Osteonecrosis is bone death caused by poor blood supply to the area. It is most common in the hip and shoulder.

Osteonecrosis occurs when part of the bone does not get blood and dies. After a while the bone can break off. If this condition is not treated, bone damage gets worse. Eventually, the affected part of the bone may collapse.

Osteonecrosis can be caused by disease, or a severe trauma, such as a break or dislocation, that affects the blood supply to the bone. Many times, no trauma or disease is present. This is called "idiopathic osteonecrosis" -- meaning it occurs without any known cause.

The following can cause osteonecrosis:

• Long-term treatments with steroids
• Excessive alcohol use
• Sickle cell disease
• Radiation therapy
• Gaucher disease
• Decompression sickness
• Dislocation or fractures around a joint

Some diseases that may be associated with the development of this condition include:

• Gout
• Atherosclerosis
• Diabetes

Osteonecrosis is most common in people between ages 30 and 60. Most cases in adults occur at the hip joint. The condition can also occur due to childhood cancer therapy.

Legg-Calvé-Perthes disease is a similar condition seen in children and adolescents.