Restoring Somatotopic Sensory Feedback in Lower Limb Amputees through Noninvasive Nerve Stimulation

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 paper aims to (a) investigate the potential of transcutaneous electrical nerve stimulation (TENS) as noninvasive means for restoring somatotopic sensory feedback in lower limb amputees and (b) evaluate the effect of the system over a 4-week experimental protocol. The first phase of the study involved 13 participants (6 with TTA and 7 with TFA), and the second one evaluated the long-term effect of TENS on ambulation performance of 2 participants (S1 with TTA and S7 with TFA). The proposed system enhanced participant's ambulation significantly increasing the body weight 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 symmetry index from 11% to 5%, P < 0.0055; S7: stance phase symmetry index from -4% to -2%, P < 0.0055). It led to a postamputation neuropathic pain reduction in S1 (neuropathic pain symptom inventory score diminished from 6 to 0). This demonstrates how TENS enhanced prosthesis embodiment, enabling greater load bearing and more physiological gait patterns. This study highlights TENS as noninvasive solution for restoring somatotopic sensory feedback, addressing the current limitations and paving the way for further research.