At this time the majority of acetabular replacements in total hip replacement rely on bone ingrowth or bone ongrowth. Long term success has been well established but is this success the result of good luck or good management? Numerous systems exist with the simplest perhaps being that of the placement of a hemispherical cup in a hemispherically reamed acetabulum. Beyond this, a wide variety of added complexity exists with the presumption that these increased complexities provide improved stability and hence more secure primary and secondary fixation. The computer model that has been established demonstrates the geometry of fixation of hemispherical cups as compared to rim fit cups and looks at the requirements of acetabular distortion before secure fixation can be achieved. The model attempts to explain why on some occasions an apparently ideally reamed acetabulum is not secure without some form of augmentation of fixation. The model provides a basis for considering the various options of acetabular fixation

There are nearly no studies which describe the influence of the ileotibial tract (IT) on force distribution in the knee joint in a qunatitative manner. Therfore the aim of this work was to develop a complex 3-D computer model of the lower extremity, consisting of bones, joints and muscle models describing their dynamic behaviour including a special IT model. The computer model provided the possibility to simlate training of the muscular system. Thus the computer model provided among others the possibility to simulate training of the lateral thigh muscles and vastus lateralis with the aim to tension the IT, with the option to calculate force distribution in the knee and compare it with the effect of a tibial osteotomy. Patients with varus knees were examined. Kinematic data during walking together with forceplate and EMG data wer collected, before and after tibial osteotomy. The anatomy of the patients was recorded by MRI. Gait and MRI data were the input in the new developed three dimensional computer model. The scaled geometrical data by Delp (1990) and the MRI data were combined to represent the individuals anatomy. The model of the lower extremity included 43 muscles with origins/insertions and force-length properties described by Delp (1990). The muscle model was improved by including force-velocity properties and a new muscle tendon parameter (tendon stiffness). A functional scaling method was developed to fit the muscle models to individual anatomy. The IT complex was modelled as a coupled unit of IT, tensor fascia latae and gluteus maximus. Muscle and joint forces were determined using an optimization approach minimizing the cube of the sum of muscle forces divided by their upper bounds. Simulated muscle training of the lateral thigh muscles and vastus lateralis led to an increased tensioning of the IT. As a result the lateral knee force raised considerably similar to the increase after osteotomy. However the decrease in the medial compartment was small and not comparable with the effect of a valgus osteotomy. Tensioning of the IT leads apparently to an overall larger resulting knee force stabilizing the joint, but is not able to reduce medial knee force to an extent that can avoid osteotomy

Background and Literature Research: Fixed sagittal mal-rotation of pelvis is commonly encountered in patients with ankylosing spondylitis. The pelvis positioning for total hip arthroplasty in these patients can be a pitfall to an oblivious surgeon, and gives rise to mal-positioning of the acetabular component and subsequently leads to dislocation of the arthroplasty. Objective: To quantify the effect of sagittal pelvic rotation on the positioning of acetabular component using three dimensional computer model. Materials and Methods: Ten embalmed cadaveric pelvis with intact ligaments were scanned in 1 mm slices using computed tomogram (CT). The image reconstruction was done by the software “MIMICS” in microcomputer. The resulting three dimensional models can be rotated freely using “MIMICS.” Insertion of acetabular component was stimulated in different sagittal rotation of the pelvis. The ratio of the longitudinal to the transverse dimension of the obturator foramen was noted, and the uncovered area of the acetabular components was calculated. Discussion: Pelvic rotation on the sagittal plane cannot be easily measured by radiographs. The shape of the obturator foramen on plane pelvic radiographs centered at pubic symphysis varies with the pelvic rotation on the sagittal plane and thereby serves as an indirect way to measure pelvic rotation. The shape of obturator foramen on plain radiographs therefore provided a guideline for patient positioning and the alignment of insertion of acetabular component during surgery

INTRODUCTION

Knee contact force during activities after total knee arthroplasty (TKA) is very important, since it directly affects component wear and implant loosening. While several computational models have predicted knee contact force, the reports vary widely based on the type of modeling approach and the assumptions made in the model. The knee is a complex joint, with three compartments of which stability is governed primarily by soft tissues. Multiple muscles control knee motion with antagonistic co-contraction and redundant actions, which adds to the difficulty of accurate dynamic modeling. For accurate clinically relevant predictions a subject-specific approach is necessary to account for inter-patient variability.

