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Gait in Individuals with Chronic Hemiparesis: One-Year Follow-up of the Effects of a Neuroprosthesis That Ameliorates Foot Drop

Laufer, Yocheved PT, DSc; Ring, Haim MD; Sprecher, Elliot PhD; Hausdorff, Jeffrey M. PhD

Journal of Neurologic Physical Therapy: June 2009 - Volume 33 - Issue 2 - p 104-110
doi: 10.1097/NPT.0b013e3181a33624

Purpose: Foot drop is a common cause of gait impairment in individuals with hemiparesis. The objective of this study was to determine the short-term and long-term effects on functional gait of a neuroprosthesis that provides functional electrical stimulation (FES) to correct footdrop.

Methods: Sixteen individuals (mean age, 55.0 ± 14.6 years) with chronic hemiparesis (mean years since insult, 5.3 ± 4.8) were assessed immediately before receiving the neuroprosthesis and two months and one year after using the device. Both follow-up assessments were conducted with FES operating; the one-year follow-up also assessed gait without FES. Outcome measures were gait velocity on an even surface during a 10-m walk, during a six-minute walk, over obstacles, and over a carpet. Foot switches used during the six-minute walk determined stance time, stride time variability, and gait asymmetry. The effect of time and the one-year carryover effect on gait without FES were determined, with significance set at P = 0.05.

Results: The neuroprosthesis had a significant short-term and long-term effect on most measured variables. Thus, mean 10-m walk gait velocity improved in two months from 0.67 m/sec to 0.86 m/sec and continued to increase to 1.06 m/sec by the one-year assessment. A carryover effect on gait velocity and stance time without FES were also noted. The 10-m gait velocity without the neuroprosthesis increased by 23.8% by the one-year follow-up assessment.

Conclusions: The neuroprosthesis appears to improve gait performance, and gains were further enhanced over time and carried over to gait even without FES. These results suggest orthotic and therapeutic effects on footdrop after prolonged use of the neuroprosthesis.

Department of Physical Therapy (Y.L., E.S.), Faculty of Social Welfare and Health Sciences, University of Haifa, Haifa, Israel; Department of Physical Therapy (Y.L.), University of Delaware, Delaware; Neurological Rehabilitation Department (H.R.), Loewenstein Rehabilitation Center, Raanana, Israel; Department of Rehabilitation Medicine (H.R.), Sackler Faculty of Medicine, Tel-Aviv University; Movement Disorders Unit (J.M.H.), Neurology Department, Tel-Aviv Sourasky Medical Center; Department of Physical Therapy (J.M.H.), Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel; and Division on Aging (J.M.H.), Harvard Medical School, Boston, Massachusetts.

Supported by Bioness Neuromodulation, Ltd.

Address correspondence to: Yocheved Laufer, E-mail:

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Ankle dorsiflexion plays an important role in the swing and initial stance phase of the gait cycle and is frequently impaired in individuals with upper motor neuron lesions.1 The impairment, termed footdrop, is caused by a combination of weak dorsiflexors and increased spasticity and stiffness of the plantar flexors.2 Footdrop is conventionally treated with an ankle-foot orthosis (AFO), which helps the affected individual to clear the foot during the swing phase while also providing stability during stance.1,3 Functional electrical stimulation (FES) to the common peroneal nerve was first introduced in the early 1960s as an alternative approach to the AFO.4 FES entails the use of electrical stimulation applied to activate the dorsiflexors during the swing phase of gait, promoting foot clearance. Depending on the technology used, stimulation can also be timed to continue during the early stance phase, thus alleviating the tendency of some individuals to hyperextend the knee at this phase.5,6

Research on the effect of FES to the common peroneal nerve has focused primarily on gait velocity and energy expenditure during a short walk (typically a 10-m course) on an even surface and has demonstrated that FES increases gait velocity while decreasing physiological cost.7–11 However, walking a short distance in a laboratory environment does not truly simulate the demands of functional ambulation. A few studies, primarily in the past decade, have evaluated other gait-related functions, such as gait velocity on uneven surfaces and around obstacles,12,13 gait endurance,5,14 and stride time variability (STV),5 demonstrating similar positive effects. Moreover, despite the fact that long-term use of FES is reported11 and is expected to increase further with advances in technology,15,16 most studies do not extend their evaluation beyond six months of FES application. Thus, long-term follow-up studies are clearly warranted.

