Objectives. Third-body wear is believed to be one trigger for adverse results with metal-on-metal (MOM) bearings. Impingement and subluxation may release metal particles from MOM replacements. We therefore challenged MOM bearings with relevant debris types of cobalt–chrome alloy (CoCr), titanium alloy (Ti6Al4V) and polymethylmethacrylate bone cement (PMMA). Methods. Cement flakes (PMMA), CoCr and Ti6Al4V particles (size range 5 µm to 400 µm) were run in a MOM wear simulation. Debris allotments (5 mg) were inserted at ten intervals during the five million cycle (5 Mc) test. . Results. In a clean test phase (0 Mc to 0.8 Mc), lubricants retained their yellow colour. Addition of metal particles at 0.8 Mc turned lubricants black within the first hour of the test and remained so for the duration, while PMMA particles did not change the colour of the lubricant. Rates of wear with PMMA, CoCr and Ti6Al4V debris averaged 0.3 mm. 3. /Mc, 4.1Â mm. 3. /Mc and 6.4 mm. 3. /Mc, respectively. . Conclusions. Metal particles turned simulator lubricants black with rates of wear of MOM bearings an order of magnitude higher than with control PMMA particles. This appeared to model the findings of black, periarticular joint tissues and high CoCr wear in failed MOM replacements. The amount of wear debris produced during a 500 000-cycle interval of gait was 30 to 50 times greater than the weight of triggering particle allotment, indicating that MOM bearings were extremely sensitive to third-body wear. Cite this article: Bone Joint Res 2015;4:29–37

Abstract. Introduction. Back pain affects 80% of the population at some stage in their life with significant costs to society. Mechanisms and causes of pain have been investigated by studying the behaviour of functional spinal units (FSUs) subjected to displacement- or load control protocols in 6 degrees of freedom (DOF). Load control allows specimens to move physiologically in response to applied loads whereas displacement control constrains motion to individual axes. The displacement control system of the Bath University six-axis spine simulator has been validated and the load control system is in the process of iterative development. Objectives. The objective was to build a computational model of the spine simulator to develop a complete 6 DOF load control system to enable accurate specimen testing under load control. Methods. SolidEdge part files of the simulator assembly exported to MATLAB Simulink® were used to generate a full model of the simulator. Results from displacement tests using a helical spring specimen in the simulator were used to validate the performance of the simulator model in displacement control. The model was then used to develop a 6 DOF load control system including matrix transformations to ensure correct load tracking. Results. Model results for displacement control matched the physical test data within 12% and replicated coupling loads. The developed load control model demonstrated good control in all 6 axes, maintaining zero-commanded loads. Furthermore, peak-to-peak errors in non-zero-commanded loads and moments were below 10% and 15% respectively. Conclusions. The computational model proved a valuable tool in understanding the assembly and functioning of the spine simulator. The in-silico development and validation of the 6 DOF load control system will allow seamless implementation of load control within the spine simulator. The ultimate outcome of this will be the ability to assess the behaviour of FSUs subjected to biofidelic loading conditions

