pathway between stable core positions of a dislocation is accurately reproduced. DFT data indicates that the shape of the 'Peierls energy barrier' is a single-hump curve, including transitional configurations close to the so-called 'hard' structure. Interatomic potentials have, up

Flow, simulation and dynamics. Including a contribution of Vienna University (TU Wien); Stroemung, Simulation und Dynamik. Mit einem Beitrag der TU Wien

Energy Technology Data Exchange (ETDEWEB)

Kauder, K. [ed.

1998-12-31

This report covers the following topics: Gas-flow through clearances in screw vacuum pumps - part 1, gas flow research at a plane screw type machine model - part 2, two-phase screw-type engine - problems of the filling process, oil as a design parameter in screw-type engines - use of non-newtonian oils, experimental determination of the dynamic properties of screw compressors, hot gas screw-type engine - simulations as a basis for construction - part 3. [Deutsch] Dieser Bericht hat folgende Inhalte: Gasspaltstroemungen in Schraubenspindel-Vakuumpumpen - Teil 1, Gasspaltstroemungen in einem ebenen Schraubenmaschinenmodell - Teil 2, Zweiphasen-Schraubenmotor-Probleme des Fuellungsvorganges, Oel als Konstruktionselement - Einsatz nicht-newtonscher Oele, die experimentelle Bestimmung der dynamischen Eigenschaften von Schraubenkompressoren, die Heissgasschraubenmaschine - simulationsgestuetzte Auslegung - Teil 3

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.

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.

Influence of glide path on the screw-in effect and torque of nickel-titanium rotary files in simulated resin root canals

Directory of Open Access Journals (Sweden)

Jung-Hong Ha

2012-11-01

Full Text Available Objectives The purpose of this study was to investigate the screw-in effect and torque generation depending on the size of glide path during root canal preparation. Materials and Methods Forty Endo-Training Blocks (REF A 0177, Dentsply Maillefer were used. They were divided into 4 groups. For groups 1, 2, 3, and 4, the glide path was established with ISO #13 Path File (Dentsply Maillefer, #15 NiTi K-file NITIFLEX (Dentsply Maillefer, modified #16 Path File (equivalent to #18, and #20 NiTi K-file NITIFLEX, respectively. The screw-in force and resultant torque were measured using a custom-made experimental apparatus while canals were instrumented with ProTaper S1 (Dentsply Maillefer at a constant speed of 300 rpm with an automated pecking motion. A statistical analysis was performed using one-way analysis of variance and the Duncan post hoc comparison test. Results Group 4 showed lowest screw-in effect (2.796 ± 0.134 among the groups (p < 0.05. Torque was inversely proportional to the glide path of each group. In #20 glide path group, the screw-in effect and torque decreased at the last 1 mm from the apical terminus. However, in the other groups, the decrease of the screw-in effect and torque did not occur in the last 1 mm from the apical terminus. Conclusions The establishment of a larger glide path before NiTi rotary instrumentation appears to be appropriate for safely shaping the canal. It is recommended to establish #20 glide path with NiTi file when using ProTaper NiTi rotary instruments system safely.

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.

Evolution of Additively Manufactured Injection Molding Inserts Investigated by Thermal Simulations

DEFF Research Database (Denmark)

Hofstätter, Thomas; Pedersen, David B.; Tosello, Guido

Injection molding using inserts from vat polymerization, an additive manufacturing technology, has been investigated for pilot production and rapid prototyping purposes throughout the past years. A standard mold is equipped with additively manufactured inserts in a rectangular shape of (20 x 20 x 2...

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

The Automated Threaded Fastening Based on On-line Identification

Directory of Open Access Journals (Sweden)

Nicolas Ivan Giannoccaro

2008-11-01

Full Text Available The principle of the thread fastenings have been known and used for decades with the purpose of joining one component to another. Threaded fastenings are popular because they permit easy disassembly for maintenance, repair, relocation and recycling. Screw insertions are typically carried out manually. It is a difficult problem to automat. As a result there is very little published research on automating threaded fastenings, and most research on automated assembly focus on the peg-in-hole assembly problem. This paper investigates the problem of automated monitoring of the screw insertion process. The monitoring problem deals with predicting integrity of a threaded insertion, based on the torque vs. insertion depth curve generated during the insertions. The authors have developed an analytical model to predict the torque signature signals during self-tapping screw insertions. However, the model requires parameters on the screw dimensions and plate material properties are difficult to measure. This paper presents a study on on-line identification during screw fastenings. An identification methodology for two unknown parameter estimation during a self-tapping screw insertion process is presented. It is shown that friction and screw properties required by the model can be reliably estimated on-line. Experimental results are presented to validate the identification procedure.

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...

