WATCH | Breakthrough treatments help paralysed people walk again

Five years after he was paralysed in a snowmobile accident, Jered Chinnock has learned to walk again aided by an electrical implant, in a potential breakthrough for spinal injury sufferers.

A team of doctors at the Mayo Clinic in the US say that Chinnock, using a front-wheeled walker, was able to cover the equivalent of the length of a soccer field, issuing commands from his brain to transfer weight and maintain balance — all previously thought impossible for paralysed patients.

Chinnock, now 29, severed his spinal cord in the middle of his back when he crashed his snowmobile in 2013. He is completely paralysed from the waist down, and cannot move or feel anything below the middle of his torso. 

Doctors implanted a small electronic device in Chinnock's spine in 2016. 

The wirelessly operated implant, about the size of a AA battery, generates electrical pulses to stimulate nerves that — due to the injury — had been permanently disconnected from the brain. 

WATCH | Breakthrough implant helps paralysed man to walk again

"What this is teaching us is that those networks of neurons below a spinal cord injury can still function after paralysis," said Kendall Lee, neurosurgeon at the Mayo Clinic and lead study author.

Within weeks of the device being switched on, Chinnock began to take his first steps since the accident — but was still suspended in a harness.

Astonishingly, after several more sessions of rehab and physiotherapy, he was able to support most of his own body weight and take steps on a treadmill. 

"We didn't limit our expectations and continued to safely advance his performance as he gained function," said Kristin Zhao, director of the Mayo Clinic's Assistive and Restorative Technology Laboratory.

"This is important because the patient's own mind was able to drive the movement in the legs," she said.

Although the device was able to help generate power and control in Chinnock's lower body, it did nothing to restore sensation in his legs. 

This initially proved challenging. Without the physical feeling of walking registering in his brain, it was hard for him to make the instantaneous balance adjustments most of us make without thinking.

The team overcame the problem by installing mirrors at knee height so Chinnock could see what position his legs were in while walking. 

Eventually he was able to walk on the treadmill with only periodic glances down at his legs.

Footage of the experiment shows him walking jerkily on a slow-moving treadmill, using a metal rail for balance.

While the device's effect is remarkable, Chinnock is still paralysed once it is turned off. 

"It is important to understand that even with the success that this individual had in stepping ability during the research, he still performs his daily activities from a wheelchair," said Lee.

For safety reasons, Chinnock currently only uses the device under supervision, but the implications of the study — that paralysis may not be permanent after severe spinal injury — could be massive. 

"Our results, combined with prior evidence, emphasise the need to reassess our current understandings of spinal cord injury in order to realise the potential of emerging technologies for functional recovery once thought to be permanently lost," Lee said. 

The study, which was published in the journal Nature Medicine, was conducted in conjunction with the University of California and was partly funded by the Christopher and Dana Reeve Foundation.

Christopher Reeve, best known for his starring role in the Superman films, was left paraplegic after a horse-riding accident in 1995.

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Two patients in an experimental US rehabilitation program for paralysed people have been able to walk again thanks to electrical stimulation of their spinal cords, and two others have been able to stand or sit, according to a study published in the New England Journal of Medicine.

The Kentucky Spinal Cord Injury Research Centre at the University of Louisville had previously reported in 2014 that some paralysed patients had regained feeling thanks to electrical stimulation.

This time, the centre announced that after months of retraining two participants in its experimental programme were able to walk with the support of a walker or a cane, stimulated with an electrode in the spinal column linked to an implant in the abdomen.

Two other participants were able to stand up or sit down. 

"All four participants could not do these actions in trials when the stimulator was off," the study's authors said.

The researchers said the physiological mechanisms at work were not fully understood. But they suggested this could be linked to the fact that despite being completely paralysed, the two patients who were able to walk had retained some sensation below the level of their injury.

"The spinal cord can relearn to walk independently," Susan Harkema, the centre's leader told NBC News.

"We can retrain it to function even though there is that injury disconnecting it from the brain," she said.

WATCH | Breakthrough treatments help a paralysed man and women walk again

Kelly Thomas, one of the two patients who learned to walk, said her first steps were "an emotional milestone in my recovery that I'll never forget."

"One minute I was walking with the trainer's assistance and, while they stopped, I continued walking on my own," she said.

She now lives at home, where she is able to move from room to room or go outside with the help of a walker. 

To do so, she must activate the electric stimulator using a small remote.

Each step she takes still requires a monumental effort.

"It's not a quick fix to being paralysed," she told CNN. But she added: "Nothing's going to be able to stop me in life, because I took something that was thought to be impossible and I turned it into possible."