MICROBIOLOGICAL PROFILES AND ANTIBIOTIC RESISTANCE PATTERNS IN SHOULDER, HIP, AND KNEE PERIPROSTHETIC JOINT INFECTIONS: A FIVE-YEAR RETROSPECTIVE SINGLE-CENTRE COHORT STUDY

Introduction & Aim Periprosthetic joint infection (PJI) is a serious complication of joint arthroplasty. Increasing antimicrobial resistance complicates its management and may compromise treatment effectiveness. Understanding the local microbiological aetiology and resistance patterns of PJI is essential for guiding empirical antimicrobial therapy. This study aimed to characterise the pathogens causing PJI in the shoulder, hip, and knee, and to analyse their resistance profiles within a five-year single-centre cohort. Methods We retrospectively reviewed all microbiological samples collected from orthopaedic surgical procedures from June 2020 to March 2025. Microbiologically confirmed PJIs of the shoulder, hip, and knee were included and defined as: (i) at least two samples positive for the same microorganism with an identical susceptibility pattern from either tissue or tissue and synovial fluid; or (ii) one positive synovial fluid culture. An infection-episode was defined as 30 days from a PJI-related diagnostic or surgical procedure code. Results A total of 239 PJI episodes involving 278 isolated pathogens were identified in 200 patients. Monomicrobial infections accounted for 87% (n=208), while polymicrobial infections accounted for 13% (n=31). Staphylococcus aureus was the most frequently isolated pathogen (27%, n=74/278), followed by coagulase-negative staphylococci (26%, n=72/278). Gram-negative and anaerobic bacteria were also commonly isolated (12%, n=32/278). Conventional Danish empirical regimens, such as cefuroxime and cloxacillin, provided coverage for fewer than 70% of hip and knee PJIs and for approximately 85% of shoulder PJIs. Empirical regimens with over 90% coverage for hip and knee PJIs included vancomycin combined with meropenem, piperacillin–tazobactam, or ciprofloxacin. Vancomycin alone had similar coverage for shoulder PJIs. Conclusions Traditional Danish empirical antimicrobial regimens for PJI may provide inadequate coverage, especially for hip and knee PJIs. Our findings support tailoring empirical therapy for suspected PJI to the affected joint and local microbiological resistance patterns, rather than relying on standardised regimens, to improve antimicrobial effectiveness.