Avascular Necrosis (Osteonecrosis)

Avascular necrosis is the death of bone tissue due to a lack of blood supply. Also called osteonecrosis, avascular necrosis can lead to tiny breaks in the bone and the bone’s eventual collapse.

The blood flow to a section of bone can be interrupted if the bone is fractured or the joint becomes dislocated. Avascular necrosis is also associated with long-term use of high-dose steroid medications and excessive alcohol intake.

Anyone can be affected by avascular necrosis. However, it’s most common in people between the ages of 30 and 60. Because of this relatively young age range, avascular necrosis can have significant long-term consequences. And it can affect the knee, hip and other bones of the body.

Avascular necrosis is also known as osteonecrosis, aseptic necrosis, and ischemic necrosis.

Cause

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 many patients with avascular necrosis, the cause of interrupted blood flow is unknown.

Signs & Symptoms

Many people have no symptoms in the early stages of avascular necrosis. As the condition worsens, the affected joint may hurt only when weight is put on it. Eventually, the joint may hurt even when lying down.

Pain can be mild or severe and usually develops gradually. Pain associated with avascular necrosis of the hip may be focused in the groin, thigh or buttock. In addition to the hip, the areas likely to be affected are the shoulder, knee, hand and foot.

Knee
For a patient suffering from avascular necrosis of the knee, sometimes the pain is so severe that the sufferer cannot put weight on the affected knee and cannot walk properly. The affected knee will usually swell up as well.

It is sometimes associated with a medial meniscus posterior horn root tear.

AVN Knee

Hip
For a patient suffering from avascular necrosis of the hip, he/she may walk with a limp (Trendelenburg’s gait). The hip joint may be stiff compared to the normal side. And the affected leg may be shorter than the normal leg.

AVN Hip

Some people develop avascular necrosis bilaterally — for example, in both hips or in both knees.

Diagnosis

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

Imaging tests
Many disorders can cause joint pain. Imaging tests can help pinpoint the source of pain. The 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 may indicate avascular necrosis.
  • Bone scan – A small amount of radioactive material is injected into the vein. This tracer travels to the parts of the bones that are injured or healing and shows up as bright spots on the imaging plate.

Treatment

The goal is to prevent further bone loss. Specific treatment usually depends on the amount of bone damage already occurred.

Medications and Therapy

In the early stages of avascular necrosis, symptoms can be reduced with medication and therapy. Options are:

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

Surgical and Other Procedures

Because most patient don’t start having symptoms until avascular necrosis is fairly advanced, the doctor may recommend surgery. The options include:

  • Core decompression – The surgeon removes part of the inner layer of the bone. In addition to reducing the pain, the extra space within the 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 the body.
  • Bone reshaping (osteotomy) – In this procedure, a wedge of bone is removed above or below a weight-bearing joint, to help shift the weight off the damaged bone. Bone reshaping might allow the patient to postpone joint replacement.
  • Joint replacement – If the diseased bone has already collapsed or other treatment options aren’t helping, the patient might need surgery to replace the damaged parts of the joint with plastic or metal parts (eg. knee replacement, hip replacement)
  • Regenerative medicine treatment – Bone marrow aspirate and concentration is a novel procedure that in the future 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 hip bone is removed and stem cells inserted in its place, potentially allowing for growth of new bone.
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