Avascular Necrosis of Bone and Lupus

Avascular Necrosis of Bone and Lupus
Marvin E. Steinberg, MD

Avascular necrosis of bone (AVN) is a disorder in which an avascular (lacking in blood supply) area of bone undergoes necrosis (dies). AVN is not common, but it is encountered in a certain number of patients with lupus. The area most often affected is the hip and in particular the upper part of the thigh bone (the femoral head) which makes up the ball of this ball-and-socket joint. This problem primarily affects younger adults. In 50 to 60 percent of cases it occurs in both hips. The goal for treatment of AVN is to save the natural hip joint if possible and not to have to replace the affected femoral head with an artificial joint. In order to accomplish this, early diagnosis is very important. Other bones may also be affected by AVN, but much less often than the hip. (These include the knee, the shoulder, and rarely the small bones of the wrist and the foot or ankle.) The following discussion will, therefore, focus on the hip.

Causes

Many things can cause AVN. One of the most common causes is a fracture through the thigh bone which results in tearing of the blood vessels that nourish the femoral head. AVN can also occur without a fracture or other major injury. These same blood vessels can be blocked by blood clots (thrombi or emboli). They can also be blocked by fat droplets which form in the circulating blood, by clumps of abnormal red blood cells (as in sickle cell disease), and occasionally by nitrogen bubbles (which form in individuals such as deep sea divers who work under different atmospheric pressures). AVN can also result from inflammation or narrowing of the arteries, and from increased pressure outside the blood vessels. it is frequently seen with excess use of alcohol. A very small percentage of people who use corticosteroids for prolonged periods of time will also develop it. Why this is so is unclear. It may be that certain individuals are especially sensitive to steroids and form circulating fat droplets as a result. Although some authorities are of the opinion that the blood vessel changes in lupus itself can result in AVN, there are almost no cases of AVN reported in patients with lupus who have not been treated with steroids.

Within a few hours after the blood circulation to the bone is blocked, the cells in the bone marrow and the bone begin to die. The body then makes an attempt to repair the damage. During this repair process the pressure within the bone begins to build. In approximately 80 percent of cases, a steady progression of damage takes place. The dead area of bone becomes weakened and begins to collapse. This starts in the soft bone underneath the surface of the joint. Eventually, however, the joint surface itself becomes involved, and actual flattening of the normally round femoral head results. The cartilage of the joint is subjected to abnormal stresses and undergoes gradual degeneration (breakdown). Since this cartilage gets its nourishment from the fluid within the joint and not from the blood supply of the underlying bone, it remains alive for quite some time after the initial degeneration begins. In the later stages, cartilage damage ultimately leads to advanced degenerative arthritis involving the entire hip joint.

Clinical Course

At first the patient with AVN has no symptoms. Later the buildup of pressure within the femoral head may cause a mild and vague type of pain. Once collapse of the joint surface occurs, the pain usually increases dramatically and may become severe. Some patients however have only mild discomfort in spite of significant involvement of the joint. As the process continues, most patients develop a limp and note some decrease in motion of the hip joint.

Early on, routine x-rays in AVN are entirely normal. As the softer bone below the joint surface begins to collapse, a fluid filled space is left which shows up as a dark semi-circle or "crescent sign" on the x-ray. Later actual flattening of the normally round femoral head may be seen. Thinning of the cartilage of the joint results in narrowing of the joint space. This will show on an x-ray. Still later the characteristic picture of advanced degenerative joint disease is seen on the x-ray and may be accompanied by complete loss of the joint space, the formation of spurs (or osteophytes), large cysts, and areas of dense bone.

There are other special imaging techniques which are frequently used to diagnose AVN in addition to plain x-rays. Often these techniques show clear changes in the bone before such changes can be detected on the routine x-ray. These include bone scans, computerized tomography (CAT) scans, and magnetic resonance imaging (MRI). During the last few years, MRI has proven to be the single best method for the early diagnosis of AVN. The MRI does not use x-rays but uses magnetic waves to show very early changes in the marrow of the bone, bone itself, and other tissues in and around the hip joint. It is a very safe technique and is both very sensitive and very specific for AVN.

Treatment

In 80 or 90 percent of cases of AVN, the condition will progress even if we restrict activities and limit weight bearing on the joint by having the patient use canes or crutches. For this reason, it is usually best not to try to treat the hip "conservatively" if it is important to save the joint. (The shoulder and knee do better with "conservative management" than the hip does, and this is usually the treatment of choice for these joints.)

Although there is no completely effective method for preventing early AVN of the hip from progressing, there are a number of surgical procedures which give better results than conservative medical management. These should be very seriously considered during the early stages of AVN, before there has been any collapse of the joint. They include drilling small or large holes to relieve the pressure, bone grafting, osteotomy (cutting across the bone to change its position), and electrical stimulation. There have been some encouraging reports about the use of electrical stimulation, but this technique is still in a somewhat experimental stage. Another new procedure which seems quite promising is the use of a bone graft containing its own blood vessels which can be attached to the arteries and veins in the region of the hip. Although none of these surgical treatments gives consistent or completely satisfactory results, progress is being made, and the use of one of these techniques will usually give better results than non-operative management, as mentioned earlier.

Once there has been definite flattening of the femoral head, these early surgical interventions are seldom of much value. At this stage, patients should be treated conservatively with measures designed to decrease their pain and preserve function of the hip. Such measures include restricted activities, use of a cane, and non-steroidal anti-inflammatory drugs or mild pain relievers.

When pain and disability have progressed to the point that conservative methods of treatment are no longer effective in relieving symptoms, reconstructive surgery should be considered. There are two commonly used procedures: The replacement of only the upper end of the femur (the "ball") with an "endoprosthesis" and the replacement of both the ball and the socket with a "total hip replacement". Of these two operations, the use of a total hip replacement seems to give the most consistent and durable results. It leads to complete or nearly complete relief of pain and relatively normal function in 90 to 95 percent of patients. With modern techniques and devices these artificial hips should continue to function for at least ten to fifteen years in the majority of patients. In the younger individual they will rarely last a lifetime, but when they do wear out, they can be replaced.

Summary

AVN is a rather uncommon complication in patients with lupus and is probably related to the need to use corticosteroids rather than to the underlying disease itself. The area most frequently involved is the hip and specifically the femoral head. Although the condition may heal spontaneously (without any treatment) in 10 to 20 percent of diagnosed cases, most of the time it will get worse without specific treatment. The goal is therefore to diagnose this condition as early as possible and to use any one of a number of surgical procedures which may prevent or slow down its progression. Although the results with the present surgical methods of treatment are not as good as we would like, they are generally better than simply relying on symptomatic treatment. We remain optimistic that some of the newer methods will give better results. When the condition has become fairly advanced, such preventative measures are of little value and patients are treated symptomatically for as long as possible. When sufficient pain and disability have developed, reconstructive surgery is usually needed. Of the available measures, total hip replacement gives the best results. This procedure can allow patients to resume a relatively normal lifestyle with little pain or disability.

=========================================================== This information is for "informational purposes" and is not meant to be used for medical diagnosis. Always consult your physician on matters such as this.