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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.

The Rheo Knee is a lighter prosthetic, and the battery life is much longer, making it suitable for patients who are relatively active or who don't need the added power of a motor. The Power Knee weighs about as much as a human leg, while the Rheo knee weighs less at about 3.6 pounds.

Ian Fothergill, Ossur's clinical project manager and prosthetist, says his company's products produce roughly 70 percent to 85 percent of the functionality of a normal limb. A high-end mechanical prosthesis reproduces roughly 50 percent of a leg's original functionality.

Otto Bock's C-Leg and the Rheo Knee each cost some $35,000 to $40,000, while the Power Knee costs as much as $100,000. A basic mechanical leg, including customization and fitting, can cost up to $25,000.

Ossur also aims to introduce a bionic foot, but has plans to take the usage of technology in the human body into even more advanced realms.

Trials into areas such as osteointegration, in which prosthetics are fused with healthy bone tissue, are under way in Germany. The company also has struck partnerships with technology providers to improve wound care by having sensors detect the amount of oxygen in the injury.

The role of disease
Most of the roughly 65,000 amputations in the U.S. each year result from disease, with over 90 percent of those caused by complications from diabetes, according to the American Diabetes Association. The battlefield takes its toll, too, of course: in the current conflicts in Iraq and Afghanistan, more than 400 U.S. soldiers have lost one or more limbs.

The U.S. government is helping combatants left limbless from battlefield injuries. In 2006, the Veterans Administration plans to spend $11 million to develop advanced prosthetics. The VA's budget for such research has risen by about 20 percent per year since the U.S. invaded Afghanistan. The Pentagon is getting involved, too, allocating a planned $73 million for grants to researchers who can develop new prosthetic arms.

In other applications, Cyberkinetics Neurotechnology Systems is developing a brain implant to enable more natural motion for prosthetics. Researchers at Northwestern, Johns Hopkins and Brown universities are also working with ways to wire a prosthetic limb directly into a patient's nervous system. In some cases, a postage-size chip implanted in the brain of stroke victims has restored some function to limbs paralyzed by the attack.

Many experts in the bionics field view the next five years as a turning point for combining technology and biology. Hugh Herr, who directs the biomechatronics group at MIT's media lab, cites two drivers of innovation in the area: availability of funding and progress in several different branches of science. Spending by the military and other groups continues to climb, while advances have been made in battery longevity, chip design, tissue regeneration and robotics, he says.

For Herr, who lost his legs in a mountain climbing accident when he was 17, advanced prosthetics are hardly a fantasy. "I think we're at the point in history where we're going to see the innovation curve steepen," he says. "This is a great time to be alive in this field."

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