Functional Electronic Stimulation/Short-term and Long-term Effect of FES System Post-Stroke

Clinical Review and Evidence Gap
The current literature on Functional Electronic Stimulation (FES) systems focuses on comparing the gait outcomes between the FES systems and other orthotic interventions, for example an AFO. Though this information is critical in determining the relevance and place in the clinical management of drop foot preceding a stroke, it is also important to know of the other benefits that can be associated with specific interventions to ensure the best possible result for the patients.

The purpose of this evidence gap map is to facilitate informed judgment and evidence-based decision making in developing the most appropriate clinical management and practice by providing user-friendly tools for accessing evidence and thereby enabling policy makers and practitioners to explore the findings and quality of the existing evidence on a topic quickly and efficiently.

What is the FES system?
A Functional Electrical Stimulation, commonly known as the FES System, is defined as “the application of electrical pulses to certain nerve points in the body to help in accomplishing purposeful tasks…generating pulses at the correct times causing the Tibialis Anterior muscle to be contracting during the swing phase of the gait cycle and hence help the patient lift the foot and prevent it from dragging on the ground during the swing.” (Ibrahim, Tosun, & Yigitoglu, 2013).

What the literature doesn’t currently focus on is the short term improvement of brain plasticity processes after stroke with the use of the FES system. One of the main comorbidities post stroke is drop foot, which results in an inefficient gait pattern and often increases risks of falls as the foot does not effectively and efficiently clear the ground due to weak or insufficient voluntary ankle dorsiflexion. “Drop foot is a common problem in people suffering stroke, multiple sclerosis, cerebral palsy, or spinal cord injury where some of the motor functions are lost. Drop foot is identified by the inability to lift the foot while it is brought forward during the gait swing cycle, resulting in the foot being on the ground all the time. This condition is due to the loss of communication between the central nervous system and the peroneal nerve which causes lack of activity in the ankle dorsiflexion. Regular use of a foot-drop stimulator strengthens activation of motor cortical areas and their residual descending connections.” (Ibrahim, Tosun, & Yigitoglu, 2013).

The most common treatment method for drop foot is an ankle foot orthosis (AFO), limiting the plantarflexion to neutral (0°). They have many drawbacks, though, due to the bulkiness, lack of cosmesis and restriction of movement, that often leads to rejection of the device. The advantage of an FES system over an AFO is that it is a viable option to overcome those aforementioned downfalls of the AFO. The main drawback, though, is the cost to the individual, whereby the positives may not overweigh the financial burden. So it is imperative to be able to determine whether the device provides more than cosmesis, increased range of motion and light weight use. Can it produce muscle training and learning and in turn, improves wearers quality of life for the long term?

Current Evidence in the Literature
The current literature does not support, nor oppose the theory of muscular plasticity and neural learning with the long term use of the FES system. Currently the application of the FES system to patients experiencing drop foot is a secondary option, often only prescribed as a luxury to those who can afford it, though if there are further positive indications in terms of a reduction in the drop foot without any intervention as a result of learning, then that should be at the forefront of the orthotists decision making.

A study by Damiano and colleagues who’s aim was to determine whether repetitive functional electrical stimulation (FES) for unilateral foot drop increases tibialis anterior (TA) muscle size compared with an untreated baseline and the contralateral side in cerebral palsy, measured the muscle size and dorsiflexion angle 3 months after using intervention compared to baseline, and then at follow up post intervention. The results showed that at first follow up, the intervention resulted in increased muscle thickness and cross sectional area of Tibialis Anterior and maximum ankle dorsiflexion improved or maintained during the intervention. At the next three month follow up, the results showed muscle size gains had been preserved but the ankle dorsiflexion returned to baseline. Though this study is helpful in measuring the muscle gains and ankle dorsiflexion over a 6 month period, it does not specify short term outcomes of the muscle and nerve learnings. (http://nnr.sagepub.com.ez.library.latrobe.edu.au/content/27/3/200.full.pdf+html)

A recent trial involving 32 chronic, ambulatory, hemiparetic patients with a single drop foot received either physiotherapy or FES treatment. It resulted in the FES group walking significantly faster and more efficiently than the physiotherapy, however there was no improvement when the FES stimulator was not used (Hesse & Werner, 2003).

The questions to be asked from these studies are ‘Would the results have been different if the participants used the training mode for certain parts of the day? Would this illicit muscle learning? And within the trial groups, should there be subgroups to determine how many minutes, or periods of training, if any, will they have an effect on muscle plasticity?

Van der Linden et al also studied the effect of FES applied to the ankle dorsiflexors and quadriceps in 14 children with cerebral palsy. They too found a statistically significant orthotic effect on peak dorsiflexion and swing and the foot to floor angle at IC, though no long term treatment effects were made either (Van der Linden et al., 2014).

