Avascular Necrosis (osteonecrosis) can be an extremely debilitating problem, affecting up to 20,000 people a year. The term 'osteonecrosis' means bone death, and this occurs at a joint surface where a portion of the bone that makes up a joint loses its blood supply which causes the bone to die. As the bone that makes up the joint surface dies it can be painful and ultimately collapse - leading to further pain and deformity of the joint.

The etiology is often related to chronic steroid use for managment of diseases like asthma or lupus, a history of alcoholism, or a significant joint trauma.  It most commonly affects the hip, knee, ankle shoulder and elbow joints.

Because osteonecrosis is often painless at first, it may not be diagnosed in its earliest stages. Doctors suspect osteonecrosis in people who develop unexplained pain in the hip, knee, or shoulder, particularly if these people have risk factors for osteonecrosis.

X-rays of the affected area usually show osteonecrosis unless the disorder is in its earliest stages. If x-rays appear normal, however, MRI is usually performed because this is the best test for detecting osteonecrosis early, before changes appear on ordinary x-rays. The x-rays and MRI also show whether the bone has collapsed, how advanced the disorder is, and whether the joint is affected by osteoarthritis. If doctors discover nontraumatic osteonecrosis in one hip, they also examine the other hip with an x-ray or MRI.

More about osteonecrosis of :

Hip

Knee

Ankle (talus)