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Outcomes still modest a century after Perthes discovery

By Jennie McKee

JAAOS article examines treatment controversies and research directions

One hundred years ago, three investigators—Arthur Legg, MD, an American orthopaedic surgeon; Jacques Calvé, a French surgeon; and Georg Clemens Perthes, a German surgeon—independently identified the degenerative childhood hip disorder that bears their names, recognizing it as a separate disease entity from tuberculosis. Their descriptions were published within months of each other, and Dr. Legg made a presentation at the American Orthopaedic Association annual meeting.

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Although many studies have been performed to learn more about this hip disorder, according to Harry K.W. Kim, MD, author of a review article about Legg-Calvé-Perthes disease that appears in the November issue of the Journal of the AAOS, more research is needed to unlock the biologic etiology of the disease, and to develop better treatments, especially for older children.

AAOS Now: What has been discovered about Legg-Calvé-Perthes disease in the past 100 years?

Dr. Kim: We know that Perthes is a self-healing disease: Whether or not we treat the disease, the affected femoral head that has become necrotic will go through a healing process by itself. The necrotic bone is removed and new bone forms, but the femoral head may not heal in its normal, round shape, especially in children older than 8 years (Fig. 1).

A deformed femoral head is an important long-term prognostic factor. It increases the risk of osteoarthritis developing, usually when patients reach their 50s or 60s. Long-term follow-up studies suggest that approximately 50 percent to 60 percent of these Perthes patients will eventually have evidence of arthritis or undergo hip replacement.

The current thinking is that a combination of genetic and environmental factors causes this multifactorial disease. The disease may even have several etiologies that share a common pathway in disease progression and manifestation.

AAOS Now: How have treatment strategies progressed?

Dr. Kim: Treatment has gone through several stages. In the 1950s and 1960s, children were admitted to hospitals and placed on bed rest for months, almost as though they were being treated for tuberculosis. Various devices and braces were used in the 1970s and 1980s to try to restrict weight-bearing or put the leg in a certain position thought to be beneficial. Because braces didn’t work very well, surgery became more popular. Recent prospective studies have shown that surgery is beneficial in certain older patients, but not in others.

Treatment has moved from something completely nonrational—putting kids on bed rest—to surgery, but we still have much to learn regarding what the best treatment is for individual Perthes patients.

AAOS Now: Have experimental studies revealed anything about the pathogenesis of the femoral head deformity?

Dr. Kim: Many studies on Perthes disease have been based on radiographs, which provide very limited information about the disease process—what the cells are doing at the tissue level. Because of the limited availability of clinical samples for research, we had to find an alternative way to study this disease, which was to use an experimental model.

Experimental investigations using an animal model have shown that an imbalance of bone formation and bone resorption most likely plays an important role in the pathogenesis of the femoral head deformity. A significant amount of bone is being removed, and not enough new bone forms at the same time during the early stage of healing, the so-called fragmentation or resorptive stage of Perthes. This net loss weakens the femoral head, which is one of the factors that leads to the deformity.

My fellow researchers and I, as well as other investigators who have conducted experimental studies, have shown that if bone resorption can be controlled and bone formation can be stimulated, the femoral head may heal faster and be better preserved; however, this type of study has not yet been performed in a clinical setting.

AAOS Now: What are some of the key prognostic factors?

Dr. Kim: The degree of deformity is one of the important factors and can be assessed by using the lateral pillar and Catterall’s classifications, which are both based on radiographic findings. The lateral pillar classification evaluates how much of the lateral pillar—the lateral third of the femoral head—has collapsed. The greater the collapse, the worse the prognosis. Catterall’s classification determines the percentage of femoral head involved, which can range from less than 25 percent to 100 percent.

Both classifications provide clinically useful information about a patient’s outcome when the child sees an orthopaedist after the deformity has already occurred. But they provide little information when the disease is identified early and the deformity has not yet occurred.

The other important factor is the patient’s age. Patients younger than 6 years tend to heal better and have a rounder femoral head at the end of growth. Patients older than 8 years have a much lower chance of having a round femoral head, which leads to an increased risk of having osteoarthritis later in life.

AAOS Now: What are some of the controversial issues related to current treatment strategies?

Dr. Kim: The controversies are related to what the best treatments are for patients depending on age. Perthes affects children from ages 2 years to 14 years, representing a wide spectrum in terms of patient size and hip development. In general, patients younger than 6 years at the onset of Perthes disease appear to do well with nonsurgical treatments, while older patients may be best managed with surgery.

Whether surgeons should perform surgery on patients in the early stages of the disease or wait until the disease can be classified by the lateral pillar or Catterall classification is also controversial. Classification requires the femoral head to deform, resulting in a delay in treatment. If the goal of treatment is to prevent the deformity as well as arthritis in the patient’s later years, operating before a significant deformity develops may be more beneficial, given that we are seeing positive results with earlier surgeries.

AAOS Now: How effective is surgery in treating Perthes disease?

Dr. Kim: Some recent studies, including a prospective, multicenter study performed in Norway, have shown that when patients are younger than 6 years, they have similar outcomes, whether they are treated with femoral osteotomy, physiotherapy, or a brace. Because surgery provides no added benefits to these patients, it would appear that nonsurgical management may be the best strategy for this age group.

A large, retrospective study from the Texas Scottish Rite Hospital for Children has also shown that even without specific treatment, most children younger than 6 years have good outcomes. A multicenter, prospective study performed by the Perthes Study Group showed that some patients in this age group have better outcomes with femoral osteotomy or Salter’s innominate osteotomy. Although the success rates of the surgical treatments were higher than those of nonsurgical treatments, it is important to note that only 40 percent to 60 percent of the patients who underwent surgery had a round femoral head at maturity, which tells us that there is much room for improvement in treatment of older patients.

AAOS Now: What are some of the most important research directions for Perthes disease?

Dr. Kim: One is related to the controversy about whether surgeons should wait and classify the deformity or whether they should treat early in older patients with Perthes. Surgeons need an earlier prognosticator that could help determine whether a patient would benefit from treatment before the head has deformed. We are trying to evaluate whether magnetic resonance imaging will be useful in giving us that kind of information.

Another issue is whether postoperative treatments—such as prolonged non-weightbearing or activity restrictions that allow the femoral head to heal before the child loads the joint too much—will improve outcomes after the child undergoes femoral or Salter’s innominate osteotomy. Some of us think that return to weightbearing and activity after surgery should be based on how the femoral head is healing, rather than on a set time point, because of individual differences in healing time.

Finally, we have recognized that mechanically oriented treatment alone is not sufficient. We need to better understand the biologic factors involved in the etiology and progression of the disease and develop biologically oriented treatments that can control bone resorption and speed up bone formation, thus improving the healing process and shortening the course of the disease.

Disclosure information: Dr. Kim—Orthofix; Novartis; and Medtronic.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

Additional Link:
Legg-Calvé-Perthes Disease 100 Years On: What Have We Learned?

AAOS Now
November 2010 Issue
http://www.aaos.org/news/aaosnow/nov10/clinical1.asp