Abstract. BACKGROUND. Hemi-arthroplasty (HA) as a treatment for fractured neck of femur has slightly increased since 2019 and remarkably after the COVID pandemic. The main drawback of the treatment is ongoing cartilage deterioration that may require revision to THR. OBJECTIVE. This study assessed cartilage surface damage in hip HA by reproducing anatomical motion and loading conditions in a hip simulator. METHODS. Experimental design. HA tests were conducted using porcine acetabula and CoCr femoral heads. Five groups (n=4) were included: a control group comprising natural tissue and four HA groups where the acetabula were paired with metal heads to allow radial clearance (RC) classed as small (RC<0.6mm), large (2mm<RC<4mm), extra-large (4mm<RC), and oversized (RC<−0.6mm). Tests were carried out in an anatomical hip simulator that reproduced a simplified twin peak gait cycle, adapted for porcine hip joints, from the ISO 14242 standard for wear of THR prostheses (peak load of 900N). The test length was 6 hours, with photogrammetry taken at 1-hour intervals. Ringers solution was used as a lubricant. RESULTS. No changes were observed in the control group. However, cartilage surface changes were observed in all hemi-arthroplasty groups. Discolouration on the cartilage surface was noticeable at the posterior-superior part of the acetabulum after 1-hour (extra-large and oversized groups). Damage severity and location were characteristic of each clearance group. Of all the groups, the oversized group showed more significant damage. No labrum separation was seen after the simulation. CONCLUSIONS. These results are relevant to understand the effect of femoral head clearance on cartilage damage risk after HA. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Orthopaedic training sessions, vital for surgeons to understand post-operative joint function, are primarily based on passive and subjective joint assessment. However, cadaveric knee simulators, commonly used in orthopaedic research,. 1. could potentially benefit surgical training by providing quantitative joint assessment for active functional motions. The integration of cadaveric simulators in orthopaedic training was explored with recipients of the European Knee Society Arthroplasty Travelling Fellowship visiting our institution in 2018 and 2019. The aim of the study was to introduce the fellows to the knee joint simulator to quantify the surgeon-specific impact of total knee arthroplasty (TKA) on the dynamic joint behaviour, thereby identifying potential correlations between surgical competence and post-operative biomechanical parameters. Eight fellows were assigned a fresh-frozen lower limb each to plan and perform posterior-stabilised TKA using MRI-based patient-specific instrumentation. Surgical competence was adjudged using the Objective Structured Assessment of Technical Skills (OSATS) adapted for TKA. 2. All fellows participated in the in vitro specimen testing on a validated knee simulator,. 3. which included motor tasks – passive flexion (0°-120°) and active squatting (35°-100°) – and varus-valgus laxity tests, in both the native and post-operative conditions. Tibiofemoral kinematics were recorded with an optical motion capture system and compared between native and post-operative conditions using a linear mixed model (p<0.05). The Pearson correlation test was used to assess the relationship between the OSATS scores for each surgeon and post-operative joint kinematics of the corresponding specimen (p<0.05). OSATS scores ranged from 79.6% to 100% (mean=93.1, SD=7.7). A negative correlation was observed between surgical competence and change in post-operative tibial kinematics over the entire range of motion during passive flexion – OSATS score vs. change in tibial abduction (r=−0.87; p=0.003), OSATS score vs. change in tibial rotation (r=−0.76; p=0.02). When compared to the native condition, post-operative tibial internal rotation was higher during passive flexion (p<0.05), but lower during squatting (p<0.033). Post-operative joint stiffness was greater in extension than in flexion, without any correlation with surgical competence. Although trained at different institutions, all fellows followed certain standard intraoperative guidelines during TKA, such as achieving neutral tibial abduction and avoiding internal tibial rotation,. 4. albeit at a static knee flexion angle. However, post-operative joint kinematics for dynamic motions revealed a strong correlation with surgical competence, i.e. kinematic variability over the range of passive flexion post-TKA was lower for more skilful surgeons. Moreover, actively loaded motions exhibited stark differences in post-operative kinematics as compared to those observed in passive motions. In vitro testing on the knee simulator also introduced the fellows to new quantitative parameters for post-operative joint assessment. In conclusion, the inclusion of cadaveric simulators replicating functional joint motions could help quantify training paradigms, thereby enhancing traditional orthopaedic training, as was also the unanimous opinion of all participating fellows in their positive feedback

To investigate the utility of virtual reality (VR) simulators in improving surgical proficiency in Orthopaedic trainees for complex procedures and techniques. Fifteen specialty surgeons attending a London Orthopaedic training course were randomised to either the VR (n = 7) or control group (n = 8). All participants were provided a study pack comprising an application manual and instructional video for the Trochanteric Femoral Nail Advanced (TFNA) procedure. The VR group underwent additional training for TFNA using the DePuy Synthes (Johnson and Johnson) VR simulator. All surgeons were then observed applying the TFNA in a Sawbones model and assessed by a blinded senior consultant using three metrics: time to completion, 22-item procedure checklist and 5-point global assessment scale. Participant demographics for the VR and control groups were similar in context of age (mean [SD]: VR group, 31.0 [2.38] years; control group, 30.6 [2.39] years), gender (VR group, 5 [71%] men; control group, 8 [100%] men) and prior experience with TFNA (had applied TFNA as primary surgeon: VR group, 6 [86%]; control group, 7 [88%]). Although statistical significance was not reached, the VR group, on average, outperformed the control group on all three metrics. They completed the TFNA procedure faster (mean [SD]: 18.2 [2.16] minutes versus 19.78 [1.32] minutes; p<0.189), performed a greater percentage of steps correctly (79% versus 66%; p<0.189) and scored a higher percentage on the global assessment scale (75% versus 65%; p<0.232). VR simulators offer a safe and accessible means for Orthopaedic trainees to prepare for and supplement their theatre-based experience. It is vital, therefore, to review and validate novel simulation-based systems and in turn facilitate their improvement. We intend to increase our sample size and expand this preliminary study through a second upcoming surgical course for Orthopaedic trainees in London

