Another look: is there a flaw to current hip septic arthritis diagnostic algorithms?

BACKGROUND: Septic arthritis is an emergency. In 1999 Kocher et al. identified four clinical criteria to distinguish hip septic arthritis from transient synovitis in children (nonweightbearing, erythrocyte sedimentation rate ≥ 40 mm/L, white blood cell count > 12 × 10(9)/L, temperature > 38.5°C). Subsequent authors evaluating the same criteria produced conflicting results. This calls into question the use of such diagnostic algorithms. The reasons for the differences remain unclear.

QUESTIONS/PURPOSES: To what degree do studies, evaluating the predictive ability of diagnostic algorithms for septic arthritis, differ with regard to their results? Why do these differences exist? Is there a flaw in the statistical handling of the data?

METHODS: Using PubMed, original studies evaluating the clinical criteria for distinguishing hip septic arthritis and transient synovitis in children were identified. Clinical and statistical methods were examined.

RESULTS: Six studies evaluated the clinical criteria. Two found all four criteria able to distinguish septic arthritis from transient synovitis. There was significant variation between the studies in the risk engendered by the presence of each criteria. The differences were the result of the fact that in all cases, sample sizes were too small and in three cases, there were too few episodes of septic arthritis for a reliable predictive algorithm to be produced.

CONCLUSIONS: Differing results between studies appear as a result of sample size and insufficient cases of septic arthritis in some cohorts. Transferable and reliable results can be achieved if sufficiently large samples with an adequate number of cases of septic arthritis are recruited.