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Bionic Ankle

Allen Rasmussen of Gillette, who lost his lower right leg in a mining accident about four years ago, tries out a BiOM bionic ankle under the supervision of Kamil Leman, a prosthetist, on May 14 at Precision Prosthetics in Casper. The computerized ankle allows patients to walk more naturally and with less discomfort than with a conventional prosthesis.

Bill Rossin dreads even a simple trip to the grocery store.

The Casper man lost his left leg below the knee in 2011 while working for a trucking company. He gets around with a prosthetic limb, but mobility has a price.

“If I move more than just sitting there, I’m in pain,” he said.

With a conventional prosthetic leg, every step puts pressure on the lower end of the remaining limb. That causes soreness over time.

Two years ago, a Massachusetts company developed a powered ankle that users say significantly reduces pain while making it easier to navigate rough terrain. It could soon find use in Wyoming.

The state Workers’ Compensation Division is in the process of approving the powered limb for three injured workers, said Hayley Douglass, spokeswoman with the Wyoming Department of Workforce Services. Those who’ve tried it say it’s more comfortable and stable than a conventional artificial limb.

Rossin was among the injured workers trying the $70,000 limb during a demonstration earlier this month at Precision Prosthetics in Casper. Walking felt more natural, he said, and there was virtually no pain.

“It acts like an ankle,” he said. “It gives you a lot of freedom back.”

BiOM, the company behind the prosthetic, received more than $4 million in funding from the federal government, which was looking for ways to help troops injured in Afghanistan and Iraq. The result was a battery-powered limb that mimics the human calf, said BiOM Regional Director Ryan Bretz

A motor and Kevlar belt inside the prosthesis compress a carbon fiber spring, pushing the leg

forward. Tiny computers in the ankle determine how much power the user needs. They can sense the user’s pace, or whether he’s on flat or sloped ground, and adjust accordingly.

“It walks just the way they want to walk,” Bretz said. “So if they want to walk faster, the motor propels them.”

Walking on uneven terrain can be challenging on a conventional prosthetic leg. That’s because it’s difficult for users to properly plant their feet, said Precision Prosthetics owner Kamil Leman.

The powered ankle, in contrast, flexes so the foot remains in better contact with the ground. That keeps users safer when they move up and down slopes, Leman explained.

The bionic prosthesis is less painful, he added, because it can better mimic the human body.

“The ankle moves like a natural ankle, instead of being stiff,” Leman said.

Alan Rasmussen noticed the difference. The Gillette man lost his right leg below the knee in a December 2009 mining accident. He uses a conventional prosthetic, but came to Casper to test the bionic ankle and a vacuum pump that allows for a better seal between the socket and his remaining limb.

As Leman looked on, Rasmussen walked back and forth inside a clinic room. He stepped with confidence and only a slight limp.

The bionic ankle allowed for faster movement and longer steps, Rasmussen said. He expects it would make it easier to walk long distances and scramble up sloped surfaces when he goes hunting.

“Between the ankle and the vacuum pump, I don’t think you could get any closer to having your foot back,” he said.

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Contact Joshua Wolfson at 307-266-0582 or at Visit to read his blog. Follow him on Twitter @joshwolfson.


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