Osteonecrosis

Avascular necrosis occurs when blood flow to a bone is interrupted or reduced. Reduced blood supply can be caused by:

• Joint or bone trauma. An injury, such as a dislocated joint, might damage nearby blood vessels. Cancer treatments involving radiation also can weaken bone and harm blood vessels. 
• Fatty deposits in blood vessels. The fat (lipids) can block small blood vessels, reducing the blood flow that feeds bones.
• Certain diseases. Medical conditions, such as sickle cell anemia and Gaucher's disease, also can cause diminished blood flow to bone.

For about 25 percent of people with avascular necrosis, the cause of interrupted blood flow is unknown.

Risk factors

Risk factors for developing avascular necrosis include:

• Trauma. Injuries, such as hip dislocation or fracture, can damage nearby blood vessels and reduce blood flow to bones.
• Steroid use. Use of high-dose corticosteroids, such as prednisone, is a common cause of avascular necrosis. The reason is unknown, but one hypothesis is that corticosteroids can increase lipid levels in your blood, reducing blood flow.
• Excessive alcohol use. Consuming several alcoholic drinks a day for several years also can cause fatty deposits to form in your blood vessels.
• Bisphosphonate use. Long-term use of medications to increase bone density might contribute to developing osteonecrosis of the jaw. This rare complication has occurred in some people treated with high doses of these medications for cancers, such as multiple myeloma and metastatic breast cancer.
• Certain medical treatments. Radiation therapy for cancer can weaken bone. Organ transplantation, especially kidney transplant, also is associated with avascular necrosis.

Medical conditions associated with avascular necrosis include:

• Pancreatitis
• Diabetes
• Gaucher's disease
• HIV/AIDS
• Systemic lupus erythematosus
• Sickle cell anemia

Complications

Untreated, avascular necrosis worsens with time. Eventually, the bone can collapse. Avascular necrosis also causes bone to lose its smooth shape, potentially leading to severe arthritis.

Prevention

To reduce your risk of avascular necrosis and improve your general health:

• Limit alcohol. Heavy drinking is one of the top risk factors for developing avascular necrosis.
• Keep cholesterol levels low. Tiny bits of fat are the most common substance blocking blood supply to bones.
• Monitor steroid use. Make sure your doctor knows about your past or present use of high-dose steroids. Steroid-related bone damage appears to worsen with repeated courses of high-dose steroids.
• Don't smoke. Smoking increases the risk.

During a physical exam your doctor will likely press around your joints, checking for tenderness. Your doctor might also move the joints through a variety of positions to see if your range of motion has been reduced.

Imaging tests

Many disorders can cause joint pain. Imaging tests can help pinpoint the source of pain. Options include:

• X-rays. They can reveal bone changes that occur in the later stages of avascular necrosis. In the condition's early stages, X-rays usually appear normal.
• MRI and CT scan. These tests produce detailed images that can show early changes in bone that might indicate avascular necrosis.
• Bone scan. A small amount of radioactive material is injected into your vein. This tracer travels to the parts of your bones that are injured or healing and shows up as bright spots on the imaging plate.

The goal is to prevent further bone loss.

Medications and therapy

In the early stages of avascular necrosis, symptoms might be eased with medication and therapy. Your doctor might recommend:

• Nonsteroidal anti-inflammatory drugs. Medications, such as ibuprofen (Advil, Motrin IB, others) or naproxen sodium (Aleve) might help relieve the pain associated with avascular necrosis.
• Osteoporosis drugs. Medications, such as alendronate (Fosamax, Binosto), might slow the progression of avascular necrosis, but the evidence is mixed.
• Cholesterol-lowering drugs. Reducing the amount of cholesterol and fat in your blood might help prevent the vessel blockages that can cause avascular necrosis.
• Blood thinners. If you have a clotting disorder, blood thinners, such as warfarin (Coumadin, Jantoven), might be recommended to prevent clots in the vessels feeding your bones.
• Rest. Reducing the weight and stress on your affected bone can slow the damage. You might need to restrict your physical activity or use crutches to keep weight off your joint for several months.
• Exercises. A physical therapist can teach you exercises to help maintain or improve the range of motion in your joint.
• Electrical stimulation. Electrical currents might encourage your body to grow new bone to replace the damaged bone. Electrical stimulation can be used during surgery and applied directly to the damaged area. Or it can be administered through electrodes attached to your skin.

Surgical and other procedures

Because most people don't develop symptoms until avascular necrosis is fairly advanced, your doctor might recommend surgery. The options include:

• Core decompression. The surgeon removes part of the inner layer of your bone. Besides reducing your pain, the extra space within your bone stimulates the production of healthy bone tissue and new blood vessels.
• Bone transplant (graft). This procedure can help strengthen the area of bone affected by avascular necrosis. The graft is a section of healthy bone taken from another part of your body.
• Bone reshaping (osteotomy). A wedge of bone is removed above or below a weight-bearing joint, to help shift your weight off the damaged bone. Bone reshaping might enable you to postpone joint replacement.
• Joint replacement. If your diseased bone has collapsed or other treatments aren't helping, you might need surgery to replace the damaged parts of your joint with plastic or metal parts.
• Regenerative medicine treatment. Bone marrow aspirate and concentration is a newer procedure that might be appropriate for early stage avascular necrosis of the hip. Stem cells are harvested from your bone marrow. During surgery, a core of dead hipbone is removed and stem cells inserted in its place, potentially allowing for growth of new bone. More study is needed.