The spatio-temporal mechanical environment of healthy and injured human cartilage during sustained activity and its role in cartilage damage.

Recently we presented a computational model of articular cartilage calibrated for normal human tissue explants. This model was able to capture the transient deformation of cartilage experiencing a cyclic load. The model takes into account the tension-compression nonlinearity of the cartilage and incorporates the dependency of the compressive stiffness and fluid permeability of cartilage on the deformation-dependent aggrecan concentration in cartilage tissue. As such it represents a leading constitutive model of articular cartilage. Here we build on the previous study to develop an experimentally validated computational model to simulate mechanical consolidation response of intact and previously injured cartilage under sustained static loading, to develop our understanding of the implications for rates of tissue damage. We see that the type of prior injuries compromise the cartilage function in different ways. Relatively rapid consolidation is predicted for cartilage with a complete meniscectomy and that with a full thickness defect, indicating the inability of cartilage with such injuries to sustain interstitial fluid pressurisation for long periods of time, as does uninjured cartilage. By comparing the consolidation response of articular cartilage predicted by computational model against experimental measurements of the apparent friction coefficient following static loading, we find a strong linear positive correlation exists between cartilage degree of consolidation (DoC) and friction coefficient at the joint. As the DoC of articular cartilages can be estimated in vivo via medical imaging, the DoC can be used as an index to non-invasively evaluate the apparent friction coefficient between opposing cartilage surfaces, and so estimate the likelihood of frictional surface wear and/or cartilage damage.