Background. A new knee simulator has been developed at Ghent University. This simulator provides the unique opportunity of evaluating the knee kinematics during activities of daily living. The simulator therefore controls the position of the ankle in the sagittal plane while keeping the hip at a fixed position. This approach provides full kinematic freedom to the knee. To evaluate and validate the performance of the simulator, the development of and comparison with a numerical simulation model is discussed in this paper. Methods. Both a two and three dimensional simulation model have been developed using the AnyBody Modelling System (AMS). In the two dimensional model, the knee joint is represented by a hinge. Similarly, the ankle and hip joint are represented by a hinge joint and a variable amplitude quadriceps and hamstrings force is applied. In line with this simulation model, a hinge model was created that could be mounted in the UGent knee simulator to evaluate the performance of the simulated model. The hinge model thereby performs a cyclic motion under varying simulated muscle loads while recording the ankle reaction forces. In addition to the two dimensional model, a three dimensional model has been developed. More specifically, a model is built of a sawbone leg holding a posterior stabilised single radius total knee implant. The physical sawbone model contains simplified medial and lateral collateral ligaments. In line with the boundary conditions of the UGent knee simulator, the simulated hip contains a single rotational degree of freedom and the ankle holds four degrees of freedom (three rotations, single translation). In the simulations, the knee is modelled using the force-dependent kinematics (FDK) method built in the AMS. This leaves the knee with six degrees of freedom that are controlled by the ligament tension in combination with the applied quadriceps load and shape of the implant. The physical sawbone model goes through five cycles in the UGent simulator using while recording the kinematics of the femur and tibia using a set of markers rigidly attached to the femur and tibia bone. The position of the implant with respect to the markers was evaluated by CT-scanning the sawbone model. Results and Discussion. In a first step, the reaction forces at the ankle in the 2D model were evaluated. The difference between the simulated and measured reaction force is limited and can be explained from a slight variation of the attachment point of the simulated muscle loads. For the 3D model, the kinematic patterns have been evaluated for both the simulation and physical model using Grood & Suntay definitions. The kinematic parameters display realistic trends, however, no exact match has been obtained for all parameters so far. The latter might be attributed to a number of simplifications in the simulation model as well as elastic deformation of the physical sawbone model. Conclusion. A three dimensional model of a knee implant in the UGent Knee Simulator has been developed. The simulated kinematic patterns appear realistic though no exact match with the measured patterns has been obtained. Future research will therefore focus on the development of a more realistic experimental and numerical model

Background. In-vitro testing of knee joints remains vital in the understanding of knee surgery and arthroplasty. However, based on the design philosophy of the original Oxford knee simulator, this in-vitro testing has mainly focused on squatting motion. As the activities of daily living might drastically differ from this type of motion, both from a kinematic and kinetic point of view, a new knee simulator is required that allows studying more random motion patterns. This paper describes a novel knee simulator that overcomes the limitations of traditional Oxford simulators, providing both kinematic and kinetic freedom with respect to the applied boundary conditions. Methods. This novel test simulator keeps the hip at a fixed position, only providing a single rotational degree of freedom (DOF) in the sagittal plane. In addition, the ankle holds four DOF, including all rotational DOF and the translation along the medio-lateral axis. Combining these boundary conditions leaves five independent DOF to the knee; the knee flexion angle is actively controlled through the positioning of the ankle joint in the antero-posterior and proximal-distal direction. The specimens' quadriceps muscle is actively controlled, the medial and lateral hamstrings are passively loaded. To validate the performance of this simulator, two fresh frozen specimens have been tested during normal squatting and cycling. Their kinematic patterns have been compared to relevant literature data. Results. Kinematic patterns in line with literature data are observed for the squatting motion, e.g. displaying femoral rollback for both specimens. In contrast, the kinematic patterns that are observed during cycling differ remarkably from the patterns of the squatting movement. Conclusion. The results provide confidence in the working principle of the presented knee simulator, the mechanical design and all processing steps. In addition, the remarkable differences observed in kinematic patterns between different studied motions indicate the need for broadening the research view to relevant motion patterns, beyond squatting

Variations in component positioning of total hip replacements can lead to edge loading of the liner, and potentially affect device longevity. These effects are evaluated using ISO 14242:4 edge loading test results in a dynamic system. Mediolateral translation of one of the components during testing is caused by a compressed spring, and therefore the kinematics will depend on the spring stiffness and damping coefficient, and the mass of the translating component and fixture. This study aims to describe the sensitivity of the liner plastic strain to these variables, to better understand how tests using different simulator designs might produce different amounts of liner rim deformation. A dynamic explicit deformable finite element model with 36mm Pinnacle metal-on-polyethylene bearing geometry (DePuy Synthes, Leeds, UK) was used with material properties for conventional UHMWPE. Setup was 65° clinical inclination, 4mm mismatch, 70N swing phase load, and 100N/mm spring. Fixture mass was varied from 0.5-5kg, spring damping coefficient was varied from 0-2Ns/mm. They were changed independently, and in combination. Maximum separation values were relatively insensitive to changes in the mass, damping coefficient, or both. The sensitivity of peak plastic strain, to this range of inputs, was similar to changing the swing phase load from 70N to approximately 150N – 200N. Increasing the fixture mass and/or damping coefficient increased the peak plastic strain, with values from 0.15-0.19. Liner plastic deformation was sensitive to the spring damping and fixture mass, which may explain some of the differences in fatigue and deformation results in UHMWPE liners tested on different machines or with modified fixtures. These values should be described when reporting the results of ISO14242:4 testing. Acknowledgements. Funded by EPSRC grant EP/N02480X/1; CAD supplied by DePuy Synthes

