What is Osteonecrosis? ON (the shortened name for this disease) is not particularly common, afflicting approximately 20,000 new patients per year in the U.S. Most patients tend to be relatively young, with an average age of 38 (although any age can be affected).
Since the diagnosis does not seem to affect longevity there are several hundred thousand patients in the U.S. alone who are living with the disease. The term literally means “death of bone” (osteo=bone, necrosis=death), and the disease can affect virtually any bone, although most cases involve only the hip, knee, shoulder or ankle joints in decreasing order of frequency. ON of the hip accounts for more than 90% of the cases.
Two Major Forms of Osteonecrosis: Post-Traumatic and Non-Traumatic. Minor trauma is not believed to cause ON. Even a major injury does not often result in ON. Certain kinds of fracture, where the blood vessels to part of a bone have been physically damaged, may result in ON. Non-traumatic ON has been associated with a wide variety of diseases including gout, lupus, sickle cell disease, kidney or liver disease, and clotting disorders. In addition, high dosage steroid (cortisone) use is sometimes associated with ON, as well as high alcohol consumpution. Finally, as many as 30% of all patients with osteonecrosis are otherwise completely healthy with no associated risk factor. This is called “idiopathic,” a medical term meaning “of unknown cause.”
Who’s at Risk? If a person is completely healthy, the risk of getting osteonecrosis is quite small, probably less than 1 in 100,000. Another way to understand this is that most of the people who get ON probably have an underlying health problem. Children, as young as 4 and extending to the teens, get a form of ON which is called Legg–Calvé–Perthes disease (LCPD) after the doctors who first described it. However, most patients are between 30 and 50 with an average age of 38. Patients over the age of 50 are likely to have developed ON either by a fracture of the hip or more rarely in association with disease of the major blood vessels to the lower leg. Although the specific cause of the bone death is not precisely known except in the case of fracture, a number of conditions have been associated with ON. The most common includes a history of high dose steroid treatment for certain medical condition (including Lupus, COPD, an organ transplant, etc). Low dose steroids (cortisone, prednisone, etc) commonly used for bee stings, poison ivy and acute allergies are not thought to cause ON. The next most common associated condition is a history of alcohol intake. The higher the intake the higher the risk. The mechanisms by which these two risk factors (alcohol and steroids) cause ON are not well understood. The third most common group are those patients who have no risk factors at all, and these patients are a true medical mystery. No matter what the cause, the symptoms and course of the disorder are remarkably similar.
First Symptoms: Unfortunately, many patients with ON have had the disease for quite some time before symptoms become noticeable. The initial symptoms are usually pain or aching in the affected joint with activity, which subsides after the activity has stopped.
Symptoms usually begin slowly and may initially be intermittent. As the disease progresses, the pain increases and is associated with stiffness. Limping becomes common. In the hip, the most common joint affected, the pain is usually felt in the groin.
Diagnosis: The principle diagnostic tool is the x-ray. By the time most patients have significant symptoms, the disease is advanced enough to be seen on standard xrays, where the xray will show the area of bone that is involved. The very earliest stages of ON, while not visible on an xray, can be detected by MRI which will detect tissue changes. Occasionally, your doctor may order a CAT scan which is a special series of x-rays, interpreted by the computer to show the three dimensional structure of the bone. Any of these tests will help the doctor to determine whether you have ON as well as how advanced the disease is.
Prevention: There are no known effective preventive measures. Steroids should only be taken as absolutely necessary and alcohol consumption should always be in moderation. Some experimental drug protocols are being evaluated which may have a place In treatment or prevention in the future.
Treatment and the concept of Risk vs. Benefit Ratio: Before entering into a description of some of the treatments available for ON, it is important that the risk/benefit ratio concept be understood. Any surgical procedure has a certain element of risk involved. Even no treatment at all has the risk that the disease will progress, so doing nothing is not risk free. Some procedures may have a lower likelihood of success but may have a very little downside risk. Other procedures may have a higher degree of success, but also have a higher degree of risk. The physician must consult with the patient in assessing all the factors that evaluate both risk and benefit for the patient in their particular circumstance. What is right for one patient may be absolutely wrong for another. This is particularly true for ON because each patient presents with a unique set of factors (age, associated disease, specific joint(s) involved, extent and progression of disease). Any treatment needs to be determined between yourself and your treating physician.
Extent of disease: The femoral head is the most frequent bone involved and will be used for this discussion. It is rare for the entire weightbearing surface of the femoral head to be involved. However, if more than half of the surface is involved, treatments designed to preserve the femoral head have a much lower chance of success.
Progression of the disease: As mentioned earlier, the earliest stages of the disease, before there are significant symptoms, can only be detected by MRI. Once it can be seen on x-ray, it is not actually the dead bone that can be seen but the response of the living bone to the area of necrosis (dead tissue). The advanced stages begin when the dead bone starts to fail mechanically through a process of microfractures of the bone.
