What is the recommended imaging modality for diagnosing hip dysplasia (developmental dysplasia of the hip) in infants?

Recommended Imaging Modality for Diagnosing Hip Dysplasia in Infants

Ultrasound is the preferred imaging modality for diagnosing developmental dysplasia of the hip (DDH) in infants between 4 weeks and 4 months of age, while radiography of the pelvis is recommended for infants older than 4 months. 1, 2

Age-Based Imaging Recommendations

0-4 weeks of age

• Clinical examination only - imaging is not recommended for initial evaluation of infants younger than 4 weeks with equivocal physical examination or risk factors 1, 2
• Allows time for physiologic laxity to resolve spontaneously

4 weeks to 4 months of age

• Ultrasound of the hips is the preferred imaging modality 1, 2
• Optimal timing for screening ultrasound is after 2 weeks of age 2
• Advantages:
  • Visualizes cartilaginous structures not seen on radiographs
  • Allows dynamic assessment of hip stability
  • No radiation exposure
  • Can be performed before ossification of femoral head 3

4-6 months of age

• Transition period from ultrasound to radiography
• Radiograph of the pelvis becomes the preferred imaging method 1, 2
• Ultrasound may still be a feasible alternative at 6 months 4

>6 months of age

• Radiograph of the pelvis is the recommended imaging modality 1, 2
• Better visualization of bony structures as ossification progresses

Special Considerations

Risk-Based Screening

• For infants with risk factors (female gender, breech presentation, family history, etc.):
  • American Academy of Pediatrics recommends ultrasound for all female infants born in breech position 2, 5
  • Optional hip imaging for male infants born in breech position 2, 5

Monitoring During Treatment

• For infants undergoing treatment with Pavlik harness:
  • Ultrasound is preferred for monitoring treatment response in children younger than 6 months 1
  • Can confirm concentric hip reduction and assess treatment response 1
  • Radiographs are typically obtained at or near conclusion of treatment to document bony acetabular development 1

Technical Considerations

• Graf classification system is used to evaluate hip dysplasia severity on ultrasound 6
• Key measurements include:
  • Alpha angle (bony acetabular angle)
  • Beta angle (cartilaginous acetabular angle)
  • Femoral head coverage percentage

Common Pitfalls to Avoid

1. Premature radiographic evaluation: Radiographs before 4 months may miss dysplasia due to incomplete ossification of the femoral head
2. Delayed diagnosis: Waiting too long for imaging when risk factors or abnormal physical exam findings are present
3. Overreliance on a single examination: Serial examinations and imaging may be necessary as DDH can evolve over time
4. Inadequate positioning during ultrasound: Proper technique is essential for accurate measurements
5. Misinterpretation of physiologic immaturity: Graf type IIa hips (alpha angles 50-59°) in infants under 3 months often normalize spontaneously 2

By following these age-appropriate imaging recommendations, clinicians can optimize early detection and treatment of developmental dysplasia of the hip, potentially avoiding more invasive interventions and improving long-term outcomes.