Complications and Obesity in Arthroplasty—A Hip is Not a Knee

Background: Obesity has previously been demonstrated to be an independent risk factor for increased complications after total hip and knee arthroplasties (THA and TKA). The purpose of this study was to compare the effects of obesity and body mass index (BMI) to determine whether the magnitude of the effect was similar for both procedures. Methods: We queried the American College of Surgeons National Surgical Quality Improvement Program database to identify patients who underwent primary THA or TKA between 2010 and 2014. Patients were stratified by procedure and classified as nonobese, obese, or morbidly obese according to BMI. Thirty-day rates of wound complications, deep infection, total complications, and reoperation were compared using univariate and multivariate logistic regression analyses. Results: We identified 64,648 patients who underwent THA and 97,137 patients who underwent TKA. Obese THA patients had significantly higher rates of wound complications (1.53% vs 0.96%), deep infection (0.31% vs 0.17%), reoperation rate (2.11% vs 1.02%), and total complications (5.22% vs 4.63%) compared with TKA patients. Morbidly obese patients undergoing THA were also found to have significantly higher rates of wound complications (3.25% vs 1.52%), deep infection (0.84% vs 0.23%), reoperation rate (3.65% vs 1.60%), and total complications (7.36% vs 5.57%). Multivariate regression analysis identified increasingly higher odds of each outcome measure as BMI increased. Conclusion: This study demonstrates that the impact of obesity on postoperative complications is more profound for THA than TKA. This emphasizes the importance of considering patient comorbidities in the context of the specific procedure when assessing risks of surgery.