The human sensorimotor nervous system is a highly plastic structure. Recent studies in healthy volunteers suggest that short-term (eg, 30 minutes) sensory and motor electrical stimulation, such as that delivered by FES, may facilitate the excitability of the cortex and its connections to the spinal cord.17–19 These reactions may have therapeutic implications, with repetitive stimulation affecting motor performance after an insult to the central nervous system. A therapeutic effect of FES to the common peroneal nerve, namely, a carryover effect on gait performance that persists beyond the period of stimulation, was already suggested in the early 1960s. Liberson et al4 reported that after stimulation with FES, some users exhibited spontaneous, transitory dorsiflexion. However, only a few studies have addressed this issue in individuals with hemiparesis, with conflicting results.10,20–23 For example, although Granat et al21 showed no carryover effect after 11 weeks of FES application, Taylor et al23 demonstrated that individuals with stroke who used FES daily for 4.5 months and were assessed in a 10-m walk test without stimulation increased their gait speed by 14% and reduced their energy cost by 19%. These studies clearly indicate the need to examine possible long-term training effects on a variety of gait performance measures.

The primary objectives of this study are twofold: (1) to compare the short-term and long-term effects of an FES neuroprosthesis designed to correct footdrop (the NESS L300®, Bioness Inc., Valencia, CA) after its daily application for two months and one year and (2) to determine the carryover effect of applying the neuroprosthesis daily for one year on gait when examined without the assistance of the stimulation.

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Sixteen subjects (15 men, 1 woman) ranging in age from 28 to 76 years (mean, 55.0 ± 14.6 years) participated in this study. Of the 16 subjects, 13 (81%) presented with footdrop as the result of a cerebral vascular accident and three (19%) had footdrop as the result of a traumatic brain injury. Subjects were recruited from two outpatient clinics during a nine-month period. Inclusion criteria were (1) diagnosis of an upper motor neuron lesion; (2) hemiparesis for at least six months; (3) observed footdrop during the swing phase of gait; (4) calf muscle spasticity not higher than grade 4 according to the Modified Ashworth Scale; (5) passive ankle range of motion to neutral position; (6) a score of at least 23/30 on the Mini-Mental State Examination; (7) no skin lesion in the area of the electrodes; (8) no acute medical condition; (9) no depression as defined by the Diagnostic and Statistical Manual of Mental Disorders, 4th edition criteria. The study was approved by the Institutional Review Board of the Lowenstein Rehabilitation Hospital, Raanana, Israel, and all subjects signed an informed consent form before participation.

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Subjects who were referred for FES to correct a footdrop were fitted with the NESS L300 neuroprosthesis (Fig. 1). As described previously,5 the device uses a gait sensor fitted into the shoe to detect gait cycle events, such as heel strike and toe-off. Microcomputer-based algorithms provide ongoing adjustments of the precise timing of stimulation in accordance with real-time gait events, thereby permitting necessary adjustments with changes in terrain. This information is transmitted by wireless radiofrequency signals, which control the electrical stimulation to the common peroneal nerve. The stimulation unit and electrodes are embedded into a lightweight orthosis, which can be easily placed at the appropriate anatomic location using only one hand. The L300 neuroprosthesis also includes a gait log, which enables the clinician to note the number of steps and/or hours of use. The default parameters of the system are biphasic symmetrical pulses, phase duration 200 μsec, and pulse frequency 30 Hz. However, the clinician uses a hand-held computer (personal digital assistant) to set the parameters of the system to achieve an optimal dorsiflexion response with slight eversion, which ensures foot clearance during the swing phase and heel contact in the initial stance phase. Slight variations in the systems parameters are occasionally made, with intensity set for most subjects between 30 and 35 mA. Using the personal digital assistant, the clinician also adjusts the timing of stimulation as necessary (eg, adding stimulation during the stance time to avoid knee hyperextension). A small wireless control unit is used by the participant to activate the system and to provide information regarding system status.



