Screw Head Research Articles

Diamond-like carbon coating reduces connection screw head stripping after multiple tightening.

The stability of implant-abutment joint is fundamental for the long-term success of implant rehabilitation. The screw loosening, fracture, and head deformation are among the most common mechanical complications. Several surface treatments of titanium screws have been proposed to improve their resistance and stability. Diamond-like carbon (DLC) coating of the materials is widely used to increase their wear resistance and durability. The present study aimed to evaluate the effect of carbon fiber coating on the screw head on screw removal torque and screw head stripping. One hundred titanium implant screws were used, 50 without coating (Group 1) and 50 with DLC coating of the screw head (Group 2). Each screw was tightened with a torque of 25Ncm and unscrewed ten times. The removal torque was measured with a digital cap torque tester for each loosening. Optical 3d measurement of the screw head surface was performed by a fully automatic machine before and after multiple tightening to investigate surface modifications. The reverse torque values decreased with repeated tightening and loosening cycles in both groups without significant differences (p>0.05). Optical measurements of surface dimensions revealed average changes of 0.0357mm in Group 1 and 0.02312mm in Group 2, which resulted to be statistically significant (p<0.001). The DLC coating of the retention screw head can prevent its distortion and wear, especially after multiple tightening.

Feasibility of a novel type of complex anterior cervical fixation by using Mimics software

To investigate the feasibility of mimics software in analyzing a new type of complex anterior cervical fixation -- anterior transpedicular screw fixation+zero notch internal fixation. From January 2021 to September 2022, 50 normal pedestrians who underwent cervical spine CT scanning were selected for C1-C7 segment scanning, including 27 males and 23 females, aged from 25 to 65 years old with an average of (46.0 ± 9.0) years old. The dicom format is exported and engraved into the CD, and use the mimics software to perform 3D reconstruction of each segment. A simulated screw is placed on the image according to the critical value of zero notch screw (head and tail angle 44°, internal angle 29°). The position of zero notch screw in each segment is observed to determine the feasibility of anterior transpedicular screw fixation plus zero notch internal fixation. For the upper zero notch screws the three-dimensional images of the cervical spine across all 50 subjects within the C3-C7 segments demonstrated safe position, with no instances of intersection with ATPS. For the lower zero notch screw, in C3-C4 and C4-C5, 4 out of 50 subjects are in the safe position in the three-dimensional images of cervical vertebrae, and 46 cases could achieve secure screw placement when the maximum caudal angle is(32.3±1.9) ° and (36.1±2.2) °, respectively. In C5-C6 and C6-C7 segments, no lower zero notch screws intersected with ATPS, and all screws are in safe positions. Lower cervical anterior pedicle screw fixation plus zero notch internal fixation can achieve successful nail placement through the selected entry point and position.

Retrospective analysis of augmentation procedures with umbrella screws, a novel tenting technique: a consecutive case series in 279 patients.

The consecutive case series accesses the results and experiences of ridge augmentation using an umbrella screw tenting technique. In total, 279 patients were treated between 26 May 2015 and 16 June 2021, including horizontal and vertical ridge defects. Sex, age, smoking behavior, jaw, graft material, soft tissue thickness, extent of horizontal/vertical augmentation, resorption rate, and occurrence of early/late exposure were evaluated. Bone gain was determined by resorption at the screw head. Only cases without premature screw removal were evaluated metrically (n = 201). All other augmentations were evaluated according to whether implantation was possible with or without further augmentation (n = 27). A target performance index was calculated, which should enable evidence-based comparability of different augmentation methods in future. In total, 54 wound dehiscences (39 early, 15 late exposures) occurred, which corresponds to 24.08% of the augmented sites; 42 umbrella screws were removed prematurely. In all cases an implantation was possible at the desired position afterwards. Cases with a vertical augmentation component showed a higher prevalence of exposure (early, P = .000; late, P = .024). The extent of the vertical augmentation was only relevant for early exposure (P = .048). Mean bone gain of 4.23 ± 1.69 mm horizontally and 4.11 ± 1.99 mm vertically could be achieved. Regression analysis showed that there was no limit in horizontal/vertical direction. Mean percentage target performance index was 75.90 ± 20.54 for vertical and 82.25 ± 16.67 for horizontal portions. The umbrella technique is an effective augmentation method, which can be applied to any defect morphology.

