A 7-Year-Old Boy With Left Hip and Knee Pain

Derik L. Davis, MD; Ogechukwu R. Menkiti, MD; Brighita Weinberg, MD

Disclosures

August 31, 2016

Imaging plays an important role in establishing the diagnosis of Legg-Calvé-Perthes disease, grading the disease severity, and guiding clinical treatment. Early radiographic signs are nonspecific and related to synovitis. Capsular bulging is noted, with displacement of the fat pads around the capsule. More characteristic features include the appearance of a subchondral peripheral fracture of the femoral epiphysis (crescent sign). This fracture is best seen when the patient is in the frog-leg position.

Later stages show a decrease in size, sclerosis, flattening, fragmentation, and fissuring of the epiphysis. These findings represent a combination of processes, including compaction and infarction of bone trabeculae, new bone formation, calcification of saponified fat in the marrow, and relative density to the adjacent osteopenia. The epiphysis may also become displaced laterally, producing the appearance of medial joint space widening. A lucent and cystic metaphysis is an accompanying sign. Widening of the femoral head and neck (coxa magna) can occur. The greater trochanter appears larger when compared with the shortened femoral neck. Coxa plana and coxa vara may be radiographic findings seen in chronic disease.

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- and T2-weighted images, which is consistent with early osteonecrosis. Revascularization is demonstrated as a bright signal, similar to fat on T1-weighted images. The asterisk sign (low signal intensity on T1-weighted images and bright signal intensity on T2-weighted images 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 in 80% of cases. Articular cartilage irregularities and joint effusion have bright signal intensity on T2-weighted images. MRI also provides excellent prognostic information by revealing the extent of infarction, growth plate abnormality, and loss of femoral containment within the acetabulum. Bone scintigraphy, arthrography, and ultrasonography can serve as adjunctive modalities in some cases.[1,2,3,4]

The differential diagnosis for Legg-Calvé-Perthes disease includes focal and systemic disorders that can cause osteonecrosis of the hip. Systemic diseases that can lead to osteonecrosis of the hip include sickle cell anemia and other hemoglobinopathies, Gaucher disease, steroid arthropathy, Cushing syndrome, and hypothyroidism; focal processes that do so include posttraumatic osteonecrosis, posttreatment osteonecrosis in congenital hip dislocation, slipped capital femoral epiphysis, and inflammatory arthropathies. Inflammatory diseases can induce osteonecrosis of the hip as well; these include toxic synovitis, septic arthritis, osteomyelitis, synovitis secondary to osteoid osteoma, and juvenile chronic arthritis. Other hip dysplasias include multiple epiphyseal dysplasia and, in children younger than age 5 years, Meyer dysplasia (which is localized to the epiphysis only).[2,3,4]

Children with Legg-Calvé-Perthes disease most commonly present with a limp as well as hip and/or knee pain. The family often denies an incident of associated trauma, although an inciting injury may be reported in a minority of cases. Some children without pain are unexpectedly diagnosed with the disease. Upon physical examination, an antalgic gait, thigh atrophy, and decreased range of motion to internal rotation and abduction of the hip are found. Pain is also elicited on palpation of the groin.

Children between the ages of 3 and 5 years generally have the best prognosis for Legg-Calvé-Perthes disease, whereas those over the age of 8 years typically have the worst prognosis.[1,2,3,6,7] Several classification schemes have been devised to grade the severity of disease based on radiographic findings, with no consensus as to the best classification system. The Catterall criteria are one example of a well-established and commonly used grading system. Group I involves less than one fourth of the epiphysis, affecting only the anterior portion. No crescent sign, collapse, sequestration, or metaphyseal involvement is seen. Group II shows more advanced changes affecting the anterior portion, but not more than one half of the epiphysis is affected. Osseous structural abnormalities, the crescent sign, and collapse are seen, with possible focal abnormalities within the metaphysis. Group III encompasses nearly the entire epiphysis, with diffuse metaphyseal abnormalities. Group IV represents the complete involvement of the epiphysis. Children in Groups III and IV have the worst prognoses; however, those patients in Groups I and II may develop more advanced disease at follow-up. Additional Catterall risk factors for potential increased morbidity include a V-shaped radiolucency in the lateral aspect of the epiphysis (Gage sign), lateral subluxation of the epiphysis, calcification lateral to the epiphysis, and a horizontal appearance of the physis.[2,3,4]

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