Introduction. An understanding of anatomic variability can help guide the surgeon on intervention strategies. Well-functioning thumb metacarpophalangeal joints (MCPJ) are essential for carrying out typical daily activities. However, current options for arthroplasty are limited. This is further hindered by the lack of a precise understanding of the geometric variation present in the population. In this paper, we offer new insight into the major modes of geometric variation in the thumb MCP using Statistical Shape Modelling. Methods. Ten participants free from hand or wrist disease or injury were recruited for CT imaging (Ethics Ref:14/LO/1059). 1. Participants were sex matched with mean age 31yrs (range 27–37yrs). Metacarpal (MC1) and proximal phalanx (PP1) bone surfaces were identified in the CT volumes using a greyscale threshold, and meshed. The ten MC1 and ten PP1 segmented bones were aligned by estimating their principal axes using Principal Component Analysis (PCA), and registration was performed to enable statistical comparison of the position of each mesh vertex. PCA was then used again, to reduce the dimensionality of the data by identifying the main ‘modes’ of independent size and shape variation (principal components, PCs) present in the population. Once the PCs were identified, the variation described by each PC was explored by inspecting the shape change at two standard deviations either side of the mean bone shape. Results. For the ten MC1s, over 80% of the variation was described by the first two PCs (Table 1). Figure 1 shows the effect of the variation in PC1. The majority of geometric variation of the ten PP1s was also described by the first two PCs, with PC1 describing 78.9%. Figure 2 shows the effect of this component on the mean bone geometry. Both the distal articulating surface (head) of the MC1 and the proximal articulating surface (base) of the PP1 vary in overall size. However, the MC1 head also varies in shape (curvature), whereas the PP1 base does not appear to undergo noticeable variation in shape. In this study population, smaller MC1 was observed to correlate with a flatter head, whereas the PP1 head shape did not vary with size. Discussion. The flatter MC1 head (smaller height-radius ratio) may have implications for MCPJ instability, and possibly for osteoarthritic degeneration. A recent study predicted similar trends for the first CMC joint. 2. Previous investigation also observed correlation between MC1 head curvature and MCPJ RoM. 3. , which may explain clinical observations of differing thumb movement strategies. This study used a convenience sample and cannot describe a full population's variability, though the high variance captured by only two PCs suggests adequate external validity amongst similar populations. Further confidence would be gained from studying the joint (i.e. single PCA containing both bones), and wider populations. Significance. These data: provide more precise description of anatomic variation; may offer insights into thumb movement strategies and MCPJ osteoarthritic degeneration. 4. ; and support implant design for individuals whose anatomy can bear an anatomic reconstruction. For any figures or tables, please contact the authors directly

Introduction. A deep squat (DS) is a challenging motion at the level of the hip joint generating substantial reaction forces (HJRF). As a closed chain exercise, it has great value in rehabilitation and muscle strengthening of hip and knee. During DS, the hip flexion angle approximates the functional range of hip motion risking femoroacetabular impingement in some morphologies. In-vivo HJRF measurements have been limited to instrumented implants in a limited number of older patients performing incomplete squats (< 50° hip flexion and < 80° knee flexion). On the other hand, total hip arthroplasty is being increasingly performed in a younger and higher demanding patient population. These patients clearly have a different kinetical profile with hip and knee flexion ranges going well over 100 degrees. Since measurements of HJRF with instrumented prostheses in healthy subjects would be ethically unfeasible, this study aims to report a personalised numerical solution based on inverse dynamics to calculate realistic in-silico HJRF values during DS. Material and methods. Thirty-five healthy males (18–25 years old) were prospectively recruited for motion and morphological analysis. DS motion capture (MoCap) acquisitions and MRI scans with gait lab marker positions were obtained. The AnyBody Modelling System (v6.1.1) was used to implement a novel personalisation workflow of the AnyMoCap template model. Bone geometries, semi-automatically segmented from MRI, and corresponding markers were incorporated into the template human model by an automated procedure. A state of-the-art TLEM 2.0 dataset, included in the Anybody Managed Model Repository (v2.0), was used in the template model. The subject-specific MoCap trials were processed to compute kinematics of DS, muscle and joint reaction forces in the entire body. Resulting hip joint loads were compared with in-vivo data from OrthoLoad dataset. Additionally, hip and knee joint angles were computed. Results. An average HJRF of 274%BW (251.5 – 297.9%BW; 95% confidence interval) was calculated at the peak of DS. The HJRF on the pelvis was directed superior, medial and posterior throughout the DS. Peak knee and hip flexion angles were 112° (108.1° – 116.5°) and 107° (104.6° – 109.4°) on average. Discussion and conclusions. A comprehensive approach to construct an accurate personalised musculoskeletal model from subject-specific MoCap data, bone geometries, and palpatory landmarks was presented. Consistently higher HJR forces during DS in young adults were demonstrated as opposed to the Orthoload dataset. Similarly, knee and hip flexion angles were much higher, which could cause the increase in HJRF. It can be concluded that DS kinetics in young adults differ from the typical total hip arthroplasty population. These models will enable further in-silico joint biomechanics studies, and could serve the purpose of a virtual test bed for implant design

