The John Insall Award: Morbid Obesity Independently Impacts Complications, Mortality, and Resource Use After TKA

Background The importance of morbid obesity as a risk factor for complications after total knee arthroplasty (TKA) continues to be debated. Obesity is rarely an isolated diagnosis and tends to cluster with other comorbidities that may independently lead to increased risk and confound outcomes. It is unknown whether morbid obesity independently affects postoperative complications and resource use after TKA. Questions/purposes The purpose of this study was to determine whether morbid obesity is an independent risk factor for inpatient postoperative complications, mortality, and increased resource use in patients undergoing primary TKA. Methods The Healthcare Cost and Utilization Project Nationwide Inpatient Sample (NIS) database was used to identify patients undergoing primary TKA from October 2005 to December 2008. Morbid obesity (body mass index ≥ 40 kg/m 2 ) was determined using International Classification of Diseases, 9 th Revision, Clinical Modification codes. In-hospital postoperative complications, mortality, costs, and disposition for morbidly obese patients were compared with nonobese patients. To control for potential confounders and comorbid conditions, each morbidly obese patient was matched to a nonobese patient using age, sex, and all 28 comorbid-defined elements in the NIS database based on the Elixhauser Comorbidity Index. Of 1,777,068 primary TKAs, 98,410 (5.5%) patients were categorized as morbidly obese. Of these, 90,045 patients (91%) were able to be matched one-to-one to a nonobese patient for the adjusted analysis. Results Morbidly obese patients had a higher risk of postoperative in-hospital infection (0.24% versus 0.17%; odds ratio [OR], 1.3; 95% confidence interval [CI], 1.1–1.7; p = 0.001), wound dehiscence (0.11% versus 0.08%; OR, 1.3; 95% CI, 1.0–1.7; p = 0.28), and genitourinary-related complications (0.60% versus 0.44%; OR, 1.3; 95% CI, 1.1–1.5; p