The cost-effectiveness of surgical treatment of medial unicompartmental knee osteoarthritis in younger patients: a computer model-based evaluation

Abstract

Background: Surgical options for the management of medial compartment osteoarthritis of the varus knee include high tibial osteotomy, unicompartmental knee arthroplasty, and total knee arthroplasty. We sought to determine the cost-effectiveness of high tibial osteotomy and unicompartmental knee arthroplasty as alternatives to total knee arthroplasty for patients fifty to sixty years of age.

Methods: We built a probabilistic state-transition computer model with health states defined by pain, postoperative complications, and subsequent surgical procedures. We estimated transition probabilities from published literature. Costs were determined from Medicare reimbursement schedules. Health outcomes were measured in quality-adjusted life-years (QALYs). We conducted analyses over patients' lifetimes from the societal perspective, with health and cost outcomes discounted by 3% annually. We used probabilistic sensitivity analyses to account for uncertainty in data inputs.

Results: The estimated discounted QALYs were 14.62, 14.63, and 14.64 for high tibial osteotomy, unicompartmental knee arthroplasty, and total knee arthroplasty, respectively. Discounted total direct medical costs were $20,436 for high tibial osteotomy, $24,637 for unicompartmental knee arthroplasty, and $24,761 for total knee arthroplasty (in 2012 U.S. dollars). The incremental cost-effectiveness ratio (ICER) was $231,900 per QALY for total knee arthroplasty and $420,100 per QALY for unicompartmental knee arthroplasty. Probabilistic sensitivity analyses showed that, at a willingness-to-pay (WTP) threshold of $50,000 per QALY, high tibial osteotomy was cost-effective 57% of the time; total knee arthroplasty, 24%; and unicompartmental knee arthroplasty, 19%. At a WTP threshold of $100,000 per QALY, high tibial osteotomy was cost-effective 43% of time; total knee arthroplasty, 31%; and unicompartmental knee arthroplasty, 26%.

Conclusions: In fifty to sixty-year-old patients with medial unicompartmental knee osteoarthritis, high tibial osteotomy is an attractive option compared with unicompartmental knee arthroplasty and total knee arthroplasty. This finding supports greater utilization of high tibial osteotomy for these patients. The cost-effectiveness of high tibial osteotomy and of unicompartmental knee arthroplasty depend on rates of conversion to total knee arthroplasty and the clinical outcomes of the conversions.

Copyright © 2015 by The Journal of Bone and Joint Surgery, Incorporated.

Figures

Fig. 1

The structure of the Markov model for high tibial osteotomy (HTO), unicompartmental knee arthroplasty (UKA), and total knee arthroplasty (TKA). Diamonds represent transition states during which a surgical intervention occurs. Ovals represent transition states during which no surgical intervention occurs. Straight arrows indicate a transition to a different transition state, and curved arrows indicate staying in the same transition state. Two transition states are not depicted: permanently living with a suboptimal prosthesis and the absorbing death state.

Fig. 2

Two-way sensitivity analyses of the rates of conversion to total knee arthroplasty (TKA) for unicompartmental knee arthroplasty (UKA) versus high tibial osteotomy (HTO) (left panel) and the utility of conversion for UKA versus HTO (right panel). Cost-effectiveness was compared when the annual rates of conversion and annual utility derived from conversion were allowed to vary. The willingness-to-pay (WTP) threshold of $100,000 per quality-adjusted life-year (QALY) is depicted by a solid line, and the WTP threshold of $50,000 per QALY is depicted by the dashed line. The base case is indicated by the white square.

Fig. 3

Cost-effectiveness scatter plot of a Monte Carlo model of 10,000 theoretical patients, fifty to sixty years of age, undergoing each surgical strategy. Each outcome is represented by a dot colored to correspond with the primary surgery. The mean values for high tibial osteotomy (HTO), total knee arthroplasty (TKA), and unicompartmental knee arthroplasty (UKA) are represented by the large diamond, square, and triangle, respectively.

Fig. 4

Cost-effectiveness acceptability curve. This figure demonstrates the probability of each surgical option being the cost-effective strategy at a given willingness-to-pay threshold, utilizing a Monte Carlo simulation of 10,000 patients. HTO = high tibial osteotomy, TKA = total knee arthroplasty, and UKA = unicompartmental knee arthroplasty.