Wear of polymeric glenoid components has been identified as a cause of loosening and failure of shoulder implants1,2 in vivo. A small number of shoulder joint simulators have been built for in vitro wear testing, however none have been capable of testing with physiological motion patterns in three axes and with physiological loading. The Newcastle Shoulder Wear Simulator was designed with three axes of motion, which are programmable so that different activities of daily living might be replicated. The simulator uses three pneumatic cylinders with integral position encoders to move five shoulder prostheses simultaneously in the flexion-extension, abduction-adduction, and internal-external rotation axes. Axial loading is applied with pneumatic cylinders supplied from a pneumatic proportional valve via a manifold, which also supplies a sixth static control station. In order to establish if that the machine can actually perform as intended, commissioning trials were conducted replicating lifting a 0.5 Kg weight to head height as a daily living activity. During the commissioning trials JRI Orthopaedics Reverse VAIOS shoulder prostheses were tested in 50% bovine serum at ambient temperature. The results show that the shoulder joint wear simulator can satisfactorily reproduce a daily living activity deliberately selected for having a large range of motion and loading. Other daily activities, such as drinking from a mug, are less demanding in the ranges of motion and loading and represent no difficulty in being reproduced on the simulator. Now successfully commissioned, this new multi-station shoulder wear simulator can wear test current and new designs of shoulder prosthesis in vitro

Drilling through bone is a complex action that requires precise motor skills of an orthopedic surgeon. In order to minimize plunging and soft tissue damage, the surgeon must halt drill progression precisely following penetration of the far cortex. The purpose of this study was to create a low-cost and easy-to-use drilling simulator to train orthopedic residents in reducing the drill plunging depth. This prospective observational study was performed in the division of orthopedic surgery of a single tertiary medical center. The participants included 13 residents and 7 orthopedic specialists. The simulator consisted of a synthetic femur bone model and ordinary modeling clay, and the training unit consisted of a disposable plastic tube (∼US$14), clamps (∼US$58) and a power drill + drill bit (standard hospital equipment). Plunging depths were measured by the simulator and compared between orthopedic specialists, the 6 “senior residents” (3+ years) and the 7 “junior residents” during a training session. Measurements were taken again 2 weeks following the training session. Initially, the plunging depths of the junior residents were significantly greater compared to those of the orthopedic specialists (7.00 mm vs 5.28 mm, respectively, p < 0.038). There was no similarly significant difference between the senior residents and the orthopedic experts ([6.33 mm vs. 5.28 mm, respectively; p = 0.18). The senior residents achieved plunging depths of 5.17 mm at the end of the training session and 4.7 mm 2 weeks later compared to 7.14 mm at the end of the training session and 6 mm 2 weeks later for the junior residents. This study demonstrated the capability of a low-cost drilling simulator as a training model for reducing the plunging depth during the drilling of bone and soft tissue among junior and senior residents

Understanding the long-term effects of total knee arthroplasty (TKA) on joint kinematics is vital to assess the success of the implant design and surgical procedure. However, while in vitro cadaveric studies quantifying post-operative biomechanics primarily reflect joint behaviour immediately after surgery,. 1. in vivo studies comprising of follow-up TKA patients often reflect joint behaviour a few months after surgery. 2. Therefore, the aim of this cadaveric study was to explore the long-term effects of TKA on tibiofemoral kinematics of a donor specimen, who had already undergone bilateral TKA, and compare them to post-operative kinematics reported in the literature. Two fresh-frozen lower limbs from a single donor (male, age: 83yr, ht: 1.83m, wt: 86kg), who had undergone bilateral TKA (Genesis II, Smith&Nephew, Memphis, USA) 19 years prior to his demise, were obtained following ethical approval from the KU Leuven institutional board. The specimens were imaged using computed tomography (CT) and tested in a validated knee simulator. 3. replicating active squatting and varus-valgus laxity tests. Tibiofemoral kinematics were recorded using an optical motion capture system and compared to various studies in the literature using the same implant – experimental studies based on cadaveric specimens (CAD). 1,4. and an artificial specimen (ART). 5. , and a computational study (COM). 6. . Maximum tibial abduction during laxity tests for the left leg (3.54°) was comparable to CAD (3.30°), while the right leg exhibited much larger joint laxity (8.52°). Both specimens exhibited valgus throughout squatting (left=2.03±0.57°, right=5.81±0.19°), with the change in tibial abduction over the range of flexion (left=1.89°, right=0.64°) comparable to literature (CAD=1.28°, COM=2.43°). The left leg was externally rotated (8.00±0.69°), while the right leg internally rotated (−15.35±1.50°), throughout squatting, with the change in tibial rotation over the range of flexion (left=2.61°, right=4.79°) comparable to literature (CAD=5.52°, COM=4.15°). Change in the femoral anteroposterior translation over the range of flexion during squatting for both specimens (left=14.88mm, right=6.76mm) was also comparable to literature (ART=13.40mm, COM=20.20mm). Although TKA was reportedly performed at the same time on both legs of the donor by the same surgeon, there was a stark difference in their post-operative joint kinematics. A larger extent of intraoperative collateral ligament release could be one of the potential reasons for higher post-operative joint laxity in the right leg. Relative changes in post-operative tibiofemoral kinematics over the range of squatting were similar to those reported in the literature. However, differences between absolute magnitudes of joint kinematics obtained in this study and findings from the literature could be attributed to different surgeons performing TKA, with presumable variations in alignment techniques and/or patient specific instrumentation, and the slightly dissimilar ranges of knee flexion during squatting. In conclusion, long-term kinematic effects of TKA quantified using in vitro testing were largely similar to the immediate post-operative kinematics reported in the literature; however, variation in the behaviour of two legs from the same donor suggested that intraoperative surgical alterations might have a greater effect on joint kinematics over time

