What is the appropriate management for a pediatric patient presenting with hip pain following an upper respiratory tract infection (URTI)?

Hip Pain After URTI in Pediatric Patients

The most critical priority is to rule out septic arthritis of the hip, which requires urgent ultrasound evaluation and possible aspiration, as this condition can cause permanent joint damage if not treated promptly. 1

Immediate Diagnostic Approach

Clinical Assessment Priority

• Septic arthritis is the diagnosis to exclude first in any child with hip pain, as it requires rapid intervention to prevent permanent damage to the joint 1
• Assess for severe pain or spasm on hip movement or palpation, temperature >37.5°C (99.5°F), and clinical signs of infection 2
• Note that hip pain following URTI may represent either reactive/transient synovitis (most common) or septic arthritis (most dangerous) 2

Initial Imaging Strategy

Start with hip ultrasound as the first-line imaging modality 1:

• US allows quick and accurate diagnosis of joint effusion and can guide aspiration 1
• A false-negative US is uncommon but could occur within 24 hours of symptom onset 1
• US can identify effusion before joint aspiration or surgery 1

Plain radiographs have limited utility 1:

• Low sensitivity and specificity for diagnosing septic hip 1
• However, may identify alternative diagnoses like fractures or other bony pathology 3

Differentiating Septic Arthritis from Transient Synovitis

High-Risk Features Suggesting Septic Arthritis

• Severe pain with any hip movement or palpation 2
• Temperature >37.5°C (99.5°F) 2
• Erythrocyte sedimentation rate ≥20 mm/hour 2
• Inability to bear weight 2

When to Aspirate

Hip aspiration is the diagnostic procedure of choice if septic arthritis is suspected 2:

• US guidance can facilitate the aspiration procedure 1
• Aspiration is mandatory when clinical and laboratory findings suggest infection 1

Advanced Imaging Considerations

MRI Indications

MRI should be obtained when 1:

• Diagnosis remains unclear after initial evaluation
• Concern for osteomyelitis, pyomyositis, or other deep infections exists 1, 4
• MRI has high sensitivity and specificity for musculoskeletal infection including septic arthritis, osteomyelitis, and pyomyositis 1
• Pyomyositis of muscles around the hip (e.g., obturator internus) can mimic septic arthritis and requires MRI for diagnosis 4

Other Imaging Modalities

• Whole-body MRI may be appropriate when suspecting multifocal osteomyelitis 1
• CT has limited role due to decreased sensitivity for bone marrow pathology and radiation concerns 1

Management Based on Diagnosis

If Septic Arthritis Confirmed

• Requires urgent surgical drainage and IV antibiotics 1
• Permanent joint damage can occur without prompt treatment 2

If Transient Synovitis Diagnosed

Transient synovitis is the most common cause of acute hip pain in children aged 3-10 years 2:

• Treatment consists of bed rest and NSAIDs 2
• Regular temperature monitoring to exclude onset of fever 2
• Re-evaluate if significant pain and limping persist 7-10 days after initial presentation 2

Critical Pitfalls to Avoid

• Do not rely on radiographs alone to exclude septic arthritis, as they have poor sensitivity 1
• Do not dismiss hip effusion as benign without considering other etiologies including fractures, osteonecrosis, and juvenile idiopathic arthritis 1
• Consider alternative diagnoses such as pelvic osteomyelitis or pyomyositis if hip effusion is absent despite signs of infection 1, 4
• Do not delay aspiration when clinical suspicion for septic arthritis is high, as femoral head destruction and permanent deformity can result from delayed treatment 2