The use of Functional Electrical Stimulation (FES) has increased recently with devices utilized to assist people experiencing foot drop. There has been an increase in the public’s awareness of these devices and their use in people living with multiple sclerosis (MS). FES, as an ambulatory aid, has been used for many years by rehabilitation professionals. These devices provide an exciting opportunity, but a web site article by Brian Hutchison of the United Spinal Association writes that "their use needs to be approached in a thoughtful way through discussions with your treatment team about pros and cons". 

Find a link to the orginal article here on the United Spinal Association website.

What is FES?
FES is a method of applying low-level electrical currents to the body to restore or improve function (Cleveland FES Center, 2008). A common example of an FES system is a heart pacemaker. There are many applications for FES in the MS population including bowel and bladder control, transfers and standing, and upper extremity function. In addition, electrical stimulation may be used for purposes other than improving muscle function, such as for therapy in spasticity and pain management as well as to improve circulation for wound healing. This paper will concentrate on FES systems to aid in stepping and walking.

How Does FES Work to Improve Ambulation?
FES is most commonly used to help with “Foot Drop” secondary to a decrease or loss of nerve signals to the muscles that dorsifl ex or lift the foot. Electronic stimulation is generally applied to the common peroneal nerve, at its most superfi cial point, directly stimulating the muscles of the lower leg to contract and lift the foot. This has the ability to be successful in people diagnosed with MS, because, in general, the peripheral nerve is intact, and the problem is in the central nervous system. Therefore, the signal from the central nervous system gets interrupted because of a plaque in the brain or spinal cord and doesn’t reach its destination; the muscles. FES bypasses the central nervous system signal and provides direct stimulation to generate a muscle contraction.

FES systems work by providing electrical stimulation through surface electrodes. The timing of the stimulation is usually achieved through a pressure sensitive switch placed beneath the heel (as part of evaluation and sometimes for training purposes, a hand switch is utilized). The switch allows proper timing of the stimulation so the muscle contraction occurs at the appropriate time to facilitate, not hinder, a proper gait pattern.

Considerations in Choosing FES
FES systems are similar to other interventions, in that they require education and research by the potential user. The critical fi rst step is to determine if you are an appropriate candidate for FES. As described above, FES is used to assist in facilitating ankle dorsifl exion, in those who have neurological weakness or foot drop. It is important to recognize, however, that there are other reasons that a person may “drag their foot” and these could be confused with a foot drop secondary to neurological weakness. A person may have loss of range of motion at their ankle which decreases their ability to lift their foot. This could be due to increased spasticity of the calf muscles, shortening of the Achilles tendon or an orthopedic problem. In addition, weakness at the hip or knee can also cause a person to “drag their foot” when walking. Careful assessment by a physician or physical therapist will allow better identifi cation of the gait abnormalities and should be the first step when considering FES.

Secondly, one needs to consider other medical conditions. Individuals who have a pacemaker, suffer from seizures or have peripheral nervous system conditions should not use FES. While these are not absolute contraindications, caution must be exercised in people with known heart disease, controlled epilepsy, recent surgery where muscle contraction may disrupt healing, poor skin conditions, and hypersensitivity to electrical stimulation. Also, individuals who are mentally unimpaired are generally better candidates because they will better understand how the systems are used and can provide
better feedback. It is important to discuss any conditions with one’s physician to see if FES may be contraindicated. Some patients may not tolerate the electrical stimuli. For this reason, we strongly encourage patients to try out the devices before they purchase one to assure that the device works for their particular situation, and that they are able to tolerate the electrical stimulation.

Thirdly, these FES systems are designed to help individuals with stepping and walking. Therefore, using them while sleeping or during other daily activities, such as driving, is not appropriate. Finally, cost can
be an issue with FES systems. Some devices are FDA-approved and available for people living with MS(www.waildaide.com; www.bioness.com).

The devices, however, are very expensive. While insurance reimbursement varies considerably, it is rare that the FES system will be covered for someone with a diagnosis of MS.

