Bionic leg restores natural walking speed and steps: ‘It didn’t feel like my leg was amputated’

CNN
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Amy Pietrafitta has learned to walk seven times.

First it was as a child and then after an industrial burn led to the amputation of her left leg in 2018. Since then, she’s had her “first steps” in prosthetic legs for running, water, high heels, rowing and walking daily.

Her last “first steps” were different. This time, she was fitted with 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.

“It 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, which is fully controlled 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 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 prosthetic to sense its position and movement and send this information 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, showed that participants who had a specialized amputation and neuroprosthesis increased their walking speed by 41%, matching the range and abilities of people without leg amputations. The results also suggested that the bionic limb could be controlled using only 18% of natural proprioception.

This is the first bionic leg fully controlled by the human nervous system to demonstrate natural walking speeds and gait patterns, according to Dr. where the research took place.

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

Herr started the project after observing a trend in prosthetics being increasingly controlled by robotic algorithms rather than the human nervous system.

“We want to rebuild human bodies,” he said. “We want to rebuild and give people what they want. We don’t just want to build prettier and prettier 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.

According to Pietrafitta and Dr. Matthew J. Carty, lead surgeon on the first AMI procedure and a co-author of the new study.

“This is a fundamental paradigm shift in how we think about amputation in relation to technology: treating it as a restorative procedure as opposed to a failure,” Carty said.

The technology also allows users to switch between speeds without changing the prosthesis. This reduces the hassle of switching legs, avoids unwanted attention and restores a sense of normalcy, according to Pietrafitta.

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

Restoring normal walking is about more than getting from point A to point B. According to Pietrafitta, it’s about re-entering society.

“It meant my life could start over. … I could go out there and live the way I wanted to,” she said. very difficult for people to come in and see you in pain.”

For John Rheinstein, a lower and upper limb prosthetist and clinical 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) as a result of advances in understanding and dealing with the emotional impacts of losing a limb,” he wrote in an email.

About 1.9 million Americans live with limb loss, a figure expected to double by 2050, largely due to rising rates of diabetes, a known risk factor, according to a 2018 report published by the Federal Agency for Research and Quality of Health Care.

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

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

“Demonstrating to payers the value of the outcomes we provide 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, the BionX emPOWER prosthesis is the only motorized prosthesis on the market, according to Herr, and many people with limb loss are unable to use it.

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

At Brigham and Women’s Hospital in Boston, where Carty is a staff surgeon in the Division of Plastic Surgery, AMI is now the standard of care for amputees, Carty said.

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

The more surgeons, prosthetists, researchers and patients work together on new developments, the better, according to Rheinstein, who hopes the AMI technique will “bring attention to the importance of carefully planned amputation surgery for the rehabilitation of successful patient”.

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

“We’re finally producing systems we’ve seen in the movies.”