Chondral and osteochondral injuries: mechanisms of injury and repair responses

Acute and repetitive impact and torsional loading of joints can damage the articular surface, causing pain, joint dysfunction and effusions, and in some instances, progressive joint degeneration. These injuries often remain undetected and their incidence, pathogenesis, natural history, and optimal treatment remain poorly understood. Advances in arthroscopy and joint imaging have improved the ability of physicians to identify articular surface injuries, and reports of new methods of promoting restoration of articular surfaces have increased interest in their treatment. Three classes of chondral and osteochondral injuries can be identified based on the type of tissue damage and the repair response: (1) damage to the joint surface that does not cause visible mechanical disruption of the articular surface but does cause chondral damage and may cause subchondral bone injury, (2) mechanical disruption of the articular surface limited to articular cartilage, and (3) mechanical disruption of articular cartilage and subchondral bone. In most instances joints can repair damage that does not disrupt the articular surface if they are protected from further injury. Mechanical disruption of articular cartilage stimulates chondrocyte synthetic activity, but it rarely results in repair of the injury. Disruption of subchondral bone stimulates chondral and bony repair, but it rarely restores an articular surface that duplicates the biological and mechanical properties of normal articular cartilage. The extent and effectiveness of the chondral and osseous repair responses vary with age: in general younger individuals, especially skeletally immature people, have more effective repair of articular surface injuries. To be of value to patients a treatment of an articular surface injury must produce better short- and long-term results than the natural repair response. Thus, before selecting a treatment for a patient with a chondral or osteochondral injury the surgeon should define the type of injury and understand its likely natural history.