Time to move beyond BMI alone in predicting arthroplasty infections: A large single-center retrospective cohort study

Background and Aims: A high body mass index (BMI) has traditionally been a strict criterion for surgical eligibility for arthroplasty based on the increased risk for periprosthetic joint infection (PJI). Individuals with obesity are two to four times more likely to undergo joint arthroplasty. There are limited data on how well BMI predicts PJI risk and whether strict BMI-based surgical criteria are justified. Methods: This retrospective single-center cohort study included all primary total hip arthroplasties (THAs) and total knee arthroplasties (TKAs) performed at our institution between 1 January 2008 and 28 November 2023. Survival was analyzed using the Kaplan–Meier method, with PJI as the primary outcome. The association between BMI and PJI was assessed using logistic regression and Cox proportional hazards regression. Results: A total of 54,879 arthroplasties (23,544 hip and 31,335 knee arthroplasties) were included. The median age was 68 years (interquartile range (IQR): 60–75), and 60.0% of patients were female. The risk for PJI was highest in patients with a BMI >45. After THA, the lowest risk for PJI was seen with a BMI <25 (1.0%) and between 25 and 30 (1.1%) after TKA. After THA, a J-shaped association between BMI and PJI was observed in logistic regression analysis, as the risk for PJI increased in patients with both low and high BMIs. A J-shaped association between BMI and PJI was also observed in Cox regression analysis after both TKA and THA. Men had a higher risk for PJI after THA than women, whereas no sex variation was observed after TKA. Conclusion: The risk for PJI does not increase linearly with BMI and the risk differs between women and men. When BMI exceeds 45, risk levels become notably high. Otherwise, the absolute risk differences between different BMI categories are relatively low. Emphasis should be placed on individualized risk assessment and shared decision-making rather than focusing solely on BMI.