Pediatric Applications of Functional Electrical Stimulation

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By Phil Stevens, MEd, CPO, FAAOP
functional electrical stimulation(FES)

Hanger Clinic National Orthotics Specialist Curt Bertram with WalkAide patient Amber Konkol. Photograph courtesy of Hanger.

Applications of functional electrical stimulation (FES) devices are most prevalent within adult populations, particularly patients with cerebral vascular accident, multiple sclerosis, and spinal cord injury. However, during the last several years, there has been increased interest in the use of FES on children and adolescents with cerebral palsy (CP). This article presents a brief history of the early trials of FES in this pediatric population and a detailed discussion of more recent literature findings.

Historical Studies

The application of FES in CP is described as early as the 1970s when switches inside a child's shoes were used to trigger electrical stimulations that facilitated dorsiflexion during the swing phase of gait.1,2 These early trials were followed by several additional attempts in the 1990s to improve function through various regimens of electrical stimulation.3,4,5

In one such effort, stimulation was applied over the anterior tibialis for 30 minutes a day over a 30-day period. These were static events, meaning that stimulation was applied as a static exercise rather than as part of the dynamic activity of walking. This protocol resulted in reported increases in both passive and active range of motion into dorsiflexion, as well as increased anterior tibialis strength. However, the authors reported little resultant change in gait.3

In a separate approach, stimulation was applied variously to the anterior tibialis, the triceps surae, and the medial hamstring to treat different gait deficits. Stimulation was used as static exercises; it was also applied during gait using a handheld remote to stimulate the various muscle groups according to their appropriate timing during ambulation. Limited to a smaller series of detailed cases, the author reported improvements in foot position, balance, posture, and range of motion.4,5

Transitional Observations

Among the hallmarks of modern FES interventions is their ability to be conveniently worn by the patient and incorporated into daily ambulation. A clinical trial published by Durham et al. in 2004 represents a transition toward this application of modern FES systems on pediatric patients.6 The publication reports on a cohort of children with hemiplegia who were fit with the Odstock Drop Foot Stimulator (ODFS) III, which allowed the stimulator to be worn on a belt around the child's waist. The ODFS was wired to electrodes over the peroneal nerve and a force-sensitive resistor placed under the metatarsal heads, which acted as a switch to trigger the stimulation of the anterior tibialis.

The results of the trial suggest that the dynamic application of FES over a 12-week period led to improved pre-positioning of the affected limb in anticipation of heel strike, and improved gait symmetry. Subjective findings, elicited through a questionnaire at the trial's conclusion, suggest that compliance was a struggle for some subjects, but that those who completed the trial were interested in continuing to use FES. Comments also indicate that the stimulator was large, and the various wires made the system difficult for children to manage in a school environment.6

Modern FES Applications

Hanger Clinic patient Amber Konkol

Hanger Clinic patient Amber Konkol with her mother Christine Konkol.
Photograph courtesy of Hanger.

The WalkAide® FES device addresses many of the concerns cited by the families of the children enrolled in the Durham et al. trial. In place of a bulky stimulator unit worn around the waist and connected to electrodes and foot switches via long wires, the WalkAide is contained in a single cuff worn just below the knee. This carries the stimulation unit and positions the electrodes in the desired location. Additionally, because the WalkAide is typically triggered by the relative tilt of the lower leg throughout gait, the need for external foot switches is uncommon. A smaller-size cuff is available for pediatric applications.

The first clinical trial of the WalkAide in children with CP has been the subject of two recent publications.7,8 The first of these focuses on the general acceptance and effectiveness of the modality within this population. The trial reported on a one-month accommodation to daily FES use for a cohort of children and adolescents with mild to moderate hemiplegic CP (Gross Motor Function Classification System [GMFCS] levels I and II) with a mean age of 13 (ages ranged from seven-and-a-half to 20 years old). A three-month trial of daily FES use followed the accommodation period.

Acceptability

In contrast to the Durham et al. trial, where compliance was identified as a concern and pediatric subjects were apparently overwhelmed by the size and complexity of the ODFS III FES system, the acceptability of the WalkAide appeared to be quite high. Of the 21 subjects originally enrolled in the study, 19 successfully completed the one-month accommodation period, and all but one of those chose to continue using the FES system at the conclusion of the three-month trial period.7 The reasons for withdrawing from the study were predictable to clinicians experienced in FES and included stimulation intolerance, triggering of dystonic posturing of the foot, and a perception that the benefit failed to justify the inconvenience of daily use. However, the incidence of these challenges among this population was much lower than expected.

