Avascular necrosis (AVN), also called osteonecrosis, aseptic necrosis, or ischemic bone necrosis, is a condition that occurs when there is loss of blood to the bone. Because bone is living tissue that requires blood, an interruption to the blood supply causes bone to die. If not stopped, this process eventually causes the bone to collapse.
Avascular necrosis most commonly occurs in the upper leg. Other common sites are the upper arm, knees, shoulder, and ankles.
There is no specific test to diagnose ankylosing spondylitis, but imaging by X-ray and MRI may show evidence of inflammation of the sacroiliac joint between the sacrum (the triangular bone at the lowest part of the back) and the ilium (the bone felt on the upper part of the hip). Some symptoms include:
Inflammatory back pain (gradual in onset, lasting over three months, with stiffness and pain that is worse in the morning and improved with movement)
Reduced mobility of the spine
As many as 20,000 people develop AVN each year. Most are between the ages of 20 and 50. For healthy people, the risk of AVN is small. Most cases are the result of an underlying health problem or injury. Possible causes include:
Dislocation or fracture of the thigh bone (femur). This type of injury can affect the blood supply to the bone, leading to trauma-related avascular necrosis. AVN may develop in 20% or more of people who dislocate a hip.
Chronic corticosteroid use. Long-term use of these inflammation-fighting drugs, either orally or intravenously, is associated with 35% of all cases of nontraumatic AVN. Although the reason for this is not completely understood, doctors suspect these drugs may interfere with the body's ability to break down fatty substances. These substances collect in the blood vessels -- making them narrower -- and reduce the amount of blood to the bone.
Excessive alcohol use. Much like corticosteroids, excessive alcohol may cause fatty substances to build in the blood vessels and decrease the blood supply to the bones.
Blood clots, inflammation, and damage to the arteries. All of these can block blood flow to the bones.
Other conditions associated with nontraumatic AVN include:
Gaucher's disease, an inherited metabolic disorder in which harmful quantities of a fatty substance accumulate in the organs
Decompression sickness, a condition that occurs when the body is subjected to a sudden reduction in surrounding pressure, causing the formation of gas bubbles in the blood
Symptoms of Avascular Necrosis
In its early stages, AVN typically cause no symptoms; however, as the disease progresses it becomes painful. At first, you may experience pain when you put pressure on the affected bone. Then, pain may become more constant. If the disease progresses and the bone and surrounding joint collapse, you may experience severe pain that interferes with your ability to use your joint. The time between the first symptoms and collapse of the bone may range from several months to more than a year.
Treatment for Avascular Necrosis
The goals of treatment for AVN are to improve or ensure function of the affected joint, stop the progression of bone damage, and reduce pain.