Feasibility of Flow Cytometric Bacterial Count in Synovial Fluid to Detect Periprosthetic Joint Infection in Hip and Knee Arthroplasty

Background: Rapid and accurate preoperative diagnosis of periprosthetic joint infection (PJI) in patients undergoing revision arthroplasty remains challenging. Intraoperative differentiation between PJI and aseptic failure is limited by the lack of rapid and reliable diagnostic tools. Flow cytometric bacterial cell count of synovial fluid may represent a promising adjunct in this setting. This study explores the feasibility of using flow cytometric bacterial count of synovial fluid in the detection of PJI in patients during revision arthroplasty. Methods: In this exploratory pilot study, 93 patients provided informed consent. After exclusion of dry taps (n = 33), synovial fluid samples were collected intraoperatively from 60 patients undergoing revision total hip (THA) or total knee arthroplasty (TKA) at three hospitals in the Netherlands. Sixty samples were analyzed using the Sysmex UF-4000 to quantify flow cytometrically bacterial cells. Infection status was retrospectively determined according to the criteria of the European Bone and Joint Infection Society (EBJIS). Group differences were assessed using non-parametric analyses. Results: After exclusions due to dry taps and technical issues, samples of 43 patients could be analyzed. Of these patients, 16 had a confirmed PJI. Bacterial counts were significantly higher in patients with PJI compared with aseptic failure (median 1029 [IQR 287–4089] vs. 251 [IQR 92–433], p < 0.01). Conclusions: Flow cytometric synovial fluid analysis using the Sysmex UF-4000 demonstrated the ability to differentiate between patients with a PJI and with aseptic failure based on bacterial counts. However, this study was underpowered for diagnostic accuracy claims, and the feasibility of using flow cytometric bacterial count over established parameters such as total leukocyte and PMN% remains unclear at this stage.