Clinical Use of the Odstock Dropped Foot Stimulator: Its Effect ion the Speed and Effort of Walking

Transcription

1 1577 Clinical Use of the Odstock Dropped Foot Stimulator: Its Effect ion the Speed and Effort of Walking Paul N. Taylor, MSc, Jane H. Burridge, Phi), Anna L. Dunkerley, MSc, Duncan E. Wood, PhD, Jonathan A. Norton, BSc(Hons), Christine Singleton, MCSP, lan D. Swain, PhD ABSTRACT. Taylor PN, Burridge JH, Dunkerley AL, Wood DE, Norton JA, Singleton C, Swain ID. Clinical use of the Odstock dropped foot stimulator: its effect on the speed and effort of walking. Arch Phys Med Rehabil 1999:80: Objective: To assess the clinical effectiveness of the Odstock dropped foot stimulator by analysis of its effect on physiological cost index (PCI) and speed of walking. This functional electrical stimulation (FES) device stimulates the common peroneal nerve during the swing phase of gait. Design: A retrospective study of patients who had used the device for 4~/2 months. Subjects: One hhndred fifty-one patients with a dropped foot resulting from an t~pper motor neuron lesion. Setting: A medical physics and biomedical engineering department of a district general hospital specializing in the clinical application of FES and a neurophysiotherapy department at a separate hospital. Main Outcome Measures: Changes in walking speed and effort of walking, as measured by PCI over a 10-meter course. Results: There was a 92.7% compliance with treatment. Stroke patients showed a mean increase in walking speed of 27% (p <.01) and reduction in PCI of 31% (p <.01) with stimulation, and changes of 14% (p <.01) and 19% (p <.01), respectively, whil~ not using the stimulator. Multiple sclerosis patients gained sirrlilar orthotic benefit but no "carry-over." Conclusions: The measured differences in walking with and without stimulatiola were statistically significant in the stroke and multiple sclerosis groups. In this study use of the stimulator improved walking. Those with stroke demonstrated a shortterm "carry-over" effect by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation HE INCIDENCE OF STROKE in the United Kingdom is T approximately 100,000 per year, 1 of whom more than 80% survive. Approximately 75% of the survivors will have a reduced quality of life. Although there are no precise statistics on how many stroke patients have a dropped foot, 20% of the survivors has been suggested as a conservative estimate. 2 From the Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, SalisbUry, Wiltshire (Mr. Taylor, Dr. Burridge, Ms. Dunkerley, Dr. Wood, Dr. Swain); the Neurophysiotherapy Department, City Hospital, Birmingham (Ms. Singleton); and Implanted Devices Group, Department of Medical Physics and Bioengineering, Univershy College London, London (Mr. Norton), United Kingdom. Submitted for publication August 19, Accepted in revised form April 27, Presented in part at the VI Vienna International Workshop on Functional Electrostimulation, September 22-24, 1998, Vienna. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which ~he authors are associated. Reprint requests to P~ul Taylor, Department of Medical Physics and Biomedical Engineering, Salisbury I~istdct Hospital, Salisbury, Wiltshire SP2 8B J, UK by the AmeriCan Congress of Rehabilitation Medicine and the American Academy of Physical M~dicine and Rehabilitation /99/ /0 Patients with other neurologic conditions including multiple sclerosis (MS), incomplete spinal cord injury (SCI), and traumatic brain injury may also suffer from a dropped foot. Functional electrical stimulation (FES) for the correction of dropped foot after upper motor neuron damage has been used since the late 1950s and early 1960s. 3 However, its use in clinical practice has not been common in the UK. The Odstock Dropped Foot Stimulator ~ (ODFS) is one of the few FES systems in clinical use in the UK. At the time of writing more than 400 people had used the ODFS. The ODFS was the subject of a randomized controlled trial in which 32 stroke patients who had had a stroke at least 6 months previously were allocated either to a treatment group who used the device and received 10 sessions of physiotherapy or a control group who only received the 10 sessions of physiotherapy. 47 Both groups received physiotherapy from Bobathtrained physiotherapists. Physiotherapy was provided in the first month of the trial, after which the treatment group continued to use the ODFS. After 3 months the treatment group showed a statistically significant increase in walking speed of 16% and reduction in the physiological cost index (PCI) of 29% when the stimulator was used, while no changes were seen in the control group. 