After the initial application of the device, subjects were instructed to gradually increase their daily use of the neuroprosthesis, so that by the end of the first week they were using it one hour per day, by the end of the second week they were using it four hours per day, and by the end of the fourth week they were using it throughout the day. Each subject was evaluated at three time points: before the fitting of the neuroprosthesis (T1), two months later (T2), and one year after initial application of the device (T3). The assessment at T1 evaluated gait without the neuroprosthesis or the AFO, whereas during the second and third assessments, gait performance was evaluated with the stimulation applied. In addition, at the one-year follow-up assessment, gait was also evaluated without the neuroprosthesis (T3 without the neuroprosthesis) to assess any potential carryover effects, with the order of conditions (ie, with and without FES) randomized. The participants were allowed to rest between the two evaluations. All outcome measures were obtained from four walking test conditions, as listed below. The order of the tests was maintained in all assessments, with ample periods of rest between tests provided as necessary. Subjects were allowed to use any assistive device (eg, cane) that they normally used at home, while walking safely at a comfortable pace without running, with the same assistive device used for repeated assessments.

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Outcome Measures

Gait Velocity

Gait velocity was determined in meters per second (m/sec) under the following four conditions. (1) A 10-m walk velocity (10mV). For this test, walking was timed with a digital stopwatch over the middle 10 m of a 14-m marked distance (results of this variable, but only with FES operating, were previously published).24 (2) Six-minute walk velocity (6minV). For this test, the subjects were instructed to walk as far as they could for six minutes back and forth along a 50-m hallway, turning around each time they reached the end of the hallway. The distance covered was measured to the nearest meter. (3) Carpet walk velocity. Adopting the protocol used in the Emory Functional Ambulation Profile,25 walking was timed with a digital stopwatch over the course of a 10-m walk on a carpet. (4) Obstacle walk velocity. Also based on the Emory Functional Ambulation Profile protocol,25 the subjects were requested to step over two bricks spaced 1.5 m apart and around a trash can spaced two m after the second brick.

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Gait Cycle Dynamics

The following variables were obtained during the six-minute walk test, using force-sensitive insoles placed in the subjects' shoes (B&L Footswitches, Tustin, CA), which were connected to a data logger (JAS Research Inc., Belmont, MA), enabling measurement of temporal parameters of gait. Stride time (gait cycle duration) was determined for each stride and analyzed to assess stride time dynamics (as previously described26–28). STV was assessed with the coefficient of variation using the following calculation: 100 × [standard deviation (SD) of stride time/mean stride time]. Gait asymmetry index was measured as a marker of interlimb coordination and was calculated as follows: (swing time paretic − swing time nonparetic)/(swing time paretic + swing time nonparetic). Thus, an asymmetry index of zero would indicate a perfectly symmetrical gait with both lower extremities maintaining equal swing periods. The percentage of the single stance phase was calculated as the percentage of time in the gait cycle spent as single stance on the paretic limb (equal to the swing phase of the nonparetic limb).

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Statistical Analysis

Descriptive measures are summarized as mean ± SD or percentage, as indicated. Separate one-way repeated-measures analyses of variance, with four levels of a single factor (T1, T2, T3 with FES, and T3 without FES), were used to examine the effect of time and the carryover effect on each outcome measure. Analyses of variances were followed by preplanned comparisons based on adjusted Tukey-Kramer tests. Significance was determined at P ≤ 0.05. The analysis was performed using SAS, version 9.1 (SAS Institute, Cary, NC).

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The data presented are for a subset of patients whose performance two months after application of the NESS L300 was previously described.5 Included here are only 16 subjects who were also available for the one-year follow-up assessment. Of the eight subjects not available for the one-year follow-up evaluation, one subject stopped using the neuroprosthesis after a tendon transfer; a second subject stopped its use because she felt that she had improved sufficiently and no longer needed the device; the other six subjects reported by phone that they continued using the device with satisfaction, but were followed by another clinic and could not come to the clinic for assessment. Data regarding the effect of the neuroprosthesis on functional abilities and social participation of this subgroup are described in detail elsewhere.24 The time between diagnosis and initial assessment ranged between 0.5 and 16 years (mean, 5.3 ± −4.8 years). Before initiation with the neuroprosthesis, three (19%) subjects had used no orthotic device, one (6%) had used a Dicuts band (OrtoPed, Canada), and 12 (75%) used an AFO. Only five (31%) of the subjects did not use any assistive device for walking, and 11 (69%) used a cane. As indicated by the L300 gait log, all the subjects continued using the neuroprosthesis over the entire one-year follow-up period, with full adherence considered with unit application for at least 80% of the days. One subject had to suspend its use for a two-week period due to skin irritation, but resumed using the device once that condition resolved.

Group means and SDs of all measured gait performance variables are presented in Table 1. There was a significant effect of time for all variables. Preplanned comparisons between time points revealed significant improvements between T1 and T2 in all variables (Table 2).





