Combination of Synovial Fluid IL-4 and Polymorphonuclear Cell Percentage Improves the Diagnostic Accuracy of Chronic Periprosthetic Joint Infection

Abstract Background: Synovial fluid biomarkers have been confirmed with promising diagnostic value for chronic periprosthetic joint infection (PJI), even there was still no “gold standard”. Interleukin-4 (IL-4) and polymorphonuclear cells (neutrophil) count in synovial fluid play a crucial role in mediating local inflammation of bacterial infections and therefore could be valuable biomarkers for PJI. Methods: The purpose of this study was to investigate the diagnostic capacity of synovial fluid IL4 (SF-IL4) and polymorphonuclear cell percentage(SF-PMN%) for chronic PJI. According to the 2013 Musculoskeletal Infections Society(MSIS 2013) criteria, chronic PJI is defined as occurred more than 6 weeks after the primary arthroplasty. A total of 110 patients who scheduled to undergo revision arthroplasty from January 2019 to October 2020 were enrolled. 11 patients were eliminated by exclusion criteria. 43 of 99 patients were classified as infected and 56 as not infected. In all patients, SF-IL4 and SF-PMN% were measured in synovial fluid, serum CRP, ESR levels were measured preoperatively. The area under the curve(AUC) for each biomarker was analyzed, the diagnostic value and optimal cutoff values were calculated. Results: The demographic data was not statistically different. The SF-IL4 and SF-PMN% showed a great diagnostic accuracy of chronic PJI from aseptic failure patients with AUC of 0.97(95% confidence interval (CI), 0.92-0.99) and 0.89(95%CI, 0.82-0.95) separately, which was higher than the serum ESR (0.72), and serum CRP (0.83). We set 1.7 pg/mL and 75% as the optimal cut-off values of SF-IL4 and SF-PMN% individually. Combination of SF-IL4 and SF-PMN% improved the diagnostic ability for chronic PJI with a specificity of 97.0%, and 96.0% accuracy.Conclusion: Synovial fluid IL-4 was a valuable biomarker for chronic PJI detection. Combination of SF-IL4 and SF-PMN% provided higher specificity and accuracy when met the cut-off values of 1.7 pg/mL and 75% simultaneously.