Introduction. According to proposal of Noble, the femoral bone marrow cavity form of patients who underwent Total Hip Arthroplasty (THA) can be classified under 3 categories; those are Stovepipe, Normal and Champagne-fluted. We developed typical sodium chloride femoral model was created by 3D prototyping technique. The purpose was to identify the relationship of pressure zone of the surrounding areas between femoral bone marrow cavity form and hip stem. Materials and Method. As opponent clarified stem design concept Zweymüller type model was used. According to CT data with the patients who underwent THA, the sodium chloride femoral model was custom-made and selected as the representative model based on Noble's 3 categories. Eight models of each category were used to performed mechanical test. Result. In mechanics test, the result of comparison between the contact pressure zones of zone 1–7, significant differences of contact pressure zones were identified between the Stovepipe group and Normal group in zone 3, 4 and 5. In zone 3 and 5, such significant differences were also identified between Champagne-fluted group and Normal group. In Stovepipe group, a significant difference of the contact pressure zone was observed at the proximal and distal. In Champagne-fluted group and the Normal group, a significant difference was observed in the contact pressure in distal femur (3, 4, 5 Zone) and (Zone1, 2, 6, 7) proximal femur. Discussion. Although in most studies Sawbone® is used for femoral models, the focus of this research is of those who possess a characteristic femur with marrow cavity form. Therefore, sodium chloride bone model was used instead. In comparison in terms of applicability between sodium chloride bone model and regular model, the failure of all 24 joints of sodium chloride bone model were unconfirmed in mechanics test. Moreover, the possibility that its performance in mechanics test is equivalent to Sawbone®is considered. The design concept for Zweymüller type achieves the ability to load distribute within a wide range of cortical bone across the middle position to distal femur. It's determined by the concept that a wide range of contact pressure was admitted at middle position and distal femur in the Champagne-fluted group and the Normal group. On the other hand, the contact pressure zone of Stovepipe was not able to meet the expected level at distal femur. The method of this research is control its stress condition within the stem design. By this point, it is considered possible that the stability of various stem design was able to be forecasted and the assessment of stableness was positive. Conclusion. On the basis of Noble's categories, 3 types of bone models were created by 3D prototyping technique, and pressure distribution measurement were performed. The result from the pressure distribution indicated that even in Zweymüller stem had anxiety of securing force in Champagne-fluted type and Stovepipe type canal. We believe the method of in vivo study can develop to assess the stability of implant preoperatively

Introduction. In vitro findings (Bladed CL et al. ORS 2011 and J Biomed Mater Res B Appl Biomater, 2012) have suggested that UHMWPE wear particles containing vitamin-E (VE) may have reduced functional biologic activity and decreased osteolytic potential. Currently, there is no in vivo data determining the effects of wear debris from this new generation of implants. In this study we hypothesized that particles from VE-stabilized, radiation cross-linked UHMWPE (VE-UHMWPE) would cause reduced levels of osteolysis in a murine calvarial bone model when compared to virgin gamma irradiated cross-linked UHMWPE. Methods. Study groups: 1). Radiation cross-linked VE-UHMWPE, 0.8% by weight, diffused after 100 kGy; 2). Radiation cross-linked virgin UHMWPE (virgin UHMWPE); 3). Shams. Particle generation and implantation: UHMWPE was sent to Bioengineering Solutions for particle generation. After IACUC approval, C57BL/6 mice (n = 12 for each group) received 3 mg of particulate debris overlying the calvarium and euthanized after 10 days. Micro-CT scans: Performed using an X-Tek-HMX-ST-225 with 70 kV voltage and 70 μA current. Topographical Grading Scale: Each calvarial bone was blindly scored with the following scale: 0 = No osteolysis, defined as intact bone; 1 = Minimal osteolysis, affecting 1/3 or less of the bone area; 2 = Moderate osteolysis, affecting at least 2/3 of the bone area; 3 = Severe osteolysis, defined as completely osteolytic bone. Histology H&E and TRAP staining was performed. Statistical Analysis: Inter-rater analysis was performed using Cohen's kappa analysis. Inter-rater coefficient >0.65 was considered as high inter-rater agreement. Comparison between groups was made using one-way ANOVA with post hoc Bonferroni correction for multiple comparisons. Correlations are reported as Spearman's rho. A p-value<0.05 was considered statistically significant. Results. More than 83% of the VE-UHMWPE and more than 85% of the virgin UHMWPE particles measured less than 1 μm in mean particle size. There was a statistically significant greater level of osteolysis visualized on the topographical grading scale in calvaria implanted with virgin UHMWPE wear particles. The micro-CT findings were confirmed histologically (Fig. 1). A greater amount of inflammatory tissue overlaying the calvaria was observed in the virgin UHMWPE group when compared to both shams and VE-UHMWPE groups. Post hoc analysis revealed significant difference between VE-UHMWPE and virgin UHMWPE for the topographical osteolysis grading score (p = 0.002) but no difference in osteoclast count (p = 0.293). Discussion/Conclusion. This is the first in vivo study reporting the effects of clinically-relevant UHMWPE particles generated from a VE-UHMWPE implant that is in current clinical use. These results suggest that VE-UHMWPE particles have reduced osteolysis potential in vivo when compared to virgin, highly cross-linked UHMWPE in a murine calvarial bone model