Background: Neglected ruptures of the tendoachilles pose a difficult surgical problem. Intervening scar tissue has to be excised which cannot be repaired by end-to-end anastamosis. Several techniques for reconstruction of chronic ruptures have been described. The flexor hallucis longus (FHL) tendon transfer is considered advantageous over other tendon transfers. One disadvantage of FHL is it has limited excursion. There are no data to determine the optimal positioning of the FHL tendon to the calcaneum.

Materials and Methods: Two computer programmes (MSC.visualNastran Desktop 2002™ and Solid Edge® V19 were used to generate a human ankle joint model. This model is able to reproduce dorsi- and plantarflexion. Different attachment points of FHL tendon transfer to the calcaneum were investigated.

Results: The lowest muscle force to produce plantarflexion (single stance heel rise) was 1355N. Plantarflexion increased for a more anterior attachment point. The maximal plantarflexion was 33.4° for anterior attachment and 24.4° for posterior attachment. There was no significant difference in these figures when the attachment point was moved to either a medial or lateral position.

Clinical relevance: Optimal FHL tendon transfer positioning is a compromise between achieving plantarflexion for normal physiological function versus the force generating capacity and limited excursion of FHL. A more posterior attachment point is advantageous in terms of power. The range of motion is 10° less than when attachment is more anterior, the arc of motion (24.4°) is still physiological. We recommend that FHL is transferred to the calcaneum in a posterior position.

Data from the wait list management system and hospital databases was used to develop a computer model simulating the resource requirements required during patient flow into, through, and out of orthopaedic surgery for TKR, THR and knee arthroscopy. Results from the simulation model suggested that inpatient beds, rather than operating room time was the constraining resource and an extra twenty-five beds and 30% more OR time would stabilize and subsequently reduce the wait time at the institution. In addition, simulations suggested that pooling surgeon wait lists reduced patient wait time. Simulation models are an effective resource allocation decision-making tool for orthopaedic surgery. To develop and implement a wait list simulation model to analyze the existing system and guide resource allocation decision-making at the QEII Health Sciences Centre. The simulation model suggests an immediate increase in inpatient surgical beds from sixty-six to ninety-one followed by a 30% increase in OR time in thirty months to stabilize and subsequently reduce patient wait times. Simulations showed that pooling surgeon waiting lists reduced patient wait time, however, dividing orthopaedics resources among two facilities had little effect. Adding twenty-five beds reduced the wait time growth rate substantially, but not to zero, while adding fifty beds reduced the wait time growth rate to zero. Adding twenty-five beds and 30% more OR time had the same result as adding fifty beds. Simulation models can be effective for guiding resource allocation decisions for orthopaedic surgery. Recommendations based on the wait list simulation model results were immediately adopted by the provincial Department of Health. A simulation model of the orthopaedic surgery system at the institution was created using Arena simulation software. Empirical statistical distributions were developed based on Wait List Management System and administrative data to assign values to model variables: number of patient referrals seen per office session; proportion of patient referrals actually converting to a surgery booking; type of procedure required; admission status; time required for surgery; and length of stay. The model was tested, and validated. Several scenarios with adjusted levels of resources variables (OR time, number of surgeons, length of stay, inpatient bed availability) were simulated

Patients with cancer and bone metastases can have an increased risk of fracturing their femur. Treatment is based on the impending fracture risk: patients with a high fracture risk are considered for prophylactic surgery, whereas low fracture risk patients are treated conservatively with radiotherapy to decrease pain. Current clinical guidelines suggest to determine fracture risk based on axial cortical involvement of the lesion on conventional radiographs, but that appears to be difficult. Therefore, we developed a patient-specific finite element (FE) computer model that has shown to be able to predict fracture risk in an experimental setting and in patients. The goal of this study was to determine whether patient-specific finite element (FE) computer models are better at predicting fracture risk for femoral bone metastases compared to clinical assessments based on axial cortical involvement on conventional radiographs, as described in current clinical guidelines. 45 patients (50 affected femurs) affected with predominantly lytic bone metastases who were treated with palliative radiotherapy for pain were included. CT scans were made and patients were followed for six months to determine whether or not they fractured their femur. Non-linear isotropic FE models were created with the patient-specific geometry and bone density obtained from the CT scans. Subsequently, an axial load was simulated on the models mimicking stance. Failure loads normalized for bodyweight (BW) were calculated for each femur. High and low fracture risks were determined using a failure load of 7.5 × BW as a threshold. Experienced assessors measured axial cortical involvement on conventional radiographs. Following clinical guidelines, patients with lesions larger than 30 mm were identified as having a high fracture risk. FE predictions were compared to clinical assessments by means of diagnostic accuracy values (sensitivity, specificity and positive (PPV) and negative predictive values (NPV)). Seven femurs (14%) fractured during follow-up. Median time to fracture was 8 weeks. FE models were better at predicting fracture risk in comparison to clinical assessments based on axial cortical involvement (sensitivity 100% vs. 86%, specificity 74% vs. 42%, PPV 39% vs. 19%, and NPV 100% vs. 95%, for the FE computer model vs. axial cortical involvement, respectively). We concluded that patient-specific FE computer models improve fracture risk predictions of femoral bone metastases in advanced cancer patients compared to clinical assessments based on axial cortical involvement, which is currently used in clinical guidelines. Therefore, we are initiating a pilot for clinical implementation of the FE model

