Restoring hand grasping for patients with a complete tetraplegia with selective epineural stimulation: a parsimonious...

BACKGROUND: We explored epineural stimulation as a parsimonious approach to restore wrist and finger functions in individuals with complete tetraplegia. METHODS: Two epineural multicontact cuff electrodes were implanted in four participants with complete tetraplegia for 28 days. The electrodes were wrapped around two nerves above the elbow, the median nerve and the radial nerve, respectively. The electrodes were connected via percutaneous cables to an external 56-channels electrical stimulator. Electrical stimulation parameters and electrode configurations were empirically adjusted to evoke hand gestures. Voluntary actions by the participant (e.g., muscle contractions, shoulder movements, or button presses) were associated with specific 3D current configurations to enable the triggering of diverse pre-programmed stimulation sequences. RESULTS: The electrodes remained in place throughout the entire month, with no technical failure observed. The impedance of the contacts remained stable over time. The activation thresholds of the standard bipolar configuration (so called “Ring”) also demonstrated good stability across sessions. Participants were able to perform at least six functional tasks. P1 and P2 were assigned six preselected tasks—derived from the Motor Capacities Scale (MCS)—while P3 and P4 were given five preselected tasks—two of which were derived from the Motor Capacities Scale (MCS)—as well as five additional self-chosen tasks. An analytical evaluation was applied to the tasks derived from the MCS. The other tasks were graded using a binary outcome: success or failure. Execution times were also analyzed. For P3 and P4, a functional assessment was carried out based on perceived usefulness, usability (System Usability Scale), performance, satisfaction and acceptability with an emphasis on a user-centered approach by the Canadian Occupational Performance Measure. CONCLUSIONS: This article summarizes the observations made during a 1-month follow-up of four participants with complete motor deficit of the wrists and hands who experienced epineural stimulation with the use of electrodes implanted around two arm nerves. This minimalist approach in terms of implanted components enabled them to perform various daily tasks without external assistance. The results—in terms of tolerance, electrode stability and functional success—pave the way for a new neuroprosthetic solution. Trial registration numbers NCT04306328 and NCT05555914.