Legg-Calvé-Perthes disease in dogs: a comparison to human Legg-Culvé-Perthes disease.

The femoral heads of 12 dogs with naturally occurring Legg-Calvé-Perthes disease were studied by light and electron microscopic techniques. In the early stages of the disease, the bony capital femoral epiphysis was necrotic, but the articular cartilage and growth plate cartilage were not affected. By the early stages of repair, the femoral head had collapsed. the articular cartilage was thickened and furrowed at the sites of collapse, and the chondrocytes appeared more metabolically active. Sites of bone resorption were associated with osteoclasts and macrophages. In some specimens there were areas of necrosis in the metaphysis which interrupted normal enchondral ossification in the growth plate. By the final stages of repair, the epiphysis was almost completely revascularized with the exception of the central proximal segment. In some areas, repair tissue had penetrated into the deeper layers of the articular cartilage. The flattening of the femoral head in Legg-Calvé-Perthes disease appears to be the result of several processes: mechanical collapse, asymmetric growth, and disturbed enchondral ossification at the growth plate.