Connecting the S2 alar-iliac screw head to the satellite rod for surgical correction of degenerative sagittal imbalance.

The S2AI screw technique has several advantages over the conventional iliac screw fixation technique. However, connecting the S2AI screw head to the main rod is difficult due to its medial entry point. We introduce a new technique for connecting the S2AI screw head to a satellite rod and compare it with the conventional method of connecting the S2AI screw to the main rod. Seventy-four patients who underwent S2AI fixation for degenerative sagittal imbalance and were followed up for ≥ 2years were included. All the patients underwent long fusion from T9 or T10 to the pelvis. The S2AI screw head was connected to the satellite rod (SS group) in 43 patients and the main rod (SM group) in 31 patients. In the SS group, the satellite rod was placed medial to the main rod and connected by the S2AI screw and domino connectors. In the SM group, the main rod was connected directly to the S2AI screw head and supported by accessory rods. Radiographic and clinical outcomes were evaluated in both groups. There were no significant differences in postoperative complications, including proximal junctional failure, proximal junctional kyphosis, rod breakage, screw loosening, wound problems, and infection between the two groups. Furthermore, the correction power of sagittal deformity and clinical results in the SS group were comparable to those in the SM group. Connecting the S2AI screw to the satellite rod is a convenient method comparable to the conventional S2AI connection method in terms of radiological and clinical outcomes.

Determining optimal length of coracoid graft in the modified Bristow procedure for anterior shoulder instability: A three-dimensional finite element analysis.

There is a lack of consensus concerning the coracoid graft length in the modified Bristow procedure. We attempted to determine the optimal graft length using the three-dimensional finite element method. In a shoulder model with a 25% anterior glenoid defect, a coracoid graft of varying lengths (5, 10, 15, and 20 mm) was fixed using a half-threaded screw. First, a compressive load of 500 N was applied to the screw head to determine the graft failure load during screw tightening. Next, a tensile load (200 N) was applied to the graft to determine the failure load due to biceps muscle traction. In the screw compression, the failure loads in the 5-, 10-, 15-, and 20-mm models were 252, 370, 377, and 331 N, respectively. In the tensile load applied to the coracoid graft, the failure load exceeded 200 N for both the 5- and 10-mm models. The 5-mm graft had a high risk of fracture during intraoperative screw tightening. As for the biceps muscle traction, the 5- and 10-mm-grafts had a lower failure risk than the 15- and 20-mm-grafts. Therefore, we believe that the optimal length of the coracoid graft is 10 mm in the modified Bristow procedure.

Development and Validation of a Screw Interlock Recognition Method based on Logistic Regression

Conventional robotic screw methods rely on position control and the use of a threshold value, normally a contact force value, to detect the contact between tool and screw, so the nut-runner can be placed correctly on the workpiece. In the case of a dynamic workspace, the variance of the workpiece position will likely cause the nut-runner to be positioned incorrectly and will significantly decrease the success rate of the screw task.This paper proposes a novel method based on a logistic regression model for flexible Human-Robot-Collaboration (HRC) screw assembly operations in highly dynamic workspaces. The proposed method is part of a screwing strategy based on impedance control and developed for HRC applications. The screwing strategy consists of a spiral movement executed by the robot while approaching the workpiece and it is used as a search procedure to find the screw. The proposed method is used to detect when the tool correctly interlocks with the screw head so the robot can proceed with the screwing process. The goal is to stop the spiral movement timely when the nut-runner has correctly interlocked with the screw head to ensure a successful screw task and avoid potential damage to the nut-runner or the workpiece.The proposed screw interlock recognition method utilizes a logistic regression model to observe the contact forces between tool and screw head. The learning model is trained using force data collected from experiments and then its feasibility is validated with further testing.