In vitro validation of a novel mechanical model for testing the anchorage capacity of pedicle screws using physiological load application.

Science.gov (United States)

Liebsch, Christian; Zimmermann, Julia; Graf, Nicolas; Schilling, Christoph; Wilke, Hans-Joachim; Kienle, Annette

2018-01-01

Biomechanical in vitro tests analysing screw loosening often include high standard deviations caused by high variabilities in bone mineral density and pedicle geometry, whereas standardized mechanical models made of PU foam often do not integrate anatomical or physiological boundary conditions. The purpose of this study was to develop a most realistic mechanical model for the standardized and reproducible testing of pedicle screws regarding the resistance against screw loosening and the holding force as well as to validate this model by in vitro experiments. The novel mechanical testing model represents all anatomical structures of a human vertebra and is consisting of PU foam to simulate cancellous bone, as well as a novel pedicle model made of short carbon fibre filled epoxy. Six monoaxial cannulated pedicle screws (Ø6.5 × 45mm) were tested using the mechanical testing model as well as human vertebra specimens by applying complex physiological cyclic loading (shear, tension, and bending; 5Hz testing frequency; sinusoidal pulsating forces) in a dynamic materials testing machine with stepwise increasing load after each 50.000 cycles (100.0N shear force + 20.0N per step, 51.0N tension force + 10.2N per step, 4.2Nm bending moment + 0.8Nm per step) until screw loosening was detected. The pedicle screw head was fixed on a firmly clamped rod while the load was applied in the vertebral body. For the in vitro experiments, six human lumbar vertebrae (L1-3, BMD 75.4 ± 4.0mg/cc HA, pedicle width 9.8 ± 0.6mm) were tested after implanting pedicle screws under X-ray control. Relative motions of pedicle screw, specimen fixture, and rod fixture were detected using an optical motion tracking system. Translational motions of the mechanical testing model experiments in the point of load introduction (0.9-2.2mm at 240N shear force) were reproducible within the variation range of the in vitro experiments (0.6-3.5mm at 240N shear force). Screw loosening occurred continuously in

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

Cooperative learning using simulation to achieve mastery of nasogastric tube insertion.

Science.gov (United States)

Cason, Melanie Leigh; Gilbert, Gregory E; Schmoll, Heidi H; Dolinar, Susan M; Anderson, Jane; Nickles, Barbara Marshburn; Pufpaff, Laurie A; Henderson, Ruth; Lee, Frances Wickham; Schaefer, John J

2015-03-01

Traditionally, psychomotor skills training for nursing students involves didactic instruction followed by procedural review and practice with a task trainer, manikin, or classmates. This article describes a novel method of teaching psychomotor skills to associate degree and baccalaureate nursing students, Cooperative Learning Simulation Skills Training (CLSST), in the context of nasogastric tube insertion using a deliberate practice-to-mastery learning model. Student dyads served as operator and student learner. Automatic scoring was recorded in the debriefing log. Student pairs alternated roles until they achieved mastery, after which they were assessed individually. Median checklist scores of 100% were achieved by students in both programs after one practice session and through evaluation. Students and faculty provided positive feedback regarding this educational innovation. CLSST in a deliberate practice-to-mastery learning paradigm offers a novel way to teach psychomotor skills in nursing curricula and decreases the instructor-to-student ratio. Copyright 2015, SLACK Incorporated.

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

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.

Estudo da influência do diâmetro do orifício piloto na resistência ao arrancamento do parafuso pedicular The influence of pilot hole diameter on screw oullout resistance

Directory of Open Access Journals (Sweden)

José Roberto Benites Vendrame

2008-01-01

Full Text Available A influência do diâmetro do orifício piloto em relação ao diâmetro interno do parafuso na resistência ao arrancamento do parafuso pedicular foi o objetivo do estudo. Foram utilizados parafusos de 5, 6 e 7 mm do sistema USS de fixação vertebral, os quais foram inseridos nos corpos de prova de madeira, poliuretana e osso. O orifício piloto para a inserção do parafuso foi realizado com brocas de diâmetro inferior, igual e superior ao diâmetro interno do parafuso. Ensaios mecânicos de arrancamento foram realizados em máquina universal de teste. Nos corpos de prova de madeira, poliuretana e osso a realização do orifício piloto com brocas de diâmetro maior que o diâmetro interno do parafuso produziu diminuição da força máxima de arrancamento dos implantes nos ensaios de arrancamento, tendo sido observada diferença estatística. O diâmetro da perfuração do orifício piloto em relação ao diâmetro interno do parafuso exerce influência na resistência ao arrancamento do implante, tendo sido observado aumento da resistência ao arrancamento com a utilização de brocas de diâmetro menor que o diâmetro interno e redução da resistência ao arrancamento com a utilização de brocas com diâmetro maior que o diâmetro interno do parafuso.The influence of the diameter of the pilot hole compared to the inner diameter of the screw on the pull-out resistance of a pedicular screw was studied. 5-, 6-, and 7-mm USS system screws for vertebral fixation were inserted into wood, polyurethane and bone test bodies. The pilot hole for screw insertion was drilled with burrs of smaller, equal or wider diameter than the inner diameter of the screw. Mechanical pull-out assays were performed using a universal testing machine. In the wood, polyurethane and bone test bodies, a pilot hole drilled with burrs of a wider diameter than the inner diameter of the screw produced reduced maximum pull-out strength on the implants, with statistical

