What is the best imaging modality for hip dysplasia screening in infants?

Best Imaging Modality for Hip Dysplasia Screening in Infants

Ultrasound is the preferred imaging modality for screening developmental dysplasia of the hip (DDH) in infants from 4 weeks to 4 months of age, while radiographs become the preferred method for infants older than 4 months. 1

Age-Based Imaging Recommendations

The optimal screening approach for DDH varies by age:

• 0-4 weeks: Clinical examination only
• 4 weeks-4 months: Ultrasound of the hips
• >4 months: Radiograph of the pelvis 1

Rationale for Ultrasound in Younger Infants

Ultrasound is superior for younger infants because:

• It allows visualization of the largely cartilaginous hip structures that aren't visible on radiographs
• It enables dynamic assessment of hip stability
• It avoids radiation exposure
• It provides quantitative measurements using the Graf classification system 2

The optimal timing for screening ultrasound is after 2 weeks of age, with the primary indication being infants 4 weeks to 4 months with suspected DDH 1.

Graf Classification System for Ultrasound Assessment

Ultrasound findings are classified using the Graf system:

• Alpha angles between 50-59° are classified as immature but normally located (Graf type IIa)
• Type IIa hips will likely normalize spontaneously without intervention in infants under 3 months 1
• 84-95% of Graf type II hips normalize by 3 months of age 1

Radiographs for Older Infants

After 4 months of age, radiographs become the preferred imaging method because:

• Ossification of the femoral head has progressed
• Bony landmarks are more visible
• Regular radiographic assessment is necessary to monitor for residual dysplasia 1

Risk Factors Requiring Special Attention

Infants with the following risk factors should receive particular attention for DDH screening:

• Female gender (4-8 times more common)
• Firstborn status
• Large birth weight
• Family history of DDH
• Breech presentation 1, 3

Common Pitfalls and Caveats

1. Timing matters: Screening too early (before 2 weeks) may lead to false positives due to normal physiologic laxity in newborns
2. Follow-up is essential: Even with normal initial screening, follow-up ultrasound should be scheduled at 6-8 weeks for high-risk infants 1
3. Female infants with type IIa hips: Up to 15% may not resolve spontaneously and require closer monitoring 1
4. Technical adequacy: Ensure proper technique and image quality for accurate assessment, as poor imaging can lead to misdiagnosis 4
5. Don't rely solely on imaging: Physical examination findings remain important, particularly limitation of hip abduction (most important clinical sign after 3 months) 1

Physical Examination Components

Always combine imaging with thorough physical examination:

• Ortolani test (reduction of dislocated hip)
• Barlow test (provocation of hip instability)
• Assessment of hip abduction
• Evaluation for asymmetry of thigh or gluteal folds
• Check for leg length discrepancy (Galeazzi sign) 1