Hip

Etiology

Newborn infants have ligamentous laxity that, if significant enough in the hip, may lead to spontaneous dislocation and reduction of the femoral head. Persistence of this spontaneous pattern can lead to pathologic changes, such as flattening of the acetabulum, muscle contractures that limit motion, and joint capsule tightening. The left hip is affected three times as often as the right hip, possibly because of in utero positioning.

Physiologic risk factors for DDH include a generalized ligamentous laxity, perhaps from maternal hormones that are associated with pelvic ligament relaxation (estrogen and relaxin). Female infants are at higher risk (9:1); family history is positive in 20% of all patients with DDH.

Other risk factors include breech presentation, firstborn child (60%), oligohydramnios, and intrauterine and postnatal infant positioning. In breech presentations, the fetal pelvis is situated in the maternal pelvis. This can increase hip flexion and limit overall fetal hip motion, causing further stretching of the already lax joint capsule and exposing the posterior aspect of the femoral head. The altered relationship between the acetabulum and femoral head causes abnormal acetabular development. Postnatal positioning of the hips in a tight swaddle with the hips adducted and extended can displace the hip joint.

Congenital muscular torticollis, metatarsus adductus, and clubfoot are associated with DDH. An infant with any of these three conditions should receive a careful examination of the hips.

Clinical Manifestations

Every newborn requires a screening physical examination for DDH; further evaluation through at least the first 18 months of life is part of the physical examination for toddlers. DDH evolves over time, so the examination may change as the patient ages. The examination starts with inspection for asymmetric thigh and gluteal folds with the hips and knees flexed. A relative shortening of the femur with asymmetric skinfolds is a positive Galeazzi sign and indicates DDH. Range of motion should be assessed with the pelvis stabilized and the child supine on the examining table, not in the parent’s lap ( Fig. 199.1 ). Hip abduction should easily reach or exceed 75 degrees, and hip adduction should reach 30 degrees. Limitations may indicate contractures associated with DDH, especially decreased abduction.

The Barlow test attempts to dislocate an unstable hip ( Fig. 199.2 ). The examiner should stabilize the infant’s pelvis with one hand and grasp the abducted and flexed thigh in the other hand. The hip should be flexed to 90 degrees. Next, begin to adduct the hip while applying a posterior force to the anterior hip. A hip that can be dislocated in this method is readily felt (clunk feeling) and is a positive test. It may reduce spontaneously once the posterior force is removed, or the examiner may need to perform the Ortolani test.

The Ortolani test attempts to reduce a dislocated hip ( Fig. 199.3 ). The examiner should stabilize the pelvis and hold the leg in the same method as for the Barlow test. The infant’s hip should be in 90 degrees of flexion. Abduct the hip while applying anterior pressure to the lateral thigh over the greater trochanter. A positive test is the palpable reduction of the dislocation, which may be felt (clunk). After 2 months of age, the hip may develop muscular contractures, preventing positive Ortolani tests.

These tests should be performed with only gentle force and done one hip at a time. The test may need to be repeated multiple times, as they can be difficult to interpret. A click, which is not pathologic, may occur from breaking the surface tension of the hip joint or snapping gluteal tendons.

Bilateral fixed dislocations present a diagnostic dilemma because of the symmetry on exam. The Klisic test is useful in this situation; it is done by placing the third finger over the greater trochanter and the index finger over the anterior superior iliac spine, then drawing an imaginary line between the two. The line should point to the umbilicus in a normal child. However, in a dislocated hip, the greater trochanter is elevated, which causes the line to project lower (between the umbilicus and pubis). This test is helpful in identifying bilateral DDH, which can otherwise be difficult to diagnose because of the symmetry found on examination.

Older children with unrecognized DDH may present with limping. A patient with increased lumbar lordosis and a waddling gait may have an unrecognized bilateral DDH.

Radiographic Evaluation

Ultrasound is used for initial evaluation of infants with DDH and should be done for females with a positive family history or breech presentation in both sexes. Ultrasound should be obtained after 6 weeks of age in the absence of abnormal examination findings to avoid confusion with physiologic laxity. Because the femoral head doesn’t begin to ossify until 4–6 months of age, plain radiographs can be misleading until patients are older. Plain radiographs are the imaging study of choice once the child reaches 6 months of age.

Treatment

The treatment of DDH is individualized and depends on the child’s age at diagnosis. The goal of treatment is a stable reduction that results in normal growth and development of the hip. If DDH is suspected, the child should be sent to a pediatric orthopedic specialist.

The Pavlik harness is an effective treatment up to 6 months of age. It provides hip flexion to just over 90 degrees and limits adduction to no more than neutral. This positioning redirects the femoral head toward the acetabulum. The hip must be reduced within 1–2 weeks of beginning the Pavlik harness, although the infant will need more time in the device. The Pavlik harness is successful in treating approximately 95% of dysplastic or subluxated hips, and 80% successful for treatment of true dislocations. Persistently dislocated hips should not remain in a Pavlik harness for more than 2 weeks for fear of iatrogenic acetabular damage. Patients failing the Pavlik harness warrant treatment with a rigid abduction orthosis.

Children over 6 months or those who have failed nonoperative treatment should undergo closed reduction using a hip spica cast. This is done under general anesthesia; reduction is evaluated with an intraoperative arthrogram then confirmed by postoperative computed tomography (CT) or magnetic resonance imaging (MRI). If closed reduction fails, open reduction is indicated. Patients over 18 months of age may require a pelvic and femoral osteotomy.

Complications

The most important and severe complication of DDH is iatrogenic avascular necrosis of the femoral head. This can occur from excessive flexion or abduction during positioning of the Pavlik harness or hip spica cast. Infants under 6 months of age are at highest risk. Pressure ulcers can occur with prolonged casting. Redislocation or subluxation of the femoral head and residual acetabular dysplasia can occur.