Purpose

Angiogenesis and osteogenesis are essential for bone growth, fracture repair, and bone remodeling. VEGF has an important role in bone repair by promoting angiogenesis and osteogenesis. In our previous study, endothelial progenitor cells (EPCs) promoted bone healing in a rat segmental bone defect as confirmed by radiological, histological and microCT evaluations (Atesok, Li, Schemitsch 2010); EPC treatment of fractures resulted in a significantly higher strength by biomechanical examination (Li, Schemitsch 2010). In addition, cell-based VEGF gene transfer has been effective in the treatment of segmental bone defects in a rabbit model (Li, Schemitsch et al 2009); Purpose of this study: Evaluation of VEGF gene expression after EPC local therapy for a rat segmental bone defect.

The treatment of paediatric supracondylar humeral fractures is likely one of the first procedures involving X-ray guided wire insertion that trainee orthopaedic surgeons will encounter. Pinning is a skill that requires high levels of anatomical knowledge, spatial awareness, and hand-eye coordination. We developed a simulation model using silicone soft-tissue and 3D-printed bones to allow development and practice of this skill at no additional risk to patients. For this model, we have focused on reusability and lowering raw-material costs without compromising fidelity. To achieve this, the initial bone model was extracted from open-source computed tomography scans and modified from adult to paediatric size. Muscle of appropriate robustness was then sculpted around the bones using 3D modelling software. A cutaneous layer was developed to mimic oedema using clay sculpturing on a plaster-casted paediatric forearm. These models were then used for 3D-printing and silicone casting respectively. The bone models were printed with settings to imitate cortical and cancellous densities and give high-fidelity tactile feedback upon drilling. Each humerus costs NZD $0.30 in material to print and can be used 1–3 times. Silicone casting of the soft-tissue layers imitates differing relative densities between muscle and oedematous cutaneous tissue, thereby increasing skill necessary to accurately palpate landmarks. Each soft-tissue sleeve cost NZD $70 in material costs to produce and can be used 20+ times. The resulting model is modular, reusable, and replaceable, with each component standardised and easily reproduced. It can be used to practice land-mark palpation and Kirschner wire pinning and is especially valuable in smaller centres which may not be able to afford traditional Saw Bones models. This low-cost model thereby improves equity while maintaining quality of simulation training

Introduction. Obtaining accurate anatomical landmarks may lead to a better morphologic understanding, but this is challenging due to the variation of bony geometries. A manual approach, non-ideal for surgeons or engineers, requires a CT or MRI scan, and landmarks must be chosen based on the 3D representation of the scanned data. Ideally, anatomical landmarking is achieved using either a statistical shape model or template matching. Statistical modeling approaches require multitude of training data to capture population variation. Prediction of anatomical landmarks through template matching techniques has also been extensively investigated. These techniques are based on the minimization or maximization of an objective or cost function. As is the nature of non-rigid algorithms, these techniques can fail in the local maxima if the template and new bone models have noise or outliers. Therefore, a combination of rigid and non-rigid registration techniques is needed, in order to obtain accurate anatomical landmarks and improve the prediction process. Objective. The objective of this study was to find a way to efficiently obtain accurate anatomical landmarks based on an existing template's landmarks for use in a forward solution model (FSM) to predict patient specific mechanics. Methods. Initially, the 3D meshes for a template bone and new bone of question are imported into the FSM. Landmarks on the template are also loaded with imported data. Then, the template and new bones are located at arbitrary positions within the global coordinate system. If determined to be placed at significantly different positions, the user will re-align the bones to ensure that they are close enough for the process to commence. After initially aligning the bones, the new bone model will appear closer to the template. The template bone model is then registered to the new model using Iterative Closest Point (ICP) with scaling to find the initial regions of correspondence. For each anatomical landmark on the template, initial corresponding landmarks on the new bone are defined as being its closest point. To refine landmarks on the new bone, local corresponding regions are determined between the template and new bone models. Local corresponding regions on the template and new bone models are then registered again using ICP with a scaling algorithm to refine the landmark locations on the new model as seen in Figure 1. Results. Regardless of differences in size, geometry, and initial position, the algorithm has proven to be successful in transferring landmarks from the template bone to the new bone model (Figure 2). The results also revealed that predicted landmarks on the new bone (purple) are properly defined with respect to the landmarks on the template bone (green) (Figure 2). This process allows for the FSM to be parametric in nature for patient specific analyses. Discussion and Conclusion. The FSM successfully transferred anatomical landmarks from a template to a new bone model. It has also been proven to work on more than just the femur and pelvis. Future investigations using this process for surgical planning/implant sizing will be used for both our hip and knee FSMs. For any figures or tables, please contact authors directly