Folding and insertion thermodynamics of the transmembrane WALP peptide

International Nuclear Information System (INIS)

Bereau, Tristan; Bennett, W. F. Drew; Pfaendtner, Jim; Deserno, Markus; Karttunen, Mikko

2015-01-01

The anchor of most integral membrane proteins consists of one or several helices spanning the lipid bilayer. The WALP peptide, GWW(LA) n (L)WWA, is a common model helix to study the fundamentals of protein insertion and folding, as well as helix-helix association in the membrane. Its structural properties have been illuminated in a large number of experimental and simulation studies. In this combined coarse-grained and atomistic simulation study, we probe the thermodynamics of a single WALP peptide, focusing on both the insertion across the water-membrane interface, as well as folding in both water and a membrane. The potential of mean force characterizing the peptide’s insertion into the membrane shows qualitatively similar behavior across peptides and three force fields. However, the Martini force field exhibits a pronounced secondary minimum for an adsorbed interfacial state, which may even become the global minimum—in contrast to both atomistic simulations and the alternative PLUM force field. Even though the two coarse-grained models reproduce the free energy of insertion of individual amino acids side chains, they both underestimate its corresponding value for the full peptide (as compared with atomistic simulations), hinting at cooperative physics beyond the residue level. Folding of WALP in the two environments indicates the helix as the most stable structure, though with different relative stabilities and chain-length dependence

Folding and insertion thermodynamics of the transmembrane WALP peptide

Energy Technology Data Exchange (ETDEWEB)

Bereau, Tristan, E-mail: bereau@mpip-mainz.mpg.de [Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); Bennett, W. F. Drew [Department of Chemistry, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1 (Canada); Pfaendtner, Jim [Department of Chemical Engineering, University of Washington, Seattle, Washington 98195 (United States); Deserno, Markus [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Karttunen, Mikko [Department of Mathematics and Computer Science & Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, MetaForum, 5600 MB Eindhoven (Netherlands)

2015-12-28

The anchor of most integral membrane proteins consists of one or several helices spanning the lipid bilayer. The WALP peptide, GWW(LA){sub n} (L)WWA, is a common model helix to study the fundamentals of protein insertion and folding, as well as helix-helix association in the membrane. Its structural properties have been illuminated in a large number of experimental and simulation studies. In this combined coarse-grained and atomistic simulation study, we probe the thermodynamics of a single WALP peptide, focusing on both the insertion across the water-membrane interface, as well as folding in both water and a membrane. The potential of mean force characterizing the peptide’s insertion into the membrane shows qualitatively similar behavior across peptides and three force fields. However, the Martini force field exhibits a pronounced secondary minimum for an adsorbed interfacial state, which may even become the global minimum—in contrast to both atomistic simulations and the alternative PLUM force field. Even though the two coarse-grained models reproduce the free energy of insertion of individual amino acids side chains, they both underestimate its corresponding value for the full peptide (as compared with atomistic simulations), hinting at cooperative physics beyond the residue level. Folding of WALP in the two environments indicates the helix as the most stable structure, though with different relative stabilities and chain-length dependence.

Comparison of accuracy of lag screw placement in cephalocondylic nails and sliding hip screw plate fixation for extracapsular fractures of the neck of femur

OpenAIRE

Shyam Kumar, A. J.; Parmar, V.; Bankart, J.; Williams, S. C.; Harper, W. M.

2006-01-01

This study compared the accuracy of lag screw placement between extracapsular femoral fractures fixed with sliding hip screw plate systems and those fixed with cephalocondylic nails. It involved 75 retrospective radiographs of fractures fixed with either a cephalocondylic nail (32) or a sliding hip screw plate system (43). Postoperative anteroposterior and lateral radiographs of the hip were scanned using a digital X-ray scanner and measured using computer software. Measurements were conducte...

Comparative evaluation of insertion torque and mechanical stability for self-tapping and self-drilling orthodontic miniscrews - an in vitro study.

