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We Can Build a Better Artificial Limb

Modern replacements for lost limbs are far from optimal. A U of Idaho researcher seeks to change that

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In 2012, Oscar Pistorius became the first amputee to compete in the Summer Olympics, finishing second in a 400-meter heat. Running with two j-shaped carbon fiber prosthetic limbs, Pistorius bested his more able-bodied competitors, earning him the nickname "Blade Runner."

Craig McGowan, an assistant professor of biological sciences at the University of Idaho who has worked with Pistorius, says the runner succeeded not just because of his athletic prowess but because he got lucky, finding a prosthetic device that worked well for him early in his career.

Most amputees, says McGowan, aren't as lucky in finding a comfortable prosthesis that enables them to live an active lifestyle. Commonly, he says, finding and fine-tuning a prosthesis for an amputee is an art, a process of trial and error, that still results in devices that strain bodies.

"These guys are beating themselves up with these things," says McGowan of prostheses. "It's pretty clear to me that they are not integrating with the body that well, and we just don't even know how they integrate with the body."

McGowan hopes that his research will turn the art of finding a prostheses for amputees into a science.

With funding from a one-year Murdock Charitable Trust Exceptional Opportunity Grant, he's using computers to model the mechanics of something that most of us take for granted: how legs run. The next step in his research will be creating a simulation of an amputee runner, which will shed light on how the device interacts with the body's neuromuscular system. Ultimately, he hopes his research will result in prostheses that allow their users to run and stay active without putting wear and tear on the rest of their bodies.

Typically, amputees are prescribed basic prostheses that allow them to perform day-to-day activities, says McGowan. Beyond that, he says, are blade-like prostheses used for running or jogging. These prostheses store energy when their user brings them down on the ground. The energy is then released when the user takes their weight off of it, much the same way a spring functions. McGowan says this process of loading and unloading energy works well enough, but it's far from optimal.

He says that prostheses made for running help propel their users forward, but they also push and pull on joints and muscles in unnatural ways. Common complaints from amputees include back, knee and hip pain, according to McGowan, which prevents them from leading active lives.

McGowan says that prostheses have been developed using a limited model that treats the body as a single point of mass, propelled by legs acting like springs. This model has produced functional prostheses, but the problem, says McGowan, is that the body isn't just a point of mass and legs aren't springs.

"It's this really simplified way of understanding how animals and people move, and that's worked great up to a point," he says. "This model has no muscle and no joints, so it doesn't tell you how this behavior is being achieved."

Natural legs have tendons and muscles that cause them to stiffen and loosen at key moments while running, says McGowan. Amputee runners compensate for the fixed stiffness of their prostheses by swinging their legs rapidly. A better prosthetic device, says McGowan, would mimic how natural legs stiffen and loosen while running, allowing their users to move more swiftly while putting less strain on their bodies.

But first, McGowan needs to fill a big gap in existing research.

Currently, McGowan and his students are creating a computer-based simulation model of how non-amputees run. The model will highlight, in exacting detail, how muscles and joints work together while running. Next, McGowan plans on building a model of how an amputee runs. He hopes that comparing amputee runners to non-amputee runners will yield a prosthesis that better mimics a natural leg and integrates with the body's neuromuscular system.

McGowan isn't sure exactly what the end result will be, but he anticipates it'll be a prosthesis with some sort of mechanical component that compensates for how a natural leg stiffens and loosens.

When asked if his research could lead to the development of a prosthesis that functions even better than a natural leg, McGowan seems content with what nature has produced.

"Years of evolution has produced a pretty good model," he says. ♦