Research Questions

  1. What are the clinical outcomes of MPKs compared with NMPKs? For example, are MPKs associated with meaningful improvement in physical function or reductions in incidences of falls or osteoarthritis compared with NMPKs? What is the effect of MPKs versus NMPKs on additional health outcomes, such as low-back pain, depression, obesity, diabetes, or cardiovascular disease?
  2. What are the economic outcomes of MPKs compared with NPMKs? For example, are MPKs associated with reductions in direct and indirect health care costs compared with NMPKs?

Due to recent advances in technologies, prosthetic knees and feet allow for more-dynamic movements and improve user quality of life, but payers have recently started questioning their value for money. To explore this issue, we simulated the differential clinical outcomes and costs of microprocessor-controlled knees (MPKs) compared with non-MPKs (NMPKs). We conducted a literature review of the clinical and economic impacts of prosthetic knees, convened technical expert panel meetings, and implemented a simulation model over a ten-year time period for unilateral transfemoral Medicare amputees with Medicare Functional Classification Levels of 3 and 4.

We found that compared with NMPKs, MPKs are associated with sizeable improvements in physical function and reductions in incidences of falls and osteoarthritis. Our simulation results show that over a ten-year time period, compared with NMPKs, MPKs are associated with an incremental cost of $10,604 per person and an increase of 0.91 quality-adjusted life years per person, resulting in an incremental cost of $11,606 per quality-adjusted life year gained. The results suggest that the economic benefits of MPKs are in line with commonly accepted criteria for good value for money and with those of other medical devices that are currently covered by U.S. payers.

Key Findings

Clinical Benefits

  • The main clinical benefit of MPKs is derived from reductions of falls with injuries and osteoarthritis incidences. The computer software in MPKs allows for the knee to dynamically adjust to uneven terrain, leading to improved stability and user confidence. The increased stability is thought to reduce cognitive burden and energy expenditure. The combination of these aspects is assumed to reduce the risk of falls. Because MPK users are two times less likely to become a faller, MPK users avoid fall-related injuries, mortalities, and expenses.
  • MPK users gain about 0.09 life years per person over a ten-year time period compared with NMPK users, but about 0.91 quality-adjusted life years per person, with the difference attributed to the improvement in quality of life. This finding is consistent with prior evidence that MPKs are associated with improved mobility, safety, user confidence, activities of daily living, ability to live independently, and satisfaction, and thus substantially better quality of life for amputees, with improvements ranging from 10 percent to 37 percent.

Economic Benefits

  • MPKs are associated with a reduction of $3,676 per person per year in direct health care costs and $909 per person per year in indirect costs, such as lost wages and caregiving expenses.
  • Because of the higher cost of MPK devices, overall annual cost is $15,083 per MPK patient and $13,382 per NMPK patient, a net increase of $1,702 based on current payment levels for devices and repair services.
  • It appears that the economic benefits of MPKs are comparable to those of total knee replacement and better than the implantable cardioverter defibrillator. Therefore, MPKs do provide good value for money from a societal perspective.


  • More studies are needed to expand the evidence on advanced prosthetics and to validate and refine our estimates. More research should be conducted in the areas of falls, fall-related costs, and osteoarthritis to either confirm the findings from the few existing studies we cited or fill the knowledge gaps for the amputee population. For example, the probabilities of falls and the average number of falls per faller per year were based on only three studies and most fall-related cost data came from studies of nonamputee populations. Similarly, more studies should be conducted to link osteoarthritis to the type of prosthetic used — the current analysis is based only on expert opinion.
  • To further develop the simulation model in the short term, studies can be conducted to establish the link between types of prosthetics and the quantifiable biomechanical metrics that can be connected to health outcomes based on existing studies. For example, external flexion moments associated with knee instability have been demonstrated to be associated with osteoarthritis but little research has examined the relationship between destabilizing external moments in transfemoral amputees and knee devices. More importantly, long-term population-based studies are often required to establish the link between types of prosthetics and health outcomes that can only be measured during a long observation period, including obesity, diabetes, or cardiovascular disease. The prosthetics research community may leverage existing medical record and claims data, or establish patient registries for prosthetics users and accumulate data for future long-term studies.
  • It might be fruitful to develop methodologies to convert Prosthesis Evaluation Questionnaire scores to health utility scores, or develop a preference-weighted utility score system directly, which can be used for quality of life adjustment purposes.

Table of Contents

  • Chapter One


  • Chapter Two


  • Chapter Three


  • Chapter Four


  • Chapter Five


Research conducted by

This research was sponsored by the American Orthotic and Prosthetic Association (AOPA), and conducted by RAND Health.

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