Introduction. 3D printed Patient Specific Guides (PSGs) can improve the accuracy of joint-replacement. Pre-operative CT bone models are used to design a PSG that fits the patient's specific bone geometry. A key design requirement is to maximize docking robustness such that the PSG can maintain a stable position in the planned location. However, current PSG designs are typically manually defined, lack a quantitative assessment of robustness, and have an unknown consistency of docking rigidity between patients. Limited research exists on the stability and robustness of surgical guides, and no software packages are available to facilitate this analysis. Our goal was to develop such a software. Methods. In this paper, the contact between a patient's bone and the PSG is modelled using robotic grasping theory, and its docking robustness is quantified by analysis of the PSG's grasp wrench space (GWS) (i.e. the combination of contact forces and torques between the bone and PSG). To this end, a PSG design and analysis tool with a graphical user interface was developed in MATLAB. This tool allows the user to load shapes (e.g. STL bone models), select and manipulate possible contact points, and optimize the contact point locations according to the largest-minimum resisted wrench (LRW) that the grasp can resist in any direction. The LRW is a grasp quality metric equivalent to the radius of the largest (hyper)sphere contained within the convex hull of the GWS, and its value can be evaluated using frame-variant GWS calculations (i.e. centroid-dependent) or frame-invariant GWS calculations (i.e. centroid-independent). Results. Multiple 2D and 3D shapes were loaded into the software and contact points were selected to form a ‘grasp’ and compute their wrench spaces. For a square with four contact points, the frame-variant LRW is calculated to be 0.4240 and the frame-invariant LRW is calculated to be 0.4999. These values are expected to increase after contact point optimization, with a higher value indicating higher docking robustness. A realistic contact set for a shoulder arthroplasty PSG was created by modelling the glenoid of a patient's scapula and selecting seven contact points. For this configuration, a frame-variant LRW was calculated to be 0.0034 and a frame-invariant LRW is 0.0181. Discussion. To date we have developed a software capable of using robotic grasping theory to analyse and validate the robustness of existing surgical guides. A set of contact points similar to those used in clinical PSGs produced a much smaller quality metric value compared to the ideal grasp for a simple shape. This quality metric value is constrained by the wrench component with the smallest value and it is clear that producing a PSG design with a robust ‘grasp’ (i.e. high docking rigidity) is non-trivial. In the future, the result of this software will be compared to experimental results to validate its predictions. Once validated, design optimization capabilities will be implemented that can significantly improve the PSG docking rigidity. For any figures or tables, please contact authors directly

Introduction. Untreated hip osteoarthritis is a debilitating condition leading to pain, bone deformation, and limited range of motion. Unfortunately, studies have not been conducted under in vivo conditions to determine progressive kinematics variations to a hip joint from normal to pre-operative and post-operative THA conditions. Therefore, the objective was this study was to quantify normal and degenerative hip kinematics, compared to post-operative hip kinematics. Methods. Twenty unique subjects were analyzed; 10 healthy, normal subjects and 10 degenerative, subjects analyzed pre-operatively and then again post-operatively after receiving a THA. During each assessment, the subject performed a gait (stance and swing phase) activity under mobile, fluoroscopic surveillance. The normal and diseased subjects had CT scans in order to acquire bone geometry while implanted subjects had corresponding CAD models supplied. Femoral head and acetabular cup centers were approximated by spheres based on unique geometries while the component centers were pre-defined as the center of mass. These centers were used to compare femoral head sliding magnitudes on the acetabular cup during the activity for all subjects. Subjects were noted to have separation with changes in center magnitudes of more than 1 mm during gait. Utilizing 3D-to-2D registration techniques, the hip joint kinematics were derived and assessed. This allowed for visualization of normal subject positioning, pre-op bone deterioration, and implant placement within the bones. Results. None of the normal, experienced femoral head sliding (FHS) within the acetabulum. Two of the normal subjects revealed tendencies more similar to a degenerative hip. However, 4/10 of the degenerative subjects saw significant FHS with an average maximum of 1.344 0.522 mm. It was interesting to note that none of the implanted subjects experienced FHS, demonstrating improved kinematic trends more normal-like and revealing better kinematic patterns post-operative compared to their pre-operative conditions. Discussion. Overall, analysis has revealed trends of degenerative hips experiencing more abnormal hip kinematics due to lower surface area and greater magnitudes of femoral center head displacement. The implanted subjects saw decreased amounts of displacement which correlated to increases in contact area. These results more closely matched normal hip kinematics and showed an improvement over their diseased condition. It seems that the surgeon in this study better replicated the stem version angle to the pre-operative conditions, leaving less transverse stress of the femoral head on the acetabular cup, possibly leading to the femoral head remaining within the acetabular cup and the subjects not experiencing FHS. Significance. Pre-operative, degenerative hip subjects displayed abnormal femoral hip displacement at greater magnitudes to normal hip subjects. After THA, these subjects saw reduced magnitudes of displacement more in line with normal hip kinematics. For any figures or tables, please contact authors directly