Eventually, this will result in damage to the other side of the joint, and need for a total joint replacement. The greater the extent of the disease and the more advanced the progression, the less likely that the joint can be saved. Fortunately, joint replacement procedures today are highly successful, even in relatively young patients affected by ON.
It is always the physicians desire to preserve the normal joint whenever possible. Unfortunately, many patients present with advanced, extensive disease.
NonSurgical Treatement: Protected weight-bearing crutches or a walker are very useful in alleviating the pain associated with ON. Such devices can also be useful in protecting the joint between the time of diagnosis and scheduling of elective surgery, and are helpful in limiting progression while other medical conditions are managed. Protected weight-bearing alone is never adequate treatment for ON and will not result in cure of the condition, no matter how long it is maintained. Only rarely, when an associated medical condition necessitates a patient not being able to have surgery, would protected weight-bearing devices be recommended long term.
Core Decompression: This is a simple surgical procedure, which involves taking a plug of bone out of the involved area. It is applicable for mild to moderate degree of involvement that has not yet progressed to collapse. Because this involves creating a hole in the bone, six weeks of protected weight-bearing is necessary to avoid fracture through the hole, one of the complications of the procedure. There is some controversy about this procedure with a few cases that have been reported showing generally poor results. However, in centers that do this procedure frequently, most have reported good results in the appropriate cases.
Bone Grafting: When a section of the bone has died, as is the case in ON, for some reason it doesn’t seem to heal. One of the methods which may cause the bone to heal is surgical removal of the dead bone and filling the empty space with bone graft which is either taken from the patient or from the bone bank. The success of this approach depends upon the quantity of bone that has died. During the healing process, which is normally 6 to 12 months, the patient must be on weight-bearing restriction.
Vascularized Bone Grafting: Regular bone graft, whether from the bone bank or from the patient is itself dead bone. It serves as a scaffold for the body to build new bone around but the body also has to grow a new blood supply. For this procedure, a bone with its blood vessels is taken from the patient and hooked up to blood vessels near the hip. The dead bone is removed from the femoral head and replaced with the grafted bone that carries with it its own blood supply. The advantage of this approach is that the body doesn’t have to rebuild a new blood supply and the bone graft retains its physical and mechanical properties. Healing and complete filling of the defect still has to take place, during which time crutches or a walker has to be used. The disadvantage of this treatment is that a substantial piece of bone must betaken from the lower leg (the fibula, the smaller bone of the lower leg below the knee). Some patients will develop difficulties in the area from which the bone graft is taken. The operation takes several hours and requires a team experienced in these techniques.
Osteotomy: Usually it is the main weight-bearing area of the bone that is involved with ON. In some cases the bone can be cut below the area of involvement and rotated or turned so that another portion of the bone that is not involved in the ON can become the new weightbearing area. These operations are not very common anymore, but may apply in special circumstances.
Femoral Head Resurfacing: Initially only the femoral head is involved, not the socket of the hip joint. FHR involves implanting a metal hemisphere over the femoral head, which exactly matches the size of the original femoral head. This is similar to capping a tooth when the root is still good, as opposed to pulling the tooth and putting in a false tooth. It is understood that over a period of many years, the metal head will gradually wear out the socket which will require a total hip replacement. This procedure is designed to “buy time” for the younger individual whose extent of disease or degree of progression is such that one of the preservative procedures listed above cannot be performed. In summary: Most patients with ON are under 50. It is generally believed that total hip replacement today will not last the 30+ most of these patients will require. Therefore, if two procedures are likely to be necessary, it is important that the first procedure does not make the second procedure more difficult or less likely to succeed. A total hip replacement following a failed femoral head resurfacing is more likely to be successful than revision total hip replacement which follows a failed primary total hip replacement.
Femoral Head Replacement: This is basically half a total hip replacement. All comments about femoral head resurfacing apply to femoral head replacement. However, because a femoral head replacement also puts a stem inside the femoral bone (the femoral shaft) it is a little more extensive than the resurfacing procedure. If it needs to be revised, it is a little more difficult to convert to a total hip replacement than the resurfacing procedure.
Total Hip Replacement: When the ON is advanced to the point that there is involvement of the socket as well, then the only thing that will be effective is either a hip fusion (making the hip completely stiff) or a total hip replacement. Total hip replacement is one of the most successful surgical procedures ever devised. Success rates are usually above 95%!
The issue to be considered with total hip replacements for patients with ON is that it is not uncommon for the patient to have a further life expectancy of more than 40 or even 50 years. With current technology we don’t think that it is likely that a total hip replacement will last that long. For this reason, many physicians will want to try an alternative procedure to put off total hip replacement for a few years even when it is known that that procedure will not in itself be successful forever. If your ON disease is advanced, and/or extensive, then total hip replacement may be the most sensible choice.