Childhood Avascular Necrosis — Legg-Calvé-Perthes Disease

Introduction

Legg-Calvé-Perthes disease (LCPD) is an idiopathic avascular necrosis of the developing femoral head in the pediatric patient. First described independently by Arthur Legg in Boston, Jacques Calvé in France, and Georg Perthes in Germany in 1909-1910, the disease remains one of the most challenging entities in pediatric orthopedics: the etiology is incompletely understood, the natural history is highly variable, and the optimal treatment continues to be debated. The condition is characterized by an interruption of the blood supply to the femoral head, followed by a sequential process of necrosis, fragmentation, reossification, and remodeling that, depending on the extent of head involvement and the age at presentation, may produce a near-normal hip or a severely deformed and prematurely arthritic joint. This chapter synthesizes content from Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, Miller’s Review, and Operative Hip Arthroscopy to cover the epidemiology, etiology, pathophysiology, stages of disease, clinical and radiographic features, classification systems, treatment principles, surgical procedures, and long-term outcomes of LCPD. The differential diagnosis with other childhood causes of femoral head osteonecrosis is also briefly addressed.

Epidemiology and Risk Factors

The incidence of LCPD varies widely with geography and ethnicity: approximately 1 in 1,200 in populations of European descent in the United Kingdom, 1 in 9,000 in African American populations, and intermediate rates in other groups. The condition affects boys four to five times more often than girls; girls present at a slightly younger age and tend to have a worse prognosis. The peak age of onset is 4-8 years, with a broader range from 2 to 12 years. Bilateral disease occurs in 10-20% of cases, but synchronous bilateral involvement of identical stages is rare; when both hips show identical stages of disease at the same time, an alternative diagnosis — particularly multiple epiphyseal dysplasia or spondyloepiphyseal dysplasia — must be considered. The etiological associations of LCPD include: low birth weight and small stature; delayed skeletal maturation (typical Perthes children have a bone age 1-2 years behind chronological age); a higher prevalence in lower socioeconomic groups in many studies; second-hand cigarette smoke exposure; and prothrombotic states (factor V Leiden, protein C and protein S deficiencies, antithrombin deficiency, hypofibrinolysis) in a subset of cases — though the role of thrombophilia in the average sporadic case is uncertain. A history of mild trauma is common but is not thought to be causative. The disease is not familial in the great majority of cases, and the modest familial clustering observed in some series is attributed to shared environmental factors rather than direct heredity.

Etiology and Pathogenesis

The fundamental insult in LCPD is a vascular event that interrupts the blood supply to the femoral head; the resulting infarction, with subsequent attempts at revascularization and reossification, drives the clinical course. The vascular anatomy is critical: in the child between 4 and 9 years of age, the lateral epiphyseal vessels (branches of the medial femoral circumflex artery) are the dominant supply to the femoral head, while the contribution from the ligamentum teres artery is minimal and the metaphyseal vessels are blocked by the physeal cartilage from reaching the epiphysis. This narrow vascular window — when the lateral epiphyseal vessels are the sole supply — corresponds precisely to the age at which LCPD has its peak incidence. Disruption of these vessels — whether by repeated micro-thrombotic events, mechanical compression from an effusion or by transient synovitis, or by some idiopathic event — produces the avascular insult that initiates the disease. The pathological sequence proceeds through four classical stages described by Waldenström: (1) the initial avascular stage, in which the bone of the femoral head dies but the radiographic appearance is initially normal followed by increased radiodensity as the surrounding live bone becomes osteopenic; (2) the fragmentation stage, in which the necrotic bone is gradually resorbed and replaced by ingrowing vascular fibrous tissue, producing the characteristic patchy lytic appearance; (3) the reossification stage, in which new woven bone is laid down on the dead trabecular bone scaffold; and (4) the residual or healed stage, in which the femoral head reaches its final shape. The entire sequence takes 2-4 years from onset to healing, with the variability depending on age at onset (older children have longer disease courses), extent of head involvement, and effectiveness of treatment.

