From the Journals

Sensory feedback may smooth walking with a prosthetic leg



A prosthetic leg that elicits the sensation of knee motion and the feeling of the sole of the foot touching the ground may improve walking performance and reduce phantom limb pain, according to a proof-of-concept study with two patients.

Prosthetic leg is shown Huntstock/thinkstockphotos

With the bionic leg system, the patients performed better during clinically important tests indoors and outdoors, study author Stanisa Raspopovic, PhD, explained during a press briefing about the research. The findings were published in Nature Medicine.

The results indicate that the use of sensory feedback “could be common practice” in prosthetic devices in the future, he said. Dr. Raspopovic is a researcher at Swiss Federal Institute of Technology Zürich and a founder of SensArs Neuroprosthetics, which is based in Lausanne, Switzerland.

Neural prosthetics allow the nervous system and external devices to interact. These brain-machine interfaces may improve quality of life for patients with brain or spinal cord injuries, degenerative disease, or loss of limbs.

“Conventional leg prostheses do not convey sensory information about motion or interaction with the ground to above-knee amputees, thereby reducing confidence and walking speed in the users,” the study authors wrote. Users may also have high levels of mental and physical fatigue, and the lack of physiologic feedback from the extremity to the brain may contribute to the generation of phantom limb pain.

To evaluate whether neural sensory feedback restoration could address these issues, investigators conducted a study with two patients who had undergone transfemoral amputations as a result of traumatic events. The patients were implanted with four intraneural stimulation electrodes in the remaining tibial nerve. The prosthetic leg device included sensors to represent foot touch and pressure and knee joint angle. The sensors transmitted sensory signals to the nervous system through the stimulation electrodes in the tibial nerve.

When the patients walked outdoors over a path traced in the sand, “participants’ speeds were significantly higher when sensory feedback was provided,” the authors wrote. One participant walked 3.56 m/min faster, and the other walked 5.68 m/min faster.

The participants also rated their confidence in the prosthesis on a scale from 0 to 10. For patient 1, self-rated confidence improved from 4.85 to 7.71 with the device. Patient 2 reported a confidence level that climbed from 2.7 to 5.55.

When tested indoors, both patients reached a 0.5 km/hour higher speed on the treadmill when stimulation was provided and both had a lower mean rate of oxygen uptake during the sensory feedback trials, the study authors reported.

Levels of phantom limb pain also decreased significantly after 10-minute stimulation sessions, but not during control sessions.

Longer studies with more patients are required, and fully implantable devices without transcutaneous cables need to be developed, the authors wrote.

Grants from the European Research Council, European Commission, and Swiss National Science Foundation funded the research. Dr. Raspopovic and two coauthors hold shares of SensArs Neuroprosthetics, a start-up company dealing with the commercialization of neurocontrolled artificial limbs.

SOURCE: Petrini FM et al. Nat Med. 2019 Sep 9. doi: 10.1038/s41591-019-0567-3.

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