What is the appropriate workup and management for a 9‑year‑old child presenting with bilateral hip and groin pain without a clear history of trauma?

Bilateral Hip/Groin Pain in a 9-Year-Old Child

Immediate Action Required

Start with plain radiographs (AP pelvis and frog-leg lateral hip views) immediately, followed by urgent assessment for infection if fever or elevated inflammatory markers are present. 1, 2

The bilateral nature of symptoms in a 9-year-old significantly narrows your differential and demands urgent exclusion of septic arthritis, which can cause permanent joint damage if treatment is delayed. 1

Initial Diagnostic Workup

First-Line Imaging

• Obtain plain radiographs of the pelvis and both hips as the mandatory first imaging test to screen for fractures, slipped capital femoral epiphysis (SCFE), Legg-Calvé-Perthes disease, osteomyelitis, or tumors. 1, 2
• Radiographs are highly reliable at age 9 since femoral head ossification is well-established. 1

Critical Clinical Assessment

• Check for fever immediately - this raises urgent concern for septic arthritis or osteomyelitis and changes your entire diagnostic pathway. 1
• Assess for trauma history, though bilateral presentation makes traumatic etiology less likely. 1
• Examine gait pattern - limping, refusal to bear weight, or altered gait patterns are red flags. 1, 3
• Evaluate range of motion - limited hip abduction or other restrictions suggest significant pathology. 1

Laboratory Studies

• Obtain inflammatory markers: ESR, CRP, complete blood count with differential, and ferritin. 2
• These help differentiate infectious from inflammatory causes and guide urgency of intervention. 2

Key Differential Diagnoses for Bilateral Hip Pain

Infectious Causes (Medical Emergency)

• Septic arthritis - requires urgent diagnosis and treatment within hours to prevent permanent joint damage. 1
• Osteomyelitis - particularly pubic rami osteomyelitis can present with bilateral groin pain and mimic septic arthritis. 4
• If fever or elevated inflammatory markers present, perform ultrasound of both hips urgently to assess for joint effusion. 1, 2
• If effusion detected, proceed immediately to ultrasound-guided joint aspiration for cell count, Gram stain, and culture on at least one hip. 2

Inflammatory/Rheumatologic Causes

• Juvenile idiopathic arthritis - can present with bilateral hip involvement and systemic symptoms. 1
• Polymyalgia rheumatica-like presentation (rare in children but consider if systemic symptoms present) - characterized by bilateral hip/shoulder pain with morning stiffness and elevated inflammatory markers. 2
• Consider RF, anti-CCP, and ANA testing if inflammatory arthritis suspected. 2

Developmental/Mechanical Causes

• Bilateral SCFE - though uncommon, can occur bilaterally in 20-40% of cases, particularly in obese children. 3, 5
• Legg-Calvé-Perthes disease - avascular necrosis of femoral head, can be bilateral in 10-15% of cases. 6, 3
• Apophyseal avulsion fractures - particularly in athletic children, though bilateral presentation is unusual. 5, 7

Athletic/Overuse Injuries

• Athletic pubalgia - increasingly common in children involved in competitive sports (soccer, hockey, ballet, running). 7
• Stress injuries to pelvis or proximal femur from repetitive activity. 7

Diagnostic Algorithm

If Fever Present or Inflammatory Markers Elevated:

1. Urgent ultrasound of both hips to detect effusion. 1, 2
2. If effusion present: Immediate ultrasound-guided aspiration for synovial fluid analysis. 2
3. If aspiration negative but high clinical suspicion: Obtain MRI to evaluate for osteomyelitis, pyomyositis, or psoas abscess. 2, 4

If No Fever and Normal/Mildly Elevated Inflammatory Markers:

1. If radiographs show abnormality: Treat accordingly based on specific finding (SCFE requires urgent orthopedic consultation). 1
2. If radiographs negative or equivocal: Proceed to MRI of pelvis and hips without contrast. 2
   • MRI is superior for detecting early osteomyelitis, stress fractures, avascular necrosis, labral tears, inflammatory changes, and occult malignancy. 2, 6

Advanced Imaging Indications

MRI without contrast is the next appropriate test after negative or equivocal radiographs when diagnosis remains unclear. 2

• MRI detects soft tissue pathology, cartilage abnormalities, bone marrow edema, and early infectious/inflammatory changes not visible on radiographs. 8, 6
• Ultrasound has limited utility beyond detecting joint effusions due to small field of view and inability to assess deep structures. 8, 1
• CT scan is reserved for specific indications like evaluating psoas abscess or lymphadenopathy if malignancy suspected. 2
• Bone scintigraphy can localize pathology when symptoms are diffuse but has been largely replaced by MRI. 6

Critical Pitfalls to Avoid

Referred Pain Pattern

• Hip pathology commonly refers pain to the thigh, knee, or buttock - don't be misled by the child pointing to the knee. 8, 1
• Always examine and image the hips even when child localizes pain elsewhere in the lower extremity. 1

Negative Radiographs Don't Exclude Pathology

• Approximately 10% of fractures are only visible on follow-up radiographs, particularly toddler's fractures and stress fractures. 1
• Early osteomyelitis, septic arthritis, and avascular necrosis may have normal initial radiographs. 6, 4
• If clinical suspicion remains high despite negative radiographs, proceed directly to MRI rather than waiting for follow-up films. 2, 6

Time-Sensitive Diagnoses

• Septic arthritis requires intervention within hours - don't delay aspiration if clinical suspicion is high. 1
• Acute SCFE is an orthopedic emergency requiring immediate surgical stabilization to prevent avascular necrosis. 3, 5
• Bilateral presentation doesn't exclude infection - both hips can be infected simultaneously or sequentially. 4

Bilateral Presentation Considerations

• Bilateral symptoms make traumatic etiology less likely but don't exclude stress injuries in athletic children. 7
• Consider systemic causes (inflammatory arthritis, infection, malignancy) more strongly with bilateral presentation. 2, 3
• Don't assume bilateral = benign - septic arthritis and SCFE can both present bilaterally. 3, 4