What's the difference between osteonecrosis and Perthes disease? Our son has Perthes so when I try to read about it, I get confused with the discussion of osteonecrosis.

Osteonecrosis means death of the bone tissue. When caused by a loss of blood supply to the area, it is also known as avascular necrosis. Perthes disease is an entity all its own but it is a type of osteonecrosis. A loss of blood or vascularization to the head of the femur (thigh bone) can cause the bone to start to die and collapse.

It is usually a self-limiting disorder. This means that the blood supply will return and the bone will repair itself. This is different from other types of osteonecrosis where bone destruction doesn't stop or repair itself.

With Legg-Perthes disease, changes occur in the shape of the femoral head and the acetabulum (hip socket). This takes place during the process of developing and healing in this condition. This may lead to degenerative arthritis young in adult life.

With osteonecrosis, the dead or dying tissue has to be removed. Sometimes the bone is replaced with bone from a bone bank. In some conditions, the bone is replaced with a rolled up tendon graft. With Perthes disease, healing can occur without removing the bone and even without surgery.