5 No significant carry-over effect was seen, although a trend was present. Users of the ODFS showed a reduction in quadriceps spasticity, measured by the Wartenberg Pendulum Drop Test, 8 which was only seen in the control group while physiotherapy continued. 6 The treatment group also showed a reduction in depression score on the Hospital Anxiety and Depression scale, suggesting an improvement in quality of life. The trial results were presented to the South and West Regional Health Authority Development and Evaluation Committee who subsequently recommended the ODFS for use in the National Health Service. 7 This study details the walking speed and PCI results from a much larger patient group who received the ODFS administered as a clinical service. Preliminary reports have been presented elsewhere. 9 METHODS The ODFS is a single-channel stimulator providing electrical stimulation to the common peroneal nerve and motor point of the tibialis anterior muscle. The stimulation, timed to the gait cycle by using a foot switch placed in the shoe, causes ankle dorsiflexion with slight eversion and elicits a flexor withdrawal reflex 4,5 in the swing phase of gait. This reflex consists of ankle dorsiflexion, hip and knee flexion, with external rotation of the hip. The components of the movement may be varied by adjusting the electrode position and stimulation amplitude. The stimulator, kept in a pocket or worn on the belt, is housed in a box measuring X 2.5cm and powered by a PP3 9-volt battery. The stimulator gives an asymmetrical biphasic output waveform of maximum amplitude 80mA, with a 3001asec pulse duration and a frequency of 40 pulses per second. Stimulation is applied by means of skin-surface electrodes b placed, typically, over the common peroneal nerve as it passes over the head of the fibula and over the motor point of tibialis anterior. The

2 1578 CLINICAL USE OF THE ODFS, Taylor Table 1: Stroke Subjects Who Stopped Using the Foot Stimulator Within the 41/2-Month Period (n = 9) Mean Age Mean ]]me Side of Mean Speed Mean Speed Mean PCI Mean PCI Mean % Speed Mean % (yrs) Since Stroke (mo) Hemiplegia NS1 (m/sec) $1 (m/sec) NS1 (beats/m) $1 (beats/m) $1 to NS1 PCI Sl to NS _ left, 5 right.33 ± _ ± ± ± 11.2 Values reported mean _+ standard deviation. Abbreviations: NS1, measurement taken at the first assessment without the ODFS; $1, measurement taken at the first assessment with the ODFS; $1 to NS1, the immediate orthotic effect from using the stimulator. stimulator's output is normally triggered by heel rise on the affected side and continues until heel strike occurs. Stimulation can also be triggered by heel strike from the contralateral leg, which is a useful function if heel contact is unreliable on the affected side. It may also be possible to stimulate for a fixed time, again useful if heel contact is inconsistent. The rise and fall of the stimulation envelope can be adjusted, an essential feature because a sudden contraction of the tibialis anterior could cause a stretch reflex in the calf muscles. Additionally, adding an extended ramp at the end of the stimulation can prevent "foot flap" due to the premature ending of dorsiflexion. Patient Selection All patients were referred by their consultant or general practitioner and assessed for their suitability for treatment at an assessment clinic. Patients were judged suitable for treatment if they had a unilateral dropped foot that was caused by an upper motor neuron lesion and was corrected by electrical stimulation. Patients were able to move from sitting to standing unaided and able to walk at least 10m with appropriate aids. Patients had to be able to have at least a basic understanding of the ODFS and its intended use and have access to assistance from a caregiver, if necessary. Tolerance of the sensation of the stimulation was essential. Patients with other upper motor neuron lesions have used the ODFS, but this study only details the results from those with stroke, MS, and incomplete SCI. Treatment Two clinic appointments were made on consecutive days for fitting of the ODFS. On the first day the stimulator was set up and its use explained to the patient. On the second day the patient was asked to attend wearing the device so the clinician could assess the patient's ability to set up the device independently. Further adjustments were made and training given as necessary. Patients were followed up 6 weeks later, a further 3 months later, and then every 6 months while they continued to use the stimulator. Further visits to the clinic were also made if the patients experienced difficulties between scheduled appointments. When setting up the stimulator for the first time, great emphasis is put on training the user, and the caregiver if appropriate, to correctly identify