Introduction. A good anatomic fit of a Total Knee Arthroplasty is crucial to a good clinical outcome. The big variability of anatomies in the Asian and Caucasian populations makes it very challenging to define a design that optimally fits both populations. Statistical Shape Models (SSMs) are a valuable tool to represent the morphology of a population. The question is how to use this tool in practice to evaluate the morphologic fit of modern knee designs. The goal of our study was to define a set of bone geometries based on SSMs that well represent both the Caucasian and the Asian populations. Methods. A Statistical Shape Model (SSM) was built and validated for each population: the Caucasian Model is based on 120 CT scans from Russian, French, German and Australian patients. The Asian Model is based on 80 CT scans from Japanese and Chinese patients. We defined 7 Caucasian and 5 Asian bone models by using mode 1 of the SSM. We measured the antero-posterior (AP) and medio-lateral (ML) dimensions of the distal femur on all anatomies (input models and generated models) to check that those bone models well represent the studied population. In order to cover the whole population, 10 additional bone models were generated by using an optimization algorithm. First, a combined Asian-Caucasian SSM was generated of 92 patients, equally balanced between male and female, Caucasian and Asian. 10 AP/ML dimensions were defined to obtain a good coverage of the population. For a given AP/ML dimension, Markov chain Monte Carlo sampler was used to find the most average shape with AP/ML dimensions as close as possible to the target dimensions. The difference of the AP/ML dimensions of the generated models to the target dimensions was computed. A chi-squared distribution was used to assess how average the resulting shapes were compared to typical patient shapes. Results. The AP-ML dimensions of the 7 Caucasian bones and the 5 Asian bones well cover the range of the respective populations. For the Caucasian Femur, the AP/ML dimensions range from (53,6/64,9mm) for size 1 to (67,7/80,7mm) for size 7. For the Asian Femur, the AP/ML dimension range from (53,0/62,4mm) for size 1 to (60,5/72,4mm) for size 5. The dimensions of the 10 additionally generated bones differed in average (± 1 standard deviation) by 0,2±0,4mm in AP and 0,5±0,5mm in ML to the target dimensions. The maximal deviation was 0,9mm in AP and 1,0mm in ML. All 10 bones had a P-value of P < 10. -27. according to the chi-squared distribution. Conclusion. The proposed models of 7 Caucasian and 5 Asian bones well represent both populations. The 10 additional geometries enable to get a complete coverage of the population. Since they are very close to average, all these bone models provide more generalized reference shapes compared to individual patients. By performing a virtual implantation on those anatomies, the anatomical fit of implants to these populations can be evaluated. For any figures or tables, please contact authors directly

The minimisation of errors incurred during the learning process is thought to enhance motor learning and improve performance under pressure or in multitasking situations. If this is proven in surgical skills learning, it has the potential to enhance the delivery of surgical education. We aimed to compare errorless and errorful learning using the high-speed burr. Medical students (n=30) were recruited and allocated randomly to an errorless or errorful group. The errorless learning group progressively learnt tasks from easy to difficult on cedar boards simulating bone. The errorful learning group also progressed through the same tasks but not in order of difficulty. Transfer tasks assessed students’ performance of cervical laminoplasty on saw bone models to assess their level of learning from previous stages. During transfer task 2, students completed the procedure under time pressure and in the presence of distractors, in order to simulate real-life stressors in theatre. Accuracy, precision and safety of the procedure were scored by expert opinions from spine surgeons blinded to the grouping of the participants. Both errorless and errorful learners demonstrated improvements in performance with increasing amounts of practice (demonstrated by the decreased time taken for the task as well as improvement in accuracy of the cuts (depth, width and smoothness). The performance of both groups was not impaired by the incorporation of a secondary task which required participants to multitask. No statistically significant difference in performance was noted between the two groups. In contrast to previous research, there was no significant difference between errorless or errorful learning to develop skills with a high-speed, side-cutting burr. In both groups, practical learning during the session has led to improvement in overall performance with the burr relevant to cervical laminoplasty

INTRODUCTION. Simulation plays an important role in surgical education and the ability to perfect surgical performance. Simulation can be enhanced by adding various layers of realism to the experience. Haptic feedback enhances the simulation experience by providing tactile responses and virtual reality imagery provides an immersive experience and allows for greater appreciation of three-dimensional structures. In this study, we present a proof-of-concept haptic simulator to replicate key steps of a cervical laminoplasty procedure. The technology uses affordable components and is easily modifiable so that it can be used from novice through to expert level. Custom models can be easily added ensuring the simulator can be used in a wide range of orthopaedic applications from baseline education through to day of surgery pre-operative simulation. METHOD. We used the Unity Game Engine, the 3D Systems “Touch” Haptic Feedback Device (HFD), and a Meta Quest VR headset. Our system uses a number of complex algorithms to track the shape and provide haptic feedback of a virtual bone model. This allows for simulation of various tools including a high-speed burr, Kerrison rongeur and intraoperative X-rays. RESULTS. Our simulator replicates the tactile sensations of bone-burring tasks. Although we focused on the cervical laminoplasty procedure, the system can load data from CT scans, enabling the simulation of multiple other procedures. The parts cost of our system, $10,000 NZD, is a fraction of the cost of traditional surgical simulators. DISCUSSION. Our simulator reduces financial barriers to accessing orthopaedic simulators. Trainees can perform hands-on practice without compromising patient safety. The immersive nature of VR, combined with realistic haptic feedback, enables trainees to develop the dexterity and three-dimensional understanding of detailed bony work. Further refinements are needed before we can perform validation studies on our system. CONCLUSIONS. We present an affordable surgical simulator capable of simulating bony surgical procedures in a VR environment using haptic feedback technology and consumer-grade components. ACKNOWLEDGEMENTS. This research was made possible by the generosity of the Wishbone Trust

