Effect of Age on Cost-Effectiveness of Unicompartmental Knee Arthroplasty Compared with Total Knee Arthroplasty in the U.S.

Background: Trade-offs between upfront benefits and later risk of revision of unicompartmental knee arthroplasty compared with those of total knee arthroplasty are poorly understood. The purpose of our study was to compare the cost-effectiveness of unicompartmental knee arthroplasty with that of total knee arthroplasty across the age spectrum of patients undergoing knee replacement. Methods: Using a Markov decision analytic model, we compared unicompartmental knee arthroplasty with total knee arthroplasty with regard to lifetime costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs) from a societal perspective for patients undergoing surgery at forty-five, fifty-five, sixty-five, seventy-five, or eighty-five years of age. Transition probabilities were estimated from the literature; survival, from the Swedish Knee Arthroplasty Register; and costs, from the literature and the Healthcare Cost and Utilization Project (HCUP) database. Costs and QALYs were discounted at 3.0% annually. We conducted sensitivity analyses to test the robustness of model estimates and threshold analyses. Results: For patients sixty-five years of age and older, unicompartmental knee arthroplasty dominated total knee arthroplasty, with lower lifetime costs and higher QALYs. Unicompartmental knee arthroplasty was no longer cost-effective at a $100,000/QALY threshold when total knee arthroplasty rehabilitation costs were reduced by two-thirds or more for these older patients. Lifetime societal savings from utilizing unicompartmental knee arthroplasty in all older patients (sixty-five or older) in 2015 and 2020 were $56 to $336 million and $84 to $544 million, respectively. In the forty-five and fifty-five-year-old age cohorts, total knee arthroplasty had an ICER of $30,300/QALY and $63,000/QALY, respectively. Unicompartmental knee arthroplasty became cost-effective when its twenty-year revision rate dropped from 27.8% to 25.7% for the forty-five-year age group and from 27.9% to 26.7% for the fifty-five-year age group. Conclusions: Unicompartmental knee arthroplasty is an economically attractive alternative in patients sixty-five years of age or older, and modest improvements in implant survivorship could make it a cost-effective alternative in younger patients.