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Avascular Necrosis of the Hip

What Is Avascular Necrosis of the Hip (AVN)?

Avascular necrosis is a disease resulting from the temporary or permanent loss of the blood supply to the bones. Without a blood supply, the bone tissue dies and this causes the bone to collapse. If the process involves a bone near a joint, it often leads to collapse of the joint surface. This disease also is known as osteonecrosis, aseptic necrosis, and ischemic bone necrosis.

Although it can happen in any bone, avascular necrosis most commonly affects the ends of long bones such as the femur, the bone extending from the knee joint to the hip joint. The disease may affect just one bone, more than one bone at the same time, or more than one bone at different times. Avascular necrosis usually affects people between 30 and 50 years of age; about 10,000 to 20,000 people develop avascular necrosis each year.

The amount of disability that results from avascular necrosis depends on what part of the bone is affected, how large an area is involved, and how effectively the bone rebuilds itself. Normally, bone continuously breaks down and rebuilds—old bone is torn away and reabsorbed, and replaced with new bone. The process keeps the skeleton strong and helps it to maintain a balance of minerals. In the course of avascular necrosis, however, the healing process is usually ineffective and the bone tissues break down faster than the body can repair them. If left untreated, the disease progresses, the bone collapses, and the joint surface breaks down, leading to pain and arthritis.

What Causes Avascular Necrosis?

Avascular necrosis has several causes. Loss of blood supply to the bone can be caused by an injury (trauma-related avascular necrosis) or by certain risk factors (non-traumatic avascular necrosis), such as some medications (steroids) or excessive alcohol use.
Injury

When a joint is injured, as in a fracture or dislocation, the blood vessels may be damaged. This can interfere with the blood circulation to the bone and lead to trauma-related avascular necrosis. Studies suggest that this type of avascular necrosis may develop in more than 20 percent of people who dislocate their hip joint.

Steroid Medications

Corticosteroids such as prednisone are commonly used to treat diseases in which there is inflammation, such as systemic lupus erythematosus, rheumatoid arthritis, and vasculitis. Studies suggest that long-term, systemic (oral or intravenous) corticosteroid use is associated with 35 percent of all cases of non-traumatic avascular necrosis. However, there is no known risk of avascular necrosis associated with the limited use of steroids. Patients should discuss concerns about steroid use with their doctor.

Doctors aren’t sure exactly why the use of corticosteroids sometimes lead to avascular necrosis. They may interfere with the body’s ability to break down fatty substances. These substances then build up in and clog the blood vessels, causing them to narrow. This reduces the amount of blood that gets to the bone. Some studies suggest that corticosteroid-related avascular necrosis is more severe and more likely to affect both hips (when occurring in the hip) than avascular necrosis resulting from other causes.

Alcohol Use

Excessive alcohol use and corticosteroid use are two of the most common causes of non- traumatic avascular necrosis. In people who drink an excessive amount of alcohol, fatty substances may block blood vessels causing a decreased blood supply to the bones that results in avascular necrosis.

Other Risk Factors

Other risk factors or conditions associated with non-traumatic avascular necrosis include Gaucher’s disease, pancreatitis, radiation treatments and chemotherapy, decompression disease, and blood disorders such as sickle cell disease.

Who Is Likely To Develop Avascular Necrosis?

Avascular necrosis strikes both men and women and affects people of all ages. It is most common among people in their thirties and forties. Depending on a person’s risk factors and whether the underlying cause is trauma, it also can affect younger or older people.

What Are the Symptoms?

In the early stages of avascular necrosis, patients may not have any symptoms. As the disease progresses, however, most patients experience joint pain—at first, only when putting weight on the affected joint, and then even when resting. Pain usually develops gradually and may be mild or severe. If avascular necrosis progresses and the bone and surrounding joint surface collapses, pain may develop or increase dramatically. Pain may be severe enough to limit the patient’s range of motion in the affected joint. The period of time between the first symptoms and loss of joint function is different for each patient, ranging from several months to more than a year.

How Is Avascular Necrosis Diagnosed?

After performing a complete physical examination and asking about the patient’s medical history (for example, what health problems the patient has had and for how long), the doctor may use one or more imaging techniques to diagnose avascular necrosis. As with many other diseases, early diagnosis increases the chances of treatment success.

It is likely that the doctor first will recommend an x ray. X rays can help identify many causes of joint pain, such as a fracture or arthritis. If the x ray is normal, the patient may need to have more tests. Research studies have shown that magnetic resonance imaging, or MRI, is the most sensitive method for diagnosing avascular necrosis in the early stages. The tests described below may be used to determine the amount of bone affected and how far the disease has progressed.

