Avascular necrosis (osteonecrosis) is bone death that occurs when the blood supply to the bone is decreased or stopped. Without an adequate blood supply, the bone dies.

Any bone can be affected, but avascular necrosis most often affects the ends of the long bones, such as the upper leg bone at the hip.

Avascular necrosis may be caused by an injury, such as forceful impact in a car crash, or may occur as a complication of a hip fracture or dislocation. Conditions such as sickle cell disease, gout, or lupus may lead to avascular necrosis. Long-term use of alcohol or medicines, such as corticosteroids, increases the risk of avascular necrosis.