A 5-year-old boy presents with fever, refusal to bear weight, and right hip held in flexion-abduction-external rotation. Ultrasound demonstrates joint effusion; hip aspiration yields 95,000 WBC/mm³. The Kocher criteria for septic arthritis of the hip include four variables. If all four criteria are present, the predicted probability of septic arthritis is:
- A ~40%
- B ~99.6% ✓
- C ~73%
- D ~93%
Correct answer: B. ~99.6%
Explanation
The Kocher predictors for pediatric septic arthritis of the hip are: (1) non-weight-bearing, (2) ESR >40 mm/h, (3) temperature >38.5°C, and (4) serum WBC >12,000/mm³. When all four criteria are present, the predicted probability of septic arthritis is 99.6% (Kocher et al., JBJS 1999). This clinical decision tool guides urgent surgical drainage. The modified Caird criteria add CRP >2 mg/dL as a fifth variable. With only 1 criterion present, probability is <3%. Emergency arthrotomy, joint irrigation, and systemic antibiotics are indicated with high predictor scores.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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