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

Background: The clinical challenge of unexpected positive intraoperative cultures (UPICs) persists in 2-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 2-stage resection arthroplasty of the knee and to assess both the infection-free and revision-free survivorship of the implanted prosthesis.

Methods: This retrospective study included 450 2-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 2-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 criteria for PJI before implantation.

Results: After 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. Rerevision 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, one UPIC, and ≥ two 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).

Conclusions: An 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.

Level of evidence: III.