RETROSPECTIVE STUDY

The Effects of the Odstock Drop Foot Stimulator onPerceived Quality of Life for People With Stroke andMultiple Sclerosisner_250 58..64

Catherine Barrett, MSc, BSc, MCSP* · Paul Taylor, PhD, MSc, BSc, CEng†

*School of Health and Social Care, University of Bournemouth, Talbot Campus, Poole, Dorset, UK; and †School of Design, Engineering andComputing, University of Bournemouth, Talbot Campus, Poole, Dorset, UK

ABSTRACTIntroduction. Gait speed is often used as a proxy for gait quality. However, some users of FES devices for correction of dropped footchoose to continue to use the device despite no significant change in speed. The Psychosocial Impact of Assistive Devices Scale (PIADS)was used to evaluate the effects of the Odstock Dropped Foot Stimulator (ODFS) on perceived quality of life (QOL) for people with strokeand multiple sclerosis (MS) and was compared with change in walking speed. Method. A total of 21 people with stroke and 20 with MScompleted the PIADS questionnaire after 18 weeks of using the ODFS. Walking speed was recorded more than 10 m with and withoutstimulation. Results. Both groups recorded positive median scores for all three sections of the PIADS questionnaire: Competence (1.25stroke, 0.91 MS), Adaptability (1.25 stroke, 0.50 MS), and Self-esteem (0.88 stroke, 0.75 MS). These were significantly greater for thestroke than the MS group for Competence, p = 0.04 and Adaptability, p = 0.006. There was no significant correlation between changes inPIADS and changes in walking speed. Conclusions. FES for correction of dropped foot has a beneficial effect on perceived QOL forpeople with stroke and MS but this is not correlated with an objective measures of gait.

KEY WORDS: FES, gait, MS, quality of life, stroke.

IntroductionThe terms assistive device or assistive technology are usedto describe any aid to daily living that enhances functionwithin an individual’s environment (1). Drop foot stimula-tors are one type of assistive device that can be used to aidwalking and improve perceived quality of life (QOL) forthose with neurologic disorders such as stroke and multiplesclerosis (MS). Use of drop foot stimulation can be tracedback almost 50 years (2), and although modern technology

has improved functionality and reliability, the basic prin-ciples of application have changed very little. Surface orimplanted electrodes are placed over the common pero-neal nerve or its branches, delivering pulses of electricity toproduce ankle dorsiflexion and eversion in order to lift thefoot through the swing phase of walking and place it in asafe position for weight bearing at first contact, stabilizingthe ankle. The stimulation is timed to the gait cycle, oftenusing a pressure sensitive foot switch placed inside the

Received: March 3, 2009; First revision: June 8, 2009; Accepted: July 15, 2009. Address correspondence and reprint requests to: PaulTaylor, PhD, MSc, BSc, CENG, National Clinical FES Centre, Laing Building, Salisbury NHS Foundation Trust, Odstock Lane,Salisbury, Wiltshire, SP2 8BJ, UK. Email: p.taylor@salisburyfes.comFor more information on author guidelines, an explanation of our peer review process, and conflict of interest informed consent policies,please go to http://www.wiley.com/bw/submit.asp?ref=1094-7159&site=1

doi: 10.1111/j.1525-1403.2009.00250.xNEUROMODULATION: TECHNOLOGY AT THE NEURAL INTERFACE

Volume 13 • Number 1 • 2010http://www.blackwell-synergy.com/loi/ner

© 2009 International Neuromodulation Society

shoe, although tilt sensors (3) and the electroneurogramfrom sensory nerves have also been used (4). Stimulationbegins when the heel lifts from the ground, continuinguntil weight is returned to the foot switch.

