Restoring somatotopic sensory feedback in lower limb amputees through noninvasive nerve stimulation
image: (A) The participant with TTA wore his own aesthetic prosthesis with an instrumented insole placed under the foot. (B) Voltage and force signals of the 6 FSRs embedded in the insole and the measured vGRF. (C) The force information was encoded in stimulation patterns (PA, PF, and PW) via a linear modulation. (D) The stimuli were delivered to the participant’s tibial nerve through superficial electrodes placed near the popliteal fossa for the elicitation of referred tactile sensations in the phantom. For the participant with TFA, the working principle of the instrumented prosthesis is the same except for the stimulated nerve (i.e., sciatic rather than the tibial one) and the electrode positioning (i.e., along the femur axis rather than near the popliteal fossa). (E) Overview of the 4-week experimental protocol: Mi, mapping session; SIDi, SID session; Gi, session with G-EO System; Ti, gait analysis; Di, day.
Credit: Andrea Demofonti, Università Campus Bio-Medico di Roma.
Patients with lower limb amputation experience ambulation disorders since they rely exclusively on visual information in addition to the tactile information they receive from stump–socket interface. The lack of sensory feedback in commercial lower limb prostheses is essential in their abandonment by patients with transtibial amputation (TTA) or transfemoral amputation (TFA). Recent studies have obtained promising results using invasive interfaces with peripheral nervous system presenting drawbacks related to surgery. “This research aims to investigate the potential of transcutaneous electrical nerve stimulation (TENS) as noninvasive means for restoring somatotopic sensory feedback in lower limb amputees.” said the author Andrea Demofonti, a researcher at Università Campus Bio-Medico di Roma, “ And we also evaluate the effect of the system over a 4-week experimental protocol.”
For the first time, a full characterization of the evoked sensations in terms of perceptual thresholds, referred sensation, size, and similarity of the evoked regions was performed in 13 participants with lower limb amputation (6 with TTA and 7 with TFA). In both groups of patients, the proposed system was able to elicit natural, painless, and tactile sensations in the phantom limb with a good level of repeatability (SSIM always greater than 75%). Subsequently, the effect of TENS on ambulation performance of 2 participants (S1 with TTA and S7 with TFA) was evaluated in terms of lower limb kinematics, spatiotemporal parameters, and vGRF over a 4-week experimental protocol. The possibility for patients to perceive their missing limb again during walking via TENS significantly improved their walking capabilities. The proposed system significantly increased the BW distribution between legs (S1: from 134% to 143%, P < 0.0055; S7: from 66% to 72%, P < 0.0055) and gait symmetry (S1: step length SI from 11% to 5%, P < 0.0055; S7: stance phase SI from −4% to −2%, P < 0.0055).
The obtained results represent a huge progress beyond the current state of art and make this study a milestone in the literature of the field. This is the first study demonstrating the potential of a noninvasive sensory feedback restoration system based on TENS for the elicitation of somatotopic tactile sensations in participants with 2 different levels of amputation (TTA or TFA) and the introduction of such a sensory feedback can improve amputee’s ambulation performance and contribute to the reduction of postamputation neuropathic pain. This study paves the way for further investigations since it demonstrated how TENS is able to overcome the main drawbacks of both invasive (i.e, the need for surgery) and noninvasive (i.e., the elicitation of a nonsomatotopic feedback) methods currently adopted in the literature eliciting homologous and somatotopic sensations in the patients’ missing limb in a noninvasive way. “In the future, evidence from a larger population should be gathered to confirm the obtained results. Moreover, the trial should be conducted in a more realistic scenario to evaluate whether unevenness and slopes of the terrain can negatively affect the participant’s ambulation.” said Andrea Demofonti.
Authors of the paper include Andrea Demofonti, Marco Germanotta, Andrea Zingaro, Gaia Bailo, Sabina Insalaco, Francesca Cordella, Irene Giovanna Aprile, and Loredana Zollo.
This study was partly supported by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement no. 899822 (SOMA project), by the Italian Ministry of Health (Ricerca Corrente), by the Italian Ministry of Research under the complementary actions to the National Recovery and Resilience Plan (NRRP) “Fit4MedRob - Fit for Medical Robotics” Grant (PNC0000007), and by Fondazione ANIA with the project “Development of bionic prostheses characterized by personalized interfaces and sensory feedback for amputee patients with macro lesion after car accident”.
The paper, “Restoring Somatotopic Sensory Feedback in Lower Limb Amputees through Noninvasive Nerve Stimulation” was published in the journal Cyborg and Bionic Systems on Apr. 29, 2025, at DOI: 10.34133/cbsystems.0243.