Strength Of Screws Research Articles

Patient-specific mechanical analysis of pedicle screw insertion in simulated osteoporotic spinal bone models derived from medical images.

Biomechanical study. To investigate the mechanical characteristics of bone models created from medical images. Recent advancements in three-dimensional (3D) printing technology have affected its application in surgery. However, a notable gap exists in the analyses of how patient's dimorphism and variations in vertebral body anatomy influence the maximum insertional torque (MIT) and pullout strength (POS) of pedicle screws (PS) in osteoporotic vertebral bone models derived from medical images. Male and female patients with computed tomography data were selected. Dimensions of the first thoracic (T1), fourth lumbar (L4), and fifth lumbar (L5) vertebrae were measured, and bone models consisting of the cancellous and cortical bones made from polyurethane foam were created. PS with diameters of 4.5 mm, 5.5 mm, and 6.5 mm were used. T1 PS were 25 mm long, and L4 and L5 PS were 40 mm long. The bone models were secured with cement, and the MIT was measured using a calibrated torque wrench. After MIT testing, the PS head was attached to the machine's crosshead. POS was then calculated at a crosshead speed of 5 mm/min until failure. The L4 and L5 were notably larger in female bone models, whereas the T1 vertebra was larger in male bone models. Consequently, the MIT and POS for L4 and L5 were higher in female bone models across all PS diameters than in male bone models. Conversely, the MIT for T1 was higher in male bone models across all PS; however, no significant differences were observed in the POS values for T1 between sexes. The mechanical properties of the proposed bone models can vary based on the vertebral structure and size. For accurate 3D surgical and mechanical simulations in the creation of custom-made medical devices, bone models must be constructed from patientspecific medical images.

Duplex Fluorinated and Atomic Layer Deposition-Derived ZrO2 Coatings Improve the Corrosion Resistance and Mechanical Properties of Mg-2Zn-0.46Y-0.5Nd (wt.%) Alloy Plates and Screws.

This study investigated the corrosion resistance and mechanical properties of Mg-2Zn-0.46Y-0.5Nd (wt.%) alloy plates and screws with fluorinated coatings and atomic layer deposition (ALD)-derived zirconia (ZrO2) coatings in vitro under physiological stress conditions. Synthetic polyurethane hemimandible replicas were split and fixed as the following three groups of magnesium alloy plates and screws: no additional surface coating treatment (Group A), with fluorinated coatings (Group B), and with duplex fluorinated and ALD-derived 100 nm ZrO2 coatings (Group C). A circulating stress of 1-10 N was applied to the distal bone segment, and a 4-week simulated body fluid immersion test was employed to study the remaining material volume and the mechanical properties of the different groups. Compared with Group A and Group B, the degradation rate of magnesium alloy plates and screws' head regions was significantly slowed down under the protection of duplex MgF2/ZrO2 coatings (p < 0.01). There was no significant difference in the degradation rate of the screw shaft region between groups (p = 0.077). In contrast to fluoride coatings, duplex MgF2/ZrO2 coatings maintained the mechanical strength of magnesium alloy plates and screws after a 14 day in vitro SBF immersion test. We conclude that duplex MgF2/ZrO2 coatings exhibited a certain protective effect on the Mg alloy plates and screws under physiological stress conditions.

Estimating the Single Shear Strength Performance of Joints Using Screws and Nails with Decayed Wood

To enable the long-term use of existing wooden structures, appropriately evaluating the extent of damage of the biodeterioration of structural performance, including members and joint systems, is necessary. To give one example, accurately estimating the single shear strength performance of nail and screw joints with decay is crucial. Therefore, this study proposes a method to model this by dividing wood into multiple layers with different strength performance, considering the grade of deterioration in a cross-section of decayed wood. The model was used to differentiate the sound layer and three decayed layers (multilayer) according to the extent of the damage. The estimated values, which were produced using the proposed model, were compared to the single shear strength of screw and nail joints with decay using two species of wood, namely Abies sachalinensis (Todomatsu) and Cryptomeria japonica (Sugi). The results point to a good fit between the average value of the experimental results and the estimated values of the proposed model. Compared with the existing (single-layer) model, the proposed model improved the accuracy of estimating the strength of wood undergoing early deterioration and therefore was considered usable.

