Total ankle arthroplasty (TAA) is an alternative to ankle arthrodesis, replacing the degenerated joint with a mechanical motion-preserving alternative. Implant loosening remains a primary cause of TAA revision, and has been associated with wear-mediated osteolysis. Differing implant designs have a major influence on the wear performance of joint replacements. Providing a range of implant sizes allows surgeons a greater intra-operative choice for varying patient anatomy and potential to minimise wear. Minimal pre-clinical testing exists in the literature that investigates the effect of implant size on the wear behaviour. The aim of this study therefore was to investigate the effect of two different implant sizes on the wear performance of a TAA. Six ‘medium’ and six ‘extra small’ BOX® (MatOrtho Ltd, UK) TAA implants, of the same conceptual design and polyethylene insert thickness, were tested in a modified 6 station pneumatic knee simulator. 5 million cycles (Mc) of wear simulation were completed for each implant size, under kinematics aiming to replicate an ankle gait cycle (Figure 1) [1]. The simulator used had six degrees of freedom, of which four were controlled. The maximum axial load was 3150N, equivalent to 4.5 times body weight of a 70kg individual. The flexion profile ranged from −15° plantarflexion to 15° dorsiflexion. Rotation about the tibial component ranged from −2.3° of internal rotation to 8° external rotation, and anterior/posterior (AP) displacement ranged from 3.1 mm anterior to −0.9 mm posterior displacement. The lubricant used was 25% bovine serum supplemented with 0.04% sodium azide to prevent bacterial degradation. The wear of the TAA polyethylene inserts were determined gravimetrically after each Mc, with unloaded soak controls used to compensate for the uptake of moisture by the polyethylene.Background
Materials & Methods
Total hip replacement (THR) patients are often considered a homogenous group whereas in reality, patients are heterogeneous. Variation in revision rates between patient groups suggest that implants are exposed to different environmental conditions in different patients [1]. Previous reports suggest that for every unit increase of BMI, there is a 2% increased risk of revision of a THR [2]. The aim of this study was to better understand the effect of patient-specific characteristics such as BMI on hip motions and to explore the possible impact on wear. 137 THR patients, at least 12 months post-surgery, underwent 3D kinematic (Vicon, Oxford, UK) and kinetic (AMTI, USA) analysis whilst walking at self-selected walking speed. 3D kinematic data were then mapped onto a modelled femoral cup at 20 pre-determined points to create pathways for femoral head contact, which were then quantified by deriving the aspect ratio (AR). Patients were stratified into three groups determined by BMI scores; healthy weight (BMI ≤25 kg/m2) (n=34); overweight (BMI >25kg/m2 to ≤ 30 kg/m2) (n=66) and obese patients (BMI > 30 kg/m2) (n=37). Comparisons were made using 95% confidence intervals (CI) and one way ANOVAs.Introduction
Methods
One of the known mechanisms which could contribute to the failure of total hip replacements (THR) is edge contact. Failures associated with edge contact include rim damage and lysis due to altered loading and torques. Recent study on four THR patients showed that the inclusion of pelvic motions in a contact model increased the risk of edge contact in some patients. The aim of current study was to determine whether pelvic motions have the same effect on contact location for a larger patient cohort and determine the contribution of each of the pelvic rotations to this effect. Gait data was acquired from five male and five female unilateral THR patients using a ten camera Vicon system (Oxford Metrics, UK) interfaced with twin force plates (AMTI) and using a CAST marker set. All patients had good surgical outcomes, confirmed by patient-reported outcomes and were considered well-functioning, based on elective walking speed. Joint contact forces and pelvic motions were obtained from the AnyBody modelling system (AnyBody Technologies, DK). Only gait cycle regions with available force plate data were considered. A finite element model of a 32mm head on a featureless hemispherical polyethylene cup, 0.5mm radial clearance, was used to obtain the contact area from the contact force. A bespoke computational tool was used to analyse patients' gait profiles with and without pelvic motions. The risk of edge contact was measured as a “centre proximity angle” between the cup pole and centre of the contact area, and “edge proximity angle” between the cup pole and the furthest contact area point away from the pole. Pelvic tilt, drop and internal-external rotation were considered one at a time and in combinations.Introduction
Methods
The knee is the commonest joint to be affected by osteoarthritis, with the medial compartment commonly affected. Knee osteoarthritis is commonly bilateral, yet symptoms may initially present unilaterally. Higher knee adduction moment has been associated with the development and progression of medial compartment knee osteoarthritis. To assess the effect of lateral wedge insoles on the asymptomatic knee of patients with unilateral symptoms of medial compartment knee osteoarthritis.Background
Objectives
