What is the recommended imaging protocol for a child with hip trauma?

Imaging Protocol for Pediatric Hip Trauma

Plain radiographs (AP pelvis and cross-table lateral hip) are the mandatory first-line imaging for all children with hip trauma, followed by CT without IV contrast if radiographs are negative/indeterminate but clinical suspicion remains high, and MRI without IV contrast for soft tissue evaluation or assessment of epiphyseal vascularity. 1

Initial Imaging: Plain Radiographs

Standard radiographic views are essential and must include:

• Anteroposterior (AP) pelvis view for hip symmetry assessment 1
• AP view of affected hip with 15 degrees internal rotation 1
• Cross-table lateral view of the affected hip (NOT frog-leg lateral due to risk of fracture displacement) 1

Radiographs provide rapid diagnosis to:

• Detect hip fractures and dislocations 1
• Reduce morbidity by enabling immediate treatment 1
• Can be performed portably without moving the patient 1

Advanced Imaging When Radiographs Are Negative/Indeterminate

CT Without IV Contrast: The Next Step

If radiographs are negative or indeterminate but clinical suspicion for fracture persists, CT hip without IV contrast is the appropriate next imaging study. 1

CT advantages in pediatric hip trauma:

• Detects radiographically occult fractures with 94% sensitivity and 100% specificity 1
• Reveals occult hip fractures in 24.1% of patients with negative radiographs 1
• Changes management in 20% of cases 1
• Faster to obtain than MRI or bone scan 1
• Essential for detecting acetabular fractures, which may be underestimated on plain films in children due to partially calcified bone 2

Critical post-reduction imaging:

• CT is mandatory after reduction if joint space remains widened on radiographs 3
• Detects labral entrapment causing joint space asymmetry 3
• Identifies posterior acetabular wall fractures that may be missed on plain radiographs in children 2

MRI Without IV Contrast: For Specific Indications

MRI is indicated when:

• CT is negative but pain persists and clinical suspicion remains high 4
• Soft tissue injury is suspected (abductor tendon tears, muscle injuries, ligamentous damage) 5
• Assessment of epiphyseal vascularity is needed (alternative to bone scan) 3
• Posterior acetabular wall involvement needs definitive characterization in cases of post-reduction instability 2

MRI provides near 100% sensitivity for occult fractures and superior soft tissue detail. 4

Pediatric-Specific Considerations

Children differ from adults in several critical ways:

• Hip dislocations can occur with minor trauma in younger children, whereas adolescents require higher-energy mechanisms 6, 7
• Transient hip dislocation with spontaneous incomplete reduction is a diagnostic pitfall in adolescents—any asymmetric joint space widening warrants additional investigation 7
• Partially calcified pediatric bone makes acetabular fracture assessment challenging on plain films and CT alone 2

Post-reduction protocol:

• Obtain immediate post-reduction radiographs to confirm concentric reduction 3, 7
• Perform CT if joint space remains widened to detect labral entrapment or bone fragments 3
• Consider radionuclide bone scan between 2-3 weeks post-injury to assess epiphyseal vascularity and detect avascular necrosis risk 3
• MRI with specific sequences may serve as alternative to bone scan for assessing epiphyseal vitality 3

Critical Pitfalls to Avoid

Timing is crucial:

• Urgent reduction within 6 hours reduces osteonecrosis risk 7
• Delayed diagnosis increases risk of avascular necrosis, coxa magna, and osteoarthritis 7
• Surgical delay beyond 12 hours significantly increases mortality risk 1

Common imaging errors:

• Do NOT use frog-leg lateral views in acute trauma (risk of fracture displacement) 1
• Do NOT rely on clinical examination alone to exclude fracture 8
• Do NOT order CT with IV contrast—there is no evidence supporting its use and it adds unnecessary risk 1, 8
• Do NOT use bone scan as initial or next imaging study—insufficient evidence and inferior to CT/MRI 1
• Do NOT use ultrasound for acute traumatic hip pain evaluation—insufficient evidence 1

Post-reduction vigilance:

• Any persistent joint space widening after reduction mandates CT evaluation 3, 7
• Closed reduction in adolescents requires caution due to risk of femoral head displacement during manipulation 7
• Open reduction is indicated when closed reduction fails or when bone/soft tissue interposition is detected 7