A study by Stein et al, though, had differing results on the therapeutic benefits from the FES system. It was a study on the walking performance of subjects with chronic non progressive and progressive disorders with foot drop, whereby both groups had an orthotic benefit from the FES, but this effect lasted for a shorter with in progressive disorders (Stein et al., 2010).

As shown above, the current research has differing and contradicting results, as with the case of the study by Scheffler with MS sufferers, whereby the did not find a statistically significant effect of the FES to the timed 5m level walk test and TUG test, but improvements on the stair ascent and descent tests were shown. Interestingly though, 10 out of the 11 participants preferred the FES over no device and 9 out of 11 preferred it over the AFO, with similar results in a qualitative study by Bulley et al with stroke patients as the subject (Sheffler, Hennessey, Knutson & Chae., 2009; Bulley, Shiels, & Salisbury., 2011).

A study conducted by Taylor et al, with whom conducted a retrospective study to assess the effectiveness of the FES system in terms of its effect on walking speed and PCI in stroke victims, found continued orthotic effect in 6 subjects both in terms of speed and PCI. After the 4 ½ month mark, 9 subjects discontinued use of the FES, 7 had an initial orthotic effect in speed and PCI, and as mentioned 6 had continuing effect. A carry over effect was experienced by 4 subjects and 2 in their PCI, but interestingly, one subjects’ mobility improved that much that the device was no longer required (Taylor et al., 1999). In this study, the majority of users use the FES device every day, however in the questionnaire provided in the study, 15.1% of the subjects said that the reason they use the device is because their walking was better when the stimulator was not sued, if they used it periodically. The time this carry-on effect lasted differed between each individual, with for example one participant claiming her improved walking was maintained when she wears the device for 1 day every 3 weeks. Of the participants who discontinued use of the FES, 24% attributed the disuse to their walking have improved. This study is a platform for further study in this field to build on this knowledge.

Research Question and Design
Changes over time measured when the device is off have been referred to as a therapeutic effect. This “therapeutic effect” is the major advantage FES systems have over AFOs, which do not provide any neural learning, though the research on the advantage is scarce, therefore the provision of FES systems is currently minimal. The research question I have created is:

•	Does the FES system produce short and long term improved neural plasticity in patients who have suffered from stroke?

•	Do these benefits, along with reduced drop foot and improved gait provide a means for FES system prescribed as primary intervention in stroke victims?

Introduction
One of the main comorbidities post stroke is drop foot, which results in an inefficient gait pattern and often increases risk of falls as the foot does not effectively clear the ground because of weak or absent voluntary ankle dorsiflexion.1 The conventional treatment of foot drop includes an ankle–foot orthosis (AFO),2 a brace that passively limits ankle plantar flexion to neutral (0°). AFOs have several drawbacks (eg, they are bulky, not cosmetically pleasing, and restrict movement), which may lead to rejection of the devices.3⇓-5 An alternative foot-drop treatment is functional electrical stimulation (FES) of the common peroneal (fibular) nerve to elicit ankle dorsiflexion during the swing phase of the step cycle. Several foot-drop stimulators are commercially available,3,5⇓⇓-8 and several reviews have been published on the effects of foot-drop stimulators in adults with hemiparesis.9⇓-11 Foot-drop stimulators have an immediate orthotic effect, as the FES-induced ankle dorsiflexion improves gait biomechanics. In addition, prolonged FES use may result in physiological changes such as increased muscle strength, improved volitional control, increased joint range of motion,9,10,12 and increased walking speed, even when the device is turned off.5,6,8,13,14 Changes over time measured when the device is off have been referred to as a therapeutic effect.

Materials and Method
The ideal study would entail a randomised control of stroke victims within the first 2 years of their stroke in the mean age of stroke victims. If possible, a study number over at least 100 would be preferable to be able to generalise the results to the wider population. There should be a control group who use an AFO and the intervention group who use the FES system. At baseline the following parameters should be measured: muscle size of TA, cross sectional area of TA, ROM of ankle, gait compensations, patient comfort, patient confidence in device, patient ease of use and patient satisfaction survey will be measured to be compared at one week, one month, 3 months and 6 months.

Results
I hypothesise that the FES system will produce improved results in most parameters, but may be less successful in the ease of use section, as it is very dependent on the correct positioning of the device under the patella and stroke sufferers with impaired cognitive ability may struggle with the accuracy. In terms of comfort, satisfaction, reduction of gait compensations, muscle size and cross sectional area of TA and ROM of the ankle I predict improvements in all of these areas when using the FES system, and a statistically significant difference in the muscle size and patient satisfaction in comparison to the AFO study group.

Conclusion
This would allow us to get an insight into not only the physical effects, but the psychological effects; advantages and disadvantages of either device and will allow us to better determine the best practice in the management of foot drop after stroke.