Intraoperative Responses May Predict Chronic Performance of Composite Flat Interface Nerve Electrodes on Human Femoral Nerves.

Peripheral nerve cuff electrodes (NCEs) in motor system neuroprostheses can generate strong muscle contractions and enhance surgical efficiency by accessing multiple muscles from a single proximal location. Predicting chronic performance of high contact density NCEs based on intraoperative observations would facilitate implantation at locations that maximize selective recruitment, immediate connection of optimal contacts to implanted pulse generators (IPGs) with limited output channels, and initiation of postoperative rehabilitation as soon as possible after surgery. However, the stability of NCE intraoperative recruitment to predict chronic performance has not been documented. Here we report the first-in-human application of a specific NCE, the composite flat interface nerve electrode (C-FINE), at a new and anatomically challenging location on the femoral nerve close to the inguinal ligaments. EMG and moment recruitment curves were recorded for each of the 8 contacts in 2 C-FINE intraoperatively, perioperatively, and chronically for 6 months. Intraoperative measurements predicted chronic outcomes for 87.5% of contacts with 14/16 recruiting the same muscles at 6 months as intraoperatively. In both 8-contact C-FINEs, 3 contacts elicited hip flexion and 5 selectively generated knee extension, 3 of which activated independent motor unit populations each sufficient to support standing. Recruitment order stabilized in less than 3 weeks and did not change thereafter. While confirmation of these results will be required with future studies and implant locations, this suggests that remobilization and stimulated exercise may be initiated 3 weeks after surgery with little risk of altering performance.

Posture shifting after spinal cord injury using functional neuromuscular stimulation--a computer simulation study.

The ability for individuals with spinal cord injury (SCI) to affect changes in standing posture with functional neuromuscular stimulation (FNS) was explored using an anatomically inspired musculoskeletal model of the trunk, pelvis and lower extremities (LE). The model tracked trajectories for anteriorly and laterally shifting movements away from erect stance. Forces were applied to both shoulders to represent upper extremity (UE) interaction with an assistive device (e.g., a walker). The muscle excitations required to execute shifting maneuvers with UE forces <10% body-weight (BW) were determined via dynamic optimization. Nine muscle sets were examined to maximize control of shifting posture. Inclusion of the Psoas and External Obliques bilaterally resulted in the least relative UE effort (0.119, mean UE effort = 45.3N ≡ 5.4% BW) for anterior shifting. For lateral shifting, the set including the Psoas and Latissimus Dorsi bilaterally yielded the best performance (0.025, mean UE effort = 27.8 N ≡ 3.3% BW). However, adding the Psoas alone bilaterally competed favorably in overall best performance across both maneuvers. This study suggests suitable activation to specific muscles of the trunk and LE can enable individuals with SCI to alter their standing postures with minimal upper-body effort and subsequently increase reach and standing work volume.

Neurotherapeutic and neuroprosthetic effects of implanted functional electrical stimulation for ambulation after incomplete spinal cord injury.

The purpose of this single-subject study was to determine the neurotherapeutic and neuroprosthetic effects of an implanted functional electrical stimulation (FES) system designed to facilitate walking in an individual with a longstanding motor and sensory incomplete spinal cord injury. An implanted pulse generator and eight intramuscular stimulating electrodes were installed unilaterally, activating weak or paralyzed hip flexors, hip and knee extensors, and ankle dorsiflexors during 36 sessions of gait training with FES. The neurotherapeutic effects were assessed by a comparison of pre- and posttraining volitional walking. The neuroprosthetic effects were assessed by a comparison of posttraining volitional and FES-assisted walking. Treatment resulted in significant (p < 0.005) volitional improvements in 6-minute walking distance and speed, speed during maximum walk, double support time, and 10 m walking speed. Posttraining FES-assisted walking resulted in significant additional improvements in all these measures, except 10 m walking speed. When the subject was using FES-assisted gait, maximum walking distance, peak knee flexion in swing, peak ankle dorsiflexion in swing, and knee extension moment also significantly increased. Neuroprosthetic gains were sufficient to enable the subject to advance from household ambulation to limited community ambulation. Additionally, the subject could perform multiple walks per day when using FES-assisted gait, which was impossible with volitional effort alone.

