What causes osteonecrosis (avascular necrosis)?

Avascular necrosis (or osteonecrosis) is defined as a lack of blood flow which causes tissue death. A-without, Vascular -- blood supply, necrosis -- tissue death. 

A blockage in the blood supply to tissue will cause the death of tissue or cells. 
Francisco J. Borja, MD
Orthopedic Surgery
Avascular necrosis, also known as osteonecrosis, may affect just one bone or more than one. The blood flow to a section of bone can be interrupted if the bone is fractured or the joint becomes dislocated. Other causes include steroid use and excessive alcohol consumption. Because bones need a blood supply to sustain them, avascular necrosis results in bone tissues breaking down faster than the body can repair them. 

The cause of decreased blood flow to the bones is not always apparent. The most common causes are broken bones or dislocated joints that cause damage to nearby blood vessels. Other known causes include build-up of pressure in the bone, which can be caused by Gaucher's disease or other conditions. Clogged or narrowed blood vessels, some steroid medications, and heavy drinking are also known to cause osteonecrosis.

Dr. Robin Miller, MD
Internal Medicine
Osteonecrosis occurs when the blood supply to the bone is cut off. The bone will eventually die and collapse. The femoral head of the hip joint is the most common bone involved.

Risk factors for this condition include the long-term use of steroids such as prednisone, alcohol abuse, joint injuries such as hip fracture and certain diseases (such as sickle cell anemia, Gaucher’s disease, diabetes and gout), and cancer.

Osteonecrosis of the jaw has gotten a lot of press due to the increased risk that can occur with the use of bisphosphonates such as Fosamax for osteoporosis. This is a rare complication that primarily has occurred in some cancer patients undergoing chemotherapy who also were being treated with intravenous bisphosphonates.

In a few patients taking oral bisphosphonates osteonecrosis of the jaw has occurred. These were people who had active dental problems and/or who had a recent tooth extraction.

Treatment of osteonecrosis is aimed at symptom control, and depending on the cause and which bone is involved the doctor may prescribe surgery.

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