Science.gov (United States)

Tepedino, Michele; Masedu, Francesco; Chimenti, Claudio

2017-05-30

The aim of the present study was to evaluate the relationship between insertion torque and stability of miniscrews in terms of resistance against dislocation, then comparing a self-tapping screw with a self-drilling one. Insertion torque was measured during placement of 30 self-drilling and 31 self-tapping stainless steel miniscrews (Leone SpA, Sesto Fiorentino, Italy) in synthetic bone blocks. Then, an increasing pulling force was applied at an angle of 90° and 45°, and the displacement of the miniscrews was recorded. The statistical analysis showed a statistically significant difference between the mean Maximum Insertion Torque (MIT) observed in the two groups and showed that force angulation and MIT have a statistically significant effect on miniscrews stability. For both the miniscrews, an angle of 90° between miniscrew and loading force is preferable in terms of stability. The tested self-drilling orthodontic miniscrews showed higher MIT and greater resistance against dislocation than the self-tapping ones.

Calculations of steady-state and reactivity insertion transients in a research reactor simulating the PWR

International Nuclear Information System (INIS)

Mladin, Mirea; Mladin, Daniela; Prodea, Ilie

2010-01-01

In 2008, IAEA started a Coordinated Research Project for benchmarking the thermalhydraulic and neutronic computer codes for research reactor analysis against the experimental data. In this framework, for the first year of research contract, the Institute for Nuclear Research engaged in steady-state analysis of SPERT-III reactor and also in the simulation of the reactivity insertion tests performed in this reactor during mid sixties. In the first part, the paper describes a Monte Carlo input model of the oxide core selected for investigation and the results of the steady-state neutronic calculations with respect to hot and cold core reactivity excess and control rods worth. Also, prompt neutron life and reactivity feed-back coefficients were examined. These results were compared with the data provided in the reactor specification document concerning neutronic design calculated data. The second part of the paper is dedicated to calculation of the reactivity insertion transients with RELAP5 and CATHARE2 thermalhydraulic codes, both including point reactor kinetics models, and to comparison with experimental data. (authors)

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

Core structure of screw dislocations in Fe from first-principles; Simulation ab initio des coeurs de dislocation vis dans le fer

Energy Technology Data Exchange (ETDEWEB)

Ventelon, L

2008-11-15

The various methods appropriate for the simulation of dislocations within first-principles calculations have been set up, improved and compared between them. They have been applied to study screw dislocations in body-centered cubic iron using the SIESTA code. A non-degenerate core structure is obtained; its detailed analysis reveals a dilatation effect. Taking it into account in an anisotropic elasticity model, allows explaining the cell-size dependence of the energetics, obtained within the dipole approach. The Peierls potential obtained in ab initio suggests that the metastable core configuration at halfway position in the Peierls barrier, predicted by empirical potential, does not exist. We show how to construct tri-periodic cells optimized to study kinked dislocations. Using empirical potential, we demonstrate the feasibility of ab initio calculations of Peierls stress and kink formation. (author)

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.

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.)

In vivo evaluation of immediately loaded stainless steel and titanium orthodontic screws in a growing bone.

Directory of Open Access Journals (Sweden)

Kerstin Gritsch

Full Text Available The present work intends to evaluate the use of immediate loaded orthodontic screws in a growing model, and to study the specific bone response. Thirty-two screws (half of stainless steel and half of titanium were inserted in the alveolar bone of 8 growing pigs. The devices were immediately loaded with a 100 g orthodontic force. Two loading periods were assessed: 4 and 12 weeks. Both systems of screws were clinically assessed. Histological observations and histomorphometric analysis evaluated the percent of "bone-to-implant contact" and static and dynamic bone parameters in the vicinity of the devices (test zone and in a bone area located 1.5 cm posterior to the devices (control zone. Both systems exhibit similar responses for the survival rate; 87.5% and 81.3% for stainless steel and titanium respectively (p = 0.64; 4-week period, and 62.5% and 50.0% for stainless steel and titanium respectively (p = 0.09; 12-week period. No significant differences between the devices were found regarding the percent of "bone-to-implant contact" (p = 0.1 or the static and dynamic bone parameters. However, the 5% threshold of "bone-to-implant contact" was obtained after 4 weeks with the stainless steel devices, leading to increased survival rate values. Bone in the vicinity of the miniscrew implants showed evidence of a significant increase in bone trabecular thickness when compared to bone in the control zone (p = 0.05. In our study, it is likely that increased trabecular thickness is a way for low density bone to respond to the stress induced by loading.

In vivo evaluation of immediately loaded stainless steel and titanium orthodontic screws in a growing bone.

