In developmental dysplasia of the hip (DDH), the hips atbirth may be dislocated or dislocatable. The femoral head andacetabulum develop from the same mesenchymal cells; by11 weeks’ gestation, the hip joint is formed. There are two typesof DDH: teratologic and typical. Teratologic dislocationsoccur early in utero and are usually associated with neuromuscular disorders (spina bifida, arthrogryposis). Typical dislocations occur in the neurologically normal infant and can occurbefore or after birth. The true incidence of DDH is unknown, but it may be as high as 1.5 cases per 1000 infants.
Newborn infants have ligamentous laxity that, if significant enough in the hip, may lead to spontaneous dislocation and reduction of the femoral head. Persistence of this spontaneous pattern can lead to pathologic changes, such asflattening of the acetabulum, muscle contractures that limitmotion, and joint capsule tightening. The left hip is affectedthree times as often as the right hip, possibly because of inutero positioning.
Physiologic risk factors for DDH include a generalized ligamentous laxity, perhaps from maternal hormones that are associated with pelvic ligament relaxation (estrogen and relaxin). Female infants are at higher risk (9:1); family history is positive in 20% of all patients with DDH.
Other risk factors include breech presentation, firstbornchild (60%), oligohydramnios, and postnatal infant positioning. In breech presentations, the fetal pelvis is situated in thematernal pelvis. This can increase hip flexion and limit overall fetal hip motion, causing further stretching of the alreadylax joint capsule and exposing the posterior aspect of thefemoral head. The altered relationship between the acetabulum and femoral head causes abnormal acetabular development. Postnatal positioning of the hips in a tight swaddlewith the hips adducted and extended can displace the hip joint.
Congenital muscular torticollis, metatarsus adductus, and clubfoot are associated with DDH. An infant with any of these three conditions should receive a careful examination of the hips.
Every newborn requires a screening physical examination forDDH; further evaluation through at least the first 18 months of life is part of the physical examination for toddlers. DDHevolves over time, so the examination may change as the patientages. The examination starts with inspection for asymmetricalthigh and gluteal folds with the hips and knees flexed. A relativeshortening of the femur with asymmetrical skin folds is a positive Galeazzi sign and indicates DDH. Range of motion shouldbe assessed with the pelvis stabilized and the child supine onthe examining table, not in the parent’s lap (Fig. 199-1). Hipabduction should easily reach or exceed 75°, and hip adductionshould reach 30°. Limitations may indicate contractures associated with DDH, especially decreased abduction.
Normal at birth to 1 month of age Often normal, 1 to 9 months of age
Figure 199-1 Hip abduction test. Place the infant supine, flex the hips 90°, and fully abduct the hips. Although the normal abduction range is broad, hip disease should be suspected in any patient who lacks more than 30° to 45° of abduction. (From Chung SMK: Hip Disorders in Infants and Children, Philadelphia, 1981, Lea & Febiger, p 69.)