Spinal cord stimulation improves sensory link to prosthetic feet, cuts phantom limb pain in Pitt study

After racking up more than 30 years’ worth of experience in treating chronic pain, spinal cord stimulators have recently begun to expand their remit. Even as the devices continue to tack on new indications across various forms of pain, researchers are now studying the use of the technology in restoring mobility and limb function after a stroke, paralysis or other injuries.

In the latest such example of that work, a study published Thursday in Nature Biomedical Engineering tasked spinal cord stimulation tech with improving the connections between the brain and a prosthetic foot in lower-limb amputees.

The proof-of-concept study—which included just three participants and was led by researchers from the University of Pittsburgh School of Medicine—proved successful, according to the study’s authors. The result paves the way for further clinical trials examining a potential new use for spinal cord stimulators.

In the study, the researchers rigged a standard spinal cord stimulation system to deliver its sensory signals—via electrodes implanted over the spinal cord in the lower back—as the participants stood or walked on their prosthetic legs. The level of stimulation was programmed to automatically change with the amount of pressure being exerted on the leg, based on transmissions from wireless sensors embedded into a shoe insole underneath the prosthetic foot.

The system proved to be an accurate mimic of the sensations associated with walking and standing, supported by marked improvements in the participants’ balance and stability. According to the study, one participant experienced a 19-point improvement on the 100-point Sensory Organization Test, which assesses balance control. In addition, one participant saw their score on the 30-point, stability-focused Functional Gait Assessment improve by five points.

On top of the improved sensory connections between the participants and their prosthetic devices, the system also helped to reduce the phantom limb pain associated with their amputated limbs. Altogether, the trio of patients reported an average reduction of 70% in their phantom limb pain—a particularly notable achievement, according to the researchers, since that form of pain is very common among lower-limb amputees and often doesn’t respond to standard pain medications.

In a Pitt press release, the researchers highlighted the fact that their system was created using commercially available technologies already widely used by doctors.

“We are leveraging those technologies to produce meaningful improvement in function and reduction of pain,” said Lee Fisher, Ph.D., senior author of the study and an associate professor of physical medicine and rehabilitation at Pitt. “That’s exciting, and we’ve been building it for a while.”

They also noted that the system proved successful across individuals who’d undergone amputation for various reasons, as two of the participants’ amputations stemmed from diabetic peripheral neuropathy, while the third’s was a traumatic case.

“We are able to produce sensations as long as the spinal cord is intact,” Fisher said in the release, adding that that broad accessibility means the system could potentially be available sooner than later: “Our approach has the potential to become an important intervention for lower-limb amputation and, with proper support from industry partners, translated into the clinic in the next five years."