Modern Prosthetic Knees Cut Falls, Morbidity, Mortality in Amputees

Alicia Ault

October 20, 2017

WASHINGTON, DC — A new study by the RAND Corp showing that amputees who receive microprocessor-controlled prosthetic knees (MPKs) have fewer falls and injuries than those who get older devices could lead to broader insurance coverage of the newer devices.

More than 3500 Americans undergo an above-the-knee amputation each week. Half are due to vascular disease, including those affected by diabetes, 45% to trauma, and the remainder due to cancer or a congenital deformity. Of the 185,000 new amputees each year, only 25% to 30% receive a prosthetic leg and knee.

According to the American Orthotic & Prosthetic Association (AOPA), which paid for the RAND study and sponsored a press briefing here, Medicare spending on the 40-year-old mechanical prosthetic knees (which cost $5000 to $10,000) has increased over the past 8 years, while spending on the newer, more expensive MPKs (which cost $30,000 to $100,000) has declined, in part because no evidence has supported the switch to the MPKs.

"There hasn't been necessarily the 'aha' moment — the evidence that says, what's the benefit, why should Blue Cross and Blue Shield or Medicare pay more for particular technologies, and now we have that," Michael Oros, president of the American Orthotic & Prosthetic Association, told Medscape Medical News.

With the study in hand, AOPA is considering either asking Medicare to revisit its local coverage determination policy for MPKs or seeking to do a pilot project through the Center for Medicare and Medicaid Innovation showing that an additional population — those considered functional level 2 by Medicare (a patient with the ability to traverse low-level environmental barriers, such as curbs or stairs) — may also benefit from MPKs, Mr Oros told Medscape Medical News.

Current Medicare policy — which, although guided by local coverage determinations, is similar nationwide —covers MPKs only for amputees who are fairly ambulatory — that is, who can walk with a variable cadence using a prosthetic and who have demands beyond simple locomotion. Those amputees are considered a 3 on Medicare's four-level functional scale. Private insurers follow that model.

Often, even requests for MPKs for level 3 amputees are denied "out of the gate," said Mr Oros, who is also CEO of the prosthetic maker Scheck & Siress, Chicago, Illinois.

"This is not a case of amputees wanting to have access to new technology just because it is new," he said. "To the contrary, new tech vs old tech can be a life-and-death issue for an amputee," he stressed.

MPKs Not New, Enable Improved Stability and Confidence With Fewer Falls

The MPKs — which have been available for some 2 decades — allow the knee to dynamically adjust to uneven terrain, leading to improved stability and user confidence, according to the RAND Corp.

That organization's study found that MPK users are two times less likely to fall — with a 79% relative risk reduction in injurious falls — which leads to fewer fall-related deaths, about three per 10,000 person years, compared with 14 per 10,000 with older prosthetics. The group also documented a 30% relative risk reduction in osteoarthritis in the contralateral knee.

RAND found that MPKs are associated with a reduction of $3676 per person per year in direct healthcare costs and $909 per person per year in indirect costs, such as lost wages and caregiving expenses.

MPK costs are a bit higher overall because of the cost of the device and maintenance — at $15,083 per MPK patient compared with $13,382 per non-MPK patient. But MPKs are still good value, said Soeren Mattke, DSc, MPH, managing director for health advisory services at RAND Corp in Boston, Massachusetts.

The economic benefits of MPKs are comparable to those of total knee replacement and better than the implantable cardioverter defibrillator (ICD), said Dr Mattke. He noted that his study had some limitations, including that it was a simulation — using literature reviews of clinical and economic impacts of prosthetic knees and the input of technical expert panels to create the model.

"But, it's a good start," he said, noting that "it is the first attempt to quantify the benefits" of the MPKs.

Mayo Clinic Data Add Weight

The Mayo Clinic has also been making efforts to quantify MPKs' benefits, having found in a small study that patients who received the newer devices had fewer falls.

Initial results of that controlled trial — led by Kenton Kaufman, PhD, were presented at the American Academy of Orthotists & Prosthetists annual meeting in March 2017.

Fifty people — who already were using an older knee prosthetic — were switched to an MPK and then switched back to the non-MPK. At baseline, they had a median of two falls per person per month. Those falls reduced to zero with the MPK but went back up to 1.5 per person per month when patients were switched back to a non-MPK. With the MPK, patients spent just 50% of the time sitting, compared with 60% of the time at baseline.

"The quality of the gait more than doubled under the microprocessor knee and they reported an improved quality of life," said Dr Kaufman, who spoke at the AOPA briefing.

The reduction in falls was also important, he said, noting that another retrospective population-based study from the Mayo Clinic, published in June in Prosthetics and Orthotics International, found that falls led to substantial increases in health costs (Prosthet Orthot Int. 2017; DOI:10.1177/0309364617704804).

The results of the study, conducted in adults who underwent transfemoral amputations between 2000 and 2014, found that the average additional cost in the 6 months following a fall was $18,000 for those who required an emergency-department visit and $26,000 for those who had to be hospitalized.

Those figures did not include indirect costs, such as lost wages, caregiving expenses, and transportation costs, so is likely to be an underestimate, said Dr Kaufman.

"Even if an amputee with the older technology avoids death due to a fall, he or she may suffer very serious consequences from a fall-related injury," he concluded.

RAND Corp is an independent, nonprofit, and nonpartisan research institution to inform public policy debates. Funding came from the American Orthotic and Prosthetic Association, a national trade association. The studies were made possible using the resources of the Rochester Epidemiology Project, which is supported by the National Institute on Aging of the National Institutes of Health.  It was also made possible in part by the Mayo Clinic Robert D and Patricia E Kern Center for the Science for Health Care Delivery. 

RAND Corp. Economic value of advanced transfemoral prosthetics. Published online October 19, 2017. Study

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