PERIPROSTHETIC JOINT INFECTION, PATELLOFEMORAL ARTHROSIS, AND ASEPTIC LOOSENING REMAIN THE MAIN REASONS FOR TOTAL KNEE ARTHROPLASTY FAILURE: A MULTICENTRE 24-YEAR STUDY

While large-scale data on total knee arthroplasty (TKA) failures are well established in national joint registries, recorded reasons for failure lack granularity. Understanding reasons for TKA failures is crucial for optimising patient outcomes. This study aimed to identify reasons for TKA failures and trends in failure over the last two decades. A total of 20,235 primary TKAs were identified across the three Auckland tertiary hospitals from 2000–2023. Clinical coding and national joint registry data were cross-referenced to identify any ‘failures’, defined as subsequent revision or reoperation for periprosthetic joint infection (PJI). Failure reasons were determined from systematic review of operative notes, microbiology, and imaging. For revisions outside of Auckland, records were obtained from operating surgeons. For analysis, failures were grouped by time from index procedure (five-year bands) and by year (2000-2014, 2014-2023) and compared using chi-squared tests. A total of 714 failures were identified (3.5%). The three most common reasons were PJI (51.2%), patellofemoral (PF) arthrosis (15%), and aseptic loosening (12.2%). The proportion of PJI failures was greatest at early follow-up (56% within 5 years of index procedure vs. 21% at 15-20 years, p<0.001), whereas aseptic loosening was more prevalent at late follow-up (29% at 15-20 years vs. 9% within 5 years, p<0.001). PF arthrosis rates were consistent across 20 years (p=0.14). PJI failures increased from 43% of all failures in 2000-2014 to 61% in 2014-2024 (p=0.02). There was no difference for aseptic loosening (2000-2014: 14% vs. 2014- 2024: 10%, p=0.51) or PF arthrosis (2000-2014: 14% vs. 2014-2024: 16%, p=0.84). PJI remains the leading cause for failure, while proportions of failures due to aseptic loosening and PF arthrosis are unchanged over the last two decades. These findings emphasize the need for continued optimisation of infection control, implant development and patient selection strategies for TKA.