Computational biomechanics/biotribological modelling of natural and artificial hip joints

The excellent hip function and potential degeneration are closely linked with the unique structure of the joint cartilage that is principally composed of a solid phase and a fluid phase. Once damaged, the joint may need to be replaced by prosthesis in order to restore function in hip kinematics and kinetics. However, to what extent this can be achieved has yet to be quantified. On the other hand, the role of fluid pressurisation which plays in hip function has been poorly understood. The aim of this thesis was to address these issues. To evaluate the gait abnormality, particularly in terms of hip contact forces, a musculoskeletal model of lower extremity was constructed in a rigid-body dynamics frame, and the hip kinematics and kinetics were determined and cross-compared for a group of asymptomatic total hip replacement (THR) patients, THR patients with symptoms of symptomatic leg length inequality (LLI) and normal healthy people. Significant abnormal patterns in gait kinetics were observed for the asymptomatic THR patients, and this abnormality was greater for the LLI patients. To understand contact mechanics and the associated fluid pressurisation within the hip cartilage, a three dimensional finite element (FE) hip model with biphasic cartilage layers were developed. The protocol was compared to other solvers. A set of sensitivity studies were undertaken to evaluate the influence of model parameters, and then the model was evaluated under a range of loads with different activities. In all the cases, the fluid supported over 90% of the load for a prolonged period, potentially providing excellent hip function and lubrication. The musculoskeletal model and FE joint were combined to investigate the performance of the non-operated joint of the THR / LLI patients during gait which was found to function in a mechanically abnormal but not adverse environment. Lastly, the methodology of the biphasic hip modelling was validated using an experimental porcine hip of hemiarthroplasty. Good agreement was achieved between the FE predictions and the experimental measurement of the contact area.