Science.gov (United States)

Gritsch, Kerstin; Laroche, Norbert; Bonnet, Jeanne-Marie; Exbrayat, Patrick; Morgon, Laurent; Rabilloud, Muriel; Grosgogeat, Brigitte

2013-01-01

The present work intends to evaluate the use of immediate loaded orthodontic screws in a growing model, and to study the specific bone response. Thirty-two screws (half of stainless steel and half of titanium) were inserted in the alveolar bone of 8 growing pigs. The devices were immediately loaded with a 100 g orthodontic force. Two loading periods were assessed: 4 and 12 weeks. Both systems of screws were clinically assessed. Histological observations and histomorphometric analysis evaluated the percent of "bone-to-implant contact" and static and dynamic bone parameters in the vicinity of the devices (test zone) and in a bone area located 1.5 cm posterior to the devices (control zone). Both systems exhibit similar responses for the survival rate; 87.5% and 81.3% for stainless steel and titanium respectively (p = 0.64; 4-week period), and 62.5% and 50.0% for stainless steel and titanium respectively (p = 0.09; 12-week period). No significant differences between the devices were found regarding the percent of "bone-to-implant contact" (p = 0.1) or the static and dynamic bone parameters. However, the 5% threshold of "bone-to-implant contact" was obtained after 4 weeks with the stainless steel devices, leading to increased survival rate values. Bone in the vicinity of the miniscrew implants showed evidence of a significant increase in bone trabecular thickness when compared to bone in the control zone (p = 0.05). In our study, it is likely that increased trabecular thickness is a way for low density bone to respond to the stress induced by loading.

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...

Numerical simulation of the insert chemistry of the hollow cathode from the deep space 1 ion engine 30,000 Hrs life test

OpenAIRE

Coletti, Michele; Grubisic, Angelo; Gabriel, Stephen

2007-01-01

A model for the insert chemistry developed by the authors and based on the knowledge of the BaO – CaO – Al2O3 ternary system the ELT discharge cathode insert from the Deep Space 1 life test has been simulated. The computed data show a good agreement with the experimental one; the agreement increase with the imposition of boundary conditions closer to the experimental evidence. Tungsten deposition effect have been introduced into the model using experimental data and further improving the agre...

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

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

Simulation-based medical education training improves short and long-term competency in, and knowledge of central venous catheter insertion: A before and after intervention study.

Science.gov (United States)

Cartier, Vanessa; Inan, Cigdem; Zingg, Walter; Delhumeau, Cecile; Walder, Bernard; Savoldelli, Georges L

2016-08-01

Multimodal educational interventions have been shown to improve short-term competency in, and knowledge of central venous catheter (CVC) insertion. To evaluate the effectiveness of simulation-based medical education training in improving short and long-term competency in, and knowledge of CVC insertion. Before and after intervention study. University Geneva Hospital, Geneva, Switzerland, between May 2008 and January 2012. Residents in anaesthesiology aware of the Seldinger technique for vascular puncture. Participants attended a half-day course on CVC insertion. Learning objectives included work organization, aseptic technique and prevention of CVC complications. CVC insertion competency was tested pretraining, posttraining and then more than 2 years after training (sustainability phase). The primary study outcome was competency as measured by a global rating scale of technical skills, a hand hygiene compliance score and a checklist compliance score. Secondary outcome was knowledge as measured by a standardised pretraining and posttraining multiple-choice questionnaire. Statistical analyses were performed using paired Student's t test or Wilcoxon signed-rank test. Thirty-seven residents were included; 18 were tested in the sustainability phase (on average 34 months after training). The average global rating of skills was 23.4 points (±SD 4.08) before training, 32.2 (±4.51) after training (P Simulation-based medical education training was effective in improving short and long-term competency in, and knowledge of CVC insertion.

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

Effects of Multilevel Facetectomy and Screw Density on Postoperative Changes in Spinal Rod Contour in Thoracic Adolescent Idiopathic Scoliosis Surgery.

Directory of Open Access Journals (Sweden)

Terufumi Kokabu

Full Text Available Flattening of the preimplantation rod contour in the sagittal plane influences thoracic kyphosis (TK restoration in adolescent idiopathic scoliosis (AIS surgery. The effects of multilevel facetectomy and screw density on postoperative changes in spinal rod contour have not been documented. This study aimed to evaluate the effects of multilevel facetectomy and screw density on changes in spinal rod contour from before implantation to after surgical correction of thoracic curves in patients with AIS prospectively. The concave and convex rod shapes from patients with thoracic AIS (n = 49 were traced prior to insertion. Postoperative sagittal rod shape was determined by computed tomography. The angle of intersection of the tangents to the rod end points was measured. Multiple stepwise linear regression analysis was used to identify variables independently predictive of change in rod contour (Δθ. Average Δθ at the concave and convex side were 13.6° ± 7.5° and 4.3° ± 4.8°, respectively. The Δθ at the concave side was significantly greater than that of the convex side (P < 0.0001 and significantly correlated with Risser sign (P = 0.032, the preoperative main thoracic Cobb angle (P = 0.031, the preoperative TK angle (P = 0.012, and the number of facetectomy levels (P = 0.007. Furthermore, a Δθ at the concave side ≥14° significantly correlated with the postoperative TK angle (P = 0.003, the number of facetectomy levels (P = 0.021, and screw density at the concave side (P = 0.008. Rod deformation at the concave side suggests that corrective forces acting on that side are greater than on the convex side. Multilevel facetectomy and/or screw density at the concave side have positive effects on reducing the rod deformation that can lead to a loss of TK angle postoperatively.