Introduction. Traditionally, conventional radiographs of the hip are used to assist surgeons during the preoperative planning process, and these processes generally involve two-dimensional X-ray images with implant templates. Unfortunately, while this technique has been used for many years, it is very manual and can lead to inaccurate fits, such as “good” fits in the frontal view but misalignment in the sagittal view. In order to overcome such shortcomings, it is necessary to fully describe the morphology of the femur in three dimensions, therefore allowing the surgeon to successfully view and fit the components from all possible angles. Objective. The objective of this study was to efficiently describe the morphology of the proximal femur based on existing anatomical landmarks for use in surgical planning and/or forward solution modeling. Methods. Seven parameters are needed to fully define femoral morphology: head diameter, head center, neck shaft axis, femoral canal, proximal shaft axis, offset, and neck shaft angle. A previous algorithm has been developed in-house to automatically locate anatomical landmarks of patient specific bone models. Once the bone model has been aligned and scaled based on these landmarks, the femoral head diameter and center are calculated by iteratively fitting a sphere to the corresponding femoral head point cloud. An iterative cylindrical fitting algorithm is used to describe the neck shaft axis. The femoral canal is determined using three steps: 1) the femur is sliced at 10mm increments below the lesser trochanter, 2) the femoral canal boundary is determined at each slice, and 3) the largest circle is fit within each slice's canal boundary. The proximal shaft axis is described by fitting a line to the canal circle center locations. Offset is defined as the distance from the head center to the proximal shaft axis. Finally, the neck shaft angle is the angle between the neck shaft axis and the proximal shaft axis. Results. The goal pertaining to femoral component morphology is to provide meaningful information that can be used to determine how the femoral stem fits within the canal. Regardless of differences in bone sizes and geometries, the algorithm has proven to be successful in describing the femoral morphology of a patient-specific bone model. Discussion. These results lay the groundwork for an automatic stem fitting algorithm, which is described in a subsequent abstract. The morphology knowledge of the femoral head, femoral neck, femoral canal, and various axes can be coupled with known THA component parameters (such as offset, neck length, neck shaft angle, etc.) to allow our algorithms to predict the “best selection” and “best fit” for the femoral stem. This can also be applied to the acetabulum and can then be used as a surgical planning tool as well as a parameter when modeling postoperative predictions. For any figures or tables, please contact authors directly

Introduction. Osteotomy is a key step in distraction osteogenesis. Various techniques of osteotomy have been described with its own benefits and pitfalls. Percutaneous osteotomy using multiple drill holes is one of the most widely used osteotomy techniques. It still remains a challenge however to keep the drill holes aligned prior to the osteotomy. Moreover, the efficacy of percutaneous irrigation practice to keep the temperature low during drilling with this technique is also debatable. With an aim to overcome these challenges, we are introducing a device called the Double Barrel Drill Sleeve (DBDS) to perform percutaneous osteotomies. We attempted to compare this method to the conventional multiple drill holes technique using laboratory experiments and clinical data. Materials & Methods. DBDS has two adjacent parallel barrels that can fit 3.2 to 3.5 mm diameter drill bits. It has a guide member at the drilling end that can be inserted through a pre drilled hole at the near and far cortices of a bone. This provides a constant rotating point for drilling of holes through the barrels. An osteotomy simulation was performed to compare percutaneous drilling with DBDS vis-a-vis a conventional single drill sleeve (SDS) by qualified orthopaedic surgeons, mainly to assess the drilling patterns of both techniques. Percutaneous drilling was done on PVC pipes wrapped in thick sponge to simulate tubular bone with surrounding soft tissue. We also assessed the effect of indirect irrigation on temperature during drilling using the DBDS against a control group on a cadaveric bone model. Ultimately we reviewed our patients who had undergone osteotomy for distraction osteogenesis with DBDS and the conventional technique, and compared their outcomes. Results. Completion time for the osteotomy simulation in the DBDS group was significantly faster than the conventional drilling group; 74 seconds to 179 seconds. There was significantly less drilling deviation from the midpoint in the DBDS group as compared to the SDS group. Mean bone temperature during drilling with indirect irrigation using DBDS was significantly lower (32.6'C) compared to the control group (48.4'C). There was no significant difference in healing index between patients treated with DBDS and the conventional method. None of these patients developed non union. Conclusions. Percutaneous drilling with DBDS was quicker and more linear compared to the conventional method. Its double-barreled feature allows effective indirect irrigation during drilling. A comparable healing index in both of the techniques shows its clinical efficacy. These attributes make DBDS a usefull tool to overcome some of the pitfalls associated with the conventional multiple drill holes technique

