About Osteonecrosis

Osteonecrosis (ON) is not particularly common, afflicting approximately 20,000 new patients per year in the U.S. However, patients are relatively young, with an average age of 38 (although any age can be affected). Since the diagnosis does not affect longevity there are several hundred thousand patients in the U.S. alone who are living with the disease. The purpose of this pamphlet is to provide you with information to help you understand the condition and some of the important issues with treatment.

What is osteonecrosis?
The term literally means death of bone (osteo=bone, necrosis=death). It has been known by a number of other names including ischemic necrosis of bone, aseptic necrosis and AVN (standing for avascular necrosis). AVN has been quite popular in its use because it is shorter to say and write. More recently the term ON has been adopted.

ON can affect virtually any bone, but for practical purposes most cases involve only the hip, knee, shoulder or ankle joints in decreasing order of frequency. In fact, ON of the hip accounts for more than 90% of the cases.

There are two major forms of ON, post-traumatic and non-traumatic. Minor trauma is not believed to cause ON. Even major injury does not often result in ON. Certain kinds of fracture, where the blood vessels to part of the bone have been physically damaged, may result in ON.

Non-traumatic ON has been associated with a wide variety of diseases including gout, lupus, sickle cell disease, kidney or liver disease, and clotting disorders. In addition, high dosage steroid (cortisone) use is sometimes associated with ON, as well as high alcohol consumpution. Finally, as many as 30% of all patients with osteonecrosis are otherwise completely healthy with no associated risk factor. This is called "idiopathic," a medical term meaning "of unknown cause."

Who's at Risk?
If a person is completely healthy, the risk of getting osteonecrosis is quite small, probably less than one in 100,000. Another way to understand this is that most of the people who get ON probably have an underlying health problem. Children, as young as 4 and extending to the teens, get a form of ON which is called Legg-Calve-Perthe's disease (Perthe's for short) after the doctors who first described it. Most patients are between 30 and 50 with an average age of 38. Patients over the age of 50 are likely to have developed ON either by a fracture of the hip or more rarely in association with disease of the major blood vessels to the lower leg. Although the specific cause of the bone death is not precisely known except in the case of fracture, a number of conditions have been associated with ON. The most common includes a history of high dose steroid treatment for some medical condition (including Lupus, chronic lung disease, an organ transplant, etc). Low dose steroids (cortisone, prednisone, etc) commonly used for bee stings, poison ivy and acute allergies are not thought to cause ON. The next most common associated condition is a history of alcohol intake. The higher the intake the higher the risk.

The mechanisms by which these two risk factors (alcohol and steroids) cause ON are not well understood. The third most common group, are those patients who have no risk factors at all, and these patients are a true medical mystery. No matter what the cause, the symptoms and course of the disorder are remarkably similar.

First Symptoms
Unfortunately many patients with ON have had the disease for quite some time before symptoms are present. The initial symptoms are usually pain or aching in the affected joint with activity, which subsides after the activity has stopped. Symptoms usually begin slowly and may initially be intermittent. As the disease progresses, the pain increases and is associated with stiffness. Limping becomes common. In the hip, the most common joint affected, the pain is usually felt in the groin.

Diagnosis
The principle diagnostic tool is the x-ray. By the time that most patients have significant symptoms, the disease is advanced enough to be seen on standard x-rays. In most cases the x-ray will show the area of bone that is involved. However, the very earliest stages of the ON cannot be seen on a regular x-ray. A widely used and relatively new tool is called an MRI which stands for Magnetic Resonance Imaging. These special images are able to detect tissue changes that may not be seen on plain x-ray. Occasionally, your doctor may order a CAT scan which is a special series of x-rays, interpreted by the computer to show the three dimensional structure of the bone. Any of these tests will help the doctor to determine how advanced the disease is in your case.

Prevention
There are no known effective prevention measures. However steroids should only be taken as necessary and alcohol consumption should always be in moderation. Some experimental drug protocols are being evaluated which may have a place in treatment or prevention in the future.