What is Functional Electrical Stimulation (FES)?

Functional Electrical Stimulation (FES) is a technique used to elicit muscle contractions using electrical impulses. It is employed in various applications, primarily for the restoration of function in individuals with neurological impairments. FES can be applied for both upper and lower extremity rehabilitation, and it can be delivered through surface or implanted electrodes.

History of Functional Electrical Stimulation (FES)

Functional Electrical Stimulation (FES) was first tried in the United States in the 1960s for stroke patients, but it wasn’t used regularly until later because it was considered experimental.

By the late 1970s, research showed it could help with foot drop and finger movements in stroke patients. In the mid-1980s, researchers in Salisbury, UK, started using FES for people with spinal cord injuries. They later developed devices for people with MS in the early 1990s, and these treatments continue today.

Currently, researchers are studying if FES can help with swallowing, hand and arm movements, and breathing problems in people with lung disease and stroke. It also has potential future uses for treating MS.

Applications of Functional Electrical Stimulation (FES) in neurorehabilitation

• Upper Extremity Rehabilitation: Focuses on restoring grasp-release function.
• Lower Extremity Rehabilitation: Aims at enabling standing and walking in paraplegic subjects.
• Stroke Rehabilitation: Helps restore mobility in limbs affected by stroke, addressing issues like foot drop and impaired hand movements.
• Spinal Cord Injury: Aids in muscle strengthening and control for individuals with paralysis or limited movement due to spinal cord damage.
• Multiple Sclerosis (MS): Assists in managing symptoms such as muscle weakness and stiffness, improving mobility and quality of life.
• Parkinson’s Disease: Used to alleviate symptoms like muscle rigidity and freezing of gait, enhancing movement and balance.
• Muscle Atrophy: Helps maintain muscle mass and strength in individuals with conditions causing muscle wasting.
• Foot Drop: Specifically targets the ability to lift the front part of the foot, facilitating walking and reducing the risk of falls.
• Swallowing Disorders: Investigated for its potential to improve swallowing function in patients with dysphagia, enhancing nutritional intake and quality of life.
• Respiratory Disorders: Explored for assisting breathing in conditions like chronic obstructive pulmonary disease (COPD) and spinal cord injuries affecting respiratory muscles.

FES continues to be researched for its expanding applications across various neurological and musculoskeletal conditions, offering promising avenues for rehabilitation and functional improvement.

We will briefly discuss each rehabilitation method shortly.

Methods of Functional Electrical Stimulation (FES) Delivery

Method	Description	Advantages	Disadvantages
Surface Electrodes	Electrodes placed on the skin surface.	Non-invasive, easy to apply.	Limited to superficial muscles, less precise.
Subcutaneous Electrodes	Electrodes placed under the skin.	More precise muscle activation.	Requires minor surgery, potential for infection.
Intramuscular Electrodes	Electrodes placed within the muscle.	Focused muscle contraction.	Invasive, potential for discomfort.
Epimysial Electrodes	Electrodes placed on the muscle surface.	Effective for deep muscles.	Requires surgical placement.
Nerve Electrodes	Electrodes placed around or near nerves.	Direct nerve activation.	Invasive, complex placement.

Lower Extremity Rehabilitation

The smallest set of muscles is necessary to perform the basic function of walking.

Key Muscle Groups:

Key Studies and Techniques

• Single Channel Implantable Stimulator: Implanted near the peroneal nerve, eliciting the flexor pattern.
• Kralj and Bajd Technique: Utilizes two channels per leg for standing and reciprocal walking.
  • Channel 1: Knee extensors
  • Channel 2: Flexion withdrawal of hip, knee, and ankle via peroneal nerve stimulation.

Implementation Examples

Technique	Description	Channels Used	Feedback
Surface Stimulation (Kralj and Bajd)	Two channels for knee extensors and flexion reflex.	4 (2 per leg)	Open loop, user-initiated.
Marsolais System	Utilizes up to 16 muscles with percutaneous electrodes.	16+	Open loop with feedback for knee and hip position.
Holle and Thoma	Multichannel implantable system for knee and hip extensors.	Multichannel	Open loop.

Flow Chart for Walking Sequence (Kralj and Bajd Technique)

Upper Extremity Rehabilitation

Functional Control

• Grasp-Release Function: Controlled via surface or implanted techniques.
• Commonly Used Muscles: Finger and thumb flexors and extensors, thumb abductor and adductor.

Implementation Examples

Technique	Description	Channels Used	Feedback
Surface Stimulation	External electrodes for grasp-release.	Variable	Open loop with visual feedback.
Implantable Stimulators (Pasniczek, Keith)	Implanted electrodes for fine muscle control.	Multichannel	Closed loop with sensory feedback.