Patients with advanced cancer can develop bone metastases in the femur which are often painful and increase the risk of pathological fracture. Accurate segmentation of bone metastases is, amongst others, important to improve patient-specific computer models which calculate fracture risk, and for radiotherapy planning to determine exact radiation fields. Deep learning algorithms have shown to be promising to improve segmentation accuracy for metastatic lesions, but require reliable segmentations as training input. The aim of this study was to investigate the inter- and intra-operator reliability of manual segmentation of femoral metastatic lesions and to define a set of lesions which can serve as a training dataset for deep learning algorithms. F. CT-scans of 60 advanced cancer patients with a femur affected with bone metastases (20 osteolytic, 20 osteoblastic and 20 mixed) were used in this study. Two operators were trained by an experienced radiologist and then segmented the metastatic lesions in all femurs twice with a four-week time interval. 3D and 2D Dice coefficients (DCs) were calculated to quantify the inter- and intra-operator reliability of the segmentations. We defined a DC>0.7 as good reliability, in line with a statistical image segmentation study. Mean first and second inter-operator 3D-DCs were 0.54 (±0.28) and 0.50 (±0.32), respectively. Mean intra-operator I and II 3D-DCs were 0.56 (±0.28) and 0.71 (±0.23), respectively. Larger lesions (>60 cm. 3. ) scored higher DCs in comparison with smaller lesions. This study reveals that manual segmentation of metastatic lesions is challenging and that the current manual segmentation approach resulted in dissatisfying outcomes, particularly for lesions with small volumes. However, segmentation of larger lesions resulted in a good inter- and intra-operator reliability. In addition, we were able to select 521 slices with good segmentation reliability that can be used to create a training dataset for deep learning algorithms. By using deep learning algorithms, we aim for more accurate automated lesion segmentations which might be used in computer modelling and radiotherapy planning

Orthopaedic impaction-instruments are used to drive implants into the bone of the patient. Pre-clinical experimental testing protocols and computer models of those are used to assess robustness and functional efficiency of such instruments. This generally involves impaction of the instrument mounted on a substrate that should represent the mechanics of the patient. In this study, the effects of the substrate on stressing of the impaction-instruments were investigated using dynamic finite element analysis. Model results were compared with experimental data from lab protocols, which have been derived to recreate the mechanics of cadaveric implantations, which represent clinical conditions. FEA models of selected experimental protocols were created in which a simplified instrument was impacted on substrates with varying material properties and boundary conditions. After impaction, the instrument settled into a modal vibration which then decayed over time. The resulting axial strain data from the computational model was compared to strain-gauge data collected from experimental measurements. Strain signal amplitude, frequency and decay were compared. The damping-ratio was derived from the decay of the strain signal. The computational model slightly over-predicted the initial experimental strain amplitudes in all cases, but the frequency of the cyclic strain signals matched. However, the model underestimated the experimentally measured rate of signal decay. Inclusion of implant seating and soft-tissue conditions had little effect on decay. Clinical failures of impaction-instruments may be related to multiple fatigue cycles for each impaction and should be modelled accurately to allow failure prediction. Any soft substrate results in an impedance mismatch at the instrument interface, which reflects the pressure wave and causes vibration with a frequency related to the speed-of-sound in the instrument, and its geometry. While this could be accurately modelled computationally, signal decay was underestimated. Further experimental quantification of energy losses will be important to understand vibration decay

