Breaking the Mold in Prosthetic Arms

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Army photo

Retired U.S. Marine Corps Capt. Jon Kuniholm (left) and Army Maj. Marc Hoffmeister pause during roped team movement on Pika Glacier in Alaska, 2008.

Few entrepreneurs can claim as intimate a connection to their products as Jonathan Kuniholm. As an engineer working at the forefront of some of the latest research to improve prosthetic arms, Kuniholm discovered that the efforts had overlooked a much simpler but utterly crucial question for improving amputees’ quality of life: how can they benefit from devices if they don’t wear them at all?

Kuniholm has been trying to answer that question for the past eight years.

After completing masters degrees in mechanical engineering and industrial design, he was beginning a PhD in biomedical engineering at Duke when he volunteered to serve in the Marine reserves. Almost immediately after he was activated Kuniholm deployed to Anbar Province in western Iraq. On New Year’s Day 2005, he was part of a team that responded to an ambush near the Tigris River when an IED hidden in an olive oil can exploded, killing a Marine named Brian Parello and tearing through Kuniholm’s right arm.

Just hours after he had picked a bluegrass song on a guitar at the New Year’s Eve talent show he was on a flight home where surgeons amputated his right arm below the elbow.

When Kuniholm was fitted with his first prosthetics he learned something that still shocks most people: The most popular prosthetic arm on the market is a design that was patented in 1912 and hasn’t changed much since World War II. In the age of mini computers and brilliant robotics, the body-powered hook prosthesis is most often the easiest one to use. “My reaction was, this was just crazy,” Kuniholm says of being fitted with his first prosthetic arms. “We can do much better.”

After recovering from his injuries, Kuniholm signed on to a Department of Defense project to research the latest technology and improve myoelectric hands. After spending more than $150 million, there have been some great success stories, and many amputees are happy with their robotic prosthetics, but for all of the money and the work of some of the country’s most brilliant minds, very few significant new products have hit the broader market. Figuring out how to mass produce the advancements made in the laboratory is important, but Kuniholm learned there was a much more basic problem: even if robotic hands could greatly improve the lives of an amputee, he or she might not wear a device in the first place.

Prosthetics attach to the stumps of amputated limbs with what’s known as a socket. While sockets have undergone significant changes over the decades, the improvements have mostly been in the materials and not in the design. Leather sockets gave way to carbon fiber with rubber sleeves to pad the hard shell. “The way I describe that whole concept,” Kuniholm says, “is if you took a pair of Dutch wooden shoes and you updated them by making them out of carbon fiber and give people a pair of rubber socks to wear in them.”

According to a survey by the International Society of Prosthetics and Orthotics that examined studies over the past 25 years, many upper limb amputees “reject” their prosthetics, that is, they elect not to use any kind prosthetic arm (across the many studies, the number averages out to nearly half of upper limb amputees). Of those who reject their prosthetics, nearly 90 percent cited fit and discomfort. Functionality is overwhelmingly the reason amputees use a prosthetic; when they chose not to wear a prosthesis, it is usually because of comfort.

Here Kuniholm saw problem wasn’t being addressed in the lab, so the engineer became an entrepreneur. He started by thinking about prosthetic sockets like sneakers. During World War II, athletic shoes looked very much like Converse Chuck Taylors, a simple piece of leather or canvas glued to a rubber sole. Over decades, shoe companies have made vast improvements in the comfort and performance of running shoes. The same concept could apply to prosthetic arms–why start with the premise that sockets had to be made of hard composite materials and unbreathable rubber padding, he thought. The sneaker industry has proven it can design a shoe that’s stiff where it needs to be stiff but flexible for places where the foot requires more movement.

So Kuniholm started a company called Stumpworx and set out to design a better socket. In his pitch video he shows a photo of his stump rubbed raw after a day of moving heavy things in his house. That’s a problem Kuniholm believes he can solve. He has an initial prototype that permits more movement and like running shoes, it allows for changes in the size of the arm. On a hot day when an amputee may be working, or even just walking outside, his socket won’t cause friction and rubbing when a stump swells.

Kuniholm has entered the Duke Start Up Challenge, an entrepreneurship competition that partly takes into account Facebook votes. If he wins, he will use the money to fund a second, more thorough prototype and begin collecting data on amputees. “What I’m after here is to solve a problem that society has completely failed to solve for us,” he says. “Entrepreneurs create and entrepreneurs change. The real motivation is trying to make something different.”

Eight years after losing his arm, Kuniholm wears a body-powered hook; his myoelectric arms sit in his closet. With continued research, he may one day use a state of the art robotic hand as a replacement for the one he lost. But in the mean time, he hopes Stumpworx will help more amputees keep using any kind of prosthetic arm. In the grand scheme of prosthetics research, it may seem a simpler problem, but it may well be lead to a solution that is the larger victory.