An investigation of biphasic failure criteria for impact-induced fissuring of articular cartilage.

Articular cartilage consists of both solid and fluid phases with fissures observed on the surface occurring in the solid portion. In order to determine which of the solid phase stresses provides the best predictor for the initiation of a fissure, elastic stresses from a series of in vitro impact experiments were used to derive stresses in the solid phase of the cartilage. This stress information was then analyzed using a logistic regression to identify the best predictor of fissuring. The mechanical analysis indicated that low-magnitude tensile solid hoop stress develops in the solid phase within the contact zone in impacts involving the two smaller radius interfaces. The logistic regression, however, indicated that maximum shear stress in the solid (which is equal to the shear stress from the elastic analysis) was the best predictor of the occurrence of a fissure. This study helps support the suggestion that in stress fields dominated by compression, the maximum shear stress from an elastic analysis may be used to predict fissure initiation in cartilage.