Pathology of Osteochondritis Dissecans

The initial change takes place in the bone. A segment of the bone undergoes avascular necrosis. The changes in the overlying cartilage are secondary.

Initially the cartilage overlying an area of dissecans appears to be normal, but with loss of subchondral bony support, it undergoes degenerative changes-softening, fibrillation, fissring and it loses its sheen.

Local trauma can cause separation of the subchondral bony fragment.

Healing of the avascular bone occurs by revascularization and repair by creeping substitution. If healing does not occur, the interzone between the osteocartilaginous fragment and surrounding cartilage is filled in by dense fibrous tissue. There may be zones of avascular fibrocartilaginous tissue. These findings indicate delayed union or nonunion of a fracture.

The pathologic picture invokes both ischemic necrosis and trauma as factors in the pathogenesis of osteochondritis dissecans.

The source of the tissue that fills the defect is the subchondral.

Osteochondritis dissecans is more common in the male. It occurs in young adults and in children.

The prognosis and management in the two age groups differ.

The knee joint is most commonly but although other joints, such as the elbow, ankle, hip, shoulder  and patella may also be involved.