Temporal trends in the rate of complications and prolonged length of stay relative to body mass index in patients undergoing total knee arthroplasty from 2012 to 2020

Background: Elevated body mass index (BMI) is a risk factor for complications following total knee arthroplasty (TKA). Thus, we believe it is important to constantly re-evaluate the relationship between BMI and complication risk following TKA. Method: Patients undergoing primary TKA were identified in a national database from 2012-2020. Rates of major complications, minor complications, and length of stay (LOS) greater than 2 days were calculated. The prevalence of postoperative outcomes were calculated per unit of BMI and then multiplied by a factor of 10^{^2} or 10^{^3} in order to create adjusted-BMI (aBMI). To isolate the effect of aBMI on postoperative outcomes, changes over time were analyzed using linear regression analysis controlling for age, sex, American Society of Anesthesiology (ASA) classification and smoking status. Results: 365,333 patients were included. Mean BMI 33 ± 6.8. 10,616 (2.9%) of patients had a major postoperative complication, 9,345 (2.6%) minor complications, 3,277 (0.9%) had a deep or superficial surgical site infection (SSI). 133,563 (37%) of patients had LOS > 2 days. From 2012-2020, the ratio of major complications to aBMI decreased significantly by an average of −2.7% per year. The ratio of patients with LOS > 2 days to aBMI decreased significantly by −27% per year. The ratio of SSI to aBMI increased significantly by 10.8% per year. Conclusions: From 2012 to 2020, the ratio of major complications and extended LOS following TKA as a function of BMI has decreased significantly, while the ratio of SSI as a function of BMI has doubled.