Also known as osteonecrosis, aseptic necrosis or ischemic bone necrosis, avascular necrosis (AVN) occurs when the blood supply to bones is temporarily or permanently blocked. It affects between 10,000 and 20,000 people in the United States each year. Without an adequate blood supply, bone tissue dies, bones develop tiny cracks and, eventually, collapse. If a joint is affected, the joint may collapse. AVN usually occurs at the ends of long bones, such as the femur, the bone between the hip and the knee. It can, however, affect any bone including, most commonly, the upper arm bone, knees, shoulders and ankles. AVN can strike one bone, more than one bone at the same time or different bones at different times.
Bones are in a continual process of breaking down, absorbing the old bone and rebuilding new bone. Bones rebuild themselves after an injury, as well as during normal growth. In AVN, bones break down faster than the body can rebuild them. If untreated, avascular necrosis leads to the bones and joint surfaces breaking down and collapsing, this in turn leads to pain and arthritis. Although people can get AVN at any age, individuals between 30 and 50 are at the greatest risk for AVN.
At first, patients with AVN experience no symptoms. The time it takes for the disease to progress from first symptoms to loss of joint function varies by patient, and may range from months to more than a year. Over time as the disease progresses, most patients have stiffness and then pain in the affected joint. The condition also may lead to muscle spasms in the affected area. At first, the pain only occurs when weight is put on the affected joint, but over time the joint hurts all the time. The pain may be mild or severe, and usually develops gradually. If the joint surface collapses, pain may increase suddenly. The range of motion in the affected joint is sometimes limited. If AVN strikes the hip joint, disabling osteoarthritis may develop.
Cause and Risk Factors
AVN may be caused by an injury, such as a dislocated joint, called trauma-related avascular necrosis, or by various risk factors, called non-traumatic avascular necrosis. When a joint is fractured or dislocated, damage to the blood vessels may occur, compromising blood flow. This type of trauma-related avascular necrosis affects about 20 percent of people who dislocate a hip joint.
When used for a long time, steroid medications, which are used as anti-inflammatories to combat rheumatoid arthritis, irritable bowel disease and vasculitis, can lead to non-traumatic avascular necrosis. Such long-term use of steroids appears to be related to about 35 percent of cases of non-traumatic AVN. Although the cause is unknown, it may be that steroid use decreases the body's ability to break down fatty substances in blood vessels, which then block blood flow to bones.
Alcohol abuse is a common cause of non-traumatic AVN. Although the exact mechanism by which this occurs is not well understood, it is thought that people who drink alcohol excessively may harm their body's ability to break down fatty substances, which can build up in blood vessels, hence reducing the flow of blood to bones.
A number of other conditions also carry the risk of getting AVN, including Gaucher's disease, pancreatitis, chemotherapy and radiation treatments, decompression diseases, such as the bends as a result of scuba diving, and blood disorders, such as sickle cell disease.
It is crucial to detect the disease early, since the earlier it is detected, the better the odds are of treating it effectively. Diagnosis begins with a complete physical examination, including questions about any other health conditions that may affect the bones and joints.
In certain cases, a biopsy may be performed where a portion of the affected bone is removed for study to confirm the presence of AVN. Since a biopsy requires surgery it is usually done when the physician continues to suspect AVN despite normal test results. There are other invasive tests that can be used to detect increased pressure in bone.
Several imaging techniques are be used to correctly diagnose AVN:
- An X-ray may be ordered first to diagnose the cause of joint pain. If AVN is advanced, an X-ray may show bone damage. If AVN is in its early stages, the X-ray will not show the early damage caused by the disease. After diagnosis, X-rays may be used to monitor the later progression of the disease.
- Magnetic resonance imaging (MRI) is the most common technique for diagnosing AVN. MRI is the most effective tool for detecting the early stages of AVN, since MRIs detect chemical changes in bone marrow. An MRI, unlike an X-ray, computed tomography (CT) scan or bone scan, can show the area of the bone affected, including areas that are not yet causing symptoms.
- A bone scan or bone scintigraphy is usually used for patients who have normal X-rays and the physician still suspects AVN. A harmless radioactive dye is injected into the affected bone and a scan is taken that can detect how the dye travels through the bone and where normal bone rebuilding is occurring. A single bone scan covers the entire body, so AVN in any bone will be detected. A bone scan will not detect AVN at its earliest stages.
- A computed tomography (CT) scan provides the doctor with a three-dimensional picture of the bone and with "slices" of the bone, which are far clearer than X-rays or bone scans. Although many doctors are confident in making a diagnosis of AVN without a CT scan, such a scan can help determine the extent of damage caused by the disease.
Without treatment, avascular necrosis will lead to severe pain and substantial limitation of movement within a couple of years. Outcomes depend on what part of a bone is affected, how large an area is affected and whether the bone is able to rebuild itself. The earlier AVN is detected, the greater the chance for successful treatment, although treatment usually is an ongoing process.
Several different treatment options are available to help prevent further bone loss and reduce pain. The choice of treatment depends on factors including the age of the patient, stage of the disease, location and amount of bone affected, and underlying cause of the disease. Physicians generally start by recommending conservative treatment before recommending more invasive surgical approaches.
Conservative Treatment Options
Conservative treatment may delay surgery for some patients. Conservative approaches include medicines to reduce fatty substances (lipids). Nonsteroidal anti-inflammatories may be used to help reduce pain. If AVN is detected early, limiting activities, keeping weight off the affected joint and the use of crutches can sometimes allow the joint to naturally rebuild and slow the damage caused by AVN. Range-of-motion exercises can also be used to maintain the use of a joint, while electrical stimulation may be used to promote bone growth. Heat may be used to help ease the pain caused by the disease.
Surgical Treatment for AVN
Although conservative treatments can slow the damage caused by AVN and can be effective in the short term, in the long term, surgery may be the only option to repair damaged joints.
There are four main surgical treatment options for AVN:
- Core Decompression: A surgeon removes the inner layer of bone, which reduces pressure in the bone and increases blood flow, allowing more blood vessels to form. This procedure works most effectively for patients who are in the early stages of AVN, thus highlighting the importance of diagnosing the condition early before a joint collapses.
- Bone Graft: Though research is still being conducted on the effectiveness of treatment, this technique may be used to support a joint. Healthy bone is removed from one part of the body, such as the leg, and grafted onto the diseased area to strengthen it. A vascular graft includes arteries and veins to increase blood flow to the affected area. It may take six to 12 months to recover from a bone grafting procedure.
- Osteotomy: A procedure during which the surgeon may opt to reshape the bone to reduce stress on the area affected by AVN. With this procedure, the recovery time is usually long, three to 12 months, with the patient's activity extremely limited during this period. Surgeons usually elect to perform an osteotomy when a patient has advanced AVN and a large area of bone has been affected.
- Arthroplasty or total joint replacement: This common procedure is used if a joint has been destroyed by AVN. The diseased joint is replaced by an artificial joint, either in part or entirely. There are several types of replacements available and patients should discuss with their physician which type is best for their particular condition.