INTRODUCTION. Proper ligament engagement is an important topic of discussion for total knee arthroplasty; however, its importance to total ankle arthroplasty (TAA) is uncertain. Ligaments are often lengthened or repaired in order to achieve balance in TAA without an understanding of changes in clinical outcomes. Unconstrained designs increase ankle laxity,. 1. but little is known about ligament changes with constrained designs or throughout functional activity. To better understand the importance of ligament engagement, we first investigated the changes in distance between ligament insertions throughout stance with different TAA designs. We hypothesize that the distance between ligaments spanning the ankle joint would increase in specimens following TAA throughout stance. METHODS. A validated method of measuring individual bone kinematics was performed on pilot specimens pre- and post-TAA using a six-degree-of-freedom robotic simulator with extrinsic muscle actuators and motion capture cameras (Figure 1). 2. Reflective markers attached to surgical pins and radiopaque beads were rigidly fixed to the tibia, fibula, talus, calcaneus, and navicular for each specimen. TAAs were performed by a fellowship-trained foot and ankle surgeon on two specimens with separate designs implanted (Cadence & Salto Talaris; Integra LifeSciences; Plainsboro, NJ). Each specimen was CT-scanned after robotic simulations of stance pre- and post-TAA. Specimens were then dissected before a 3D-coordinate measuring device was used to digitize the ligament insertions and beads. Ligament insertions were registered onto the bone geometries within CT images using the digitized beads. Individual bone kinematics measured from motion capture were then used to record the point-to-point distance between centers of the ligament insertions throughout stance. RESULTS. Results from the pilot specimens are presented for the calcaneofibular ligament (CFL) only. The distance between the CFL insertions was larger throughout stance following Cadence implantation (Figure 2A) and was decreased throughout most of stance following Salto Talaris implantation (Figure 2B). The percent change in CFL distance with respect to static standing was also increased with the Cadence implant (Figure 2C) and similar to intact following Salto Talaris implantation (Figure 2D). Ankle motion was similar to intact with the Cadence (Figure 3A) and was decreased with the Salto Talaris (Figure 3B). DISCUSSION. This study suggests that ligament length during stance changes following TAA. The Cadence implant similarly replicated ankle kinematics but CFL length was increased throughout stance which supports our hypothesis. In contrast, the Salto Talaris implant reduced ankle motion and decreased the CFL length. Although the slack length and pre-strain of the CFL were unknown, the distance between insertions from the pilot specimens provides preliminary insight into how ligament mechanics change post-TAA during functional activity. CLINICAL RELEVANCE. Preliminary results of ligament length changes throughout stance may indicate that ligament mechanics change post-TAA and could affect patient outcomes. Changes may be even more pronounced when a soft tissue release or reconstruction is performed to correct malalignment. For any figures or tables, please contact the 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

INTRODUCTION. Mechanical properties mapping based on CT-attenuation is the basis of finite element (FE) modeling with heterogeneous materials and bone geometry defined from clinical-resolution CT scans. Accuracy between empirical and computational models that use constitutive equations relating CT-attenuation to bone density are well described, but material mapping strategy has not gained similar attention. As such, the objective of this study was to determine variations in the apparent modulus of trabecular bone cores mapped with various material mapping strategies, using a validated density-modulus relationship and co-registered µFEMs as the gold standard. METHODS. Micro-CT images (isotropic 32 µm) were used to create µFEMs from glenoid trabecular bone cores of 14 cadaveric scapula. Each µFEM was loaded in unconstrained compression to determine the trabecular core apparent modulus (E. app. ). Quantitative CT (QCT) images (isotropic 0.625 mm) were subsequently acquired and co-registered QCT-FEMs created for each of the 14 cores. The QCT-FEMs were meshed with either linear hexahedral (HEX8), linear tetrahedral (TET4), or quadratic tetrahedral (TET10) elements at 3 mesh densities (0.3125 mm, 0.46875 mm, 0.625 mm). Three material mapping strategies were used to apply heterogeneous element-wise (element-averaging of the native HU field (Mimics V.20, Materialise, Leuven BE)) or nodal (tri-linear interpolation of HU Field or E Field (Matlab V. R2017a, Natick, RI, USA)) material properties to the QCT FEMs. Identical boundary conditions were used and E. app. between the µFEMs and QCT-FEMs was compared (Figure 1). The QCT density of each hexahedral mesh with element size equal to voxel dimensions was used to compare the QCT density mapping between tetrahedral meshes and material mapping strategy. RESULTS. For tetrahedral meshes the mean QCT density error was 2.4±2.7%, 4.3±4.4%, and 1.6±2.5%, for tetrahedral mesh densities of 0.3125, 0.46875, and 0.625 mm, respectively. Nodal material mapping differs by TET4 and TET10 and therefore for tri-linear interpolation the QCT density error was 0.4±1.6%, 3.5±3.3%, and 2.0±2.2%, for TET4 mesh densities of 0.3125, 0.46875, and 0.625 mm, respectively. The errors were −0.6±1.4%, 2.0±1.4%, 0.2±1.9% for TET10 mesh densities of 0.3125, 0.46875, and 0.625 mm, respectively. Percentage errors in E. app. as a function of bone volume fraction (BV/TV) by material mapping strategy were lowest for HEX8 QCT-FEMs mapped with element-based HU (MIMICS). This was also the best mapping strategy for both TET4 and TET10 QCT-FEMs. The node-based material mapping using the HU field was best for TET4 QCT-FEMs with 0.625 mm elements. The node-based E field mapping had the lowest errors for TET10 QCT-FEMs but had greater errors than the other two mapping strategies for all element types (Figure 2). DISCUSSION. This study compared material mapping strategy, element type, and element density in QCT-FEMs compared to co-registered µFEMs. It was found that QCT-FEMs with hexahedral elements most closely match µFEMs when element averaging of the native HU field is used. This mapping strategy also showed relatively lower errors with linear and quadratic tetrahedral elements compared to node-based material mapping strategies. If modeling parameters are carefully considered when developing QCT-FEMs, models have the potential to accurately replicate micro-level trabecular bone apparent properties. For any figures or tables, please contact the authors directly

