The pathology of Legg-Perthes disease and its comparison with aseptic necrosis.

A review of pathological material obtained in cases of Legg-Perthes disease and in aseptic necrosis in the adult shows some similarities in distribution of the involved segment of the femoral head. X-ray signs of separation of the central avascular segment from the superior lateral and medial viable segments of the femoral head are recognizable. Crushing in of the weight-bearing segment then occurs and is recognized by flattening of the femoral head outline. At this point the child is in danger of suffering lateral displacement of the viable lateral segment leading to an incongruous extruded femoral head in relation to the acetabulum. Treatment measures must be taken prior to the occurrence of this lateral epiphyseal fracture in order to prevent the development of the stage of the disease where the prognosis is poor.