Obesity and Primary Total Knee Arthroplasty: The Absolute Versus Relative Risk of Periprosthetic Joint Infection at 15 Years

Background: When indicating patients for primary total knee arthroplasty (TKA), surgeons and patients must understand the absolute and relative risks of periprosthetic joint infection (PJI) to make an informed decision. We sought to evaluate the long-term risk of PJI following primary TKA stratified by body mass index (BMI) and PJI-related risk factors. Methods: We identified 25,160 primary TKAs performed from 2000 to 2021 at a single institution. Patients were stratified as having 0, 1, or >= 2 PJI risk factors (diabetes, chronic kidney disease, nonprimary osteoarthritis, immunosuppression, or active smoking) and into BMI categories. The 15-year cumulative risk of PJI was evaluated by BMI and PJI risk factors. Results: For the entire cohort, the 15-year absolute risk of PJI was 3%. For patients who did not have PJI risk factors, the absolute risk of PJI at 15 years was 3% in normal weight, 4% in class III obesity, and 4% in class IV obesity. Patients who had class III obesity had a 3-time higher relative risk of PJI when than normal-weight patients (P = 0.01). Among patients who had >= 2 PJI risk factors, the absolute risk of PJI at 15 years was 5% in normal weight and 6% in patients who have class III obesity. Conclusions: Healthy patients who had class III obesity had a 3-time increased risk of PJI relative to healthy, normal-weight patients; however, the absolute risk of PJI at 15 years after primary TKA was 4% in this group. Surgeons and patients must consider both a 3-time increased relative risk of PJI and a 4% absolute risk of PJI at 15 years after primary TKA when considering surgery in otherwise healthy patients who have BMI >= 40. Level of Evidence: IV. (c) 2024 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.