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C. Legg-Calvé-Perthes disease

Figure 1 shows loss of the normal shape of the left capital femoral epiphysis compared with the contralateral hip. The contour is flattened, most severely along the lateral aspect. The left femoral ossification center is small, sclerotic, and slightly subluxed laterally. There are radiolucent fissures superiorly and a large irregular cystic lucency in the left proximal femoral metaphysis. Figure 2 reveals prominent left physeal widening.

Legg-Calvé-Perthes disease afflicts children aged 3–12 years (peak, 4–8 years), particularly males and white children. About 90 percent of patients have unilateral disease; the remaining 10 percent often initially present with unilateral symptoms but later develop contralateral disease. Concurrent bilateral hip involvement is uncommon.

The most common presentation is a limp with hip or knee pain and no associated trauma, but some cases are asymptomatic. Physical examination findings include an antalgic gait, thigh atrophy, groin pain on palpation, and decreased ROM to internal rotation and abduction of the hip. Chronic disease may cause leg-length discrepancy and degenerative joint disease, eventually resulting in osteonecrosis of the capital femoral epiphysis.

Early radiographic signs are nonspecific and related to synovitis; there is capsular bulging, with pericapsular fat pad displacement. More characteristic features include the appearance of a subchondral peripheral fracture of the femoral epiphysis (crescent sign), best seen with the patient in the frog-leg position. Later stages show decreased epiphyseal size, sclerosis, flattening, fragmentation, and fissuring, as well as possible lateral epiphyseal displacement (appearing as medial joint space widening) accompanied by a lucent and cystic metaphysis. The greater trochanter appears larger when compared with the shortened femoral neck. Radiographic findings of chronic disease include coxa plana, coxa magna, and coxa vara.

Magnetic resonance imaging (MRI) is useful for early diagnosis when radiographs are normal or when the diagnosis is in doubt. MRI can demonstrate areas of low signal intensity within the capital femoral epiphysis on T1- (T1WI) and T2-weighted images (T2WI), findings consistent with early osteonecrosis. Revascularization is seen as a bright signal, similar to the appearance of fat on T1WI. In 80 percent of cases, the asterisk sign (low T1WI signal intensity and bright T2WI signal intensity in the epiphyseal marrow) and the double-line sign (a low signal intensity line representing the line between the necrotic and viable bone and a bright signal intensity line representing the granulation tissue) are seen. Articular cartilage irregularities and joint effusion have bright T2WI signal intensity. MRI also provides excellent prognostic information by revealing the extent of infarction, growth plate abnormality, and loss of femoral containment within the acetabulum. Adjunctive modalities in some cases include bone scintigraphy, arthrography, and ultrasonography. There are several classification schemes for, but no consensus on, grading Legg-Calvé-Perthes disease severity based on radiographic findings. The Catterall criteria is a commonly used grading system consisting of four groups. Group I involves less than one-fourth of the epiphysis (only the anterior portion). Group II shows more advanced changes in the anterior portion, osseous structural abnormalities, the crescent sign, and collapse, with possible focal metaphyseal abnormalities, but no more than one-half of the epiphysis is affected. Group III involves nearly the entire epiphysis, with diffuse metaphyseal abnormalities. Group IV represents complete epiphyseal involvement.

Priorities in treating Legg- Calvé-Perthes disease include maintaining the shape of the femoral head and containing it within the acetabulum. Therapy is individualized and directed by the patient’s symptoms, the disease severity based on imaging studies, and the child’s bone age. Patients younger than 6 years or older children classified in Catterall Group I may require only conservative management, such as ROM exercises, traction, avoidance of weight bearing, bracing, or bed rest and anti-inflammatory medications. Older children or those with advanced disease (Catterall Groups III and IV) may require surgery.