A young man paralysed from the waist down after a snowmobile accident has made medical history by walking independently following pioneering surgery.
Doctors in the US used an electrode implanted below the injury site to stimulate surviving nerves in the spinal cord.
In tests the 29-year-old patient was able to stand up and walk 102 metres while pushing a front-wheeled walker.As soon as the remote-controlled electrode was turned off, he became paralysed again.
It was the first time the unidentified man had been able to walk by himself since his accident five years ago.
Neurosurgeon Dr Kendall Lee, who co-led the team from the Mayo Clinic in Rochester, Minnesota, said: "After implant and turning on the stimulation the patient was able to regain voluntary control of the movement of his legs.
"The reason why this is important is because the patient's own mind, thought, was able to drive movement in his legs.
"Just as important is that we were able to get him to stand independently and take his own steps.
"It's very exciting, but still very early in the research stage."
The man had suffered a severe spinal cord injury in the middle of his back, resulting in complete loss of movement and sensory function below the torso.
Unlike peripheral nerves, spinal cord nerves cannot repair themselves.
For this reason spinal injuries are often life-changing and devastating, resulting in disabling paralysis.
The technique used by the Mayo Clinic team, described in the journal Nature Medicine, relied on repurposed decades-old technology.
The electrode was adapted from the kind of electrical stimulation device commonly used to treat pain.
However, it had to be placed in a precise location below the injury site and tuned to provide just the right kind of pulsed signal.
Exactly how electrically stimulating a severed spinal cord was able to restore voluntary movement remains an unanswered question.
It may depend on residual nerve fibres keeping open a channel of communication with the brain, the scientists believe.
The surgery was conducted under general anaesthetic and involved inserting an electrode in the epidural space, the fat-filled hollow region surrounding the spinal cord.
A battery implanted in the abdomen was connected to the electrode via a hidden wire beneath the skin.
In the first week after surgery, the patient had to use a harness to reduce the risk of falling and help him regain body balance.
After 25 weeks he no longer needed a harness.
Over the course of a year, he achieved milestones that included walking 102 metres, taking 331 steps, and walking continuously for 16 minutes.