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

Analyzing shoulder kinematics is challenging as the shoulder is comprised of a complex group of multiple highly mobile joints. Unlike at the elbow or knee which has a primary flexion/extension axis, both primary shoulder joints (glenohumeral and scapulothoracic) have a large range of motion (ROM) in all three directions. As such, there are six degrees of freedom (DoF) in the shoulder joints (three translations and three rotations), and all these parameters need to be defined to fully describe shoulder motion. Despite the importance of glenohumeral and scapulothoracic coordination, it's the glenohumeral joint that is most studied in the shoulder. Additionally, the limited research on the scapulothoracic primarily focuses on planar motion such as abduction or flexion. However, more complex motions, such as internally rotating to the back, are rarely studied despite the importance for activities of daily living. A technique for analyzing shoulder kinematics which uses 4DCT has been developed and validated and will be used to conduct analysis. The objective of this study is to characterize glenohumeral and scapulothoracic motion during active internal rotation to the back, in a healthy young population, using a novel 4DCT approach. Eight male participants over 18 with a healthy shoulder ROM were recruited. For the dynamic scan, participants performed internal rotation to the back. For this motion, the hand starts on the abdomen and is moved around the torso up the back as far as possible, unconstrained to examine variability in motion pathway. Bone models were made from the dynamic scans and registered to neutral models, from a static scan, to calculate six DoF kinematics. The resultant kinematic pathways measured over the entire motion were used to calculate the ROM for each DoF. Results indicate that anterior tilting is the most important DoF of the scapula, the participants all followed similar paths with low variation. Conversely, it appears that protraction/retraction of the scapula is not as important for internally rotating to the back; not only was the ROM the lowest, but the pathways had the highest variation between participants. Regarding glenohumeral motion, internal rotation was by far the DoF with the highest ROM, but there was also high variation in the pathways. Summation of ROM values revealed an average glenohumeral to scapulothoracic ratio of 1.8:1, closely matching the common 2:1 ratio other studies have measured during abduction. Due to the unconstrained nature of the motion, the complex relationship between the glenohumeral and scapulothoracic joints leads to high variation in kinematic pathways. The shoulder has redundant degrees of freedom, the same end position can result from different joint angles and positions. Therefore, some individuals might rely more on scapular motion while others might utilize primarily humeral motion to achieve a specific movement. More analysis needs to be done to identify if any direct correlations can be drawn between scapulothoracic and glenohumeral DoF. Analyzing the kinematics of the glenohumeral and scapulothoracic joint throughout motion will further improve understanding of shoulder mechanics and future work plans to examine differences with age

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

Background. Stemless prostheses are recognized to be an effective solution for anatomic total shoulder arthroplasty (TSA) while providing bone preservation and shortest operating time. Reverse shoulder arthroplasty (RSA) with stemless has not showed the same effectiveness, as clinical and biomechanical performances strongly depend on the design. The main concern is related to stability and bone response due to the changed biomechanical conditions; few studies have analyzed these effects in anatomic designs through Finite Element Analysis (FEA), however there is currently no study analyzing the reverse configuration. Additionally, most of the studies do not consider the effect of changing the neck-shaft angle (NSA) resection of the humerus nor the proper assignment of spatial bone properties to the bone models used in the simulations. The aim of this FEA study is to analyze bone response and primary stability of the SMR Stemless prosthesis in reverse with two different NSA cuts and two different reverse angled liners, in bone models with properties assigned using a quantitative computed tomography (QCT) methodology. Methods. Sixteen fresh-frozen cadaveric humeri were modelled using the QCT-based finite element methodology. The humeri were CT-scanned with a hydroxyapatite phantom to allow spatial bone properties assignment [Fig. 1]. Two implanted SMR stemless reverse configurations were considered for each humerus: a 150°-NSA cut with a 0° liner and a 135°-NSA cut with a 7° sloped liner [Fig. 2]. A 105° abduction loading condition was simulated on both the implanted reverse models and the intact (anatomic) humerus; load components were derived from previous dynamic biomechanical simulations on RSA implants for the implanted stemless models and from the OrthoLoad database for the intact humeri. The postoperative bone volume expected to resorb or remodel [Fig. 3a] in the implanted humeri were compared with their intact models in sixteen metaphyseal regions of interest (four 5-mm thick layers parallel to the resection and four anatomical quadrants) by means of a three-way repeated measures ANOVA followed by post hoc tests with Bonferroni correction. In order to evaluate primary stability, micromotions at the bone-Trabecular Titanium interface [Fig. 3b] were compared between the two configurations using a Wilcoxon matched-pairs signed-rank test. The significance level α was set to 0.05. Results. With the exception of the most proximal layer (0.0 – 5.0 mm), the 150°-NSA configuration showed overall a statistically significant lower bone volume expected to resorb (p = 0.011). In terms of bone remodelling, the 150°-NSA configuration had again a better response, but fewer statistically significant differences were found. Regarding micromotions, there was a median decrease (Mdn = 3.2 μm) for the 135°-NSA configuration (Mdn = 40.3 μm) with respect to the 150°-NSA configuration (Mdn = 43.5 μm) but this difference was non-significant (p = 0.464). Conclusions. For the analyzed SMR Stemless configurations, these results suggest a reduction in the risk of bone resorption when a 0° liner is implanted with the humerus cut at 150°. The used QCT-based methodology will allow further investigation, as this study was limited to one single design and load case. For any figures or tables, please contact the authors directly