Summary Statement. In the present hip simulator studies, bearings with the newest generation of HXLPE, stabilised with vitamin E, did not show increased wear under severe conditions, such as accelerated ageing, component mal-orientation and third body wear. Introduction. Unfortunately, acetabular hip components cannot always be implanted in optimal condition. Therefore, we performed hip simulator studies with cups made from highly cross-linked, vitamin E stabilised UHMWPE in i) artificially aged condition, ii) with an inclination angle corresponding to 80 ° in vivo and iii) with third bodies coming from the Ti coating of the acetabular cup. Methods. For these hip simulator studies, seleXys cup inlays, size 28/EE, and RM Pressfit samples 50/28 (Mathys Ltd Bettlach, Switzerland) were used. Standard PE parts and vitamys® inlays (highly cross-linked, vitamin E stabilised UHMWPE) were tested in the same series. PE cups were machined out of sintered GUR 1020 slabs, packaged and gamma-sterilised in inert atmosphere at 30 kGy. The vitamys® material was made in-house by adding 0.1 wt.-% of vitamin E (Merck KGaA, Darmstadt/Germany) to GUR 1020 powder from Ticona GmbH, Kelsterbach/Germany. Cross-linking used 100 kGy gamma-irradiation and the final sterilisation was gas plasma. Artificial ageing was done under pressurised oxygen at 70 °C according to ASTM F2003 for 14 days (standard PE) and 60 days (vitamys®), respectively. The hip simulator test protocol of ISO 14242 was kept for the artificially aged cups, but the inclination angle altered to 80 ° for the test with the steep cup position. In the third test, the test fluid (diluted bovine serum stabilised with sodium azide and EDTA) was altered by adding about 10 Ti particles to the bearing for the first million cycles. This test condition imitates third body wear by particles shed from the coating of the RM cups. All testing was conducted at the RMS Foundation (Bettlach / Switzerland) on a servo-hydraulic six-station hip simulator (Endolab, Thansau/Rosenheim, Germany) at a temperature of 37±1°C. At lubricant change interval of 500’000 cycles, the inlays were measured gravimetrically with an accuracy of 0.01 mg. Results. The wear rate of the standard UHMWPE in the condition aged for 14 days reached 45 mg/Mcycle, corresponding to a 57 % increase over non-aged cups. For the vitamys® cups, the wear rate was virtually unchanged even after 60 days ageing (5.8 mg/Mcycle vs. 5.9 mg/Mcycle). For standard UHMWPE tested with an inclination of 80°, wear was 16% lower than those of the inlays with 45° inclination. Whereas for the vitamys® inlays, the wear rate was about the same for both inclination angles (5.4 mg/Mcycle vs. 5.9 mg/Mcycle,). The addition of Ti particles increased the wear rate of standard UHMWPE to 35 mg/Mcycle. However, vitamys® was hardly affected by the third bodies: the wear rate stood at 7.8 mg/Mcycle. Conclusions. Based on the present simulator study, it seems that hip bearings with the newest generation of HXLPE, stabilised with vitamin E, are exempt from increased wear rate when subjected to severe conditions, such as accelerated ageing, component mal-orientation and third body wear