Biomechanical comparison of a new undercut thread design vs the V-shape thread design for pedicle screws

BACKGROUND CONTEXTThread shape is regarded as an important factor influencing the fixation strength and osseointegration of bone screws. However, commercial pedicle screws with a V-shaped thread are prone to generating stress concentration at the bone-screw interface, thereby increasing the risk of screw loosening. Thus, modification of the pedicle-screw thread is imperative. PURPOSEThis study aimed to investigate the fixation stability of pedicle screws with the new undercut thread design in comparison to pedicle screws with a V-shaped thread. STUDY DESIGNIn vitro cadaveric biomechanical test and finite element analysis (FEA). METHODSPedicle screws with the undercut thread (characterized by a flat crest feature and a tip-facing undercut feature) were custom-manufactured, whereas those with the V-shaped thread were procured from a commercial supplier. Fixation stability was assessed by the cyclic nonpullout compressive biomechanical testing on cadaveric female osteoporotic vertebrae. The vertical displacement and rotation angle of the 2 types of pedicle screws were calculated every 100 cycles to evaluate their resistance to migration and rotation. FEA was conducted to investigate the stress distribution and bone damage at the bone-screw interface for both types of pedicle screws. RESULTSBiomechanical testing revealed that the pedicle screws with the undercut thread exhibited significantly lower vertical displacement and rotation angles than the pedicle screws with the V-shape thread (p<0.05). FEA results demonstrated a more uniform stress distribution in the bone surrounding the thread in the undercut design than in the V-shape design. Additionally, bone damage resulting from the pedicle screw was lower in the undercut design than in the V-shape design. CONCLUSIONSPedicle screws with an undercut thread are less prone to migration and rotation and thus more stable in the bone than those with a V-shape thread. CLINICAL SIGNIFICANCEThe undercut thread design may reduce the incidence of pedicle-screw loosening.

Bone Allograft Pedicle Screw Augmentation: A Biomechanical Study.

We performed a comprehensive cadaveric biomechanical study to compare the fixation strength of primary screws, screws augmented with bone allograft, and screws augmented with polymethylmethacrylate cement. To evaluate a novel technique for screw augmentation using morselized cortico-cancellous bone allograft to fill the widened screw track of failed pedicle screws. To date, there are no known biological methods available for failed pedicle screw augmentation or fixation. Biomechanical tests were performed using 2 different testing modalities to quantify fixation strength including axial screw pullout and progressive cyclic displacement tests. Fifty vertebrae were instrumented with pedicle screws. Our study showed that bone allograft augmentation using the same diameter screw was noninferior to the fixation strength of the initial screw. In the axial pullout test, screws undergoing bone allograft repair failed at 25% lower loads compared with native screws, and screws augmented with cement showed approximately twice as much strength compared with native screws. In the cyclic displacement test, screws fixed with cement resisted loosening the best of all the groups tested. However, screws augmented with bone graft were found to have an equal strength to native screw purchase. our study did not find a correlation with bone mineral density as a predictor for failure in axial pullout or cyclic displacement tests. Bone allograft augmentation for pedicle screw fixation was noninferior to the initial screw purchase in this biomechanical study. This bone allograft technique is a viable option for screw fixation in the revision setting when there is significant bone loss in the screw track.

Do Iliac Screws Placed Close to the Sciatic Notch Have Greater Pullout Strength?

