LET ME UPGRADE YOU

We’re about to get prosthetics that can not only move for you but feel for you

Johnny Matheny wants you to try something tomorrow: Put on some pants, and a belt—and then shove your dominant hand between your waist and your belt, so it’s strapped in at the wrist. Now brush your teeth, take a shower, make coffee, and do everything else you need to do—with just the other hand.

I tried it. It wasn’t just slow and frustrating, it was damn near impossible. One example: to clean my teeth, I had to open the toothpaste bottle, put it down, pick up the toothbrush, stick it handle-first between my clenched teeth, pick up the bottle again, squeeze some out, put the bottle back down, take the toothbrush out of my mouth, then go at my teeth. It took me 10 minutes.

But Matheny does it every day, at least since his left arm was amputated in 2008 because of cancer. As he told me when we met this past summer, the world is designed for the two-handed. Which is why he’s volunteered himself to be the human guinea pig for the latest and greatest prosthetic experiment currently going on at the Defense Advanced Research Projects Agency (DARPA), the US military’s research wing. He’s gotten a metal socket grafted into his humerus bone and electronic device implants in the nerve bundles of his chest and back, and DARPA has designed and built the most advanced, robotic prosthetic to date specifically with Matheny in mind. (Sadly, his insurance won’t pay for it—it did after all cost millions to develop—so he can only use it during tests at DARPA’s lab.)

Matheny has become one of a handful of modern-day Vasco de Gamas of the human nervous system. Not a decade ago, the best options for those who lost their arms or legs to cancer, infection, enemy fire, or other accidents looked a lot like they did a century ago: rigid, unmoving stumps, maybe with a hook at the end to grasp. But thanks to intrepid patients like Matheny—and innovative neuroscientists, engineers, designers, physical trainers, and surgeons—we’re nearing a time when prosthetic designs will make the leap from rough and clumsy tools to customized, integrated, and elegant replacements that not only obey signals directly from your brain but transmit sensations back to it. The ultimate goal: a replacement limb that can basically do everything important your old one did, without the sunburns and bleeding.

The keys to this cyborg future are two related forms of surgery. The first, targeted muscle reinnervation (TMR), gives amputees the ability to control advanced robotic prosthetics using just their minds. The second, targeted sensory reinnervation (TSR), which is much more experimental, potentially allows the prosthetic to transmit sensations like touch, cold or heat back to the brain.

 The ultimate goal: a replacement limb that can basically do everything important your old one did, without the sunburns and bleeding. 

This year, Melissa Loomis became one of the first people to have a successful form of both.

One afternoon in 2015, the 43-year-old broke up a fight between her dogs and a raccoon outside her house in Canton, Ohio. The wild animal bit her before running away. What at first seemed like little more than a scratch soon became severely infected, and Loomis ended up in the hospital.

A local orthopedist, a hand and upper extremity specialist named Ajay Seth, was assigned to the case. “I told her that I would for sure be able to save her arm,” he says. But things got worse, and he had no choice but to amputate the arm above the elbow. So he committed himself to a new mission: “I would make her the most advanced person in the world when it came to prosthetics.”

Seth had recently learned about TMR. Invented by two Northwestern University surgeons, Todd Kuiken and Gregory Dumanian, in the early 2000s, it’s been performed on about 200 patients, including Johnny Matheny.

Nerves of left upper extremity
TSR and TMR surgeries typically involve the ulnar, radial, and median nerves of the arm. (Gray's Anatomy of the Human body, 1918 (Public Domain))

Three major nerves (median, ulnar, and radial) in the arm carry impulses from the brain down through the limb. But when the limb is gone, those impulses have nowhere to go; Seth likens it to traveling down a dead-end street. In TMR, you take those nerves and remap them onto muscles in the upper arm, either the bicep or tricep—tricking the brain into thinking that muscle is the forearm, and can, therefore, control the wrist, hand, and fingers.

Of course those aren’t real hands or fingers. They are for all intents and purposes phantom appendages. And except for the few advanced prosthetic limbs such as those Matheny is helping to develop at DARPA, there’s no consumer product—nothing Loomis could take home.

At the time, however, Loomis was suffering from severe phantom limb pain in the hand she had lost. “It felt like my hand was crushed in a vice,” she says, “like there was an object closing my hand that I was constantly trying to break free of. I could feel the hand but it was like I couldn’t open my fingers, like it was in a tight fist.” Seth told her that past studies suggested a chance TMR surgery could ease some of that pain. “I said, ‘What is there to lose?’ I had had so many surgeries at that point. What was one more?”

But Seth wanted more for for Loomis than just pain relief.

Just two years ago, an overview study published in Current Surgery Reports noted the “large gap” that existed in the world of advanced prosthetics: “In particular, the ability to provide physiologically relevant sensory feedback—to have the amputee feel the prosthetic hand as their own—has not yet been achieved.” The authors of the study, a team at the University of Alberta in Canada led by Jacqueline Hebert, believed that they had come up with a solution to close that gap: targeted sensory reinnervation (TSR) surgery.

TSR works alongside TMR: As you reroute those three key nerves, you also open them up. Each of the major nerves is actually a bundle of nerve fibers, and somewhere inside that bundle, running all the way from shoulder to wrist, is the one little fiber that sends impulses the other way, transmitting sensations from the tips of your fingers to the depths of your brain. Once you find that tiny fiber, you peel it back from just above where the amputation was to the top of the arm. Along the way, you attach it to the small cutaneous nerves that enable us to feel sensation on our skin. In essence, you create a literal map of the hand on the patient’s upper arm. If you pressed the “thumb” she would feel pressure on her thumb.