Clinical Features

The presentation is typically of a young child (4-8 years) with intermittent hip, groin, or referred knee pain, an antalgic gait, and a limp that worsens with activity. The pain may be exquisitely mild and easily attributed to growing pains or minor injury; many children present after weeks or months of symptoms when the limp becomes obvious to the family or a teacher. Examination reveals reduced hip abduction and internal rotation (the most consistent finding, with the contralateral hip serving as a normal control), a Trendelenburg gait pattern, mild hip joint tenderness, and a slight apparent shortening of the affected limb in some cases. The classical positions of the hip in LCPD are flexion, abduction, and external rotation when at rest. The differential diagnosis includes transient synovitis (which resolves within days, in contrast to weeks of symptoms in LCPD), septic arthritis (which presents acutely with systemic illness), juvenile inflammatory arthritis, leukemia and lymphoma, sickle cell disease (in appropriate populations), other causes of avascular necrosis (sickle cell, corticosteroid therapy, post-traumatic), and slipped capital femoral epiphysis (older children).

Imaging

Plain radiographs (AP pelvis and frog-lateral views of both hips) are the standard initial imaging study and demonstrate the characteristic stages of disease. The earliest radiographic finding is a small ossific nucleus (compared with the unaffected side), followed by a thin crescent-shaped subchondral lucency representing subchondral fracture through the necrotic bone (the “Caffey sign” or “crescent sign,” best seen on frog-lateral views). As the disease progresses, the epiphysis becomes increasingly dense (the “white femoral head” of the avascular stage), then fragments with patchy lucencies (fragmentation stage), then progressively reossifies. The metaphysis may show changes — a small lateral metaphyseal cyst is a recognized sign — and the femoral neck may become wide and short (coxa magna and coxa breva) in the residual stage. MRI, particularly perfusion-weighted MRI with gadolinium, has become important for early diagnosis in the pre-radiographic stage and for assessment of the extent of femoral head involvement. The classical MRI signs are: marrow edema on T2-weighted images in the affected region; loss of normal enhancement on gadolinium-enhanced sequences corresponding to the avascular area; the “double-line” sign on T2-weighted images (a low- signal inner line of necrotic bone with a high-signal outer line of granulation tissue at the reactive interface); and the eventual appearance of the same morphological changes seen on plain radiographs as the disease progresses.

Classification Systems

Multiple classification systems address two distinct questions in LCPD: the extent of femoral head involvement (which predicts prognosis), and the morphological outcome at skeletal maturity (which determines long-term arthritis risk). Catterall Classification The Catterall classification, described in 1971, divides cases by the extent of femoral head involvement on plain radiographs taken in the fragmentation stage. Group I involves the anterior portion only; Group II involves a larger anterior portion with a clear demarcation; Group III involves most of the femoral head with a small medial preserved portion; Group IV involves the entire femoral head. The classification was the basis of the “head at risk” signs — Gage sign (radiolucent V-shaped defect in the lateral epiphysis), lateral subluxation, calcification lateral to the epiphysis, metaphyseal cyst, horizontal physis — which were used to identify the more severe cases requiring containment treatment. The Catterall system is now used less often because of poor inter-observer reliability and the difficulty of accurate classification in early disease. Salter-Thompson Classification The Salter-Thompson classification (1984) divides cases by whether the subchondral fracture line (the Caffey crescent sign) extends through less than half of the femoral head (Group A, better prognosis) or more than half (Group B, worse prognosis). The classification has the advantage of early predictive value but the disadvantage of requiring the presence of a visible crescent sign for classification.

Herring Lateral Pillar Classification The Herring classification, described in 1992 and validated in multiple large series, is the most widely used modern classification. It divides cases by the height of the lateral pillar of the femoral head — the lateral 15-30% of the head as seen on the AP radiograph — at the maximum fragmentation stage. Group A: lateral pillar at full original height. Group B: lateral pillar maintains more than 50% of original height. Group B/C border: lateral pillar at 50% of height with very narrow remaining pillar. Group C: lateral pillar less than 50% of original height. The Herring classification has better inter-observer reliability than the Catterall system and correlates strongly with the final outcome: Group A hips have universally good outcomes regardless of treatment; Group B hips have good outcomes if treated by containment in children over 8 years; Group C hips have poor outcomes regardless of treatment. Stulberg Classification The Stulberg classification (1981) describes the morphological outcome at skeletal maturity. Type I: completely normal hip. Type II: spherical femoral head but with abnormalities of the femoral neck or acetabulum. Type III: ovoid (non-spherical but congruent) femoral head with congruent acetabulum (aspherical congruency). Type IV: flat femoral head with congruent flat acetabulum (aspherical congruency). Type V: flat femoral head with incongruent normal acetabulum (aspherical incongruency). The classification correlates strongly with the risk of premature osteoarthritis: Stulberg I and II hips do well into late adulthood; Stulberg III hips develop arthritis in middle age; Stulberg IV and V hips develop early and progressive arthritis.