The first randomized controlled trial to confirm the effi-cacy of drop foot stimulation was reported using theOdstock Drop Foot Stimulator (ODFS) in 1997 (5). Thirty-two people with stroke received ten sessions of physio-therapy over one month while the treatment group (N =16) received additional common peroneal nerve stimula-tion for three months using the ODFS. The treatmentgroup demonstrated a significant increase in walking speedand a significant reduction in energy expenditure whenwalking with stimulation compared with walking withoutstimulation more than 10 m. Subsequent research trialsconfirmed these findings using a variety of similar footdrop stimulation devices and showed similar benefits tospeed of walking and reductions in energy expenditurewhen walking over both 10-m and longer distances (3,6–8).

A retrospective audit showed that the device was wellaccepted, with only 8% of a sample of 145 service userschoosing to discontinue use of the ODFS over a period oftwo years (9). This value is considerably lower than theaverage assistive device abandonment rate of 29.3%reported by Scherer (10). Suggestions for this low level ofrejection focused on QOL-related issues, such as reducedperceived effort of walking and increased confidence dueto reductions in trips and falls (5,9,11). These suggestionswere supported by Malone et al. (12), who conducted aseries of structured interviews with 12 ODFS users andreported that the ODFS had a positive effect on activities ofdaily living with increased opportunities for work, social,and leisure activities. More recently, Burridge et al. (8) andStein et al. (3) have confirmed that similar drop footdevices are well accepted by patients and have positiveeffects on QOL.

In our clinical experience, ODFS users frequently con-tinue to use a device in the absence of a measurableimprovement in walking speed and energy expenditure.The reported improvements in users’ QOL are frequentlyused to explain why this might be, and these theories aresupported by the assistive technology literature. This hasshown that the most important factors influencing deviceretention are QOL-related issues, for example device con-venience, comfort, cosmetic appearance, and effort of usecompared with the rewards gained (10,13–16). There are,however, currently no published studies using validatedoutcome measures which confirm the effects of the ODFSon psychological well-being and investigate how this relatesto objective changes in physical performance.

The Psychosocial Impact of Assistive Devices Scale(PIADS) is a 26-item, self-rating questionnaire, designed toevaluate the effect of assistive devices on perceived QOL(17). It was developed as a generic measure, applicable to

all forms of assistive technology and to all client groups. Itwas created because it was identified that existing genericmeasures of QOL tend to relate to disease progression andhealth status and do not reflect changing function andparticipation abilities as a result of using an assistive device(18).

The PIADS was used for one year between January 2005and January 2006 at the National Clinical FES Centre, Sal-isbury, UK to evaluate the effect of the ODFS on the QOLof people with stroke and MS. Additionally, PIADS scoreswere compared with objective measures of speed and effortof walking to investigate anecdotal reports that measurablechanges in walking performance bear little relation to theperceived effect of the ODFS on QOL.

MethodBetween January 2005 and January 2006, new patientsattending an FES clinic were fitted with single or dualchannel common peroneal nerve stimulation to correctunilateral or bilateral drop foot. Amplitude ranged from 20to 100 mA, with a pulse width between 3 and 365 msec andfrequency fixed at 40 Hz (19). Device set-up took place overtwo one-hour clinic sessions on consecutive days, andreviews were carried out six and 18 weeks later, in line withclinical protocol (20). Subjects were asked to use the ODFSas much as they felt able to during this time period.

When the device was set up and 18 weeks later, walkingspeed was recorded with and without stimulation over10 m. The total distance walked each time was 12 m, allow-ing 1 m at either end for acceleration and deceleration.Walking test protocol involved a warm-up 10-m walkwithout electrical stimulation (walk 1), followed by asecond walk without stimulation (walk 2), and finally a walkwith electrical stimulation (walk 3). Walks 2 and 3 wereused to produce the clinical data.

The clinic where the study was based has employed thismethod, instead of the better known technique of calculat-ing the means of three walks without stimulation and threewalks with stimulation collected in a random order, forapproximately two years. This change in practice was imple-mented after a retrospective audit suggested that the newprotocol is as statistically robust as the more widely usedmethod, with the added advantage of being less physicallydemanding for patients, consequently increasing thenumber of subjects able to complete the data collectionprocess. (21).

In addition to completing 10-m walking tests, 18 weeksafter being fitted with an ODFS, patients were asked tocomplete the PIADS questionnaire to assess the effects ofthe device on perceived QOL.