Detailed image of the neural "hand" mapped onto Melissa Loomis' bicep
Detailed image of the neural “hand” mapped onto Melissa Loomis’ bicep. (Ajay Seth)

Each dot shows one fingertip in Loomis’s newly mapped “hand” — red is the thumb, black is the middle finger, green is the index finger, blue is the ring finger, and purple is the pinky.

In theory, if you had an advanced enough prosthetic device, the patient could feel with that, too. All you’d have to do is figure out a way to send electrical signals from the tips of the prosthetic fingers to the “map” of those same fingers on the patient’s arm—and that’s technology that DARPA’s already worked out.

According to Jaret Olson, one of Hebert’s colleagues and the director of University of Alberta’s Division of Plastic Surgery, their team has performed the procedure successfully on a three patients in Canada. Seth resolved that Loomis would be the first in the US to have the surgery. He read the literature, talked to the University of Alberta team, and made one small adjustment: To keep these ultra-thin nerves from coming apart, he wrapped them with AxoGuard Nerve Protector, which is made from natural tissue and, as Seth puts it, helps “make those nerves almost native.”

The surgery took over 16 hours—six of them spent just finding that one thin sensory nerve thread—and so far seems a dazzling success. “After the surgery, it felt like I could move my hand, and the pain went away,” says Loomis. It took a while for her to learn how to control those phantom movements. “It took about a month of practicing to open and close my fists,” she says. “I’m just now getting my fingers down, where I can do my thumb individually.”

The bigger news is that Loomis is now the first patient ever to feel sensation on all five fingers of a prosthetic hand—albeit one not actually attached to her body.

 “It was a tingling sensation—like putting your tongue on a battery. You could feel it jolt up the finger.” 

“We teamed up with Walter Reed [National Military Medical Center] and the [DARPA] Advanced Physics Laboratory, and have been doing trials with the prosthetic arm they have,” says Seth. “It’s the only limb in the world that can move and feel.” They helped verify that the TSR surgery actually worked: Loomis and Seth visited their facilities in Baltimore, where Loomis’s upper arm was wrapped in a band that could transmit electric signals to the prosthetic built for Matheny, which lay a few feet away. (Since Matheny is a muscular 200 pounds and has metal implants designed specifically to help carry the weight of the device, there was no way Loomis, a small woman, could physically support it).

Loomis was able to not only move the robotic arm and hand with just her thoughts, but could feel when someone touched the prosthetic fingers. To do the tests, Loomis would close her eyes or turn her back to the prosthetic, and a researcher would touch one of the fingers and ask her to name which one. She nailed it almost every time. It felt, she says, like “a tingling sensation—like putting your tongue on a battery. You could feel it jolt up the finger.”

Melissa Loomis uses DARPA's advanced prosthetic limb to dunk a foam basketball
Melissa controls DARPA’s advanced prosthetic limb, dunking a foam basketball into a basket held by her surgeon, Ajay Seth. (Ajay Seth)

At the moment the prosthetic limb can only transmit a sensation of touch. But, in principle, Loomis can feel pressure and cold as well. Seth and his team have extensively tested the virtual “hand” on her arm: “I’ve tricked her brain into thinking the inside of her arm is actually her hand,” says Seth. “If you take a Sharpie marker, there are five fingers there that are the exact same size as her real fingers.” When they put an ice cube up against her right “index finger,” Loomis actually feels the tip of her invisible digit getting cold.

In short, they’ve set her nerves up to carry sensations that are beyond what current prosthetic technology can detect. To date, the most successful work to restore true sensory feeling has involved engineering implants that sit inside the body and can read and process electrical impulses coming in from the prosthetic, and then send those through the nervous system up to the brain. But systems like these are still very crude; scientists are still working out nuances like just how much electricity the nerves should be sending for different sensations.

TSR bypasses this problem by using the body’s native software—rewiring a nervous system that already knows exactly how to tell the brain what’s what. “The thing that’s unique about this is that you get away from the internal hardware,” says Michael McLaughlin, who leads the prosthetics program at the Johns Hopkins University Applied Physics Laboratory. “For a lot of amputees this could be a good solution. It’ll be more robust than anything implantable.”

But because there’s been no way—until Loomis’s successful TSR—to return complex feelings like pressure and temperature to amputees, there’s been no need for a prosthetic that could read those senses. So now Loomis and Seth are working with engineers at both Walter Reed and the Advanced Physics lab to make one come about. “At this point, there’s no reason to do [the surgery] again,” says Seth. “There’s no prosthetic on the market that can feel. What we’re doing now is using the results that Melissa has had to incorporate that into a prosthetic.”

When I mention this to Loomis, she tells me that “I’m usually the last to know. It’s exciting and a little bit weird.” The fact that she’s now the tip of the spear when it comes to prosthetic research hasn’t sunk in. While she waits to find out what’s next, she focuses on playing with her dogs, volunteering at the local pound, and working her 28th year at a local retirement and assisted-living facility. “I’m just me,” she says, “doing what I do.”

Loomis keeps practicing, though, wherever she is—when she pours a pot of coffee at work, for example, she “uses” both hands, curling her invisible right fingers around the glass as she grasps the handle with her corporeal left—with the hope that in the near future, she’ll have a prosthetic that can integrate directly with her body and mind.

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