Introduction. Hip arthroplasty is considered common to patients aged 65 and over however, both Jennings, et al., (2012) and Bergmann (2016) found THA patients are substantially younger with more patients expecting to return to preoperative activity levels. With heavier, younger, and often more active patients, devices must be able to support a more demanding loading-regime to meet patient expectations. McClung (2000) demonstrated that obese patients can display lower wear-rates with UHMWPE bearing resulting from post-operative, self-induced reduced ambulatory movement, thus questioning if obese kinematics and loading are indeed the worst-case. Current loading patterns used to test hip implants are governed by ISO 14242-1 (2014). This study aimed to characterize a heavy and active population (referred to as HA) and investigate how the gait profile may differ to the current ISO profile. Method. A comprehensive anthropometric data set of 4082 men (Gordon, CC., et.al., 2014) was used to characterize a HA population. Obese and HA participants were classed as BMI ≥30 however HA participants were identified by applying anthropometric ratios indicative of lower body fat, namely “waist to height” (i.e. WHtR <0.6) and “waist to hip” (i.e. WHpR <0.9). Findings. Of 491 obese participants 61 were identified as HA (i.e. BMI> 30, WHpR<0.9; WHtR<0.6) (Figure 1). These characteristics were validated against a population of elite rugby players that were found to be a true reflection of HA patients (Figure 2). Combining the Army and Rugby populations resulted in a weight of 123kg for the 95. th. percentile, which based on 3× body weight (as referenced in ISO14242-1) would equate to a peak simulator load of 3620N. Conclusion. Characterization of a HA population was successfully defined as clinically obese by BMI, but with WHtR and WHpR associated with lower body fat. The author was unable to identify gait characteristics of a HA population through existing literature. Future Work. A gait-lab based study will be used to compare literature-based kinematics of obese subjects to those of HA subjects. A worst-case gait cycle can then be established for standard walking and other activities and translated into hip simulator parameters for HA patients

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 & aims. Different racial groups show variations in femoral morphometry. Femoral anteroposterior measurement and mediolateral measurement are key variables in designing femoral implant for TKR. Their aspect ratio determines the shape and mediolateral sizing for the proper patellofemoral tracking and uniform stress distribution over the resected distal femoral surface. Method. We reviewed the current literature in December 2013 in common medical databases including the Cochrane Library, PubMed and Medline. Keywords included combinations of: Anthropometry, Knee, Arthroplasty, Femur, Morphometry, Geometry. We selected papers including femoral morphometric data collected from populations of different ethnic origins. Papers covered populations in the USA, China, Germany, Thailand, Korea, India, Japan and Malaysia. Results. We have analysed femoral morphometry variables among different ethnic groups from the available data. Gross size of the resected femur can be defined in terms of antero-posterior (AP) and medio-lateral (ML) dimensions, an in the aspect ratio of femoral medio-lateral to femoral antero-posterior dimensions (fML/fAP). The Korean population showed the least value of fAP among all the groups, followed by Thai, Japanese, Indian, Malaysian and Chinese showing the increasing order among the sub-groups of Asian Population. American population shows the next higher fAP measurements from Asian population. German follows, and Arab quantify the largest value of this femoral anthropometric variable. fML varies by huge difference among male and female data in all populations. Thai, Indian, Malaysian, Arab, Japanese, Korean, German, Chinese and American; this sequence is the increasing order of fML. More trapezoid-shaped and narrower ML, this variation in female group leads to over-hang the implant for a given fAP. Generally, the aspect ratios are measured higher in these smaller female knees, and lower in larger male knees. Conclusions. Anthropometric data measuring distal femoral segment in different ethnic groups shows that the Asian population requires custom-fit implant design based on the morphological data. It would be more appropriate to introduce several medio-lateral options in sizing the implant for given antero-posterior dimensions

Introduction. Precise implant matching with a resected bony surface is a crucial issue to ensure a successful total knee arthroplasty (TKA). Extremely undersized or oversized components should be avoided. Therefore, we should measure the exact anthropometric data of the resected bony surface preoperatively or intraoperatively. The purpose of this study was to intraoperatively analyze the exact anthropometric proximal tibial data of Japanese patients undergoing TKA and correlate these measurements to the dimensions of current prosthetic systems. Patients and Methods. Three hundred and seventy-three knees in 299 Japanese patients were included in this study. There were 246 women and 53 men with a mean age of 74 (range: 63–85) years. All TKAs were performed by 3 senior surgeons (TS, AK, and NM). The bone cut in the proximal tibia was made perpendicular to the longitudinal axis of the tibia in the frontal plane. Intraoperative measurements of the proximal tibial cut surface were taken after proximal tibial preparation. Akagi's line (center of the posterior cruciate ligament tibial insertion to the medial border of the patellar tendon attachment) was adopted as the anteroposterior axis line of the proximal tibia. A mediolateral (ML) line was drawn perpendicular to Akagi's line. Then, anteroposterior (AP), lateral anteroposterior (lAP), and medial anteroposterior (mAP) lines were drawn as shown in Figure 1. Results. There was a significant positive correlation between lAP and ML dimensions. Although there also was a significant positive correlation between lAP and mAP dimensions, individual knees presented much scatter (Figure 2). The lAP dimension was smaller than the mAP dimension in all knees by a mean of 4.5 ± 1.9 mm. The proximal tibia exhibited asymmetry between the lateral and medial plateaus. The recent data of 177 knees indicated that Akagi's line was located 1.0 ± 1.2 mm medial to the AP line. A comparison of the morphologic data and the dimensions of the implants, one of which was a symmetric tibial component (NexGen: Zimmer, Warsaw, Indiana), and the other asymmetric (Genesis II: Smith & Nephew, Memphis, Tennessee), indicated that an asymmetric tibial component could be beneficial in maximizing the coverage of the tibial plateau. However, the size variation of the asymmetric tibial component was poor and the lAP and mAP dimensions showed much scatter; thus, we should measure the proximal tibia and choose the proper tibial component during surgery. Conclusions. This study provides important reference data that may be useful for designing proper tibial components for Japanese patients

