Fastest Man On Earth An Amputee? The Remarkable Promise Of Next-Generation Prosthetics

 @rpalmerscience on August 31 2012 3:27 PM
South Africa's Oscar Pistorius
South Africa's Oscar Pistorius -- the first double-amputee runner to compete in the Olympic Games -- sprints during a men's 400-meter heat Saturday in the Olympic Stadium at the London 2012 Olympic Games. Reuters

South African Olympian and "Blade Runner" Oscar Pistorius may have fallen short of the medal podium in this year's London Olympics, but what about four years from now? Thanks to recent advances in prosthetics technology, we're on the cusp of an era where Paralympians with souped-up joints and carefully engineered limbs could easily blow past the merely human Olympians - and where ordinary amputees can live extraordinarily normal lives.

Pistorius was born with both legs lacking a fibula, the smaller of the two bones running from the knee to the ankle. His parents decided to amputate his legs before he began walking so he could get used to prosthetics from an early age.

Initially, he was barred from running in the 2008 Beijing Olympics by the International Association of Athletics Competitions, after a German scientist reported that his carbon-fiber Cheetah blades allowed him to use less energy to run at the same speed as an able-bodied athlete. On appeal, the IAAF reversed its decision after further scientific testing that showed while Pistorius might have an advantage when running at full speed in a straight line, the blades disadvantaged him at the start and acceleration stages of his running, resulting in no net advantage.

However, it may soon be hard to make a case that the best prosthetics provide no advantage.

"It's possible Paralympic athletes could one day run faster than Usain Bolt," David James of the Centre for Sports Engineering Research at Sheffield Hallam University told the Associated Press.

The improvement in prosthetics design has accelerated in recent years. Pistorius' equalizing performance would have been unthinkable without the Flex-Foot, a curved carbon graphite prosthesis created by American inventor Van Phillips and sold to Iceland-based company Ossur, which makes the Cheetah limbs Pistorius uses.

"I think the reason why we've come such a long way over the last 50 years is because of the types of materials that are being used," says Sarah Deans, a prosthetics researcher at the University of Strathclyde in Scotland. "Carbon fiber materials have a much lower weight and a very high strength ratio when compared to post-war materials like wood and metal and leather."

Far from attempting to perfectly replicate life - which can sometimes result in mannequin-esque limbs that drag the wearer several levels down into the Uncanny Valley - many cutting-edge prosthetics are redesigning legs and arms from the ground up. This growing lack of fidelity to facsimile is partially aesthetics, but mostly for practical reasons.

"Think about the human foot, which has 26 bones and a number of joints. When someone damages their foot, it's very difficult to reconstruct that skeletal architecture because it's very complex," Deans says.

Instead of trying to recreate what eons of evolutionary history has thrown together, high-performance prosthetics designers are turning out streamlined forms like Pistorius' Cheetah blades. The sleek design is also seen in the designs of Aviya Serfaty, who dreamed up a model called the Outfeet, which is specifically designed to mimic the shape of a woman's leg:

Outfeet_Aviya Serfaty from aviyaya on Vimeo.

The Outfeet has skins that can be stretched onto its body, and snap-on heels for more formal occasions.

Deans says many of the amputees she sees are eager to sport stylish legs that stand out from the crowd. But there's still a market for limbs that try to be true-to-life.

Scottish company Touch Bionics specializes in upper-limb silicone prostheses, most of which are known as "passive," or unbendable. In 2011, Touch Bionics unveiled a system called Living Image, which scans a patient's skin and features to provide a reference for the company's artists, who hand-paint the prosthetic to match - with hairs, freckles, and tattoos included, if desired.

"Clients have been very satisfied, especially with the color of the 'skin,'" Touch Bionics spokesman Danny Sullivan told the Daily Mail last October. "The aim is to create a prosthetic that is as close a match as possible."

Upper-limb amputees present a more challenging case to prosthetics designers than lower-limb amputees. An arm and hand have more degrees of freedom than a leg and foot, and a functional upper-limb prosthetic needs more precise control.

Many existing bionic arms can mimic natural movements, but only in a series of linear steps. In order to pick something up, a user has to move an elbow, then the wrist, then open the hand, then close the hand, then move the wrist, then move the elbow again. Sounds exhausting, no?

Designers are hoping that integrating a patient's existing nerves and neural system into the prosthetic will allow for smoother and more graceful movements. They're also trying to build artificial limbs that provide sensory feedback that can communicate things like temperature and pressure to the user. Feedback would have many uses, ranging from warning a user against picking up a hot object that would damage his or her prosthesis to letting the user know their own strength (you would not want to squeeze a pet hamster with the same amount of force you'd use to pick up a dumbbell, for instance).

Many prosthetics interface with a patient's nervous system via electrodes placed on the skin that read signals sent to the missing limb. For more precise movements - making fingers move - researchers have explored using wireless devices called injectable myoelectric sensors, or IMES. These are little devices, about the size of a grain of rice each, that can retransmit electrical signals from an amputee's muscles in the residual part of his or her arm.

In May, a U.S. veteran Joe Delauriers, who lost both legs and an arm in Afghanistan, tested out the latest prosthetic arm developed by the Applied Physics Laboratory at Johns Hopkins University. The prototype, called the Modular Prosthetic Limb or MPL, can be controlled via surface electrodes or through a new surgical technique called targeted muscle reinnervation. In this process, nerves that once controlled the amputee's arm or hand are transferred to his or her chest, allowing them to control the prosthesis with his or her thoughts. In a rewired patient, when the user's brain sends the signal to move parts of the lower arm or hand, the signal is redirected to the upper arm and read by sensors in the prosthesis.

But what's on the horizon? Scientists are investigating ways to make artificial muscles out that would be activated by electric power much in the way that biological muscle tissue is activated by a nerve signal.

"In the future, you might see nanotube technology that could produce the same structure as in a biological leg and give you the same amount of energy," Philippa Oldham, head of manufacturing at the English charity Institute of Mechanical Engineers, told the AP.

Combine that with powered ankle and knee joints and you might have a recipe for a record-breaking Bionic Man at the 2016 Olympics.

But not all amputees are looking to win a gold medal. Most technology improvements like translating nerve signals for smoother movements and building more realistic feedback mechanisms,

"I'm looking now at what will motivate or be a barrier to an ordinary person using an ordinary prosthesis," Deans says. "I'm not talking about running a 10K - I'm talking about simply walking to the local grocery store to pick up a newspaper."

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