Comparative Performance Evaluation of One-Stage and Two-Stage Object Detectors for Screw Head Detection and Classification in Disassembly Processes

The process of manually detecting and removing screws during disassembly can be time-consuming and demanding. Automated systems utilizing imaging and deep learning can rapidly and accurately identify screws based on features like head shape and size. Different deep learning methods have varying screw detection capabilities. Choosing the right method significantly impacts system effectiveness, robustness and efficiency. Several generic deep learning architectures have been proposed to address this problem. However, there is little guidance on their suitability for specific scenarios. This paper aims to provide qualified guidance for selecting suitable deep learning methods for screw head detection. The proposed approach involves researching existing object detection methods and choosing two representatives – one employing a one-stage approach, the other using two-stage. These selected methods will be implemented identically and their performance evaluated via rigorous analysis and comparison. The dataset comprises synthetic and real images of 6 screw types across 3 products. YOLOv5 was selected for one-stage detectors, Faster R-CNN for two-stage. Results show the one-stage YOLOv5 generally outperforms Faster R-CNN in precision, recall, speed and training times, while Faster R-CNN delivered superior recall with smaller training datasets.

Effect of screw angulation and multiple insertions on load-to-failure of polyaxial locking system

Purpose Polyaxial locking plates rely on the alignment between the thread-to-thread connections of the screw head and the plate hole. These implants have provided substantial support for surgeons. In particular, extended screw positioning have proven to be beneficial in the fixation of challenging fractures. This study aimed to investigate the mechanical properties of ChM 5.0 ChLP polyaxial screws inserted in off-axis trajectories, including multiple insertions and to correlate these parameters with the screw head and the plate hole thread-to-thread engagement. Methods Polyaxial locking screws were inserted into the plates at various angles (0°,10°,15°, -15° off-axis). Multiple time inserted screws were placed firstly at 15°, then 0° and finally -15° off-axis in the same plate hole. A microCT scan of the plate-hole and screw-head interface was conducted before destructive tests. Representative screws from each group were also examined by Scanning Electron Microscope. Results The standard insertion at 0° sustained the greatest maximum bending strength without relocation in the screw hole. Screws inserted at 10° and 15° (one time) showed a significant reduction in load-to-failure of up to 36% and 55%, (p = 0.001) (p = 0.001) respectively. Screws inserted at -15° after a maximum of three multiple insertions with angle shift, showed a total reduction in force of up to 70% (p = 0.001). A microCT analysis of thread engagement showed significant correlations. However, the results obtained for multiple insertions were highly variable. Conclusions ChM 5.0 ChLP polyaxial locking system has valuable properties that foster fracture fixation, providing various surgical options. Nevertheless, the freedom of off-axis placement and multiple insertions of the screws comes at the price of reduced force. When possible surgeons should minimize the angles of insertions.

Effect of screw angulation on the bending performance of polyaxial locking interfaces: a micro-CT evaluation

Polyaxial locking plates rely on a specific thread-to-thread interface of the screw head and the plate hole. The objective of this study was to evaluate the mechanical performance of single screw interfaces when inserted off-axis and to establish correlations between those parameters and the engagement of the screw head and the plate hole thread. Three polyaxial locking screw systems were inserted into the corresponding plates at various angles (0°, 5°, 10°, and 15° off-axis). The screws were tested until failure. A micro-CT was performed to examine the interface between the plate hole and the screw head. The standard insertion at 0° sustained the greatest maximum bending strength without relocation in the screw hole. Screws inserted at 15° showed a significant reduction in force of up to 44%, 55% and 57%, respectively. Micro-CT analysis of the interface showed a significant loss of thread engagement for off-axis insertion. Polyaxial plates offer additional advantages for off-axis placement of screws. However, this flexibility is related to a significant decrease in both thread engagement and bending strength compared to monoaxial insertion. Regardless the insertion angle, the loss of stability is comparable when screws are placed off-axis. Surgeons are advised to consider off-axis insertion as a salvage option, providing access to better bone stock.