the movement produced by the stimulation and techniques used to modify it by changing the electrode positions. Written instructions are also given. The exact electrode position may vary from day to day, possibly because of the varying amounts of calf tone. It was necessary to have regular and frequent follow-up, particularly in the early stages of using the device, to ensure its correct application. Assessments Walking speed and PCI, 1 which is an indication of the amount of effort in walking, were obtained concurrently at each appointment. The patients were asked to "walk briskly" on linoleum over a 10-meter course with lm at either end for acceleration and deceleration. Patients normally walked this course three times with stimulation and three times without. The order of stimulation/nonstimulation was randomized to compensate for any fatigue. The mean speed and PCI for stimulated and nonstimulated walking was calculated. Occasionally, some patients were not able to complete six lengths of the course, so fewer "runs" were recorded. Walking speed has been shown to correlate well to other more complicated measures of gait. 2 PCI is based on the assumption that the amount of energy expended by skeletal muscle is proportional to the increase in oxygen uptake of the body and that this is proportional to the increase in heart rate caused by performing this increased activity.l.lt This assumes that the heart rate has reached a steady state in response to a constant level of activity. For this reason PCI is typically recorded using a "figure of eight" course with the subject walking several hundred meters. This was considered not practical for this group of patients, many of whom would not be capable of extended distances. It has been shown that nonsteady-state measurements of PCI can give a reliable indication of the amount of effort expended if a consistent method is used. l~ Repeated measurements with a sample of patients showed that PCI did not vary significantly with increasing distance, so the 10-m course was considered valid. The PCI is calculated by the following formula: PCI = change in heart rate from resting to steady speed of walking (beats/min)/walking speed (m/min). The final units of the PCI are beats per meter (beats/m). The heart rate was measured using a heart rate monitoff consisting of an electrocardiogram detector strapped to the chest and a receiver with a display unit that was worn on the wrist, in the manner of a wrist watch. The data in this study were obtained retrospectively from the records of these routine measurements kept in the patient's notes. The walking speed and PCI were also recorded for a group of normal, age-matched subjects and were collected in a similar manner to that used in the study. The volunteers walked the 10-m course 10 times, 100m in total. The results from the first three "runs" were then compared with subsequent "runs" to determine if the PCI value changed with increasing distance. Table 2: Subjects With MS Who Stopped Using the Foot Stimulator Within the 41/2-Month Period (n = 2) Mean Age Mean ]]me Mean Speed Mean Speed Mean PCI Mean PCI Mean % Mean % (yrs) of MS (mo) NS1 (m/sec) $1 (m/sec) NSl (beats/m) $1 (beats/m) Speed $1 to NS1 PCI $1 to NS1 63 _ _ ± _ ± _ _ Values reported as mean _+ standard deviation. Abbreviations as in table 1.

3 CLINICAL USE OF THE ODFS, Taylor 1579 Table 3: Stroke Subjects Who Discontinued Using the Foot Stimulator After the 41/2-Month Assessment (n -- 9) Speed (m/sec) PCI (beats/m) NS1.37 _ NS $ $ Values reported are mean _+ standard deviation. Abbreviations: NS1, imeasurement taken at the first assessment without the ODFS; NS3, measurement taken at the third assessment (at 41/2 mo) without l~he ODFS: Sl, measurement taken at the first assessment with the ODFS; $3, measurement taken at the third assessment (at 41/2 mo) with the ODFS. Analysis This study compares the data obtained at the initial set-up appointment and at the third appointment, 4½ months later. Patient data were grouped according to their pathology. In addition, patients who had a right hemiplegia as a result of a stroke were analyzed separately from those with a left hemiplegia. All data were plotted and shown to be normally distributed. The statistical tests performed were paired t tests for withinsubject changes and Student's t tests for comparing the performance of left and right hemiplegic subjects. These tests assumed unequal variance. Absolute mean values and mean changes with confidence intervals are presented. Because multipl~ paired t tests were applied, it is statistically possible that some of the significant results may have resulted by chance. If a 95% confidence is assumed, then out of the 46 tests