Commentary on an article by Harry K.W. Kim, MD, MSc, FRCSC, et al.: “How Much Varus Is Optimal with Proximal Femoral Osteotomy to Preserve the Femoral Head in Legg-Calvé-Perthes Disease?”

Few disorders in pediatric orthopaedics are as confusing for families and physicians as Legg-Calvé-Perthes disease, which is diagnosed by exclusion and has an unknown etiology. Its symptoms wax and wane. In some patients, the hip heals well after a few years, yet other young adults develop early hip degeneration. Some of our treatments may not help. Much of our knowledge about this condition has come from Texas Scottish Rite Hospital for Children and from Dr. Harry Kim. This group has contributed an understanding of the biology of the disorder—that it is characterized by early predominance of bone resorption with delayed reossification. Texas Scottish Rite Hospital for Children has also led the way in the study of the clinical aspects of Legg-Calvé-Perthes disease with their two-decade-long, surgeon-randomized, prospective treatment study (a subset of which is the focus of this article)1. The current state of our clinical research and practice is to restrict active treatment to those children who really need it and to avoid unwanted effects of our surgical treatment. The article by Kim and coauthors in this issue of The Journal fills in another piece of the puzzle. The concept of containment is central to the treatment of Legg-Calvé-Perthes disease. This “mechanical” idea involves letting the acetabulum mold the vulnerable femoral head while it heals. Containment can be achieved by bracing, by iliac osteotomy or acetabular augmentation, or by femoral osteotomy. Three-dimensional analysis by Rab2 showed that no method achieves complete containment. However, there is no “biological” treatment available that can speed up the healing of the femoral head. The article by Kim et al. starts with the assumption that femoral varus osteotomy is beneficial for some patients with Legg-Calvé-Perthes disease. The landmark 2004 prospective study from Texas Scottish Rite Hospital for Children supported this concept1. The proper role of surgery is for children more than eight years old who have moderate involvement of the lateral pillar of the proximal femoral epiphysis (lateral pillar classification type B or B/C). There are larger series of femoral osteotomies for Legg-Calvé-Perthes disease in the literature3,4, but the surgeon-randomized design that minimizes selection bias and maximizes the follow-up to maturity in the series reported by Kim et al. makes it one of the best cohorts to study. The subset of patients undergoing femoral osteotomy was the smallest group of patients who were actively treated. If the procedure is truly beneficial, one would expect a dose-response relationship. In fact, this study showed no such relationship to be the case. Perhaps the sample size was too small or other factors, such as enforced rest in the months after surgery and altered joint load caused by a change in the mechanics of the proximal part of the femur, may have influenced the results. We know that for proximal femoral osteotomy to be most effective, it should be done in early stages of Legg-Calvé-Perthes disease3,5. Appropriately, 96% of the hips in the series of Kim et al. were operated on in the initial or early fragmentation stage. We also know that proximal femoral varus osteotomy leads to an increased incidence of limp secondary to abductor weakness4. In the prospective study from Texas Scottish Rite Hospital for Children, the authors agreed that a neck-shaft angle of 110° to 115° was desirable1. This angle was achieved in most, for the neck-shaft angle immediately after surgery was a mean of 115°. The ability of patients with Legg-Calvé-Perthes disease to correct surgically created varus differs from that of patients with cerebral palsy or developmental dysplasia of the hip. Legg-Calvé-Perthes disease results in a high rate of physeal damage and causes shortening of the proximal part of the femur secondary to epiphyseal flattening. The patients in the series by Kim et al. had a mean improvement of only 9° in the neck-shaft angle between the time of proximal femoral osteotomy and skeletal maturity. Kim et al. concluded that, for patients who undergo femoral osteotomy for Legg-Calvé-Perthes disease, there is no need to impart as much varus to the proximal part of the femur as most experts, including themselves, had previously advised. Kim et al. now advise a modest change in varus angulation of 10° to 15°. A change of 10° of varus is indeed small—less than what has been recommended in any previous article I could locate. Reading between the lines, this recommendation reiterates the theme, like most other evidence in the literature regarding Legg-Calvé-Perthes disease, that we should avoid overtreatment. The real key to progress with regard to the treatment of Legg-Calvé-Perthes disease is to work toward a better understanding of the biology of the disorder and new ways to improve the speed and extent of healing. The authors are to be congratulated for their focus on understanding the biology and clinical outcomes of Legg-Calvé-Perthes disease.