Avascular hip necrosis. Illustration of a frontal section through a child's hip joint, showing the start of Perthes disease (avascular necrosis of the femoral head), one of several hip disorders that can affect babies and children. Also known as osteonecrosis, this is the death of bone tissue (black area) due to a loss of blood supply. The tissue death causes the bone to collapse. The condition is also known as Legg-Calve-Perthes disease. The joint tissues include cartilage (pink), the synovial membrane (blue), and the joint capsule (red). For a set of four images illustrating childhood hip disorders, see C029/0661. For the individual images, see C029/0657-60.