Chronic nerve health following implantation of femoral nerve cuff electrodes

Abstract

Background Peripheral nerve stimulation with implanted nerve cuff electrodes can restore standing, stepping and other functions to individuals with spinal cord injury (SCI). We performed the first study to evaluate the clinical electrodiagnostic changes due to electrode implantation acutely, chronic presence on the nerve peri- and post-operatively, and long-term delivery of electrical stimulation. Methods A man with bilateral lower extremity paralysis secondary to cervical SCI sustained 5 years prior to enrollment received an implanted standing neuroprosthesis including composite flat interface nerve electrodes (C-FINEs) electrodes implanted around the proximal femoral nerves near the inguinal ligaments. Electromyography quantified neurophysiology preoperatively, intraoperatively, and through 1 year postoperatively. Stimulation charge thresholds, evoked knee extension moments, and weight distribution during standing quantified neuroprosthesis function over the same interval. 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 (SEM). Changes in saphenous nerve action potentials and needle electromyography suggested minor nerve irritation perioperatively. Conclusions This is the first human trial reporting acute and chronic neurophysiologic changes due to application of and stimulation through nerve cuff electrodes. Electrodiagnostics indicated preserved nerve health with strengthened responses following stimulated exercise. Temporary electrodiagnostic changes suggest minor nerve irritation only intra- and peri-operatively, not continuing chronically nor impacting function. These outcomes follow implantation of a neuroprosthesis enabling standing and demonstrate the ability to safely implant electrodes on the proximal femoral nerve close to the inguinal ligament. We demonstrate the electrodiagnostic findings that can be expected from implanting nerve cuff electrodes and their time-course for resolution, potentially applicable to prostheses modulating other peripheral nerves and functions. Trial registration ClinicalTrials.gov NCT01923662 , retrospectively registered August 15, 2013.

Implanted High Density Cuff Electrodes Functionally Activate Human Tibial and Peroneal Motor Units Without Chronic Detriment to Peripheral Nerve Health

“…However, the absence of large changes to recruitment order in the contacts tested is consistent with the interpretation that these changes in threshold were not likely due to significant movement of the cuff. Such changes in charge thresholds postoperatively agree with the results of our previous study which demonstrated an acute increase in charge thresholds postoperatively with a maximum at two months before their return to near baseline at six months. Differences in activation thresholds for muscles within a single contact tended to increase over the four‐month period, although these changes only minimally affected the recruitment order, which indicates that they were likely produced by differences in fascicle‐to‐contact distance and encapsulation that could serve to increase requisite charge.…”

“…In the setting of an AIS C classification, these changes demonstrate a preservation of the subject's preoperative functional and clinical neuromuscular health. This investigation complements our previous study, which documented changes to similar parameters in a subject with femoral nerve C‐FINEs implanted in the vicinity of the inguinal ligament .…”

“…Only the four contacts per cuff yielding the most selective and strongest responses were connected to percutaneous leads to minimize the risk of infection and improve subject comfort. These contacts were chosen based on the results of the intraoperative RCs, which have previously been shown to predict chronic performance . Specifically, the charge necessary to achieve 50% recruitment of the desired muscles was valued alongside intraoperative manual muscle testing and observation to make the final selections.…”

“…Electrical stimulation of peripheral nerves using non‐penetrating nerve cuff electrodes (NCEs) has been previously demonstrated to be effective in restoring function in subjects with lower‐extremity paralysis from spinal cord injury (SCI), stroke, or multiple sclerosis . NCEs with sufficient contact density can reliably activate distinct populations of nerve fascicles, allowing for independent control of different motor functions activated by the same nerve.…”

Selective Nerve Cuff Stimulation Strategies for Prolonging Muscle Output

“…The C-FINEs ( Figure 2) consist of thin layers of flexible silicone elastomer sandwiching a narrow layer of polyether ether keytone (PEEK) polymer stiffening bar with an array of platinum contacts on the top and bottom of the cuff. This configuration has been shown to gently reshape the nerve into an elongated oval [23] which allows individual contacts along the width of the nerve to selectively access different fascicles with minimal to no effect on nerve health [24], [25].…”