Bionic leg restores natural walking speed and stride: ‘I didn’t feel like my leg was amputated’ | CNN

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Amy Pietrafitta learned to walk seven times.

First as a child and then, after an industrial burn led to the amputation of her left leg in 2018. Since then, she has taken her “first steps” in prosthetics for running, water, high heels, rowing and everyday walking.

Her last “first steps” were different. This time, she was given a bionic leg that was fully connected to her brain, allowing her to walk and move like anyone else. With this new leg, she said, she couldn’t even tell there was a difference.

“I didn’t feel like my leg was amputated,” said the 47-year-old from Massachusetts. “It was the happiest moment of my life.”

Pietrafitta was part of a study of a new neuroprosthesis from the Massachusetts Institute of Technology that is controlled entirely by the nervous system. Her leg was amputated using a new muscle-pairing technique called agonist-antagonist myoneural interface, or AMI, which preserves signaling between the muscles and the brain.

The neuroprosthesis uses sensors placed between the reconstructed amputation site and the bionic leg to transmit electrical signals from the brain. This allows the prosthesis to sense its position and movement and send this information back to the patient, enabling a sense of proprioception: the brain’s ability to sense self-motion and location in space.

The study, published Monday in the journal Nature Medicine, found that participants who had the specialized amputation and neuroprosthesis increased their walking speed by 41 percent, matching the ranges and abilities of people without leg amputations. The results also suggested that the bionic limb could be controlled with just 18 percent of natural proprioception.

According to Dr. Hugh Herr, principal investigator and lead author of the study and co-director of the Yang Center for Bionics at MIT, where the research took place, this is the first bionic leg that is fully controlled by the human nervous system and exhibits natural walking speeds and gait patterns.

“It feels natural, like the limb is made of flesh and bone. It’s like the central brain is not aware that the limb has been amputated, because the brain is getting normal sensations,” said Herr, who had both legs amputated below the knee after a climbing accident in 1982.

Herr started the project after noticing a trend where prosthetics were increasingly controlled by robotic algorithms rather than the human nervous system.

“We want to rebuild human bodies,” he said. “We want to rebuild people and give them back what they want. We don’t just want to build more and more beautiful robotic tools or devices.”

To test the interface, 14 participants were divided into two groups and fitted with bionic prosthetic legs. Seven had undergone AMI surgery and seven had not.

The results suggested that people with AMI amputations were better able to navigate real-world environments, including ramps, stairs, blocked paths and even an “American Ninja Warrior”-style course, said Pietrafitta and Dr. Matthew J. Carty, the lead surgeon on the first AMI procedure and a co-author of the new study.

“This is a fundamental paradigm shift in the way we think about amputation in combination with technology: we treat it as a restorative procedure rather than a failure,” Carty said.

The technology also allows users to switch between speeds without swapping prosthetics, reducing the hassle of switching legs, avoiding unwanted attention and restoring a sense of normalcy, Pietrafitta said.

“It felt normal. … I was ready to run. I kept wanting to take my hands off [the supports]to get out and get moving,” she said.

Restoring normal walking is about more than just getting from A to B. According to Pietrafitta, it’s about returning to society.

“It meant my life could start over. … I could go out and live the way I wanted to,” she said. “When you’re at home and bedridden, family and friends start to dwindle away. It’s too hard for people to come in and see you in pain.”

For John Rheinstein, a lower- and upper-limb prosthetics specialist and clinic manager at the Hanger Clinic in New York, the physical prosthesis is only one part of a successful amputation outcome.

“Care has improved over the years (in part) due to advances in understanding and treating the emotional impact of limb loss,” he wrote in an email.

According to a 2018 report from the federal Agency for Healthcare Research and Quality, an estimated 1.9 million Americans are living with limb loss, a number that is expected to double by 2050. This is largely due to the increasing incidence of diabetes, a known risk factor.

Herr said his team aims to make fully neuro-controlled prostheses commercially available within five years. However, the 2018 report estimates that fewer than half of amputees receive prescriptions for prostheses.

People with amputations can have difficulty obtaining prescriptions and insurance coverage for prosthetics, especially for options with more advanced technology. Rheinstein cites insurance coverage for prosthetics — particularly the lack of coverage for activity-specific prosthetics — as one of the most difficult parts of his patients’ rehabilitation journey.

“Demonstrating to payers the value of the outcomes we deliver and how outcomes-based prosthetic care reduces overall health care costs” is one of the biggest challenges facing the industry today, he said.

For example, according to Herr, the BionX emPOWER prosthesis is the only motor-powered prosthesis on the market, and many people with limb loss do not have access to one.

Although AMI neuroprostheses are not available to the public, Herr said the AMI surgery has been performed on about 60 people worldwide.

At Brigham and Women’s Hospital in Boston, where Carty is a surgeon in the Department of Plastic Surgery, AMI is now the standard treatment for amputations, Carty said.

“The [hospital’s] “The ethics board has determined that it is unethical to offer the standard amputation because we now know that the AMI amputation is so beneficial,” Herr said. “We hope that it will be standard not just in Boston, but in clinical sites around the world.”

The more surgeons, prosthetists, researchers and patients collaborate on new developments, the better, Rheinstein says. He hopes the AMI technique will “focus attention on the importance of a carefully planned amputation surgery for a patient’s successful rehabilitation.”

“Hollywood has given us visions of these remarkable bionic people for decades… but the scientific reality is slower than science fiction,” Herr added.

“We are finally producing systems that we have seen in movies.”