Age and C-reactive protein as modifiers of Kocher criteria in pediatric septic knee monoarthritis

Introduction: Although Kocher criteria can distinguish a septic hip from an aseptic cause, they may not apply to a septic knee. We aimed to identify predictors to discriminate septic and aseptic causes of acute knee monoarthritis in children who underwent arthrocentesis.Methods: We conducted a retrospective cohort study among children who underwent arthrocentesis for suspected septic arthritis of the knee. Collected data included demographic, clinical and laboratory characteris-tics. We performed univariate and multivariable analyses to identify predictors of the septic knee. We further investigated accuracy of different predictive models.Results: A total of 60 patients who underwent arthrocentesis for suspected knee septic arthritis were included in this study. Septic arthritis of the knee was confirmed in 32 (53%) patients. Age & LE; 5 years (OR 4.237, [95% CI 1.270-14.127], p = 0.019), WBC > 12,000 cells/mm3 (OR 5.059, [95% CI 1.424-17.970], p = 0.012), and CRP > 2 mg/dL (OR 3.180, [0.895-11.298], p = 0.074) were the most important predictors of a septic knee. Three-tier model comprising these three factors (AUC 0.766) and 4-tier model with addition of fever > 38.5 & DEG;C (AUC 0.776) performed better than Kocher criteria (AUC 0.677), modified Kocher criteria (AUC 0.699) and Full Model (adding age & LE; 5 years and CRP > 2 mg/dL to Kocher criteria) (AUC 0.746). Full Model successfully ruled out septic arthritis if all 6 criteria were negative.Conclusion: Based on these findings, we propose an algorithm to identify low, intermediate and high-risk patients for knee septic arthritis. Our proposed two-step algorithm incorporating major (age, WBC, CRP) and minor (fever, ESR, non-weight bearing) criteria can serve as a simple decision-support tool to justify arthrocentesis in children with suspected knee septic arthritis.(c) 2022 Elsevier Inc. All rights reserved.