What is the appropriate diagnostic workup and management for a 2-year-old patient with left hip and knee pain and limping after a fall?

Diagnostic Workup and Management for 2-Year-Old with Left Hip and Knee Pain and Limping After Fall

Begin with bilateral tibia/fibula radiographs (AP and lateral views) as the initial imaging study, since spiral tibial fractures are the most common cause of limping in children under 4 years of age, accounting for the vast majority of fractures in this age group even without clear trauma history. 1

Immediate Clinical Assessment

Rule Out Infection First

• Check temperature immediately - fever >101.3°F (38.5°C) combined with refusal to bear weight indicates septic arthritis until proven otherwise, which can cause permanent joint damage within hours if untreated 2, 3
• Assess for systemic toxicity signs: lethargy, irritability, poor feeding 2
• If fever is present with localized hip symptoms, obtain urgent hip ultrasound to assess for joint effusion, followed by ultrasound-guided aspiration for cell count, Gram stain, and culture 2

Systematic Physical Examination

• Examine the entire lower extremity from hip to foot systematically - 2-year-olds cannot verbalize or accurately localize symptoms, and hip pathology refers pain to the thigh, knee, or buttock in up to 30% of cases 2, 4
• Palpate for focal tenderness, swelling, erythema, and warmth along the entire limb 2
• Assess weight-bearing ability - complete refusal to bear weight raises concern for fracture or septic arthritis 4
• Evaluate the "three As" (anxiety, agitation, analgesic requirement) which indicate serious pathology when verbal communication is limited 2

Initial Imaging Strategy

If Afebrile with Non-Localized Symptoms

• Obtain bilateral tibia/fibula radiographs (AP and lateral) as first-line imaging 1, 4
• Spiral tibial fractures ("toddler's fractures") are the most common cause of nonlocalized limp in children under 4 years, occurring in 4-20% of limping children in this age group 1

Critical Pitfall About Initial Radiographs

• 10-41% of toddler's fractures appear completely normal on initial radiographs and only become visible on follow-up films obtained 7-10 days later 1, 2, 4
• Never assume normal radiographs exclude fracture in a 2-year-old with persistent symptoms 2, 4

If Symptoms Localize to Hip or Knee

• For hip localization: obtain hip radiographs (AP pelvis and frog-leg lateral) 1
• For knee localization in this age group: still consider hip pathology first due to referred pain patterns 2, 4
• Hip ultrasound should be considered even when symptoms cannot be well localized, as hip pathology frequently refers pain elsewhere 1

Management Based on Initial Findings

If Initial Radiographs Are Normal

• Provide short-course NSAIDs for analgesia 2
• Arrange mandatory follow-up in 7-10 days for repeat radiographs of the same area 1, 4
• Instruct parents to return immediately if symptoms worsen, fever develops, or child becomes unable to bear weight 1

If Symptoms Persist or Worsen Despite Normal Initial Imaging

• Obtain hip ultrasound to evaluate for joint effusion, even if hip was not the primary complaint 1, 4
• Consider MRI of the lower extremity if radiographs and clinical follow-up fail to provide diagnostic clues - MRI is highly sensitive for stress fractures, soft-tissue pathology, and occult bone injuries 1
• Consider Tc-99m bone scan for whole-body imaging if the examination remains nonfocal and symptoms persist, as it can localize pathology when other modalities are negative 1

Additional Diagnostic Considerations

Less Common But Important Diagnoses in This Age Group

• Traumatic hip dislocation - can present with knee pain due to referred pain patterns; requires urgent reduction within 6-12 hours to prevent avascular necrosis 5, 6
• Subperiosteal hematoma of the iliac bone - mimics femoral neck fracture, can be detected by ultrasound of the iliac region 7
• Transient synovitis - most common cause of acute limp overall, but diagnosis of exclusion after ruling out infection and fracture 3

When to Obtain Advanced Imaging Immediately

• MRI without IV contrast is appropriate as next imaging study after negative radiographs if there is high suspicion for occult fracture or internal derangement 1
• MRI has better sensitivity than radiographs for osteochondritis, apophysitis, osteonecrosis, or tumor 1

Critical Management Pitfalls to Avoid

• Never focus only on the site of reported pain - young children frequently mislocalize pain, and hip pathology commonly presents as knee pain 2, 5, 8
• Never delay septic arthritis workup in a febrile child refusing to bear weight - joint damage occurs within hours 2
• Never discharge without clear follow-up plan - approximately 10% of fractures only appear on follow-up radiographs 1, 4
• Never ignore persistent symptoms despite normal initial imaging - consider hip ultrasound, repeat radiographs, or advanced imaging 1, 4