Natural history of early onset and late-onset Legg-Calve-Perthes disease.

Legg-Calve-Perthes disease develops after interruption of the blood supply to the capital femoral epiphysis. This results in various changes in the femoral epiphysis and metaphysis, the capital femoral epiphysis, growth plate, and the acetabulum. The necrotic bone of the epiphysis is gradually replaced by new bone, and over 2 to 4 years complete healing of the epiphysis occurs. The evolution of this process can be clearly seen on radiographs and the disease can be divided into distinct stages. In the early stages of the disease, the epiphysis may extrude outside the confines of the acetabulum and this predisposes to femoral head deformation. The propensity for femoral head extrusion is greater in the older child, and consequently the likelihood of femoral deformation is higher in children who are older.