Examination of muscular contributions to knee joint contact loads during healthy and pathological gait

It is thought that abnormalities in knee loads during walking are instrumental in the development and degradation of the joint tissues. These loads are extremely difficult to measure in-vivo and thus typically have been inferred from the external loads acting on the joint and muscle activity data (EMG) which are both relatively easy to measure. Large external adduction moments have been implicated in the development and progression of OA, knee joint pain, and worse outcomes after knee surgery such as high tibial osteotomy and it is thought this is due to these increasing the load sustained by the medial compartment of the knee. However, any estimates of joint loading should also include the contribution of the muscles as these have the capacity to stabilise the knee against large external loads, but may increase the joint contact loads as a result. Muscle activation patterns are known to be different in pathological gait, but it is not known whether these correspond to increased joint loads, as EMG does not necessarily represent muscle force. EMG-driven musculoskeletal modelling is a tool which facilitates the estimation of muscle force from EMG and this thesis is concerned with the application of such a model to gait to examine the contribution of the muscles to joint stabilisation and the subsequent joint contact forces. In order to apply the EMG-driven neuromuscular skeletal model to different subjects, an analytical scaling technique was developed to facilitate adjustment of selected muscle properties according to anthropometric dimensions. It adjusts these properties such that the force generating range of each muscle is preserved across subjects. It is suggested that this provides a good rationale for scaling muscle properties, and it is shown that the developed algorithm best achieves this compared to some other scaling techniques which have been presented previously.