The Value of Total Knee Replacement in Patients With Knee Osteoarthritis and a Body Mass Index of 40 kg/m2 or Greater : A Cost-Effectiveness Analysis

Abstract

Background: Total knee replacement (TKR) is an effective and cost-effective strategy for treating end-stage knee osteoarthritis. Greater risk for complications among TKR recipients with a body mass index (BMI) of 40 kg/m² or greater has raised concerns about the value of TKR in this population.

Objective: To assess the value of TKR in recipients with a BMI of 40 kg/m² or greater using a cost-effectiveness analysis.

Design: Osteoarthritis Policy Model to assess long-term clinical benefits, costs, and cost-effectiveness of TKR in patients with a BMI of 40 kg/m² or greater.

Data sources: Total knee replacement parameters from longitudinal studies and published literature, and costs from Medicare Physician Fee Schedules, the Healthcare Cost and Utilization Project, and published data.

Target population: Recipients of TKR with a BMI of 40 kg/m² or greater in the United States.

Time horizon: Lifetime.

Perspective: Health care sector.

Intervention: Total knee replacement.

Outcome measures: Cost, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratios (ICERs), discounted at 3% annually.

Results of base-case analysis: Total knee replacement increased QALYs by 0.71 year and lifetime medical costs by $25 200 among patients aged 50 to 65 years with a BMI of 40 kg/m² or greater, resulting in an ICER of $35 200. Total knee replacement in patients older than 65 years with a BMI of 40 kg/m² or greater increased QALYs by 0.39 year and costs by $21 100, resulting in an ICER of $54 100.

Results of sensitivity analysis: In TKR recipients with a BMI of 40 kg/m² or greater and diabetes and cardiovascular disease, ICERs were below $75 000 per QALY. Results were most sensitive to complication rates and preoperative pain levels. In the probabilistic sensitivity analysis, at a $55 000-per-QALY willingness-to-pay threshold, TKR had a 100% and 90% likelihood of being a cost-effective strategy for patients aged 50 to 65 years and patients older than 65 years, respectively.

Limitation: Data are derived from several sources.

Conclusion: From a cost-effectiveness perspective, TKR offers good value in patients with a BMI of 40 kg/m² or greater, including those with multiple comorbidities.

Primary funding source: National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health.

Figure 1.

Health states and treatment sequence in the OAPol Model among TKR recipients. Patients may spend several cycles in the same state or transition to another health state. The arrows specify transitions between health states, defined as probabilities in the input parameters of the OAPol Model. “sufficient” pain relief refers to a post-TKR health state associated with quality-of-life improvement. Death may occur from every health state. BMI = body mass index; OAPol = Osteoarthritis Policy; TKR = total knee replacement.

Figure 2.

Deterministic sensitivity analysis results. This figure shows the effect of varying input parameters on the cost-effectiveness of TKR in patients with a body mass index of 40 kg/m² or greater in 2 age groups: 50 to 65 years(top) and >65 years (bottom). The x-axis reports the ICER, calculated as the ratio of the difference in costs (total medical costs with and without TKR) to the corresponding difference in QALE. In each analysis, all parameters were held at base-case values except for the parameters shown on the y-axis, which were varied according to the range of values listed. The leftmost end of each bar represents the ICER when the parameter of interest is set to the most favorable value; the rightmost side represents the ICER at the parameter’s least favorable value. The exception for this is starting pain; because of the U-shaped relationship between starting pain and outcomes of knee replacement, the minimum ICER for the group aged 50 to 65 y corresponds to a 10% increase in starting pain, and the minimum ICER for the group aged >65 y corresponds to a 20% increase in starting pain. For all parameters, the ΔQALE at the left and right of each bar indicates the respective QALE benefit per 100 persons. The black vertical line shows the base-case ICER. as reported in Table 2. Costs are reported in 2018 U.S. dollars. ICER = incremental cost-effectiveness ratio; QALE = quality-adjusted life expectancy; TKR = total knee replacement.

Figure 3.

Probabilistic sensitivity analysis results for patients with a body mass index of 40 kg/m² or greater and aged 50 to 65 years (top) or older than 65 years (bottom). The curves show the proportion of simulations (out of 1000) for which TKR was cost-effective at a given WTP threshold. The WTP thresholds, measured in 2018 U.S. dollars per QALY, are listed along the x-axis. Each of the 1000 analyses are independently sampled model input parameters from the distributions specified in Supplement Tables 25 and 26. QALY = quality-adjusted life-year; TKR = total knee replacement; WTP = willingness-to-pay.