Background: Distinguishing septic arthritis from transient synovitis
of the hip in children can be challenging. Authors of recent retrospective
studies have used presenting factors to establish algorithms for predicting
septic arthritis of the hip in children. This study differs from previous work
in three ways: data were collected prospectively, C-reactive protein levels
were recorded, and the focus was on children in whom the findings were so
suspicious for septic arthritis that hip aspiration was performed.
Methods: Over four years, we prospectively collected data on every
child (a total of fifty-three) who underwent hip aspiration because of a
suspicion of septic arthritis at our institution. Diagnoses of confirmed
septic arthritis, presumed septic arthritis, and transient synovitis were
determined on the basis of the results of Gram staining, culture, and a cell
count of the hip aspirate. Presenting factors and laboratory values were
recorded. To evaluate the strength of predictors, we performed univariate and
multivariate analysis on data from forty-eight patients who met the inclusion
criteria.
Results: Univariate analysis showed that fever, the C-reactive
protein level, and the erythrocyte sedimentation rate were strongly associated
with the final diagnosis (p < 0.05). On multivariate analysis, the
C-reactive protein level and erythrocyte sedimentation rate were found to be
significant predictors. However, the erythrocyte sedimentation rate was not
independent of the C-reactive protein level on backward elimination, and the
C-reactive protein level was the only risk factor that was strongly associated
with the outcome at a 5% significance level. Patients with five predictive
factors had a 98% chance of having septic arthritis, those with four factors
had a 93% chance, and those with three factors had an 83% chance.
Conclusions: This prospective study of children who presented with
findings that were highly suspicious for septic arthritis of the hip builds on
the work of previous authors. We found fever (an oral temperature
>38.5°C) was the best predictor of septic arthritis followed by an
elevated C-reactive protein level, an elevated erythrocyte sedimentation rate,
refusal to bear weight, and an elevated serum white blood-cell count. In our
study group, a C-reactive protein level of >2.0 mg/dL (>20 mg/L) was a
strong independent risk factor and a valuable tool for assessing and
diagnosing children suspected of having septic arthritis of the hip.
Level of Evidence: Diagnostic Level I. See Instructions
to Authors for a complete description of levels of evidence.