Sensory neuroprosthesis improves postural stability during Sensory Organization Test in lower-limb amputees

Abstract

To maintain postural stability, unilateral lower-limb amputees (LLAs) heavily rely on visual and vestibular inputs, and somatosensory cues from their intact leg to compensate for missing somatosensory information from the amputated limb. When any of these resources are compromised, LLAs exhibit poor balance control compared to able-bodied individuals. We hypothesized that restoring somatosensation related to the missing limb via direct activation of the sensory nerves in the residuum would improve the standing stability of LLAs. We developed a closed-loop sensory neuroprosthesis utilizing non-penetrating multi-contact cuff electrodes implanted around the residual nerves to elicit perceptions of the location and intensity of plantar pressures under the prosthetic feet of two transtibial amputees. Effects of the sensory neuroprosthesis on balance were quantified with the Sensory Organization Test and other posturographic measures of sway. In both participants, the sensory neuroprosthesis improved equilibrium and sway when somatosensation from the intact leg and visual inputs were perturbed simultaneously. One participant also showed improvement with the sensory neuroprosthesis whenever somatosensation in the intact leg was compromised via perturbations of the platform. These observations suggest the sensory feedback elicited by neural stimulation can significantly improve the standing stability of LLAs, particularly when other sensory inputs are depleted or otherwise compromised. Individuals with lower limb amputation face challenges in maintaining their balance when navigating uneven terrains or encountering perturbations during walking 1-3. The fear of falling and decreased balance confidence are prevalent among lower limb amputees (LLAs) 2,4 , which are important factors in their mobility and participation in social activities 4-8. Compared to individuals without lower limb loss, LLAs have slower walking speeds, possibly because of decreased gait stability and the need for increased conscious attention while walking on uneven or changing terrains 1. In a survey of community-dwelling LLAs, more than 50% reported that they had fallen at least once in the past year 4,9. Amputees typically place more trust in the intact limb, which results in overuse and destructive long-term consequences, such as osteoarthritis of the intact knee and/or hip 10. Decreased loading on the affected limb can also lead to osteopenia and subsequent osteoporosis. With the growing number of people who lose limbs due to vascular diseases or trauma, it is important to develop assistive technologies that improve standing stability in this population. Three main sensory systems, the visual, vestibular, and somatosensory, contribute to stable posture during stance 11,12. Theses inputs are integrated and processed in the central nervous system which generates appropriate movement strategies and motor commands to maintain postural stability 13,14. However, when any of the sensory inputs are absent or inaccurate, the CNS adjusts the gains for each ...

Ambulatory searching task reveals importance of somatosensation for lower-limb amputees

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Evaluating Sensory Acuity as a Marker of Balance Dysfunction After a Traumatic Brain Injury: A Psychophysical Approach

“…The interventions that specifically target the sensory mechanisms have shown to be effective in improving standing balance. E.g., Charkhkar et al (2020) showed that the enhanced perception of the plantar pressures under the prosthetic feet achieved using artificial sensory feedback can significantly improve the postural stability of lower limb amputees. Similarly, Petrini et al (2019) showed that real-time tactile and proprioceptive feedback provided by sensory neuroprosthetic promoted improved mobility, fall prevention, and agility during active tasks in transfemoral (above-knee) amutees.…”

Solving musculoskeletal biomechanics with machine learning

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