# Legg-Calve-Perthes Disease

## Introduction

Legg-Calve-Perthes disease (LCPD) is idiopathic osteonecrosis of the femoral head in children. It results from a disruption of the blood supply to the capital femoral epiphysis, leading to a predictable sequence of necrosis, fragmentation, and reossification. The ultimate goal of treatment is to maintain a spherical femoral head that is congruently contained within the acetabulum, thereby minimizing the risk of premature degenerative arthritis.

## Epidemiology

LCPD typically affects children between 4 and 10 years of age, with peak incidence at 5 to 7 years. Boys are affected 4 to 5 times more frequently than girls. Bilateral involvement occurs in 10 to 15% of cases, though the two sides are usually affected asynchronously. The disease is more common in Caucasian populations. Affected children characteristically demonstrate delayed skeletal maturation, with bone age lagging behind chronological age, and they tend to be shorter in stature and more physically active than their peers.

## Etiology and Pathogenesis

The exact etiology remains unknown, but several mechanisms have been proposed including vascular disruption to the capital femoral epiphysis from single or repeated insults, thrombophilia and coagulation abnormalities such as elevated factor V Leiden or protein C and S deficiency, and venous congestion with elevated intraosseous pressure. The disease follows a predictable pathologic sequence through four stages. The initial or necrosis stage involves an ischemic event with cessation of growth of the ossific nucleus. During the fragmentation stage, resorption of necrotic bone occurs simultaneously with revascularization, and the femoral head is at its weakest and most deformable. The reossification stage sees new bone replace the fragmented areas, and the final shape of the head is determined during this period. Finally, the remodeling stage involves progressive remodeling until skeletal maturity.

## Clinical Presentation

A painless limp is the most common initial presentation. When pain is present, it is typically localized to the groin, anterior thigh, or referred to the knee, and for this reason the hip should always be examined in a child presenting with knee pain. Physical findings include an antalgic gait with a decreased stance phase on the affected side, limited internal rotation and abduction of the hip, mild flexion contracture, and thigh atrophy on the affected side. A Trendelenburg sign may also be present.

## Imaging

### Radiography

AP pelvis and frog-lateral views are essential for evaluation. Early findings include a smaller or denser ossific nucleus and a subchondral fracture known as the crescent sign. During the fragmentation stage, irregular lucencies appear within the epiphysis along with lateral subluxation. The reossification stage shows progressive reconstitution of the ossific nucleus. Key radiographic signs of severity include the Gage sign, which is a radiolucency in the lateral epiphysis and metaphysis, the crescent sign representing a subchondral fracture line best seen on the frog-lateral view, lateral calcification indicating ossification lateral to the epiphysis, and metaphyseal cysts suggesting more extensive involvement.

### MRI

MRI is more sensitive than radiographs for early detection and staging. It evaluates the extent of epiphyseal necrosis and femoral head coverage. Perfusion MRI can assess revascularization during treatment, and the modality is also useful for evaluating hinge abduction and labral pathology.

## Classification Systems

### Catterall Classification

The Catterall classification is based on the extent of epiphyseal involvement on the AP radiograph during fragmentation. Group I involves only the anterior epiphysis (less than 25%) and carries an excellent prognosis. Group II involves the anterior and central epiphysis (up to 50%) with the lateral column maintained. Group III features a large sequestrum (75%) with only a small posteromedial fragment preserved. Group IV involves the whole head (100%) and has the poorest prognosis.

### Herring Lateral Pillar Classification (Preferred)

| Group | Lateral Pillar Height | Prognosis | Treatment Implications |
|-------|----------------------|-----------|----------------------|
| A | Full height maintained | Excellent | Observation; most do well regardless of treatment |
| B | > 50% height maintained | Intermediate | Age-dependent; observe if < 6 years |
| B/C Border | ~50% height | Poor (especially age > 8) | Surgical containment recommended if > 8 years |
| C | < 50% height | Poorest | Surgical containment recommended |

The Herring lateral pillar classification is assessed during the early fragmentation stage on the AP radiograph and evaluates the height of the lateral one-third (lateral pillar) of the femoral head. Group A maintains full height of the lateral pillar and carries an excellent prognosis. Group B maintains lateral pillar height greater than 50% with an intermediate prognosis. The B/C border group has lateral pillar height at approximately 50% and carries a worse prognosis, especially in children over age 8. Group C has lateral pillar height less than 50% and the poorest prognosis.

