Which imaging modality is the gold standard for diagnosis of developmental dysplasia of hip in infants under 4 months of age?

Explanation

## Imaging in Developmental Dysplasia of Hip **Key Point:** Ultrasound is the gold standard for diagnosing DDH in infants under 4 months of age because the femoral head and acetabulum are largely cartilaginous and not visible on plain radiographs. ### Why Ultrasound is Gold Standard in Infants | Feature | Ultrasound | Plain X-ray | CT | MRI | |---------|-----------|-----------|----|---------| | **Visualization of cartilage** | Excellent | Poor | Poor | Excellent | | **Radiation exposure** | None | Yes | High | None | | **Age suitability** | <4 months (best) | >4 months | Not routine | Not routine | | **Cost** | Low | Low | High | High | | **Availability** | High | High | Limited | Limited | | **Real-time assessment** | Yes (dynamic) | No | No | No | ### Ultrasound Technique (Graf Classification) - **Type I (Normal):** Alpha angle >60°, beta angle <55° - **Type IIa (Immature):** Alpha angle 50–60°, requires follow-up - **Type IIb (Immature):** Alpha angle 50–60°, increased beta angle; requires treatment - **Type III (Dysplastic):** Alpha angle <50°, femoral head partially dislocated - **Type IV (Dislocated):** Femoral head completely dislocated from acetabulum **High-Yield:** Ultrasound can assess **dynamic stability** (Barlow and Ortolani maneuvers under real-time visualization), which is impossible with static imaging. ### Plain Radiographs - **Limitations:** Cartilaginous structures not visible; unreliable before 4 months. - **Useful after 4 months:** When ossification of femoral epiphysis begins. - **Hilgenreiner-epiphyseal angle (HEA):** Measured on AP pelvis; >60° suggests dysplasia. ### CT and MRI - **Role:** Reserved for complex cases, surgical planning, or assessment of associated abnormalities. - **Not first-line:** Unnecessary radiation (CT) or cost/time (MRI) for routine screening. **Clinical Pearl:** The American Academy of Pediatrics (AAP) recommends ultrasound screening for all infants with risk factors (family history, female gender, breech presentation, oligohydramnios) and clinical suspicion.