Prognostic Implications of Unexpected Positive Intraoperative Cultures in Two-Stage Knee Arthroplasty Reimplantations: A Minimum Five-Year Retrospective Analysis

BackgroundThe clinical challenge of unexpected positive intraoperative cultures (UPICs) persists in two-stage resection arthroplasty for managing periprosthetic joint infections (PJIs) following total knee arthroplasty (TKA). This study aimed to investigate the incidence of UPICs during the definitive reimplantation phase of two-stage resection arthroplasty of the knee and to assess both the infection- and revision-free survivorship of the implanted prosthesis.MethodsThis retrospective study included 450 two-stage resection arthroplasties of primary knee prostheses performed between January 2012 and April 2017. Patients were excluded if they: (1) underwent three or more staged resections; (2) had ambiguous clinical documentation or deviated from the two-stage protocol; or (3) underwent revision arthroplasty prior to the PJI. Additionally, patients presumed aseptic before the second-stage reimplantation were excluded if they lacked joint aspiration or met the 2011 Musculoskeletal Infection Society (MSIS) criteria for PJI before implantation.ResultsAfter exclusions, 300 patients were analyzed. Among them, 14% had UPIC during the second-stage reimplantation. The follow-up time was 2,316 (range, 1,888 to 3,737) days and 2,531 (range, 1,947 to 3,349) days for UPIC and negative intraoperative culture (NIC) groups, respectively. Re-revision due to subsequent PJI occurred in 26.2% of UPIC patients and 15.1% of NIC patients. The 2-year infection-free survival rates for the NIC, 1 UPIC, and ≥ 2 UPIC cohorts were 99.5, 98.2, and 94.3%, respectively, while the 5-year survival rates were 92.1, 91.1, and 54.3%, respectively. The unfavorable survivorship was significantly different in multiple UPIC cases (P < 0.001). Multiple UPICs with pathogens consistent with the first-stage findings were strongly associated with the risk of reinfection (P < 0.001).ConclusionsAn UPIC was identified in 14% of second-stage reimplantations. Patients who had multiple UPICs demonstrated truncated survivorship and suboptimal outcomes relative to the NIC and single UPIC cohorts, especially with pathogen consistency to the first-stage surgery.