Introduction. The human wrist is a highly complex joint, offering extensive motion across various planes. This study investigates scapholunate ligament (SLL) injuries’ impact on wrist stability and arthritis risks using cadaveric experiments and the finite element (FE) method. It aims to validate experimental findings with FE analysis results. Method. The study utilized eight wrist specimens on a custom rig to investigate Scapho-Lunate dissociation. Contact pressure and flexion were measured using sensors. A CT-based 3D geometry reconstruction approach was used to create the geometries needed for the FE analysis. The study used the Friedman test with pairwise comparisons to assess if differences between testing conditions were statistically significant. Result. The study found significant variations in scaphoid and lunate bone movement based on ligament condition. Full tears increased scapholunate distance in the distal-proximal direction and decreased in the medial-lateral direction. Lunate angles shifted from flexion to extension with fully torn ligaments. Conversely, the scaphoid shifted significantly from extension to flexion with full tears. A proximal movement was observed in the distal-proximal direction in all groups, with significant differences in the partial tear group. Lateral deviation of the scaphoid and lunate occurred with ligament damage, being more pronounced in the partial tear group. All groups exhibited statistically significant movement in the volar direction, with the full tear group showing the least movement. Also, radiocarpal joint and finger contact pressure and contact area were studied. Whereas the differences in contact area were not significant, scapholunate ligament tears resulted in significantly decreased finger contact pressures. FEA confirmed these findings, showing notable peak radiocarpal contact pressure differences between intact and fully torn ligaments. Conclusion. Our study found that SLL damage alters wrist stability, potentially leading to early arthritis. The FEA model confirmed these findings, indicating the potential for the clinical use of computer models from CT scans for treatment planning

The best treatment method of large acetabular bone defects at revision THR remains controversial. Some of the factors that need consideration are the amount of residual pelvic bone removed during revision; the contact area between the residual pelvic bone and the new implant; and the influence of the new acetabular construct on the centre of rotation of the hip. The purpose of this study was to compare these variables in two of the most used surgical techniques used to reconstruct severe acetabular defects: the trabecular metal acetabular revision system (TMARS) and a custom triflanged acetabular component (CTAC). Pre- and post-operative CT-scans were acquired from 11 patients who underwent revision THR with a TMARS construct for a Paprosky IIIB defect, 10 with pelvic discontinuity, at Royal Adelaide Hospital. The CT scans were used to generate computer models to virtually compare the TMARS and CTAC constructs using a semi-automated method. The TMARS construct model was calculated using postoperative CT scans while the CTAC constructs using the preoperative CT scans. The bone contact, centre of rotation, inclination, anteversion and reamed bone differences were calculated for both models. There was a significant difference in the mean amount of bone reamed for the TMARS reconstructions (15,997 mm. 3. ) compared to the CTAC reconstructions (2292 mm. 3. , p>0.01). There was no significant difference between overall implant bone contact (TMARS 5760mm. 2. vs CTAC 5447mm. 2. , p=0.63). However, there was a significant difference for both cancellous (TMARS 4966mm. 2. vs CTAC 2887mm. 2. , p=0.008) and cortical bone contact (TMARS 795mm. 2. vs CTAC 2560mm. 2. , p=0.001). There was no difference in inclination and anteversion achieved. TMARS constructs resulted on average in a centre of rotations 7.4mm more lateral and 4.0mm more posterior. Modelling of two different reconstructions of Paprosky IIIB defects demonstrated potential important differences between all variables investigated

Background. The complex deformities in cavovarus feet may be difficult to assess and understand. Weight-bearing CT (WBCT) is increasingly used to evaluate complex deformities. However, the bone axes may be difficult to calculate in the setting of severe deformity. Computer-assisted 3D-axis calculation is a novel approach that may allow for more accurate assessment of foot alignment / deformity. The aim of this study was to assess differences in measurements done manually on 2D slices of WBCT versus 3D computer models in normal and cavus feet. Methods. We retrospectively analyzed WBCT scans from 16 normal and 16 cavus feet in patients with Charcot-Marie Tooth. Eight measurements were assessed: Talus-1. st. metatarsal angle (axial plane), Forefoot arch angle (coronal plane), and Meary's angle, calcaneal pitch, cuneiform to floor, cuneiform to skin, navicular to floor and navicular to skin distance (sagittal plane). 2D measurements were performed manually and 3D measurements were performed using specialised software (BoneLogic, DISIOR). Results. There was no significant difference in the measured variables (2D manual versus 3D automated) in normal feet. In the cavus group, 3D assessment calculated increased values for the sagittal angles: Meary's 7.3 degrees greater (p = 0.004), calcaneal pitch 2.4 degrees greater (p = 0.011)), and lower values for the axial talus-1. st. MT angle, 10.6 degrees less (p = 0.001). Conclusion. There were no significant differences in the normal group. This suggests 3D automated techniques can reliably assess the alignment of bony axes. However, the 3D axis calculations suggest there may be greater sagittal and lesser axial deformity in cavus feet than measured by 2D techniques. This discrepancy may be on account of the rotation seen in cavovarus feet, which may not be readily assessed manually. 3D automated measurements may therefore have a role in better assessing and classifying the cavus foot which may ultimately help inform treatment algorithms