Summary Statement. The tensile properties of a number of synthetic fibre constructs and porcine MCLs were experimentally determined and compared to allow the selection of an appropriate synthetic collateral ligament model for use in a kinematic knee simulator. Introduction. As patient expectations regarding functional outcomes of total knee arthroplasty rise the need to assess the kinematics of new implants in vitro has increased. This has traditionally been done using cadaveric models, which can demonstrate high physiological relevance but also substantial inter-specimen variability. More recently there has been a shift towards the use of in silico and non-cadaveric methods. Such methods require significant simplifications of the joint and the modelling of soft tissue structures such as the collateral ligaments. Collateral ligaments are often modelled in in silico studies but have not, in the published literature, been modelled in in vitro knee kinematic simulators. Tensile testing of ligament tissue, to provide reference data, and the subsequent analysis of potential synthetic analogues was carried out. The overall aim of the study was to develop a synthetic ligament analogue for use in kinematic knee simulators. Methods. Porcine MCLs were chosen as these are of a similar size and are a readily available alternative to human ligaments. Six porcine knee specimens were sourced and the MCLs dissected by an orthopaedic registrar. Testing was carried out on an Instron MTS fitted with a 5kN load cell. Each specimen was subjected to 5 pre-conditioning loading cycles before cross-sectional and length measurements were made. Each specimen was then cyclically loaded from 0–200N for 30 cycles before being loaded to failure at a rate of 100mm/min. Ten potential synthetic analogues were also assessed using the same procedure: the Lars 80 (Corin Ltd) synthetic ligament reconstruction system and a selection of readily available synthetic constructs. Results. The porcine specimens demonstrated 6% ± 1% strain (mean ± standard error) after 30 cycles of loading, and a tensile stiffness of 100 N/mm ± 8.9 N/mm. The results of the load to failure tests also indicated a substantial toe region and highlighted the substantial variability associated with cadaveric specimens. The Lars system demonstrated a tensile stiffness of nearly 9 times that of the porcine specimens. However, non-parametric Mann-Whitney U analyses indicated that three of the synthetic samples did not have statistically significantly different tensile stiffness values compared to the porcine specimens (p < 0.05). Of these samples, the polyester braided cord demonstrated the longest and most physiologically relevant toe region. All of the polyester load-displacement traces fell within the range demonstrated by the porcine specimens. Discussion/Conclusion. The tensile properties of the porcine specimens analysed were similar to those reported in in the literature for human ligaments1. Porcine MCLs are thus a fair model of human collateral ligaments and were a suitable reference material for the selection of a synthetic analogue. The tensile testing carried out in the present study indicated that commercially available synthetic ligaments are over engineered in terms of strength and inappropriate for use in kinematic analysis. However, a polyester braided cord did demonstrate appropriate basic mechanical properties and would be appropriate as an analogue model on kinematic knee rigs

Background. Training within surgery is changing from the traditional Halstedian apprenticeship model. There is need for objective assessment of trainees, especially their technical skills, to ensure they are safe to practice and to highlight areas for development. In addition, due to working time restrictions in both the UK and the US, theatre time is being limited for trainees, reducing their opportunities to learn such technical skills. Simulation is one adjunct to training that can be utilised to both assess trainees objectively, and provide a platform for trainees to develop their skills in a safe and controlled environment. The insertion of a dynamic hip screw (DHS) relies on complex psychomotor skills to obtain an optimal implant position. The tip-apex distance (TAD) is a measurement of this positioning, used to predict failure of the implant. These skills can be obtained away from theatre using workshop bone simulation, however this method does not utilise fluoroscopy due to the associated radiation risks. FluoroSim is a novel digital fluoroscopy simulator that can recreate digital radiographs with workshop bone simulation for the insertion of a DHS guide-wire. In this study, we present the training effect demonstrated on FluoroSim. The null hypothesis states that no difference will be present between users with different amounts of exposure to FluoroSim. Methods. Medical students were recruited from three London universities and randomised into a training (n=23) and a control (n=22) cohort. All participants watched a video explanation of the simulator and task and were blinded to their allocation. Training participants completed 10 attempts in total, 5 attempts in week one, followed by a one week wash out period, followed by 5 attempts in week 2. The control group completed a single attempt each week. For each attempt, 5 metrics were recorded; TAD, procedural time, number of radiographs, number of guide-wire retires and cut-out rate (COR). Results. No significant difference was present for any metric between the groups at baseline; randomisation had produced heterogeneous groups minimising selection bias. Intragroup training effect (comparison of initial and last attempt) was significant for all metrics in the training group (p < 0.05) but for no metrics in the control group. The intergroup training effect (comparison of training group attempt ten to control group attempt ten) was present for procedural time, number of radiographs and number of guide-wire retries (p < 0.05). Significance was not reached for TAD and COR. Conclusion. FluoroSim shows skill acquisition with repeat exposure, so the null hypothesis can be rejected. This study has demonstrated the merits of FluoroSim as a training adjunct for psychomotor skill development in a DHS setting

