Obesity paradox among patients undergoing total knee arthroplasty: a retrospective cohort study

BACKGROUND: Obesity has been recognized as the risk factor for postoperative complication for surgical patients. However, recent studies have showed protective effect of obesity in surgical and non-surgical patients. Our study is to examine the association of body mass index(BMI) with early postoperative complications in patients undergoing total knee arthroplasty. MATERIALS AND METHODS: All patients who had primary total knee arthroplasty between January 2014 and December 2019 were included. Medical records were retrospectively reviewed and BMI was categorized as underweight(BMI < 18.5), normal weight(18.5 < BMI < 24.9), overweight I(25 < BMI < 27.4), overweight II(27.5 < BMI < 29.9), obese I(30 < BMI < 34.9) and obese II(BMI ≥ 35). The association between BMI and occurrence of early postoperative complications was examined and logistic regression was used to calculate relationship between BMI and early postoperative complications. RESULTS: A total of 2969 patients were included in our analysis. The overall complication rate in patients undergoing total knee arthroplasty was 14.8%, with the highest complication being 22.2% in the underweight group, the second highest in the normal weight group(17.5%), the lowest in the overweight I(13.8%) and obese I(12.0%) group and then higher again in obese II group(16.7%). In multivariable analyses, overweight I (OR 0.737, 95% CI 0.559–0.972, P = 0.031) and obese I (OR 0.631, 95% CI 0.449–0.885, P = 0.008) were associated with lower risk of early postoperative complications after total knee arthroplasty. CONCLUSION: In this retrospective study, overweight and obese patients had a lower risk of early postoperative complications after total knee arthroplasty. Further studies are necessary to confirm and investigate the mechanism of obesity paradox in this surgical population. TRIAL REGISTRATION: This study had been registrated in www.chictr.org.cn on 25/10/2021 and the registration ID was ChiCTR2100052408.