Principles of Treatment

The treatment of LCPD is guided by two principal considerations: containment of the femoral head within the acetabulum during the period of biological plasticity (so that the head heals in a spherical shape molded by the round acetabulum), and minimization of the deforming forces on the softened femoral head during the avascular and fragmentation stages. The basic concepts of treatment have evolved through several phases over the twentieth century: prolonged non-weight-bearing and abduction casting (the original Catterall principle); abduction bracing; containment surgery (femoral varus or pelvic osteotomy); and, in modern practice, more selective use of any of these approaches based on age at presentation and Herring classification.

Observation and Symptom Control For younger children (less than 6 years) and for older children with Herring Group A disease, observation and symptom control are appropriate. Activity modification, restricted weight-bearing as needed, non-steroidal anti-inflammatory drugs for pain, physiotherapy to maintain hip range of motion (particularly internal rotation and abduction), and serial radiographic follow-up at 3-6 month intervals are the standard.

Non-Operative Containment In the older child (6-8 years) with Group B disease and substantial hip involvement, non- operative containment with an abduction brace (the Atlanta or Scottish-Rite brace are historical examples) attempts to hold the femoral head in abduction so that the spherical portion of the head is contained within the acetabulum. The brace must be worn continuously, the child’s activity is restricted, and treatment may be prolonged over months to years. The evidence for non-operative bracing is mixed, with some series showing modest benefit and others showing no improvement over no treatment; modern practice has largely moved away from prolonged bracing in favor of operative containment or observation.

Operative Containment In children over 8 years of age with Herring Group B or B/C border disease, and in selected children with Group A disease and significant subluxation, operative containment provides the most reliable means of maintaining the femoral head within the acetabulum during the biological plasticity period. The standard options are femoral varus-derotation osteotomy and pelvic osteotomy (Salter, Pemberton, or shelf procedure), or a combination of the two. The femoral varus-derotation osteotomy is performed in the proximal subtrochanteric region, removing a lateral-based wedge to produce 15-25° of varus and 15-30° of derotation. The osteotomy reorients the femoral head so that the previously uncovered anterolateral portion is brought under the acetabular roof, achieving containment. The cost is a degree of permanent shortening of the affected limb (typically 1-2 cm) and a slight Trendelenburg gait, both of which are generally well tolerated. The osteotomy is fixed with a paediatric blade plate or pediatric DCP plate. The Salter innominate osteotomy redirects the acetabulum to cover the anterolateral femoral head, achieving containment from the acetabular side rather than the femoral side. The procedure can be combined with femoral osteotomy or used alone, particularly when the acetabulum is dysplastic. The shelf acetabuloplasty provides a buttress of bone over the laterally uncovered femoral head, used as a salvage procedure when other containment options are not feasible. The Herring Multicenter Perthes Study, published in 2004, compared non-operative and operative treatments in a large prospective cohort. The results, often summarized as the foundation of modern Perthes treatment guidelines, were: in children under 8 years of age, no significant difference between treatments — all groups did similarly well; in children over 8 years of age with Herring Group B disease, operative containment (either femoral or pelvic osteotomy) produced significantly better outcomes than non-operative treatment; in Group C disease, no treatment improved outcomes, but operative treatment did not worsen them either.

Salvage Procedures Once the femoral head has healed in a deformed shape (Stulberg III, IV, or V) and adjacent symptoms develop in the older child or adolescent, salvage procedures address the resulting impingement, instability, or arthritis. Valgus-extension proximal femoral osteotomy redirects the deformed femoral head out of the impingement zone. Femoral head-neck offset correction (open or arthroscopic) addresses the cam impingement that develops from the deformed femoral head. Pelvic osteotomies — particularly periacetabular osteotomy — address residual acetabular dysplasia. Hip arthroscopy is increasingly used for the management of impingement and labral pathology associated with healed Perthes deformity. Total hip arthroplasty is the definitive late treatment for the patient with established secondary arthritis.