Biomechanical evaluation of variable angle locking systems. A micro-CT analysis.

Formerly poor bone stock and periprosthetic fractures used to jeopardize monaxial constructs. Polyaxial locking screws have substantially supported those particular fixation constructs. However, those systems rely on complex alignment between the screw head and the plate hole. This study aimed to investigate the mechanical properties of several polyaxial systems and to correlate these parameters with the screw head and the plate hole engagement. Polyaxial locking systems were tested with screws inserted into the corresponding plates at various angles (0°, 5°, 10°, 15°). A micro-CT scan of the plate-hole and screw-head interface with the quantification of average thread engagement was performed before destructive tests. The screw-plate interface of each system was tested in a cantilever bending setup. Representative screws and plates were also examined by SEM. The standard insertion at 0° sustained the greatest maximum bending strength in all analyzed systems. Point-loading thread-in and cut-in screws inserted off-axis showed a significant reduction in bending strength (p<0.001) (p=0.041) (p<0.001). In contrast, locking cap screws maintained similar bending strength with disregard to the angle of insertion (p<0.4849). A micro-CT analysis confirmed that the average thread engagement of point-loading thread-in, cut-in and locking-cap screws was significantly reduced when placed off-axis (p=0.005) (p<0.001) (p=0.002) (p<0.001). The locking-cap mechanisms maintained the highest average thread engagement among all analyzed systems. The mechanical performance of polyaxial locking plates usually comes at the price of reduced bending strength. Surgeons should limit polyaxial insertions depending on the particular system's characteristics.

Does A Hinged Operating Table Facilitate Sagittal Correction in Transforaminal Lumbar Interbody Fusion With Smith-Peterson Osteotomy? A Radiographic Analysis.

Osteotomies allow the restoration of appropriate sagittal alignment; however, closure of osteotomies can be challenging. Typical closure involves compressing pedicle screw heads across the rods, potentially causing screw loosening and failure. Motorized hinged operating tables are often used to assist with controlled closure of osteotomies without manual compression, but there is no published research quantifying the amount of correction provided solely by changes in the table angle. What is the incremental amount of correction achieved by change in the table angle versus instrumented manipulation during osteotomy closure in transforaminal lumbar interbody fusion (TLIF) with Smith-Petersen osteotomy? Sixty-one patients undergoing Smith-Peterson osteotomy and bilateral TLIF using a motorized hinged table from October 2019 to March 2022 were prospectively enrolled. Two patients did not undergo surgery, two did not have table extension, and seven did not have data collected intraoperatively because of disruptions in research protocols owing to the coronavirus-19 pandemic. Fifty patients (24 male, 26 female) who underwent a total of 73 osteotomies were included in the final analysis. The mean ± standard deviation age was 61 ±11 years, and the mean BMI was 31 ± 6 kg/m 2 . Patients were positioned prone on the table and flexed to 10° for decompression, Smith-Petersen osteotomy, and TLIF. The table was then extended in 5° increments, and radiographs were taken until 10° of extension was achieved or the osteotomy was fully closed. Changes in segmental lordosis across the operative site for each 5° increment were measured to the nearest degree by two reviewers. Intraclass correlation coefficients for segmental lordosis measurements at each table angle change were calculated as 0.97 to 0.98, with all p values < 0.001, indicating excellent agreement. Table change from 10° to 5° yielded a mean segmental lordosis change of 1.9° ± 1.5° (73 osteotomies), 5° to 0° yielded a change of 1.3° ± 0.9° (73 osteotomies), 0° to -5° yielded a change of 1.3° ± 1.0° (69 osteotomies), and -5° to -10° yielded a change of 1.1° ± 1.3° (61 osteotomies). Rod placement and compression yielded a mean 1.8° ± 2.0° of additional segmental lordosis. Using a motorized hinged table facilitated an average of 5.6° of total segmental lordosis correction during controlled Smith-Peterson osteotomy closure without the need for cantilevering forces across spinal instrumentation. Surgeons can use this technique to reduce the compression forces needed to close osteotomies, which could eliminate a potential source of complications.Level of Evidence Level II, therapeutic study.

