Mechanical Engineering - Theses
Permanent URI for this collection
Search Results
1 - 1 of 1
-
ItemIn vitro measurement and computational modelling of knee-joint contact mechanics during simulated load-bearing activity( 2016)The knee is one of the most complex joints in the human body. Knee joint disorders, such as osteoarthritis (OA), undermine the mobility and quality of life of those affected. Abnormal joint loading is widely acknowledged to be one of the primary causes of the onset and progression of knee OA. Yet, knee joint contact mechanics is still not well understood. This lack of understanding is partially due to the practical and ethical challenges involved in obtaining in vivo contact stress measurements at the patient-specific level. As a result of these difficulties, computational finite element (FE) modelling has emerged as a non-invasive alternative for research into knee joint contact mechanics. The present dissertation aimed to improve the current state of art of knee joint FE modelling and to enhance the techniques used to validate model contact predictions. An apparatus was designed and built to enable physiological dynamic loading simulations on cadaveric knee joints whilst bony kinematics and joint contact distributions were measured using a bi-plane fluoroscopy system and a real-time pressure measurement system, respectively. A subject-specific knee joint FE modelling framework incorporating a hyperelastic constitutive cartilage material model was developed, and the contact predictions of the tibiofemoral and patellofemoral joints were individually validated against in vitro experimental data. Contact mechanics of the tibiofemoral and patellofemoral joints were analysed during a simulated stair descent activity and a knee flexion task under quadriceps load, respectively. Sensitivity analyses were performed to identify the model parameters that had the greatest influence on the accuracy of model-predicted joint contact mechanics. The FE models closely reproduced the contact pressure patterns of both joints observed in the experimental measurements. Specifically, the shape and location of the contact region were qualitatively similar between the FE results and experimental data throughout the trial cycles, and the high contact pressure sub-regions were also successfully predicted. The FE model predictions of peak contact pressure, contact area, contact force and centre of pressure (COP) matched reasonably well with the experimental data for both joints. The root mean square errors (RMSE) were on the order of 15% (as a percentage of the corresponding peak experimental values). The average distance between the COPs of the model and experimental results was around 2.5 mm. The element-wise contact pressure comparison showed a typical error of about 25%. Strong correlations existed between the predicted and measured contact variables over time, with Pearson correlation coefficients typically larger than 0.8. The patellofemoral joint contact force was higher on the lateral facet in both the experimental and the FE results, consistent with previous findings by other studies. The results showed that changes in the stiffness of cartilage and meniscus, contact friction coefficients and model geometries consistently affected the predictions of the contact variables in both joints. Furthermore, inaccurate model geometries decreased the correlations between the experimental and calculated results. In general, the peak contact pressure was more sensitive to changes in model inputs compared to contact force and contact area. This finding demonstrates that peak contact pressure predictions require more accurate model inputs, in particular, the material properties and geometries of the deformable soft tissues. Overall, the present dissertation provided a novel experimental and FE modelling framework to investigate joint contact mechanics in the human knee joint. It is hoped that the validated subject-specific knee FE model can be used in future in vivo studies to explore knee joint biomechanical function, simulate different joint pathologies, assist clinical diagnosis and assess the likely outcomes of therapeutic treatments.