Introduction. Total knee arthroplasty is the standard treatment for advanced knee osteoarthritis. Patient-specific instrument (PSI)has been reported by several authors using different techniques produced by implant companies. The implant manufacturers produce PSI exclusively for their own knee implants and for easy straightforward cases. However, the PSI has become very expensive and unusable as a universal or an open platform. In addition, planning the implant is done by technicians and not by surgeons and needs long waiting time before surgery (6 weeks). Methods. We proposed a new technique which is a device and method for preparing a knee joint in a patient undergoing TKA surgery of any knee implant (prosthesis). The device is patient specific, based on a method comprised of image-based 3D preoperative planning (CT, MRI or computed X-ray) to design the templates (PSI) that are used to perform the knee surgery by converting them to physical templates using computer-aided manufacturing such as computer numerical control (CNC) or additive-manufacturing technologies. The device and method are used for preparing a knee joint in a universal and open-platform fashion for any currently available knee implant. Results. All patient-specific implants and any knee implant could be produced. The technique was applied on NExGen implant (Zimmer)on 21 patients, PFC implant (Depuy, J & J) on 5 patients, Scorpio NRG implant (Stryker) on 24 patients and SLK Evo implant (Implant International) on 81 patients. The >15 degrees varus gave a mean of 10.44 degrees in 56.67% of cases and the <15 degrees varus gave a mean of 24.04 degrees in 43.33% of cases. The total varus of 5–30 degrees gave a mean of 16.33 degrees in 90.9% of cases and the total valgus of 20–40 gave a mean of 25 degrees in 9.1% of cases. The fixed flexion deformity of < 20 degrees gave a mean of 9.4 degrees in 75.3% of cases while the fixed flexion deformity of >20 gave a mean of 31.87 degrees in 24.7% of cases. Discussion. The system is based on CT images, generic data of implant sizes, average bone geometry and standard TKA parameters for bone cutting, mechanical axis and rotation (e.g., zero-degree coronal cut, adjustable posterior slope, femoral flexion, epicondylar axis, no notching or overhang, etc.). The method of planning and completing virtual surgery of TKA includes several steps based on 3D reconstruction and segmentation of computed tomography (CT) or MRI scan data. The universal device and method are suitable to be used for any commercially and currently available knee implant. They are used for all on-shelf implants and all patient-specific instruments. The device is specifically designed for TKA and the planning is based on the 3D files of a universal TKA prosthesis. There are four standard sizes of the universal TKA prosthesis which were built depending on the average bone geometry. These 4 sizes are 55, 60, 65 and 70 mm. These sizes are consistent with the six most common implants available today: NexGen Zimmer, PFC Depuy, Sigma Knee, Triathlon Stryker, Vanguard Biomet, and Smith & Nephew Proflex. However, for extreme cases, one size above or below the maximum and minimum range can be used. The device has 2 parts: a femoral part and a tibial part, both of which are independent of any commercially available knee implant

Introduction. Female gender, old age (men >60y and women > 55y), severe acetabular dysplasia, poor proximal femoral bone geometry, large (>1cm) femoral head cysts, limb-length discrepancy (> 2cm) and small prosthetic head size (less than 50mm for men and less than 46mm for women) are risk factors for hip resurfacing arthroplasty (HRA). Purpose. To present clinical and radiographic results of HRA in patients having risk factors. Patients and methods: A total of 39 HRA was inserted in 33 patients (11 men and 22 women). Birmingham hip resurfacing (Smith & Nephew, UK) was used in 9 hips and Adept (Finsbury, UK) was used in 30 hips. Among the 30 hips inserted Adept, 11 cups were fixed with rim screws. The mean age of the patients at the time of operation was 52 years. The mean weight and height of the male and female patients were 70.4kg and 167cm, 58.5kg and 154.4cm, respectively. The median head size of the male and female patients was 50mm and 42mm, respectively. Preoperative diagnosis was primary osteoarthritis in 6 hips and secondary osteoarthritis due to aceatbular dysplasia (DDH) in 33 hips. Risk factors of HRA were listed for each patient. The Harris hip score and visual analogue pain scale (VAS) were measures of clinical outcome. Radiographic review was performed retrospectively. MRI and CT images were acquired in 29 hips and 2 hips, respectively, at a mean of 4.8 years after HRA to find periprosthetic soft tissue abnormality such as a psedotumor. Kaplan-Meier method was used to calculate implant survivorship. Results. Two hips had no risk factor, whereas 37 hips had at least one risk factor. Risk factors were listed as follows: female gender in 27, old age in nine, severe acetabular dysplasia in 25, poor proximal femoral bone geometry in 11, head cysts in 13, limb-length discrepancy in three and small head size in 21. There were two revisions in two men. One hip was revised because of acute infection. The patient had a risk factor (old age). Another hip was revised because of cup loosening. The patient had two risk factors (severe acetabular dysplasia and small head size). The mean follow-up period for unrevised hips was 5 years (range, 2 to 8 years). The Harris hip score improved from 47.3 points preoperatively to 96.5 points at the latest follow-up (p<0.001). VAS improved from 65 preoperatively to 5 at the latest follow-up (p<0.001). Using revision for any reason as the endpoint, the Kaplan-Meier survivorship was 94.9% at 5years. No implant was loose at the latest radiographic examination. MRI and CT of the hip revealed no pseudotumor. Discussion. In this series, only two patients had no risk factor for HRA. Although majority of our patients were women with acetabular dysplasia and small head size, clinical and radiographic results of HRA were good up to five years (Figs 1 and 2: pre- and post-operative X-ray of 49y women having five risk factors). Conclusion. Clinical and radiographic results of HRA were good in patients who have risk factors

