Approach
Developmental dysplasia of the hip (DDH) is typically identified through a screening exam of the hips of infants. In the first 3 to 6 months of life, dislocation and subluxation of the hip are most accurately diagnosed by physical exam using the Barlow and Ortolani tests. Thereafter, hip abduction (which is limited) becomes the best physical exam technique to identify DDH. In the first 6 months of life, ultrasound testing may be used as an adjunct to clinical exam. Beyond 6 months of life, plain radiographs of the hip provide useful data to assess the relationship between the ossifying femoral head and the acetabulum.
History
When considering DDH, it is valuable to ascertain risk factors. Risk factors strongly associated with DDH include a positive family history, female sex, and breech presentation at or near delivery at term. The presence of multiple risk factors (e.g., breech female with a positive family history) should increase suspicion for the condition.[10]
Some cases of DDH will be identified later in infancy (e.g., after 6 months of age), either by screening exam, which demonstrates restricted abduction, or by parental reports of abnormal positioning of the leg, or delayed crawling/walking. Some cases of DDH present beyond the first year of life, typically with pain or abnormal gait as the presenting symptoms.
Physical exam
Routine exam of the hips should be conducted at all well-child checks throughout the first year of life. The Barlow and Ortolani tests are traditionally used to identify neonatal hip instability. The infant should be examined on a solid surface, and exam should be performed on one hip at a time. For the Barlow technique, the hip is flexed to 90° and adducted. The examiner's hand is placed on the knee, and posterior pressure is placed through the hip in an attempt to identify dislocatable hips. For the Ortolani technique, the hip is flexed to 90° and abducted, with the examiner's fingers placed laterally over the greater trochanter of the hip joint. The examiner then uses anterior pressure over the trochanter in an attempt to identify a dislocated hip that is relocatable.
In each of the tests, a positive exam is identified by a hip that is grossly unstable. The term "clunk" is often used to describe this finding, but is often confused with innocuous clicks that may be palpated in the hip and/or knee during these provocative tests. An agitated, crying baby will negatively affect the sensitivity of the two tests.
Between the ages of 3 and 6 months, the Barlow and Ortolani tests become increasingly difficult to perform because of the increased bulk and strength of musculature around the hip. Once this occurs, the optimal test for DDH is an assessment of abduction at the hip; limitations in abduction will be found in DDH because of shortening of the muscles in the affected hips.[17] Other exam findings, such as different knee heights with the patient supine and the legs flexed (Galeazzi sign), may be useful.
If faced with a child who has a normal physical exam, there is limited evidence that performing subsequent hip physical exam screening of children up to 6 months of age will detect additional children with DDH.[10]
Ultrasound evaluation
Before 6 months of age, ultrasound is preferred over radiographs for evaluation of DDH due to insufficient ossification of the hip. In the absence of clinical findings, ultrasound should be delayed until about 6 weeks of age to reduce false positive results. In the presence of positive instability examination, there is limited evidence to support obtaining an ultrasound in infants less than 6 weeks of age.[10] Guidelines disagree about the value of a screening ultrasound for DDH in infants with risk factors but a normal exam. However, one study used decision-analysis methodology to conclude that use of screening physical exams along with selective use of ultrasound in those with risk factors led to optimal outcomes.[18] Ultrasound has a high degree of sensitivity for DDH but poor specificity, leading to the risk of overtreatment. In addition, studies of intra- and interobserver reliability have consistently demonstrated variability in radiologists' interpretation of hip ultrasounds, primarily in the mildest form of DDH where the acetabulum is dysplastic (usually due to acetabular immaturity). Most cases (>90%) initially identified solely by ultrasound will spontaneously normalize between 6 weeks and 6 months of age.[5] Infants whose hips are found to be dislocated or subluxable under provocative testing with ultrasound warrant referral to a pediatric orthopedist. In addition, many primary care providers often refer patients with mild dysplastic hips for definitive evaluation by a pediatric orthopedist. Serial ultrasound evaluations should be used for patients with mild sonographic abnormality without instability. In situations where access to a pediatric orthopedist is limited, mild dysplasia (e.g., immaturity of acetabulum without instability) can be followed with serial ultrasound to ensure hip maturation and normal parameters.
Radiographic evaluation
The American Academy of Orthopaedic Surgeons (AAOS) indicates that there is low quality evidence supporting the use of an anterior pelvis x-ray instead of ultrasound to assess DDH in infants beginning at 4 months of age.[10] Beyond 6 months of age, hip radiographs are typically preferred to ultrasound as the ossific nucleus has started to ossify. An abnormal hip exam is an indication for radiographic evaluation. Normal radiographic findings usually do not warrant serial radiographic evaluation unless the clinical exam suggests a problem.
AAOS: appropriate use criteria: developmental dysplasia of the hip Opens in new window
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