FEM simulation on forming vacuum hexagon socket screws using tube workpiece

This study proposes a new forming design concept to produce vacuum hexagon socket screws using tube workpiece, and uses the finite element simulation software DEFORM-3D to simulate the multi-pass forming process of vacuum hexagon socket screws. The simulated material is SUS-304 stainless steel, and the frictional conditions are assumed to be constant shear friction, the die is assumed to be a rigid body. In the past, the traditional vacuum hexagon socket screw manufacturing process used a multi-pass process to manufacture a standard screw using a solid workpiece (wire rod), and then drilling an air channel in the core of the screw. This process not only wastes time, but also needs to increase the processing cost. In this study, the time and cost of drilling the air channel can be reduced by forming the vacuum hexagon socket head screw through the hollow tube. The finite element simulation results confirm that this design is a feasible method. The pass schedule can be reduced from 6 stages to 3 stages, the maximum effective stress decreased by 28.13%, and the total forming force decreased by 57.66%. The research results can be provided to relevant industry as the reference.

Prospective measurement of outcomes and complications of tibial tuberosity advancement using novel mini plates in small breed dogs.

Cranial cruciate ligament (CrCL) disease is a common orthopedic disease in canine patients. Tibial osteotomy procedures for the treatment of cranial cruciate ligament disease in small breed dogs (<15 kg) have previously been limited. A total of 22 client-owned dogs, 26 stifles, with cranial cruciate ligament disease were treated with novel mini-tibial tuberosity advancement plates. The most common intraoperative complications included the need for plate-cage overlap in 7 stifles (26.92%) and screw head fracture in 1 (3.85%). Post-operative complications included tibial tuberosity fracture (3.85%), post-operative medial patella luxation (7.69%), and persistent lameness (7.69%). Of the 26 stifles evaluated in the medium term (>6-12 months) post-operatively, 92.3% had no lameness, with the remaining 7.7% having Grade 1 lameness. A good to excellent clinical outcome was noted in all 26 stifles that underwent TTA with novel mini plates.

Screw preload loss under occlusal load as a predictor of loosening risk in varying dental implant designs

PurposeScrew loosening is a critical aspect of an implant design, as it can lead to implant failure. This study proposes a methodology and qualitatively assesses the potential of screw loosening risk for various types of screw heads and implant fixture-abutment connections. It is assumed that the risk of screw loosening is related to the drop in loosening moment under occlusal loads. The methodology and an assumption is verified by confronting the results with laboratory tests. MethodsNumerical simulations supplemented with semi-empirical equations were employed to estimate a loosening moment change under occlusal loads. The loosening risk was estimated by comparing the value before and after application of a compressive occlusal load of 150N. The procedure was carried out for 289 implant designs with smooth transition between flat to tapered shape of a screw head and an fixture-abutment connection. All analyses were conducted using Abaqus software. Pearson and Spearman correlation coefficients for normalised change in a screw loosening moment drop has been computed for numerical and laboratory tests. ResultsThe statistical analysis (Pearson, ρ = 0.8, Spearman, rs = 0.85) indicates very high correlation and confirms that the general tendencies observed in laboratory tests are reflected in the proposed procedure. The procedure was used for various geometries and the following results are presented: a screw loosening drop, implant stiffness and a tightening moment. The loosening moment drop achieves the extreme values of 6% and 24%. The biggest drop is an effect of a conical implant-abutment connection and a flat screw head while the lowest was recorded for a flat implant-abutment interface regardless of a screw head type. A low drop is also observed for a strongly conical screw head. ConclusionsThe proposed methodology exhibited very good correlation when confronted with laboratory tests, supporting a screw preload reduction under occlusal load as a key factor in screw loosening. Analysis across a wide spectrum of implant designs revealed geometry significantly impacts loosening potential under occlusal loads. Two key features were identified as favourable - an abutment-fixture butt joint and a tapered screw. The results also enable prediction of qualitative geometry effects on loosening risk.