A fracture of the distal radius may lead to malunion of bone segments, which gives discomfort to the patient and may lead to chronic pain, reduced range of motion, reduced grip strength and finally to early osteoarthritis. A treatment option to realign the bone segments is a corrective osteotomy. In this procedure the surgeon tries to improve alignment by cutting the bone at, or near, the fracture location and by fixating the bone segments in an improved position, using a plate and screws. Standard corrective osteotomy of the distal radius is most often planned using two orthogonal radiographs to find correction parameters for restoring the radial inclination, palmar tilt and ulnar variance, to normal. However, 2D imaging techniques hide rotations about the bone axis and may therefore cause a misinterpretation of the correction parameters. We present a new technique that uses preoperative 3-D imaging techniques to plan positioning and to design a patient-tailored fixation plate that only fits in one way and realigns the bone segments as planned in six degrees of freedom. The procedure uses a surgical guide that snugly fits the bone geometry and allows predrilling the bone at specified positions, and cutting the bone through a slit at the preoperatively planned location. The patient-tailored plate fits the same bone geometry and uses the predrilled holes for screw fixation. The method is evaluated experimentally using artificial bones and renders realignment highly accurate and very reproducible (derr < 1.2 ± 0.8 mm and ϕerr < 1.8 ± 2.1°). In addition, the new method is evaluated clinically (n=1) and results in accurate positioning (derr ≤ 1.0 mm and ϕerr ≤ 2.6°). Besides using a patient-tailored plate for corrective distal radius osteotomy, the method may be of interest for corrective osteotomy of other long bones, mandibular reconstruction and clavicular reconstruction as well. In all of these cases the contralateral side can equally be used as reference for reconstruction of the affected side. The two-step method of predrilling and cutting using a surgical guide, followed by the utilisation of a patient-tailored plate for fixation and accurate 3D positioning at the same time, seems very easy to utilise during surgery, since it does not require complex navigation, robotic equipment or tracking tools. Custom treatment with a patient-tailored plate may reduce the reoperation rate, since repositioning is likely to be better than conventional malunion treatment using 2D imaging techniques and a standard anatomical plate. The patient-tailored plating technology is expected to have a great impact on future corrective osteotomy surgery

Aims

This study explored the shared genetic traits and molecular interactions between postmenopausal osteoporosis (POMP) and sarcopenia, both of which substantially degrade elderly health and quality of life. We hypothesized that these motor system diseases overlap in pathophysiology and regulatory mechanisms.

In robot-assisted orthopaedic surgery, registration is a key step, which defines the position of the patient in the robot frame so that the preoperative plan can be performed. Current registration methods have their limitations, such as the requirement of immobilisation of the limbs or the line of sight (LOS) issues. These issues cause inconvenience for the surgeons and interrupt the surgical workflow in the operating room. Targetting these issues of current registration methods, we propose a camera-robot registration system for joint replacement. The bone geometry, which is measured directly by a depth camera, is aligned to a preoperatively obtained bone model to calculate the pose of the target. Simultaneously, in order to avoid registration failure caused by LOS interruptions, the depth camera tracks objects that may occlude the target bone, and a robot manipulator is used to move the camera away from the nearest obstacle. The optimal camera motion is calculated based on the position and velocity of the obstacle, which avoids the occlusion efficiently without changing the target position in the camera frame. Inverse kinematics of the robot is used to project the Cartesian velocity of the end-effector into the joint space, with kinematic singularities considered for stable robotic control. An admittance controller is designed as the human-robot interface so that the surgeon can directly set the robot configuration by hand according to the actual environment. Simulations and experiments were conducted to test the performance. The results show that the proposed obstacle avoidance method can effectively increase the distance between the obstacle and the LOS, which lowers the risk of registration failure due to obstacle occlusion. This pilot study is promising in reducing distractions to the surgeon and can help achieve a fluent and surgeon-centred workflow

Introduction. Geometric variations of the hip joint can give rise to repeated abnormal contact between the femur and acetabular rim, resulting in cartilage and labrum damage. Population-based geometric parameterisation can facilitate the flexible and automated in silico generation of a range of clinically relevant hip geometries, allowing the position and size of cams to be defined precisely in three dimensions. This is advantageous compared to alpha angles, which are unreliable for stratifying populations by cam type. Alpha angles provide an indication of cam size in a single two-dimensional view, and high alpha angles have been observed in asymptomatic individuals. Parametric geometries can be developed into finite element models to assess the potential effects of morphological variations in bone on soft tissue strains. The aim of this study was to demonstrate the capabilities of our parameterisation research tool by assessing impingement severity resulting from a range of parametrically varied femoral and acetabular geometries. Methods. Custom made MATLAB (MathWorks) and Python codes. [1]. were used to generate bone surfaces, which were developed into finite element models in Abaqus (SIMULIA). Parametric femoral surfaces were defined by a spherical proximal head and ellipse sections through the neck/cam region. This method produced surfaces that were well fitted to bone geometry segmented from CT scans of cam patients and capable of producing trends in results similar to those found using segmented models. A simplified spherical geometry, including the labrum and acetabular cartilage, represented the acetabulum. Femoral parameters were adjusted to define relevant variations in cam size and position. Two radii (small and large cams) and two positions (anterior and superior cams) were defined resulting in four models. Alpha angles of these parametric femurs were measured in an anterior-posterior view and a cross-table lateral view using ImageJ (NIH). A further model was developed using a femur with a medium cam size and position, and the level of acetabular coverage and labrum length were varied. Bones were modelled as rigid bodies and soft tissues were modelled as transversely isotropic linearly elastic materials. With the acetabulum fully constrained in all cases, the femurs were constrained in translation and rotated to simulate flexion followed by internal rotation to cause impingement against the labrum. Results and Discussion. Models generated using the parametric approach showed that potential for tissue damage, indicated through local strain, was not predicted by measured alpha angle, but resulted from cam extent and position as defined by the ellipses. When variations were made to the acetabular rim, an increase in bone coverage had the greatest effect on impingement severity, indicated by strain in the cartilage labral-junction. An increase in labral length increased labral displacement, but had less effect on cartilage-labral strain. Patient specific models currently require full image segmentation, but there is potential to further develop these parametric methods to assess likely impingement severity based on a series of measures of the neck and acetabulum when three-dimensional imaging of patients is available