PIADS ScoresThe PIADS scores reflect the degree of perceived benefit toQOL gained as a result of using the ODFS. Scores range

EFFECTS OF THE ODSTOCK DROP FOOT STIMULATOR 59

from -3 (maximum negative effect) to +3 (maximum posi-tive effect), with 0 indicating no overall effect. The ques-tionnaire is divided into three distinct aspects of QOLproducing three separate averaged scores: Competence,Adaptability, and Self-esteem. “Competence” refers to theperceived impact of the assistive device on function, per-formance, and productivity. “Adaptability” refers to theenabling and liberating effects of the device, and “Self-esteem” reflects the Aid’s effect on issues such as self-confidence and well-being (17).

Statistical AnalysisAs the data generated by the PIADS questionnaires wasclearly not normally distributed, differences between thethree PIADS sections after 18 weeks of use were evaluated forboth conditions using Faurier’s analysis for non-parametricdata. Differences in PIADS scores between the two patientgroups were evaluated using Mann–Whitney U-tests for com-parison of non-parametric unmatched data. For walkingspeed, orthotic effects from use of FES (i.e. values recordedwith stimulation compared with values without stimulationon the same day), and training effects (changes in unassistedwalking speed between weeks 0 and 18), for both patientgroups were assessed using Wilcoxon tests for non-parametric matched pairs comparison. Walking test dataand PIADS scores were correlated using Spearman’s RankOrder Correlation Co-efficient to establish any associationbetween the effects of the ODFS on objective measures ofwalking performance and perceived QOL.

Results

Demographic DetailsThe PIADS scores were obtained for a total of 21 peoplewith stroke, 20 people with MS. The type of MS was notknown. Table 1 shows the demographic details for thethree groups. One stroke patient and three MS patientshad discontinued use of the stimulator by January 2007,between one and two years after stimulator set-up (8.7% ofthe total sample).

PIADS ScoresThe PIADS scores were compared for the stroke and MSgroups, and are illustrated in Figure 1. Both groups of sub-jects recorded positive QOL scores for each section of thePIADS questionnaire.

Median scores for each of the PIADS sections are com-pared in Table 2.

Median scores for each PIADS section were comparedbetween stroke and MS groups using the Mann–WhitneyU-test. The p values are illustrated in Table 2 and differ-ences significant at the 5% level are marked asterisk. Sig-nificant differences were detected between groups for theCompetence and Adaptability sections but not the Self-esteem section of the questionnaire.

Faurier’s Analyses (F-tests), assessing for any significantdifferences between the scores for Competence, Adaptabil-ity, and Self-esteem, were performed for both the strokeand MS group. The p values also are illustrated in Table 2.

0

0.5

1

1.5

2

2.5

3

PIA

DS

S

co

re

PIADS Scores

CVAMS

FIGURE 1. Psychosocial Impact of Assistive Devices Scale (PIADS)scores for Odstock Dropped Foot Stimulator (ODFS) users at 18weeks. The bar is the 50 percentile, the box indicates 25–75 percen-tiles, the whisker 5–95 percentiles and the crosses the extremes of thedata.

TABLE 1. Demographic details

Age(years)

Time sincediagnosis (years) Male Female

Unilateraldropped foot

Bilateraldropped foot

Number dischargedby Jan 07

Stroke (N = 21)Mean 62 4.2 15 6 21 0 1SD 13 3.87Range 33–81 1–16

Multiple sclerosis (N = 20)Mean 56 10.7 8 12 16 4 3SD 6.9 7.73Range 41–70 2–30

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No significant differences between PIADS scores for thethree QOL domains were detected for either group.

Walking TestsWalking speed and PCI values for the stroke and MS groupsrecorded at week 18 on the same day as the PIADS ques-tionnaire was administered, are shown in Table 3. Signifi-cant orthotic benefits, detected using the Wilcoxon Test,are marked asterisk.