Purpose. The majority (73%) of orthopaedic surgeons in Canada prefer using semitendinosus-gracilis (STG) autograft for ACL reconstruction. However, there is large variation in tendon size between individuals which makes pre-operative estimation of graft size unpredictable. Inadequate graft size may require an alternative source of graft tissue that should be planned prior to surgery. The purpose of this study is to determine if clinical anthropometric data and MRI measurements of STG tendons can be used to predict hamstring graft size. Method. One-hundred and fourteen patients with ACL deficiency awaiting reconstruction using hamstring autograft were retrospectively evaluated. The following information was obtained from patient charts: height, weight, body mass index (BMI), age, and gender. Cross-sectional area (CSA) of gracilis (G) and semitendinosus (ST) tendons were determined from pre-operative MRI scans using NIH ImageJ analysis software. Actual STG graft diameters were obtained from operative reports. Correlations between patient height, weight, BMI, age, gender, ST-CSA, G-CSA, STG-CSA and intraoperative graft size were calculated to determine the association between these variables. Multiple stepwise regression was performed to assess the predictive value of these variables to intraoperative graft diameter. In addition, three investigators with no radiological experience made independent measurements of the ST and G tendons to determine the inter-rater reliability (ICC) of MRI measurements. Results. All variables were independently correlated with intraoperative graft size (p<0.001). However, based on multiple stepwise regression analysis, only models including STG-CSA (r2=.212; p<.001); STG-CSA and sex (r2=.285; p<.001); and STG-CSA, sex and weight (r2=.294; p<.001) were found to be significant predictors of graft size (when co-variation in other factors was controlled). Inter-class correlation coefficients demonstrated very high agreement between raters for measurements of the ST, G and STG (.816, .827, .863, respectively). Conclusion. Measurement of tendon CSA from MRI images is very reliable. A model including STG-CSA, sex and weight was found to be strongly predictive of hamstring graft diameter for ACL reconstruction. This model may enhance our ability to predict adequate graft size and identify instances that other graft tissues may be a better option. The results of this study may improve pre-operative planning for ACL reconstruction

Introduction. Dislocation of total hip replacements (THRs) remains a severe complication after total hip arthroplasty. However, the contribution of influencing factors, such as implant positioning and soft tissue tension, is still not well understood due to the multi-factorial nature of the dislocation process. In order to systematically evaluate influencing factors on THR stability, our novel approach is to extract the anatomical environment of the implant into a musculoskeletal model. Within a hardware-in-the-loop (HiL) simulation the model provides hip joint angles and forces for a physical setup consisting of a compliant support and a robot which accordingly moves and loads the real implant components [2]. The purpose of this work was to validate the HiL test system against experimental data derived from one patient. Methods. The musculoskeletal model includes all segments of the right leg with a simplified trunk. Bone segments were reconstructed from a human computed tomography dataset. The segments were mutually linked in the multibody software SIMPACK (v8.9, Simpack AG, Gilching, Germany) by ideal joints starting from the ground-fixed foot. Furthermore, inertia properties were incorporated based on anthropometric data. Inverse dynamics was used to obtain muscle forces. Thus, optimization techniques were implemented to resolve the distribution problem of muscle forces whereas muscles were assumed to act along straight lines. For validation purposes the model was scaled to one patient with an instrumented THR [1]. Averaged kinematic measurements were used to obtain joint angles for a knee-bending motion. Then, the model was exported into real-time capable machine code and embedded into the HiL environment. Real implant components of a standard THR were attached to the endeffector of the robot and the compliant support. Finally, the HiL simulation was carried out simulating knee-bending. Experimentally measured hip joint forces from the patient [1] were used to validate the HiL simulation. Results. According to the joint angles obtained a knee-bending motion was carried out during the HiL simulation (Fig. 1). Predicted components of the hip joint force were in-between the envelopes of measured in-vivo data with partial deviation of the y-component (Fig. 2). The force application by the robot agreed well with the force values provided by the model. Discussion. Previous quasi-static mechanical setups for testing subluxation and dislocation of THRs neglected the impact of soft tissue structures on actual joint loading. Therefore, we combine the advantages of robot-based testing and numerical simulations within a HiL approach for dynamic analyses of THRs [2]. Thereby, validation is required to enhance the credibility of test results. The data presented demonstrate that the HiL test system with the embedded musculoskeletal model is capable of providing comparable THR loading as derived from in-vivo data. Certain deviations of the joint force's y-component will be the focus of up-coming model improvements. By considering dislocation-associated movements such as deep knee-bending, the influence of implant design and positioning on THR stability can be evaluated under reproducible, physiological-like conditions in subsequent studies