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Osteonecrosis, also referred to as avascular necrosis, aseptic necrosis, or ischemic necrosis of bone, is the death of a segment of bone caused by an impaired blood supply.
Causes
Osteonecrosis or avascular necrosis is not a specific disease but a condition in which there is death of a localized area of bone. There are two general categories of osteonecrosis: traumatic and nontraumatic.
Traumatic osteonecrosis is the most common. The most frequent cause of traumatic osteonecrosis is a displaced (separated) fracture, most often affecting the hip, which occurs in older people. A displaced fracture may damage the blood vessels supplying the upper end of the thigh bone (the femoral head), resulting in death of the bone. This death of bone occurs less often in other areas of the body.
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Nontraumatic osteonecrosis occurs without direct trauma or injury. This type may be caused by a disease or condition that results in the blockage of small blood vessels that supply certain areas of the bone. The areas most commonly affected are the femoral head, which is part of the hip joint; the knee; and the upper arm at the shoulder. This disorder occurs most commonly among men and people between the ages of 30 and 50 and often affects both hips or both shoulders. The most common causes are high doses of corticosteroids (especially when given for long periods of time) and chronic, excessive alcohol use. A number of other causes have been identified, but these occur much less often. These other causes include certain blood-clotting disorders, sickle cell disease, liver disease, tumors, Gaucher disease, radiation therapy, and decompression sickness (which occurs in divers who surface too quickly—see Diving and Compressed Air Injuries: Decompression Sickness). A number of disorders that are treated with high doses of corticosteroids also may be associated with osteonecrosis. In these cases, it may not be clear whether the cause is the disorder or the corticosteroids.
In about 20% of people with osteonecrosis, the cause is unknown, and these people are thus said to have idiopathic osteonecrosis. If one bone has nontraumatic osteonecrosis, the same bone on the opposite side of the body also has it about 60% of the time, even if there are no symptoms.
Spontaneous osteonecrosis of the knee (SPONK) can occur in older women (occasionally men) who have no specific risk factors for the disorder. SPONK is thought to be caused by an insufficiency fracture. An insufficiency fracture is caused by normal wear and tear on bone that has been affected by osteoporosis. SPONK occurs without direct trauma or injury.
Symptoms
As osteonecrosis progresses, more and more tiny fractures may occur, particularly in bones that support weight, such as the hip. As a result, the bone usually collapses weeks or months after the blood supply is cut off. Most often pain develops gradually when the bone begins to collapse. At times, however, the onset of pain may be sudden and could be related to increased pressure that develops in and around the affected area of bone. Regardless of how sudden, pain is increased by moving the affected bone and generally is alleviated with rest. The person avoids moving the joint to minimize pain.
If the affected bone is in the leg, standing or walking worsens the pain and a limp develops.
In osteonecrosis of the hip, pain is usually present in the groin and may extend down the thigh or into the buttocks.
SPONK causes sudden pain along the inner part of the knee. There may be tenderness in this area, and the joint often becomes swollen with excess fluid.
Osteonecrosis of the shoulder often causes fewer symptoms than osteonecrosis that occurs in other bones.
Osteoarthritis (see Joint Disorders) develops when collapse affects a large part of the bone.
Diagnosis
Because osteonecrosis is often painless at first, it may not be diagnosed in its earliest stages. Doctors suspect osteonecrosis in people who do not improve satisfactorily after sustaining certain fractures. They also suspect the disorder in people who develop unexplained pain in the hip, knee, or shoulder, particularly if these people have risk factors for osteonecrosis.
X-rays of the affected area usually show osteonecrosis unless the disorder is in its earliest stages. If x-rays appear normal, however, magnetic resonance imaging (MRI) is usually done because it is the best test for detecting osteonecrosis early, before changes appear on ordinary x-rays. The x-rays and MRI also show whether the bone has collapsed, how advanced the disorder is, and whether the joint is affected by osteoarthritis. If doctors discover nontraumatic osteonecrosis in one hip, they also examine the other hip with an x-ray or MRI.
Prevention
To minimize the risk of osteonecrosis caused by corticosteroids, doctors use these drugs only when essential, prescribe them in as low a dose as needed, and prescribe them for as short a duration as possible. To prevent osteonecrosis caused by decompression sickness, people should follow accepted rules for decompression during diving and when working in pressurized environments (see Diving and Compressed Air Injuries: Prevention). Excessive alcohol use and smoking should be avoided. Various drugs (such as those that prevent blood clots, dilate blood vessels, or lower lipid levels) are being evaluated for prevention of osteonecrosis in people at high risk.
Treatment
Some areas affected by osteonecrosis need only nonsurgical measures to alleviate symptoms. Other areas need to be treated with a surgical procedure.
Nonsurgical measures
Several nonsurgical measures are available for treating the symptoms caused by osteonecrosis. Taking anti-inflammatory drugs or other pain relievers, minimizing activity and stress (such as weight bearing for osteonecrosis of the hip and knee), and undergoing physical therapy are ways to relieve symptoms but not cure the disorder or change its course. These measures, however, may be adequate for treatment of , the shoulder, the knee, SPONK, and small areas of osteonecrosis of the hip, which may eventually heal without treatment.
Surgical procedures
There are a number of surgical procedures that slow or stop progression of the disorder. These are most effective for treating early disease, particularly of the hip, that has not yet progressed to bone collapse.
The simplest and most common of these procedures is called core decompression, which involves taking one or more plugs of bone out of the involved area or inserting many small tracks or holes (perforations) into the area in an attempt to decrease pressure inside the bone. Core decompression often relieves pain and stimulates healing. In about 65% of people, the procedure can delay or avoid the need for total hip replacement. In younger people, core decompression may also be used even if a small amount of collapse already has taken place. The procedure is relatively simple, has a low rate of complications, and requires the use of crutches for only about 6 weeks.
Another procedure is bone grafting (transplanting bone from one site to another). For osteonecrosis of the hip, this can involve removing the dead area of bone and replacing it with more normal bone from elsewhere in the body. This graft supports the weakened area of bone and stimulates the body to form new, living bone in the affected area. An osteotomy is another procedure designed to save the affected joint. This procedure is performed particularly in the region of the hip and may be suitable for younger people in whom some degree of collapse already has occurred, which makes them poor candidates for core decompression or other procedures. Usually the osteonecrosis is in the weight-bearing area of the femoral head. Bone grafting and osteotomy are difficult procedures, however, and are not often performed in the United States. They require a person to spend up to 6 months on crutches. These procedures are done only at selected centers that have the surgical experience and facilities to achieve the best results.
A total joint replacement or other type of joint replacement procedure (arthroplasty) is the only effective procedure to relieve pain and restore motion if osteonecrosis has caused significant joint collapse and osteoarthritis. About 95% of people benefit from total replacement of the hip or knee. With modern techniques and devices, most joints should last more than 15 to 20 years. However, in younger people with osteonecrosis, a replacement joint may have to be revised or replaced at some later time. Therefore, some surgeons favor a more limited procedure, called surface replacement arthroplasty, to treat osteonecrosis of the hip in younger people. This procedure involves placing a metal cap over the femoral head rather than replacing the entire joint as is done in a standard total hip replacement. If the hip socket also is involved, a second metal cap is placed in the socket. However, these procedures are done less often now than a few years ago because the rate of local complications (problems that develop in or near the joint) and prosthesis failures (that is, the replaced joints can fail to keep working) has been increasing. Occasionally, a partial or total replacement of the extremely painful shoulder may be needed for advanced osteonecrosis that does not respond well to nonsurgical treatment.
Last full review/revision August 2012 by Marvin E. Steinberg, MD
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