Cement-Augmented Screw Fixation with PHILOS Plating for Osteoporotic Proximal Humeral Fractures: An Observation of Mid- and Long-Term Curative Efficacy.

The mid- and long-term clinical outcomes of cement-augmented screws in the treatment of osteoporotic proximal humeral fractures have rarely been reported. The aim of this study was to observe the mid- and long-term efficacy of combined cement-augmented screw fixation and PHILOS plating in the treatment of osteoporotic fractures of the proximal humerus. This study retrospectively analyzed data from 19 patients with osteoporotic fractures of the proximal humerus who had undergone internal fixation at the Guizhou Provincial People's Hospital from February 2017 to May 2021. The cohort was comprised of six males and 13 females, aged 75-87 (mean age: 82.52 ± 1.24) years. According to the Neer classification, three, 12, and four patients had two-part, three-part, and four-part fractures, respectively. All patients were treated with open reduction internal fixation with cement-augmented screws and PHILOS plating. Time until fracture healing was recorded postoperatively. Patients were observed for postoperative complications, including humeral head necrosis, loosening or breaking of the augmented screws, screw perforation of the humeral head, and varus fracture displacement. Visual analog scale and Constant scores of the shoulder joint were compared 1, 3, 6, and 12 months after surgery. Scores at the most recent follow-up were used to evaluate shoulder joint function. Measured data conforming to a normal distribution were expressed as mean ± SD. Analysis of variance or rank sum tests were used for intergroup comparisons. A value of p < 0.05 was considered significant. All 19 patients followed up for 1-4 (average: 2.13 ± 0.61) years. Fractures united in all cases, with a healing time of 8-14 (average: 10.25 ± 1.72) weeks. There were no cases of humeral head necrosis, screw loosening, fractures, or perforation of the humeral head. One patient had mild varus fracture displacement with a reduced neck-shaft angle. There were significant differences in visual analog scale and Constant scores 1, 3, and 6 months after surgery (p < 0.05). The visual analog scale score was 0 at final follow-up in all cases. The Constant score of the shoulder joint was excellent, good, fair, and poor in two, 12, four, and one case, respectively, yielding an excellent and good rate of 73.68%. Cement-augmented screw fixation combined with PHILOS plating of osteoporotic proximal humeral fractures had good mid- and long-term clinical efficacy. It should be considered a new option for fracture treatment in such patients.

Risk Factors of Proximal Screw Breakage of Locking Plate (ZPLP®) after MIPO for Distal Femur Fractures -Analysis of Patients with Plate Removal after Bony Union.

Locking a compression plate is a more favorable surgical technique than intramedullary nailing in the treatment of distal femur fractures. This study analyzed the risk factors of proximal screw breakage retrospectively, which was confirmed in the patients with plate removal after bony union. A total of 140 patients who were fixed by MIPO using ZPLP from 2009 to 2019 were identified. A total of 42 patients met the inclusion criteria and were included. The screw breakage group (12 patients) and the non-breakage group (30 patients) were compared. Approximately 12 (28.6%) of 42 plate-removal patients showed proximal screw breakage. The breakage of proximal screws developed at the junction of the screw head and neck. The number of broken proximal screws averaged 1.4 (1~4). The breakage of the proximal screw even after the bony union is more frequent in older patients (p = 0.023), the dominant side (p = 0.025), the use of the cortical screw as the proximal uppermost screw (p = 0.039), and the higher plate-screw density (p = 0.048). Advanced age, dominant side, use of the cortical screw as the uppermost screw, and higher plate-screw density were related to proximal screw breakage. When the plate is removed after bony union or delayed union is shown in these situations, the possibility of proximal screw breakage should be kept in mind.