X Ray

An x ray is a common tool that the doctor may use to help diagnose the cause of joint pain. It is a simple way to produce pictures of bones. The x ray of a person with early avascular necrosis is likely to be normal because x-rays are not sensitive enough to detect the bone changes in the early stages of the disease. X rays can show bone damage in the later stages, and once the diagnosis is made, they are often used to monitor the course of the condition.

Magnetic Resonance Imaging (MRI)

MRI is quickly becoming a common method for diagnosing avascular necrosis. Unlike x rays, bone scans, and CT (computed/computerized tomography) scans, MRI detects chemical changes in the bone marrow and can show avascular necrosis in its earliest stages. MRI provides the doctor with a picture of the area affected and the bone rebuilding process. In addition, MRI may show diseased areas that are not yet causing any symptoms.

Bone Scan

Also known as bone scintigraphy, bone scans are used most commonly in patients who have normal x rays. A harmless radioactive dye is injected into the affected bone and a picture of the bone is taken with a special camera. The picture shows how the dye travels through the bone and where normal bone formation is occurring. A single bone scan finds all areas in the body that are affected, thus reducing the need to expose the patient to more radiation. Bone scans do not detect avascular necrosis at the earliest stages.

Computed/Computerized Tomography

A CT scan is an imaging technique that provides the doctor with a three-dimensional picture of the bone. It also shows “slices” of the bone, making the picture much clearer than x rays and bone scans. Some doctors disagree about the usefulness of this test to diagnose avascular necrosis. Although a diagnosis usually can be made without a CT scan, the technique may be useful in determining the extent of bone damage.

Biopsy

A biopsy is a surgical procedure in which tissue from the affected bone is removed and studied. Although a biopsy is a conclusive way to diagnose avascular necrosis, it is rarely used because it requires surgery.

What is the Treatment of Avascular Necrosis?

Appropriate treatment for avascular necrosis is necessary to keep joints from breaking down. If untreated, most patients will suffer severe pain and limitation in movement within 2 years.

Several treatments are available that can help prevent further bone and joint damage and reduce pain. To determine the most appropriate treatment, the doctor considers the following aspects of a patient’s disease:

  • The age of the patient.
  • The stage of the disease—early or late.
  • The location and amount of bone affected—a small or large area.
  • The underlying cause of avascular necrosis—with an ongoing cause such as corticosteroid or alcohol use, treatment may not work unless use of the substance is stopped.

The goal in treating avascular necrosis is to improve the patient’s use of the affected joint, stop further damage to the bone, and ensure bone and joint survival. To reach these goals, the doctor may use one or more of the following treatments:

  • Reduced Weight Bearing—If avascular necrosis is diagnosed early, the doctor may begin treatment by having the patient remove weight from the affected joint. The doctor may recommend limiting activities or using crutches. In some cases, reduced weight bearing can slow the damage caused by avascular necrosis and permit natural healing. When combined with medication to reduce pain, reduced weight bearing can be an effective way to avoid or delay surgery for some patients. Most patients eventually will need surgery, however, to repair the joint permanently.
  • Core Decompression—This surgical procedure removes the inner layer of bone, which reduces pressure within the bone, increases blood flow to the bone, and allows more blood vessels to form. Core decompression works best in people who are in the earliest stages of avascular necrosis, often before the collapse of the joint. This procedure sometimes can reduce pain and slow the progression of bone and joint destruction in these patients.
  • Osteotomy—This surgical procedure reshapes the bone to reduce stress on the affected area. There is a lengthy recovery period, and the patient’s activities are very limited for 3 to 12 months after an osteotomy. This procedure is most effective for patients with advanced avascular necrosis and those with a large area of affected bone.
  • Bone Graft—A bone graft may be used to support a joint after core decompression. Bone grafting is surgery that transplants healthy bone from one part of the patient, such as the leg, to the diseased area. There is a lengthy recovery period after a bone graft, usually from 6 to 12 months. This procedure is complex and its effectiveness is not yet proven. Clinical studies are under way to determine its effectiveness.
  • Joint Replacement or Arthroplasty—Total joint replacement is the treatment of choice in late-stage avascular necrosis and when the joint is destroyed. In this surgery, the diseased joint is replaced with artificial parts. It may be recommended for people who are not good candidates for other treatments, such as patients who do not do well with repeated attempts to preserve the joint. Various types of replacements are available, and people should discuss specific needs with their doctor.

For most people with avascular necrosis, treatment is an ongoing process. Doctors may first recommend the least complex and invasive procedure, such as protecting the joint by limiting movement, and watch the effect on the patient’s condition. Other treatments then may be used to prevent further bone destruction and reduce pain. It is important that patients carefully follow instructions about activity limitations and work closely with their doctors to ensure that appropriate treatments are used.