Kinds Of Screws Research Articles

Twist and finite twist analysis of 2UPR-SPR parallel mechanism based upon screw theory

This paper discusses the issue on mobility analysis of parallel mechanism. The analysis is focused on the two-rotational and one-translational 2UPR-SPR parallel mechanism which has interesting motion properties that one rotation of this mechanism has fixed direction, while the other rotation and the translation have variable directions. Twist analysis is conducted to obtain the feasible velocities of the moving platform at any configuration of the mechanism, and finite twist analysis is carried out to obtain the feasible displacements of the moving platform when the mechanism moves away from the initial configuration to any configuration. The obtained parametric velocity space at any configuration and parametric displacement manifold from the initial configuration to any configuration are formulated, which are proved to contain the same motion information and have the same effect in mobility analysis. Through analyzing the 2UPR-SPR mechanism, it is revealed that both twist and finite twist are effective to describe continuous motions of rigid body or mechanism. This enriches the relation between twist and finite twist, and unifies the applications of these two kinds of screws in mobility analysis.

Breakage risk of different sacroiliac screws in unilateral sacral fractures a finite element analysis

ObjectiveTo compare the breakage risk of lengthened sacroiliac screws and ordinary sacroiliac screws to treat unilateral vertical sacral fractures and provide a reference for clinical application.MethodsA finite element model of Tile C pelvic ring injury (unilateral type Denis II fracture of the sacrum) was produced. The sacral fractures were fixed with a lengthened sacroiliac screw and ordinary sacroiliac screw in 6 types of models. The maximal von Mises stresses and stress distributions of the two kinds of screws when standing on both feet were measured and compared.ResultsThe maximal von Mises stress of the lengthened screw was less than that of the ordinary screw. Compared with ordinary screw, the stress distribution in the lengthened screw was more homogeneous.ConclusionsThe breakage risk of screws fixed in double segments is lower than that of screws fixed in single segments, the breakage risk of lengthened screws is lower than that of ordinary screws, and the breakage risk of screws fixed in S2 segments is lower than that of screws fixed in S1 segments.

Comprehensive analysis of pedicle screw implantation in the C7 vertebra using computed tomography-based three-dimensional models

BackgroundFrom a biomechanical point of view, pedicle screws (PS) are better than other kinds of screws for implantation in the seventh cervical vertebra (C7). However, the application of PS is limited because of the high risk of severe complications. It is essential to define the optimal entry point and trajectory. The aim of this study was to comprehensively analyze the starting point and trajectory for C7 PS insertion using three dimensional (3D) models.MethodsOverall, 60 subjects aged 18 to 67 years old were included. All CT images were used to construct 3D computer models of the C7 vertebrae. A new coordinate system was established for the next evaluation. The pedicle axis was calculated with respect to the entire pedicle; then, the ideal entry point, screw diameter and length, sagittal angle and lateral angle were assessed.ResultsAll the ideal entry points were located at the medial superior to lateral notch (LN), and the mean distance between the entry point and LN was 5.86 ± 1.67 mm in the horizontal direction and 3.47 ± 1.57 mm in the vertical direction. The mean distance between the entry point and the middle point of the inferior edge of the C6 articular process (MP) was 0.74 ± 1.83 mm in the horizontal direction. The mean sagittal angle of the pedicle axis was 90.42°, and the mean pedicle transverse angle was 30.70°. The average diameter and length of the PS were 6.51 ± 0.76 mm and 31.58 ± 4.40 mm, respectively.ConclusionsThis study provided a novel method to calculate the ideal starting point and trajectory for C7 PS insertion. These measurements may be helpful for preoperative planning. It is recommended that 3D CT imaging is used preoperatively to carefully evaluate the anatomy of each individual.

Crestal bone loss in ultrashort implants: retrospective study on two different type of fixture.

Aim This was to assess variation of mean crestal bone loss (CBL) when two different types of ultrashort implants are placed in the upper or in the lower jaw and to evaluate differences in terms of success and survival rates. Materials and methods 99 ultrashort implants were retrospectively evaluated assessing differences at three different time-points (placement, prosthetic loading, end of follow-up) in terms of CBL in the upper and lower jaw. Correlations between CBL and diameter, platform switching, site of placement (upper or lower), type of implants, clinical crown/implant ratio and anatomical crown/implant ratio were statistically performed and success and survival rate were assessed. Results Statistically significant correlations were found between CBL and implant diameter, kind of screw and anatomical crown/implant ratio at the end of follow up. No correlation was highlighted between CBL and platform switching, and site of placement (upper or lower jaw). Survival and success rates were comparable and were found to be 96.37% in the upper jaw and 94.46% in the mandible. Conclusion CBL in ultrashort implants is an issue deserving great attention, therefore to know features and behaviours of different ultrashort implants in different quality of bone and clinical conditions represents a cut above to obtain and maintaining success in this particular kind of rehabilitation.

