A biomechanical investigation of unconstrained shear failure of the osteochondral region under impact loading.

This paper presents an investigation into the biomechanics of failure of the osteochondral region under conditions in which the cartilage/bone system was subjected to impact loading in shear through the cartilage layer only. The relationships between the nature of structural integration of the osteochondral region, its mechanism of failure in shear, and its dynamic fracture toughness were examined. The exact mechanism of osteochondral failure was found to be dependent on skeletal maturity. Shear fracture in the immature tissue always occurred subchondrally as a discontinuous propagation of a relatively large, fast moving crack. By contrast, failure in the skeletally mature tissue occurred by the rapid advance of a smaller crack which propagated within the well-defined tidemark region. RELEVANCE: The junction between the compliant articular cartilage and the rigid bone, because it represents an abrupt change in mechanical properties, is a region of potential weakness in the joint system. Clinical findings confirm that failure can occur in the osteochondral region when there is a substantial component of shear loading, and that the immature junction is more susceptible to mechanically induced failure than the mature. This study provides a quantitative assessment of the failure characteristic of the immature and mature osteochondral region under high rates of loading.