Late effects: Avascular necrosis

What is avascular necrosis?

Blood carries essential nutrients and oxygen to the bones. When the blood supply is disrupted, the bone tissues begin to break down (necrosis).  This can weaken the bone and eventually result in its collapse. If this occurs near a joint, it can lead to the collapse of the joint surface, resulting in pain and inflammation (arthritis). Avascular necrosis is also referred to as AVN, aseptic necrosis, osteonecrosis and ischemic bone necrosis. 

Avascular necrosis can occur in any bone, but most commonly affects the ends (epiphysis) of long bones such as the thigh bone (femur), causing hip and knee problems. Other common sites include the bones of the upper arms, shoulders, and ankles.

Avascular necrosis can occur in a single bone, but more commonly occurs in several bones at one time. Avascular necrosis can sometimes be disabling, depending on what part of the bone is affected, how large an area is involved, and how well the bone rebuilds itself. Normal bone continuously breaks down and rebuilds itself. This process keeps the bones strong. Avascular necrosis is the result of bone tissues breaking down faster than the body can repair them. If the disorder progresses, it can lead to pain and arthritis.

What causes avascular necrosis?

Avascular necrosis is caused by interruption of the blood supply to the bone. If blood vessels are blocked with fat, become too thick or too small, or get too weak, they may not be able to provide the amount of blood necessary for the bone tissue to survive.

What are the risk factors for avascular necrosis?

Corticosteroids (such as prednisone and dexamethasone) given during treatment for a range of blood disorders can affect the bone and blood vessels, resulting in avascular necrosis. People who have undergone haematopoietic stem cell transplantation are also at risk for developing avascular necrosis. Other factors that increase the risk of avascular necrosis in people who have received corticosteroid therapy or a transplant include receiving total body irradiation (TBI), undergoing an allogeneic transplant (from someone other than yourself), and having prolonged treatment with corticosteroids for graft-versus-host disease following transplantation.

Steroids and avascular necrosis

Corticosteroids (such as prednisone and dexamethasone) are commonly used for treatment of many blood disorders such as leukemia, myeloma and lymphoma. Dexamethasone is also sometimes used for treatment of nausea and vomiting associated with chemotherapy and to control brain swelling. There is no clear explanation as to how corticosteroids cause avascular necrosis, but it is believed that they may interfere with the body’s ability to break down fatty substances. These substances can clog the blood vessels, causing them to narrow. This reduces the amount of blood that gets into the bone.

What are the symptoms of avascular necrosis?

People in the early stages of avascular necrosis may not have any symptoms. However, as the disorder progresses, most people will experience some joint pain. At first, the person may only experience pain when bearing weight on the affected bone or joint.

As the disorder progresses, symptoms may be present even at rest. Pain may develop gradually and its intensity can range from mild to severe. If avascular necrosis progresses and the bone and surrounding joint surfaces collapse, the pain can increase considerably and may become severe enough to limit movement in the affected joint. The period of time between the first symptoms of avascular necrosis and the loss of joint function is different for each person and ranges from several months to years.

How is avascular necrosis diagnosed?

An x-ray is usually the first test to be done when avascular necrosis is suspected. It can help distinguish avascular necrosis from other causes of bone pain, such as fracture. In the early stages of avascular necrosis, an x-ray may appear normal, so other tests may be needed to establish the diagnosis.

Once the diagnosis has been made, and in the later stages of avascular necrosis, x-rays are useful in monitoring the course of the condition.  MRI is one of the most useful tools in diagnosing avascular necrosis because it can detect avascular necrosis in the earliest stages, when symptoms are not yet present. Bone scans are sometimes used to diagnose avascular necrosis. They are useful because one scan can show all the areas in the body affected by avascular necrosis. However, bone scans do not detect avascular necrosis at the earliest stages.  A CT scan provides a three-dimensional image of the bone and can be useful in determining the extent of bone damage. Surgical procedures such as a bone biopsy can conclusively diagnose avascular necrosis, but are not commonly done.

How is avascular necrosis treated?

The goals of treatment for avascular necrosis are to improve the person’s use of the affected joint, reduce pain, stop bone damage, and ensure joint survival. Treatment can be conservative or surgical. In order to decide the best treatment for a patient, the following factors are considered:

• The person’s age
• The stage of the disorder (early or late)
• The location and the amount of bone affected (small or large)

Conservative treatment

Conservative treatments may be used alone or in combination, but they may not provide lasting improvement:

• Medication - to reduce pain
• Reduced weight bearing - to slow the damage and promote natural healing. Crutches may be recommended to limit weight or pressure on the affected joint.
• Range of motion exercises – to keep the joints flexible. This is also important to maintain movement and increase circulation in the joints. This can promote healing and may relieve pain.

Some people may require surgery to permanently repair or replace the joint.

Surgical treatment

Core decompression

Core decompression is a surgery that removes the inner layer of bone. This may reduce pressure within the bone and create an open area for new blood vessels to grow. Sometimes a piece of healthy bone with good blood vessels (bone graft) is put in this area to speed up the process. This procedure works best in the early stages of avascular necrosis and should help relieve pain and promote healing.

Osteotomy

Osteotomy is a surgery that involves taking out a piece of bone, usually a wedge, to reposition the bone so that the tissue lacking blood supply (avascular area) bears less weight than an adjacent healthy area.

Arthroplasty

Arthroplasty is also referred to as joint replacement. The affected bone is removed and replaced with an artificial joint. This treatment may be needed in the late stages of avascular necrosis and when a joint is destroyed.

Health promoting behaviours/interventions

• Avoid activities that put a lot of stress on your joints. Activities that stress the joints include running, jumping, football, soccer, volleyball, basketball and similar sports. Activities that are good for joints with avascular necrosis are swimming and bicycling
• Be consistent with recommended exercises
• Rest joints when they hurt
• Let your doctor or physiotherapist know if there are any changes in your symptoms
• Take pain or anti-inflammatory medications as prescribed