Introduction. Although total hip arthroplasty is a very successful operation, complications such as: dislocation, aseptic loosening, and periprosthetic fracture do occur. These aspects have been studied in large populations for traditional stem designs, but not for more recent short stems. The design rationale of short stems is to preserve bone stock, without compromising stability. However, due to their smaller bone contact area, high peak stresses and areas of stress shielding could appear in the proximal femur, especially in the presence of atypical bone geometries. In order to evaluate this aspect, we quantified the stress distribution in atypical proximal femurs implanted with a commercially available calcar guided short stem. Methods. Geometrical shape variations in neck-shaft angle (NSA), neck-length (NL) and anteversion (AV), were determined three-dimensionally in the Mimics Innovation Suite (Materialise N.V., Leuven, Belgium) from a CT dataset of 96 segmented femurs. For each shape variation, the femurs that had the two lowest, two average and two highest values were included (18 femurs). Using scripting functionality in Mimics, CAD design files of the calcar guided Optimys short stem (Mathys, Bettlach, Switzerland) were automatically sized and aligned to restore the anatomical hip rotation center. Stem size and position were manually corrected by an orthopedic surgeon before finite element (FE) models were constructed using a non-manifold assembly approach (Figure 1). Material properties were estimated from the CT dataset and loads representing walking and stair climbing were applied [1]. Stress-shielding was evaluated by the change in average strain energy density pre- and post-operatively in three different regions (calcar, midstem, tip) each being subdivided in four quarters (medial, lateral, anterior, posterior) (Figure 2). Results. Stress shielding in the proximal femur was seen in all models, especially in the calcar-medial region. In that region, the largest variation in stress shielding was observed for the models with an atypical NSA, ranging from 57% to 96%. The lowest amount was found in a patient with an average NSA (124°), and the highest amount was found in a patient with a small NSA (109°) (Figure 2). In the models selected for their varying neck lengths, calcar-medial stress shielding increased from 69% (NL 53 mm) to 97% (NL 66 mm). Stress shielding was least sensitive to variations in AV, ranging from 79% to 92%. Similar patterns were observed for walking and stair climbing loads. Discussion. Stress shielding was smallest in femurs where the load-transfer between implant and bone was located more proximally, while higher levels of stress shielding occurred when the load transfer was more pronounced at the tip of the stem (Figure 3). Two femurs with an average NSA and NL showed substantially lower stress shielding than the 16 other femurs. This may suggest that the calcar guided Optimys short stem prevents stress shielding especially in average femurs, but less so in atypical femurs. Hence, a larger study population should be investigated to support this hypothesis. For any figures or tables, please contact the authors directly

Shortened humeral stem implants can be advantageous as they preserve more of the patient's bone and are not limited by the canal for placement in the proximal body. However, traditional longer stems may help stabilize the implant through interaction with the dense cortical bone of the canal. We developed an FEA model to gage the contributions of design features such as stem length, coatings, and interference fit. Models were constructed in FEMAP and solved using the NX Nastran advanced nonlinear static solver. The Turon (DJO Surgical) implant geometry was imported from a Solidworks CAD file and bone geometry was taken from a statistical shape model by Materialise representing the mean humeral geometry of 95 healthy humeri (avg age = 69.9 years). Implant and cancellous bone were considered to be linear homogeneous materials, and the cortical shell was modeled as orthotropic. Interference fits between the implant and cancellous bone surfaces were modeled using the gap feature of NX Nastran with friction coefficients corresponding to the surface finish. Loading was applied through a control node located at the center for the replacement head. Two loading conditions were analyzed, one representing torsion about the neck axis with a magnitude of 3140 Nm and one representing the peak load vector during activities of daily living. Using resection plane nodes at the intersection of the implant and bone, the histograms of micromotion and the associated 5. th. , 50. th. , and 95. th. percentile values were calculated. For a traditional length stem, the dominate effect on the predicted micromotion at the resection plane was the interference fit in the coating region. The contribution of a traditional length stem to resection plane micromotion was complex and depended on the presence of the stem and the amount of interference fit in the coating region

Introduction. The purpose of this study was to experimentally evaluate impingement and dislocation of total hip replacements while performing dynamic movements under physiological-like conditions. Therefore, a hardware-in-the-loop setup has been developed, in which a physical hip prosthesis actuated by an industrial robot interacts with an in situ-like environment mimicked by a musculoskeletal multibody simulation-model of the lower extremity. Methods. The multibody model of the musculoskeletal system comprised rigid bone segments of the lower right extremity, which were mutually linked by ideal joints, and a trunk. All bone geometries were reconstructed from a computed tomography set preserving anatomical landmarks. Inertia properties were identified based on anthropometric data and by correlating bone density to Hounsfield units. Relevant muscles were modeled as Hill-type elements, passive forces due to capsular tissue have been neglected. Motion data were captured from a healthy subject performing dislocation-associated movements and were fed to the musculoskeletal multibody model. Subsequently, the robot moved and loaded a commercially available total hip prosthesis and closed the loop by feeding the physical contact information back to the simulation model. In this manner, a comprehensive parameter study analyzing the impact of implant position and design, joint loading, soft tissue damage and bone resection was implemented. Results. The parameter study revealed a generally high dislocation risk for the seating-to-rising with adduction scenarios. Improper implant positioning or design could be compensated by adjusting prosthesis components correspondingly. Gluteal insufficiency or lower joint loading did not result in higher impingement or dislocation risk. However, severe malfunction of the artificial joint was found for proximal bone resection. Discussion. Previous testing setups ignored the impact of active muscles or relied on simplified contact mechanics. Herein, total hip replacement stability has been investigated experimentally by using a hardware-in-the-loop simulation. Thereby, several influencing factors such as implant position and design as well as soft tissue insufficiency and imbalance could be systematically evaluated with the goal to enhance joint stability

