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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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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.