Scapular notching is a common problem following reverse shoulder arthroplasty (RSA). This is due to impingement between the humeral polyethylene cup and scapular neck in adduction and external rotation. Various glenoid component strategies have been described to combat scapular notching and enhance impingement-free range of motion (ROM). There is limited data available detailing optimal glenosphere position in RSA with an onlay configuration. The purpose of this study was to determine which glenosphere configurations would maximise impingement free ROM using an onlay RSA prosthesis. A three-dimensional (3D) computed tomography (CT) scan of a shoulder with Walch A1, Favard E0 glenoid morphology was segmented using validated software. An onlay RSA prosthesis was implanted and a computer model simulated external rotation and adduction motion of the virtual RSA prosthesis. Four glenosphere parameters were tested; diameter (36mm, 41mm), lateralization (0mm, 3mm, 6mm), inferior tilt (neutral, 5 degrees, 10 degrees), and inferior eccentric positioning (0.5mm, 1.5mm. 2.5mm, 3.5mm, 4.5mm). Eighty-four combinations were simulated. For each simulation, the humeral neck-shaft angle was 147 degrees and retroversion was 30 degrees. The largest increase in impingement-free range of motion resulted from increasing inferior eccentric positioning, gaining 15.0 degrees for external rotation and 18.8 degrees for adduction. Glenosphere lateralization increased external rotation motion by 13. 6 degrees and adduction by 4.3 degrees. Implanting larger diameter glenospheres increased external rotation and adduction by 9.4 and 10.1 degrees respectively. Glenosphere tilt had a negligible effect on impingement-free ROM. Maximizing inferior glenosphere eccentricity, lateralizing the glenosphere, and implanting larger glenosphere diameters improves impingement-free range of motion, in particular external rotation, of an onlay RSA prosthesis. Surgeons’ awareness of these trends can help optimize glenoid component position to maximise impingement-free ROM for RSA. Further studies are required to validate these findings in the context of scapulothoracic motion and soft tissue constraints

Background. Cementless Total Knee Arthroplasty has been developed to reduce the incidence of failure secondary to aseptic loosening, osteolysis and stress-induced osteopenia, especially in younger and more active patients. However, failures are still more common compared to cemented components, especially those involving the tibia. It is hypothesized that this is caused by incomplete contact between the tibial tray and the underlying bony surface due to: (i) inadequate flatness of the tibial osteotomy, or (ii) failure of implantation to spread the area of contact over the exposed cancellous surface. In the present study we compare the contact area developed during implantation of a cementless tray as a function of the initial flatness of the tibial osteotomy. Method. Eight joint replacement surgeons prepared 14 cadaveric knees for cementless TKR using a standard instrumentation set (ZimmerBiomet Inc). The tibial osteotomy was created using an oscillating bone saw and a 1.27mm blade (Stryker Inc) directed by a slotted cutting guide mounted on an extramedullary rod and fixed to the tibia with pins and screws. The topography of the exposed cancellous surface was captured with a commercial laser scanner (Faro Inc, Halifax, approx. 33,000 surface points). 3D computer models of each tibial surface were generated in a CAD environment (Rapidform, Inuus). After scanning, a cementless tibial tray was implanted on the prepared tibial surface using a manual impactor. The tray-tibia constructs were dissected free of soft tissue, embedded in mounting resin, and sectioned with a diamond wafering saw. Points of bone-tray contact and interface separation were identified by stereomicroscopy and incorporated in the 3D computer models. Maps were generated depicting contacting and non-contacting areas Each model was subdivided into 7 zones for characterizing the distribution of interface contact in terms of anatomic location. Results. The flatness for the tibial osteotomies averaged 1.1±0.35 mm (range: 0.56–1.81mm). After impaction, 79.8±0.3% of the tibial surface had plastically deformed to establish a contacting interface with the implant. 15.1% of the bony surface was within 0.2mm of the tray and 17.6% was within 0.3mm. Gaps large enough to impede ingrowth only occupied 2.6% of the exposed tibial These non-contacting areas were typically located centrally at the ACL, PCL and canal zones. There was an inverse linear relationship between the initial flatness of the tibial osteotomy and the percentage of tray-bone contact. Conclusions. The amount of direct contact between the bone and implant is critical for the development of stability in cementless fixation. We found a relationship between ultimate bony contact and initial flatness. However, we also found that during impaction of the implant, bony contact increased through deformation of the most prominent peaks of the cancellous surface. Interface gaps were consistently observed in central areas of the tibia surface located above the medullary canal which may be reduced through selection of trays with distal keels. For any figures or tables, please contact authors directly

