Osteonecrosis can be caused by an injury or can occur spontaneously.
Typical symptoms include pain, limited range of motion of the affected joint, and, when the leg is affected, a limp.
The diagnosis is based on symptoms, the person's risk of osteonecrosis, and the results of x-rays and magnetic resonance imaging.
Stopping smoking, stopping excessive alcohol use, and minimizing the use of or lowering the dose of corticosteroids reduce the risk of developing the disorder.
Various surgical procedures can be done if nonsurgical measures (such as rest, physical therapy, and pain relievers) do not relieve symptoms.
Each year in the United States, about 20,000 people develop osteonecrosis. The hip is most commonly affected, followed by the knee and shoulder. The wrist and ankle are affected less often. Osteonecrosis does not usually affect the shoulder or other less commonly affected sites unless the hip is also affected. However, osteonecrosis of the jaw (ONJ) is a disorder involving only the jaw bone.
Osteonecrosis is not a specific disease but a condition in which death of the bone is confined to one or more specific (localized) areas. There are two general categories of osteonecrosis:
Traumatic osteonecrosis is the most common. The most frequent cause of traumatic osteonecrosis is a displaced fracture. In a displaced fracture, a bone breaks into two or more parts and moves so that the fractured ends are not lined up. The type of displaced fracture that causes osteonecrosis most often affects the hip (see Hip Fractures) and most commonly occurs in older people.
A displaced fracture or a dislocation may damage the blood vessels supplying the upper end of the thighbone (the femoral head, part of the hip joint), resulting in death of this part of the bone. This death of bone occurs less often in other areas of the body.
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
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). A number of disorders that are treated with high doses of corticosteroids (such as lupus) 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.
If one bone has nontraumatic osteonecrosis, the same bone on the opposite side of the body sometimes has it also, even if there are no symptoms. For example, if one hip is affected, about 60% of the time the other hip is affected.
Spontaneous osteonecrosis of the knee (SPONK or SONK) can occur in older women (occasionally men) who have no specific risk factors for the disorder. SPONK differs from other forms of osteonecrosis. SPONK is thought to be caused by an insufficiency fracture. An insufficiency fracture occurs without direct trauma and is caused by normal wear and tear on bone that has been affected by osteoporosis. However, osteonecrosis of the knee can also result from trauma or any of the nontraumatic risk factors of osteonecrosis.
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, pain may begin suddenly 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 typically 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.
Spontaneous osteonecrosis of the knee 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. Bending the knee may be painful, and people may have a limp.
Osteonecrosis of the shoulder often causes fewer symptoms than osteonecrosis that occurs in the hip or knee.
Osteoarthritis (damage to the cartilage covering the joint surfaces) develops over time, often after a large part of the bone collapses.
Because many of the risk factors for the development of osteonecrosis affect the whole body (for example, chronic corticosteroid use, excessive alcohol intake, sickle cell disease), osteonecrosis may occur in multiple bones. In sickle cell disease, osteonecrosis may occur in different long bones and may mimic painful sickle crises.
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 having 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.
Blood tests may be done to detect an underlying disorder (such as a blood-clotting disorder).
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 prevention of decompression sickness and see Diving Safety Precautions and Prevention of Diving Injuries).
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.
Some areas affected by osteonecrosis need only nonsurgical measures to relieve symptoms. Other areas need to be treated with a surgical procedure.
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, spontaneous osteonecrosis of the knee, and small areas of osteonecrosis of the hip, which may spontaneously heal without treatment. Osteonecrosis heals without treatment in some people if the disorder is diagnosed early and if the affected area is small and not in the major weight-bearing area.
Spontaneous osteonecrosis of the knee is usually treated without surgery, and pain usually resolves.
There are a number of surgical procedures that slow or possibly prevent progression of the disorder. These procedures are done to preserve the joint and are most effective for treating early osteonecrosis, particularly of the hip, that has not yet progressed to bone collapse. If bone collapse has occurred, a type of joint replacement procedure may be done to decrease pain and improve function.
Core decompression, the simplest and most common of these procedures, involves drilling one or 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 prevent 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 about 6 weeks. Most people have satisfactory or good results overall. However, results for any particular person can be hard to predict. About 20 to 35% of people require a total hip replacement.
During core decompression, surgeons may inject a person's own bone cells into the small hole or holes. This enhancement to the core decompression procedure may help heal the femoral head (which is part of the hip joint).
Bone grafting (transplanting bone from one site to another) is another procedure. 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 done 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. An osteotomy changes the position of the bone so that the weight of the body is now supported by a normal area of the femoral head and not by the collapsed area.
Bone grafting and osteotomy are difficult procedures, however, and are not often done 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 is an 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 (see Hip replacement). With modern techniques and devices, most daily activities can be resumed within 3 months and most joints should last more than 15 to 20 years.
In younger people with osteonecrosis, a total joint replacement may have to be revised (called revision surgery) or replaced at some later time. However, with modern devices, revision surgery has become much less common. Because total joint replacement is now so successful, there is much less need to do other procedures that replace part of the joint or remove the surface cartilage and place a cap on each bone end.
Occasionally, a partial or total replacement of an extremely painful knee or shoulder may be needed for advanced osteonecrosis that is not alleviated by nonsurgical treatment.