Exploration of Hand Grasp Patterns Elicitable Through Non-Invasive Proximal Nerve Stimulation

Henry Shin,Zach Watkins,Xiaogang Hu

doi:10.1038/s41598-017-16824-1

Abstract

Various neurological conditions, such as stroke or spinal cord injury, result in an impaired control of the hand. One method of restoring this impairment is through functional electrical stimulation (FES). However, traditional FES techniques often lead to quick fatigue and unnatural ballistic movements. In this study, we sought to explore the capabilities of a non-invasive proximal nerve stimulation technique in eliciting various hand grasp patterns. The ulnar and median nerves proximal to the elbow joint were activated transcutanously using a programmable stimulator, and the resultant finger flexion joint angles were recorded using a motion capture system. The individual finger motions averaged across the three joints were analyzed using a cluster analysis, in order to classify the different hand grasp patterns. With low current intensity (<5 mA and 100 µs pulse width) stimulation, our results show that all of our subjects demonstrated a variety of consistent hand grasp patterns including single finger movement and coordinated multi-finger movements. This study provides initial evidence on the feasibility of a proximal nerve stimulation technique in controlling a variety of finger movements and grasp patterns. Our approach could also be developed into a rehabilitative/assistive tool that can result in flexible movements of the fingers.

Highlights

In order to help restore some of these lost hand functions, a wide variety of functional electrical stimulation (FES) techniques have been developed[6,7,8]
A multi-finger pattern which is less obvious from the clustering, but was still commonly observed, was Thumb-Index-Middle finger flexion, which we considered a pinching pattern (Cluster [4], Fig. 5D) Besides the coordinated multi-finger motions, the nerve stimulation was able to elicit independent single finger motions of the thumb (Cluster 3-1), index finger (Cluster [], Fig. 5B), and middle finger (Cluster 4-1), independent ring finger and pinky movements were less common and were largely correlated with other finger movements
This study sought to explore the feasibility of transcutaneous proximal nerve stimulation in the activation and control of different finger motions

Summary

Introduction

In order to help restore some of these lost hand functions, a wide variety of functional electrical stimulation (FES) techniques have been developed[6,7,8]. Most of the stimulation approaches use a large diameter electrode pad placed on the skin surface in proximity to the innervation zones of the targeted muscles These techniques can typically only access a limited number of muscles, most of which are superficial muscles[10]. A spatially distributed multi-pad electrode grid has been used to distribute the stimulus current to different regions of the muscle belly[8,13,14] This approach has been shown to be able to delay muscle fatigue onset, reduce discomfort, and increase the selectivity of muscle activation. Low amplitude current delivered to selective nerve fibers can activate targeted muscles to elicit precise finger movements. This approach requires invasive surgical procedures, and the long-term stability of the implants still needs improvement. The findings can facilitate the development of non-invasive nerve stimulation techniques that can help individuals with hand weakness/paralysis in regaining functional finger movement

Objectives

Methods

Results

Conclusion