Neuroprosthetic Leg Restores Feeling, Eases Phantom Pain

Megan Brooks

September 10, 2019

A leg prosthesis that works with neural implants to restore sensory feedback can improve walking speed and confidence while reducing fatigue and phantom limb pain in above-knee leg amputees, new research suggests.

 

"We are the first group reporting sensory feedback restoration in above-knee amputees," coinvestigator Stanisa Raspopovic, PhD, Institute of Robotics and Intelligent Systems, Swiss Federal Institute of Technology, Zurich, Switzerland, said during a press briefing.

The results of the proof-of-concept study, which was conducted in two volunteers, "make us believe this could be a common practice in the next prosthetic devices," Raspopovic added.

The findings were published online September 9 in Nature Medicine.

Sensory Feedback

For patients who have undergone above-knee amputations, conventional leg prostheses do not provide sensory information about motion or interaction with the ground, which can be mentally and physically taxing. In addition, the lack of neural sensory feedback from the remaining extremity to the brain may contribute to phantom limb pain.

To develop a neuroprosthetic leg, the research team created an interface to connect a leg prosthesis with the residual nerves present in the user's thigh, thus providing sensory feedback.

The investigators used off-the-shelf prostheses and attached sensors under the sole of the prosthetic foot and collected data from the integrated angle sensor of the electronic knee.

Immediately after implant, the patients described natural sensations "close to lifelike," Raspopovic said.

During a 3-month period, the two volunteers underwent a series of tests with and without neurostimulation. In both individuals, walking speed and self-reported confidence in walking increased significantly during trials that involved stimulation compared to no-stimulation trials. This was the case in both a laboratory setting and outdoors while walking over "difficult terrain," said Raspopovic.

"Interestingly, the results were achieved with two proficient prosthetic users, for whom one might expect limited room for improvement to exist in prosthesis use. Thus, we hypothesize that such a system could be even more useful with participants with a lower walking ability or during rehabilitation," the researchers write.

Provides Rationale for Larger Studies

Stimulation was also associated with less mental and physical fatigue and a marked reduction in phantom limb pain, which both patients had been experiencing before the trial.

"After 1 month of neurostimulation, in one patient, the pain went completely away, and in the other patient, pain was reduced by more than 80%," lead author Francesco Petrini, CEO of SensArs, a start-up company involved in commercializing neurocontrolled artificial limbs, said at the briefing.

The results from this proof-of-concept trial provide a rationale for larger studies of the clinical value of neuroprostheses that restore sensory feedback to amputees, the investigators said.

Petrini reported that efforts are underway to develop a wireless neurostimulation device that can be fully implanted into the patient, like a pacemaker.

"Our final goal is to make this technology available for every amputee in the world," he said.

Funding for the study was provided by grants from the European Research Council, the European Commission, and the Swiss National Science Foundation. Raspopovic and Petrini hold shares of SensArs Neuroprosthetics.

Nat Med. Published online September 9, 2019. Abstract

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