In Summers' case, the researchers explained that when his spinal cord was stimulated in this way, nerves in the cord -- plus feeling in the legs -- directed the muscle and joint movement that is needed to allow him to stand and walk on a treadmill.
This was done with assistance, the researchers added. In addition, Summers has been able to stand and take steps, also with help.
In addition to epidural spinal cord stimulation to help retrain nerves there to send signals to produce certain movements, Summers underwent repeated motion training to retrain his muscles, the researchers said.
It took more than two years to complete the retraining project. After that, the device that causes electrostimulation was implanted in Summers' back. Before that, Summers had no voluntary control over his movement, the investigators said.
The report was published in the May 20 online edition of The Lancet.
Whether epidural spinal cord stimulation will work with most spine injured patients is unknown. Summers was classified "B" on the American Spinal Injury Association system, meaning he had some sensation below the point of the injury.
However, if epidural spinal cord stimulation will have any benefit to patients classified as "A" -- where there is no sensation below the injury -- is unclear, the researchers said.
Other concerns focus on whether it will be possible to develop better hardware -- currently, the researchers are using a stimulation device originally designed to relieve pain. In addition, experiments in animals have shown that some drugs might improve the
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