Optimal iliac screw position in relation to the sciatic notch remains unknown. In 12 cadavers undergoing S2 alar-iliac (S2AI) screw placement, we tested the pullout strength of screws placed in proximity to the sciatic notch (≤5 mm) vs farther away from the sciatic notch (>5 mm). A biomechanical, cadaver-based study was performed on 12 cadavers undergoing bilateral S2AI screw insertion. The position of the S2AI screw regarding the sciatic notch was dichotomized as ≤5 mm from the sciatic notch on the right side and >5 mm on the left side, confirmed using c-arm fluoroscopy. The primary outcome was the pullout strength of the screw (N). Secondary outcomes were stiffness (N/mm), yield force (N), and work to failure (N mm). Ischial tuberosity was embedded into polymethyl methacrylate and secured to a custom 3-axis vise grip mounted to a 14.5-kN load cell. Pullout testing was performed at 5 mm/min. Force and displacement data were collected at 100 Hz and evaluated using MATLAB. The Mann-Whitney test was performed. Of 24 S2AI screws, 3 screws could not be tested because of cement-bone interface failure. A positive though nonsignificant trend of screw pullout strength was found for screws close to the notch compared with those farther from the notch (861.8 ± 340.7 vs 778.7 ± 350.8 N, P = .859). Similarly, screws close to the notch demonstrated a higher trend of stiffness (149.4 ± 145.4 vs 111.34 ± 128.2 N/mm, P = .320) and force to yield (806.9 ± 352.0 vs 618.6 ± 342.9 N, P = .455). Conversely, screws farther from the notch had a higher but similarly nonsignificant area under the force-displacement curve (10 867.0 ± 9565.0 vs 14 196.6 ± 9578.3 N mm, P = .455), which might be due to excess sheer/translation force that could not be reliably quantified. Although placing S2AI screws ≤5 mm of the sciatic notch provided stronger fixation in 3 of 4 biomechanical testing categories, these results were not statistically significant. Therefore, placing S2AI screws ≤5 mm of the sciatic notch did not provide stronger fixation.

Enhance the performance of steel-wood composite screw connections with fast-curing adhesive

In composite floors composed of the H-steel and the wood panel, screw connection is one of the design keys. In this paper, the method of using fast-curing epoxy resin to anchor the screw tip was proposed, and six sets of pull-out tests and five sets of push-out tests of epoxy-wood-combined anchored screws were conducted to analyze the influence of the effective meshing length and the epoxy meshing ratio on the connection performance, respectively. Firstly, compared with ordinary screws, the pull-out stiffness and strength of epoxy-anchored screws were increased by 79.8 % and 153.9 %, respectively. Secondly, compared with the ordinary screw connection, the initial shear stiffness and capacity of the steel-wood composite connection were increased by 60.0 % and 22.8 % when the epoxy meshing ratio was 0.25, respectively. Thirdly, the modified effective meshing length of epoxy-anchored screws was proposed. Finally, based on the calculation formula for screws with two plastic hinges in Eurocode 5, the two parameters of pull-out resistance and yield moment for the screw were modified, thus improving the calculation accuracy of shear capacity for combine-anchored screw connections by about 21.0 %.

Comparison of the Fixation Strengths of Screws between the Traditional Trajectory and the Single and Double Endplate Penetrating Screw Trajectories Using Osteoporotic Vertebral Body Models Based on the Finite Element Method.

This is a finite element (FE) study. To compare the fixation strength of traditional trajectory (TT) and single and double endplate penetrating screw trajectories (SEPST/DEPST) to the osteoporotic vertebral body model based on the FE method. SEPST/DEPST have been developed to enhance the fixation strength in patients with diffuse idiopathic hyperostosis (DISH). This technique was also applied to patients with osteoporosis. However, determining the superiority of SEPST/ DEPST is difficult because of the heterogeneous patient backgrounds. Twenty vertebrae (T12 and L1) from 10 patients with osteoporosis (two males and eight females; mean age, 74.7 years) were obtained to create the 10 FE models. First, a single screw was placed with TT and SEPST/DEPST, and the fixation strength was compared by axial pullout strength (POS) and multidirectional loading tests. Second, two screws were placed on the bilateral pedicles with TT and SEPST/DEPST, and the fixation force of the vertebrae in the constructs in flexion, extension, lateral flexion, and axial rotation was examined. SEPST and DEPST had 140% and 171% higher POS values than TT, respectively, and the DEPST result was statistically significant (p =0.007). The multidirectional fixation strength was significantly higher in DEPST and SEPST than in TT in the cranial, caudal, and medial directions (p <0.05) but not in the lateral direction (p =0.05). The vertebral fracture strength at the lower instrumented vertebra of the DEPST tended to be higher than that of TT. The vertebral motion angles in SEPST and DEPST were significantly smaller in lateral bending (p =0.02) and tended to be smaller in flexion and extension than in TT (p =0.13). This study may provide useful information for spine surgeons in deciding whether to choose the SEPS or DEPS technique for augmenting fixation in osteoporotic vertebral fracture surgery.

