Intraoperative Purulence Is Not Reliable for Diagnosing Periprosthetic Joint Infection

Purulence, defined as presence of pus, is based on subjective interpretation yet has been considered a definite sign of periprosthetic joint infection (PJI). 583 patients undergoing revision arthroplasty due to presumed PJI were retrospectively studied. PJI definition was independent of purulence, based on the definition of Musculoskeletal Infection Society recently modified by International Consensus Group on PJI. 498 patients fulfilled the criteria for definite PJI and 59 patients were deemed as aseptic. Purulence had sensitivity, specificity, positive and negative predictive values of 0.82, 0.32, 0.91, and 0.17, respectively. Purulence was not correlated with higher culture positivity yet was associated with higher synovial WBC counts (mean of 34.8 versus 5.2 × 10³/μL in patients without purulence [P < 0.001]). In the absence of objective definition for purulence and in light of its inadequate test characteristics compared to a multi-criteria definition, purulence cannot serve as a single absolute diagnostic criterion for PJI. Level of Evidence: Level I, Diagnostic Studies.