The incidence of Legg-Calve-Perthes disease varies worldwide from 1 in 1200 to 1 in 12,500. The onset of symptoms is between 4 and 9 years of age in 80 percent of patients, with a range of age between 2 and 13 years of age. It is bilateral in 10 percent of cases.
The disease process is characterized as an avascular necrosis of the femoral head complicated by subsequent subchondral stress fracture. Resorption of areas of bone within the femoral head (rarefaction) is followed by the laying down of new bone. Collapse and flattening of the femoral head may ensue, along with the potential for subluxation. The result is a painful hip joint associated with restricted range of motion, muscle spasm, and soft tissue contractures.
Clinically, the child with Legg-Calve-Perthes disease presents with limp and pain of weeks' to months' duration. Pain is usually mild, chronic, and dull. It is most noticeable in the groin, the anteromedial thigh, and the knee. It is exacerbated by physical activity, relieved by rest, and associated with an antalgic limp. There are no associated systemic symptoms. Hip range of motion is restricted; there may be a flexion-abduction contracture as well. Thigh muscle atrophy, due to disuse, is common.
The radiographic findings associated with Legg-Calve-Perthes disease depend on the stage of the disease process. During the incipient stage (1 to 3 months), the radiograph of the hip demonstrates only widening of the cartilage space of the affected hip and a smaller size of the ossific nucleus of the femoral head ( Fig 132-6).
The second radiographic sign is the appearance of the subchondral stress fracture line in the femoral head (Caffey's sign). The third radiologic finding is increased opacification of the femoral head, brought on by deposition of new bone upon avascular trabeculae, calcification of the sclerotic marrow, and collapse and crowding of the avascular trabeculae in the dome of the epiphysis. Ultimately, deformities of the femoral head and neck become apparent, along with subluxation and extrusion of the femoral head from the acetabulum.
FIG. 132-6. Legg-Calve-Perthes disease. The right hip illustrates joint-space widening, reduced size of the ossific nucleus of the femoral head, and increased opacification of the femoral head.
The other commonly employed imaging modalities include the technetium-99m bone scan and MRI. The scan demonstrates markedly reduced uptake of nuclide within the affected femoral head. These findings precede apparent plain film radiographic abnormalities. MRI offers superior resolution and sensitivity, with areas of low signal intensity reflecting necrotic regions within the femoral head. Arthrogram-like images of the cartilaginous portions of the femoral head and acetabular rim are produced. Excellent visualization of deformities and flattening of the femoral head is possible as well as subluxation or anterolateral extrusion of the femoral head from the acetabulum.
The differential diagnosis of coxa plana includes toxic tenosynovitis of the hip, which shares many similar features with early Legg-Calve-Perthes disease. Careful review of the radiographs is necessary to exclude the findings associated with coxa plana, as mentioned previously. If doubt exists, technetium-99m bone scan or MRI imaging studies should be considered.
The differentiation of coxa plana from acute rheumatic fever (ARF) is based on the natural history and responsiveness of ARF to salicylates. Tuberculous arthritis of the hip may mimic coxa plana. Differential screening tests should include a tuberculin skin test and determination of the ESR. Unilateral tumors, such as eosinophilic granuloma, osteoid osteoma, osteoblastoma, and lymphoma, should be considered and excluded by laboratory studies and computed tomography (CT) scan. Bone dysplasias are often confused with Legg-Calve-Perthes disease. Hypothyroidism, sickle cell disease, and Gaucher disease should also be excluded.
Care in the emergency department involves the consideration or establishment of the accurate diagnosis and orthopedic consultation. Treatment efforts are directed toward restoration of full range of motion of the hip and stabilization of the femoral head within the acetabulum, with resumption of normal activities as rapidly as possible. All except the most mildly affected children are hospitalized initially and treated with traction. The duration of traction and the timing of further therapy directed at containing the femoral head within the acetabulum (orthotics versus surgical containment) depend on the severity of the coxa plana and the responsiveness of the hip irritability to traction therapy.
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