🦠 Septic Arthritis (SURGICAL EMERGENCY)
• Fever, refusal to bear weight, acutely inflamed joint
• High ESR, CRP, WBC
• Most common pathogens: S. aureus, K. kingae (<5y), Group A Strep
• Kocher criteria: fever >38.5°C, non-weight-bearing, ESR >40, WBC >12,000 → higher risk if more criteria met
🩺 Transient Synovitis (Most Common)
• Age 3-8 years, often after viral URI
• Afebrile or low-grade fever, can bear weight
• Normal or mildly elevated inflammatory markers
• Self-limited (≤7 days), no joint aspiration needed if classic
⚠️ Avascular Necrosis & SCFE
• Legg-Calvé-Perthes (LCP): age 4-8, insidious limp, hip pain referred to knee, limited abduction/IR
• Slipped capital femoral epiphysis (SCFE): obese adolescent, knee pain, external rotation with hip flexion, bilateral in 20-40%
📋 Approach
• X-ray: AP and frog-leg views of pelvis/hips
• Ultrasound for hip effusion
• Hip aspiration for suspected septic arthritis
• Neurologic causes: cerebral palsy (spastic diplegia most common)
📌 Decision strategy: Septic arthritis requires immediate aspiration/OR. Transient synovitis = most common cause of acute limp. SCFE in obese adolescent with knee pain → get hip x-rays.