Functional electrical stimulation
More specifically, FES can be used to generate muscle contraction in otherwise paralyzed limbs to produce functions such as grasping, walking, bladder voiding and standing.
In other words, the FEST is used as a short-term intervention to help an individual's central nervous system re-learn how to execute impaired functions, instead of making them dependent on neuroprostheses for the rest of their life.
[3] Initial Phase II clinical trials conducted with FEST for reaching and grasping, and walking were carried out at KITE, the research arm of the Toronto Rehabilitation Institute.
[10] However, special care must be taken in designing safe FES devices, as electric current through tissue can lead to adverse effects such as decrease in excitability or cell death.
This may be due to thermal damage, electroporation of the cell membrane, toxic products from electrochemical reactions at the electrode surface, or over-excitation of the targeted neurons or muscles.
The percutaneous electrodes consist of thin wires inserted through the skin and into muscular tissue close to the targeted nerve.
However, it is worth mentioning that some groups, such as Cleveland FES Center, have been able to safely use percutaneous electrodes with individual patients for months and years at a time.
Biphasic, charged balanced pulses are employed as they improve the safety of electrical stimulation and minimize some of the adverse effects.
Electrical stimulation had been utilized as far back as ancient Egypt, when it was believed that placing torpedo fish in a pool of water with a human was therapeutic.
[28] Kralj and his colleagues described a technique for paraplegic gait using surface stimulation, which remains the most popular method in use today.
The Parastep's digital design allows a considerable reduction in rate of patient-fatigue by drastically reducing of stimulation pulse-width (100–140 microseconds) and pulse-rate (12–24 per sec.
[31] Also, Parestep-based walking was reported to result in several medical and psychological benefits, including restoration of near-normal blood flow to lower extremities and holding of bone density decline.
Implanted systems have the advantage of being able to stimulate the hip flexors, and therefore, to provide better muscle selectivity and potentially better gait patterns.
[39] These technologies have been found to be successful and promising, but at the present time these FES systems are mostly used for exercise purposes and seldom as an alternative to wheelchair mobility.
[28] In the acute stage of stroke recovery, the use of cyclic electrical stimulation has been seen to increase the isometric strength of wrist extensors.
Patients who will elicit benefits of cyclic electrical stimulation of the wrist extensors must be highly motivated to follow through with treatment.
Functional electrical stimulation has been found to be effective for the management of pain and reduction of shoulder subluxation, as well as accelerating the degree and rate of motor recovery.
The scores suggested that FES decreases spasticity of wrist flexors as compared to non-FES and motor outcomes showed improved recovery in upper extremities, specifically when using the BCI-FES system.
Among closed-loop FES, which system is more effective (either BCI-FES or EMG-FES) remains unspecified, because as of right now no randomized controlled clinical trial has been conducted to directly compare the two and their benefits when in the context of neurorehabilitation.
[41] Drop foot is a common symptom in hemiplegia, characterized by a lack of dorsiflexion during the swing phase of gait, resulting in short, shuffling strides.
At the moment just before the heel off phase of gait occurs, the stimulator delivers a stimulus to the common peroneal nerve, which results in contraction of the muscles responsible for dorsiflexion.
[42][43][44][45][46] Drop foot stimulators have been used successfully with various patient populations, such as stroke, spinal cord injury and multiple sclerosis.
The term "orthotic effect" can be used to describe the immediate improvement in function observed when the individual switches on their FES device compared to unassisted walking.
Liberson et al., 1961[23] was the first to observe that some stroke patients appeared to benefit from a temporary improvement in function and were able to dorsiflex their foot for up to an hour after the electrical stimulation had been turned off.
[51] Further qualitative analysis including all participants from the same study found improvements in activities of daily living and a reduced number of falls for those using FES compared with exercise.
[54] However, a further large observational study (n=187) was supportive of previous findings and found a significant improvement in orthotic effect for walking speed.
A recent randomised controlled trial (n=32) found significant orthotic and training effects for children with unilateral spastic cerebral palsy.
[57] The reviewers summarised the evidence as the treatment having the potential to improve a number of different areas including muscle mass and strength, spasticity, passive range of motion, upper extremity function, walking speed, positioning of the foot and ankle kinematics.
NICE have stated that "current evidence on the safety and efficacy (in terms of improving gait) of functional electrical stimulation (FES) for drop foot of central neurological origin appears adequate to support the use of this procedure provided that normal arrangements are in place for clinical governance, consent and audit".
