Functional Electrical Stimulation: SCI Applications
In this article
How is FES used in spinal cord injury rehabilitation?
Kacie Raulerson explores functional electrical stimulation after spinal cord injury through movement, hand function and other functional applications. The manuscript draws on2007–2008 reviews. Those historical examples and eligibility descriptions retain their source context rather than becoming a current device catalogue.
What is functional electrical stimulation?
Functional Electrical Stimulation (FES) is used to specifically stimulate nerve fibers because a much lower amount of current is required to generate an action potential when compared to that of a muscle fiber. FES uses electrical stimulation of otherwise intact neuromuscular systems to assist functional actions affected by spinal cord injury.
The microprocessor used to stimulate the nerve fibers contains programs to coordinate muscle actions involved in sitting, standing, and walking. The microprocessor’s purpose is to imitate the neural triggers that would pass through a healthy spinal cord to the appropriate peripheral nerves below the injury site.
These stimuli would, in turn, trigger action potentials in the peripheral nerves. This would activate muscle contractions in the muscle fibers associated with each specific site that is being stimulated. Electrodes are considered the interface between the electrical stimulator and the nervous system.
Which everyday functions can FES assist?
FES systems can help increase a patient’s level of independence in day-to-day life by providing some assistance while standing to try to reach something, transferring from bed to chair, or other movements. While these are some ways to increase independence, there are also medical benefits to FES therapy.
These include increased blood flow, maintaining muscle mass, particularly in the lower limbs, positive effects on digestion, bladder, and bowel function. Psychological benefits such as increased self-esteem and lower rates of depression have also been shown to be a beneficial result of FES therapy.
How do therapeutic and functional applications differ?
Therapeutic applications of FES include prevention of muscle atrophy through exercise and cardiovascular conditioning. Functional applications of FES are used to regain vital bodily functions that have been lost due to a Spinal Cord Injury (SCI). A SCI is defined as damage to any part of the spinal cord or nerves at the end of the spinal canal.
Such injuries often cause permanent changes in strength, sensation, and other bodily functions below the site of the injury. The severity of a SCI is referred to as its’ “completeness.” A SCI is considered “complete” if all feeling and motor function are lost below the location of the injury.
If there is some motor function and sensory (feeling) below the site of the injury, the injury is considered “incomplete.”
What lower-limb applications are described?
FES systems for lower limbs are generally used in the attempt to help those that have suffered a SCI restore the use of their lower limb function with tasks such as walking or standing. Electrodes are placed on the peroneal nerve to generate a reflex with the flexion of the hip, knee and ankle to stimulate the swing phase of gait while learning to walk again.
“Stepping” can be performed by these electrodes stimulating the nerve to engage the quadriceps muscle on the stance side causing knee extension. When these two stimulations are coordinated, the stepping and then walking motion is achieved. Being an ideal candidate for FES differs based on the type of injury and the type of therapy that the physicians are considering.
For example, a 2007 paper stated that for lower limb FES, the ideal candidates are persons with T4-T12 paraplegia who have intact lumbo-sacral LMN and still show good upper body strength but, walking is slow, while energy expenditure is considered high.
What historical hand-function devices are discussed?
Devices used for those with a “complete” injury that are considered quadriplegic are mainly used to help restore the grasp and pinch function. Historical examples discussed in the cited 2007–2008 sources include the Freehand system and the HandMaster. Their inclusion here does not establish a current, exhaustive FDA device list.
The Freehand system is surgically implanted and is programmed to synthesize the movement of the muscles used for these actions. The HandMaster is a non-invasive option that has three surface electrodes that stimulate the finger flexors and extensors. While this may seem like the more viable option since it is non-invasive, with the help of implantable systems, individuals are often able to perform elbow extension due to the greater number of muscles stimulated.
Regaining grasp and pinch strength can greatly increase a patient’s level of independence. Depending upon the severity of the SCI and the patient’s recovery both can result in significant progress in rehabilitation. A 2008 paper stated that ideal candidates for devices such as the HandMaster and the Freehand system typically have injuries to the C5-C6, with adequate motor innervation of the forearm and hand muscles.
They should also have good passive range of motion, good upper trunk support, intact vision, and controlled spasticity.
Which breathing-related applications are discussed?
FES can also be used to prevent the long-term use of mechanical ventilation. This is achieved by electrical stimulation of the phrenic nerve. This is another surgically implanted device that delivers electrical stimulation to the diaphragm to promote breathing function. The manuscript’s historical account describes waiting at least a year after injury for this approach; that description should not be read as a universal timing rule for current devices.
This method has benefits when comparing it to traditional mechanical ventilators. Patients can have a better ability to speak, improvement in their comfort levels and reduces their needed physician care. The site of the nerve damage for this FES treatment plan is usually located at C3 or above, although generally more suitable for C1/C2 injuries than those lower due to the horn cells that may have been damaged.
Which other functional applications are described?
Additional functional applications of FES include control of the bladder and bowel and electro-ejaculation. Often times with a SCI, voluntary control of the bowel and bladder function can be lost or drastically impaired.
By surgically implanting an FES bladder system, patients are able to urinate on demand, reducing their risk for urinary tract infections, increasing independence and quality of life.
This same device can be used for bowel movements by activating the sensory reflex pathway via radio frequency signals that are placed on the sacral spinal nerves. Benefits of this technique are reduction in the time required for bowel evacuation and decreased risk of constipation and impaction.
Lastly, a functional benefit of FES is, electro-ejaculation for the purposes of harvesting viable sperm for artificial insemination or in-vitro fertilization. To perform this procedure, a probe is inserted in the rectum sending electrical currents to stimulate the nerves to contract the pelvic muscles resulting in ejaculation.
What questions remain for FES research?
FES is still a developing therapy that scientists are learning more about as the years and research progress. While it has been shown to be beneficial for many over the years there is still more to be discovered. Additional research is needed on how this type of therapy can affect and help the body heal.
This not only applies to the short-term application, but specifically in the long-term when recovering and living with a chronic SCI.
Questions about the source discussion
Are the named historical devices an exhaustive current approval list?
No. The manuscript’s examples come from older reviews and do not establish present-day device availability or every current approval.
Is FES for spinal cord injury used the same way in every case?
No. It discusses different applications and selection considerations according to injury and functional goals; the specific source context remains important.
References
“Therapeutic applications of FES include prevention of muscle atrophy through exercise and cardiovascular conditioning.”
“The severity of a SCI is referred to as its’ “completeness.””
“Patients can have a better ability to speak, improvement in their comfort levels and reduces their needed physician care.”