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

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

Answer: (C)

In infants around three months, the hip is largely cartilage, so imaging that looks at soft tissues rather than bone is most informative. Ultrasound of the hip lets you directly visualize the cartilaginous femoral head and acetabulum, assess how well the head is seated in the socket, and evaluate laxity with dynamic positioning. It also enables quantitative grading, such as Graf angles, to classify dysplasia and monitor response to treatment. Because there is no radiation and the technique is quick and widely available, it’s ideal for confirming developmental dysplasia in this age group. Plain hip X‑rays and frog-leg views rely on bony ossification that hasn’t fully formed yet, making them insensitive in a 3‑month‑old, while CT offers excellent detail but exposes radiation and isn’t needed when ultrasound provides adequate information.