How to Tell a Septic Hip from Transient Synovitis

On the Shoulders of Giants

I'm hip enough for this study.
This was a validation of a prior clinical decision rule to distinguish transient synovitis of the hip vs. septic arthritis, based on four independent predictors (the Kocher Criteria):

  1. a history of fever > 38.5C (101.3F)
  2. non-weight-bearing
  3. an erythrocyte sedimentation rate of 40 mm/hr or more
  4. and a serum white blood-cell count of >12,000 cells/mm(3).

Overall diagnostic performance was 0.86 AUROC (area under the receiver operating characteristic curve) vs 0.96 in the derivation study.  A perfect test would be an AUROC of 1.  Sensitivity with 1 of 4 predictors was 100%; specificity 26%.  Sensitivity was 90% with any 2 predictors; specificity 68%.  The authors thought the study was limited because CRP was not available at their hospital during enrollment and thought it would have improved the rule as a predictor.

How should we use this in practice?  If a child has fever and limp or no fever and presents non-weight bearing, they need lab evaluation.  If they have no concerning labs, the probability of septic arthritis is very low, but only children with no predictors are unequivocally safe for discharge.  Any child with 1 or more predictors needs orthopedic consultation to consider hip arthrocentesis or admission for observation.

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