Pull-out strength of screws in long bones at different insertion angles: finite element analysis and experimental investigations

Abstract Different types of plates are available to allow insertion of screws for internal fixation of long bone fractures. The aim of the study was to determine the effect of the insertion of screws at different angles on a long bone to the pull-out strength. Using 3D printed bone models, we tested the pull-out strength of screws in long bones at insertion angles between 0 and 40° with both finite element analysis and on printed models experimentally and compared the results. Test samples and cortical screws used were modeled with SolidWorks software and analyzed with Ansys software. As the screw insertion angle increases, the pull-out forces on the test specimens increase from 61.14 ± 3.5 N at 0° to 273 ± 6.8 N at 40° with an exception of a small drop between 15 and 20° from 235.4 ± 6.2 to 233 ± 6.9 N. Both methods showed an increase in the pull-out strength of screws as the insertion angle increases. This might be applicable in the clinical practice of bone fixation. Further studies on plate and screw fixation are needed to complement the findings.

Effect of Wood Densification and GFRP Reinforcement on the Embedment Strength of Poplar CLT

Embedment strength is an important factor in the design and performance of connections in timber structures. This study assesses the embedment strength of lag screws in three-ply cross-laminated timber (CLT) composed of densified poplar wood with densification ratios of 25% and 50%, under both longitudinal (L) and transverse (T) loading conditions. The embedment strength was thereafter compared with that of CLT reinforced with glass-fiber-reinforced polymer (GFRP). The experimental data was compared with results obtained using different models for calculating embedment strength. The findings indicated that the embedment strength of CLT specimens made of densified wood and GFRP was significantly greater than that of control specimens. CLT samples loaded in the L direction showed higher embedment strength compared to those in the T direction. In addition, 50% densification had the best performance, followed by 25% densification and GFRP reinforcement. Modelling using the NDS formula yielded the highest accuracy (mean absolute percentage error = 10.31%), followed by the Ubel and Blub (MAPE = 21%), Kennedy (MAPE = 28.86%), CSA (MAPE = 32.68%), and Dong (MAPE = 40.07%) equations. Overall, densification can be considered as an alternative to GFRP reinforcement in order to increase the embedment strength in CLT.

A new concept for expansion screws on the cervical spine using shape memory alloy - a feasibility study

Background: In general, sufficient anchoring of screws in the bone material ensures the intended primary stability. Methods: Shape memory materials offers the option of using temperature-associated deformation energy in a targeted manner in order to do justice to the special situation of osteoporotic bones or the potential lack of anchoring. An expansion screw was developed that takes this possibility and these requirements into account. Using finite element analysis, the variability of screw configuration and actuator was assessed from shape memory. In particular, the dimensioning of the screw slot, the actuator length and the actuator diameter as well as the angle of attack in relation to the intended force development were considered. Results: As a result of the finite element analysis, a special configuration of expansion screw and shape memory element could be found. Accordingly, with an optimal screw diameter of 4 mm, an actuator diameter of 0.8 mm, a screw slot of 7.8 mm in length and an angle of attack of 25 degrees, the best compromise between individual components and high efficiency in favor of maximum strength can be predicted. Conclusion: Shape memory material offers the possibility of using completely new forms of power development. By skillfully modifying the mechanical and shape memory elements, their interaction results in a calculated development of force in favor of a high primary stability of the screw material used. Activation by means of body temperature is a very elegant way of initializing the intended locking and screw strength.

Pullout strength of different pedicle screws after primary and revision insertion: an in vitro study on polyurethane foam