Opposing Flanks vs Parallel Flanks – the Influence of Headless Screw Design on Compression and Pull- Out Resistance

Category: Basic Sciences/Biologics; Basic Sciences/Biologics Introduction/Purpose: Screws generate and maintain compression against distracting forces when performing osteotomy or fusion surgery. Headless screws with opposing flank angles (OFA) between the threads of the head and shaft are purported to achieve better compression. The purpose of this study was to compare OFA designs against traditional parallel flank angle (PFA) headless screws and headed screws to determine differences in compression and pull-out resistance (POR). Methods: In this biomechanical in-vitro study, four screw designs were compared: headless screws with OFA (Screw_A and Screw_B), headless screws with PFA (Screw_C), and headed screws (Screw_D). All screws were 4.0x50mm partially threaded cannulated screws. Screw_B had a 1.4mm shorter head length and 0.5mm narrower head thread diameter than Screw_A and Screw_C, which were similar. A custom apparatus was designed for measuring compression and POR. Osteotomies were created on synthetic bone blocks (density 0.32g/cm3) simulating cancellous bone. Screws were inserted perpendicular to osteotomies in accordance with manufacturer guidance and maximum compression recorded. Increasing distracting forces were then applied to the blocks until the screws pulled out. For each screw type, five screws were tested. Results: There was no significant difference in maximum compression between screw designs: Screw_A=38.7N±14.2N, Screw_B=48.7N±15.6N, Screw_C=51.9N±36.4N, Screw_D=32.0N±9.2N; p=0.921. When assessing POR, all screws failed at the head-bone interface (screw heads subsided into block). Pull-out forces significantly differed between all groups: Screw_A=466N±29.0N, Screw_B=310N±22.0N, Screw_C=399N±46.0N, Screw_D=183N±12.9N; p&lt; 0.001 (ANOVA). Screw_Ahad the highest POR but the other OFA design (Screw_B) had significantly lower POR. Conclusion: Screw design, whether headless (OFA or PFA) or headed did not appear to influence compression generated. However, headed screws had significantly lower POR than headless designs. Within headless designs, OFA may increase POR, but other screw head features (number / diameter of threads) had an apparently greater influence than flank angle.

Comparing Original and Universal Screwdrivers and How They Affect Friction in the Screw.

The present study focused on investigating whether universal screwdriver kits cause less friction between the screwdriver and the abutment screw than original screwdrivers. For this purpose, 2 original screwdrivers (Straumann and BEGO) and a universal screwdriver kit (bredent) were investigated. On 1 implant per screwdriver, 26 abutments were properly attached one after the other with the corresponding abutment screws. After tightening the abutment screw, the force required to pull the screwdriver off the screw head was determined with a spring balance. For both manufacturers, greater pull-off forces were measured when using the original screwdrivers than when using the universal screwdriver. The pull-off force (mean ± SD) required for the Straumann original screwdriver was 3.7 ± 1.4 N, while that required for the universal screwdriver was 0.1 ± 0.1 N (P < .001). The pull-off force was 1.5 ± 1.5 N for the BEGO original screwdriver and 0.7 ± 0.9 N for the universal screwdriver (P = .19). Using original manufacturer-supplied screwdrivers could thus minimize the risk of the screwdriver slipping out of the screw head during dental treatment and being swallowed or aspirated by the patient.

