Diagnosis of DDH in the newborn involves a discerning clinical and ultrasonographic examination. Commonly, newborns do not have pain, clinical deformity, or loss of motion, so any abnormal examination finding can be quite subtle. The natural history of untreated DDH can vary from spontaneous resolution, or subclinical instability leading to dysplasia after childhood, or progressive subluxation and eventual dislocation. Therefore, all newborns undergo a clinical examination at birth to evaluate for possible instability, which is repeated throughout the newborn period as examination findings can become normal within 4 weeks. A positive Ortolani maneuver (clunk on entry of the femoral head into the hip joint) is appreciated with gentle pressure on the posterior greater trochanter pushing the hip anteriorly with the hips flexed and abducted and signifies a dislocated hip that can be reduced. A negative Ortolani maneuver is a hip that is irreducible and remains dislocated. A positive Barlow maneuver (clunk on exit of the femoral head out of the hip joint) is appreciated with gentle posterior pressure with the hip and knee flexed with neutral rotation and abduction.³ Whereas many joints have subtle clicks through an arc of motion, a clunk is a more significant audible and palpable change in femoral head position signifying either femoral head dislocation or reduction depending on the maneuver performed. Diagnosing DDH after 6 months of age with physical examination can be more challenging as the Barlow and Ortolani maneuvers become less reliable. After 3 months of age, limited hip abduction in the flexed position becomes the most reliable diagnostic sign. The examiner may also see asymmetric groin, gluteal, or thigh folds in dislocated hips in infants older than 3 months. Unilateral dislocations will present with a positive Galeazzi sign and leg length discrepancy. Once the child reaches walking age, a dislocated hip will cause a Trendelenburg gait secondary to abductor insufficiency or toe walking to make up for the leg length discrepancy.

There is controversy regarding the use of diagnostic imaging during screening. Some countries universally screen all newborns with ultrasonography of the hip in conjunction with clinical examination. However, this risks overtreatment and high false-positive rates as a result of physiologic laxity. In North America, selective ultrasonography screening of only high-risk infants has been determined as the optimal strategy for early detection. High-risk newborns are those with positive family history, intrauterine breech position, or abnormal clinical examination results. Of those screened, 1 in 100 have clinical signs of hip instability and only 1.5 in 1,000 hips have true dislocation.⁴

Ultrasonography is the imaging modality of choice in the first 4 to 6 months of life before the secondary ossification center of the femoral head has ossified. The initial ultrasonographic examination should be performed at 2 and 8 weeks of age because the results have prognostic implications, with more severely dysplastic hips responding poorly to treatment if the diagnosis is delayed. Those with positive Ortolani or Barlow maneuvers should be evaluated within the first couple of weeks of life to begin early treatment. Those with a negative examination but risk factors can wait up to 6 to 8 weeks to reduce the possibility of a false-positive image. Patients with risk factors for DDH but normal findings on initial ultrasonography should be followed and undergo radiographic examination at 6 months of age because there is a 29% chance of having residual dysplasia despite the initial normal ultrasonography findings.⁵

The Graf method of ultrasonography is well accepted for analysis of hip dysplasia. The alpha angle is the measurement of the acetabular inclination. Osseous coverage of the femoral head can also be measured. The beta angle represents the cartilaginous femoral head coverage or chondrolabral angle. In normal hips the alpha angle is greater than 60° and the beta angle is less than 55°; the severity of dysplasia is worse with increasing Graf grade (Figure 1).

Most physicians use the dynamic standard minimum examination, which combines evaluating the static hip
morphology as well as dynamic stability (Figure 2). This real-time ultrasonographic assessment of the hip is performed with and without stress maneuvers in both the coronal and transverse planes of a hip in neutral and in flexion.⁶ Femoral head coverage is measured, and any value greater than 50% is considered normal. The ultrasonographic pubofemoral distance has recently been shown to have better interrater reliability than the Graf method. The pubofemoral distance correlates with femoral head coverage and can be followed with DDH treatment. Cutoff values are 6.0 mm in hip flexion and adduction, 4.6 mm in neutral, and 4.9 mm in flexion.⁷ A newborn younger than 4 weeks can have up to 4 mm of displacement when stressed, less than 50% coverage, and a subluxated femoral head more than 2 mm secondary to physiologic laxity. The most recent clinical practice guidelines do not recommend ordering hip ultrasonography after 4 months of age,⁸ because the femoral head ossific nucleus is often large enough to obscure the acetabulum.

Multiple classifications and measurements have been established to better characterize the severity of hip dysplasia. To be implemented before the ossific nucleus of the proximal femur is present, the International Hip Dysplasia Institute developed a classification based on the location of the proximal femoral metaphysis relative to the Hilgenreiner line, the Perkin line, and a dividing line at 45° (Figure 3). The Tönnis classification uses the presence of the ossific nucleus and its location relative to the quadrants formed by the Hilgenreiner and Perkin lines. The Tönnis grade correlates with long-term outcomes; each increase in one Tönnis grade will
double the likelihood of failure of nonsurgical management.⁹,¹⁰ Acetabular index is more commonly measured in infantile DDH, and it is particularly more reliable in children younger than 8 years. In a normal developing hip, this value decreases with age, but in DDH it remains elevated. As the pediatric acetabulum ossifies and further develops, other radiographic measures can be used to further describe the shape of the acetabulum. The Tönnis angle of acetabular inclination is measured from the medial to lateral edge of the sourcil and is measured relative to the horizontal. A normal Tönnis angle is 0° ± 10°. The lateral center-edge angle (center-edge angle of Wiberg) and the anterior center-edge angle (angle of Lequesne) are useful measurements (Figure 4),
obtained on AP and false-profile radiographs of the pelvis, respectively; in patients older than 5 years, the measurements can characterize femoral head coverage and acetabular deficiency. These are more commonly used in older patients with hip dysplasia, as discussed later in this section. Patients with a history of DDH should be followed to skeletal maturity because there is a risk for residual dysplasia even with successful treatment as infants.