In an important breakthrough for lower-limb amputees, an Army veteran who lost part of his leg in Iraq walked like the healthy man he is again as he helped take the wraps off of the world’s first robotic ankle, developed by a team at MIT.

Garth Stewart, 24, lost his left leg below the knee in an explosion in Iraq. The new powered ankle-foot prosthesis helps Stewart walk by propelling him forward using tendon-like springs and an electric motor.

The device, a prototype, is said to improve balance, lessen fatigue, and provide amputees with a more “fluid” step. It is capable of varying its stiffness over irregular terrain, successfully mimicking the action of a biological ankle. It could become available as soon as summer 2008.

Biomechatronics Moving Sidewalk

MIT Media Lab Professor Hugh Herr and a team of researchers developed the robotic ankle-foot. Herr, head of the biomechatronics research group at the Media Lab, is a VA research investigator. 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.

“It’s wild,” he said, “like you’re on one of those moving walkways in the airport.”

Professor Hugh Herr Due to the fact that standard prostheses only provide a passive spring response during walking, they constrain the amputee with an unnatural gait and force them to expend some 30 percent more energy on their walk over a non-amputee, and their average walking speed is 30-40 percent lower. The new ankle is lighter, more flexible, and generates energy for walking over and above what can be released from a spring alone.

How it Works

The robotic foot includes a device outfitted with multiple springs, and a small battery-powered motor. Energy produced from the forward motion of the person wearing the prosthesis is stored in the power-assisted spring, and then released as the foot pushes off.

Additional mechanical energy is also added to help momentum. It is much the same principal as hybrid electric cars that convert braking energy into electricity.

Joel Kupersmith, M.D., chief research and development officer for the VA, outlined the top priority for the department as providing state-of-the-art prosthetic care for veterans - particluarly those returning from Iraq and Afghanistan. Research, he said, is a key part of this endeavor.

“The robotic ankle is a sterling example of how our leading-edge research improves veterans' lives,” Kupersmith said. “Up to now, prosthetic devices have not been able to duplicate the complex functions of our feet and ankles as we walk and run.

The complex 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.” ** What Next? **

According to Professor Herr, within the next year he hopes to introduce small, wireless implants into his own muscles near the neuromuscular juncture. The idea is that, when the muscles contract, the electrical impulse will send precise information to a micro computer in order to better control the artificial limb.

Looking longer term, Herr is working to investigate whether an implant could be used to mechanically attach the artificial limb directly to the amputee’s residual limb bone. The dream is to transmit loads directly to the bone structure of the amputee, eliminating the discomfort now experienced with conventional prostheses.

Adapted from a Massachusetts Institute of Technology Press Release

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