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.

Atomistic simulations of dislocation processes in copper

DEFF Research Database (Denmark)

Vegge, T.; Jacobsen, K.W.

2002-01-01

We discuss atomistic simulations of dislocation processes in copper based on effective medium theory interatomic potentials. Results on screw dislocation structures and processes are reviewed with particular focus on point defect mobilities and processes involving cross slip. For example......, the stability of screw dislocation dipoles is discussed. We show that the presence of jogs will strongly influence cross slip barriers and dipole stability. We furthermore present some new results on jogged edge dislocations and edge dislocation dipoles. The jogs are found to be extended, and simulations...

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

Influência do diâmetro do orifício piloto na resistência ao arrancamento dos parafusos do corpo vertebral The influence of pilot hole diameter on screw pullout resistance

Directory of Open Access Journals (Sweden)

Helton L. A. Defino

2007-01-01

Full Text Available Foram realizados ensaios mecânicos com o objetivo de avaliar a influência do diâmetro do orifício piloto em relação ao diâmetro interno do parafuso na resistência ao arrancamento dos parafusos do sistema de fixação vertebral aplicados no corpo da vértebra. O estudo foi realizado em duas etapas. Na primeira etapa foram utilizados corpos de prova de poliuretana para a colocação de parafusos de 5mm e, 6mm , e na segunda etapa os parafusos foram inseridos na face lateral dos corpos das vértebras lombares de suínos. O orifício piloto foi realizado com brocas de diâmetro menor, igual ou maior que o diâmetro interno do parafuso. Foram realizados ensaios mecânicos de arrancamento em máquina universal de teste para a avaliação da força máxima de arrancamento dos implantes. Foi observado que o diâmetro do orifício piloto em relação ao diâmetro interno do parafuso influencia na resistência ao arrancamento dos implantes.Mechanical assays were performed in order to assess the influence of pilot hole diameter versus screw's inner diameter on screw pullout resistance in the vertebral fixation systems applied to the vertebral body. The study was conducted in two stages. In the first, polyurethane test bodies were used for placing 5 and 6 mm screws, and, in the second stage, the screws were inserted into the lateral surface of the lumbar vertebral bodies of pigs. The pilot hole was built with drills with smaller, similar or larger diameter than screws' inner diameter. Mechanical pullout assays were performed using a universal test machine for the assessment of maximum pullout screw resistance. The diameter of the pilot hole versus screw's inner diameter was shown to influence screw pullout resistance.

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.

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

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.

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.

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

Use of computed tomography to define a sacral safe corridor for placement of 2.7 mm cortical screws in feline sacroiliac luxation.

Science.gov (United States)

Philp, Helen; Durand, Alexane; De Vicente, Felipe

2018-06-01

Objectives This study aimed to define a safe corridor for 2.7 mm cortical sacroiliac screw insertion in the dorsal plane (craniocaudal direction) using radiography and CT, and in the transverse plane (dorsoventral direction) using CT in feline cadavers. A further aim was to compare the values obtained by CT with those previously reported by radiography in the transverse plane. Methods Thirteen pelvises were retrieved from feline cadavers and dissected to expose one of the articular surfaces of the sacrum. A 2.7 mm screw was placed in the sacrum to a depth of approximately 1 cm in each exposed articular surface. Dorsoventral radiography and CT scanning of each specimen were performed. Multiplanar reconstructions were performed to allow CT evaluation in both the dorsal and transverse planes. Calculations were made to find the maximum, minimum and optimum angles for screw placement in craniocaudal (radiography and CT) and dorsoventral (CT) directions when using a 2.7 mm cortical screw. Results Radiographic measurement showed a mean optimum craniocaudal angle of 106° (range 97-112°). The mean minimum angle was 95° (range 87-107°), whereas the mean maximum angle was 117° (108-124°). Measurement of the dorsal CT scan images showed a mean optimum craniocaudal angle of 101° (range 94-110°). The mean minimum angle was 90° (range 83-99°), whereas the mean maximum angle was 113° (104-125°). The transverse CT scan images showed a mean dorsoventral minimum angle of 103° (range 95-113°), mean maximum angle of 115° (104-125°) and mean optimum dorsoventral angle of 111° (102-119°). Conclusions and relevance An optimum craniocaudal angle of 101° is recommended for 2.7 mm cortical screw placement in the feline sacral body, with a safety margin between 99° and 104°. No single angle can be recommended in the dorsoventral direction and therefore preoperative measuring on individual cats using CT images is recommended to establish the ideal individual angle in the

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.

