Outcomes of patients with unexpected diagnosis of infection at total hip or total knee arthroplasty revisions.

PURPOSE: The pre-operative differential diagnosis between periprosthetic joint infections (PJIs) and aseptic failure is challenging particularly in low virulence and biofilm-related infections. This study aimed to assess the incidence and survival of patients with unexpected PJIs in a presumed aseptic revision of total hip (THA) and knee (TKA) arthroplasties. METHODS: A retrospective analysis of a prospective cohort of patients was performed with 295 patients undergoing THA (n = 241) or TKA (n = 54) revision for presumed aseptic causes. Patients were diagnosed with unexpected PJI taking into account leukocyte count in the synovial fluid, sonicate, synovial culture, and tissue cultures of samples collected during surgery. The primary endpoint was the infection-free implant survival rate at theone year follow-up. RESULTS: The unexpected PJIs were 60 out of 295 (20.3%), whereas 235 (79.7%) were aseptic revisions. In the unexpected PJI group, 6 (11.1%) patients underwent knee revision and 54 (22.4%) hip revision. At the one year follow-up, one patient (1.6%) in the unexpected PJI group and 3 (1.3%) in the aseptic group (p = 1.0) failed for infection. The infection-free implant survival rate at the one year follow-up was 98.3% (C.I. 95%, 94.9-99.9%) for the unexpected PJI group and 98.7% (C.I. 95%, 97.3-99.9%) (p = 0.82) for the aseptic group. CONCLUSION: The incidence of unexpected PJIs in a presumed aseptic revision of THAs and TKAs has been previously underestimated. The infection-free implant survival rate at the one year follow-up in patients with unexpected PJIs was not significantly lower compared with patients undergoing aseptic revision.