Introduction. Aseptic acetabular component failure rates have been reported to be similar or even slightly higher than femoral component failure. Obtaining proper initial stability by press fitting the cementless acetabular cup into an undersized cavity is crucial to allow for secondary osseous integration. However, finding the insertion endpoint that corresponds to an optimal initial stability is challenging. This in vitro study presents an alternative method that allows tracking the insertion progress of acetabular implants in a non-destructive, real-time manner. Materials and Methods. A simplified acetabular bone model was used for a series of insertion experiments. The bone model consisted of polyurethane solid foam blocks (Sawbones #1522-04 and #1522-05) into which a hemispherical cavity and cylindrical wall, representing the acetabular rim, were machined using a computer numerically controlled (CNC) milling machine (Haas Automation Inc., Oxnard, CA, USA). Fig. 1 depicts the bone model and setup used. A total of 10 insertions were carried out, 5 on a low density block, 5 on a high density block. The acetabular cups were press fitted into the bone models by succeeding hammer hits. The acceleration of the implant-insertor combination was measured using 2 shock accelerometers mounted on the insertor during the insertion process (PCB 350C03, PCB Depew, NY, USA). The force applied to the implant-insertor combination was also measured. 15 hammer hits were applied per insertion experiment. Two features were extracted from the acceleration time signal; total signal energy (E) and signal length (LS). Two features and one correlation measure were extracted from the acceleration frequency spectra; the relative signal power in the low frequency band (PL, from 500–2500Hz) and the signal power in the high frequency band (P Hf, from 4000–4800 Hz). The changes in the low frequency spectra (P Lf, from 500–2500 Hz) between two steps were tracked by calculating the Frequency Response Assurance Criterion (FRAC). Force features similar to the ones proposed by Mathieu et al., 2013 were obtained from the force time data. The convergence behavior of the features was tracked as insertion progressed. Results. Differences were noted visually between the acceleration data recorded at the beginning of insertion and towards the end, both in the time domain (fig. 2A) as well as in the frequency domain (fig. 2B). These differences were also captured by the proposed features. Fig. 3 shows a typical representation of how the time (A), frequency (B) and force (C) features evolved during insertion. Based on a simple convergence criterion, the insertion endpoint could be determined. Conclusions. The convergence behavior, and the insertion endpoint thus identified, of the force-based and acceleration based features correlated well. The different features capture the changes in damping and stiffness of the implant-bone system that are occurring as the insertion progresses and combining them improves the robustness of the endpoint detection method. For any figures or tables, please contact the authors directly

Introduction. Knee ligament laxity and soft tissue balance are important pre- and intra- operative balancing factors in total knee arthroplasty (TKA). Laxity can be measured pre-operatively from short-leg radiographs using a stress device to apply a reproducible force to the knee, whereas intra-operative laxity is routinely measured using a navigation system in which a variable surgeon-applied force is applied. The relationship between these two methods and TKA outcome however, has not been investigated. This study aims to determine how intra-operative assessments of laxity relate to functional radiographic assessments performed on pre-operatively. We also investigate how laxity relates to short-term patient-reported outcomes. Method. A prospective consecutive study of 60 knees was performed. Eight weeks prior to surgery, patients had a CT scan and functional radiographs captured using a Telos stress device (Metax, Germany). This device applies a force to the knee joint while bracing the hip and ankle causing either a varus or valgus response. 3D bone models were segmented from the CT scan and landmarked to generate patient specific axes and alignments. Individual bone models were registered to the 2D stressed X-rays in flexion and extension. Reference axes identified on the registered 3D bone models were used to measure the coronal plane laxity. These laxity ranges were compared with those measured by a navigation system (OMNINAV, OMNI Life Science, MA) used during surgery, and Knee Injury and Osteoarthritis Outcome Scores (KOOS) captured 6 months postoperatively. Results. Laxity measurements were acquired from 54 patients (58 knees; 4 bilaterals). The average age was 65±15 years old and 57% (n=31) of the patients were female. The midpoints of the laxity curves generated by Telos and navigation techniques show significant strong correlations in extension (r = 0.83, p < 0.001) and flexion (r = 0.53, p < 0.001). However, the laxity ranges measured by the two techniques did not. On average the navigation system produced significantly larger laxity range measurements than the Telos stressed x- ray technique in both extension (Nav: 8.4° ± 2.0°; Telos: 4.0° ± 2.4°; p < 0.001) and flexion (Nav: 5.0 ± 2.4; Telos: 3.0 ± 2.4; p < 0.001). Telos-generated laxity ranges indicate that patients who have initially greater laxity in extension than flexion (laxity range difference > 2°) have significantly better 6-month pain KOOS than those who show greater laxity in flexion (laxity range difference < −2°) (p = 0.018), see Figure 1. This correlation does not hold however, when examining laxity ranges generated by the navigation system, see Figure 2. Discussion and Conclusions. Significantly larger navigation-generated laxity ranges may be caused by: variable forces applied by the surgeon while the patient is under anaesthetic, surpassing the patient's functional limit; as well as due to the altered physical state of the knee during surgery. More sophisticated techniques to reproducibly assess intra-operative soft tissue balance may be required to accurately define laxity range. Results indicate that functional Telos-generated laxity ranges may provide unique insight into the relationship between laxity and postoperative outcomes that cannot be attained with passive navigated measurements