performed, between two and three tests may have given spurious results. Values for the Controls RESULTS A group of 27 age-matched, able-bodied subjects of mean age 52.8 ± 20.0 (SD) years were measured 10 times over the 10-m course. The mean walking speed was 1.63 ±.22 (SD) m/sec, and the mean PCI was (SD) beats/m. No statistical difference was found between the mean of the first three "runs" and the mean of the second set of three "runs" or the mean of the final four "runs" using Student's t test for both the speed and PCI data. Patient Results Subjects who did not complete 41/2 months of stimulator use. Eleven subjects who started using the ODFS discontinued its use before the assessment at 4½ months (tables 1 and 2). At their initial assessment, 8 subjects had shown an increase in walking speed of greater than 10%, while 7 had shown a decrease in PCI of over 10%, indicating that the device was initially of orthotic benefit to them. Of the stroke subjects, 3 did not retum to clinic and were lost to follow-up; 2 subjects were unable to find electrode positions reliably; 2 others became seriously ill through nonrelated medical conditions and were unable to continue; 1 subject had cognitive problems and was considered more likely to fall when using the ODFS; and 1 subject chose not to use the device. The two subjects with MS who stopped using the device both had problems with spasticity, which prevented effective use of the device; one had increased calf tone, and the second had spasticity about the knee and hip. The mean initial walking speed of the stroke subjects was lower than those subjects who completed the 4½-month period. This was shown to be statistically significant using Student's t test (p <.05). Likewise, the initial PCI was also shown to be higher (p <.05). Initial assessment data from this group is not included in the analysis of subjects who continued to use the device. Subjects who discontinued using the stimulator after the 41/2-month assessment. Nine ODFS users, all of whom had had a stroke, stopped using the device between the 4V2-month assessment and the next assessment 6 months later (tables 3 and 4). Their mean age was 62 _ 17.8yrs and their mean time poststroke was months. There were six right-side and three left-side hemiplegic subjects. Seven subjects had an initial orthotic effect greater than 10% increase in speed, and six a reduction of more than 10% in PCI. The continuing orthotic benefit was experienced by six subjects, in terms of both speed and PCI. However, a carry-over effect was only experienced by four subject in terms of speed and two in PCI. One subject's mobility improved, so the device was no longer required. Another subject's mobility deteriorated, so the ODFS was not able to provide sufficient assistance. One subject had leg ulcers (not caused by using the ODFS), which prevented use of the electrodes. One subject developed edema of the lower leg, increasing the distance between the skin surface and the nerve and preventing a good contraction of the muscle at amplitude of stimulation that could be tolerated. One subject discontinued because of an unrelated health problem; another subject died. Three others discontinued for the following reasons: one because of an inability to reliably place the electrodes, one received insufficient help from the stimulator; and one because of a preference not to use the device. A further 40 subjects continued using the stimulator but had not yet reached the next 6-month assessment. Data from this group are included in the analysis in the next section. Subjects who continued to use the stimulator. One hundred forty subjects continued to use the ODFS for the full 41/2 months, of whom 111 had had a stroke, 21 had MS, and 8 had had a SCI (table 5). Speed and PCI results, both with and without the stimulator, are presented in figures 1 and 2. Subjects with stroke. The average age of the stroke patients was 55.4 ± 18.2yrs. The average time since stroke was yrs (range, lmo to 23.9yrs). Fifty-eight of the stroke Table 4: Changes in Speed and PCI for Stroke Subjects Who Discontinued Using the Foot Stimulator After 41/2 Months J BS3-NSI* $3-$1 $3-NS3 S3-NS1 S1-NS1 Speed i PCI Speed PCI Speed PCl Speed PCI Speed PCI Mean CI.05,,03.20,.35.14, , , , ,.02.11,.45.09,.05.08,.25 % Change p.63! < < Speed reported in msters per second; PCI reported in beats per meter. Abbreviations: NS3-NSl, the carry-over effect (at 41/2 mo); $3-$1, the change in performance when using the ODFS; $3-NS3, the continuing orthotic benefit aftert 41/2 mo of use; S3-NS1, the total orthotic effect from using the stimulator over a 41/2-mo period; S1-NS1, the immediate orthotic effect from dsing the stimulator; CI, 95% confidence interval.

