The biomechanical effect of trunk inclination on joint moments and muscle activation in people with knee osteoarthritis

Knee osteoarthritis is a progressive disease, which is associated with pain, stiffness and disability. Previous research has demonstrated that the progression of knee OA is influenced by numerous biomechanical factors, which will affect the loading on the knee joint. Cross sectional studies have shown altered knee OA gait to be characterised by altered joint moments, increased muscle activity and increased muscular co-contraction. Furthermore, modelling studies have shown that the alterations in muscle patterns that are characteristic of knee OA lead to elevated joint loads, while longitudinal studies have demonstrated the progression of knee OA to be related to these altered muscular responses. In this thesis, I examine a new model that has the potential to explain some of the previous observed differences in joint moments and muscle activity characteristic of knee OA gait. Specifically, this thesis investigates the effect of increased sagittal plane inclination of the trunk (forward trunk lean) and the effect this could have on hip, knee and ankle moments and muscle activation patterns. Three studies were conducted. The first sought to characterise differences in sagittal trunk inclination during walking, between people with knee OA and healthy control participants. This study demonstrated that people with knee OA walk with approximately 3° more trunk flexion than healthy control subjects. In the second study, I examined the relationship between trunk inclination and a range of different biomechanical parameters, including hip extensor moments, hamstring activation levels and hamstring-quadriceps co-contraction. These results of this study showed weak to moderate correlations between hip extensor moment and the magnitude of hamstring activation during the period 15-25% of the stance phase of the gait cycle. In the final study, I explored the effect of a three-curve rocker shoe on trunk inclination and a range of other biomechanical variables. These data showed that, although there was significant reduction in trunk inclination with the rocker shoe, there was no corresponding decrease in moments or muscle activations over the period 15-25% of stance. Taken together, the results of this thesis show that people with knee OA walk with an increased trunk lean and that this may explain some of the previously observed differences in hip moments and muscle patterns. However, further work is required to establish if interventions that could reduce trunk lean (such as a rocker shoe) could lead to long-term clinical benefits for people with knee OA