Novel immersive virtual reality (IVR) technologies are revolutionizing medical education. Virtual anatomy education using head-mounted displays allows users to interact with virtual anatomical objects, move within the virtual rooms, and interact with other virtual users. While IVR has been shown to be more effective than textbook learning and 3D computer models presented in 2D screens, the effectiveness of IVR compared to cadaveric models in anatomy education is currently unknown. In this study, we aim to compare the effectiveness of IVR with direct cadaveric bone models in teaching upper and lower limb anatomy for first-year medical students. A randomized, double-blind crossover non-inferiority trial was conducted. Participants were first-year medical students from a single University. Exclusion criteria included students who undertook prior undergraduate or graduate degrees in anatomy. In the first stage of the study, students were randomized in a 1:1 ratio to IVR or cadaveric bone groups studying upper limb skeletal anatomy. All students were then crossed over and used cadaveric bone or IVR to study lower limb skeletal anatomy. All students in both groups completed a pre-and post-intervention knowledge test. The educational content was based on the University of Toronto Medical Anatomy Curriculum. The Oculus Quest 2 Headsets (Meta Technologies) and PrecisionOS Anatomy application (PrecisionOS Technology) were utilized for the virtual reality component. The primary endpoint of the study was student performance on the pre-and post-intervention knowledge tests. We hypothesized that student performance in the IVR groups would be comparable to the cadaveric bone group. 50 first-year medical students met inclusion criteria and were computer randomized (1:1 ratio) to IVR and cadaveric bone group for upper limb skeletal anatomy education. Forty-six students attended the study, 21 completed the upper limb modules, and 19 completed the lower limb modules. Among all students, average score on the pre-intervention knowledge test was 14.6% (Standard Deviation (SD)=18.2%) and 25.0% (SD=17%) for upper and lower limbs, respectively. Percentage increase in students’ scores between pre-and post-intervention knowledge test, in the upper limb for IVR, was 15 % and 16.7% for cadaveric bones (p = 0. 2861), and for the lower limb score increase was 22.6% in the IVR and 22.5% in the cadaveric bone group (p = 0.9356). In this non-inferiority crossover randomized controlled trial, we found no significant difference between student performance in knowledge tests after using IVR or cadaveric bones. Immersive virtual reality and cadaveric bones were equally effective in skeletal anatomy education. Going forward, with advances in VR technologies and anatomy applications, we can expect to see further improvements in the effectiveness of these technologies in anatomy and surgical education. These findings have implications for medical schools having challenges in acquiring cadavers and cadaveric parts

