Lower-Limb Amputees Adjust Quiet Stance in Response to Manipulations of Plantar Sensation

Abstract

Interfering with or temporarily eliminating foot-sole tactile sensations causes postural adjustments. Furthermore, individuals with impaired or missing foot-sole sensation, such as lower-limb amputees, exhibit greater postural instability than those with intact sensation. Our group has developed a method of providing tactile feedback sensations projected to the missing foot of lower-limb amputees via electrical peripheral nerve stimulation (PNS) using implanted nerve cuff electrodes. As a step toward effective implementation of the system in rehabilitation and everyday use, we compared postural adjustments made in response to tactile sensations on the missing foot elicited by our system, vibration on the intact foot-sole, and a control condition in which no additional sensory input was applied. Three transtibial amputees with at least a year of experience with tactile sensations provided by our PNS system participated in the study. Participants stood quietly with their eyes closed on their everyday prosthesis while electrically elicited, vibratory, or no additional sensory input was administered for 20 s. Early and steady-state postural adjustments were quantified by center of pressure location, path length, and average angle over the course of each trial. Electrically elicited tactile sensations and vibration both caused shifts in center of pressure location compared to the control condition. Initial (first 3 s) shifts in center of pressure location with electrically elicited or vibratory sensory inputs often differed from shifts measured over the full 20 s trial. Over the full trial, participants generally shifted toward the foot receiving additional sensory input, regardless of stimulation type. Similarities between responses to electrically elicited tactile sensations projected to the missing foot and responses to vibration in analogous regions on the intact foot suggest that the motor control system treats electrically elicited tactile inputs similarly to native tactile inputs. The ability of electrically elicited tactile inputs to cause postural adjustments suggests that these inputs are incorporated into sensorimotor control, despite arising from artificial nerve stimulation. These results are encouraging for application of neural stimulation in restoring missing sensory feedback after limb loss and suggest PNS could provide an alternate method to perturb foot-sole tactile information for investigating integration of tactile feedback with other sensory modalities.

Agonist-antagonist muscle strain in the residual limb preserves motor control and perception after amputation

“…Many ongoing efforts to restore locomotion for persons with leg amputation involve motor intent classification strategies based on electromyography (EMG) and intrinsic prosthetic signals 5 , 6 . However, in the absence of visual feedback, postural responses and balance during walking remain challenging for persons with leg amputation 7 , 8 , which may indicate that motor control and proprioceptive percepts are significantly altered in persons that have undergone a conventional amputation procedure 9 – 11 . Toward better, more biomimetic control of an external prosthesis, invasive nerve interfacing using artificial electrical stimulation has shown great potential in restoring cutaneous 12 – 14 and proprioceptive sensation 11 , 12 .…”

“…However, in the absence of visual feedback, postural responses and balance during walking remain challenging for persons with leg amputation 7 , 8 , which may indicate that motor control and proprioceptive percepts are significantly altered in persons that have undergone a conventional amputation procedure 9 – 11 . Toward better, more biomimetic control of an external prosthesis, invasive nerve interfacing using artificial electrical stimulation has shown great potential in restoring cutaneous 12 – 14 and proprioceptive sensation 11 , 12 . However, due to the complexity of afferent signaling through artificial nerve stimulation, and the relatively limited resolution of state-of-the-art implantable devices, it can be challenging to engineer stable neuroprosthetic interfaces that offer natural cutaneous and proprioceptive percepts.…”

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

“…Though the participant had previously utilized the SNP in a laboratory context and performed tasks including motor imagery, postural stability ( Shell et al, 2021 ), treadmill walking, and walking overground ( Christie et al, 2020 ), the emergence of automatic strategies to specifically gather sensory information, such as toe tapping and rocking on the prosthesis, only occurred after several months of daily use of the SNP. The implication is that in lab training alone may not be sufficient for motor learning to reach the level of automaticity, and thus daily at-home training may be required.…”

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.…”