During the three-month trial, subjects were asked to wear the FES device at least six hours a day during the times when they walked most. Compliance was fairly high among the 18 subjects who remained in the three-month trial, with an average daily FES use of 5.6 hours and an average step count of 2,087.7 Ten of the 18 subjects used the device for more than six hours a day. Usage rates of four to six hours and two to four hours were reported by four and three subjects, respectively, with a single subject using the FES device for less than two hours per day.7

Practical Considerations

Unlike many trials in the O&P profession where the interventions are poorly described, the authors took great care to document the details of FES application for these subjects. For example, there are many programming variables that can be manipulated with respect to the quality of the electrical stimulations emitted over the peroneal nerve. In contrast to adult applications where pulse widths commonly range from 100 to 200 µs, in these pediatric/adolescent applications, the pulse width was reduced to 25 to 50 µs. The authors specified the use of the largest possible electrode size to distribute the electrical stimulation over a larger surface area, beginning with a low stimulation amplitude that was increased over time and using a short ramp-up of the stimulation to improve comfort and reduce the likelihood of eliciting a spastic muscle response. All of these variables can be easily manipulated in a clinical setting and provide practitioners with valuable insights on possible ways to improve acceptance of FES in this population.

Effectiveness

Several improvements in kinematics and gait function were observed in pediatric subjects using FES. These included increased dorsiflexion at initial contact, peak swing-phase dorsiflexion, and mean dorsiflexion during swing phase. These improvements were not instantaneous but occurred progressively throughout the trial (Tables 1 and 2).

Observations of ankle kinematics were not limited to the improved ability of the foot to dorsiflex in swing phase. The authors also noted the relative plantarflexion that occurred at toe-off in both the FES and non-FES condition throughout the trial. In contrast to the use of AFOs, which traditionally restrict plantarflexion at this phase of gait, the study subjects were able to perform the physiologically appropriate ankle kinematics at toe-off in the FES condition.

Table 1

Table 1: Improvements observed at self-selected walking speeds with FES compared to without FES at initial exposure, following a one-month accommodation period and after thee months of FES use. Adapted from Prosser et al.7

Table 2

Table 2: Improvements observed at fast walking speeds with FES compared to without FES at initial exposure, following a one-month accommodation period and after three months of FES use. Adapted from Prosser et al.7

In contrast to the continuous, steady improvements in ankle kinematics, there were no appreciable changes in self-selected or fast walking velocity, cadence, or step length.7 However, it should be noted that these assessments were done over short intervals on subjects with mild to moderate hemiplegia. As such, they would not reflect the ability of FES to affect velocity over longer distances or when fatigue affects the subjects' ability to compensate for gait deficits.

Muscle Plasticity

Hanger Clinic patient Amber Konkol

Zoey Richardson.
Photograph courtesy of Innovative Neurotronics.

The more traditional treatment modality for the gait deficits in hemiplegic CP, the AFO, has long been suspected of potentially exacerbating weakness that is often present in the dorsiflexors and plantarflexors of the foot. By preventing the foot from active dorsiflexion during swing and plantarflexion at push-off, there is a common fear that this population of children may become dependent on their AFOs for function. The second publication from the Prosser et al. clinical trial was focused on the extent to which FES affected the strength and stamina of the anterior tibialis muscle in children with hemiplegia.8 This was done in part by obtaining ultrasound measurements of the muscle belly at different points throughout the clinical trial. Recalling the continuous gradual improvements in dorsiflexor function documented in the first publication from the Prosser et al. trial, it is interesting to note the same trend of gradually increasing muscle size throughout the trial. Specifically, mean muscle thickness improved by 2 percent, 9 percent, and 12 percent at one-, four-, and seven-month follow-ups post-initiation of the FES clinical trial.8 It should be noted that mean muscle thickness decreased by 1 percent during the three-month baseline observation prior to the introduction of FES, suggesting that the observed improvements were the result of FES intervention rather than a product of maturation. Thus, in contrast to the disuse atrophy that can be observed clinically with the use of AFOs in this population, the use of FES led to progressive improvement in the size and function of the targeted muscle group.

Combining Modalities

In the Prosser et al. clinical trial, the subjects were confined to those who had not received injections of botulinum toxin (Botox) in the four months preceding the study.7 This was presumably done to ensure that the improvements noted were strictly the product of FES.