Introduction. Both navigation and instrumented bone referencing use unreliable intraoperative landmark identification or fixed referencing rules which don't reflect patient specific variability. PSI, however, lacks the flexibility to adapt to soft tissue factors not known during preoperative planning, in addition to suffering error from guide fit. A novel method of recreating surgical cut planes that combines preoperative image based identification of landmarks and planning with intraoperative adjustability is under development. This method uses an intraoperative 3D scan of the bone in conjunction with a preoperative CT scan to achieve the desired cuts and so avoids issues of intraoperative identification of landmarks. Method. During TKA surgery, a reference device is placed on the exposed femur. The device is used to position a target block which is pinned to the bone (see Figure 1). The condyles and target block are then scanned, the process taking a second to complete. This 3D scan is filtered to remove extraneous bodies and noise leaving only the bony geometry and target block (see Figure 2). The scan is then reconciled to the known bone geometry taken from preoperative CT scans. A cutting block is then fixed to the target block with a reference array visible to the camera attached. Pre-planned cut planes on a computer model of the bone are compared to the position and configuration of the distal cutting guide. Software guides the surgeon in real-time on the necessary configuration changes required to align the cutting block. The cut is performed on the distal femur, the cutting guide removed from the target-block, and a second scan performed. The software repeats the filtering and alignment processes and provides the surgeon with data on how closely the performed cut matches the alignment planned. Results. Two patients underwent this method alongside traditional alignment techniques. The initial 3D scan of the distal femoral condyles of the patients was matched to their corresponding CT scans. The first case had a mean error of 0.65 mm with 85% of errors falling below a magnitude of 1.16 mm and 58% falling below the case mean (see Figure 3). The second case had a mean error of 0.39 mm with 84% of errors falling below 0.70 mm and 60% falling below the case mean. It should be noted that the error introduced was due to the omission of soft tissue such as the PCL in the CT scan. Exposed bone portions of the scan geometry matched well with the CT scan, with error magnitudes significantly below the mean. Discussion. The ability to obtain useful surgical alignment using preoperatively identified landmarks, alongside the small space requirements of a modern 3D scanner is sharply contrasted against the large space requirements and need for intraoperative probing of traditional navigation systems. Likewise, the use of preoperative planning and landmark identification to overcome intraoperative data capture variability mirrors that of PSI, but allows for potentially much greater accuracy of execution as the issue of guide fit and topology variation is avoided while intraoperative flexibility is maintained