Background. Trust in the validity of a measurement tool is critical to its function in both clinical and educational settings. Acetabular cup malposition within total hip arthroplasty (THA) can lead to increased dislocation rates, impingement and increased wear as a result of edge loading. We have developed a THA simulator incorporating a foam/Sawbone pelvis model with a modified Microsoft HoloLens® augmented reality (AR) headset. We aimed to measure the trueness, precision, reliability and reproducibility of this platform for translating spatial measurements of acetabular cup orientation to angular values before developing it as a training tool. Methods. A MicronTracker® stereoscopic camera was integrated onto a HoloLens® AR system. Trueness and precision values were obtained through comparison of the AR system measurements to a gold-standard motion capture system”s (OptiTrack®) measurements for acetabular cup orientation on a benchtop trainer, in six clinically relevant pairs of anteversion and inclination angles. Four surgeons performed these six orientations, and repeated each orientation twice. Pearson”s coefficients and Bland-Altman plots were computed to assess correlation and agreement between the AR and Motion Capture systems. Intraclass correlation coefficients (ICC) were calculated to evaluate the degree of repeatability and reproducibility of the AR system by comparing repeated tasks and between surgeons, respectively. Results. The trueness of the AR system was 0.24° (95% CI limit 0.92°) for inclination and 0.90° (95% CI limit 1.8°) for anteversion. Precision was 0.46° for inclination and 0.91° for anteversion. There was significant correlation between the two methods for both inclination (r = 0.996, p<0.001) and anteversion (r = 0.974, p<0.001). Repeatability for the AR system was 0.995 for inclination and 0.989 for anteversion. Reproducibility for the AR system was 0.999 for inclination and 0.995 for anteversion. Conclusion. Measurements obtained from the enhanced HoloLens® AR system were accurate and precise in regards to determining angular measurements of acetabular cup orientation. They exceeded those of currently used methods of cup angle determination such as CT and computer-assisted navigation. Measurements obtained were also highly repeatable and reproducible, therefore this platform is accurately validated for use in a THA training simulator

We report the findings from independent prospective clinical and laboratory-based joint-simulator studies of the performance of ceramic femoral heads of 22.225 mm diameter in cross-linked polyethylene (XLP) acetabular cups. We found remarkable qualitative and quantitative agreement between the clinical and simulator results for the wear characteristics with time, and confirmed that ceramic femoral heads penetrate the XLP cups at only about half the rate of otherwise comparable metal heads. In the clinical study, 19 hips in 17 patients were followed for an average of 77 months. In the hip-joint simulator a similar prosthesis was tested for 7.3 million cycles. Both clinical and simulator results showed relatively high rates of penetration over the first 18 months or 1.5 million cycles, followed by a very much lower wear thereafter. Once an initial bedding-in of 0.2 mm to 0.4 mm had taken place the subsequent rates of penetration were very small. The initial clinical wear during bedding-in averaged 0.29 mm/year; subsequent progression was an order of magnitude lower at about 0.022 mm/year, lower than the 0.07 mm/year in metal-to-UHMWP Charnley LFAs. Our results show the excellent tribological features of alumina-ceramic-to-XLP implants, and also confirm the value of well-designed joint simulators for the evaluation of total joint replacements

In vitro the introduction of microseparation and edge loading to hip simulator gait cycle has replicated clinically relevant wear rates and wear mechanisms in ceramic-on-ceramic bearings. [1]. , and elevated the wear rates of MoM surface replacements (SR) to levels similar to those observed in retrievals. [2]. The aim was to assess the wear of two different sized MoM total hip replacement bearings under steep cup inclination angles and adverse microseparation and edge loading conditions. Two tests were performed on the Leeds II hip joint simulator using two different size bearings (28mm and 36mm). Cups were mounted to provide inclination angles of 45 degrees (n=3) and 65 degrees (n=3). The first three million cycles were under standard gait conditions. Microseparation and edge loading conditions as described by Nevelos et al. [1]. were introduced to the gait cycle for the subsequent three million cycles. The lubricant was 25% new born calf serum. The mean wear rates and 95% confidence limits were determined and statistical analysis was performed using One Way ANOVA. Under standard gait conditions, when the cup inclination angle increased from 45 degrees to 65 degrees, the wear of size 28mm bearing significantly (p=0.004) increased by 2.7-fold, however, the larger bearings did not show any increase in wear (p=0.9). The introduction of microseparation conditions resulted in a significant (p=0.0001) increase in wear rates for both bearing sizes under both cup inclination angle conditions. Under microseparation conditions, the increase in cup inclination angle had no influence on the wear rate for both bearing sizes (Figure 1). With larger bearings, head-rim contact occurs at a steeper cup inclination angle providing an advantage over smaller bearings. The introduction of edge loading and microseparation conditions resulted in a significant increase in wear rates for both bearing sizes. The wear rates obtained in this study under combined increased cup inclination angle and microseparation were half of those obtained when SR MoM bearings were tested under similar adverse conditions. [2]. This study shows the importance of prosthesis design and accurate surgical positioning of the head and acetabular cup in MoM THRs