Does the interfacing angle between pedicle screws and support rods affect clinical outcomes after posterior thoracolumbar fusion? A retrospective clinical study

BACKGROUND CONTEXTProper alignment and tightening of the pedicle screw/rod assembly after instrumented posterior fusion of the lower spine is known to be crucial in order to achieve satisfactory clinical results. Such interfacing angle mismatches indicate stress overloading of the implant system. PURPOSEThe objective of this study is to investigate the incidence of postoperative screw/rod interfacing angle mismatch and to analyze the impact of mismatches on clinical outcome in terms of (1) revision surgery, (2) adjacent segment degeneration (ASD), and (3) pain. STUDY DESIGNThis is a monocentric retrospective observational study. PATIENT SAMPLEPatients underwent fusion surgery with pedicle screw/rod systems for predominantly degenerative pathologies. OUTCOME MEASURESPedicle screw/rod interfacing angle mismatch (mismatch is the angular deviation from 90° formed by the rod axis and the pedicle screw head axis as an indicator for missing form-fit) revision rate, ASD at the immediately adjacent cranial segment and VAS pain. METHODSRevision refers to subsequent procedures in which all or part of the original implant configuration is changed or removed. Radiographic parameters are evaluated using a/p and lateral radiographs at final follow-up. The interfacing angle mismatch between pedicle screw and rod is measured as the angle between two parallel lines on either side of each pedicle screw head and a line laterally along the associated rod. Multiple comparisons are counteracted by Bonferroni correction, adjusted significance level is at *p<.01. RESULTSPedicle screw and rod interfacing angle mismatch was found in 171/406 (42.1%) of patients undergoing fusion surgery, affecting 613/3016 (20.3%) screws. The overall revision incidence was 11.8% (48/406), and a new ASD occurred in 12.1% of all patients (49/406) with an average follow-up of 5 years. Mean VAS pain score at final follow-up was 2.0. Comparison of the two groups with and without mismatches revealed statistically significantly higher (1) numbers of revision procedures performed (26.9% vs 0.9%), (2) numbers of new ASD developed (27.5% vs 3.8%), and (3) higher VAS pain scores (2.8/10 vs 1.4/10) for cases with mismatch. When comparing patients who underwent intraoperative correction and/or reduction with those who did not, statistically significant more screw mismatches (63.4% vs 39.7%) and revision surgeries (29.3% vs 9.9%) were noted in patients who had these forceful maneuvers. CONCLUSIONSPedicle screw/rod interfacing angle mismatch is a frequent occurrence after fusion surgery. Mismatches indicate that the construct was assembled under mechanical stress. All preventable mechanical stresses, for example, unintentional uncontrolled forces on the instrumentation, should be avoided as much as possible, as they can negatively influence the clinical outcome.

Defining the Structures at Risk and an Anatomical Safe Zone for Percutaneous Antegrade Subtalar Joint Fixation With a Single Screw: A Cadaveric Study

Percutaneous antegrade (anterior to posterior) fixation for subtalar joint (STJ) arthrodesis offers various intraoperative and biomechanical advantages. Currently, the entry point for percutaneous antegrade STJ screw fixation is not clearly described and variable. To our knowledge, there are no publications that evaluate anatomic structures at risk or define an anatomically safe entry point for this fixation. The aim of this investigation was to define an anatomically safe and reproducible entry point for percutaneous antegrade STJ arthrodesis fixation, while also describing anatomic structures at risk when undertaking this method of fixation. We hypothesized that percutaneous single screw antegrade STJ fixation would encroach upon named anatomic structures in more than one cadaveric specimen. Ten cadaver limbs were used in this investigation. A percutaneous guidewire was inserted 5 mm lateral to the tibialis anterior tendon. The midpoint of the talar neck served as the sagittal plane starting point, as seen on the lateral fluoroscopic view. A cannulated 6.5-mm headed screw was inserted antegrade through the STJ into the calcaneus. Each specimen was dissected to assess the distance from the screw to nearby anatomic structures and distance from the tibialis anterior tendon to named structures. Our hypothesis was found to be incorrect, as 0/10 screws invaded neurovascular or tendinous structures. The dorsalis pedis artery and deep peroneal nerve were on average 12.1 ± 2.79 mm and 12.2 ± 2.82 mm lateral to the screw, respectively. These findings are clinically relevant and ultimately allow us to define an anatomic safe starting point for percutaneous antegrade STJ single screw fixation.