JBJS :Validation of a Clinical Prediction Rule for the Differentiation Between Septic Arthritis and Transient Synovitis of the Hip in Children

The authors previously published a rule for the differential diagnosis of septic arthritis of the hip and transient synovitis of the hip using the assessment of 4 independent predictors: history of fever, unwillingness to bear weight, erythrocyte sedimentation rate (ESR) > 40 mm/hr, and a serum white blood cell count > 12,000 cells/mm3. They rightly state the importance of validating a test on a population different from that from which it was derived, and also rightly state that the performance of the test should be expected to be poorer in the validation study.