Dislocated hips are more common in certain congenital or genetic conditions associated with laxity such as Down syndrome or other chromosomal anomalies.

CONGENITAL DYSPLASIA of the hip (CDH) effects as many as one in every one hundred live births. Radiographic techniques such as ultrasound have increased our ability to diagnose and follow the course of subtle dysplasias, but the physical examination remains the mainstay of diagnosis.

Etiology
The majority of cases of dysplasia of the hip develop in utero. These result from a combination of uterine constraints on fetal positioning, normal fetal acetabular shallowness, and inherited ligamentous laxity. A hormonal laxity is also a factor and explains the predominance of females with this disorder. The firstborn female breech infant has a one in fifteen incidence of dysplasia. Post natal dysplasia does occur and is influenced by persistent laxity as well as cultural positioning variations (swaddling in extension). The term CDH has recently been changed to DDH (developmental dysplasia of the hip) in order to emphasize its multifactorial etiology.

Risk Factors
A higher index of suspicion for DDH should exist for the firstborn child, especially if female (6:1 predominance), breech presentation, family history of DDH or laxity. Dislocated hips are more common in certain congenital or genetic conditions associated with laxity such as Down syndrome or other chromosomal anomalies.

Diagnosis
The diagnosis of DDH is based on either instability or a lack of motion. In the first six to eight weeks of life and especially in the immediate perinatal period, the diagnosis is made by the Ortolani and Barlow tests. The abnormal hip will be either dislocated or subluxable. The dislocated femoral head will lie posteriorly and may be palpated in the buttock region. A gentle lifting and spreading of the leg may reduce the femoral head back into the acetabulum, producing a feeling of a "thump." This is known as a positive Ortolani test.

However, a dislocated hip may be rendered non-reducible due to contractures and will therefore not produce this clinical finding. Other findings in the case of dislocation are shortening of the leg and resultant asymmetry of the thigh creases.

More common than a true dislocation is the subluxable hip. In this case the femoral head is within the acetabulum, but because of a shallow acetabulum in combination with capsular laxity, the femoral head may be unstable within the acetabulum. The maneuver that best demonstrates this type of problem is the Barlow test. The thigh is flexed, and adducted while pushing the femur downward. The examiner will feel the hip "piston" or even dislocate posteriorly. As normal neonatal laxity rapidly resolves, this sign may be absent after two to three weeks of life.

After the first two to three months of life, the signs of instability become very difficult to elicit, and the diagnosis is made by restriction of motion. In the case of a subluxated or dislocated hip, surrounding musculature will foreshorten and lead to a loss of abduction on examination. With hip flexed and knees bent a difference in knee height may be evident (Galeazzi sign or Allis sign). The walking child with a dislocated hip will lean toward the side of the dislocation (Trendelenburg gait), and in cases of bilateral DDH, a waddling gait may be noted. The well child examination within the first two years of life should always include a check for symmetry of abduction, leg length equality, and an examination of the walking child's gait pattern.

Radiography
As the examination is the key to the diagnosis of DDH, x rays are utilized primarily to follow the course of treatment of DDH. A pelvis x ray in the first two years of life is not useful in ruling out DDH, and a "normal" radiographic report does not exclude hip instability. Ultrasound is useful in the early months to assess the location of the unossified femoral head and to assess the competency of the acetabulum. The best use for ultrasound is the child who has a positive Barlow test in the neonatal period suggestive of instability. At the time of referral, this clinical test might become negative yet the hip may not be entirely normal. The Barlow test can be done under ultrasound and this may more clearly document an instability that requires treatment.

The majority of hips treated under one year of age can be expected to result in normal hips with no future problems.

Treatment
The treatment of DDH depends on the type of hip dysplasia encountered. A reduced but subluxable hip (positive Barlow test) is best treated with a Pavlik harness to flex and abduct the hip. This best positions the femoral head into the depths of the acetabulum al simulates normal acetabular development Double diapering does not allow sufficient flexion and is therefore not an adequate treatment. The treatment duration vanes from six to eighteen weeks until examination, radiographs, and/or ultrasound.

A dislocation but reducible hip (Ortolani) may be treated with a Pavlik harness in the infant under two months of age. If the hip reduces and becomes stable the harness is continued. If reduction fails within a period of two to three weeks, the harness is discontinued. Such a non-reducible dislocated hip is then treated with a three to four week period of traction, in order to relax muscle and neurovascular structures, which may have become tight. The hip is then gently reduced under general anesthesia and a perfect reduction is confirmed by an ultrasound or arthrogram. In certain cases adaptations and contractures may be present and prevent closed reduction. These require reduction by surgical means. Once reduced, these hips are maintained in a spica cast until stable. The treatment duration can range from six to twelve months.