A constitutive study of the age-dependent mechanical behaviour of deep articular cartilage: Model construction and...

The tensile properties of deep articular cartilage of the human femoral head have been simulated using a model based on the expected mechanical behaviour of an electrostatically cross-linked network of collagen fibrils. Articular cartilage requires a model incorporating two types of interactions, referred to as type I and type II, which differ in the amount of energy required to bring about their mechanical failure. This modified two-population (MTP) model is shown to accurately simulate the experimental tensile behaviour of 14 specimens of deep articular cartilage. Also, the MTP model simulates a failure behaviour which appears to be comparable to the actual experimental fracture of the articular cartilage specimens. A reduction in the fracture stress of the deep articular cartilage specimens with age can be interpreted through age-related changes which occur in the values of the parameters of the MTP model. This shows that the younger tissues derive their superior tensile properties through an optimum structural arrangement which is associated with a high proportion of binding equivalent to the type I interaction in the tissue model. A decline in the tensile properties with age occurs as the tissue structure falls from its optimal configuration as the proportion of type II interactions increases. Such changes may predispose the articular cartilage to the mechanical damage and deterioration which leads to the osteoarthritic degeneration of a joint. Relevance An understanding of the process of osteoarthritic degeneration requires a knowledge of the relationship between the biochemical composition and mechanical behaviour of articular cartilage. An approach is developed to examine this relationship in order to gain insight into the ultrastructural basis of the mechanical weakening of articular cartilage with age.