Load / deformation / time behaviour of articular cartilage

Abstract

This thesis is concerned with the behaviour of articular cartilage under compressive loading. An apparatus was built to apply sinusoidal and constant loading to specimens of cartilage. The majority of the tests performed were on specimens of bovine cartilage although some tests have been conducted on human patella cartilage. Confined tests, with load, deformation and flow confined to an axial direction, were considered most realistic to the conditions in the body, and so the majority of the work was on this type of test. However some tests of an 'unconfined' nature, with axial load but radial flow and deformation, were carried out. An already established computer model of this behaviour of cartilage was modified and used to reproduce the experimental results. The model is based on fluid flow phenomena only and hence agreement with the experimental work was not entirely satisfactory. However, the model does allow the effect of changes in cartilage properties to be studied. The model yielded its most useful results for sinusoidal loading, where it forecast similar results to the experimental work. The cartilage is shown to be visco-elastic under conditions of steady load, the creep deformation being achieved by fluid flowing out of the specimen. The creep deformation is shown to be recoverable on removal of load. Under sinusoidal loading, around the frequency of the walking cycle, flow processes are shown to contribute practically nothing to the sinusoidal deformations achieved, the deformations in this case arising almost entirely from the elastic compressibility of the specimens.