In a 4-year-old child with bilateral leg pain, how should radiographs be ordered?

Imaging Approach for 4-Year-Old with Bilateral Leg Pain

Start with bilateral tibia/fibula radiographs as the initial imaging study, rather than ordering full lower extremity films from pelvis to feet. 1

Rationale for Limited Initial Imaging

The ACR Appropriateness Criteria specifically addresses this clinical scenario and recommends a focused approach:

• In children under 4 years of age with nonlocalized bilateral leg pain, spiral tibial fractures (toddler's fractures) are by far the most common pathology found, accounting for the majority of fractures in this age group 1
• While it's common practice to order radiographs from pelvis through feet due to young children's inability to localize symptoms, limited tibial/fibula radiographs are suggested as the preferred initial approach rather than total extremity imaging 1
• This reduces radiation exposure while capturing the most likely pathology

Clinical Assessment Before Imaging

Before ordering any radiographs, evaluate for:

• Red flags for infection: fever, elevated inflammatory markers (ESR, CRP, WBC), localized erythema, swelling, or warmth
• Ability to bear weight: refusal to walk or limp
• Trauma history: even minor trauma can cause occult fractures
• Bilateral vs unilateral symptoms: true bilateral involvement suggests systemic causes (inflammatory, metabolic) rather than trauma

When to Expand Imaging

If initial tibial/fibula radiographs are negative but symptoms persist:

• Order follow-up radiographs in 7-10 days, as approximately 10% of tibial fractures are only visible on follow-up imaging 1
• Consider radiographs of other areas (hips, femurs, ankles/feet) if clinical reassessment suggests alternative localization
• Critical pitfall: One case series documented a child initially discharged with negative tibial films who returned with spinal discitis and epidural abscess 1—always reassess if symptoms worsen

If bilateral symptoms with systemic features (fever, elevated inflammatory markers):

• This suggests infection or inflammatory arthritis rather than trauma
• Proceed directly to MRI of symptomatic areas or consider whole-body imaging modalities
• Hip ultrasound can detect effusions if hip pathology is suspected (hip pain often refers to knee/thigh) 1

Advanced Imaging Indications

MRI lower extremity is reserved for:

• Negative radiographs with persistent symptoms after clinical and imaging follow-up
• Concern for soft-tissue pathology, stress fractures, or bone marrow abnormalities
• Suspected inflammatory or infectious conditions 1

Bone scan may localize pathology when:

• Examination remains nonfocal
• Initial workup is negative
• Symptoms persist or progress
• However, bone scans lack specificity in this scenario 1

Key Clinical Pitfalls

• Don't automatically order full lower extremity series: This increases radiation exposure unnecessarily when tibial fractures are most common
• Don't dismiss bilateral symptoms as "growing pains": True bilateral pathology warrants investigation, especially with systemic symptoms
• Don't forget follow-up imaging: Many toddler's fractures are radiographically occult initially (41% in one study) 1
• Consider non-orthopedic causes: Bilateral leg pain can represent leukemia, neuroblastoma, or inflammatory conditions—check CBC, ESR, CRP if clinical picture is atypical 2

The imaging strategy should progress from focused (bilateral tibia/fibula) to comprehensive (additional joints, MRI) based on initial results and clinical reassessment, not start with extensive imaging. 1