Which imaging modality is the test of choice to confirm developmental dysplasia of the hip in a 3-month-old?

• A. Frog leg X-rays
• B. Plain hip X-rays
• C. Ultrasound of the hip
• D. CT of the hip

Answer: (C)

In a 3-month-old, the hip joint is largely cartilaginous, so X-rays don’t reliably show developmental dysplasia because the femoral head and acetabulum aren’t yet ossified. Ultrasound, on the other hand, can visualize these cartilaginous structures and assess how the femoral head sits in the acetabulum. It also lets clinicians watch the hip move dynamically to check stability, which is crucial for accurate diagnosis and early management. Ultrasound can quantify hip morphology with measurements like the Graf angles, guiding treatment decisions, and it has the advantage of no radiation and the ability to be repeated as the infant grows.

Plain hip X-rays or frog-leg views are limited at this age due to lack of ossification, making early DDH hard to detect. CT provides detailed anatomy but involves radiation and isn’t needed for initial DDH assessment in infants. So, ultrasound of the hip is the best choice to confirm developmental dysplasia of the hip in a 3-month-old.