Introduction. The education of residents in the proper placement of pedicle screws is key to the safety of the surgery. The more experienced the surgeon, the more accurately the pedicle screws tend to be placed. A physical bone model, with properties and tactile feel similar to human bone, was developed with the intention of using the bone model to train residents in pedicle screw placement. The purpose of this study was to test whether the model improves the performance of orthopaedic residents when cannulating spinal pedicles, as judged by the number of breaches, and to gain feedback from the residents on their experiences. Materials and Methods. Six orthopaedic residents were recruited, with ethics approval. Prior to testing, the residents were given an instructional video describing the correct cannulation of a lumbar vertebra. The residents were each provided with 12 bones mounted in holders: 3 for initial skills assessment, 6 for free practice, and 3 for final skills assessment. In the pre- and post-practice sets, the 3 bone models had different properties: weak, normal and strong. The residents were asked to complete both pre and post-testing questionnaires. The number of breaches was counted in initial and final bone testing. The forces for each bone model were compared using an ANOVA; these were followed by post-hoc t-tests if significant (p<0.05). Results. All but one of the residents improved the number of breaches with practice, and the one that did not improve did not make the same breaches twice. The total number of breaches in the final testing (14) was lower than in the initial testing (31). The entry points chosen by the residents were all deemed appropriate as per the video instruction. The resident with the most experience had the least number of breaches; the resident with the least amount of experience had the most breaches. Discussion. The reduction of the number of breaches between the initial and final testing indicates that the residents did learn. Overall the response from the residents was positive; they all indicated they would like to have the simulator as part of their training; most even indicated an interest to use them outside of training hours. Almost all indicated that the bones felt more realistic than those currently available (if they were aware of them). Positively, the more surgical experience the resident had, the more their survey responses indicated a positive impression of the bones

Introduction. Regarding TKA, patient specific cutting guides (PSCG), which have the same fitting surface with patient's bones or cartilages and uniquely specify the resection plane by fitting guides with bones, have been developed to assist easy, low cost and accurate surgery. They have already been used clinically in Europe and the USA. However little has been reported on clinical positioning accuracy of PSCG. Generally, the methods of making PSCG can be divided into 3 methods; construct 3D bone models with Magnetic Resonance (MR) images, construct 3D bone models with Computed Tomography (CT) images, and the last is to construct 3D bone models with both MR and CT images. In the present study, PSCG were made based on 3D bone models with CT images, examined the positioning accuracy with fresh-frozen cadavers. Materials and Methods. Two fresh-frozen cadavers with four knees were scanned by CT. Image processing software for 3D design (Mimics Ver. 14, Marialise Inc.) was used to construct 3D bone model by image thresholding. We designed femoral cutting guides and tibial cutting guides by CAD software (NX 5.0, Siemens PLM Software Co.). CT free navigation system (VectorVision Knee, BrainLab, Inc.) was used to measure positioning error. Average absolute value of positioning error for each PSCG was derived. Results. The average absolute value of positioning error in femoral PSCG was 1.5±0.8° for varus/valgus, 2.3±1.9° for extension/flexion, 1.2±1.8 mm for bone resection. The stability of femoral PSCG was satisfactory. The average absolute value of positioning error in tibial PSCG was 4.3±2.5° for varus/valgus, 5.2±3.3° for anterior slope/posterior slope, 2.6±1.1 mm for bone resection. The stability of tibial PSCG was not sufficient. Discussion. PSCG of the present study were made based on CT images, mainly designed to be fit with cortex, keeping away from cartilage or osteophytes. The fitting surfaces of distal femoral PSCG covered anterior femoral cortex. Also, the fitting surface of tibial PSCG fit to anterior medial cortex of horizontal tibial tuberosity. The average absolute value of positioning error by tibial PSCG varied widely. The main cause for this was their contacts with patellar tendon. Lateral sides of PSCG were contacted with patella tendon near the tibial tuberosity, they were pushed medially. Positioning accuracy of the femoral PSCG is thought to be enough for clinical application

