A powered prosthetic mimics calf muscle’s movement

The most striking thing about the demonstration was how ordinary the two men looked. Pacing across the stage – first slowly, then fast – they walked naturally, with a slight bounce in their step, the way young, healthy people with strong, healthy legs would do.
The thing is, both Garth Stewart, a 24-year-old Iraq war veteran, and Hugh Herr, director of the Biomechatronics Research Group at the Massachusetts Institute of Technology, are amputees. Stewart is missing the bottom of his left leg; Herr lost the bottoms of both his legs 25 years ago, when he was 17, in a mountain-climbing accident.
What allowed them to walk with such ease at the Providence Department of Veterans Affairs Medical Center last Monday was the product of more than two decades’ effort by Herr to revolutionize prosthetics – most recently, with the support of the U.S. Department of Veterans Affairs.
Both Herr and Stewart were wearing powered ankle-foot prostheses, the first in the world, still in the development stages but expected to be widely available sometime next year.
The devices, which are powered by a battery pack attached to the ankle, aim to mimic the actions of the calf muscles when people walk. As Herr explained it at last week’s demonstration, existing prostheses mimic the spring-like action of the foot as it bounces off the ground, but human legs also get power from the calf muscles, which provide an energy boost to speed up or draw away energy when needed, such as when you walk downhill.
“The human ankle is turbo-charged,” Herr said. And that energy is so important, he added, that amputees walking on a regular prosthesis end up expending about 30 percent more energy to walk, and to compensate, they typically walk about 30 percent more slowly.
Amputees also have to draw energy from their hips to propel their legs forward, Herr noted, and that makes their gait uneven and puts a strain on their lower backs.
“Approximately 70 percent of leg amputees have back problems,” Herr said. But these new powered prostheses take the strain off the hip and the other leg. As a result, he said, “it’s a smoother ride, if you will.”
Herr, whose team is part of the MIT Media Lab, is a well-known pioneer in this field. By closely studying models of the human skeleton, muscles and physiology, he has developed elastic shoes that increase aerobic endurance in walking and running, gait-adaptive knee prostheses to help transfemoral amputees, and variable-impedance ankle-foot orthoses for patients suffering from drop foot, a gait pathology caused by stroke, cerebral palsy and multiple sclerosis.
This new project is part of a broader effort to develop next-generation prostheses spearheaded by the Center for Restorative and Regenerative Medicine at the Providence VA – a collaboration between the VA, Brown University and MIT that is also involved in several other research and outreach endeavors involving veterans.
The prosthetics project’s ultimate goal is to create “biohybrid” limbs that meld biological and manmade materials to give amputees better mobility and control of their limbs and reduce the discomfort and vulnerability to infection associated with today’s prostheses.
Dr. Roy Aaron, a professor of orthopedic surgery at Brown, created the center in 2004 with $7.2 million in funding from the VA. Since then, the federal agency has committed another $6.9 million to build a state-of-the-art rehabilitation research facility on the Providence VA campus; construction is slated to begin in the fall.
The VA, which has pioneered a wide range of medical technologies over the years – from CT scans, to kidney dialysis, to pacemakers – has 14 “centers of excellence” working on different aspects of rehabilitative medicine across the country. One in the Bronx, for example, is working on spinal-cord injury recovery; one in Boston focuses on vision injuries.
At last week’s demonstration, U.S. Sen. Jack Reed noted that the need for this kind of research is greater than ever because although “tremendous advances” in technology and health care have allowed soldiers in Afghanistan and Iraq to survive injuries “at rates that are remarkable,” record numbers are coming home with grievous injuries.
While historically 3 percent of war veterans had amputations, Reed noted, now it’s 6 percent, “so we have to recognize this increase and take serious steps” to address it.
Herr said that so far, eight veterans have tried the new powered prostheses, and all found them beneficial. No one has worn one full-time yet, though Herr said he plans to be the first person to do so, within weeks. The devices will be tested further in the fall, and then in the spring there will be a “beta test,” with doctors being asked to give these to their patients to try out, and report back on every aspect of how they worked, how easy they were to set up, etc.
Cambridge, Mass.-based iWalk, which specializes in prosthetics, has already licensed the new devices and plans to make them commercially available in about a year, Herr said. (Promotional materials on the company’s Web site, www.iwalkpro.com, call the product PowerFoot One.)
No price has been set, Herr said, but the inventors and the company are committed to keeping the prosthetics affordable, and to ensure every veteran who needs one can get it. And the cost should be fairly low, he noted, because “the novelty of this system is in the architecture, and not in the individual components” or the materials.
Stewart, an Ohio native who lost his leg to a roadside explosive device in 2003 and is now attending Columbia University, is eager to get one of the new prostheses for himself.
“Once you get used to it, it feels like you’ve got your leg back,” he told the audience last week. “I grew up on G.I. Joe, and the chance to be a cyborg …”