4 1580 CLINICAL USE OF THE ODFS, Taylor Table 5: PCI and Speed for Patients Who Used the Stimulator for 41/z Months Stroke MS SCI (n = 111) (n = 21) (n = 8) PCl (beats/m) NS _ NS3.69 _ _ $1.71 _ _ $3.59 _ _ _+.41 Speed (m/sec) NS1.57 _ _ NS _ Sl.64 _ _ $3.72 _ _ Values are reported as mean _+ standard deviation. Abbreviations as intable 3. patients had a left hemiplegia (52%), and 53 had a right hemiplegia (48%). Table 6 shows the changes in walking speed and PCI for the stroke population. The stroke patients showed a statistically significant improvement in all measurement parameters. A carry-over effect, both in an increase in walking speed of.08rn/sec (14%) and a reduction in PCI of. 17beats/m (19%) at the 4½-month stage were recorded (table 6). The immediate effect of using the stimulator was also shown to be statistically significant, with an increase in walking speed of 12% and a decrease in effort of 18%, with a similar effect recorded at 4V2 months. This indicates that the device may have a therapeutic as well as an orthotic effect for this group. No correlation between the time since stroke and changes in walking speed or PCI were found. In addition, the data on the carry-over effect that are seen with the stroke patients were analyzed separately for right and left hemiplegic patients (table 7). The mean effects were then compared with each other and no significant difference was found for the difference in PCI (p =. 19) or for the difference in the speed data (p =.09). Subjects with MS. The average age of the patients with MS was yrs with an average time since first diagnosis of yrs. Table 6 shows the changes in PCI and walking speed for the 21 MS patients in this study. This group showed a 7% (.03rn/sec) decrease in walking speed and a 16% (. 13beats/m) increase in the effort of walking when not using the ODFS, 4V2 months after starting to use the stimulator. At the initial visit the patients walked slightly faster (.03m/sec) and with less effort (.09beats/m) with the stimulator than without it. However, the ODFS was of significant orthotic benefit to the MS users, reducing PCI by 24% and increasing walking speed by 16% when the ODFS was used at the third assessment. Subjects with SCL The average age of the patients with SCI was yrs and the average time postinjury was yrs. Table 6 shows the changes that use of the stimulator made to the eight patients in this study who had an incomplete lesion of the spinal cord. While a trend towards a carry-over effect was seen, this was not significant. Orthotic benefit was recorded the first assessment, at the final assessment and overall in terms of speed, while the number of subjects may be to small to show significant effects in PCI. The total orthotic effect of using the stimulator for this group of patients was an increase in walking speed of 19% (. 10m/sec). Summary of the carry-over effect. Table 8 shows the carry-over effect for each patient group. A carry-over effect of more than 10% may be of sufficient magnitude to make a noticeable difference to mobility. A 10% increase in walking speed represents a positive result, while a 10% decrease in PCI represents a positive outcome. Over 50% of stroke and SCI users achieved this in speed and PCI; while 13% and 38% of MS users achieved this for speed and PCI, respectively. Sixty-two percent of MS users reduced their walking speed, and t.5 o E3 w 1, c~ ds s&l "N$1 "NS3 BB~I BB s3 Fig 1. Changes in walking speed (m/sec) with and without the ODFS. Box plots show the median, interquartile range, outliers (represented by circles), and extreme case of individual variables (shown by asterisk). CVA, cerebrovascular accident; MS, multiple sclerosis; SCl, spinal cord injury; NS1, measurements taken at the first assessment without the ODFS; NS3, measurements taken at the third assessment w/thout the ODFS; $1, measurements taken at the first assessment w/th the ODFS; $3, measurements taken at the third assessment w/ththe ODFS.

