Are Powered Prosthetic Legs Finally Ready for Everyday Use?
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Summary:
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U-M roboticists prove Össur’s Power Knee benefits both high- and low-mobility amputees
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Custom phase-based algorithm outperforms built-in software for gait symmetry and trip reduction
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Real-time thigh motion tracking creates natural, user-synchronized knee movement
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Lack of clinical evidence has long blocked insurance coverage, but this study can challenge that
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Two study participants switched to the Power Knee as their full-time prosthesis after the trial
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Powered prosthetic legs have been available for years, but many have rarely left the lab and entered everyday life. New research from the University of Michigan (U-M) may be changing that.
A team of U-M roboticists has demonstrated for the first time that a commercial robotic leg can benefit people with low and high mobility. Working with Össur’s Power Knee (provided by the prosthesis manufacturer) and with primary funding from the National Institutes of Health, the researchers developed and tested an advanced control algorithm that produced measurable improvements over the device’s built-in software.
Why Powered Prosthetics Have Struggled to Gain Traction
For most daily activities, passive prosthetic legs hold a practical edge: they’re lighter, simpler, and users are deeply familiar with how they behave. For particularly demanding activities, however, such as climbing stairs and hills, rising from a chair, or walking longer distances, powered prosthetics can help users stay more active while reducing the risk of overuse injuries.
Insurance coverage has been a barrier. Robert Gregg, a professor of robotics at U-M and the study’s corresponding author, noted that evidence for the advantages of robotic knees over advanced passive designs had previously been lacking—and that this gap has been a primary reason insurers have declined to cover them. He said the new results begin to fill that evidentiary void.
What the Study Tested
In this initial study, researchers focused on key activities of daily living: participants walked fast on a treadmill, sat and stood repeatedly, and completed a sequence of sitting, walking, and sitting again.
The team analyzed two fundamentally different control methods: Össur’s own default algorithm and the U-M team’s custom phase-based controller. Their algorithm creates mathematical models of human movement based on extensive data from non-disabled individuals. It measures the user’s thigh motion at every moment to decide the correct response, resulting in more natural knee movements that are better synchronized with the user.
Gregg acknowledged that the comparison wasn’t perfectly even; participants had used their passive legs daily for years, while they had only two training sessions with the powered leg. Even so, he said, benefits were observed with both the U-M controller and Össur’s built-in software.
Results Across Mobility Levels
The leg provided the largest gains when the U-M team’s control strategy was applied, enabling a more symmetrical gait, reduced tripping risk, and reduced strain on participants’ sound-side legs and hips.
Prosthesis users who required additional walking assistance, such as a cane, found that Össur’s Power Knee offered significant help across all tasks. Those who got around easily with their own prostheses saw the most improvement in gait when the U-M control algorithm was used. One participant described the experience as the closest they had felt to walking on two legs since their amputation.
Kevin Best, a robotics research associate, recent U-M PhD graduate, and the study’s first author, emphasized that the goal of their control approach goes beyond mechanics. He explained that making the prosthetic leg behave as close as possible to a natural limb serves two purposes: preventing compensatory movements that lead to overuse injuries over time, and reducing gait deviations that can draw unwanted attention to users in public.
A Learning Curve and Signs of Progress
The U-M team found that adapting to the new control algorithm is harder for long-term prosthesis users than starting fresh. But the repeated sit-to-stand trials in the study showed clear signs of adaptation; rather than feeling tired with each trial, the participants got faster and more confident across sessions.
Two study participants were satisfied with the improvements they saw with Össur’s algorithm that they decided to switch to the Power Knee as their daily prosthesis—a meaningful indication that powered prostheses are moving from laboratory exploration to real-world use.
Jeff Wensman, a certified prosthetist/orthotist at Michigan Medicine and a study co-author, said that with continued advances in robotic devices, powered prostheses now offer genuine promise for people living with limb loss. He described user-synchronized control as the critical missing link in making that promise a clinical reality.
Related Reading:
New Nerve-Reading Tech Could Make Prosthetic Legs Feel More Like the Real Thing
Researchers Develop Technology that Controls Robotic Prosthetic Legs Better
Are Prosthetics Tax-Deductible? What Those Living with Limb Loss Need to Know
