Osteochondritis Dissecans - Pathophysiology

Pathophysiology

Osteochondritis dissecans differs from "wear and tear" degenerative arthritis, which is primarily an articular surface problem. Instead, OCD is a problem of the underlying subchondral bone, which may secondarily affect the articular cartilage. Left untreated, OCD can lead to the development of degenerative arthritis secondary to joint incongruity and abnormal wear patterns.

OCD occurs when a loose piece of bone or cartilage partially (or fully) separates from the end of the bone, often because of a loss of blood supply (osteonecrosis) and decalcification of the trabecular bone matrix. The loose piece may stay in place or slide around, making the joint stiff and unstable. OCD in humans most commonly affects the knees, ankles, and elbow but can affect any joint.

In skeletally immature individuals, the blood supply to the epiphyseal bone is good, supporting both osteogenesis and chondrogenesis. With disruption of the epiphyseal plate vessels, varying degrees and depth of necrosis occur, resulting in a cessation of growth to both osteocytes and chondrocytes. In turn, this pattern leads to disordered ossification of cartilage, resulting in subchondral avascular necrosis and consequently OCD.

Four minor stages of OCD have been identified after trauma. These include revascularization and formation of granulation (scar) tissue, absorption of necrotic fragments, intertrabecular osteoid deposition, and remodeling of new bone. With delay in the revascularization stage, an OCD lesion develops. A lesion can lead to articular-surface irregularities, which in turn may cause progressive arthritic deterioration.