Osteochondritis dissecans is a necrosis that affects only a small part, lenticular, the articular cartilage and the corresponding subchondral bone.

The bone is clearly demarcated the osteocartilaginous surrounding tissue to break away and become "free" in the 'articulation (called joint mice).

Osteochondritis dissecans occurs mainly in adolescence and is initially asymptomatic; as an adult, you have the first signs of pain and limitation of joint movement.