New bionic ankle debuts at Providence VA

The first powered ankle-foot prosthesis, an important advance for lowerlimb amputees, was unveiled July 23 at the Providence VA Medical Center. Garth Stewart, a 24-year-old Army veteran who lost his left leg below the knee following an injury in Iraq, demonstrated the new prosthesis.

Stewart walked in the prosthesis, which, unlike any other, propels users forward using tendon-like springs and an electric motor. The prototype device reduces fatigue, improves balance, and provides amputees with a more fluid gait. It could become commercially available as early as the summer of 2008.

MIT Media Lab Professor Hugh Herr, a VA-affiliated investigator since 2004, led the group that developed the ankle-foot. He is also a double amputee who tested his invention. "This design releases three times the power of a conventional prosthesis to propel you forward and, for the first time, provides amputees with a truly humanlike gait," Herr said. He compared using the device to walking on a moving walkway at an airport.

Stewart said that when he first began using the prototype, "One of the first things I noticed was a huge relief in back pressure."

Herr created the device through the Center for Restorative and Regenerative Medicine, a collaborative research initiative that includes the Providence VA Medical Center, Brown University and MIT. The center was initially funded in 2004 with $7.2 million from VA, and an additional $6.9 million from the agency is now funding construction of a new state-of-the-art research building to house the center on the Providence VA campus.

Goal of center is 'biohybrid limb'

The center boasts a team of researchers with expertise in tissue engineering, orthopedics, neurotechnology, prosthetic design and rehabilitation. Their aim is to eventually create "biohybrid" limbs that integrate biological and manmade materials and function almost like natural limbs. Part of the effort involves research led by John Donoghue, PhD, on a system called BrainGate that allows movement signals from the brain to be picked up by a tiny implanted sensor and decoded into commands for prosthetics or other robotic and electronic devices. Other research is aimed at promoting osseointegration, an innovative surgical technique that allows prostheses to be anchored directly into the bone of the residual limb.

Stewart, the veteran who demonstrated the new bionic ankle on July 23, said he is looking forward to seeing more research-driven advances: "What’s really exciting is that they want, within a couple of years, to be able to graft this device to a human skeleton and then run interfaces between the brain and the nerves, so you can feel it and move it by thinking."

'Creativity, ingenuity on behalf of amputees'

Joel Kupersmith, MD, chief research and development officer for VA, remarked how the new ankle is a prime example of how VA research is advancing prosthetics care for veterans—especially those returning from Iraq and Afghanistan.

"Up to now, prosthetic devices have not been able to duplicate the complex functions of our feet and ankles as we walk and run," he said. "The ingenious computerized design of this new prosthesis changes all of this, as it constantly 'thinks' and responds, allowing the person to walk or run in a more natural and comfortable way."

Michael E. Selzer, MD, PhD, director of Rehabilitation Research and Development for VA, added: "Hugh Herr and his Media Lab group are well-known for their scientific ingenuity and creativity on behalf of amputees. This new technology represents rehabilitation research at its finest, and is yet another milestone in VA’s long history of outstanding achievements in this area."

How does the new ankle-foot benefit amputees?

The device being developed by Herr’s group is the first powered ankle-foot prosthesis. It propels the wearer forward, thanks to a unidirectional spring and force-controllable actuator. It also varies its stiffness as users walk over irregular terrain. These two properties enable the device to mimic the action of a biological ankle. Conventional ankle-foot prostheses, on the other hand, are passive. This causes users to expend up to 30 percent more energy during walking than non-amputees. As a result, they typically walk at speeds that are 30 to 40 percent slower.

Herr’s team recorded improvements from 7 to 20 percent in the "metabolic economy" of research volunteers who wore the device—even though it is two times heavier than conventional prosthetic models.

The new foot-ankle prosthesis is also expected to alleviate problems of abnormal gait that are common among below-the-knee amputees. These problems include greater-than-normal hip extension, knee flexion and ankle dorsiflexion—a movement that decreases the angle between the foot and leg—on the unaffected side, and less-than-normal flexion of the hip and knee on the affected side. Studies have associated these problems with long-term complications such as low back pain and osteoarthritis.

Updated: Oct 22, 2009

Home | About ORD | Services | Programs | News, Events & Media | Research Topics | For Veterans | For Researchers | Contact Us | Plug-ins