Avascular necrosis (AVN) is a disorder resulting from a temporary or permanent loss of blood supply to the bone. Blood carries essential nutrients and oxygen to the bones. When the blood supply is disrupted (avascular), the bone tissues begin to break down (necrosis). This can weaken the bone and eventually result in its collapse. If this occurs near a joint, it can lead to the collapse of the joint surface, resulting in pain and inflammation (arthritis). AVN is also referred to as osteonecrosis, aseptic necrosis, or ischemic bone necrosis.
AVN can occur in any bone, but most commonly affects the ends (epiphysis) of long bones such as the thigh bone (femur), causing hip and knee problems. Other common sites include the bones of the upper arms, shoulders, and ankles. AVN can occur in a single bone, but more commonly occurs in several bones at one time (multifocal AVN). AVN can sometimes be disabling, depending on what part of the bone is affected, how large an area is involved, and how well the bone rebuilds itself.
Causes of AVN
AVN is caused by interruption of the blood supply to the bone. If blood vessels are blocked with fat, become too thick or too small, or get too weak, they may not be able to provide the amount of blood necessary for the bone tissue to survive. Corticosteroids (such as prednisone and dexamethasone) given during cancer treatment can affect the bone and blood vessels, resulting in AVN.
Other factors that increase the risk of AVN in people who received corticosteroid therapy include treatment with high doses of radiation to weight-bearing bones, treatment with orthovoltage radiation (commonly used before 1970), being older than 10 at the time of treatment, and having sickle cell disease. AVN is most likely to occur during cancer treatment, but it can sometimes happen after completion of cancer therapy.
Steroids and AVN
Corticosteroids are commonly used for treatment of many cancers, such as leukemia and lymphoma. Dexamethasone is also sometimes used for treatment of nausea and vomiting associated with chemotherapy and to control brain swelling. There is no clear explanation as to how steroids cause AVN, but it is believed that they interfere with the body’s ability to break down fatty substances. These substances can clog the blood vessels, causing them to narrow. This reduces the amount of blood that gets into the bone.
Symptoms of AVN
People in the early stages of AVN may not have any symptoms. However, as the disorder progresses, most people will experience some joint pain. At first, the person may only experience pain when bearing weight on the affected bone or joint. As the disorder progresses, symptoms may be present even at rest. Pain may develop gradually and its intensity can range from mild to severe.
If AVN progresses and the bone and surrounding joint surfaces collapse, the pain can increase considerably and may become severe enough to limit movement in the affected joint. The period of time between the first symptoms of AVN and the loss of joint function is different for each person and ranges from several months to years.