FES-assisted walking for rehabilitation of incomplete spinal cord injury
T. Adam Thrasher* and Milos R. Popovic
Toronto Rehabilitation Institute, Toronto Institute of Biomaterials University
of Toronto , Canada
Introduction
This study concerns the implementation of FES-assisted walking as a practical, short-term clinical intervention for incomplete spinal cord injury (SCI). Numerous reports over the past 25 years have asserted positive therapeutic effects of FES-assisted walking on SCI. Now, there is growing evidence that FES-assisted exercise can result in recovery of voluntary muscle control and significant improvements to function [1,2]. A definite long-term improvement to voluntary function was demonstrated by Wieler et al. for a large population of SCI patients using a variety of FES-assisted walking strategies [3].
These surprising reports suggest that, under certain conditions, the damaged central nervous system is able to adapt and form new neural pathways for voluntary function. In humans, there is evidence that the injured spinal cord continues to reveal a great deal of plasticity, even several years after SCI [4]. There is a new hypothesis that electrical stimulation of motor axons coinciding with voluntary muscle effort can promote restorative modifications in the central nervous system [5]. Direct muscle stimulation, therefore, would likely have greater rehabilitative potential than the stimulation of reflexes, e.g. peroneal nerve stimulation, which is still the most popular mode of FES-assisted walking.
All these suggest that walking with direct stimulation of paretic muscles could have great rehabilitative potential, so long as the user can coordinate voluntary effort with the stimulus. In this study, we put these ideas into practice.
Methods
This study was carried out at the
Lyndhurst Centre of Toronto Rehabilitation Institute, a rehabilitation hospital
for SCI located in
Table 1; Initial subject data
|
Subject |
Age |
Gender |
SCI level |
Injury duration |
Cause |
Assistive devices |
|
A |
36 |
M |
T6-10 |
7 |
VHLS* |
2 canes |
|
B |
24 |
F |
T12 |
5 |
Fall |
2 canes + 1 long leg brace |
|
C |
46 |
M |
C5 |
7 |
Fall |
2-wheeled walker |
* Von Hippel Lindau Syndrome
At the beginning of the study, each subject was evaluated by a gait expert or physiotherapist. In the case of Subject A, this involved a full gait analysis using a motion capture system (Vicon Motion Systems), force plates (AMTI) and an Octopus electromyography system (Bortec Biomedical). Based on the expert analysis, a direct muscle stimulation program was designed for each subject. In general, the most impaired muscle groups were targeted.
Subjects attended two to five therapy sessions per week for up to 16 weeks. Walking speed and physiological cost index (PCI) were measured twice per session, before stimulation was applied. In an ordinary hallway, subjects were instructed to walk for two minutes as though they were going to mail a letter, i.e. at a self-selected comfortable walking speed. The number of steps was recorded so that cadence and average stride length could also be calculated. Heart rate was measured using a Polar Accurex Plus heart rate monitor. PCI was calculated according to the standard formula: working heart rate minus resting heart rate divided by speed in metres per minute.
Stimulation was applied using a Compex Motion stimulator (Compex SA, Switzerland) and surface electrodes. The stimulators provided open-loop stimulation sequences triggered by a pushbutton. One or more of the following five muscle groups were stimulated: gluteus maximus, quadriceps, hamstrings, tibialis anterior and gastrocnemius/soleus. Each subject was prescribed a specific muscle recruitment/stimulation strategy based on expert analysis. It was found that all subjects possessed a dominant leg and, in all three cases, stimulation was only applied to the weak leg. Minor adjustments to stimulation intensity and timing were made between sessions when deemed necessary. Figure 1 illustrates the stimulation sequence for Subject C.
Figure 1: Stimulation sequence used by Subject C (7th revision). FES was applied to this subject’s left leg only. Button was pressed by subject immediately before swing phase.
Pulse width was modulated from 0 to 300 ms. Biphasic pulses at 40 Hz frequency were used in every case. Current amplitude varied between 25 and 100 mA depending on the target muscle.
For the first 2-4 weeks, stimulation was only applied to the subjects while they were sitting. Seated exercises were performed to strengthen the muscles, reduce spasticity and familiarize subjects with FES. Once the subjects exhibited good, strong responses to the stimulation, FES-assisted walking sessions commenced. All sessions were limited to one hour each, including the speed tests, electrode donning and doffing, and calibration.
At the end of the study, the expert analysis was repeated, and a pre- vs. post-test comparison was made. Walking speed, PCI, cadence and stride length were compared between the start of treatment and the end of treatment.
Results
After 12 to 16 weeks of regular training with FES, all three subjects demonstrated significant improvements to overall gait function without FES. As shown in Figure 2, subjects A & C walked significantly faster in their last four sessions compared to their first four sessions (p<0.01, standard t-test). Subject B’s walking speed changed little.
Figure 2: Walking speed over the course of treatment. Open points indicate when sitting exercises only were performed; closed points indicate when FES-assisted walking was done.
Subject B entered the study with the ability to walk using two canes and a long leg brace on her left leg. At the end of the fifth week, she was able to walk with an anti-hyperextension brace instead of the long leg brace. By the tenth week, she could walk with no brace at all.
None of the subjects showed any significant improvement in PCI. Of the other gait parameters measured, all three subjects showed slight increases in cadence throughout the treatment. Subject B experienced a decrease in stride length after switching to the anti-hyperextension brace, and maintained this stride length until the end of the study. Subject C was the only subject to demonstrate significant increases in stride length.
Conclusions
All three subjects involved in this study
experienced improvements to overall walking function, although the type of
improvement varies. Two of the three experienced increases in walking speed,
while the third experienced a drastic reduction in assistive devices. The
results suggest that FES-assisted walking can be an effective short-term
rehabilitation intervention with long-term results, even for subjects that are
many years post-injury who have been categorized as “neurologically stable” by
rehabilitation institutions. Further study is warranted to compare the
rehabilitative effects of
References
[1] Bajd T, Kralj A, Stefancic M, Lavrac N. Use of functional electrical stimulation in the lower extremities of incomplete spinal cord injured patient. Artificial Organs, 23(5):403-409, 1999.
[2] Donaldson, Perkins TA, Fitzwater R, Wood DE, Middleton F. FES cycling may promote recovery of leg function after incomplete spinal cord injury. Spinal Cord, 38(11):680-2, 2000.
[3] Wieler M, Stein RB, Ladouceur M, Whittaker M, Smith AW, Naaman S, Barbeau H, Bugaresti J, Aimone E. Multicenter evaluation of electrical stimulation systems for walking. Arch Phys Med Rehabil, 80:495-500, 1999.
[4] Barbeau H, McCrea DA, O’Donovan MJ, Rossingnol S, Grill WM, Lemay MA. Tapping into spinal circuits to restore motor function. Brain Research Reviews, 30:27-51, 1999.
[5] Rushton DN. Functional electrical stimulation and rehabilitation – an hypothesis. Med Eng & Phys, 25:75-78, 2003.
Acknowledgments: This study was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada, The Canadian Paraplegic Association – Ontario, the Connaught Fund and the McAllister Fund. We owe special thanks to Kim Parker of the Bloorview MacMillan Children’s Centre for conducting the gait analysis.