This condition is characterized by the death of an area of cartilage and bone in the knee joint. The dead section may remain in place, forming a lesion, or it may loosen and partially detach from the surrounding bone. It may break away completely and float around inside the joint.

The cause of osteochondritis dissecans is not known. It is believed to be linked to a restriction of the blood supply to the end of the bone. The femur is the bone that is most commonly affected. Osteochondritis dissecans may be caused by acute trauma to the knee, or by repeated stress on the joint. It is more common in athletes who participate in running and jumping sports. The condition may also be linked to an arterial blockage or to genetic factors.

The most obvious symptom of osteochondritis dissecans is pain that increases with physical activity. The knee may also weaken, and it may become swollen and tender. The person may not be able to bend and extend the knee through its full range of motion. If a fragment breaks away and becomes lodged in the joint, the knee may pop or lock in place during movement.

Treatment options typically include rest, a knee brace, and physical therapy. In many cases, the knee will heal on its own. If it does not, or if a loose fragment is floating within the joint, surgery may be needed.