Why is a hip ultrasound delayed until six weeks postpartum to evaluate for developmental dysplasia of the hip (DDH)?

From the Guidelines

Hip ultrasounds for developmental dysplasia of the hip (DDH) are typically performed at six weeks after birth because this timing allows for optimal assessment while balancing early detection and avoiding unnecessary treatment. Before six weeks, many infants have physiologic hip laxity that naturally resolves without intervention, as noted in a study published in the Journal of the American College of Radiology 1. This normal laxity can lead to false positive results if screening is done too early, potentially resulting in unnecessary treatment with harnesses or braces. By six weeks, most physiologic laxity has resolved, making it easier to identify true hip dysplasia that requires treatment. Some key points to consider when evaluating the timing of hip ultrasounds for DDH include:

• The American Academy of Pediatrics (AAP) recommends selective ultrasound screening only in the highest risk group, such as girls with breech presentation at birth 1.
• The AAP also suggests ultrasound as an option in girls with a positive family history, in boys with breech presentation, and when the physical examination is inconclusive 1.
• A study of 5,170 infants screened at 1 month of age found that 99.6% remained normal and 84% to 95% of Graf type II hips normalized at 3 months, indicating that the vast majority continue to normalize after the first month of life 1. Additionally, the hip joint is still primarily cartilaginous at this age, making ultrasound the ideal imaging modality as it can visualize the cartilaginous structures that would not be visible on X-rays. The six-week timeframe strikes an important balance—it's early enough to initiate treatment when it's most effective (ideally before 3-4 months of age when ossification progresses), yet late enough to avoid overdiagnosis of transient developmental variations, as supported by the American College of Radiology 1. For high-risk infants with clinical abnormalities at birth, earlier ultrasound evaluation may be warranted.

From the Research

Waiting Period for Hip Ultrasound

The waiting period of six weeks after birth to get the hip ultrasound for evaluating developmental dysplasia of the hip (DDH) can be attributed to several factors:

• The age at which treatment is initiated can significantly impact the success rate of Pavlik harness treatment, as suggested by 2.
• Studies have shown that treatment outcomes are better when the Pavlik harness is used in infants under six months of age, with the best results often seen in those treated earlier, as indicated by 3 and 2.
• Ultrasound monitoring has been found to be effective in assessing the reduction of the hip joint and guiding treatment, allowing for earlier recognition of treatment failure and minimizing complications, as reported by 4 and 5.
• The use of ultrasound supervision in the treatment of DDH has led to a high reduction rate and minimal iatrogenic complications, as demonstrated by 4.

Factors Influencing Treatment Outcome

Several factors can influence the outcome of Pavlik harness treatment for DDH, including:

• Age at the start of treatment, with earlier treatment generally yielding better results, as suggested by 3 and 2.
• Severity of the initial hip pathology, with more severe cases being less likely to respond to treatment, as indicated by 2.
• Compliance with treatment, as highlighted by 2.
• The type of hip dysplasia, with certain types being more resistant to treatment, as reported by 2.

Ultrasound Monitoring

Ultrasound monitoring has been shown to be a valuable tool in the treatment of DDH, allowing for:

• Early recognition of treatment failure, as demonstrated by 5.
• Minimization of complications, such as avascular necrosis, as reported by 4.
• Reduction in the number of radiographs required, as indicated by 5.
• Shorter duration of therapy, as suggested by 5.