After Kelly Thomas’ truck flipped with her inside of it in 2014, she was told that she probably would never walk again. Now, with help from a spinal cord implant that she’s nicknamed “Junior,” Thomas is able to walk on her own.

Thomas and Jeff Marquis, who was paralyzed after a mountain biking accident, can now independently walk again after participating in a study at the University of Louisville that was published today in the New England Journal of Medicine. Thomas’ balance is still off and she needs a walker, but she can walk a hundred yards across grass. She also gained muscle and lost the nerve pain in her foot that has persisted since her accident. Another unnamed person with a spinal cord injury can now independently step across the ground with help from a trainer, according to a similar study at the Mayo Clinic that was also published today in the journal Nature Medicine.

“Something I was never supposed to do, ever”

For the nearly 1.3 million people who are paralyzed because of spinal cord injuries in the US, the hope is that standing and stepping can help bring more independence, improve circulation and bone density, and boost cardiovascular health. “There’s no real treatment for people with this type of injury,” says Susan Harkema, associate director of the Kentucky Spinal Cord Injury Research Center at the University of Louisville and senior author of the New England Journal of Medicine paper. “This isn’t taking them back to before their injury, but it’s giving them significant, incremental return of function, and health — and that can make their daily lives substantially better.”

Kelly Thomas and Jeff Marquis describe their experiences participating in the University of Louisville research program. Video: University of Louisville

For Thomas, when she walked without help for the first time, “it was like watching fireworks, but from the inside,” she says. “Something I was never supposed to do ever just happened. It was awesome. There’s no other feeling like it in the world.” The device that Thomas calls “Junior” is a 16-electrode array that delivers electrical stimulation to her spinal cord. With intense training, and what Harkema calls “a whisper of an intent” from Thomas’ brain, the device has helped Thomas walk again.

“I told him, ‘Okay, I’ll be your one or two percent.’”

The technique doesn’t work perfectly for everyone: two other study participants at the University of Louisville did not re-learn how to walk, though they can now stand, hold their torsos upright, and move their legs. “There’s still a ways to go for making this actually functional and letting people walk again as their main means of mobility,” says Jennifer Collinger, a professor of physical medicine and rehabilitation at the University of Pittsburgh who was not involved in the research. But even a limited ability to walk comes with health benefits, she says. “This is the first time that anybody has demonstrated functional walking activity for somebody with complete spinal cord injury.”

Thomas was 19 years old and driving near her home in Central Florida when her truck veered off the shoulder of the road, she says in a matter-of-fact way. She overcorrected, the truck went into a roll, and she hit her head on the roof, compressing her spine. In the hospital, she remembers people telling her how unlikely it was that she would ever walk again. “My surgeon told me personally, ‘I won’t say zero, but maybe one, maybe two percent,’” she says. “I told him, ‘Okay, I’ll be your one or two percent.’”

Thomas put her name down to participate in future research at the University of Louisville, and in November 2016, she got a call asking if she wanted to enroll in a study. Thomas was torn. She had already been doing extensive physical therapy and was able to stand up by then. But there was a hitch: to participate, she’d have to undergo surgery to implant Junior. “I didn’t want to lose anything that I’d worked so hard for,” she says. “I had regained so much, and the surgery scared me.”

“Whenever it’s on I can kick my legs out, I can walk.”

Junior is the RestoreAdvanced SureScan MRI Neurostimulator made by Medtronic, and it’s FDA-approved for pain management. (The Mayo Clinic study used Medtronic’s RestoreUltra SureScan MRI Neurostimulator.) Thomas controls it with a remote that communicates through her skin to a hub in her abdomen. “I have to have a remote to turn myself on and off, and when it’s off I’m completely paralyzed,” she says. “Whenever it’s on I can kick my legs out, I can walk, I can move my toes. I can do pretty much anything I need to do.”

It might sound a little strange to use a device for pain control to restore the ability to walk. But animal research has shown that rats with spinal cord injuries can learn to step again with training, drugs, and spinal stimulation. And people who are paralyzed can make stepping-like movements while lying down with spinal cord stimulation. So that hints that the parts of the spinal cord responsible for walking should still work in these patients. “If you cut the head off a snake, the snake will keep moving — you can’t even tell it’s not controlled by the head,” says Reggie Edgerton, a professor of integrative biology and physiology at the University of California, Los Angeles and a co-author on the Nature Medicine paper. “All of that is built into the spinal cord.”

This video shows the training progress of the unnamed participant in the Mayo Clinic study. Video: Zhao, et al.; Mayo Clinic; Nature Medicine.

The researchers are still investigating how this all works. But one theory is that after a spinal cord injury, those spinal networks may lose the electrical charge and information they’re getting from the brain — although some weak connections may remain. And that’s where the spinal stimulator comes in: the idea is that it essentially charges the spinal cord back up so that, with enough training and practice intending to move, Thomas’ body could re-learn how to walk. “Combined with all the sensory information you get from moving the legs in a steplike pattern, and that tiny little whisper of an intent signal that they still have coming down, that all comes together,” Harkema says.

“It’s not a quick fix to being paralyzed.”

The key was learning to work with the stimulator, Thomas says. She had to concentrate hard on moving her legs. “It’s not a quick fix to being paralyzed. You don’t turn it on and you’re just automatically back to where you were pre-injury,” she says. “You have to figure out how to use it, how to work with your body again.”

After months of training on a treadmill and walking across the ground with trainers moving her feet, she took her first consecutive steps on her own in February 2018. “I looked at the trainer, and I started crying,” Thomas says. “Oh my god, everything I had just worked so hard for for three years and been told, ‘You’re never going to do this again,’” she says. “I turned what was impossible into possible, and it was liberating.”

The researchers also don’t know why it works so well for Thomas and Marquis, but less so for the others. It could be differences between the study participants’ injuries, the training regimens, or the stimulation itself. “We still don’t know. We have to do larger trials,” Harkema says.

“We have Siri, for God’s sakes!”

But before the team can do those larger trials, the tech needs to become more accessible. Right now, the controllers have to be operated by hand, and hand function can be limited by spinal cord injuries, depending on the injury’s location. So, a key step will be to make the stimulators voice-activated. The tech exists, but applying it to a spinal stimulator takes investment from the tech sector, and that’s not in the researchers’ control, Harkema says. “We have Siri, for God’s sakes!” she says.

These days, Thomas is back home, living with her parents in Central Florida, and she tells The Verge that she’s majoring in criminal justice at the College of Central Florida. She can walk with a walker now, provided the stimulator’s on. But her next goal is to improve her balance so she can ditch the walker altogether. “If I lean too far forward, I may fall,” she says. “That’s my next step, to figure out how to catch myself if I start to fall.”