The post hoc tests comparing performance between T2 and T3 with the neuroprosthesis indicated further significant improvements in gait velocity as measured on the 10-m walk, with a trend toward additional improvement also noted for the six-minute walk test and over the carpet test. A carryover (therapeutic) effect on gait velocity, as determined by comparing performance at baseline (without the neuroprosthesis) to performance at one-year follow-up assessment without the neuroprosthesis, was observed in all four ambulation test conditions. A carryover effect was also determined for single stance time. Yet, comparison at the one-year follow-up assessment of gait velocity with and without the neuroprosthesis indicated that despite a carryover effect to gait without FES, gait velocity remained significantly higher with the neuroprosthesis operating (see Figure 2 for results of the 10-m tests).



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This study demonstrates that the L300 neuroprosthesis has a significant long-term impact on gait velocity, as well as on temporal gait parameters, leading to a more symmetrical and less variable gait pattern. These results are consistent with previous reports that observed a positive effect of common peroneal FES on routine, overground gait speed in subjects with upper motor neuron injury (see, eg, the reviews by Robbins et al9 and Kottink et al8) and extend those findings by further demonstrating the positive effects of FES on walking speed under a variety of functional conditions. Moreover, the current findings show that, in subjects with chronic hemiparesis, not only are these short-term gains maintained over a year-long course of FES, but also that the 10-m gait velocity improves even further with the progression of time and that improvements in gait velocity and single stance time are carried over to gait without the device.

Many previous studies on the effect of FES on the common peroneal nerve have focused primarily on ambulation velocity during a 10-m walk and on the Physiologic Cost Index.5,13,23,29 The observed increase of 29% in gait velocity at the two-month follow-up assessment is in accordance with previous reports on the short-term effect of FES devices, which observed significant increases in gait velocity ranging between 15% and 40% after one to six months of FES application.5,7–11,20,22,23,29 However, marked deterioration in speed and quality of walking has also been reported in patients with hemiparesis during walks of longer duration, even among individuals who were able to walk at near normal speeds over a 10-m walk test.30 Because functional ambulation indoors and outdoors requires the ability to walk for extended periods of time, as well as the ability to negotiate a variety of walking surfaces, the traditional 10-m walk test is not always sufficient to determine functional community level locomotor ability.31 The short-term 28% increase in gait velocity observed in the six-minute walk test, which was similar in magnitude to the increase in velocity over the 10-m walk, indicates that application of FES induces significant improvements in ambulation endurance, which is vital for independent community ambulation.32

These changes are important only if they entail a clinically meaningful difference. In older adults without specific impairments, as well as in adults after a hip fracture, a change in gait velocity of 0.10 m/sec has been determined as a minimal clinically important difference.33,34 To the best of our knowledge, clinically meaningful differences have not been specifically determined for subjects with hemiparesis. However, given the very low gait speed of individuals with hemiparesis, it is very likely that a change of 0.10 m/sec would also be clinically meaningful for this population. Furthermore, it is suggested that when gait velocity is used to stratify subjects into functional ambulation categories, gait velocity can be used as a clinically meaningful outcome measure.35 Thus, for example, using a three category classification of gait ability (limited household ambulation: gait velocity < 0.4 m/sec; limited community ambulation: gait velocity of 0.4–0.8 m/sec; and functional community ambulation: gait velocity >0.8 m/sec), it was demonstrated that gait velocity gains which result in a transition to a higher ambulation category are associated with better function and quality of life.35 Thus, although the gait velocity of our participants never reached the level of aged-matched norms,36,37 it seems that both the initial and the long-term improvements were clinically significant. This is further supported by our recent findings that the neuroprosthesis had significant favorable short-term and long-term effects on self-reported physical functioning in both activities of daily living and social integration.24

Although gait velocity during the 10-m walk tests remained the highest in comparison with the other testing conditions, it is worth noting that although the 10-m gait velocity increased in two months by 29%, gait velocity during ambulation on the carpet surface increased by 51%. A similar observation was recently made by Burridge et al,12 who reported a trend toward greater improvement in gait velocity on uneven surfaces compared with even surfaces when using a peroneal stimulator. The neuroprosthesis used in this study is designed not only to respond to gait cycle events, such as heel strike and heel-off, but also to respond to real-time changes in mean swing/stance time and loading by employing algorithms that adjust the relevant stimulation parameters. Thus, stimulation timing will change almost instantaneously with a shift in gait velocity or in terrain compliance, which may explain the effect of the device on walking on a carpet.

