Abstract Information

P-71

Surgically implanted nerve cuff electrodes stabilize rapidly and preserve chronic nerve health in anatomically challenging locations

1Freeberg M, 2Gilles P, 2Lombardo L, 3Dustin T, 2Ansari R, 4Triolo R
1Case Western Reserve University, Cleveland, , USA; 2Louis Stokes Cleveland VA Medical Center, Cleveland, , USA; 3Case Western Reserve University/Cleveland VA Medical Center, Cleveland, , USA; 4Case Western Reerve University/Cleveland VA Medical Center, Cleveland, OH, USA

Objective
Peripheral nerve stimulation with implanted nerve cuff electrodes can restore standing, stepping and other functions to individuals with spinal cord injury [1-3]. The purpose of this study was to determine the acute, peri-operative and post-operative effects of the chronic presence of nerve cuff electrodes and long-term (1 year) delivery of electrical stimulation on standard clinical electrodiagnostic assessments of neural health and function.

Design/Methods
A 25 year old male with bilateral lower extremity paralysis secondary to incomplete cervical spinal cord injury (C5 AIS C) sustained 6 years prior to enrollment received an implanted standing neuroprosthesis including 8-contact composite flat interface nerve electrodes (C-FINEs) placed on the proximal femoral nerves bilaterally near the inguinal ligament [4]. Electromyography quantified neurophysiology preoperatively, intraoperatively, and at 3 weeks, and 6 and 12 months post-operatively. Stimulation charge thresholds and evoked knee extension moments quantified neuroprosthesis function over the same time intervals.

Results
Femoral compound motor unit action potentials increased 31% in amplitude and 34% in area while evoked knee extension moments increased significantly (p<0.01) by 79% over 1 year of rehabilitation with standing and quadriceps exercises. Charge thresholds were low and stable, averaging 19.7 nC±6.2 (standard error). Changes in saphenous nerve action potentials and needle electromyography suggested minor nerve irritation perioperatively. Stimulated responses from 3 contacts per cuff were sufficiently strong to transition from sit-to-stand and support standing with more than 90% of body weight individually via activation of anatomically distinct motor units. Responses of individual contacts added linearly and the subject is able to stand for more than 30 minutes one year post-implant, further indicating preserved motor nerve health and function.

Conclusion
This is the first human trial reporting both acute and chronic neurophysiologic changes due to application of and stimulation through nerve cuff electrodes. Electrodiagnostic tests indicated generally healthy nerves with strengthened responses following stimulated exercise. Temporary electrodiagnostic changes suggest minor nerve irritation intra- and perioperatively, not continuing chronically nor impacting neuroprosthesis function. No long-term adverse effects of the chronic presence of the C-FINEs and application of stimulation were observed. These clinical outcomes follow chronic implantation of a neuroprosthesis that allowed the subject to stand, and indicate that it is possible to safely implant electrodes on the proximal femoral nerve close to the inguinal ligament. These results suggest the electrodiagnostic findings that can be expected from implanting nerve cuff electrodes and their time-course for resolution, which may be applicable to motor system neuroprostheses as well as devices for modulating activities of the peripheral nerves for other therapeutic or functional purposes.

Support:
National Institutes of Health Grant R01-EB001889 and US Department of Veterans Affairs Rehabilitation R&D Project 1I01RX001039.


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