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Developmental dysplasia of the hip (DDH) is a spectrum of disorders of the developing hip. DDH evolves over time and presents in different forms at different ages. DDH may not be detectable at birth, and hence, the preferred term developmental and not congenital. The American Academy of Pediatrics (AAP) defines DDH as a condition in which the femoral head has an abnormal relationship to the acetabulum.1 Dislocation is defined as complete displacement of a joint, with no contact between the original articular surfaces. Subluxation is defined as displacement of a joint with some contact remaining between the articular surfaces. Dysplasia refers to abnormal or deficient development of the acetabulum. A teratologic dislocation is a distinct condition that occurs before birth, is generally nonreducible on physical exam, and causes the hip to be stiff. Teratologic dislocations are frequently associated with neuromuscular conditions, particularly arthrogryposis and myelodysplasia, and treatment depends on the underlying condition.

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The incidence of DDH varies based on the condition studied, method of study (clinical exam vs. radiologic exam), race, and geography. Classically, the overall incidence of some form of hip instability has been reported at 1 per 1000.2 The reported rate of hip dislocation ranges from 1 to 1.5 cases per 1000 live births. Clinical instability has been documented in approximately 2.3 cases per 100 live births, and an ultrasound abnormality has been documented in approximately 8 cases per 100 live births. Bilateral DDH occurs in 20% of all patients with this disorder.

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As breech positioning can be considered a “packaging” issue (intrauterine crowding) predisposing to DDH, torticollis, metatarsus adductus, and oligohydramnios are other packaging-related conditions strongly associated with DDH. A child with torticollis has a 14% to 20% risk of also having DDH.3 Although clubfoot has not been strongly associated with DDH, up to 10% of children with metatarsus adductus will also have DDH.4 DDH is more common in females and first-born children, and most frequently affects the left hip. Family history also strongly influences the risk of DDH. The risk of a subsequent child having DDH is 6% if there are healthy parents and an affected child, 12% with an affected parent, and 35% with an affected parent and an affected child.

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Etiology

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The etiology of DDH is multifactorial, but a number of predisposing factors have been identified, including ligamentous laxity, breech positioning, and postnatal positioning. The maternal relaxin hormone, which allows the maternal pelvis to expand, crosses the placenta and can induce laxity in the child, an effect known to be stronger in females than in males. The footling breech presentation (both hips flexed) is associated with a 2% risk of DDH, and the frank breech position (one or both knees extended) is associated with a 20% risk of DDH.5 Newborn babies wrapped in a hip-extended position, common in the Native American culture, also have a higher incidence of DDH.

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