Advancing diagnostics in suspected periprosthetic joint infections using synthetic synovial fluid and microcalorimetry

Abstract. Rapid and accurate pathogen detection is essential for effective management of periprosthetic joint infections (PJIs), yet conventional culturing (CC) often yields false-negative results and requires prolonged incubation times. In the present study we compared the performance of CC to that of two alternative approaches, i.e., culturing in synthetic synovial fluid (SSF2) and isothermal microcalorimetry (IMC). A total of 79 synovial fluid (SF) samples from patients with suspected PJI were included; for these samples, CC data were available. Samples were incubated in SSF2 (aerobically and anaerobically, for 10 d), and isolates were identified by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). With IMC we determined the time to detect microbial activity in the samples (in two different media; brain heart infusion (BHI) broth and fluid thioglycolate medium (FTM)). Culturing in SSF2 yielded the highest positivity rate (53.2 %), followed by IMC and CC (34.2 % and 32.9 %, respectively). More than one-third of all positive samples were detected only after culturing in SSF2 (39.3 %), and this approach also revealed the greatest microbial diversity. IMC enabled rapid detection of microbial activity in a sample, with median detection times of 15.9 h in BHI and 15.6 h in FTM. Our results demonstrate that culturing of SF samples in SSF2 increased the diagnostic yield and that IMC reduced the time to identify clinical samples that contain viable microorganisms. This highlights the potential of these approaches; however further optimization is warranted to integrate them in diagnostic PJI workflows.