Novel immersive virtual reality (IVR) technologies are revolutionizing medical education. Virtual anatomy education using head-mounted displays allows users to interact with virtual anatomical objects, move within the virtual rooms, and interact with other virtual users. While IVR has been shown to be more effective than textbook learning and 3D computer models presented in 2D screens, the effectiveness of IVR compared to cadaveric models in anatomy education is currently unknown. In this study, we aim to compare the effectiveness of IVR with direct cadaveric bone models in teaching upper and lower limb anatomy for first-year medical students. A randomized, double-blind crossover non-inferiority trial was conducted. Participants were first-year medical students from a single University. Exclusion criteria included students who undertook prior undergraduate or graduate degrees in anatomy. In the first stage of the study, students were randomized in a 1:1 ratio to IVR or cadaveric bone groups studying upper limb skeletal anatomy. All students were then crossed over and used cadaveric bone or IVR to study lower limb skeletal anatomy. All students in both groups completed a pre-and post-intervention knowledge test. The educational content was based on the University of Toronto Medical Anatomy Curriculum. The Oculus Quest 2 Headsets (Meta Technologies) and PrecisionOS Anatomy application (PrecisionOS Technology) were utilized for the virtual reality component. The primary endpoint of the study was student performance on the pre-and post-intervention knowledge tests. We hypothesized that student performance in the IVR groups would be comparable to the cadaveric bone group. 50 first-year medical students met inclusion criteria and were computer randomized (1:1 ratio) to IVR and cadaveric bone group for upper limb skeletal anatomy education. Forty-six students attended the study, 21 completed the upper limb modules, and 19 completed the lower limb modules. Among all students, average score on the pre-intervention knowledge test was 14.6% (Standard Deviation (SD)=18.2%) and 25.0% (SD=17%) for upper and lower limbs, respectively. Percentage increase in students’ scores between pre-and post-intervention knowledge test, in the upper limb for IVR, was 15 % and 16.7% for cadaveric bones (p = 0. 2861), and for the lower limb score increase was 22.6% in the IVR and 22.5% in the cadaveric bone group (p = 0.9356). In this non-inferiority crossover randomized controlled trial, we found no significant difference between student performance in knowledge tests after using IVR or cadaveric bones. Immersive virtual reality and cadaveric bones were equally effective in skeletal anatomy education. Going forward, with advances in VR technologies and anatomy applications, we can expect to see further improvements in the effectiveness of these technologies in anatomy and surgical education. These findings have implications for medical schools having challenges in acquiring cadavers and cadaveric parts

Laboratory experiments and computational models were used to predict bone-implant micromotion and bone strains induced by the cemented and cementless Biomet Oxford medial Unicompartmental Knee Replacement (UKR) tibial implants. Methods. Ten fresh frozen cadaveric knees were implanted with cementless medial mobile UKRs, the tibias were separated and all the soft tissues were resected. Five strain gauge rosettes were attached to each tibia. Four Linear Transducers were used to measure the superior-inferior and transverse bone-implant micromotions. The cementless UKRs were assessed with 10 cycles of 1kN compressive load at 4 different bearing positions. The bone-constructs were re-assessed following cementation of the equivalent UKR. The cemented bone-implant constructs were also assessed for strain and micromotion under 10000 cycles of 10mm anterior-posterior bearing movement at 2Hz and 1kN load. The cadaveric specimens were scanned using Computed Tomography, and 3D computer models were developed using Finite Element method to predict strain and micromotion under various daily loads. Results and Discussion. Results verify computer model predictions and show bone strain pattern differences, with cemented implants distributing the loads more evenly through the bone than cementless implants. Although cementless implants showed micromotions which were greater than computer predictions, the micromotions were as expected significantly greater than those of cemented implants. The computer models reveal that bone strains approach 70% of their failure limit at the posterior and anterior corners adjoining the sagittal and transverse cuts (less pronounced in cemented implants). The base of the keel also develops high strains which can approach failure depending on the amount the implant press-fit. The contributions of the anterior cruciate and patellar tendon forces exacerbate the strains in these regions. This may explain why fractures emanate from the base of the keel and the sagittal cut

Objectives. To date, no study has considered the impact of acromial morphology on shoulder range of movement (ROM). The purpose of our study was to evaluate the effects of lateralization of the centre of rotation (COR) and neck-shaft angle (NSA) on shoulder ROM after reverse shoulder arthroplasty (RSA) in patients with different scapular morphologies. Methods. 3D computer models were constructed from CT scans of 12 patients with a critical shoulder angle (CSA) of 25°, 30°, 35°, and 40°. For each model, shoulder ROM was evaluated at a NSA of 135° and 145°, and lateralization of 0 mm, 5 mm, and 10 mm for seven standardized movements: glenohumeral abduction, adduction, forward flexion, extension, internal rotation with the arm at 90° of abduction, as well as external rotation with the arm at 10° and 90° of abduction. Results. CSA did not seem to influence ROM in any of the models, but greater lateralization achieved greater ROM for all movements in all configurations. Internal and external rotation at 90° of abduction were impossible in most configurations, except in models with a CSA of 25°. Conclusion. Postoperative ROM following RSA depends on multiple patient and surgical factors. This study, based on computer simulation, suggests that CSA has no influence on ROM after RSA, while lateralization increases ROM in all configurations. Furthermore, increasing subacromial space is important to grant sufficient rotation at 90° of abduction. In summary, increased lateralization of the COR and increased subacromial space improve ROM in all CSA configurations. Cite this article: A. Lädermann, E. Tay, P. Collin, S. Piotton, C-H Chiu, A. Michelet, C. Charbonnier. Effect of critical shoulder angle, glenoid lateralization, and humeral inclination on range of movement in reverse shoulder arthroplasty. Bone Joint Res 2019;8:378–386. DOI: 10.1302/2046-3758.88.BJR-2018-0293.R1

