IMPACT OF INTRA-ARTICULAR INJECTION OF METHYLENE BLUE ON MICROBIOLOGICAL SAMPLING IN PERIPROSTHETIC JOINT INFECTION: PERSPECTIVE AND RETROSPECTIVE EXPERIMENTAL STUDY

Introduction & Aim Periprosthetic joint infection (PJI) remains a major complication of prosthetic surgery. Radical debridement and accurate microbiological identification are essential components of surgical treatment. Intra-articular injection of methylene blue (MB) allows identification of pathological tissues to be removed through selective staining; however, its known antimicrobial effect may compromise the viability of microbiological samples. The aim of this study was to evaluate the antimicrobial activity of methylene blue and its impact on intraoperative microbiological diagnostics in the treatment of PJI. Methods A two-level analysis was conducted. First, a retrospective case–control study included patients undergoing surgical treatment for confirmed PJI. Patients were divided into those receiving intraoperative MB infiltration (MB group) and those treated without MB (standard group). The primary outcome was the rate of negative intraoperative cultures; concordance between preoperative and intraoperative isolates was also evaluated in a subgroup of patients with available preoperative microbiological data. Second, a prospective in vivo study was performed on patients undergoing surgery for PJI. For each patient, paired synovial tissue samples were obtained before and after intra-articular infiltration of diluted MB allowing direct comparison within the same biological environment. Results In the retrospective cohort (n=90), MB was used in 21 cases. The overall rate of negative intraoperative cultures was 10%, with no significant difference between the MB group (19%) and the standard group (7%) (p=0.2048). Among patients with available preoperative isolates (n=35), no significant differences were observed in concordance between pre- and intraoperative microbiological findings between groups (p=0.4830). In the prospective cohort (n=20), complete concordance (100%) was observed between paired samples obtained before and after MB infiltration. In positive cases, identical pathogens and equivalent bacterial loads were detected in both samples. No adverse events related to MB use were recorded. Conclusions Intraoperative use of methylene blue does not appear to compromise the viability of microbiological samples or the diagnostic accuracy of intraoperative cultures in PJI. Despite its demonstrated antimicrobial activity in vitro, this effect does not translate into clinically significant interference under in vivo conditions. These findings support the safe use of MB as an adjunct to improve surgical debridement without negatively impacting microbiological diagnostics.