Background. Hip fractures cause significant morbidity and mortality, affecting 70,000 people in the UK each year. The dynamic hip screw (DHS) is used for the osteosynthesis of extracapsular neck of femur fractures, a procedure that requires complex psychomotor skills to achieve optimal lag screw positioning. The tip-apex distance (TAD) is a measure of the position of the lag screw from the apex of the femoral head, and is the most comprehensive predictor of cut-out (failure of the DHS construct). To develop these skills, trainees need exposure to the procedure, however with the European Working Time Directive, this is becoming harder to achieve. Simulation can be used as an adjunct to theatre learning, however it is limited. FluoroSim is a digital fluoroscopy simulator that can be used in conjunction with workshop bones to simulate the first step of the DHS procedure (guide-wire insertion) using image guidance. This study assessed the construct validity of FluoroSim. The null hypothesis stated that there would be no difference in the objective metrics recorded from FluoroSim between users with different exposure to the DHS procedure. Methods. This multicentre study recruited twenty-six orthopaedic doctors. They were categorised into three groups based on the number of DHS procedures they had completed as the primary surgeon (novice <10, intermediate 10≤x<40 and experienced ≥40). Twenty-six participants completed a single DHS guide-wire attempt into a workshop bone using FluoroSim. The TAD, procedural time, number of radiographs, number of guide-wire retires and cut-out rate (COR) were recorded for each attempt. Results. A significant construct effect was seen for TAD and COR between novice and other users (p < 0.05). The intermediate and experienced users were not significantly different for these metrics. For all other metrics, experienced users had the highest score, contrary to expectation. Conclusion. FluoroSim was able to separate novice users from other cohorts for the two clinically significant outcome metrics. We can therefore partially reject the null hypothesis as construct validity was present for TAD and COR. We have demonstrated that FluoroSim has the potential to be a useful adjunct when learning the psychomotor skills needed for the DHS procedure away from theatre

No proven long-term joint-preserving treatment options exist for patients with irreparable meniscal damage. This study aimed to assess gait kinematics and contact pressures of novel fibre-matrix reinforced polyvinyl alcohol-polyethylene glycol (PVA-PEG) hydrogel meniscus implanted ovine stifle joints against intact stifles in a gait simulator. The gait simulator controlled femoral flexion-extension and applied a 980N axial contact force to the distal end of the tibia, whose movement was guided by the joint natural ligaments (Bartolo; ORS 2021;p1657- LB). Five right stifle joints from sheep aged >2 years were implanted with a PVA-PEG total medial meniscus replacement, fixed to the tibia via transosseous tunnels and interference screws. Implanted stifle joint contact pressures and kinematics in the simulator were recorded and compared to the intact group. Contact pressures on the medial and lateral condyles were measured at 55° flexion using Fujifilm Prescale Low Pressure film inserted under the menisci. 3D kinematics were measured across two 30 second captures using the Optotrak Certus motion-tracking system (Northern Digital Inc.). Medial peak pressures were not significantly different between the implanted and intact groups (p>0.4), while lateral peak pressures were significantly higher in the implanted group (p<0.01). Implanted stifle joint kinematics in the simulator did not differ significantly from the intact baseline (p>0.01), except for in distraction-compression (p<0.01). Our findings show that the fibre-matrix reinforced PVA-PEG hydrogel meniscal replacement restored the medial peak contact pressures. Similar to published literature (Fischenich; ABE 2018;46(11):1–12), the lateral peak pressures in the implanted group were higher than the intact. Joint kinematics were similar across groups, with slightly increased internal-external rotation in the implanted group. These findings highlight the effectiveness of the proposed approach and motivate future work on the development of a total meniscal replacement

Abstract. Objectives. Implant loosening remains a common cause of total ankle replacement (TAR) revision, and has been associated with wear-mediated osteolysis. Limited pre-clinical studies for TARs have been reported and the variety of experiment settings make it difficult to compare wear rates. Factors such as simulator control mechanism; whether pneumatic or electromechanical, may influence the integrity of the simulator outputs with respect to input profiles. This study compares the wear of a TAR, tested in electromechanical and pneumatic experimental simulators under identical input conditions. Methods. Twelve medium BOX® (MatOrtho Ltd) TARs (n=6 for each simulator) were tested in an electromechanical and pneumatic knee simulator (Simulation Solutions, UK) for 3 million cycles (Mc). Standard ‘Leeds’ displacement-controlled inputs were used. Kinematic performance was investigated by comparing the output profiles against the maximum demanded input values. The lubricant used was 25% new-born calf serum and wear was determined gravimetrically. Results. There was no significant difference (P=0.66) in wear rate between simulators (electromechanical = 15.96 ± 6.37mm. 3. /Mc; pneumatic = 14.51 ± 5.27mm. 3. /Mc). The electromechanical simulator (3157.06 ± 1.52N) achieved the maximum load (3150N), but the pneumatic simulator was unable to attain the demand (2542.34 ± 86.52N). Maximum AP displacement from the electromechanical simulator was 3.27 ± 0.07mm (3.1mm input), compared to 3.62 ± 0.95mm from the pneumatic simulator. Internal/external rotation angle was 7.97° ± 0.00 (8° input) and 7.24° ± 0.12 from the electromechanical and pneumatic simulators respectively. Both simulators achieved the demanded flexion angle (±15°). Conclusions. The outputs from the electromechanical simulator followed the input profiles more closely than the pneumatic simulator. Despite these differences, there was no significant influence on wear rate. The variation in kinematics between simulators was not sufficient to significantly change the tribological conditions of the TAR. The authors recommend the use of electromechanical simulators for future studies where more demanding and adverse conditions may be applied. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest