Management of pediatric patients with synovial fluid white blood-cell counts of 25,000 to 75,000 cells/mm³ after aspiration of the hip

Abstract

Background: In this study, we sought to elucidate the presentation, clinical course, treatments pursued, final diagnosis, and risk factors for septic arthritis in a series of children with hip pain and intermediate synovial fluid values (white blood-cell [WBC] counts of 25,000 to 75,000 cells/mm(3) [25 to 75 × 10(9) cells/L]).

Methods: We reviewed the records of pediatric patients who underwent hip aspiration between 2005 and 2012 at a tertiary-care pediatric hospital. Demographic data, laboratory values, final diagnosis, and treatment details were recorded for the subpopulation of patients with an aspirate WBC count of 25,000 to 75,000 cells/mm(3) (25 to 75 × 10(9) cells/L). Univariate and multivariable logistic regression analysis was used to assess risk factors for septic arthritis of the hip across final diagnostic groups and subgroups with WBC values of <50,000 and ≥50,000 cells/mm(3) (<50 and ≥50 × 10(9) cells/L).

Results: Forty-six children (twenty-seven males and nineteen females) with a mean age of 7.6 years met the inclusion criteria. The final diagnoses were septic arthritis of the hip (n = 15; 33%), Lyme arthritis (n = 13; 28%), transient synovitis (n = 8; 17%), and other findings (n = 10; 22%). Subjects with a synovial fluid WBC count of ≥50,000 cells/mm(3) (≥50 × 10(9) cells/L) were more likely to be diagnosed with septic arthritis of the hip (odds ratio, 4.4; 95% confidence interval, 1.1 to 16.9; p = 0.03). While septic arthritis of the hip was the most common diagnosis (48%) in patients with WBC values of ≥50,000 cells/mm(3) (≥50 × 10(9) cells/L), it also represented 17% of cases with WBC values of <50,000 cells/mm(3) (<50 × 10(9) cells/L).

Conclusions: Septic arthritis of the hip is the most common ultimate diagnosis in children with synovial fluid WBC values of 25,000 to 75,000 cells/mm(3) (25 to 75 × 10(9) cells/L) following hip aspiration, and it should be high on the differential diagnosis, even in cases with synovial fluid WBC values of <50,000 cells/mm(3) (<50 × 10(9) cells/L).