Synovial Fluid MicroRNA Biomarkers Enable Accurate Diagnosis of Hip and Knee Periprosthetic Joint Infections.

backgroundDiagnosing hip and knee periprosthetic joint infections (PJIs) is challenging, necessitating sensitive and specific biomarkers for accurate diagnosis. Cell-free microRNAs (miRNAs) are emerging as noninvasive biomarkers. We hypothesized that hip and knee PJIs are associated with unique cell-free miRNA profiles in synovial fluid, which can be used for the diagnosis of infection.

methodsSynovial fluid samples from 173 Caucasian patients undergoing septic or aseptic revision total joint replacement (TJR) of the hip or knee, as well as samples from 6 osteoarthritic knees, were analyzed. The samples were divided into a discovery group (40 samples; 50% septic) and a validation cohort (133 samples; 35% septic). Small RNA next-generation sequencing (NGS) was used to screen miRNAs in the discovery samples, with reverse transcription-quantitative polymerase chain reaction (RT-qPCR) used to confirm the NGS findings and to validate results in the independent, larger cohort. Logistic regression and cross-validation were applied to assess the diagnostic power of individual and combined miRNAs.

resultsNGS identified 132 miRNAs with significant differences (false discovery rate < 0.05) between the septic and aseptic synovial fluid samples. Of these, 18 miRNAs were further analyzed with use of RT-qPCR in the independent cohort, with miR-223-3p and miR-338-5p showing the highest increases in septic synovial fluid (log2 fold change >4) and miR-151a-3p and miR-214-3p showing the most substantial reductions. To investigate the performance of the multivariable models, logistic regression was performed by dividing the cohort into a training set (60%) and a test set (40%), which showed improved performance relative to that of the univariate models (median area under the curve [AUC] for the multivariable models, 0.96). A subgroup analysis by joint type, gender, and synovial fluid sample preparation confirmed robust miRNA biomarker performance for PJI.

conclusionsCell-free miRNA levels in the synovial fluid of patients undergoing septic hip or knee TJR were altered in response to infection, indicating immune cell activity in the joint. These miRNAs offer sensitive and specific pathogen-independent biomarkers with potential clinical applications in the diagnosis of hip and knee PJI. LEVEL OF EVIDENCE: Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.