Developmental dysplasia of the hip (DDH) is a spectrum of disorders of the developing hip ranging from a slightly shallow acetabulum (hip socket) with a well-located femoral head to a moderately shallow socket with joint subluxation to a severely shallow socket with complete dislocation of the joint. DDH evolves over time and may present in different forms at different ages. DDH may not be detectable at birth, and hence, the preferred term is 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, specifically, the acetabulum does not completely cover the femoral head. It can result in hip joint instability. 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 often are associated with other syndromes and conditions, particularly arthrogryposis and myelodysplasia, and treatment depends on the underlying condition.
The incidence of DDH varies based on the criteria for diagnosis, method of diagnosis (clinical exam vs radiologic exam), race, age of the patients, and geography. Clinical instability and ultrasound abnormalities are quite common findings in newborns, with rates of 2.3 cases per 100 live births and 8 cases per 100 live births, respectively. However, the majority of these cases in newborns resolve spontaneously. As such, the overall incidence of DDH with instability or dislocation that requires treatment is approximately 1 to 1.5 per 1000 live births. Bilateral DDH occurs in 20% of all patients with this disorder.
The natural history of untreated DDH depends on the age at diagnosis and severity of dysplasia. Most neonatal hip dysplasia and instability will resolve spontaneously by the time the infant is 2 to 3 months of age. Patients with persistent hip dysplasia typically have few problems in the first decade of life. DDH generally does not affect the patient’s ability to reach normal developmental milestones such as crawling and walking. However, a patient with persistent hip dysplasia is at risk of developing problems, including pain, leg length differences, and ultimately hip arthritis, in adolescence and young adulthood.
The etiology of DDH is multifactorial, but numerous predisposing factors have been identified. The classic risk factors for DDH include breech positioning, family history of DDH, first born, female sex, and a history of oligohydramnios. Breech positioning is considered a “packaging” issue (intrauterine crowding) predisposing to DDH. The footling breech presentation (both hips flexed) is associated with a 2% risk of DDH, and the frank breech position (1 or both knees extended) is associated with a 20% ...