Cost-effectiveness of bariatric surgery prior to total knee arthroplasty in the morbidly obese a computer model-based evaluation

Background: Obesity is associated with adverse outcomes and increased costs after total knee arthroplasty. Bariatric surgery is an effective treatment for morbid obesity, but its cost-effectiveness for weight loss prior to total knee arthroplasty is unknown. The purpose of this study was to evaluate the cost-effectiveness of bariatric surgery prior to total knee arthroplasty for patients in whom medical treatment of obesity and knee osteoarthritis had failed. Methods: A state-transition Markov model was constructed to compare the cost-utility of two treatment protocols for patients with morbid obesity and end-stage knee osteoarthritis: (1) immediate total knee arthroplasty and (2) bariatric surgery two years prior to the total knee arthroplasty. The probability of transition for each health state and its utility were derived from the literature. Costs, expressed in 2012 United States dollars, were estimated with use of administrative and claims data. Costs and utilities were discounted at 3% annually, and effectiveness was expressed in quality-adjusted lifeyears (QALYs). The principal outcome measure was the incremental cost-effectiveness ratio (ICER). One-way, two-way, and probabilistic sensitivity analyses were performed, using $100,000 per QALY as the threshold willingness to pay. Results: Morbidly obese patients undergoing total knee arthroplasty alone had lower QALYs gained than patients who underwent bariatric surgery two years prior to the total knee arthroplasty. The ICER between these two procedures was approximately $13,910 per QALY, well below the threshold willingness to pay. Results were stable across broad value ranges for independent variables. Probabilistic sensitivity analysis found that the median ICER was $14,023 per QALY (95% confidence interval, $4875 to $51,210 per QALY). Conclusions: This model supports bariatric surgery prior to total knee arthroplasty as a cost-effective option for improving outcomes in morbidly obese patients with end-stage knee osteoarthritis who are indicated for total knee arthroplasty.