FES Research in MS
Research examining FES in people with MS is very limited. One study examined the use of FES to reduce spasticity (Krause, Szecsi, & Straube, 2007). In this case study, electrical stimulation was provided to induce cycling leg movements. Spasticity was reduced following the application of electrical stimulation. In another article, on patient selection for FES, the authors described walking speed and distance as important criteria in proper patient selection (Jones et al., 1997). They indicated that the inability to walk 50 meters indicates seriously limited mobility and would limit the success of the FES device. In addition, the authors defined other important evaluation criteria including range of motion of the ankle joint and balance. Finally, the use of an FES system for walking was examined in a group of patients with stroke and MS (Taylor et al., 1999). The study showed increases in physiological cost and speed of walking in patients with MS while using the stimulator.

There is more literature examining the use of FES in individuals with spinal cord injury (SCI). Graupe and colleagues studied walking performance in individuals with thoracic level complete SCI and found that use of FES allowed considerably longer walking distances and speed (Graupe, Cerrel-Bazo, Kern, & Carraro, 2008). They also discovered that walking distance and speed was enhanced by a pre-conditioning program with emphasis on muscle strengthening, cardiovascular fi tness, and respiratory conditioning emphasizing the importance of a therapeutic training program accompanying FES use. A Cochrane Database Review, which examined different forms of locomotor training (including bodyweight supported treadmill training with or without functional electrical stimulation and robotic-assisted locomotor training), however, found that there is currently insuffi cient evidence to conclude that one locomotor strategy improves walking function more than another for people with SCI (Mehrholz, Kugler, & Pohl, 2008).

In clinical practice observation, there is evidence that FES can improve ambulation. Subjectively, people report that their ambulation distance, speed, and most importantly safety improves with the use of FES. MS presents unique challenges in that symptoms often fl uctuate making evaluation for and proper setting of the FES system more difficult. As evidenced by the paucity of research, we need further trials to better evaluate the effectiveness of this particular therapeutic intervention.

Conclusion
FES, as a tool to improve ambulation, holds tremendous promise for individuals who experience foot drop due to neurological weakness of the lower leg muscles. These devices, however, do have limitations. Careful assessment to identify appropriate candidates, as well as, proper training and follow-up, are critical for optimal success. In addition, it is important to conduct further research in this area to better understand the expected outcomes and benefi ts and provide rationale for reimbursement.

References
Bateman, A. (1997). IEE Colloquium on FES in the UK- Into the Next Millennium (Digest No: 1997/299)

Cleveland FES Center. Retrieved from http://fescenter.case.edu/site 2/GRFX/FESRG.pdf

Graupe, D., Cerrel-Bazo, H., Kern, H., & Carraro, U. (2008). Walking performance, medical outcomes and patient training in FES of innervated muscles for ambulation by thoracic-level complete paraplegics.
Neurological Research 30(2), 123-130.

Jones, R., Davies Smith, A., Nuyens, G., Whitlock, T., Peasegood ,W., Ketelaer, P., et al. (1997). IEE Colloquium on FES in the UK- Into the Next Millenium (Digest No: 1997/299)

Jones, R., Davies Smith, A., Nuyens, G., Whitlock, T., Peasegood, W., Ketelaer, P., et al. (2007). FES Cycling reduces spastic muscle tone in a patient with multiple sclerosis. NeuroRehabilitation, 22(4), 335-337.

Mehrholz, J., Kugler, J., & Pohl, M. (2008). Locomotor training for walking after spinal cord injury.
Cochrane Database Systems Review 16(2): CD006676.

Taylor, P. N., Burridge, J. H., Dunkerley, A. L., Wood, D. E., Norton, J. A., Singleton, C. et al. (1999). Clinical use of the Odstock dropped foot stimulator: Its effect on the speed and effort of walking.
Archives of Physical Medicine and Rehabilitation 80(12), 1577-1583.