Avascular Necrosis (Osteonecrosis)

Avascular necrosis (AVN), also known as osteonecrosis, is a disease that results in death of bone.  This bone death occurs in a part of the femoral head (the ball at the top of the thigh bone that sits in your hip socket).

Symptoms of avascular necrosis can be variable and often times there is no pain at first. The most common symptom is hip pain, typically in the groin region.  In the earliest stages of the disease plain x-rays are often normal. A magnetic resonance image (MRI) study can allows us to detect avascular necrosis earlier than x-rays.

Does avascular necrosis cause pain?
Avascular necrosis may be present without any pain whatsoever. There may be pain during early stages of the disease but sometimes pain develops once the degree of bone death has progressed quite far. Once the disease has progressed to a point where the bone can no longer support the stress of bearing weight, the top of the femoral ball can collapse.  It is always important to have the other hip checked as it may also be affected.

How often is the other hip affected?
It may be necessary to verify the health of the opposite hip when evaluating avascular necrosis because studies have shown that the opposite hip may not hurt, have normal x-rays, but may be affected up to 80% of the time.

Will it get worse?
The progression of avascular necrosis is linked to the size of the area of dead bone. Very small areas may improve without surgery.  Larger areas often progress to collapse of the femoral ball.

Diagnosis 

We can diagnose avascular necrosis with x-rays and MRI. There are four stages that define how bad the disease has progressed. Stage 1 has a normal x-rays but MRI reveals the dead bone. Stage 2 can be seen on regular x-ray but there is no collapse of the femoral ball. Stage 3 shows signs of collapse (called a crescent sign) on x-ray. Stage 4 has collapse on x-ray and signs of cartilage damage (osteoarthritis).

Stage 1

 

Stage 4 – X-ray

 

Stage 4 – MRI

The causes of avascular necrosis are not completely understood, but it appears to be related to an interruption in blood flow to the femoral ball. Here are some possible reasons: 
1. Damage to the blood vessels due to fracture (e.g. broken hip)
2. Damage to the inside of the blood vessels (e.g. vasculitis, radiation therapy)
3. A clot that clogs the blood vessel (e.g. sickle cell diseases, corticosteroids, alcohol)

Although the cause in bone death is clear in some cases (such as a disruption in blood flow from a break in the bone or a clot in the blood vessels) the cause in most cases is poorly understood. People who have used large amounts of steroids or alcohol for long periods of time may have a higher risk of developing this disease.
 

Non-operative treatment
Non-operative management may consist of protective weight-bearing (namely, partial weight-bearing with crutches) for six weeks then re-evaluation. Non-steroidal anti-inflammatory medications or acetaminophen may help relieve some pain. Other medication options include medications that help moderate bone loss.  However, even with protective weight bearing and medication there is a risk of the hip getting worse. 

Surgical treatment
There are several surgical treatment choices available. These choices depend on the age of the patient, amount of damage to the femoral head and the stage of the disease. For some hips in early stages of the disease (Stage 1 and Stage 2) without a large area of the ball being involved one can try and preserve the native hip ball. Procedures such as core decompression (described below), osteotomy (realignment of the ball within the socket) and bone grafting attempt to save the hip ball. Once the hip reaches later stages (Stage 3 and Stage 4) total hip replacement is the treatment of choice in most cases.  

Whether you choose non-surgical or surgical treatment, your doctor can help you to choose the best option for you.

Core Decompression

Core decompression is a procedure used for treating early stage avascular necrosis. It is a surgical procedure that involves a small incision.  The procedure involves using a drill through the femoral neck up into the area of dead bone in the femoral ball . Removing this central core of bone can possibly lower the pressure inside the bone, allowing for better blood flow and hopefully lead to healing of the ball with living bone. When properly done, this procedure has minimal side effects.  

Patients are often restricted to partial weight bearing (crutches or walker) for 6 weeks following the procedure in order to reduce the risk of the hip bone breaking from the drill holes in the bone.  The results vary depending on the size of the area of dead bone and the stage of the disease.

Total Hip Replacement
Once the hip reaches later stages (Stage 3 and Stage 4) total hip replacement is the treatment of choice in most cases.  Further information can be found on Total Hip Replacements on this website  .
 

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