Walking after incomplete spinal cord injury using an implanted FES system: a case report.

Implanted functional electrical stimulation (FES) systems for walking are experimentally available to individuals with incomplete spinal cord injury (SCI); however, data on short-term therapeutic and functional outcomes are limited. The goal of this study was to quantify therapeutic and functional effects of an implanted FES system for walking after incomplete cervical SCI. After robotic-assisted treadmill training and overground gait training maximized his voluntary function, an individual with incomplete SCI (American Spinal Injury Association grade C, cervical level 6-7) who could stand volitionally but not step was surgically implanted with an 8-channel receiver stimulator and intramuscular electrodes. Electrodes were implanted bilaterally, recruiting iliopsoas, vastus intermedius and lateralis, tensor fasciae latae, tibialis anterior, and peroneus longus muscles. Twelve weeks of training followed limited activity post-surgery. Customized stimulation patterns addressed gait deficits via an external control unit. The system was well-tolerated and reliable. After the 12-week training, maximal walking distance increased (from 14 m to 309 m), maximal walking speed was 10 times greater (from 0.02 m/s to 0.20 m/s), and physiological cost index was 5 times less (from 44.4 beats/m to 8.6 beats/m). Voluntary locomotor function was unchanged. The implanted FES system was well-tolerated, reliable, and supplemented function, allowing the participant limited community ambulation. Physiological effort decreased and maximal walking distance increased dramatically over 12 weeks.

Long-term user perceptions of an implanted neuroprosthesis for exercise, standing, and transfers after spinal cord injury.

This study was completed to understand the usage patterns, system performance, degree of satisfaction, complications, and health benefits as perceived by recipients of a surgically implanted neuroprosthesis for exercise, standing, and transfers in individuals with low-cervical or thoracic spinal cord injury (SCI). A standardized telephone survey was administered to 11 recipients of the Case Western Reserve University/Veterans Affairs (CWRU/VA) implanted standing neuroprosthesis with more than 12 months of experience with the functional electrical stimulation (FES) system. Nine implant recipients were using the neuroprosthesis regularly for standing and/or exercising at the time of the survey. All 11 implant recipients noted improved health and a reduced incidence of pressure sores, leg spasms, and urinary tract infections (UTIs). No incidents of deep-vein thrombosis, infection, cellulitis, or electrical burns because of the neuroprosthesis were noted. System recipients uniformly felt that the neuroprosthesis resulted in better overall health and general well-being. Subjects were moderately to very satisfied with the performance of the neuroprosthesis and unanimously expressed a willingness to repeat the surgery and rehabilitation to obtain the same clinical outcome. All implant recipients reported the system to be safe, reliable, and easy to use. The implanted standing neuroprosthesis appears to be a clinically acceptable and effective means of providing the ability to exercise, stand, and transfer to selected individuals with paraplegia or low tetraplegia.

Consumer perspectives on mobility: implications for neuroprosthesis design.

The purpose of this study was to systematically assess mobility issues from the point of view of persons with spinal cord injuries (SCIs), so as to guide clinicians, researchers, and developers of assistive technologies. A telephone survey was developed through focus groups and discussions with individuals with SCI and rehabilitation experts. Telephone interviews were conducted with 94 individuals with paraplegia (51.4% response rate) from a Midwestern regional rehabilitation hospital's SCI database. Respondents were asked to prioritize desired mobility functions, to identify the acceptable quality of the activities, and to assess their willingness to experience related risks. Respondents ranked walking and then standing as top priorities (64% and 25%, respectively), regardless of injury level. For most, the acceptable quality of new mobility maneuvers did not have to approach premorbid function. Invasive procedures such as surgery were often as acceptable as less-invasive therapy and exercise. Qualities and costs of standing and walking were related to what respondents had to gain or lose relative to their current level of function. Contrary to opinions based on anecdotal evidence, persons with paraplegia were willing to accept high costs for limited function in certain mobility activities. These findings should encourage clinicians to consider the needs of persons with disabilities during the development of treatment interventions.