Pathology and classification.

The most important change seen during the early and active phases of this disease is an overgrowth of the articular cartilage with a variable degree of infarction within the bony epiphysis. This accounts for the variable nature of the disease that is observed clinically. Treatment cannot alter the degree of bony infarction present; it can only attempt to control the growth disturbance that is present by maintaining the mobility of the femoral head and hence preventing the adduction contracture, which is the essential prerequisite of serious femoral head deformity.