Summary

According to exploratory model-based analyses of most recent clinical data, ISA placement can be expected to meaningfully delay the need for TKA in symptomatic patients with medial knee OA, resulting in improved patient quality of life that appears to render ISA a cost-effective, high value intervention across a wide range of tested assumptions.

Abstract

Objectives

Over the last decade, implantable shock absorbers (ISA) were developed and refined to serve as a treatment option for patients suffering from symptomatic medial knee osteoarthritis (OA). Recently, ISA outcomes have been assessed in several clinical studies (NCT03671213; NCT02934659). The potential health-economic value of the device, which rests on its ability to improve symptoms and reduce or delay the need for total knee arthroplasty (TKA), has not previously been studied. Our objective was to explore the potential cost, quality of life (QOL), and cost-effectiveness implications of ISA implantation in the United States healthcare system.

Methods

A decision-analytic Markov model was constructed to model disease progression, treatment events, and costs over remaining lifetime for a cohort of 51-year-old patients, 61% of whom were male. Patients could either be treated with ISA at the outset, or undergo standard of care (SoC) treatment, which involved TKA and revision TKA treatment according to published incidence rates. Patient symptom relief and rates for device removal or conversion to TKA were derived from study data. In absence of long-term data, it was conservatively assumed that ISA were removed no later than 10 years after implantation. After removal, the ISA cohort was subject to the same TKA and revision TKA incidence rates as the SoC cohort and modeled to cover patient lifetime. Health-related QOL (‘utility’) estimates were calculated from study-reported WOMAC pain scores at baseline and two-year follow-up. ISA lifetime was modeled based on current and prior clinical studies. Costs for ISA index implantation and removal were modeled on published values for comparable orthopedic procedures in 2021 dollars, while costs for index and revision TKA and annual OA maintenance were based on published literature. Cost-effectiveness was evaluated against willingness-to-pay thresholds of $50,000 per QALY gained (‘high value’) and $150,000 per QALY gained (‘of value’), with costs and outcomes discounted at 3% per annum. Extensive sensitivity analyses were performed.

Results

ISA placement improved WOMAC pain scores from 60.4 at baseline to 14.2 at 24 months, corresponding to a utility increase from 0.70 at baseline to 0.80, in line with the utility estimate for TKA. At 5 and 10 years, 74% and 55% were projected to remain on ISA treatment. The projected cumulative 10- and 20-year incidences of primary TKR were 24.9% vs. 58.2% (RR=0.42) and 68.6% vs. 82.5% (RR=0.83) for ISA and SoC, respectively. Over the patients’ lifetime, ISA was projected to add 0.23 QALYs (14.45 vs. 14.22 QALYs) at concurrent lifetime cost increase of $8,510 ($61,339 vs. $52,829), yielding an incremental cost-effectiveness ratio (ICER) of $36,413 per QALY gained. Incremental costs for the ISA strategy were lowest at 10-year follow-up ($1,610). Across conducted sensitivity and scenario analyses, ISA remained cost-effective.

Conclusion

According to exploratory model-based analyses of most recent clinical data, ISA placement can be expected to meaningfully delay the need for TKA in symptomatic patients with medial knee OA, resulting in improved patient quality of life that appears to render ISA a cost-effective, high value intervention across a wide range of tested assumptions.