Osteochondral Lesion in Diffuse Pigmented Villonodular Synovitis of the Knee.

Pigmented villonodular synovitis (PVNS) is a rare benign condition that is locally aggressive and may destructively invade the surrounding soft tissues and bone causing functional loss of the joint and the limb. The knee is the most affected joint (range, 28% to 70%) but involvement of the bone is not a common feature seen at this site. We present a rare case of diffuse PVNS of the knee associated with subchondral cyst of the lateral femoral condyle.