Discussion
muscle mass, exoskeleton-provided, reduced exoskeleton-provided, flexion or extension torques, knee flexion, hip flexion, SCES, chronic motor complete SCI
Percutaneous SCES enabled motor control in two persons with chronic motor complete SCI. Both participants could also volitionally modulate induced flexion or extension torques on verbal instruction in a seated position. One participant (0773) initiated hip flexion, knee flexion, and ankle dorsiflexion in a supine lying position following temporary and permanent implantation. The other participant (0772) did not show an immediate ability to volitionally generate movement or EMG activity; however, he was able to voluntarily modulate SCES-induced torque after the permanent implantation, and following interim mapping, demonstrated volitional hip and trunk control when supported in a semi-standing position. Standing configurations in 0772 may have resulted in trunk muscles modulation via inter-neuronal connections with lower lumbosacral segments, which resulted in enhanced trunk control as seen in Fig. Both participants demonstrated improved standing ability via execution of a volitional sit-to-stand with exoskeleton assistance (0772) or unassisted standing in parallel bars (0773). It is possible that the muscle activity during these activities (Figs. In participant 0773, we cannot rule out that his standing ability is related to load receptor augmentation, rather than him enabling volitional motor control, that resulted in amplification of extensor tone to sustain standing (Fig. Both participants showed increased muscle activity during EAW concurrent with enhanced EAW performance, indicated by faster walking speeds with reduced exoskeleton-provided swing phase assistance. The increased muscle activity manifested mainly as increased EMG amplitudes during the stance phase of gait as opposed to more typical patterns of alternating firing of flexors and extensors during the swing phase. The atypical EMG firing observed during EAW (without SCES) is driven primarily by the exoskeleton-provided flexion and extension patternThere are several possible reasons for the discordant results between participants. The first explanation may be differing injury levels, injury severity (AIS A or AIS B), or differences in preserved muscle mass. Previous studies have also shown position-dependent effects of SCESThese factors notwithstanding, it is likely that SCES (afferent excitation) combined with the participants’ intention to move (supraspinal control) enabled movement in varied contexts for both participantsCurrently, our registered clinical trial is scheduled to recruit 20 participants. Recruiting, implanting, and training more participants will need additional time. Furthermore, our research center is working hard within the COVID-19 precautions to ensure reasonable flow without exposing research staff or patients to additional unnecessary risks. We are reporting results on our first two participants as an interim report to demonstrate the feasibility of our research protocol and to ensure timely dissemination within the SCI community.In summary, the current report shows percutaneous SCES may enable motor control leading to functional improvements not possible with SCES off. Relatively simple mapping procedures and configurations were used to enhance performance of rehabilitation and training sessions. With these same configurations, some functional benefits manifested without the need for extensive training, such as standing with minimal use of upper extremity and stepping with a walker in one participant. It is possible that the severity of the injury, preserved muscle mass, and the accuracy and position specificity of the spinal mapping may have played a role in the findings of the current report. Further work is needed to refine mapping and training protocols to ensure optimization of this enabled motor control, and to make results more consistent across participants. Future research should investigate the efficacy of percutaneous SCES in combination with physical rehabilitation for restoration of motor control in large cohorts of persons with chronic SCI.