Table of Implementation examples in Rehabilitation

Condition	Problems Addressed	Implementation Examples	Techniques Used
Stroke Rehabilitation	Foot drop, impaired hand movements	– Foot Drop: WalkAide, Bioness L300 – Hand Function: FES systems for hand rehabilitation	Surface FES (for foot drop and hand muscles)
Spinal Cord Injury	Muscle weakness, paralysis	– NESS L300 Plus for lower limb movement – Functional Electrical Stimulation Cycling (FESC)	Surface FES (for lower limb movement), Implanted FES (for targeted muscle groups)
Multiple Sclerosis (MS)	Muscle weakness, mobility issues	– PaceX by Odstock Medical for walking – Upper limb FES systems for arm and hand function	Surface FES (for walking and upper limb function), Implanted FES (for targeted muscle groups)
Parkinson’s Disease	Gait issues, muscle rigidity	– FreeWalk for gait improvement	Surface FES (for leg muscles involved in gait)
Muscle Atrophy	Muscle loss, weakness	– FES for muscle retraining	Surface FES (for muscle groups affected)
Foot Drop	Difficulty lifting foot during walking	– WalkAide, Bioness L300	Surface FES (for foot dorsiflexors)
Swallowing Disorders	Dysphagia, difficulty swallowing	– FES for throat muscles to improve swallowing	Surface FES (for pharyngeal muscles)
Respiratory Disorders	Breathing difficulties, respiratory muscle weakness	– FES for respiratory muscle stimulation	Surface FES (for respiratory muscles), Implanted FES (for targeted respiratory muscles)

List of FES currently used for rehabilitation

S.No	Name of FES Device	Primary Purpose
1	RT300	Lower and upper limb cycling for muscle strengthening
2	Bioness L300 Go	Foot drop correction and gait improvement
3	WalkAide System	Foot drop correction and gait improvement
4	NeuroMetrix Quell	Pain relief and chronic pain management
5	Odstock Dropped Foot Stimulator	Foot drop correction and gait improvement
6	RehaMove 2	Muscle strengthening and movement restoration
7	Hasomed RehaStim	Upper and lower limb rehabilitation
8	Xcite FES Rehabilitation System	Upper and lower limb exercise and re-education
9	Cefar Rehab X2	Muscle strengthening and pain management
10	MyGait	Foot drop correction and gait improvement
11	NESS H200 Wireless	Hand and wrist function restoration
12	Bioness H200	Hand and wrist function restoration
13	Compex Rehab	Muscle strengthening and neuromuscular re-education
14	Restorative Therapies RT300	Lower and upper limb cycling for muscle strengthening
15	VIVISTIM System	Upper limb rehabilitation post-stroke
16	SaeboStim Micro	Hand function restoration and pain management
17	Empi Continuum	Muscle strengthening and pain management
18	WalkAide	Foot drop correction and gait improvement
19	StimMaster Orion	Muscle strengthening and pain management
20	NeuroRegen	Nerve regeneration and muscle re-education
21	Biostim M7	Muscle strengthening and pain management

Advanced FNS Systems

1.Closed Loop Feedback

• Purpose: Corrects for discrepancies between desired and actual actions.
• Components:
  • Sensors: Joint position, contact force.
  • Controllers: Adjust stimulation based on sensor feedback.

2. Substitutional Sensory Feedback

• Purpose: Provides cutaneous sensory cues related to movement or force.
• Techniques: Subcutaneous electrodes generate sensory feedback.

Research and Development Pathways

Research and development in Functional Electrical Stimulation (FES) focuses on advancing techniques and applications to enhance its effectiveness and expand its therapeutic scope.

Area	Focus	Goals
Technical Development	Improved sensors, stimulators, electrodes.	Smaller, lower power, higher computational capability.
Biological Sciences	Understanding neural excitation mechanisms.	Selective electrodes, alternative feedback sources.
Clinical Sciences	Application of neural prostheses.	Refined movements, integration with other modalities.

Conclusion

FES offers promising advancements in the rehabilitation of individuals with spinal cord injuries and other neurological impairments. The integration of technical, biological, and clinical research continues to enhance the efficacy and applicability of FES systems. Close collaboration among clinicians, scientists, and users is essential for the successful implementation and evolution of FES technologies.

Future Directions in Functional electrical stimulation (FES)

• Development of more sophisticated closed-loop and sensory feedback systems.
• Continued refinement of electrode and sensor technologies.
• Expanding clinical trials to demonstrate safety and efficacy.
• Integration of FES with other rehabilitation modalities for comprehensive treatment.