An increased body mass index was not associated with higher rates of 30-day postoperative complications after unicompartmental knee arthroplasty

Background: The association of postoperative complications and obesity after total knee arthroplasty (TKA) has been well described. However, the effect of an increased body-mass index (BMI) on postoperative complications after unicompartmental knee arthroplasty (UKA) is controversial. Therefore, our aim was to assess the influence of BMI on 30-day postoperative complications after UKA when analyzed as both a categorical and continuous variable. Methods: The American College of Surgeons National Quality Improvement Program (NSQIP) database was used to identify a total of 8029 patients who underwent UKA from January 1, 2008, to December 31, 2016. The database was queried for over 30 unique complications occurring within 30 days. The impact of BMI on short-term outcomes was assessed as a categorical variable using univariate and multivariate regression. Additionally, BMI was assessed as a continuous variable using spline regressions. Results: Univariate regression analysis revealed that compared to normal weight patients, overweight patients had a lower risk of major complication (odds ratio [OR], 0.506; 95% confidence interval [CI], 0.279-0.918; p = 0.025), and any complication ([OR] 0.632; 95% CI, 0.423-0.944; p = 0.025) Multivariate regression analysis found no statistically significant relationship between categorical BMI and complications or outcomes, except for morbidly obese patients who had a greater risk of superficial SSI (p = 0.026). Spline regression found no statistically significant non-linear relationships between BMI and any complication (p = 0.4687), major complications (p = 0.1567), or minor complications (p = 0.4071). Conclusion: Overweight and obese individuals who undergo UKA may not have an increased risk of 30-day postoperative complications compared to normal weight individuals. (C) 2019 Elsevier B.V. All rights reserved.