Early Detection of Developmental Hip Dysplasia

Posted by e-Medical PPT Saturday, November 10, 2012
Developmental dysplasia of the hip is the condition in which the femoral head has an abnormal relationship to the acetabulum. Developmental dysplasia of the hip includes frank dislocation (luxation), partial dislocation (subluxation), instability wherein the femoral head comes in and out of the socket, and inadequate formation of the acetabulum.
The target patient is the healthy newborn up to 18 months of age, excluding those with neuromuscular disorders, myelodysplasia, or arthrogryposis.

BIOLOGIC FEATURES AND NATURAL HISTORY :
Embryologically the femoral head and acetabulum develop from the same block of primitive mesenchymal cells. A cleft develops to separate them at 7 to 8 weeks' gestation. By 11 weeks' gestation development of the hip joint is complete. At birth the femoral head and the acetabulum are primarily cartilaginous.
Development of the femoral head and acetabulum are intimately related, and normal adult hip joints depend on further growth of these structures. Hip dysplasia may occur in utero, perinatally, or during infancy and childhood.
Dislocations are divided into 2 types:
 Teratologic dislocations occur early in utero and often are associated with neuromuscular disorders or with various dysmorphic syndromes. The typical dislocation occurs in an otherwise healthy infant and may occur prenatally or postnatally.
During the immediate newborn period, laxity of the hip capsule predominates and if significant enough, the femoral head may spontaneously dislocate and relocate. If the hip spontaneously relocates and stabilizes within a few days, subsequent hip development usually is normal.
If subluxation or dislocation persists, then structural changes develop. A deep concentric position of the femoral head in the acetabulum is necessary for development of the hip. Because the femoral head is not reduced into the depth of the socket in subluxation the acetabulum does not grow and remodel and, therefore, becomes shallow.
If the femoral head moves further out of the socket (dislocation), typically superiorly and laterally, the inferior capsule is pulled upward over the empty socket. Muscles surrounding the hip become contracted, limiting abduction of the hip. The capsule constricts; once narrows to less than the diameter of the femoral head, the hip can no longer be reduced by manual manipulative maneuvers.
The hip is at risk for dislocation during 4 periods: 1) the 12th gestational week: the fetal lower limb rotates medially, 2) the 18th gestational week: the hip muscles develop around the 18th gestational week. 3) the final 4 weeks of gestation: mechanical forces have a role (frank breech position) and 4) the postnatal period: swaddling, combined with ligamentous laxity.
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