Aims. Accurate and precise acetabular reaming is a requirement for the press-fit stability of cementless acetabular hip replacement components. The accuracy of reaming depends on the reamer, the reaming technique and the bone quality. Conventional reamers wear with use resulting in inaccurate reaming diameters, whilst the theoretical beneficial effect of ‘whirlwind’ reaming over straight reaming has not previously been documented. Our aim was to compare the accuracy and precision of single use additively-manufactured reamers with new conventional reamers and to compare the effect of different acetabular reaming techniques. Materials and Methods. Forty composite bone models, half high-density and half low-density, were reamed with a new 61 mm conventional acetabular reamer using either straight or ‘whirlwind’ reaming techniques. This was repeated with a 61 mm single use additively-manufactured reamer. Reamed cavities were scanned using a 3D laser scanner with mean diameters of reamed cavities compared using the Mann-Whitney U test to determine any statistically significant differences between groups (p<0.05) [Fig. 1). Results. Reaming errors were significantly higher in low-density bone compared to high-density bone for both reamer types and reaming techniques tested (61.9 mm (SD 0.7) vs 61.4 mm (SD 0.4), respectively; p=0.0045). Whirlwind reaming was significantly more accurate and precise than straight reaming using both conventional (61.3 mm (SD 0.1) vs 62.3 mm (SD 0.4), respectively; p<0.0001) and single use reamers (61.1 mm (SD 0.3) vs 61.7 mm (SD 0.7), respectively; p=0.0058) [Fig. 2]. The novel single use reamer was significantly more accurate than the unused conventional reamer, using both the straight (61.7 mm (SD 0.7) vs 62.4 mm (SD 0.4), respectively; p=0.0011) and whirlwind techniques (61.2 mm (SD 0.3) vs 61.3 mm (SD 0.1), respectively; p=0.0002) [Fig. 3]. Conclusion. This is the first study to our knowledge that has assessed acetabular reaming technique in both low and high density saw bones. Improved reaming accuracy and precision was seen in both devices tested when using the ‘whirlwind’ technique in both high-density and low-density bone models when compared to a straight reaming technique. The single use device assessed reamed a cavity size closer to its stated size (61mm) compared to conventional reamers. Based on this study we suggest using a careful “whirlwind” technique when performing acetabular reaming, and for the surgeon to pay particular attention when performing joint replacement in patients with reduced bone quality as there is likely to be more variability in acetabular reaming accuracy in these patients

Incidence of intraoperative fracture during cementless Total Hip Arthroplasty (THA) is increasing. This is attributed to factors such as an increase in revision procedures and the favour of cementless fixation. Intraoperative fractures often occur during the seating of cementless components. A surgical mallet and introducer are used to generate the large impaction forces necessary to seat the component, sometimes leading to excessive hoop strain in the bone. The mechanisms of bone strain during impaction are complex and occur over very short timeframes. For this reason experimental and simulation models often focus on strain shortly after the implant is introduced, or seat it quasi-statically. This may not produce a realistic representation of the magnitude of strain in the bone and dangerously under-represent fracture risk. This in-vitro study seeks to determine whether strain induced during impaction is similar both during the strike (dynamic strain) and shortly after the strike has occurred (post-strike strain). It is also asked whether post-strike strain is a reliable predictor of dynamic strain. A custom drop tower was used to seat acetabular components in 45 Sawbones models (SKU: 1522–02, Malmo, Sweden), CNC milled to represent the acetabular cavity. Ten strikes were used to seat each cup. 3 strike velocities (1.5 m/s, 2.75 m/s, 4 m/s) and 3 impact masses (600 g, 1.2 kg, 1.8 kg) were chosen to represent 9 different surgical scenarios. Two strain gages per Sawbone were mounted on the surface of the block, 2 mm from the rim of the cavity. Strain data was acquired at 50 khz. Each strain trace was then analysed to determine the peak dynamic strain during mallet strike and the static strain post-strike. A typical strain pattern was observed during seating. An initial pre-strike strain is followed by a larger dynamic peak as the implant is progressed into the bone cavity. Strain subsequently settles at a lower (tensile) value than peak dynamic post-strike, but higher than pre-strike strain. Over the 450 strikes conducted dynamic strain was on average 3.39 times larger than post-strike strain. A statistically significant linear relationship was observed between the magnitude of post-strike and dynamic strain (adjusted R. 2. =0.391, p<0.005). This indicates that, for a known scenario, post-strike strain can be used as an indicator for dynamic peak strain. However when only the maximum dynamic and post-strike strains were taken from across the 10 strikes used to seat the implant, the relationship between the two strains was not significant (R. 2. =0.300, p=0.73). This may be due to the fact that the two maximums did not often occur on the same strike. On average, max dynamic strain occurred 1.7 strikes after max post-strike strain. We conclude that peak dynamic strain is much larger than the strain immediately post-strike in a synthetic bone model. It is shown that post-strike strain is not a good predictor of dynamic strain when the max strain during any strike to seat the component is considered, or variables (such as mallet mass or velocity) are changed. It is important to consider dynamic strain in bone as well as post-strike strain in experimental or simulated bone models to ensure the most reliable prediction of fracture