Groundbreaking surgery gets amputee moving again – without 'phantom limb' effect

Groundbreaking surgery allows amputees to move without the 'phantom limb' feeling.
Groundbreaking surgery allows amputees to move without the 'phantom limb' feeling.

Climbing enthusiast Jim Ewing lost his left foot in the aftermath of a more than 15m fall from a Cayman Islands cliff.

But Ewing is scaling rock walls again with the aid of a robotic ankle and foot that work as well as his former flesh-and-blood version. This is thanks to a groundbreaking amputation procedure that eliminates the "phantom limb" effect, a disorientating side effect that makes it hard for patients to work their prosthetic limbs properly.

This August – a little more than two years after his amputation – Ewing successfully tackled the Lotus Flower Tower, a renowned 2500m peak located in the Northwest Territories of Canada.

A 'natural transition'

"When I'm connected to the robotic ankle, I can use it as if it's my very own," said Ewing, 54, of Falmouth, Maine. "It's a very natural transition going from no foot to all of a sudden having my foot back. I don't have to retrain my brain or retrain my muscles to do anything. It's pretty much a one-for-one replacement."

Losing a limb causes many disconcerting effects, as the brain tries to interpret signals from an arm or leg that's no longer there.

One of the oddest might be the fact that not only do people feel as though they have a phantom limb, but that limb's position in their mind often doesn't match the location of their prosthetic replacement.

"They can perceive a foot that is somewhere in space, but oftentimes is disembodied," said lead researcher Dr Matthew Carty, director of the Lower Extremity Transplant Program at Brigham and Women's Hospital in Boston. "It doesn't map geographically to where their prosthetic foot is. It's kind of floating to the side, or they may feel it's encased in a hard block and they can't move it."

These misleading signals can make it difficult for amputees to learn how to work a prosthetic limb properly.

New surgery erases disconnect with prosthetic limb

In July 2016, Ewing became the first person to undergo an amputation procedure designed to eliminate this disconnect.

Named after him, the Ewing Amputation recreates the normal tug-and-stretch relationship of muscles that occurs during normal movement of legs or arms.

When you move a limb, muscles on one side contract while muscles on the other side stretch, Carty explained. For example, when you lift a foot off the ground and move your ankle around, you'll feel muscles on both sides of your leg moving back and forth.

Researchers have learned that as they work, the muscles are sending constant signals to the brain's proprioceptive sensory system. Proprioception is your ability to know the exact position of your limbs at all times, allowing you to precisely coordinate their movements.

"It transmits information back to our brain where the limb is in space without us having to look at it," Carty said.

Confusing the brain

Traditional amputation screws up these signals by decoupling the muscles, Carty said. The lack of push-and-pull muscle feedback confuses the brain, creating misleading perceptions of a disembodied phantom limb.

A Ewing Amputation recreates the push/pull dynamic by surgically connecting muscles that normally operate in pairs, forcing one muscle to stretch in response to the other muscle contracting.

Fed the normal muscle signals, the brain is better able to make a person's perception of their lost limb line up with their new prosthetic, Carty said.

"The phantom limb the patient perceives maps geographically over their prosthetic device," Carty said. "When they think about moving their phantom limb, their brain superimposes that phantom limb over the prosthetic limb."

Amputees also often feel sensations of itching or pain associated with their phantom limb, as the brain struggles to make sense of discordant signals. The Ewing Amputation appears to prevent those sensations, the researchers added.

Growing success with procedure

Since Ewing, doctors have performed this amputation procedure on 11 more patients, Carty said. Ten lost their leg below the knee, and one lost their leg above the knee.

"At this point, we have enough data to say we think we've figured out a better way to do amputations, and we're in the process of testing that in a variety of different clinical scenarios," Carty said.

The research team has received funding to develop the procedure for arm amputation as well, Carty added.

Ankle not healing

Ewing had his climbing accident in December 2014, and at first, the damage to his left ankle was the least of his worries. He had life-threatening injuries throughout his body that required emergency treatment.

However, the ankle failed to heal properly during two years of recovery, remaining painful and swollen, Ewing said. A CT scan revealed that most of the bone in the ankle had died.

"It was not going to heal and recover," Ewing said. "It was not likely I would ever regain use of the foot, so I opted to have it amputated."

Carty had been working with a team at MIT to create a robotic limb that would work in conjunction with the new transplant procedure his team had dreamed up. It just so happened that a friend of Ewing is a lead researcher at MIT, who put him in contact with Carty.

Surgery not for every amputee

This sequence of events points out one drawback to the new procedure, said Dr Ageliki Vouyouka, an associate professor of surgery and radiology at the Icahn School of Medicine at Mount Sinai in New York City.

The procedure uses tissue harvested from the amputated limb to create the new connections between muscle groups, Vouyouka noted. Given this, people who lose limbs damaged by gangrene, poor blood flow or other diseases that kill off tissue would likely not be good candidates for the Ewing Amputation.

But the new procedure is a "very interesting development" that is likely to become a new standard for amputation if further testing bears it out, said Vouyouka, who was not involved with the research.

"Mostly I can see that happening for limbs lost to war trauma or civilian trauma," she said.

Easier adaptation

The new amputation procedure has provided other benefits on top of easier adaptation to his prosthetic foot, Ewing said.

"The muscle definition is much stronger. There's much more tissue there. My leg hasn't atrophied away to skin and bones, which happens quite a lot with amputations," Ewing said.

"The thinking is the residual limb is healthier because there's all this active muscle tissue there. You have improved circulation, more muscle tissue for padding and all of that," he said.

The study on Ewing's case was published recently in the online journal PRS Global Open.

Image: iStock

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