## Prognostic Factors

Age at onset is the single most important prognostic factor. Children under 6 years generally achieve good outcomes regardless of treatment, while children over 8 years have a significantly worse prognosis and are more likely to require surgical intervention. The Herring lateral pillar classification provides critical prognostic information, with Group C and B/C border involvement in children over 8 yielding the worst outcomes. Persistent loss of range of motion predicts femoral head deformity, and femoral head subluxation with lateral extrusion indicates loss of containment.

## Treatment

### Principles

The primary goal of treatment is containment, keeping the femoral head seated within the acetabulum so it acts as a mold during the biologically plastic fragmentation and reossification stages. Treatment is most impactful during the fragmentation stage.

### Nonoperative Management

Nonoperative management includes activity modification to avoid high-impact activities during fragmentation and range of motion maintenance, which is the most important nonoperative goal, achieved through abduction exercises and physical therapy. Abduction bracing with Petrie casts or a Scottish Rite orthosis aims to keep the femoral head contained, though compliance is challenging and evidence for bracing is mixed. Anti-inflammatory medications provide symptomatic relief. Observation alone is appropriate for children under 6 with lateral pillar A or B classification.

### Operative Management

Surgical intervention is indicated for children over 8 years with lateral pillar B/C border or C classification, or for any child with progressive subluxation and loss of containment. A femoral varus osteotomy redirects the femoral head deeper into the acetabulum and is the standard surgical containment method. Pelvic osteotomy, such as a Salter innominate osteotomy or shelf acetabuloplasty, increases lateral coverage of the femoral head, and combined femoral and pelvic osteotomies may be performed for severe subluxation. In cases of hinge abduction, where the deformed femoral head impinges on the lateral acetabular rim during abduction, an abduction osteotomy is contraindicated, and a valgus femoral osteotomy or shelf procedure may be required instead.

## Long-Term Outcomes

The shape of the femoral head at the end of remodeling determines the risk of premature osteoarthritis. The Stulberg classification describes the final femoral head shape. Class I and II represent spherical or mildly aspherical heads with good long-term outcomes. Class III is an ovoid head (coxa magna) with intermediate outcomes. Class IV and V represent flat or collapsed heads with incongruent joints and a high rate of early arthritis. Most patients with Stulberg I through III do well until the fifth or sixth decade of life, while Stulberg IV and V patients often require hip arthroplasty by the fourth decade.

## Clinical Pearls

Perthes disease should always be considered in a child presenting with a painless limp or knee pain, and the hip should be examined in every child with knee complaints. The Herring lateral pillar classification during the fragmentation stage is the most useful prognostic system, with Group C involvement in children over 8 years carrying the worst prognosis. Age at onset is the strongest predictor of outcome, as children under 6 generally do well regardless of treatment while children over 8 often require surgical containment. Range of motion preservation is the most important nonoperative intervention, and loss of abduction and internal rotation indicates progressive subluxation and the need for reassessment.

## References
1. Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease. Part II: Prospective multicenter study of the effect of treatment on outcome. *J Bone Joint Surg Am*. 2004;86(10):2121-2134.
2. Stulberg SD, Cooperman DR, Wallensten R. The natural history of Legg-Calve-Perthes disease. *J Bone Joint Surg Am*. 1981;63(7):1095-1108.
3. Joseph B. Natural history of early onset and late-onset Legg-Calve-Perthes disease. *J Pediatr Orthop*. 2011;31(2 Suppl):S152-S155.
4. Kim HK, Herring JA. Pathophysiology, classifications, and natural history of Perthes disease. *Orthop Clin North Am*. 2011;42(3):285-295.