BackgroundSurgeons are routinely required to remove loose or failed pedicle screws and insert a new screw in their place. However, inserting a new screw into an existing hole may compromise the holding capacity of the pedicle screw. The purpose of this study is to evaluate the pullout strength of pedicle screws with different thread designs after the primary insertion and revision surgery in a synthetic bone model.MethodsFour pedicle screws with different thread designs (single-lead-thread (SLT) screw, dual-lead-thread (DLT) screw, mixed-single-lead-thread (MSLT) screw, and proximal-unthreaded-dual-thread (PUDL) screw) were inserted into pre-drilled, untapped holes (ø 4.2 mm, length 35 mm) in Sawbone blocks of density 20 pcf. In the first sequence, a 6.0 mm screw was inserted into the predrilled foam block and the primary pullout strength of the screw was measured according to ASTM F543. In the second sequence, a 6.0 mm screw was inserted and removed, and then either a 6.5 mm screw of the same design or a different screw design was inserted into the same hole and the pullout strength recorded.ResultsIn the first sequence, the mean pullout strength of the MSLT screw was significantly (p < 0.05) greater than all other screw designs. In the second sequence, when the MSLT screw was the primary screw, using a larger MSLT screw (6.5 mm) as the revision screw did not lead to a higher pullout strength than if a 6.0 mm diameter PUDL screw was used for the revision. Using a larger DLT screw (6.5 mm) as the revision screw resulted in a significantly (p < 0.05) greater pullout strength than a 6.0 mm STL, DLT, MSLT, or PUDL screw.ConclusionsOur results indicate that employing classic oversizing of the same screw design is a safe choice for maintaining screw purchase in the bone after revision. In cases where oversizing with the same screw design is not practical, opting for a PUDL screw with the same original diameter can provide enough purchase in the bone to maintain stability.

Bone density optimized pedicle screw insertion.

Background: Spinal fusion is the most common surgical treatment for the management of degenerative spinal disease. However, complications such as screw loosening lead to painful pseudoarthrosis, and are a common reason for revision. Optimization of screw trajectories to increase implant resistance to mechanical loading is essential. A recent optimization method has shown potential for determining optimal screw position and size based on areas of high bone elastic modulus (E-modulus). Aim: The aim of this biomechanical study was to verify the optimization algorithm for pedicle screw placement in a cadaveric study and to quantify the effect of optimization. The pull-out strength of pedicle screws with an optimized trajectory was compared to that of a traditional trajectory. Methods: Twenty-five lumbar vertebrae were instrumented with pedicle screws (on one side, the pedicle screws were inserted in the traditional way, on the other side, the screws were inserted using an optimized trajectory). Results: An improvement in pull-out strength and pull-out strain energy of the optimized screw trajectory compared to the traditional screw trajectory was only observed for E-modulus values greater than 3500MPacm3. For values of 3500MPacm3 or less, optimization showed no clear benefit. The median screw length of the optimized pedicle screws was significantly smaller than the median screw length of the traditionally inserted pedicle screws, p < 0.001. Discussion: Optimization of the pedicle screw trajectory is feasible, but seems to apply only to vertebrae with very high E-modulus values. This is likely because screw trajectory optimization resulted in a reduction in screw length and therefore a reduction in the implant-bone interface. Future efforts to predict the optimal pedicle screw trajectory should include screw length as a critical component of potential stability.

A Systematic Review of Screw and Suture Button Glenoid Augmentation Constructs.

Glenohumeral dislocations often lead to glenoid bone loss and recurrent instability, warranting bony augmentation. While numerous biomechanical studies have investigated fixation methods to secure a graft to the glenoid, a review of available constructs has yet to be performed. To synthesize the literature and compare the biomechanics of screw and suture button constructs for anterior glenoid bony augmentation. Systematic review. A systematic review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. There were 2 independent reviewers who performed a literature search using the PubMed, Embase, and Google Scholar databases of studies published between 1950 and 2020. Studies were included that compared the biomechanical outcomes of fixation for the treatment of anterior shoulder instability with glenoid bone loss. Overall, 13 of the 363 studies screened met the inclusion criteria. The included studies measured the biomechanical strength of screws or suture buttons on a cadaveric or synthetic Latarjet construct. Screws and suture buttons were biomechanically similar, as both constructs exhibited comparable loads at failure and final displacement. Screw type (diameter, threading, or composition) did not significantly affect construct strength, and double-screw fixation was superior to single-screw fixation. Additionally, 2 screws augmented with a small plate had a higher load at failure than screws that were not augmented. Unicortical double-screw fixation was inferior to bicortical double-screw fixation, although construct strength did not significantly decrease if 1 of these screws was unicortical. Further, 2 screws inserted at 15° off axis experienced significantly higher graft displacement and lower ultimate failure loads than those inserted at 0° parallel to the glenoid. Suture buttons provided comparable strength to screws and offer an effective alternative to reduce screw-related complications. Augmentation with a small plate may clinically enhance construct strength and decrease complications through the dispersion of force loads over a greater surface area. Differences in screw type did not appear to alter construct strength, provided that screws were placed parallel to the articular surface and were bicortical.

