The natural history of osteochondral lesions in the ankle.

Most osteochondral lesions (defects) of the talar dome are caused by trauma, which may be a single event or repeated, less intense events (microtrauma). A lesion may heal, remain asymptomatic, or progress to deep ankle pain on weight bearing, prolonged joint swelling, and the formation of subchondral bone cysts. During loading, compression of the cartilage forces water into the microfractured subchondral bone. The increased flow and pressure of fluid in the subchondral bone can cause osteolysis and the slow development of a subchondral cyst. The pain does not arise from the cartilage lesion but most likely is caused by repetitive high fluid pressure during walking and a concomitant decrease in pH produced by osteoclasts, which sensitize the highly innervated subchondral bone. Prevention of further degeneration depends on several factors, including the repair of the subchondral bone plate and the correct alignment of the ankle joint.