The term osteochondritis dissecans (OCD) was introduced by König in 1887 (König F. 1887). This is primarily a condition affecting the subchondral bone and later the articular cartilage. OCD is seen in many joints and typically on the convex joint surfaces. If the lesion does not heal, the bony part will gradually detach from the underlying bone and eventually the overlying cartilage will separate from the surrounding cartilage. Finally, the fragment may detach completely and become one or more free fragments in the joint cavity leaving an osteochondral defect in the joint surface. The ending ”-itis” indicates that the condition originally was believed to be inflammatory. Later, several causes have been postulated, including inflammation, genetics, ischemia, defective ossification, and repetitive trauma. Still the etiology of OCD is not unequivocally settled. Experimentally an OCD-like condition has been created in growing pigs by cutting the blood supply to the growing cartilage (Ytrehus et al. 2004), and repetitive trauma may also induce the lesion (Cahill 1995).