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Overview

Osteonecrosis is a disease resulting from the temporary or permanent loss of blood supply to the bones. Without blood the bone tissue dies and ultimately may collapse. If the process involves the bones near a joint it often leads to collapse of the joint surface. Osteonecrosis is also known as avascular necrosis aseptic necrosis and ischemic necrosis.

Although it can happen in any bone osteonecrosis most commonly affects the ends (epiphysis) of the femur the bone extending from the knee joint to the hip joint. Other common sites include the upper arm bone knees shoulders and ankles. The disease may affect just one bone more than one bone at the same time or more than one bone at different times.

An estimated 2000 to 3000 Canadians develop osteonecrosis each year and most of them are between 20 and 50 years of age. Osteonecrosis is the underlying diagnosis in approximately 10 percent of hip replacements.

With proper treatment most people with osteonecrosis can lead productive lives. The amount of disability that results from osteonecrosis 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 replaced with new bone. This process - which takes place after an injury as well as during normal growth - keeps the skeleton strong and helps it to maintain a balance of minerals. In the course of osteonecrosis 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.

Symptoms

In the early stages of osteonecrosis people may not have any symptoms. As the disease progresses however most experience joint pain. At first the pain occurs only when putting weight on the affected joint. Later it occurs even when resting. Pain usually develops gradually and may be mild or severe. If osteonecrosis progresses and the bone and surrounding joint surface collapse pain may develop or increase dramatically. Pain may be severe enough to limit range of motion in the affected joint. In some cases particularly those involving the hip disabling osteoarthritis may develop. The period of time between the first symptoms and loss of joint function is different for each person but it typically ranges from several months to more than a year.

Causes

Osteonecrosis is caused by impaired blood supply to the bone but it is not always clear what causes that impairment. Osteonecrosis often occurs in people with certain risk factors (such as high-dose corticosteroid use and excessive alcohol intake) and medical conditions. However it also affects people with no health problems and for no known reason. Following are some potential causes of osteonecrosis and other health conditions associated with its development:

Steroid Medications

Aside from injury one of the most common causes of osteonecrosis is the use of corticosteroid medications such as prednisone. Corticosteroids are commonly used to treat inflammatory diseases such as systemic lupus erythematosus rheumatoid arthritis inflammatory bowl disease severe asthma and vasculitis. Studies suggest that long-term use of oral or intravenous (IV) corticosteroids is associated with nontraumatic osteonecrosis. Patients should discuss concerns about steroid use with their doctor.

Doctors are not sure exactly why the use of corticosteroids sometimes leads to osteonecrosis. They speculate that the drugs may interfere with the body's ability to break down fatty substances called lipids. These substances then build up in and clog the blood vessels causing them to narrow and to reduce the amount of blood that gets to the bone. Some studies suggest that corticosteroid-related osteonecrosis is more severe and more likely to affect both hips (when occurring in the hip) than osteonecrosis resulting from other causes.

Alcohol Use

Excessive alcohol use is another common cause of osteonecrosis. People who drink alcohol in excess can develop fatty substances that may block blood vessels causing a decreased blood supply to the bones.

Injury

When a fracture a dislocation or some other joint injury occurs the blood vessels may be damaged. This can interfere with the blood circulation to the bone and lead to trauma-related osteonecrosis. In fact studies suggest that hip dislocation and hip fractures are major risk factors for osteonecrosis.

Increased pressure within the bone may be another cause of osteonecrosis. When there is too much pressure within the bone the blood vessels narrow making it hard for them to deliver enough blood to the bone cells. The cause of increased pressure is not fully understood.

Other Risk Factors

Other risk factors for osteonecrosis include radiation therapy chemotherapy and organ transplantation (particularly kidney transplantation). Osteonecrosis is also associated with a number of medical conditions including cancer lupus and blood disorders such as sickle cell disease HIV infection Gaucher's disease Caisson disease gout vasculitis osteoarthritis and osteoporosis.

Treatment

Appropriate treatment for osteonecrosis is necessary to keep joints from breaking down. Without treatment most people with the disease will experience severe pain and limitation in movement within 2 years. To determine the most appropriate treatment the doctor considers the following:

• the age of the patient
• the stage of the disease (early or late)
• the location and whether bone is affected over a small or large area
• the underlying cause of osteonecrosis. 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 osteonecrosis 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 surgical or nonsurgical treatments.

Nonsurgical Treatments

Usually doctors will begin with nonsurgical treatments alone or in combination. Unfortunately although these treatments may relieve pain or help in the short term for most people they don't bring lasting improvement.

• Medications - Nonsteroidal anti-inflammatory drugs (NSAIDs) are often prescribed to reduce pain. People with clotting disorders may be given blood thinners to reduce clots that block the blood supply to the bone. Cholesterol-lowering medications may be used to reduce fatty substances (lipids) that increase with corticosteroid treatment (a major risk factor for osteonecrosis). In one study people who took cholesterol-lowering medications called statins along with corticosteroids significantly reduced the risk of developing osteonecrosis in the first place.
• Reduced weight bearing - If osteonecrosis 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 osteonecrosis and permit natural healing. When combined with pain medication reduced weight bearing can be an effective way to avoid or delay surgery for some patients.
• Range-of-motion exercises - An exercise program involving the affected joints may help keep them mobile and increase their range of motion.
• Electrical stimulation - This treatment has been used in several centers to induce bone growth and in some studies has been helpful when used prior to femoral head collapse.

Surgical Treatment

A number of different surgical procedures are used to treat osteonecrosis. Most people with osteonecrosis will eventually one form or another. They include:

• Core decompression - This surgical procedure removes the inner cylinder 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 osteonecrosis often before the collapse of the joint. This procedure sometimes reduces pain and slows the progression of bone and joint destruction.
• Osteotomy - This treatment involves reshaping the bone to reduce stress on the affected area. Recovery can be a lengthy process requiring 3 to 12 months of very limited activities. This procedure is most effective for patients with early-stage osteonecrosis and those with a small area of affected bone.
• Bone graft - This is the transplantation of healthy bone from another part of the body. It is often used to support a joint after core decompression. In many cases the surgeon will use what is called a vascular graft - which includes an artery and vein - to increase the blood supply to the affected area. Recovery from a bone graft can take from 6 to 12 months. The procedure is complex and its effectiveness is unproven. Clinical studies are underway to determine its effectiveness.
• Arthroplasty/total joint replacement - Total joint replacement is the treatment of choice in late-stage osteonecrosis and when the joint is destroyed. In this surgery the diseased joint is replaced with artificial parts. Total joint replacement or sometimes femoral head resurfacing is often recommended for people for whom other efforts to preserve the joint have failed. Various types of replacements are available and people should discuss specific needs with their doctor.

For most people with osteonecrosis treatment is an ongoing process. Depending upon the stage of the disease doctors may first recommend the least complex or non-operative treatment plans such as medication or reduced weight bearing. If this proves unsuccessful surgical treatments may be needed. It is important that patients carefully follow instructions about activity limitations and work closely with their doctors to ensure that appropriate treatments are used.