Mobilising the patient: With emphasis on innovative technologies

Treatment of trauma patients and fractures has changed dramatically throughout the years. From conservative methods to nowadays various kinds of screws, pins, plates and nails for optimal fixation of fractures. This lead to changes in post-operative management as well, from bedrest to (partial) weight bearing. Some patients however have very limited to no ability to mobilise, such as critical ill patients on the Intensive Care Unit, amputees or spinal cord injured patients. Due to innovations such as hydrotherapy, osseointegrated prosthesis and exoskeletons, even these people can mobilise. Thanks to innovations like these an increasing number of trauma patients are able to fully reintegrate into community life and get back to an active and independent life style.

Unfastening of Hexagonal Headed Screws by a Collaborative Robot

Disassembly is a core procedure in remanufacturing. Disassembly is currently carried out mainly by human operators. It is important to reduce the labor content of disassembly through automation, to make remanufacturing more economically attractive. Threaded fastener removal is one of the most difficult disassembly tasks to be fully automated. This article presents a new method developed for automating the unfastening of screws. An electric nutrunner spindle with a geared offset adapter was fitted to the end of a collaborative robot. The position of a hexagonal headed screw in a fitted stage was known only approximately, and its orientation in the hole was unknown. The robot was programed to perform a spiral search motion to engage the tool onto the screw. A control strategy combining torque and position monitoring with active compliance was implemented. An existing robot cell was modified and utilized to demonstrate the concept and to assess the feasibility of the solution using a turbocharger as a disassembly case study. Note to Practitioners —Remanufacturing is known to generate substantial economic, social, and environmental benefits. Disassembly is the first operation in a remanufacturing process chain. Unfastening threaded parts (“unscrewing”) is a common disassembly task accounting for approximately 40% of all disassembly activity. Like other disassembly tasks, often, unscrewing has to be carried out manually in remanufacturing due to difficulties caused by the variable and unpredictable condition of the end-of-life (EoL) products to be remanufactured. Automating unscrewing operations should reduce the labor content of disassembly, thus lowering remanufacturing costs and promoting the adoption of remanufacturing. This article proposes the use of a collaborative robot to perform autonomous unfastening of hexagonal headed screws. Collaborative robots have built-in force sensors and can be programed to carry out operations involving not only position but also active force and compliance control. They can work safely alongside human operators, enabling the latter to focus on jobs requiring high cognitive or manipulation abilities. The article presents a novel spiral search technique developed to improve the rate of successful engagement between the robot end effector and the screw heads despite uncertainties in the location of the screws. The technique was successfully demonstrated on the dismantling of a turbocharger but can readily be applied to other EoL products with hexagonal headed screws. It can also be used with other kinds of screws (e.g., Phillips screws and slotted-head screws) simply by changing the tool and tuning the robot control parameters. A limitation of the proposed technique is that it can only deal reliably with undamaged screws. In our future research, we will consider screws that are in imperfect conditions through usage and develop appropriate solutions for their removal by robots.

Percutaneous fixation of Lisfranc joint injuries: A systematic review of the literature

ObjectiveThe aim of this systematic review was to present the outcome of Lisfranc joint injuries treated with closed reduction and screw percutaneous fixation. MethodsWe searched in Pubmed and Google Scholar Databases for articles regarding screw percutaneous fixation of Lisfranc injuries. Seven studies in total were found to be compatible to our search, according to PRISMA guidelines. Four of those met the criteria of the review and they were included in the meta-analysis. A total number of 106 patients were separated into five groups according to the type of injury and the mean AOFAS score of each group was calculated. Cases in which percutaneous fixation was converted to open treatment due to poor reduction were not included in the study. In addition we compared the outcome score between types of injury according to Myerson classification as well as between purely ligamentous and osseoligamentous injuries. The characteristics of all seven selected studies, such as kind of screw used for fixation, post operative protocol, complications and outcome are mentioned as well. ResultsAverage AOFAS score was 86,2 for type A, 87,54 for type B, and 85 for type C injuries respectively. In pure dislocation group the average AOFAS score was 86,43 and in fracture dislocation group was 87,36. Good to excellent outcome can be expected in patients with different types of injury according to Myerson classification following percutaneous fixation of lisfranc joint injury. Patients with type B injury or a fracture dislocation injury might have better outcome, although this difference was not found to be statistically significant. ConclusionPercutaneous fixation of tarsometatarsal joint injuries is a relatively simple and safe method of treatment, leading to a good functional outcome, especially for Myerson type B as well as for fracture dislocation type of injuries, provided that an anatomical reduction has been achieved. Level of EvidenceLevel III, Therapeutic Study.

