Optimal Incubation Time for Synovial-Fluid Cultures in Acute and Chronic Periprosthetic Joint Infection: A Retrospective Cohort Study

Background Standard 14-day incubation protocols for periprosthetic joint infections (PJIs) lack specificity.The optimal culture duration for distinct acute and chronic PJI remains undefined. This study aimed to define the microbial time-to-positivity (TTP) and distribution in different PJI categories to evaluate the feasibility of a stratified culture strategy. Methods This retrospective study analysed the medical records of patients from 1 June 2016 to 1 July 2024. Patients who met the Musculoskeletal Infection Society (MSIS) criteria and had positive intraoperative synovial-fluid cultures were classified into Early acute PJI, Late acute PJI, and Late chronic PJI based on clinical symptoms. The microbial spectrum and TTP of synovial-fluid specimens were recorded. The microbial profiles and detection rates of different PJI subtypes were compared across different time stages. Results We included 181 patients (mean age 65 years). Among them, 41 cases were Early acute PJI; 35 cases, Late acute PJI; and 105 Late chronic PJI. All pathogens recovered within 12 days. In Early acute PJI and Late acute PJI, 90.3 and 94.3% of pathogens, respectively, grew by day 7, whereas 96.2% of Late chronic PJI isolates required up to 10 days. The rate of new microbial detection decreased sharply after day 5 of incubation. After 7 days, delayed microbial growth was predominantly seen in the Late chronic PJI cohort. Previous antibiotic exposure did not significantly affect the growth of microorganisms in acute PJI (OR = 2.52, 95% CI 0.43–14.65; P = 0.31). Conclusion Previous use of antibiotics prolongs the incubation time of microorganisms but has a limited effect on the incubation time of microorganisms in acute PJI. A 7-day incubation period is sufficient to reliably detect pathogen in acute PJI. For chronic PJI, considering the delayed growth of some pathogen, at least 10 days of culture are required.