Biomechanical evaluation of macro and micro designed screw-type implants: an insertion torque and removal torque study in rabbits.

Science.gov (United States)

Chowdhary, Ramesh; Jimbo, Ryo; Thomsen, Christian; Carlsson, Lennart; Wennerberg, Ann

2013-03-01

To investigate the combined effect of macro and pitch shortened threads on primary and secondary stability during healing, but before dynamic loading. Two sets of turned implants with different macro geometry were prepared. The test group possessed pitch shortened threads in between the large threads and the control group did not have thread alterations. The two implant groups were placed in both femur and tibiae of 10 lop-eared rabbits, and at the time of implant insertion, insertion torques were recorded. After 4 weeks, all implants were subjected to removal torque tests. The insertion torque values for the control and test groups for the tibia were 15.7 and 20.6 Ncm, respectively, and for the femur, 11.8, and 12.8 Ncm respectively. The removal torque values for the control and test groups in the tibia were 7.9 and 9.1 Ncm, respectively, and for the femur, 7.9 and 7.7 Ncm respectively. There was no statistically significant difference between the control and test groups. Under limited dynamic load, the addition of pitch shortened threads did not significantly improve either the primary or the secondary stability of the implants in bone. © 2011 John Wiley & Sons A/S.

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.

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.

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.

Estudo da influência do modo de preparação do orifício piloto e do macheamento na ancoragem dos parafusos pediculares Study of the influence of the type of pilot hole preparation and tapping on pedicular screws fixation

Directory of Open Access Journals (Sweden)

Helton Luiz Aparecido Defino

2007-01-01

Full Text Available Foram realizados ensaios mecânicos com parafusos do sistema de fixação vertebral USIS para o estudo da influência do tipo de preparo do orifício piloto com sonda ou brocas e o macheamento do trajeto do orifício piloto, na resistência ao arrancamento dos implantes. Os parafusos foram inseridos em corpos de prova de madeira, poliuretana e osso bovino. O preparo do orifício piloto foi realizado com sondas e brocas de 3,5mm. Foram formados três grupos experimentais: I-perfuração com sonda, II-perfuração com broca e III-perfuração com broca e macheamento. Após a sua inserção nos corpos de prova foram realizados ensaios de arrancamento em máquina universal de teste. Foi observado aumento da resistência ao arrancamento dos implantes com a realização do orifício piloto com sondas e a diferença estatística foi significativa em relação ao preparo com broca e broca associada ao macheamento. Não foi observada diferença na resistência ao arrancamento dos parafusos com o macheamento do trajeto do orifício piloto.Mechanical assays were performed with screws of the USIS vertebral fixation system for the study of the influence of type of pilot hole preparation with probe or burr and tapping of the pilot hole pathway on pedicular screw pullout. The screws were inserted into wood, polyurethane and bovine bone test bodies. The pilot hole was prepared with probes and burrs of 3.5 mm. Three experimental groups were formed: I -drilling with a probe, II - drilling with a burr, and III - drilling with burr and tapping. After screw insertion into the test bodies, pullout assays were performed with a universal test machine. Increased screw pullout resistance was observed when the pilot hole was drilled with a probe, with a statistically significant difference compared to preparation with a burr and with a burr in combination with tapping. No difference in screw pullout resistance was observed with tapping of the pilot hole pathway.

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

Simulation study of a depth-encoding positron emission tomography detector inserting horizontal-striped glass between crystal layers

Science.gov (United States)

Kim, Kyu Bom; Choi, Yong; Kang, Jihoon

2017-10-01

This study introduces a depth-encoding positron emission tomography (PET) detector inserting a horizontal-striped glass between the pixilated scintillation crystal layers. This design allows light spreading so that scintillation photons can travel only through the X direction and allows alteration in the light distribution so that it can generate a unique pattern diagram of the two-dimensional (2-D) flood histogram that identifies depth position as well as X-Y position of γ-ray interaction. A Monte Carlo simulation was conducted for the assessment of the depth of interaction (DOI)-PET detector. The traced light distribution for each event was converted into the 2-D flood histogram. Light loss caused by inserting the horizontal-striped glass between the crystal layers was estimated. Applicable weighting factors were examined for each DOI-PET detector. No considerable degradation of light loss was observed. The flood histogram, without overlapping of each crystal position, can be generated for the DOI detector based on each crystal block by inserting the horizontal-striped glass with a thickness of >1 mm and the modified resistive charge division networks with applicable weighting factors. This study demonstrated that the proposed DOI-PET detector can extract the three-dimensional γ-ray interaction position without considerable performance degradations of the PET detector from the 2-D flood histogram.