A biomechanical study of a novel expansive double-threaded bi-directional compression screw for internal fixation of type II odontoid fractures

Objective To measure and compare the biomechanical performance and anti-bending strength of conventional cannulated lag screw (CLS) versus our self-designed expansive double-threaded bi-directional compression screw (EDBCS) in fixation of type Ⅱ odontoid fracture. Methods Models of type Ⅱ odontoid fracture were created in 10 Chinese cadaveric specimens of axis which were then randomly subjected to fixation with either CLS or EDBCS (n = 5). Torsional stiffness and shear stiffness before and after fixation of type Ⅱ odontoid fracture were measured in all specimens. CLS and EDBCS were compared in terms of biomechanical performance in fixation. The 2 kinds of screws were also compared in terms of anti-bending strength by three-point bending test. Results The torsional stiffness and shear stiffness of CLS and the torsional stiffness of EDBCS after fixation were significantly decreased compared with before fixation (P < 0. 05). The torsional stiffness and shear stiffness of EDBCS were significantly larger than those of CLS (P < 0. 05). The maximal anti-bending strength of EDBCS (652. 3 ±0. 1 N) was significantly higher than that of CLS (576. 7 ±25. 0 N) (t = 2. 984, P = 0. 035). Conclusion Since EDBCS has better biomechanical performance in fixation of type II odontoid fracture than CLS, it may result in better fixation of the fracture theoretically. Key words: Fascia dentata; Fracture fixation, internal; Bone screws; Biomechanics

Comparison of 2 Kinds of Pedicle Screws in Primary Spinal Instrumentation

Expansive pedicle screw (EPS) and polymethylmethacrylate-augmented pedicle screw (PMMA-PS) were inserted in sheep vertebrae in vitro and were evaluated by performing biomechanical tests, radiographic examinations and histological observations. The objective of the study was to compare the biomechanical and interfacial performances of EPS and PMMA-PS in sheep lumbar vertebrae in vitro. It is a great challenge for orthopedic surgeons performing transpedicular fixation in the osteoporotic spine. It was reported that either the EPS or PMMA-PS could increase the screw stability. However, there are no studies comparing the 2 kinds of screws especially in primary spinal instrumentation. A total of 60 sheep lumbar vertebrae were randomly divided into 3 groups. A pilot hole was made in advance in all samples using the same method. Thereafter, the conventional pedicle screw (CPS) was inserted directly into the pilot hole in the CPS group; the hole in PMMA-PS group was first filled with polymethylmethacrylate (PMMA; 1.0 mL) and then inserted with CPS; and the EPS was inserted directly into the vertebrae in EPS group. After a period of 24 hours, biomechanical tests were performed to evaluate screw stability, and x-ray examination, micro-computerized tomography analysis, and histologic observation were performed to evaluate the interface between screw and bone. Compared with the stability of CPS, those of EPS and PMMA-PS were significantly enhanced. However, no significant differences were detected between the stabilities of EPS and PMMA-PS. The PMMA surrounding the screw blocked direct contact between bone and screw and formed a "screw-PMMA-bone" interface in the PMMA-PS group. There was a "screw-bone" interface in both CPS and EPS groups. Nevertheless, the expanded anterior part of EPS formed a claw-like structure pressing the surrounding bone trabeculae, which made the local bone tissue more compacted and denser than that in the CPS group. EPS can enhance the screw stability as markedly as the traditional PMMA-PS in primary surgery, and EPS can form a better immediate interface between screw and bone compared with PMMA-PS. EPS also can effectively avoid thermal injury, leakage, and compression caused by PMMA. A great feasibility was proved in this study to perform comparisons between the 2 kinds of pedicle screws in osteoporotic sheep vertebrae in vivo in the further research. In conclusion, we propose that EPS has a great application potential in augmentation of screw stability in the clinic.