Various authors have referred to the gains in gait performance made during stimulation as the orthotic effect of the device, while referring to the changes resulting from repetitive FES, which are carried over to a period when stimulation is not applied, as the therapeutic or carryover effects of the stimulation.8,38 The orthotic effect of FES is expected to reach a plateau when subjects are fully habituated to the use of the device, which is potentially one reason for the short-term focus of most previous studies. In this study, the initial increase in gait velocity in the10-m walk was 29% after two months, whereas the overall increase during gait with the neuroprosthesis after one year was 52%. Similarly, the increases in gait velocity in the six-minute walk and over carpet after two months using the neuroprosthetic were 29% and 51%, respectively, whereas the overall increases after one year were 41% and 65%, respectively. Given that the performance of individuals with chronic hemiparesis is generally expected to either remain steady or deteriorate over time in the absence of an intervention,39 these unexpected continued changes observed during gait with the FES operating suggest that prolonged use of the neuroprosthesis may have a therapeutic (ie, training) effect beyond the carryover effect.

The carryover effect to gait without the application of the neuroprosthesis was found to extend to gait velocity in all four functional ambulation test conditions, as well as to increased stance time over the paretic extremity. The only gait parameters found to be resistant to a carryover effect in this study were gait asymmetry and STV. Although not all previous studies demonstrated carryover effects,20,21,40 these results are in accordance with a growing body of evidence indicating that peroneal FES may have therapeutic effects, which persist beyond the period of stimulation.10,11,22 Although positive carryover effects are expected to involve longer periods of FES, it is impossible to evaluate whether this is the primary determining factor. Sheffler et al22 recently reported two case studies of subjects with chronic hemiparesis demonstrating carryover effects after only four weeks of FES.

Changes at the peripheral impairment level, as well as central mechanisms, might be responsible for the therapeutic effects observed both during and after stimulation. Peroneal FES has been reported to increase muscle strength2,6,40,41 and to decrease spasticity,2,6 impairments that are associated with gait performance in individuals with hemiparesis.42,43 Possible central mechanisms involve changes in cortical excitability that have been shown to be susceptible to both sensory and motor input, as delivered by electrical stimulation.17–19 In addition, task-specific practice is an essential component of motor relearning, which leads to cortical reorganization after stroke.44 The use of the peroneal FES may be related to an increase in active practice by several means. For example, unlike the AFO previously used by most of the subjects before they switched over to the FES device, the neuroprosthesis does not limit ankle movement; therefore, it may force the users to exert greater active control over their movements at both the ankle and the knee. The putative reduced energy expenditure, increased stability, and enhanced confidence associated with the neuroprosthesis also may have encouraged the individuals to walk more, in turn leading to further improvement. Additional factors that may have contributed to high compliance and increased use are the simplicity and reliability of the neuroprosthesis. For instance, the unique design of the hybrid orthosis provides for accurate and consistent electrode placement and therefore ensures repeatable balanced foot movement.

Although the subjects of this study had hemiparesis of long duration and the observed improvements are not likely to be related to spontaneous recovery, the primary limitation of the study is the lack of a control group. Thus, other factors that were not controlled for, such as activity/exercise level during the application of FES, cannot be ruled out as factors contributing to the observed changes. Furthermore, the included participants were relatively young and were able at baseline to walk independently at a gait velocity sufficient for unlimited household ambulation.35,45 Therefore, the results may not apply to older and/or more involved individuals. Clearly, in-depth kinematic and kinetic studies would also be helpful in characterizing the changes observed following the application of peroneal FES and their underlying mechanisms. As this study demonstrated therapeutic effects both during and after stimulation, future studies should also focus on the effects of the neuroprosthesis during the acute stages after injury. Finally, it should be noted that the neuroprosthesis may not be suitable for all individuals who have foot drop; for example, it may not offer sufficient stability for patients with severe spasticity or poor knee control.

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This study indicates that the long-term use of the NESS L300 neuroprosthesis may improve the functional gait performance of subjects with chronic hemiparesis. Furthermore, after its prolonged use, certain enhancements of gait performance may also be expected during walking, both with and without the application of the neuroprosthesis.

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hemiparesis; footdrop; gait; functional electrical stimulation; neuroprosthesis

© 2009 Neurology Section, APTA