5 CLINICAL USE OF THE ODFS, Taylor 1581 Fig 2. Changes in PCI (beats/m) with and without the ODFS. Box plots ishow the median, interquarti!e range, outliers (represented by circles), and extreme cases of individual variables (Shown by asterisks). CVA, cerebrovascular accident; MS, multiple sclerosis; SCI, spinal cord injury; NS1, measurements taken at the first assessment without the ODFS; NS3, measurements taken at the third assessment without the ODFS; $1, measurements taken at the first assessment with the 0DFS; $3, measurements taken ~t the third assessment withthe ODFS. 13_ O 0 ~+ 8 * 0 CVA MS SCl []NSt B NS3 Him ~t ~ s3 43% increased their PCI when they were not using the stimulator. DISCUSSION Because of the retrospective clinical nature of this study there are a number of confounding variables within it. Because no control group was used in this study it cannot be ruled out that the improvements in walking parameters seen between the first and final assessments did not result from the continuing recovery of the patients. However, this study followed a randomized controlied trial that showed no change in walking parameters of its control subjects who only received physiotherapy. Additionally the mean time since stroke and SCI was 5.4 and 10.9 years~ respectively, so it was unlikely that any further improvement in gait would be expected. It could be argued, however, that a more suitable control group would have been one that used ankle foot orthosis (AFO), because this is the primary alternative treatment. AFOs had not been universally prescribed to this patient group and had been rejected by many. To put into perspective the effect of using the ODFS, the PCI and walking speed of users can be compared with normal values of walking speed and PCI. Comparing the results of the stroke patients indicates that the orthotic use of the ODFS reduces the PCI from three times to two times the normal value, while walking speed was increased from just over one third to just under half of the normal value. The low rate of dropout from treatment is encouraging, especially for a relatively complicated device such as the Table 6: Changes in Walking Speed and PCI NS3-NS1 $3-$1 $3-NS3 S3-NS1 S1-NS1 Speed PCI Speed PCI Speed PCI Speed PCI Speed PCI Stroke(n - 111) Mean CI.05,.11.08,-.25 % Change p <.01 <.01 MS(n = 21) Mean CI.01, ,-.04 % Change p SCI(n - 8) Mean Cl.14, ,.52 % Change p Speed reported in meters per second; PCI reported in beats per meter. Abbreviations as in talble , , , ,.13.12, , , , <.01 <.01 <.01 <.01 <.01 <.01 <.01 < ,.03.23, ,.04.02, ,.00.08,.22.06, , <.01 <.01 < <.05 < , , ,.00.06, , ,.55.07,.01.02, < < <.05.07

6 1582 CLINICAL USE OF THE ODFS, Taylor Table 7: Differences in the Carry-Over Effect (at 41/2 Months) of Speed and PCI Between Hemiplegic Patients After Stroke Side of Hemiplegia Left (n = 58) Right (n = 53) Speed PCI Speed PCI Mean CI.01,.11.00, , ,-.36 % Change p <.05 <.05 <.01 <.01 Speed reported in meters per second; PCI reported in beats per meter. ODFS. This may, at least in part, be due to the emphasis placed on patient education and the follow-up service provided. It indicates that the device was well accepted by the majority of users and that it can be successfully used in the clinical setting. The results of our stroke patients differs from the original trial in that a much greater orthotic benefit was recorded in terms of increased walking speed, 27% compared with 16% in the original trial. 5 This is in part due to the lower mean walking speed recorded at the first assessment in this study, suggesting that this study deals with a slightly more disabled group. However, the final walking speed with the ODFS was similar. Although a trend was seen towards a carry-over effect in the trial, the present study shows a statistically significant effect, possibly because of the much larger number of subjects in the current cohort. There are some other differences between the two studies. The original trial lasted 3 months, versus 41/2 months in the our study. In the trial the subjects had greater contact time as they received 10 physiotherapy sessions in the first month. The outcome may have been influenced by the increased experience of the staff performing the treatment and the improvements in reliability of the ODFS over the last 5 years. More significant to the users than the increase in walking speed may be the decrease in PCI when the device was used. In a recent questionnaire survey of 160 users, results of which have been presented elsewhere 7,12 (107 were continuing to use the stimulator and had used it for an average of 19 months [range 1 to 60]), the most frequently cited primary reason for using the stimulator was that the effort of walking was reduced when the ODFS was used (44.3%). This reason was more often cited by users with MS (67%) than with stroke (26.9%), and this agrees well