Progressive deformation-induced degradation of knee articular cartilage and osteoarthritis.

Articular cartilage (AC) is a dense connective tissue in the diarthrodial joints. Osteoarthritis is a disease associated with progressive changes in the tissue structure which affects mechanical properties of the tissue. Experimental studies show that abnormal/excessive mechanical loading or changes in biochemical composition can alter the structure which leads to degradation and loss of stiffness. In this study, deformation-induced degradation of human knee articular cartilage is investigated by conducting excessive deformations and inspecting progressive changes in mechanical properties of the tissue. Evolution of the properties is formulated to predict the amount of damage and consequently to connect the loss of stiffness to the grade of osteoarthritis. It is shown that, for tensile strains up to almost 15%, the tissue may recover its initial properties without permanent damage but for higher deformations degradation is expected. The proposed model is not confined to tension as the evolution laws are expressed in a 3D framework. The model predicts higher thresholds for compression and shear (25-30%) which is in good correlation with experimental investigations. It is concluded that, modelling the alterations of mechanical properties can be an effective method for predicting degradation of the AC under excessive loading and its connection to the associated diseases.