A step in the right direction

Three paralyzed patients walk with the help of epidural spinal stimulation

It wasn’t even a fateful decision, it just happened. Jeff Marquis didn’t ride his mountain bike around the jump, as he usually did, but rolled over it – when he fell, he broke two bones in his neck. Jeff was paralyzed from the chest down. His doctors told Jeff he would never walk, run, or ride a bike again.

In 2018, Jeff Marquis walked down a hospital corridor under the watchful eye of cameras. The turnaround wasn’t a miracle. Instead, it was due to an electrode his doctors at the Kentucky Spinal Cord Injury Research Center implanted in Jeff’s spine. Electrical impulses delivered directly to his spinal nerves, called epidural spinal stimulation, allowed the neurons in Jeff’s spinal cord to process signals once again – and to get his legs moving. “When I first got injured, I was not optimistic at all about being independent in a wheelchair, much less independent in stepping or standing. Going from that not really being a possibility to being possible again is just huge. It definitely was a huge ray of sunshine”, Jeff Marquis told The Guardian.

Like Jeff Marquis, about 1.3 million people in the US are unable to walk due to spinal cord injuries. But unlike a broken bone that grows back together, severed neurons do not re-connect. The spinal cord is the highway for information between the brain and the muscles, so when injury interrupts the spinal cord, the brain and muscles cannot communicate anymore. Every patient is different, but most patients not only lose movement below the site of injury but also some feeling in their body.

Causes of spinal cord injuries in the US. Traffic accidents are the most frequent cause of SCIs.

What can be done to help people with spinal cord injuries? Two teams of researchers, one at the Kentucky Spinal Cord Injury Research Center in Louisville and one from the Mayo Clinic and UCLA, independently tried epidural spinal stimulation. They implanted a 16-electrode array, an off-the-shelf device originally used for pain management, into their patients’ spinal cords, below the site of injury, at a point in the spinal cord where signals are sent to the legs. The electrodes were hooked up to a battery pack implanted behind the stomach wall. Stimulation is turned on and off, and tuned in frequency and intensity, with a small remote control.

Epidural stimulation, combined with intensive rehab, enabled at least some of the patients in the study to walk again. Jered Chinnock, who participated in the study at the Mayo Clinic, was eventually able to walk the length of a football field. In the study led by Susan Harkema in Louisville, two patients, Jeff Marquis and Kelly Thomas, were able to stand and take steps with a walking frame, while the other two patients walked with assistance by trainers. Thomas described to The Verge how it felt to take her first steps. “It was like watching fireworks, but from the inside. Something I was never supposed to do ever just happened. It was awesome. There’s no other feeling like it in the world.”

The researchers are still figuring out how exactly epidural spinal stimulation allows, at least some, patients with spinal cord injuries to walk again. Epidural spinal stimulation is based on the principle that some small signals from the brain are still able to cross the site of injury, but these signals are not enough on their own to get the legs moving. Stimulation by the electrodes could make the spinal cord more attentive to the few signals that are still coming in. “It is like it is more aware, it actually can listen to that little whisper from the brain that is still there and it can generate the motor pattern,” co-author Claudia Angeli told The Guardian.

While some movement was seen almost immediately after implanting the stimulator, re-learning how to walk took time, said Angeli. “When we turn the simulator on and ask the individuals to move their toes or their legs, that actually happens very early, without training or therapy. But walking and standing are tasks that are a lot more complex and require a lot more coordination between different muscles. That takes training. The spinal cord has to relearn how to integrate all the signals to generate the movement.”

None of the patients can walk without stimulation, and stimulation is not a quick fix: it took many weeks of training before Marquis and Thomas could take their first steps, and then some more time until they could walk unaidedly. One patient in the Louisville study broke his hip during training. Kelly Thomas, who was paralyzed at 19 when her truck flipped and she hit her head, is now able to walk with a walking frame. “It is 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,” Thomas told The Verge, “You have to figure out how to use it, how to work with your body again.”

Norbert Weidner, Director of the Paraplegia Clinic at the University Hospital Heidelberg, cautions against too much euphoria: “The studies show that, in principle, the combination of electrical stimulation and training work.” However, the results do not have a great influence on day-to-day living for completely paralyzed patients. “Electrical stimulation on its own will not restore walking functions that are relevant for the daily life of patients with complete paralysis”, Weidner tells the Tagesspiegel.

[timeline of spinal cord injury research- For a long time, spinal cord injuries were believed to be incurable. In the past decades, researchers have been trying different approaches to heal spinal cord injuries – with varying success.]

Meanwhile, other research teams are trying out different approaches to get patients with spinal cord injuries walking again. In 2014, Darek Fidyka recovered from a complete severing of his spinal nerves when surgeons used cells taken from his nose, as well as neurons, to patch the site of injury. Other ideas being explored include, for example, using drugs to enhance the ability of neurons to regrow, or using powered exoskeletons to help patients walk again.

Jeff Marquis is optimistic. “I’ve still got a way to go until I can walk on my own, until I no longer need someone there to catch me when I fall, literally,” he told the Guardian, “I’m working on that certainly, and trying to see what else that thing can do.”

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