Background: Differentiation between septic arthritis and transient
synovitis of the hip in children can be difficult. Kocher et al. recently
developed a clinical prediction algorithm for septic arthritis based on four
clinical variables: history of fever, non-weight-bearing, an erythrocyte
sedimentation rate of =40 mm/hr, and a serum white blood-cell count of
>12,000/mm3 (>12.0 × 109/L). The purpose of
this study was to apply this clinical algorithm retrospectively to determine
its predictive value in our patient population.
Methods: A retrospective review was performed to identify all
children who had undergone a hip arthrocentesis for the evaluation of an
irritable hip at our institution between 1992 and 2000. One hundred and
sixty-three patients with 165 involved hips satisfied the criteria for
inclusion in the study and were classified as having true septic arthritis
(twenty hips), presumed septic arthritis (twenty-seven hips), or transient
synovitis (118 hips).
Results: Patients with septic arthritis (true and presumed;
forty-seven hips) differed significantly (p < 0.05) from patients with
transient synovitis (118 hips) with regard to the erythrocyte sedimentation
rate, differential of serum white blood-cell count, total white blood-cell
count and differential in the synovial fluid, gender, previous health-care
visits, and history of fever. If the four independent multivariate predictors
of septic arthritis proposed by Kocher et al. were present, the predicted
probability of the patient having septic arthritis was 59% in our study, in
contrast to the 99.6% predicted probability in the patient population
described by Kocher et al. Statistical analyses demonstrated that the best
model to describe our patient population was based on three variables: a
history of fever, a serum total white blood-cell count of
>12,000/mm3 (>12.0 × 109/L), and a previous
health-care visit. When all three variables were present, the predicted
probability of the patient having septic arthritis was 71%.
Conclusions: Although the use of a clinical prediction algorithm to
differentiate between septic arthritis and transient synovitis may have
improved the utility of existing technology and medical care to facilitate the
diagnosis at the institution at which the algorithm originated, application of
the algorithm proposed by Kocher et al. or of our three-variable model does
not appear to be valid at other institutions.
Level of Evidence: Diagnostic study, Level I-1 (testing
of previously developed diagnostic criteria in series of consecutive patients
[with universally applied reference "gold" standard]). See
Instructions to Authors for a complete description of levels of evidence.