Stroke GroupSignificant increases in 10-m walking speed with FES com-pared with without were recorded at weeks 0 and 18(orthotic benefits). A significant increase in walking speedwithout stimulation at week 18 compared with week 0 alsowas measured for the stroke group (training effect).

MS GroupA significant increase in walking speed was measured withFES compared with without at week 18 for the MS group(orthotic benefit). No significant orthotic benefits weremeasured at week 0 for this group. No training effect wasmeasured for walking speed when measurements takenwithout stimulation at week 18 were compared with thosetaken at week 0.

Relationship Between Walking Test Values andPIADS ScoresScores for each section of the PIADS questionnaire (Com-petence, Adaptability, and Self-esteem) were correlated to

the percentage changes in 10-m walking speed betweenweeks 0 and 18 without stimulation (training effects), thepercentage change in FES-assisted walking compared withunassisted walking at week 18 (orthotic effect) and percent-age change in FES-assisted walking at week 18 comparedwith unassisted walking at week 0 (Total orthotic effect)using Spearman’s Rank Order correlation co-efficient(Table 4) (19). No correlation was found between anysection of the PIADS questionnaire and percentage changein walking speed at any stage.

Discussion

Effects of the ODFS on Perceived QOLAnalysis of PIADS scores after 18 weeks of using the ODFSshowed positive effects on QOL for all three sections of thequestionnaire, suggesting that drop foot stimulation has apositive effect on Competence, Adaptability, and Self-esteem-related aspects of psychological well-being, mea-sured using the PIADS questionnaire. This confirms ODFSuser reports from past clinical audits (9,11), and is the firsttime that the ODFS has been shown to improve QOL usinga validated outcome measure.

Faurier’s analysis detected no significant differencebetween Competence, Adaptability, and Self-esteem scoresfor the stroke or MS group. This suggests that for thesepatient groups, there is no significantly greater effect fromuse of the ODFS on any particular aspect of QOL as definedby the PIADS questionnaire. However, Mann–Whitney

TABLE 2. Median PIADS scores for CVA and MS groups

Patient group

Median PIADS scores

Competence Adaptability Self-esteem

Stroke (N = 21) (range) 1.25 (0.17–2.92) 1.25 (0.00–3.00) 0.88 (0.13–2.75) p = 0.42 F-testMS (N = 20) (range) 0.915 (0.16–1.9) 0.5 (0.16–3.00) 0.75 (0.00–2.75) p = 0.31 F-test

p = 0.04* (Mann–Whitney U-test) p = 0.006* (Mann–Whitney U-test) p = 0.30 (Mann–Whitney U-test)

Values marked *significant at the 5% level.MS, multiple sclerosis; PIADS, Psychosocial Impact of Assistive Devices Scale.

TABLE 3. Median values, 10-m walking speed

Walking speed (m/s)

Stroke MS

Without FES With FES p (Wilcoxon test) Without FES With FES p (Wilcoxon test)

Week 0 Range 0.59 (0.11–1.06) 0.65 (0.11–1.09) 0.005* 0.78 (0.10–1.11) 0.79 (0.11–1.12) 0.07Week 18 0.60 (0.17–1.13) 0.66 (0.1–1.19) 0.005* 0.79 (0.09–1.35) 0.81 (0.11–1.39) 0.01*p (Wilcoxon test) 0.03* 0.55

Changes marked *significant at the 5% level.MS, multiple sclerosis.

EFFECTS OF THE ODSTOCK DROP FOOT STIMULATOR 61

U-tests used to compare stroke and MS scores for eachsection of the questionnaire revealed that scores were sig-nificantly lower for people with MS than for people withstroke for Competence and Adaptability but not for Self-esteem. Consequently, for Competence and Adaptability-related aspects of QOL, people with stroke may perceivethe benefits of the ODFS to be significantly higher thanpeople diagnosed with MS.

