Osteochondritis Dissecans (OCD) is a subchondral bony lesion of an articular surface.  OCD is thought to be multifactorial in etiology and typically leads to significant morbidity. A piece of cartilage with attached subchondral bone becomes detached, either partially or completely, resulting in a loose body in the joint space.

     OCD is rare (6 cases per 10,000 people) and 2-3 times more common in males.  It is a disease of the young and athletic, typically in children age 11-13 or adults age 17-36. 75% affect the knee, usually the medial femoral condyle.  The ankle and elbow are the next most common locations. 

     It can be classified in severity by whether there is a small area of subchondral compression (stage I), partial detachment of the fragment (II), complete detachment with the fragment remaining in the crater bed (III), or a frank loose body in the joint (IV).