The effect of ding’s screw and tension band wiring for treatment of olecranon fractures: a finite element study

BackgroundTension band wiring (TBW) is a common surgical intervention for olecranon fractures. However, high rate of complications such as loss of reduction, skin irritation, and migration of the K-wires were reported up to 80%. Ding’s screw tension band wiring (DSTBW) is a new TBW technique that has shown positive results in the treatment of other fracture types. The objective of this study was to evaluate the stability of DSTBW in the treatment of olecranon fractures by finite element analysis.MethodWe used Ding’s screw tension band fixation (DSTBW) and K-wire tension band fixation (TBW) to establish a finite element model to simulate and fix olecranon fractures. The stress distribution, opening angle, twisting angle, and pullout strength of K-wires or screws were analyzed and compared.ResultsThe maximum von Mises stress was observed on the internal fixation for 90° elbow motion in both groups. The von Mises value of the screw in DSTBW was 241.2 MPa, and the von Mises value of k-wire in TBW was 405.0 MPa. Opening angle: TBW was 0.730° and DSTBW was 0.741° at 45° flexion; TBW was 0.679° and DSTBW was 0.693° at 90° flexion. Twisting angle: TBW was 0.146° and DSTBW was 0.180° at 45° flexion; TBW was 0.111° and DSTBW was 0.134° at 90° flexion. The pullout strength of DSTBW was significantly higher than that of TBW. Maximum pullout strength of Ding’s screw was 2179.1 N, maximum pullout strength of K-wire was 263.6 N.ConclusionDSTBW technology provides stable fixation for olecranon fractures, reducing the risk of internal fixation migration and failure.

Tsetse fly inspired steerable bone drill-a proof of concept.

The fixation strength of pedicle screws could be increased by fixating along the much stronger cortical bone layer, which is not possible with the current rigid and straight bone drills. Inspired by the tsetse fly, a single-plane steerable bone drill was developed. The drill has a flexible transmission using two stacked leaf springs such that the drill is flexible in one plane and can drill along the cortical bone layer utilizing wall guidance. A proof-of-principle experiment was performed which showed that the Tsetse Drill was able to successfully drill through 5, 10 and 15 PCF cancellous bone phantom which has similar mechanical properties to severe osteoporotic, osteoporotic and healthy cancellous bone. Furthermore, the Tsetse Drill was able to successfully steer and drill along the cortical wall utilizing wall guidance for an insertion angle of 5°, 10° and 15°. The experiments conclude that the tsetse fly-inspired drilling method is successful and even allows the drilling along the cortical bone layer. The Tsetse Drill can create curved tunnels utilizing wall guidance which could increase the fixation strength of bone anchors and limit the risk of cortical breach and damage to surrounding anatomy.

Three dimensional finite element analysis of biomechanics of osteotomy ends with three different fixation methods after hallux valgus minimally invasive osteotomy.

Biomechanical study of fixation methods post hallux valgus minimally invasive osteotomy using finite element technology hasn't been reported. This study aimed to compare maximum displacement and stress distribution of osteotomy ends after minimally invasive osteotomy fixed by bandage, Kirschner wire, Herbert screw. Foot CT images of a patient with mild-moderate hallux valgus were collected. Three-dimensional finite element model of hallux valgus was established through CT image. This study simulated bandage, Kirschner wire and Herbert screw fixation, and analyzed maximum displacement and stress distribution of osteotomy ends in plantar flexion position of foot after fixation. Maximum equivalent stress of osteotomy end fixed with bandage, Kirschner wire, Herbert screw was 7.8615, 14.253, 8.3156MPa, respectively. Total displacement of osteotomy end fixed by bandage, Kirschner wire, Herbert screw was 0.26,896, 0.022,779, 0.029,195mm, respectively. Maximum stress of Kirschner wire and Herbert screw near osteotomy end was 154.7 and 46.404MPa, respectively. Fixation strength and stability of Kirschner wire and Herber screw were better than bandage. Kirschner wire had stress concentration phenomenon, with potential fracture risk. Stress of Herbert screw was evenly distributed around osteotomy end, and there was a certain stress concentration, playing an important role in maintaining fracture end stability. Herbert screw showed good fixation strength and stability, and stress distribution was uniform, which can well maintain stability of minimally invasive osteotomy ends. Findings of this study would provide a theoretical basis for selection of fixation methods after clinical minimally invasive osteotomy for hallux valgus.