This may be related to the differences in prognosisbetween the two conditions. In a previous study (22), whena group of subjects with neurologic disability were asked torate the impact of their wheelchairs on QOL using PIADS,those with a static condition such as a spinal injury reporteda significantly greater positive benefit than those with adegenerative condition such as Motor Neurone Disease.The authors suggested that this may be because those withdegenerative conditions considered the wheelchairs to becompensating for their deterioration in mobility whilethose with the static conditions felt that it was enhancingtheir participation abilities. In a similar way, people withMS may perceive the ODFS as less beneficial to QOL thanthose with stroke because they see it as a tool for slowing thedeterioration in their mobility rather than enhancingrecovery.

Effects of the ODFS on Objective Measuresof Walking

10-m Walking SpeedBoth groups experienced improvements in their walkingperformance after 18 weeks of use, demonstrating signifi-cantly faster walking speeds with stimulation comparedwith without stimulation more than 10 m (beneficialorthotic effects). Additionally, the stroke group demon-strated an orthotic benefit from stimulation at week 0 anda significant training effect, walking faster at week 18without stimulation compared with without stimulation atweek 0. These findings reflect past randomized controlledtrials and clinical audit findings for use of the ODFS andsimilar drop foot devices in both stroke and MS rehabilita-

tion, where both stroke and MS groups have shown anorthotic benefit through use of stimulation but only strokegroups have shown an additional training effect (3,5–8,19,23,24).

Relationship of Objective Measures of Walkingto QOLThe orthotic and training effects of stimulation were cor-related to PIADS scores in order to examine any relation-ship between improvements in walking speed and QOL. Nocorrelation was detected for any section of the PIADS ques-tionnaire for either patient group, which indicates thatalthough the ODFS has positive effects on both objectivemeasures of walking more than 10 m and QOL, these ben-efits do not relate to each other. This may explain whyclinically, some ODFS users continue to use a device whenobjective measures of walking show no benefit, and alsowhy some ODFS users will choose to discontinue usedespite measurable improvements in gait. Therefore thesubjective benefits of the device reflected by the PIADSscores, such as increasing confidence during walking,reducing falls, and increasing social participation, may beof more importance to ODFS users than more routinelyused objective measures. This may account for the lowdrop-out rate of 8.7% after a maximum of two years ofODFS use. This value is much smaller than the averageassistive device abandonment rate of 29.3% reported byScherer (10), and is very similar to previously reportedvalues of 8% reported by Taylor et al. in 2004 (9).

Alternatively, it may be that a different aspect of objectiveoutcome measurement related more directly to factorssuch as increased confidence and reduced risk of fallswould show a closer correlation to QOL. Recently, Haus-dorff et al. (7) reported significant improvements in gaitsymmetry and reductions in stride time variability over aneight-week period in 24 patients with chronic hemiparesisas a result of using a drop foot stimulation device. It may bethat these aspects of gait are more directly linked to gaitstability and therefore would correlate more highly withQOL measurements than walking speed did in this study.

TABLE 4. Spearman’s rank order correlation co-efficient (r) values; changes in walking speed vs. PIADS scores

Stroke Multiple sclerosis

Training effect Orthotic effect Total orthotic effect Training effect Orthotic effect Total orthotic effectr (p) r (p) r (p) r (p) r (p) r (p)

Competence 0.45 (0.03) -0.06 (0.42) -0.15 (0.27) -0.17 (0.25) -0.18 (0.025) -0.32 (0.10)Adaptability 0.11 (0.32) 0.32 (0.11) -0.08 (0.45) 0.25 (0.17) 0.2 (0.22) 0.23 (0.19)Self-esteem 0.04 (0.44) -0.08 (0.38) -0.38 (0.06) 0.23 (0.19) 0.01 (0.48) 0.22 (0.20)

Training effect: unassisted walking at week 0 compared with unassisted walking at week 18; Orthotic effect: FES assisted walking compared withunassisted walking at week 18; Total orthotic effect: FES assisted walking at week 18 compared with unassisted walking at week 0.PIADS, Psychosocial Impact of Assistive Devices Scale.

