Role of subchondral bone in the initiation and progression of cartilage damage.

Osteoarthrosis is a physiologic imbalance, a "joint failure" similar to "heart failure," in which mechanical factors play a role. The initiation and progression of cartilage damage are distinct phenomena. One of the mechanisms of initiation may be a steep stiffness gradient in the underlying subchondral bone. Progression of cartilage lesions probably requires stiffened subchondral bone. In such situations, transverse stresses at the base of the articular cartilage could cause deep horizontal splits in that tissue. The most likely cause of subchondral stiffening in an otherwise congruent joint is repeated failure of the musculoskeletal peak dynamic force attenuation mechanisms. The health and integrity of the overlying articular cartilage depends on the mechanical properties of its bony bed. In certain models of osteoarthrosis, alterations of the bony bed occur before the cartilage changes and suggest that this can occur in clinical conditions. Stiffening of the subchondral bone also can effect joint conformation, which involves deformation of articular cartilage and bone to create maximum contact areas under load.