Abstract. Background. The Oxford Domed Lateral (ODL) Unicompartmental Knee Replacement (UKR) has some advantages over other lateral UKRs, but the mobile bearing dislocation rate is high (1–6%). Medial dislocations, with the bearing lodged on the tibial component wall, are most common. Anterior/posterior dislocations are rare. For a dislocation to occur distraction of the joint is required. We have developed and validated a dislocation analysis tool based on a computer model of the ODL with a robotics path-planning algorithm to determine the Vertical Distraction required for a Dislocation (VDD), which is inversely related to the risk of dislocation. Objectives. To modify the ODL design so the risk of medial dislocation decreases to that of an anterior/posterior dislocation. Methods. The components were modified using Solidworks. For each modification the dislocation analysis tool was used to determine the VDD for medial dislocation (with bearing 0–6mm from the tibial wall). This was compared with the original implant to identify the modifications that were most effective at reducing the dislocation risk. These modifications were combined into a final design, which was assessed. Results. Modifying the tibial component plateau, changing the femoral component width and making the bearing wider medially had little effect on VDD. Shifting the femoral sphere centre medially decreased VDD. Shifting the femoral sphere laterally, increasing tibial wall height and increasing bearing width laterally increased VDD. A modified implant with a femoral sphere centre 3mm lateral, wall 2.8mm higher, and bearing 2mm wider laterally, implanted so the bearing is ≤4mm from the tibial wall with a bearing thickness ≥4mm had a minimum VDD for medial dislocation of 5.75mm, which is larger than the minimum VDD for anterior/posterior dislocation of 5.5mm. Conclusions. A modified ODL design should decrease the dislocation rate to an acceptable level, however, further testing in cadavers is required. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

A fluoroscopic based computer enhancement system was designed for accurate insertion of guide wires for hip fracture fixation while decreasing fluoroscopy time. A saw bone model was created. The femur was imaged with fluoroscopy and a three-dimensional computer model was created. The femur, fluoroscopy drum, and drill were tracked with an optical tracking device. Guide wire position was planned on the computer model. Using a tracked drill the guide wire was inserted. The number of fluoroscopic images was decreased by 85% and the number of passes required to place the guide wire in acceptable position was decreased by 60% using computer enhanced technique. A fluoroscopic based computer enhancement system was designed for accurate insertion of guide wires for hip fracture fixation while decreasing fluoroscopy time. The number of fluoroscopic images and passes required to place the guide wire in acceptable position were decreased using computer enhanced technique. Final guide wire position was not different between the two groups. Orthopedic surgeons are exposed to radiation from fluoroscopy on a daily basis. This system allowed us to insert guide wires using substantially less fluoroscopy, without compromising accuracy. An average of 13.5 images were taken for each standard technique trial compared to two images for each computer enhanced trial, representing a reduction in fluoroscopy of 85%. One pass was used for each computer enhanced trial. An average of 2.4 trials was used for standard technique. Average final error was 3.6mm using standard technique and 3.8mm using computer technique. A saw bone model with a soft tissue sleeve was created. A DRB (dynamic referencing body) was fixed to the femur. The DRB, fluoroscopy drum, and drill were tracked with an optical tracking device. The system created a 3D model from two orthogonal fluoroscopic images. Guide wire position was then planned on the computer model. Using a tracked drill the guide wire was inserted. Computer enhanced trials were compared to standard techniques in regards to number of fluoroscopic images taken, number of trials to obtain acceptable guide wire position, and accuracy of guide wire placement. Guide wire position was measured on AP and lateral x-rays. Funding: This project was funded in part through a grant from the Canadian Foundation for Innovation