A 2-year-old child with fever and painful hip is evaluated. Joint fluid aspiration yields cloudy fluid with WBC 85,000 cells/μL (90% neutrophils). The Kocher criteria for septic arthritis of the hip — which combination carries >99% probability?

• A Fever alone
• B Fever + non-weight-bearing + CRP >20 mg/L
• C Non-weight-bearing + ESR >40 mm/hr alone
• D Fever + non-weight-bearing + ESR >40 mm/hr + WBC >12,000/μL + CRP >20 mg/L (all 5 positive) ✓

Explanation

The modified Kocher criteria include: fever >38.5°C, non-weight-bearing, ESR >40 mm/hr, WBC >12,000/μL, and CRP >20 mg/L. When 4 predictors are positive the probability of septic arthritis is ~93%; all 5 positive approaches 99.6%. This guides the decision for emergency surgical drainage (arthrotomy or arthroscopic washout) of the hip joint since delayed treatment leads to avascular necrosis of the femoral head due to vascular tamponade from elevated intra-articular pressure. The clinical picture in the question already confirms septic arthritis but the Kocher criteria help stratify when empirical drainage is mandated.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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