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INTRODUCTION FOR THE NEONATOLOGIST

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The term developmental dysplasia of the hip (DDH) indicates a spectrum of pathologies from stable acetabular dysplasia (femoral head stable in hip socket but socket is shallow) to “located” hips that are unstable (femoral head can be moved in and out of the confines of the acetabulum), to frankly dislocated hips in which there is a complete loss of contact between the femoral head and acetabulum. Congruent reduction and stability of the femoral head are necessary for normal growth and development of the hip joint. The natural history of DDH is variable: Acetabular dysplasia often resolves spontaneously. Unstable or dislocated hips may reduce spontaneously, but some will require treatment to normalize.

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Whether dysplastic, dislocatable, or completely dislocated, DDH in the newborn period is pain free and asymptomatic. However, failure to diagnose this entity can have drastic results. In cases that have persistent dysplasia or untreated dislocation, infants have a significantly increased risk of developing precocious arthritis with moderate-to-severe hip pain as young adults.1,2 This pain can be debilitating. Early detection and treatment of DDH are therefore important in avoiding the devastating sequelae of a late diagnosis. Given the complexity and acuity of patients in the neonatal intensive care unit and the silent nature of this disorder, DDH can easily be overlooked in this patient population. Fortunately, the diagnosis of DDH requires only modest vigilance to detect in the majority of cases.

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INCIDENCE AND ETIOLOGY

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Developmental dysplasia of the hip occurs in 11.5 of 1000 infants, with 1–2/1000 having frank dislocations.3,4 Although all children should be screened for DDH by physical examination, there exist particular risk factors for DDH that warrant closer scrutiny. These risk factors include a positive family history (boys, 9.4/1000; girls, 44/1000); breech presentation (boys, 26/1000; girls, 120/1000); and the presence of an unstable hip examination at birth. The left hip alone is affected in 60%, the right hip in 20%, and both hips in 20% of infants.4

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Despite newborn screening programs, 1 in 5000 children will have a dislocated hip detected at 18 months of age or older.5 It is important to appreciate that not all dislocated hips are present at birth, and not all hips dislocated at birth are detectable in the newborn period.

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Dislocations can be divided into two groups: syndromic and typical. Syndromic dislocations are most frequently associated with neuromuscular conditions such as myelodysplasia and arthrogryposis or with dysmorphic syndromes such as Larsen syndrome. These abnormalities probably occur between week 12 and week 18 of gestation.3 Typical dislocations occur in otherwise-healthy infants in the third trimester or postnatal period. Syndromic dislocations are often fixed and nonreducible and require orthopedic referral. The rest of this chapter deals only with typical dislocation.

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PHYSICAL FINDINGS

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There are no pathognomonic signs of a dislocated hip. ...

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