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.

Coil Springs Layer Used to Support a Car Vertical Dynamics Simulator and to Reduce the Maximum Actuation Force

Directory of Open Access Journals (Sweden)

Dan N. Dumitriu

2015-09-01

Full Text Available A Danaher Thomson linear actuator with ball screw drive and a realtime control system are used here to induce vertical displacements under the driver/user seat of an in-house dynamic car simulator. In order to better support the car simulator and to dynamically protect the actuator’s ball screw drive, a layer of coil springs is used to support the whole simulator chassis. More precisely, one coil spring is placed vertically under each corner of the rectangular chassis. The paper presents the choice of the appropriate coil springs, so that to minimize as much as possible the ball screw drive task of generating linear motions, corresponding to the vertical displacements and accelerations encountered by a driver during a real ride. For this application, coil springs with lower spring constant are more suited to reduce the forces in the ball screw drive and thus to increase the ball screw drive life expectancy.

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

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

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

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

Feasibility study of patient-specific surgical templates for the fixation of pedicle screws.

Science.gov (United States)

Salako, F; Aubin, C-E; Fortin, C; Labelle, H

2002-01-01

Surgery for scoliosis, as well as other posterior spinal surgeries, frequently uses pedicle screws to fix an instrumentation on the spine. Misplacement of a screw can lead to intra- and post-operative complications. The objective of this study is to design patient-specific surgical templates to guide the drilling operation. From the CT-scan of a vertebra, the optimal drilling direction and limit angles are computed from an inverse projection of the pedicle limits. The first template design uses a surface-to-surface registration method and was constructed in a CAD system by subtracting the vertebra from a rectangular prism and a cylinder with the optimal orientation. This template and the vertebra were built using rapid prototyping. The second design uses a point-to-surface registration method and has 6 adjustable screws to adjust the orientation and length of the drilling support device. A mechanism was designed to hold it in place on the spinal process. A virtual prototype was build with CATIA software. During the operation, the surgeon places either template on patient's vertebra until a perfect match is obtained before drilling. The second design seems better than the first one because it can be reused on different vertebra and is less sensible to registration errors. The next step is to build the second design and make experimental and simulations tests to evaluate the benefits of this template during a scoliosis operation.

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.

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.

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.

A Biomechanical Analysis of Different Clavicular Tunnel Diameters in Anatomic Acromioclavicular Ligament Reconstruction.

Science.gov (United States)

Voss, Andreas; Beitzel, Knut; Alaee, Farhang; Dukas, Alex; Herbst, Elmar; Obopilwe, Elifho; Apostolakos, John; DiVenere, Jessica; Singh, Hardeep; Cote, Mark P; Mazzocca, Augustus D

2016-08-01

To evaluate the biomechanical stability of a tendon-to-clavicle bone interface fixation of a graft in revision acromioclavicular reconstruction. Fifteen fresh-frozen cadaveric shoulders were used. All specimens underwent bone density evaluation. For the primary reconstruction, a 5-mm semitendinosus allograft was inserted into a 5-mm bone tunnel at 25 and 45 mm from the lateral end of the clavicle using a 5.5 × 8-mm PEEK (polyether ether ketone) tenodesis screw. Each single graft was fixed in a cryo-clamp and cyclically loaded from 5 to 70 N for 3,000 cycles, followed by load-to-failure testing at a rate of 120 mm/min to simulate the revision case. To simulate tunnel widening, the tunnels of the revision series were over-drilled with an 8-mm drill, and a 5-mm semitendinosus graft with an 8 × 12-mm PEEK tenodesis screw was inserted. Biomechanical testing was then repeated. The bone mineral density analysis showed a significantly higher density at the 45-mm hole compared with the 25-mm hole (P = .001). The ultimate load to failure increased from the 5.5-mm screw to the 8-mm screw at the 45-mm hole position (P = .001). There was no statistically significant difference at the 25-mm hole position (P = .934). No statistical significance for graft elongation comparing the 5.5-mm screw and the 8-mm screw at the 25-mm (P = .156) and 45-mm (P = .334) positions could be found. Comparable biomechanical stability for the tendon-to-bone interface fixation in different clavicular tunnel diameters simulating primary and revision reconstruction was achieved. There is a lack of literature regarding revision acromioclavicular joint reconstruction, but our biomechanical results show comparable stability to primary reconstruction. These data provide support for the use of anatomic acromioclavicular ligament reconstruction in revision cases. Copyright © 2016 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.