A 7-year-old child has fever, knee pain, and refusal to weight-bear. Kocher's criteria for differentiating septic arthritis from transient synovitis include four factors. Which combination of THREE criteria confers a predicted probability of septic arthritis of approximately 93%?

• A Fever + non-weight-bearing + WBC >12,000 cells/mm³
• B Fever >38.5°C + non-weight-bearing + ESR >40 mm/hr ✓
• C Non-weight-bearing + ESR >40 mm/hr + CRP >2 mg/dL
• D Fever >38.5°C + WBC >12,000 + ESR >40 mm/hr + CRP >2 mg/dL (all 4 factors)

Explanation

Kocher's original four criteria are: fever >38.5°C, non-weight-bearing, ESR >40 mm/hr, and WBC >12,000 cells/mm³. Subsequent studies added CRP >2 mg/dL as a fifth criterion. The probability of septic arthritis increases with the number of criteria met: 0 criteria ~0.2%, 1 criterion ~3%, 2 criteria ~40%, 3 criteria ~93%, 4 criteria ~99.6%. Three criteria (fever + non-weight-bearing + ESR >40) gives ~93% probability. The question tests whether candidates know the specific three-criterion probability threshold and the original Kocher criteria composition.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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