with the greater reduction in PCI experienced by MS users when the stimulator is used at the third assessment, compared with stroke users. In the authors' experience, MS subjects are often more tenacious users of the ODFS and have a lower dropout rate than other patient groups. The improvement in walking parameters without the use of the ODFS at the third assessment of the stroke subjects represents a short-term "carry-over" effect. Most users of the stimulator would arrive at the clinic using the device and, in fact, were encouraged to do so to enable the physiotherapists to assess their ability to apply the stimulator. The majority of users use the ODFS every day. In the previously mentioned questionnaire, however, 15.1% of stroke subjects said that one of the reasons they used the device was that their walking was better when the stimulator was not used, if they used it periodically. The time that this carry-over effect lasts varies from individual to individual; one user claimed that the improvement in her walking was maintained if she used the ODFS for 1 day every 3 weeks. Of the 53 ex-users of the ODFS who completed the questionnaire, 23.6% (9 stroke, 1 SCI) gave as their primary reason for discontinuing its use that their walking had improved. It has been observed that some long-term users who use the ODFS all the time may have a tendency to become dependent on the device. This can be seen to some extent by the number of patients who have a deterioration in their walking parameters unaided (table 8). Because of this tendency, we have recently started to encourage users to spend some time walking without the stimulator, so their ability to walk unaided is not compromised. The carry-over effect was first noted by Liberson and colleagues 3 who reported, "On several occasions, after training with the brace, patients acquired the ability of dorsiflexing the foot by themselves, although the periods of spontaneous activity were only transitory." Stefancic and associates ~2 recorded electromyographic activity in the anterior tibialis and triceps surae muscle before and after 20 minutes of common peroneal stimulation in 15 hemiplegic subjects. In more than half the subjects Stefancic ~2 noted a more normal pattern of muscle activation with increased reciprocal inhibition and also low amplitude activity in previously silent muscles. Seven of the subjects also demonstrated increased voluntary muscle torque following stimulation. According to Waters and colleagues, ~3 Stefancic suggests that these effects may be due to a "central reprogramming mechanism" and may account for the shorter rehabilitation time when patients use FES in the acute stage of recovery following stroke. During a 4-week period of using a dropped foot stimulator, Granat and colleagues 14 showed significant improvements in gait parameters and in the Barthel index in 19 chronic and acute hemiplegic subjects while using a dropped foot stimulator. This improvement, however, was not maintained when treatment was discontinued. While the stimulator is being used the patient's hemiplegic gait may be replaced by one that could be regarded as more "normal." Repeated use of the stimulator may then lead to a pattern of "normal" walking being relearned centrally, in much the same manner that the abnormal gait was learned. Long-term potentiation of the required pattern of synapses may lead to a reinforcement of this pattern of walking. ~5 With time this may become the normal walking pattern and the cortical command to "walk" may activate the cells within this pattern, rather than the cells involved in the "hemiplegic" gait, because of the increased strength of the synapses involved. The effect of carry-over may be in part due to the effect on spasticity of using the ODFS. In the original randomized Speed Table 8: Summary of Carry-Over Effect >10% +10% to -10% >10% >10% +10% to - 10% >10% Increase (No Change) Decrease Decrease (No Change) Increase Stroke 63 (57%) 35 (32%) 13 (12%) 56 (50%) 24 (22%) 31 (28%) MS 3 (14%) 8 (38%) 10 (48%) 8 (38%) 4 (19%) 9 (43%) SCI 4 (50%) 3 (38%) 1 (13%) 4 (50%) 0 (0%) 4 (50%) An increase in PCI represents an increase in the effort of walking, so while a 10% increase in walking speed represents a positive result, a 10% decrease in PCI also represents a positive outcome. PCI

