High-tech prosthetics: Out on a limb

Devices like Ossur's Rheo Knee combine software, sensors and processors to help create a more natural gait. Photos: High-tech prosthetics

Advances such as telemedicine and the use of wireless devices in hospitals have become an accepted part of medical technology, but the notion of replacing limbs with computer-powered devices seems more like something out of "RoboCop" or "The $6 Million Man."

Since as far back as the Civil War, prosthetic limbs have consisted of unwieldy lumps of wood, plastic or metal. While some advances in materials have improved comfort for amputees, prosthetics still lack the responsiveness and feel of actual limbs.

Icelandic is trying to change that with its Rheo Knee. Billed as the first knee with artificial intelligence, it combines up to 15 sensors, a processor, software and a memory chip to analyze the motion of the prosthetic and learn how to move accordingly. More recently, Ossur introduced the Power Knee, which houses a motor and more sensors. The motor helps replicate some of the action of muscles that have been lost along with the limb.

High-tech prosthetics

Bionics industry researchers estimate the next five years will bring major advances, including mind-controlled prosthetics in which sensors are attached directly to a patient's brain. Already, companies and universities are developing bionic feet, new cochlear implants to restore hearing to deaf people, prosthetic arms with embedded chips to control elbow and wrist movement, and hand prosthetics with artificial intelligence to control grip.

Jesse Sullivan, who lost both arms in a 2001 electrical accident, is testing technology that allows him to use his thoughts to control a bionic arm (the other is prosthetic). Dr. Todd Kuiken at the Rehabilitation Institute of Chicago took nerves from Sullivan's shoulder and implanted them in his chest, where sensors translate nerve impulses into instructions for a processor in the bionic arm.

Technology can make prosthetics more closely mimic the human body, says Hilmar Janusson, vice president of research and development at Ossur. "This is not science fiction," he says.

In fact, processors have been used to add stability to prosthetic limbs since the mid-1990s. Otto Bock HealthCare, for example, has been successfully producing the since 1999.

Sensing speed and terrain
Prosthetics with processor-controlled knees have enabled amputees to navigate stair steps more easily by improving the way weight is carried when the leg is unbent, says Dr. Robert Ruff, acting director of research and director of neurology for the U.S. Department of Veterans Affairs. Recent advances have now taken prosthetic capabilities a step further.

"Newer limbs are also able to bear torsion, which is important for walking on an uneven surface," Ruff says. "Some also have a 'smarter foot' that has a spring that will return energy to the leg after each step."

Ossur's knee technology goes well beyond putting more spring in the step, though.

Historically, simple mechanical prosthetic knees would swing forward when a person took weight off the knee and then lock once the weight was returned. In the Rheo Knee, however, within two steps sensors in the leg calculate walking speed, judge the terrain and start compensating for potential problems.

With the Power Knee, which uses a sensor placed on an amputee's natural leg, the process can take half a step. The sensor communicates with the prosthetic via wireless Bluetooth technology.

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