Avascular necrosis has several causes. Loss of blood supply to the bone can be caused by injury (trauma-related avn or joint dislocation) or other risk factors (nontraumatic avascular necrosis). Increased pressure within the bone also is associated with avascular necrosis. The pressure within the bone causes the blood vessels to narrow, making it hard for the vessels to deliver enough blood to the bone cells.
When a joint is injured, as in a fracture or dislocation, the blood vessels may be damaged. This can interfere with the blood circulation to the bone and lead to trauma-related avascular necrosis. Studies suggest that this type of AVN may develop in more than 20% of people who dislocate their hip joint.
Corticosteroids such as prednisone are commonly used to treat diseases in which there is inflammation, such as:
Studies suggest that long-term, systemic (oral or intravenous) corticosteroid use is associated with 35% of all cases of nontraumatic avascular necrosis. However, there is no known risk with the limited use of corticosteroids. Patients should discuss concerns about steroid use with their doctor. Doctors aren't sure exactly why the use of corticosteroids sometimes leads to AVN.
Other risk factors or conditions associated with nontraumatic avascular necrosis include: