What is the best course of action for a 9-year-old girl with persistent left hip pain 1 year after an injury?

Persistent Hip Pain 1 Year Post-Injury in a 9-Year-Old Girl

Obtain plain radiographs immediately (AP pelvis and lateral hip views) followed by MRI without contrast if radiographs are negative or equivocal, as chronic pain one year after injury in a child this age most likely represents undiagnosed intra-articular pathology, avascular necrosis, or occult fracture that requires definitive imaging. 1, 2

Immediate Diagnostic Workup

First-Line Imaging

• Plain radiographs are mandatory as the initial study and must include both AP pelvis and lateral hip views to screen for femoroacetabular impingement, labral pathology, avascular necrosis (Perthes disease in this age group), occult fractures, or bony abnormalities 1, 2
• Radiographs may reveal delayed complications from the original injury including avascular necrosis, which can present months to years after trauma 3

Advanced Imaging When Radiographs Are Non-Diagnostic

• Proceed directly to MRI of the hip without IV contrast (appropriateness rating 9/9) if radiographs are negative or equivocal, as standard MRI is sufficient for detecting soft tissue pathology, early avascular necrosis, labral tears, cartilage injury, and occult fractures 1, 2
• MRI is the preferred method for diagnosing avascular necrosis in children with persistent hip pain and normal radiographs, and both hips should be imaged as bilateral involvement can occur 1, 3
• MR arthrography with intra-articular gadolinium should be considered if clinical suspicion for labral tear remains high after standard MRI, particularly given the trauma history 1

Age-Specific Diagnostic Considerations

Critical Differential Diagnoses for 9-Year-Old

• Perthes disease (idiopathic avascular necrosis of the femoral head) is the primary concern in this age group (typical onset 4-10 years), especially with trauma history that may have precipitated or unmasked the condition 3, 4
• Post-traumatic avascular necrosis from the original injury, which may not manifest on imaging for months after the initial trauma 1, 3
• Chronic labral tear or intra-articular cartilage injury from the original trauma 1
• Apophyseal avulsion fracture with non-union or chronic pain syndrome 4
• Occult stress fracture or bone contusion that never fully healed 2, 3

Red Flags Requiring Urgent Evaluation

• Rule out bone tumor or infection with persistent pain of this duration, though less likely given the trauma history 3, 4
• Slipped capital femoral epiphysis is less common at age 9 but becomes more prevalent approaching age 10-12 3, 4

Treatment Strategy Based on Imaging Results

If Imaging Reveals Structural Pathology

• Immediate orthopedic referral is required for Perthes disease, avascular necrosis, labral tears, or significant cartilage injury 3, 4
• Perthes disease management depends on age, stage, and extent of femoral head involvement and may require containment strategies or surgery 3

If Imaging Is Negative

• Initiate hip-targeted exercise therapy focusing on hip abductor strengthening (gluteus medius and minimus) with progressive loading over a minimum 3-month period 5
• Use oral NSAIDs when not contraindicated for symptomatic relief during rehabilitation 5
• Consider ultrasound-guided diagnostic injection (intra-articular hip) to definitively determine if pain is intra-articular versus extra-articular if the source remains uncertain 1, 5

Critical Pitfalls to Avoid

• Never skip plain radiographs and proceed directly to MRI, as this violates ACR guidelines and may miss important bony pathology like avascular necrosis or stress fractures 1, 2
• Do not dismiss persistent pain in a child as "growing pains" or chronic pain syndrome without completing the full imaging workup, as serious pathology like Perthes disease requires early diagnosis to prevent permanent hip damage 3, 4
• Do not diagnose based on imaging alone, as clinical correlation is essential—however, in this case, the one-year duration of symptoms after injury makes structural pathology highly likely 5, 6
• Screen for referred pain from the lumbar spine and sacroiliac joints systematically, as these commonly masquerade as hip pain in children 1, 4
• Avoid allowing unstructured rest without exercise therapy if imaging is negative, as passive rest produces inferior outcomes compared to progressive loading programs 5

Monitoring and Reassessment

• If conservative management is attempted (only after negative imaging), reassess at 4-6 week intervals using patient-reported outcomes and objective findings like gait analysis and pain provocation tests 5, 6
• If no improvement occurs after 6-8 weeks of structured conservative management with negative imaging, refer to pediatric orthopedics for surgical consultation 5, 6