Our final trial examines the related question of whether or not electrical stimulation might augment the benefits obtained from Botox.9 In this trial, subjects underwent the following pathway with assessments performed at baseline and at the conclusion of each of the described phases:

  1. Subjects were administered Botox in their affected gastrocnemius and given three weeks to ensure that the Botox had its ideal effects on the spastic muscle.
  2. Subjects underwent a four-week FES phase.
  3. Subjects experienced a four-week control phase with no intervention.
  4. Subjects underwent a second four-week FES phase.
  5. Subjects experienced a second control phase with no intervention.9

The FES phases were quite different from those in the Prosser et al trial. Rather than applying stimulation to the peroneal nerve to elicit dorsiflexion, the stimulation was applied directly to the anterior tibialis. Further, while the stimulation was dynamic-applied during walking and triggered by switches within the shoe-the FES device was only worn for 20 to 30 minutes of daily supervised use.

In the absence of any control group, it is difficult to say how the effects of the combined modalities may have compared to the use of either treatment in isolation. However, the majority of the study subjects experienced an increased dorsiflexion angle during terminal swing throughout the trial relative to the baseline assessment. Subjects were often able to maintain the improvement in dorsiflexion after FES was withdrawn, with some subjects even demonstrating further improvement during the control phase. Importantly, these assessments, which were performed at the conclusion of each of the study phases identified above, were always made without FES. Thus, any effect that FES may have had on swing-phase dorsiflexion and the pre-positioning of the foot and ankle for loading response would have been a therapeutic or carry-over effect. Though the findings are only preliminary, the results of the trial suggest that FES may serve to augment the efficacy of Botox injections and that some level of gait retraining may occur when the two modalities are combined.9

Conclusion

While the emphasis in modern FES applications has generally been toward adult treatment populations, the modality appears to hold additional promise for pediatric applications in patients with CP. While various FES concepts have been investigated over the last 40 years, FES devices are now commercially available. Early reports not only suggest high acceptance rates among children and adolescents at GMFCS levels I and II, but they also provide some indication of the stimulation characteristics that may be better tolerated in this population. The benefits of FES, including dorsiflexion motion during swing phase and the strength and stamina of the anterior tibialis muscle, appear to be more pronounced with greater exposure to FES. In addition, the combination of FES and Botox injections has shown some promise as a viable treatment. While the studies to date are limited and preliminary, they suggest that when properly applied to the right patient types, FES may constitute an appropriate method of care.

Phil Stevens, MEd, CPO, FAAOP, is in clinical practice with Hanger Clinic, Salt Lake City, Utah. He can be reached at

Editor's note: For a detailed literature review on the use of FES in the adult population, read "Exploring the Benefits of FES on Gait for Patients with Multiple Sclerosis," The O&P EDGE, February 2013.

References

  1. Gracanin, F. 1974. Functional electrical stimulation in CP children as an orthotic walking aide with neurotherapeutic effect. ISPO World Congress, Montreux, Switzerland, 113.
  2. Gracanin, F. M. Vrabic, and G. Vrabic. 1976. Six years experiences with FES method applied to children. Europa Medicophysica 12:61-8.
  3. Hazlewood, E. J. Brown, P. Rowe, and P. Salter. 1994. The use of therapeutic electrical stimulation in the treatment of hemiplegic cerebral palsy. Developmental Medicine and Child Neurology 36:661-73.
  4. Carmick, J. 1993. Clinical use of neuromuscular electrical stimulation for children with cerebral palsy, part 1: Lower extremity. Physical Therapy 73(8):505-13.
  5. Carmick, J. 1995. Managing equinus in children with cerebral palsy: Electrical stimulation to strengthen the triceps surae muscle. Developmental Medicine & Child Neurology 37(11):965-75.
  6. Durham, S. L. Eve, C. Stevens, and D. Ewins. 2004. Effect of functional electrical stimulation on asymmetries in gait of children with hemiplegic cerebral palsy. Physiotherapy 90:82-90.
  7. Prosser, L. A. L. A. Curatalo, K. E. Alter, and D. L. Damiano. 2012. Acceptability and potential effectiveness of a foot drop stimulator in children and adolescents with cerebral palsy. Developmental Medicine & Child Neurology 54(11):1044-9.
  8. Damiano, D. L. L. A. Prosser, L. A. Curatalo, and K. E. Alter. 2012. Muscle plasticity and ankle control after repetitive use of a functional electrical stimulation device for foot drop in cerebral palsy. Neurorehabilitation & Neural Repair (published online before print).
  9. Galen, S. L. Wiggins, R. McWilliam, and M. Granat. 2012. A combination of botulinum toxin A therapy and functional electrical stimulation in children with cerebral palsy-a pilot study. Technology and Health Care 20(1):1-9.