A 3-month-old female infant born to a primigravida mother presents for routine developmental screening. On physical examination, you elicit a positive Ortolani sign and Barlow sign in the left hip. Which investigation is most appropriate to confirm the diagnosis of developmental dysplasia of the hip (DDH)?

Explanation

## Investigation of Choice for DDH Confirmation in Infants **Key Point:** Ultrasound is the gold standard imaging modality for diagnosis and monitoring of DDH in infants under 6 months of age. ### Why Ultrasound is Preferred in Early Infancy At 3 months of age, the femoral head is still largely cartilaginous and not yet ossified. This anatomical fact makes ultrasound the ideal investigation because: 1. **Real-time dynamic assessment** — allows visualization of femoral head position during Barlow and Ortolani maneuvers 2. **No radiation exposure** — critical in infants who may require serial follow-up imaging 3. **Excellent soft tissue contrast** — clearly visualizes the unossified femoral epiphysis, labrum, and capsule 4. **Quantitative measurement** — Graf's method provides standardized alpha and beta angles to grade severity ### Graf's Classification (via Ultrasound) | Type | Alpha Angle | Beta Angle | Status | |------|-------------|-----------|--------| | Type I (Normal) | >60° | <55° | Normal hip | | Type II (Immature) | 50–60° | 55–77° | Requires follow-up | | Type III (Dysplastic) | <50° | >77° | Requires treatment | | Type IV (Dislocated) | <50° | >77° + displaced | Requires urgent treatment | **Clinical Pearl:** Ultrasound screening at 4–6 weeks of age is now standard in many developed countries for at-risk infants (breech presentation, positive family history, female gender). **High-Yield:** The American Academy of Pediatrics (AAP) recommends ultrasound as the imaging modality of choice for infants <6 months with clinical signs of DDH. ### Why Other Investigations Are Suboptimal at This Age See the comparison table below: | Investigation | Limitation at 3 Months | Role | |---|---|---| | X-ray pelvis | Femoral head not yet ossified; poor visualization of cartilaginous structures | Used >6 months when ossification begins | | MRI | Expensive, requires sedation, not first-line in infants | Reserved for complex cases or surgical planning | | CT scan | High radiation dose, poor soft tissue contrast for cartilage | Not used in infants; reserved for adult DDH complications | [cite:Tuli's Orthopedics 6e Ch 3]