In the United States, one-third of adults are considered obese, and demand for total knee arthroplasty (TKA) is expected to rise in these patients. Surgeons are reluctant to operate on obese patients, but it is important to understand how obesity has affected TKA utilization. This study utilizes a national database to evaluate incidence, demographics, outcomes, charges, and cost in nonobese, overweight, nonmorbidly obese, and morbidly obese TKA patients. We queried the National Inpatient Sample from 2009 to 2016 for primary TKA patients identifying 4,053,037 nonobese patients, 40,077 overweight patients, 809,649 nonmorbidly obese patients, and 428,647 morbidly obese patients. Chi-square was used to analyze categorical variables, and one-way analysis of variance was used to analyze continuous variables. Nonmorbidly obese and morbidly obese patients represented 23.2% of all TKAs. TKA utilization increased 4.1% for nonobese patients, 121.6% for overweight patients, 73.6% for nonmorbidly obese patients, and 83.9% for morbidly obese patients. Morbidly obese patients were younger (p < 0.001), female (p < 0.001), Black (p < 0.001), poor (p < 0.001), and utilized private insurance (p < 0.001). They also had the longest length of stay (p < 0.001) and the highest mortality rate (p < 0.001). More morbidly obese patients were discharged to other facilities (p < 0.001), and they had the highest rate of complications (p < 0.001). Patients with morbid obesity had the highest charges (p < 0.001), but overweight patients had the highest costs (p < 0.001). The results of this study demonstrate the rise in obese and morbidly obese patients seeking TKAs, which may be reflection of the obesity epidemic in America. Although TKA utilization has increased for morbidly obese patients, this body mass index (BMI) category also has the highest rates of charges and complications, suggesting morbid obesity to be a modifiable risk factor leading to worse surgical and economic outcomes. Obese patients undergoing TKA may benefit from preoperative optimization of their weight, in an effort to reduce the risk of adverse outcomes.
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