There are several avascular necrosis causes, some of which are related to trauma (trauma-related avascular necrosis) and some of which are not related to trauma (nontraumatic avascular necrosis). Steroid medicines and alcohol use are the two most common causes of nontraumatic avascular necrosis.

Traumatic Causes
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 avascular necrosis may develop in more than 20 percent of people who dislocate their hip joint.
 
Nontraumatic Causes
Corticosteroids, such as prednisone, are commonly used to treat diseases in which there is inflammation, such as:
--Systemic lupus erythematosus (lupus or SLE)
--Rheumatoid arthritis (RA)
--Inflammatory bowel disease (IBD)
--Vasculitis.