The experience of sensorimotor integration of a lower limb sensory neuroprosthesis: A qualitative case study

Abstract

IntroductionLower limb prosthesis users often struggle to navigate uneven terrain or ambulate in low light conditions where it can be challenging to rely on visual cues for balance and walking. Sensory feedback about foot-floor interactions may allow users to reduce reliance on secondary sensory cues and improve confidence and speed when navigating difficult terrain. Our group has developed a Sensory Neuroprosthesis (SNP) to restore sensation to people with lower limb amputation by pairing electrical stimulation of nerves in the residual limb applied via implanted neurotechnology with pressure sensors in the insole of a standard prosthesis. Stimulation applied to the nerves evoked sensations perceived as originating on the missing leg and foot.MethodsThis qualitative case study reports on the experiences of a 68-year-old with a unilateral trans-tibial amputation who autonomously used the SNP at home for 31 weeks. Interview data collected throughout the study period was analyzed using a grounded theory approach with constant comparative methods to understand his experience with this novel technology and its impacts on his daily life.ResultsA conceptual model was developed that explained the experience of integrating SNP-provided sensory feedback into his body and motor plans. The model described the requirements of integration, which were a combination of a low level of mental focus and low stimulation levels. While higher levels of stimulation and focus could result in distinct sensory percepts and various phantom limb experiences, optimal integration was associated with SNP-evoked sensation that was not readily perceivable. Successful sensorimotor integration of the SNP resulted in improvements to locomotion, a return to a more normal state, an enhancement of perceived prosthesis utility, and a positive outlook on the experience.DiscussionThese outcomes emerged over the course of the nearly 8 month study, suggesting that findings from long-term home studies of SNPs may differ from those of short-term in-laboratory tests. Our findings on the experience of sensorimotor integration of the SNP have implications for the optimal training of SNP users and the future deployment of clinical SNP systems for long-term home use.

Restored somatosensation in individuals with lower limb loss improves gait, speed perception, and motor adaptation

“…LLA01 received the surgically implanted SNP seven years prior to the time of this report, with consistent operation and stable sensory responses throughout. The data collection for this study lasted for approximately five months, during which time participants routinely visited our laboratory for other experiments following their implant surgery (13,15,18,60,61). Throughout this and other previously reported studies, the implanted C-FINEs have demonstrated stable and reliable performance as evidenced by eliciting sensations in consistent locations related to the plantar surface of the foot of the missing limb.…”

Plantar somatosensory restoration enhances gait, speed perception, and motor adaptation

“…LLA01 received the surgically implanted SNP 7 years before the time of this report, with consistent operation and stable sensory responses throughout. The data collection for this study lasted for approximately 5 months, during which time participants routinely visited our laboratory for other experiments after their implant surgery ( 13 , 15 , 18 , 60 , 61 ). Throughout this and other previously reported studies, the implanted composite flat interface nerve cuff electrodes (C-FINEs) have demonstrated stable and reliable performance, as evidenced by eliciting sensations in consistent locations related to the plantar surface of the foot of the missing limb.…”

Neural sensory stimulation does not interfere with the H-reflex in individuals with lower limb amputation

“…Among the highest priority needs desired by individuals with lower limb loss are to improve their ability to walk safely, to move around more independently, and to integrate back into the community without feeling excluded ( Manz et al, 2022 ). Lack of sensory feedback from a missing foot could contribute to the observed deficits in gait stability and lower confidence in prosthesis use ( Kim et al, 2023 ; Schmitt et al, 2023 ).…”