Functional electrical stimulation therapy for restoration of motor function after spinal cord injury and stroke: a review

Abstract

Functional electrical stimulation is a technique to produce functional movements after paralysis. Electrical discharges are applied to a person's muscles making them contract in a sequence that allows performing tasks such as grasping a key, holding a toothbrush, standing, and walking. The technology was developed in the sixties, during which initial clinical use started, emphasizing its potential as an assistive device. Since then, functional electrical stimulation has evolved into an important therapeutic intervention that clinicians can use to help individuals who have had a stroke or a spinal cord injury regain their ability to stand, walk, reach, and grasp. With an expected growth in the aging population, it is likely that this technology will undergo important changes to increase its efficacy as well as its widespread adoption. We present here a series of functional electrical stimulation systems to illustrate the fundamentals of the technology and its applications. Most of the concepts continue to be in use today by modern day devices. A brief description of the potential future of the technology is presented, including its integration with brain-computer interfaces and wearable (garment) technology.

Keywords: Functional electrical stimulation; Neuroprosthesis; Neurorehabilitation; Spinal cord injury; Stroke.

Fig. 1

Functional electrical stimulation parameters. Pulse width, amplitude, and frequency define the muscles stimulated, force, and quality of the contraction

Fig. 2

Examples of commonly used pulse shapes used for functional electrical stimulation (Modified from [6])

Fig. 3

Fundamental components of functional electrical stimulation therapy. FEST has three components. First, a patient must be actively attempting a motor task. Second, an FES system produces the intended movement which also generates the corresponding correct sensory feedback. Third, a therapist guides the limb in motion to ensure the quality and correctness of the movement. The therapist also adjusts the stimulation according to the changes observed in the patient throughout rehabilitation

Fig. 4

Textile-based neuroprostheses. a Finger extension produced using a shirt designed for implementing a neuroprosthesis for reaching and grasping. The garment includes rectangular areas (dark grey patches) made of conductive yarn that function as electrodes. b Forward reaching. Details can be found in [65]