"STRENGTHENING THE DESIGN OF SCREW DEVICES IN HORIZONTAL MACHINES"

"Methods of reducing the metal consumption and increasing the structural strength of screw devices through the use of tubular shafts with amplifiers in dangerous sections are proposed. The review of the study shows that the modernization of the design of horizontal machines with screw devices was previously carried out and there is a positive experience in the development of such structures. The configuration of the shafts of mechanical gears usually provides the necessary rigidity of the structure. The load part of such shafts is thickened, less loaded on the shank has a thinned configuration with a smaller volume of material assigned to it. Due to the use of a special annular bandage pressed onto the screw shaft, the composite shaft is reinforced, representing a solid structure of hollow cylinders interconnected by guaranteed tension. The reduction of metal consumption is ensured by reducing the mass of the shaft, only dangerous sections are reinforced with bandages, which makes it possible to significantly facilitate the design of screw devices and increase the energy efficiency of the machine as a whole. Keywords: horizontal machine, screw device, shaft, annular insert, fit, strength, rigidity."

Shear connection performance of cold-formed steel and plywood composite flooring systems: Experimental and numerical investigation

This study carries out numerical and experimental investigation on shear connection performance of flooring systems comprising of cold-formed steel joists and engineered plywood panels. A 3-D finite element model has been developed using ANSYS software which considers the nonlinear behaviour and damage of plywood panels using a maximum stress-based criterion incorporated in the FE model. The yielding behaviour of steel joists and fasteners (screws and bolts) is defined as a multilinear plastic hardening material model defined in ANSYS software. The FE model was validated against the experimental results obtained from push-out tests conducted on specimens utilising different connection arrangements. The validated FE models showed a good agreement with the experimental results of the push-out tests in terms of load-slip behaviour, ultimate peak capacity, and failure modes. Finally, the validated FE models are utilised to perform a parametric study that investigates the effect of varying various parameters, including diameter and yield strength of self-drilling screws, the thickness of plywood panels, value of friction coefficient, and the ratio of fastener diameter to the joist thickness, on the initial stiffness, failure mode and ultimate load capacity of the cold-formed steel and plywood composite connections.

Anterior occipital condyle screw placement through the endonasal corridor: proof of concept study with cadaveric analysis.

Odontoidectomy for ventral compressive pathology may result in O-C1 and/or C1-2 instability. Same-stage endonasal C1-2 spinal fusion has been advocated to eliminate risks associated with separate-stage posterior approaches. While endonasal methods for C1 instrumentationand C1-2 trans-articularstabilization exist, no hypothetical construct for endonasal occipital instrumentation has been validated. We provide an anatomic description of anterior occipital condyle (AOC) screw endonasal placement as proof-of-concept for endonasal craniocervical stabilization. Eight adult, injected cadaveric heads were studied for placing 16 AOC screws endonasally. Thin-cut CT was used for registration. After turning a standard inferior U-shaped nasopharyngeal flap endonasally, 4 mm × 22 mm AOC screws were placed with a 0° driver using neuronavigation. Post-placement CT scans were obtained to determine: site-of-entry, measured from the endonasal projection of the medial O-C1 joint; screw angulation in sagittal and axial planes, proximity to critical structures. Average site-of-entry was 6.88mm lateral and 9.74mm rostral to the medial O-C1 joint. Average angulation in the sagittal plane was 0.16° inferior to the palatal line. Average angulation in the axial plane was 23.97° lateral to midline. Average minimum screw distances from the jugular bulb and hypoglossal canal were 4.80mm and 1.55mm. Endonasal placement of AOC screws is feasible using a 0° driver. Our measurements provide useful parameters to guide optimal placement. Given proximity of hypoglossal canal and jugular bulb, neuronavigation is recommended. Biomechanical studies will ultimately be necessary to evaluate the strength of AOC screws with plate-screw constructs utilizing endonasal C1 lateral mass or C1-2 trans-articular screws as inferior fixation points.