What is the best initial test to identify Developmental Hip Dysplasia in a 6-week-old infant?

The best initial test to identify Developmental Dysplasia of the Hip (DDH) in a 6-week-old infant is an ultrasound. This imaging modality is particularly suitable for young infants because their hip joint cartilage is not fully ossified; therefore, X-rays may not adequately visualize the hip structure in this age group. An ultrasound can provide clear images of the soft tissue and cartilaginous structures of the hip, allowing for accurate assessment of joint position and development.

Ultrasound is non-invasive, does not expose the infant to radiation, and is effective for detecting abnormalities such as a dislocated or improperly positioned hip. It is the preferred method for screening and diagnosing DDH during the first few months of life when early intervention can significantly improve outcomes.

Other imaging techniques, such as MRI or CT scan, are not typically employed as first-line options in this age group for several reasons. MRI is more complicated, expensive, and time-consuming, and it often requires sedation for infants, making it less practical for routine screening. CT scans involve radiation exposure, which is avoided in very young patients unless absolutely necessary. Therefore, ultrasound emerges as the most appropriate and effective initial test for assessing developmental hip dysplasia in a 6-week-old infant.