7 CLINICAL USE OF THE ODFS, Taylor 1583 controlled trial of the ODFS, Burridge and colleagues 6 showed a significant reduction in quadriceps tone in the group who used the stimulator. Stimulation of the common peroneal nerve not only causes ankle dorsiflexion but also elicits a flexor withdrawal reflex consisting of knee and hip flexion with hip external rotation. It is reasonable to assume that the activity caused in the hamstrings may give rise to reciprocal inhibition in the quadriceps through la inhibitory interneurons and Renshaw cells and after many repetitions may lead to neuroplastic changes, reducing quadriceps tone. Quadriceps tone may also be representative of general extensor tone and so may also indicate a reductic~n in other muscle groups such as the calf muscles. It is also pbssible that the reduction in effort seen when using the stimulator may generally reduce associated reactions when the device is used, which again may lead to neuroplastic changes in the long term. The effect of the side of the hemiplegia in stroke patients is surprising. Although the patients who have a right hemiplegia have an increased occurrence of dysphasia compared with those with right-sided brain damage, the patients with left-sided brain damage (right hemiplegia) are more likely to have preserved cognition centers Within the brain. This may mean that they are able to understand the use of the stimulator better and so apply it more effectively and consistently. CONCLUSIONS This study shows that the clinical implementation of the ODFS can improve walking when used as an orthosis, as assessed by walkir~g speed and PCI, of patients who have a dropped foot resulting from an upper motor neuron lesion. In addition, patients who have had a stroke experience a shortterm "carry-over" effect when they are not using the stimulator, after using it for 492 months. Although the patients with MS do not show this improvement, they do show an improvement in gait when they are using the stimulator. The low incidence of dropout from treatment indicates that the device is acceptable for daily use by the!majority of users. AcknowledgmentS: We thank Stacey Finn and Simon Gallaghar for technical support iin building and maintaining the stimulators and Carol Donaldson for ~dministration. We also thank the UK Department of Health's Medical Devices Agency for funding the initial trial of the Odstock Dropped FOot Stimulator and the Wessex Rehabilitation Association for allowing the Salisbury team to inhabit their building. References I. Royal College of Physicians. Stroke: towards better management. London: Royal College of Physicians; Wade D, Wood V, Heller A, Maggs J, Langton Hewer R. Walking aller stroke: measurement and recovery over the first 3 months. Scand J Rehabil Med 1987; 19: Liberson W, Holmquest H, Scott M. Functional electrotherapy: stimulation of the common peroneal nerve synchronized with the swing phase of gait of hemiplegic subjects. Arch Phys Med Rebabil 1961 ;42: Burridge J, Taylor P, Hagan S, Swain I. Experience of clinical use of the Odstock dropped foot stimulator. Artif Organs 1997;21: Burridge J, Taylor P, Hagan S, Wood D, Swain I. The effects of common peroneal nerve stimulation on the effort and speed of walking: a randomized controlled clinical trial with chronic hemiplegic patients. Clin Rehabil 1997;11: Burridge J, Taylor P, Hagan SA, Wood DE, Swain ID. The effect on the spasticity of the quadriceps muscles of stimulation of the common peroneal nerve of chronic hemiplegic subjects during walking. Physiotherapy 1997;83: Taylor PN, Burridge JH, Dunkerley AL, Lamb A, Wood DE, Norton JA, et al. Patient's perceptions of the Odstock dropped foot stimulator (ODFS). Clin Rehabil 1999;13: Katz R, Rovai G, Brait C, Rymer W. Objective quantification of spastic hypertonia with clinical findings. Arch Phys Med Rehabil 1992:73: Taylor PN, Burridge JH, Dunkerley AL, Wood DE, Norton JA, Singleton C, et al. Clinical audit of 5 years provision of the Odstock dropped foot stimulator (ODFS). Artif Organs 1999:23: Nene A. Physiological cost index of walking in able-bodied adolescents and adults. Clin Rehabil 1993;7: Bailey M, Ratcliffe C. Reliability of physiological cost index in walking normal subjects using steady-state and non-steady-state and post-exercise. Physiotherapy 1995 ;81: Stefancic M, Rebersek M, Merletti R. The therapeutic effects of the Ljubljana functional electronic brace. Europa Medicophysica 1976; 12: Waters RL, McNeal DR, Faloon W, Clifford B. Functional electrical stimulation of the peroneal nerve for hemiplegia: longterm clinical follow-up. J Bone Joint Surg 1984;67A: Granat MH, Maxwell DJ, Fergusen ACB, Lees KR, Barbanel JC. Evaluation of common peroneal stimulation for the correction of dropped foot in hemiplegia. Arch Phys Med Rehabil 1996;77: Kandell ER. Cellular mechanisms of learning and the biological basis of individuality. In: Kandel ER, Schwartz JH, Jessell TM, editors. 3rd UK ed. East Norwalk (CT): Appleton and Lange; p Suppliers a. The ODFS is only available to clinicians who have been trained in its use by the Salisbury FES team. It is CE marketed and manufactured by the Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, Salisbury, Wiltshire, UK SP2 8BJ. b. Pals Electrodes; Nidd Valley Medical, Conyngham Hall, Knaresborugh, North Yorkshire, UK HG5 9AY. c. Polar heart rate monitor; Bodycare Products Ltd. 57 Fieldgate Lane, Kenilworth, Warwickshire, UK CV8 I BT.