Legg calv perthes' disease

(Arthur Thornton Legg, 1874-1939, American surgeon; Jacques Calv, 1875-1954, French orthopaedic surgeon; Georg Clemens Perthes, 1869-1927, German surgeon), idiopathic avascular necrosis of the capital femoral epiphysis. The condition generally affects Caucasian children aged 3-12 years of age, with the commonest age being 4-8 years. Boys are affected approximately 4 times as commonly as girls. Bilateral involvement occurs in approximately 15% of cases but is usually asymmetrical.

The child characteristically presents with a limp. This may be painless or the child may describe hip, groin, thigh or knee pain often aggravated by activity. Clinical examination reveals an antalgic limp, limited and painful hip rotation, particularly internal rotation. Pathological stages are of initial bone infarction or necrosis, followed by revascularisation, active resorption of dead bone and increasing immature new bone deposition with gradual formation of mature bone.

The diagnosis is usually confirmed on radiography and initial radiographic evaluation should include an AP and frog-lateral view of the pelvis. The earliest abnormality is usually a non-specific hip joint effusion, most easily detected by ultrasound. This may be suggested by widening of the medial aspect of the hip joint, however, conventional radiographs will often appear normal at this stage. Specific radiographic changes then develop with subchondral fissure-fracture in the antero-lateral aspect of the capital femoral epiphysis, this aspect is best demonstrated on the frog-lateral radiograph (Fig.1). As the condition progress there is fragmentation and sclerosis of the capital femoral epiphysis with reduction in height and possible ill defined focal lucencies within the proximal metaphysis particularly the antero-lateral aspect adjacent to the physis (Fig.2). The capital femoral epiphysis gradually becomes more flattened with lateral extrusion of the cartilage producing broadening of the femoral neck. In mild disease the femoral head may in time be restored to a normal size and shape. More severe Perthes results in a permanently flattened distorted femoral head (Fig.3) (see coxa plana) with a short wide femoral neck (see coxa magna).

MR imaging is sensitive in the early diagnosis of Perthes and for assessment of progression. The normal yellow marrow of the capital femoral epiphysis shows high signal intensity on both T1- and T2-weighted images relative to the lower signal intensity of red marrow within the metaphysis (Fig.4). During the early infarction stage of Perthes there may be patchy or diffuse reduction in signal intensity within the capital femoral epiphysis on both T1- and T2-weighted images. There may also be heterogeneous reduction in signal in the proximal metaphyseal region. A joint effusion would be seen as high signal within the joint space on T2-weighted images. Later during the fragmentation repair stage there may be mixed high and low signal areas. As revascularization and reossification proceed the epiphysis is restored to more uniform high signal intensity. Bone scintigraphy is also sensitive for the early diagnosis of Perthes and demonstrates focal perfusion defects.

Ultrasound can better demonstrate the initial hip joint effusion, however, this finding is non specific and more commonly due to transient synovitis of the hip. Persistence of a hip joint effusion for longer than two weeks should raise the suspicion of Perthes.

Later in the disease ultrasound may demonstrate thickening of the articular cartilage and progression with irregularity, flattening and fragmentation of the capital femoral epiphysis. In the healing phase ultrasound may demonstrate new bone formation and recalcification earlier than on conventional radiographs.

With advanced Perthes the aim of imaging is to assess the severity of femoral head deformity and the degree of subluxation or uncovering. These features are generally adequately assessed with AP radiographs of pelvis. Three-dimensional CT may be helpful in preoperative planning and arthrography is helpful to assess range of movement and reducibility.

HC-GL

GL