Data from the Swiss National Arthroplasty Registry SIRIS suggest that unicompartmental knee arthroplasty is associated with a lower risk of periprosthetic joint infection than total knee arthroplasty

Periprosthetic joint infection (PJI) remains a severe complication in arthroplasty. Unicompartmental knee arthroplasty (UKA) may have lower PJI rates than total knee arthroplasty (TKA) because of smaller implants and less extensive surgical exposure. However, PJI treatment after UKA is challenging due to restricted debridement and limited options for local antibiotic delivery. This study compared the revision rate for PJI and the failure rate of implant-retaining revision for PJI between UKA and TKA in the Swiss national joint registry (SIRIS). A retrospective analysis was conducted using SIRIS data from 2012 to 2024, examining the first revision after primary UKA or TKA and the re-revision rate after debridement with isolated inlay exchange for PJI. Both analyses assessed revisions for any cause and specifically for PJI. Kaplan-Meier survival curves and hazard ratios (HR) were calculated. Among 35’286 primary UKA and 188’952 primary TKA, 149 and 1’546 were revised for PJI, respectively. Revision rates for any cause were higher for UKA than TKA (HR 1.29, p < 0.001), whereas PJI-related revisions were about half as frequent (HR 0.53, p < 0.001). Following implant-retaining revision for PJI, repeat revision rates increased more rapidly for UKA than TKA, reaching 34.8% and 32.1%, respectively (HR 1.56, p = 0.099). The statistical precision for UKA was limited by small numbers. In SIRIS, the revision rate for PJI after primary UKA was about half that after primary TKA, while the revision rate for any cause was higher. These findings support the hypothesis that smaller implants and less extensive surgery may be associated with lower infection risk. Despite limited debridement options, implant-retaining revision for PJI after UKA was as successful as after TKA. Nonetheless, failure rates for such procedures remain high in Switzerland, at roughly one-third.