Other Causes of Childhood Avascular Necrosis

Although Legg-Calvé-Perthes disease is by far the commonest cause of avascular necrosis of the femoral head in childhood, several other conditions produce similar pathological and radiographic appearances and must be in the differential diagnosis. Sickle cell disease is the commonest cause of multifocal avascular necrosis in children of African or Mediterranean ancestry. The avascular events are precipitated by sickling- induced microvascular occlusion, often during sickle cell crisis. Multiple joints can be affected, with the femoral head and humeral head being the most common; the shoulder, knee, and vertebral bodies are also commonly involved. Treatment combines optimization of the underlying disease (hydroxyurea, chronic transfusion in selected cases), pain management, and joint-preserving surgery (core decompression, vascularized bone grafting) or joint replacement in advanced disease. Corticosteroid-induced avascular necrosis occurs in children receiving high-dose corticosteroids for inflammatory disease (juvenile inflammatory arthritis, inflammatory bowel disease, asthma), transplant immunosuppression, or chemotherapy. The mechanism involves a combination of direct cytotoxic effect on osteocytes, alterations in fat metabolism with fat-cell hypertrophy producing increased intramedullary pressure, and disturbances in clotting that predispose to microvascular thrombosis. The femoral head is the most common site, but the humeral head and the knee are also affected. The pattern of multifocal disease, the history of corticosteroid use, and the typical involvement of patients in adolescence or young adulthood distinguish this entity from LCPD. Post-traumatic AVN following hip dislocation, femoral neck fracture, or septic arthritis is discussed in the relevant chapters but should be remembered in the differential diagnosis. The classical history is of an antecedent traumatic or septic event, followed by months of progressive hip symptoms. Idiopathic AVN of the adolescent and young adult — Chandler’s disease in some references — is discussed in the next chapter on adult avascular necrosis. Meyer’s dysplasia is a benign condition of delayed and disorganized ossification of the femoral head in young children, often confused with early LCPD. The ossific nucleus is

small and irregular but the femoral head is not avascular and the condition resolves spontaneously without treatment. Bilateral synchronous disease in a very young child without symptoms is the typical presentation, and the radiographic appearance can be reassuringly different from LCPD on careful inspection. Multiple epiphyseal dysplasia and spondyloepiphyseal dysplasia are inherited skeletal dysplasias that produce bilateral synchronous abnormalities of the femoral head and other epiphyses. The history of short stature, family history, and involvement of other epiphyses distinguishes these conditions from LCPD.

Outcomes and Long-Term Considerations

The long-term outcome of LCPD depends primarily on the age at onset (younger is better), the extent of femoral head involvement (Herring classification), and the achievement of containment during the biological plasticity period. Stulberg I and II outcomes are achievable in the majority of children under 8 years and in those with Herring Group A disease, and these patients have hips that function well into late adulthood without premature arthritis. Stulberg III outcomes — aspherical but congruent — predict arthritis in middle age and are common in children with later onset and more extensive head involvement. Stulberg IV and V outcomes — aspherical and incongruent — are associated with early arthritis, often requiring total hip arthroplasty by the fifth decade. The classical sequelae of inadequately treated LCPD include: coxa magna (enlarged femoral head); coxa breva (short femoral neck with relative trochanteric overgrowth); coxa plana (flattened femoral head); femoroacetabular impingement (cam-type, from the aspherical femoral head); secondary acetabular dysplasia (from the deformed femoral head’s effect on acetabular development); and limb-length discrepancy. Each of these sequelae may be addressed by appropriate adolescent or adult reconstruction.

Summary and Take-Home Points

Legg-Calvé-Perthes disease is an idiopathic avascular necrosis of the developing femoral head, predominantly affecting boys aged 4-8 years, and produces a clinically and biologically variable disease whose outcome depends on age at onset, extent of head involvement, and achievement of containment during the biological plasticity period. The Waldenström stages (initial, fragmentation, reossification, residual) describe the natural pathological evolution; the Herring lateral pillar classification (A, B, B/C, C) predicts prognosis; the Stulberg classification (I-V) describes the morphological outcome at skeletal maturity and predicts long-term arthritis risk. Treatment combines symptom control, maintenance of hip motion, and — in older children with greater head involvement — containment by femoral varus-derotation osteotomy, pelvic osteotomy, or both. The Herring Multicenter Perthes Study established that operative containment is beneficial in children over 8 years with Herring Group B disease but that no treatment improves the outcome of Group C disease. Salvage procedures for the residual deformity in adolescence and adulthood — valgus osteotomy, osteochondroplasty for cam impingement, periacetabular osteotomy for residual dysplasia, and ultimately total hip arthroplasty for end-stage arthritis — address the late sequelae. The differential diagnosis of childhood

avascular necrosis includes sickle cell disease, corticosteroid-induced AVN, post-traumatic AVN, Meyer’s dysplasia, and the inherited skeletal dysplasias; each requires consideration in the appropriate clinical context.