Introduction. Joint mechanics and implant performance have been shown to be sensitive to ligament properties [1]. Computational models have helped establish this understanding, where optimization is typically used to estimate ligament properties for recreation of physically measured specimen-specific kinematics [2]. If available, contact metrics from physical tests could be used to improve the robustness and validity of these predictions. Understanding specimen-specific relationships between joint kinematics, contact metrics, and ligament properties could further highlight factors affecting implant survivorship and patient satisfaction. Instrumented knee implants offer a means to measure joint contact data both in-vivo and intra-operatively, and can also be used in a controlled experimental environment. This study extends on previous work presented at ISTA [3], and the purpose here was to evaluate the use of instrumented implant contact metrics during optimization of ligament properties for two specimens. The overarching goal of this work is to inform clinical joint balancing techniques and identify factors that are critical to implant performance. Methods. Total knee arthroplasties were performed on 4 (two specimens modeled) cadeveric specimens by an experienced orthopaedic surgeon. An instrumented trial implant (VERASENSE, OrthoSensor, Inc., Dania Beach, FL) was used in place of a standard insert. Experimentation was performed using a simVITROTM controlled robotic musculoskeletal simulator (Cleveland Clinic, Cleveland, OH) to apply intra-operative style loading and measure tibiofemoral kinematics. Three successive laxity style tests were performed at 10° knee flexion: anterior-posterior force (±100 N), varus-valgus moment (±5 Nm), and internal-external moment (±3 Nm). Tibiofemoral kinematics and instrumented implant contact metrics were measured throughout testing (Fig. 1). Specimen-specific finite element models were developed for two of the tested specimens and solved using Abaqus/Explicit (Dassault Systèmes). Relevant ligaments and rigid bone geometries were defined using specimen-specific MRIs. Virtual implantation was achieved using registration and each ligament was modeled as a set of nonlinear elastic springs (Fig. 1). Stiffness values were adopted from the literature [2] while the ligament slack lengths served as control variables during optimization. The objective was to minimize the root mean square difference between VERASENSE measured tibiofemoral contact metrics and the corresponding model results (Fig. 1). Results and Discussion. The models for both specimens successfully recreated joint kinematics with average errors less than 4° in rotations, and 3 mm in translations (not shown). Minus a systematic offset in θ for specimen 3, AFD and θ contact kinematics also realized good agreement for both specimens (Fig. 2). Contact forces were generally over-predicted, though both specimens recreated the experimental trends (Fig. 2). The present work shows continued progress towards simulation based tools that can be used for both research and to support the clinical decision making process. A separate ISTA submission presents assessment of these model's predictive capacity, while future work will evaluate additional specimens, and explore the sensitivity to uncertainties in experimental and modeling parameters. Acknowledgements. This work was supported by Orthosensor Inc. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Short stems have been developed for some years for preservation of femoral bone stock and achieve physiological proximal loading. Shortening stem length is a merit for bone stock preservation. However, it might lead to reduction of primary stability. We investigated relationship between stem length and primary stability by patient specific finite element analysis (FEA). Materials and Methods. Thirty-one hips in 31 patients were performed total hip arthroplasty with standard length tapered wedge-shaped (TW) cementless stem (CTi-II: Corin, Cirencester, UK). There were 6 males and 25 females. The average age at operation was 69 years old. The average body mass index was 23.9 kg/m2. Primary diagnoses were secondary osteoarthritis due to developmental dysplasia of the hip in 29 hips. Femoral canal shapes were normal in 21, stovepipe in 6 and champagne-flute in 4 hips. Bone qualities were type A in 6, B in 19 and C in 6 hips. The patients underwent computed tomography (CT) preoperatively and postoperatively. We constructed preoperative three dimensional (3D) femur surface models from preoperative CT data with individual bone mineral density (BMD) mapping. The postoperative 3D femur and rough stem surface models were obtained from postoperative CT data. The coordinates of the postoperative femur were transformed to fit the preoperative femur model. A precise stem model constructed using computer-assisted design data was matched to the transformed rough stem model using the iterative closest point algorithm. We obtained a patient-specific model with the proximal bone geometry, allocation of BMD and stem alignment. We estimated the average of axial and rotational micromotion (MM) at stem-bone interface and the ratio of area (MM â�¦ 40 micrometers) on the porous surface in order to analyze primary stability of TW stem with several lengths (standard (100 %), 75 %, 50 %, 40 % and 30 % length). Results. The average MM in standard length stem was 14.3 micrometers and the ratio of area with MM â�¦ 40 micrometers was 97.9 %. The average of axial and rotational MM in shorter length (75 %) stem were respectively 9.7, 8.3 micrometers. There were no differences in the average of axial and rotational MM between standard and shorter (75 %) length stems. MM at the porous surface was increased as the stem length grew shorter. The ratio of area with MM â�¦ 40 micrometers on the porous surface were reduced by 50 to 80 % in −40 % or less length stem, comparing with the standard length stem. Discussion and Conclusion. The present FEA on the stem length and MM demonstrated that primary stability in 40 % or less short length TW stem was extensively reduced, which might lead to failure of bone ingrowth on the porous surface and early loosening. Shortening of stem length less than 50 % is a risk for reduced primary stability in TW stem

Introduction. Medial unicompartmental knee arthroplasty (UKA) restores mechanical alignment and reduces lateral subluxation of the tibia. However, medial compartment translation remains abnormal compared to the native knee in mid-flexion Intra-operative adjustment of implant thickness can modulate ligament tension and may improve knee kinematics. However, the relationship between insert thickness, ligament loads, and knee kinematics is not well understood. Therefore, we used a computational model to assess the sensitivity of knee kinematics, and cruciate and collateral ligament forces to tibial component thickness with fixed bearing medial UKA. Methods. A computational model of the knee with subject-specific bone geometries, articular cartilage, and menisci was developed using multibody dynamics software (Fig 1a). The ligaments were represented with multiple non-linear, tension-only force elements, and incorporated mean structural properties. The 3D geometries of the femoral and tibial components of the Stryker Triathlon fixed-bearing UKA were captured using a laser scanner. An arthroplasty surgeon aligned the femoral and tibial components to the articular surfaces within the model (Fig 1b). The intact and UKA models were passively flexed from 0 to 90° under a 10 N compressive load. The tibial polyethylene insert was modeled by the orthopaedic surgeon to create a “balanced” knee. The modeled polyethylene insert thickness was then increased by 2 mm and decreased 2mm (in increments of 1mm) to simulate over- and under-stuffing, respectively. Outcomes were anterior-posterior (AP) translation of the femur on the tibia in the medial compartment, and forces seen by the ACL and MCL during mid-flexion (from 30 to 60° flexion). The mean differences between the intact knee model and all other experimental conditions for each outcome were calculated across mid-flexion. Results. All outcomes are presented relative to the intact knee model. A balanced medial UKA caused an average of 1.7 mm anterior translation of the medial compartment through mid-flexion (Table 1). Understuffing increased anterior translation of the medial compartment up to 3.7 mm on average. Overstuffing altered the anterior position of the medial compartment to 1.2 mm on average. The predicted ACL and MCL average loads in the balanced medial UKA differed from the intact model through mid-flexion by 2.7 N and 6.0 N, respectively (Table. 1). Overstuffing increased ACL and MCL load by 15.5 N and by 27.2 N, respectively. Understuffing by 2 mm decreased ACL and MCL load by 1.5 N at most. Discussion. A computational model incorporating a fixed-bearing medial UKA revealed that understuffing increased AP translation of the medial compartment in mid-flexion. In contrast, overstuffing increased ACL and MCL loads in mid-flexion). Thus, it is critical to achieve a compromise between insert thickness and ligament balance to obtain the most normal kinematics and ligament loads. Interestingly, no amount of over- or under-stuffing restored the AP position of the medial compartment to that of the intact model. This could be due to the inability of the flat polyethylene surface to provide “normal” AP constraint. Altogether, sensitivity analyses using computational modeling provide a valuable tool to assess the effect of implant position on knee mechanics