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

BackgroundIt 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 FindingsAfter successful induction of osteoporotic sheep, lumbar vertebrae in each sheep were randomly divided into three groups. The conventional pedicle screw (CPS) was inserted directly into vertebrae in CPS group; PMMA was injected prior to insertion of CPS in PMMA-PS group; and the EPS was inserted in EPS group. Sheep were killed and biomechanical tests, micro-CT analysis and histological observation were performed at both 6 and 12 weeks post-operation. At 6-week and 12-week, screw stabilities in EPS and PMMA-PS groups were significantly higher than that in CPS group, but there were no significant differences between EPS and PMMA-PS groups at two study periods. The screw stability in EPS group at 12-week was significantly higher than that at 6-week. The bone trabeculae around the expanding anterior part of EPS were more and denser than that in CPS group at 6-week and 12-week. PMMA was found without any degradation and absorption forming non-biological “screw-PMMA-bone” interface in PMMA-PS group, however, more and more bone trabeculae surrounded anterior part of EPS improving local bone quality and formed biological “screw-bone” interface.Conclusions/SignificanceEPS can markedly enhance screw stability with a similar effect to the traditional method of screw augmentation with PMMA in initial surgery in osteoporosis. EPS can form better biological interface between screw and bone than PMMA-PS. In addition, EPS have no risk of thermal injury, leakage and compression caused by PMMA. We propose EPS has a great application potential in augmentation of screw stability in osteoporosis in clinic.

The designs and feasibility of clinical applications about a novel percutaneous pedicle screw system

Objective To evaluate the rationality of the designs and the feasibility of applications about a novel percutaneous pedicle screw system. Methods Six human cadaver specimens were used to simulate operative procedures with the novel percutaneous pedicle screw system (group A), and Sextant sys-tem was served as a control group (group B). Compression fractured vertebral bodies harvested from fresh calf were distracted with novel percutaneous pedicle screw system to assess the distraction function of percuta-neous system and distraction effect of modified screw. Biomechanical properties of modified screw were as-sessed according to the fixation effects of three types of screw-rod systems for fractured segment. Results The mean operation time in group A [(38.2 6.20) min] and B [(56.4 12.8) min] had significant difference (P< 0.05). The excellent and good rate of screws position was 91.7% and 95.8% in group A and B, respectively, showed no significant difference. The novel percutaneous system had a good distraction function to three kinds of screws. Modified and monoaxial screws could distract mainly the anterior column of vertebral body and there was no significant difference. However, the polyaxial screws distracted mainly middle and posterior column, the distraction effect of the anterior column was not as good as previous screws (P<0.05). There were no significant differences in flexion and extension, lateral bending and rotation of all specimens in intact and fractured. Modified and monoaxial screws could provide similar three-dimensional stabilities to fractured specimens. Polyaxial screw provided poor stability in flexion and extension compared with the two previous of screws (P<0.05). There were no significant differences in lateral and rotation stability provided by three kinds of screws. Conclusion Through using novel percutaneous pedicle screw system, modified and monoaxial screws have similar distraction effect on anterior column of vertebral body, and can provide similar three-dimen-sional stability. The novel percutaneous pedicle screw system is well-designed and feasible in clinical practice. Key words: Spine; Biomechanics; Internal fixators; Bone screws

Experimental analysis of mechanical response of stabilized occipitocervical junction by 3D mark tracking technique

This study is about a biomechanical comparison of some stabilization solutions for the occipitocervical junction. Four kinds of occipito-cervical fixations are analysed in this work: lateral plates fixed by two kinds of screws, lateral plates fixed by hooks and median plate. To study mechanical rigidity of each one, tests have been performed on human skulls by applying loadings and by studying mechanical response of fixations and bone. For this experimental analysis, a specific setup has been developed to impose a load corresponding to the flexion-extension physiological movements. 3D mark tracking technique is employed to measure 3D displacement fields on the bone and on the fixations. Observations of displacement evolution on the bone according to the fixation show different rigidities given by each solution.

Determination of Joint Velocities of Robots by Using Screws

The screw theory is applied to determination of joint velocities of robot arms. The method described in this paper can be directly used for the straight line trajectory control of existing industrial robots. Joint velocities are computed by taking inner products of two kinds of screws, one of which is an element of an orthogonal basis of the screw system composed of joint screws and another is the screw representing an instantaneous motion of an end effector. The computation can be performed during a sampling period while a robot is in motion.