Developmental dysplasia of the hip (DDH)

a congenital disorder of unknown cause characterized by developmental deformity of both sides of the hip joint present at birth or in early childhood. Abnormal laxity of components rather than structural abnormality is most likely responsible for the pathogenesis of this condition.

Diagnostic methods include the Ortolani manoeuvre and Barlow manoeuvre, which can only be conducted in the first few days of life, and analysis of radiological lines drawn on anteroposterior views of the hip and pelvis. Conventional tomography, contrast arthrography, ultrasonography, computed tomography and magnetic resonance imaging are also valuable for the evaluation of the disease.

Three patterns of subluxation or dislocation are seen in this condition:

1) a dislocatable, unstable hip

2) a partially dislocated or subluxed hip, and

3) accentuated flattening of the femoral head and acetabulum

In type 1, anatomic alterations include a slight increase in femoral anteversion and mild marginal abnormalites in the acetabular cartilage with early labral eversion. In type 2, loss of femoral head sphericity, increased femoral anteversion, early labral eversion with hypertrophy, and a shallow acetabulum are seen. In type 3, inward growth and hypertrophy of the labrum (formation of a limbus) takes place. Conventional radiography is relatively insensitive to these changes until ossification of the acetabulum is advanced.

Imaging methods

Among the radiological lines that have been used to distinguish between the normal and the dislocated hip are the acetabular index (a measurement of the apparent slope of the acetabular roof); the intersection of the horizontal Hilgenreiners line (through the triradiate cartilage) with Perkins line (a vertical line drawn downward from the lateral rim of the acetabulum), which is a measure of lateral migration of the femoral head; and Shentons line, which is drawn between the medial border of the neck of the femur and the superior border of the obturator foramen. The acetabular index may be normal despite significant dysplasia of the hip.

Conventional or computed tomography may be helpful when heavy casts obscure radiographic visualization. Positive contrast arthrography is indicated when dislocation is discovered late but should be undertaken only after 23 weeks of traction to loosen soft tissue contracture. Real-time ultrasonography of the infant's hip also provides an accurate image of anatomic relationships as well as valuable information concerning function. CT scanning can usually provide accurate documentation of the adequacy of a reduction in developmental dysplasia of the hip. CT provides a clear image of the reduction in the transverse plane, so that anterior or posterior subluxation of the femoral head can be detected easily. In addition, CT allows direct measurement of acetabular anteversion, which had previously not been possible with noninvasive studies in the living patient. MR imaging likewise may be useful in the evaluation of developmental dysplasia of the hip.

Treatment

is directed toward re-establishing normal chondro-osseous development of the hip. Among the types of flexion-abduction-external rotation apparatus are the Pavlik harness, von Rosen splint and Frejka pillow. In addition, a large number of surgical procedures on the pelvis or femur have been designed for late salvage of cases with persistent acetabular maldevelopment and hip instability (Table 1).

Developmenta developmental dysplasia of the hip (DDH), Table 1.
Some operations for patients with hip instability. Femoral varus osteotomy
Pelvic (Salter) rotation
Acetabular (steel) rotation
Circumacetabular osteotomy (Pemberton)
Medialization of the femoral head (Chiari osteotomy)
Innominate (Salter) osteotomy
 
Complications
Among the complications of therapy are ischaemic necrosis of the femoral head. Failure of appearance or growth of the femoral ossification centre during an interval of approximately 1 year after reduction is good evidence of necrosis. Broadening of the femoral neck and premature fusion of a physeal segment with secondary rotation of the epiphysis may also occur. In addition, developmental coxa vara has been described as a rate late complication of treated developmental dysplasia of the hip.

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