A spinal cord stimulator combined with a shoe sensor improves balance and walking stability in people who have lost a foot – and unexpectedly, it also dramatically reduces phantom limb pain, a type of pain that seems to come from the missing limb.
Three people – each of whom lost a foot due to an injury or diabetes – tested the device in a small proof-of-concept trial. They found they had an easier time navigating challenges like standing on a swaying platform with their eyes closed, and they were less likely to fall.
The new system relies on pressure sensors on the sole of a prosthetic foot, which send electrical pulses to a surgically implanted spaghetti-like stimulation device in the lumbar area of the spine. This mimics the way sensory receptors work, adding a touch-like sensation to prosthetics.
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The device also reduced participants’ phantom limb pain – discomfort in a limb that is no longer there – by an average of 70 per cent. “There was a very profound reduction in pain while people were participating in the study,” says at the University of Pittsburgh in Pennsylvania, who worked on the research. He had expected the devices would improve mobility but says the dramatic reduction in pain “was a little surprising”.
Fisher hopes the technology will be able to help the roughly who have lost a limb. The  report phantom limb pain, which typically does not respond to pain medications.
Previous work in the field has largely focused on targeting the nerves near the amputation site to restore sensation, says at the University of Utah, who was not involved in the work. “The advantage of doing it from the spine is that there are already a bunch of devices on the market that are approved for use”, making it potentially faster and easier to roll out.
The devices were implanted for one to three months, so the next step “is to see how somebody uses it out in the world for a long period of time”, says Fisher. If all goes well in the following trials, he expects the technology could be available to patients “on the scale of five to 10 years”.
Nature Biomedical Engineering
