Avascular necrosis (AVN), or osteonecrosis, is a painful hip condition in adults that results from a compromise or injury to the blood supply to the bone directly below the weight-bearing cartilage of the ball of the hip joint.  Without a normal blood supply, the bone undergoes progressive necrosis (dies) making it weak.  As the bone weakens it can begin to collapse with continued weight-bearing.  Over time, collapse leads to persistent pain, stiffness and progressive arthritis of the hip joint.  The cause of AVN is frequently related to a variety of environmental, nutritional or medical factors including chronic corticosteroid use, prior chemotherapy, autoimmune disease, blood-clotting disorders, sickle-cell disorder or trait, and chronic alcohol use.  Some cases have no identifiable cause.  If detected early, AVN can be treated with a surgery called a core decompression in an attempt to restore the blood supply to the bone.  When AVN has become too advanced and the ball (femoral head) collapses, osteoarthritis results.  At that point, the best surgical option is a total hip replacement.