Improving Functional Electrical Stimulation to Enable Selective Finger and Wrist Movements for Dexterous Hand Use in Non-Human Primates
Nishant Ganesh Kumar, MD1, Matt Mender, BS, MS1, Ayobami Ward, MS, MD1, Luis Hernan Cubillos Guzman, BS, MS1, Joseph Costello, BS, MS1, Hisham Temmar, BS, MS1, Madison Kelberman, BS, MS1, Parag C Patil, MD, PhD1, Cynthia A Chestek, PhD2 and Theodore A Kung, MD3, 1University of Michigan, Ann Arbor, MI, 2Biomedical Engineering, Univeristy of Michigan, Ann Arbor, MI, 3Section of Plastic & Reconstructive Surgery, University of Michigan, Ann Arbor, MI
Introduction: Despite efforts to control the native hand after spinal cord injury (SCI), there remains a need for control strategies that enable dexterous hand movements. Functional electrical stimulation (FES) is a potential strategy, but existing FES methods for hand control primarily rely on surface electrodes and are limited in degrees of freedom and selectivity. We present a surgical technique that improves the current implementation of FES to facilitate selective finger movements.
Methods: Utilizing direct motor point stimulation (5mA, 10-25 microsecond pulse-width) to identify the entry point of peripheral nerves, two rhesus macaques were implanted with bipolar intramuscular electrodes in different hand flexors and extensors. Electrodes were implanted into multiple motor points for each muscle. The rhesus macaque was trained to use a manipulandum that required the use of finger and wrist muscles to mimic virtual challenges. EMG activity was recorded during task execution.
Results: In vivo, individual finger flexion in the index, middle, and ring fingers, finger extension in the index, middle-ring-small fingers, wrist extension, and wrist flexion were elicited by direct stimulation of the implanted electrodes. Recordings of muscle activation on the FDP-index electrode while the monkey either flexed or extended index or middle-ring-small finger groups are shown in Figure 1A. Using recordings from the FDP-index electrode, recordings were 41.3% higher for index flexion than the pre-movement baseline (Figure 1B). Using recordings from 6 separate electrodes (Table 1), signal selectivity is demonstrated with higher percentage changes in muscle activation compared to baseline (FDP-index higher for index flexion, FDP higher for middle-ring-small flexion, EDC higher for middle-ring-small extension). Using our approach to FES, selective index finger extension is demonstrated utilizing EIP electrodes (Figure 2).
Conclusion: Using direct motor point stimulation and intramuscular electrodes, reliable EMG recordings can be obtained from the hand with high selectivity. Improving upon existing FES methods using this technique to enable individual finger and wrist movements with increased degrees of freedom could alter the rehabilitation paradigm for SCI patients.
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