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Limitations to the Study

Clinical AuditData collected for this report were generated using clinicalaudit procedures rather than controlled research condi-tions. Consequently, PIADS questionnaires were adminis-tered by clinical staff that also provided patients with FEStreatment. It is therefore possible that patients felt com-pelled to answer questions more positively than if the ques-tionnaire had been administered by an independentresearcher. However, the given PIADS script was alwaysfollowed to minimize bias in the way questions were asked.It could also be argued that subjects were less likely to givebiased answers under real clinical conditions than undercontrolled research conditions where trial participants vol-unteer because they want to help confirm the positiveeffects of the device.

Objective Data CollectionA further limitation to the study may be the method of datacollection for the 10-m walking tests. Clinical protocol forrecording 10-m walking speed was altered at the centerwhere the study was conducted in response to an audit thatrevealed no statistical advantage in performing the morewidespread technique of calculating mean values fromthree walks without stimulation and three walks with stimu-lation in a randomized order (22). Instead, a warm-up walkis performed first to allow for acclimatization (first), fol-lowed by a walk without stimulation (second), followed by awalk with stimulation (third).

Advantage is that the number of walks the patient isrequired to perform is reduced, which increases the likeli-hood of obtaining complete data sets because the proce-dure is less physically demanding. However, this alterationin data collection technique has not been confirmed byfollow-up studies and conclusions drawn from objective10-m walk data collected in this way must therefore betreated with caution until the reliability of the technique isconfirmed.

ConclusionThis is the first study to demonstrate that FES used tocorrect dropped foot has a beneficial effect on perceivedQOL measured using a validated outcome measure. Posi-tive benefits to perceived QOL, measured using the PIADSquestionnaire, as well as small but significant improvementsin walking speed, were observed for both the stroke and MSgroups after 18 weeks of using the ODFS. This confirmsanecdotal reports that the effects of the ODFS extendbeyond routinely measured objective changes in walkingperformance.

These subjective and objective outcome measurementsappear to have no relationship to each other, suggestingthat measurements of 10-m walking speed on their own do

not form a comprehensive picture of the benefits thatpeople with neurologic disability gain from using theODFS. Both subjective and objective outcome measure-ments should therefore be used when measuring the effectsof the ODFS on people with neurologic disorders.

Conflict of InterestIn April 2006 the clinical and commercial activities ofDepartment of Medical Physics and Biomedical Engineer-ing were “spun off” from Salisbury NHS Foundation Trustto form a company Odstock Medical Limited (OML). OMLis the manufacture of the ODFS device used in this project.The majority share holding in the company remains withSalisbury NHS Foundation Trust. Members of the FESgroup at Salisbury District Hospital, including the authorsof this manuscript have been allocated “token shares” thatmay in the future have monetary value. A proportion of thesecond author’s time is seconded to Odstock MedicalLimited to provide clinical FES treatment and generalsupport. However, he remains an employee of SalisburyNHS Foundation Trust, which receives remuneration forthe seconded time.

Paul Taylor has two patents in his name relating to theODFS. These are assigned to his employer Salisbury NHSFoundation Trust, which in turn licenses the intellectualproperty to Odstock Medical Limited.

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CommentsSince 1961, when Liberson et al. first showed therapeuticeffects of applying surface electrodes over the commonperoneal nerve to correct drop foot following stroke, therehave been considerable advancements in technology pro-viding better control and reliability. However, a series ofreports from 1973 by the Odstock Center have indicatedpositive improvements in gait by using their 2-channel FESstimulator with surface electrodes (ODFS) for correctingdrop foot in patients following stroke and multiple sclerosis(MS), but they have had very little correlation in theirpatients’ quality of life (QOL). Using the PsychosocialImpact of Assistive Devices Scale (PIADS) questionnaire,this Center has now shown that FES for correction of thedropped foot has a beneficial effect on perceived QOL forpeople with stroke and MS but this has not correlated withobjective measures of gait. This important report now hasconfirmed anecdotal reports that the effects of their ODFSextend beyond routinely measured objective changes inwalking performance.

Ross Davis, MDNeurophysiologist and Neurosurgeon

Neural Engineering ClinicMelbourne Beach, Florida, USA

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