Effect of Neuromuscular ElectricalStimulation on Ankle Swelling in theEarly Period After Ankle SprainIvy OW Man, Matthew C Morrissey, Jozef K Cywinski
Background and PurposeNeuromuscular electrical stimulation (NMES) is frequently used to decrease swellingin the early period after ankle sprain. The purpose of this study was to evaluate itseffectiveness in this treatment.
SubjectsThirty-four subjects (11 female, 23 male; mean age�30.2 years) who were recoveringfrom ankle sprain participated.
MethodsOutcome measures were ankle-foot volume, ankle girth, and self-assessed anklefunction. Three testing/training sessions occurred within 5 days of injury. Subjectswere randomly assigned to 1 of 3 groups: a group that received NMES treatment, agroup that received submotor ES treatment (designed to act as a control group), anda group that received sham treatment.
ResultsThere were no statistically significant differences among the groups for ankle-footvolume and self-assessed ankle function. The statistically significant differences forankle girth may have been compromised due to the significantly different valuesamong groups at baseline. Ankle girth measurements were shown to be statisticallysignificant from session 1 to session 3 for the NMES group but not for the other 2groups.
Discussion and ConclusionThe results indicate that NMES, as designed and used in this study, is not effective indecreasing ankle-foot volume or increasing self-assessed ankle function in the earlyperiod after ankle sprain.
IOW Man, MCSP, PhD, is Lecturerin Physiotherapy, School of HealthSciences and Social Care, BrunelUniversity, Uxbridge, Middlesex,United Kingdom.
MC Morrissey, ScD, is Senior Lec-turer, Division of Applied Bio-medical Research, King’s CollegeLondon, London, United King-dom. Address all correspondenceto Dr Morrissey at: [email protected].
JK Cywinski, ScD, FACC, is affili-ated with the Institute of MedicalTechnology, Orsieres, Switzerland.
[Man IOW, Morrissey MC,Cywinski JK. Effect of neuromus-cular electrical stimulation onankle swelling in the early periodafter anklesprain. Phys Ther.2007;87:53–65.]
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Sprains occur most commonly inthe ankle, with more than25,000 ankle sprains occur-
ring each day in the United States.1
Soft tissue injuries commonly elicitthe physiological inflammatory re-sponses of redness, swelling, heat,and pain, and acute ankle sprain inju-ries are no exception.2,3 Edema for-mation is a significant hindrance tothe healing process4 and can causepain and reduced mobility.5 Nilssonand Haugen3 stated that swelling andpain are responsible for the func-tional disability that follows anklesprains.
Similar to the knee joint, where effu-sion appears to cause inhibition ofthe quadriceps femoris muscle group,decreased H-reflex excitability ofmuscles around the ankle joint hasbeen reported in the presence ofankle effusion.6 However, for thesake of completeness, not all mus-cles tested in that study showed this“decreased” excitability. Norwig7
stated that the recovery rate forankle function after a sprain injurymay be related to the control ofedema at the injury site, but no datawere provided to support this state-ment. Nonetheless, it is generallyaccepted among clinicians that theappropriate method of care follow-ing ankle sprain is functional man-agement of the injury (ie, restoringthe patient back to his or her prein-jury functional status). Voight stated,“the swelling that is secondary to theinflammation is the greatest enemyof healing. Therefore, the goal ofearly treatment should be to delay orminimise swelling.”8(p278)
Various treatment protocols are usedto control swelling in the postacutephase of ankle sprains.9 The rest, ice,compression, and elevation (RICE)regimen is probably the standardtreatment protocol used, but physi-cal therapists also use additionaladjuncts in order to minimize swell-ing. Electrical stimulation (ES), with
or without muscle contraction, isone such example.10 It is thoughtthat neuromuscular electrical stimu-lation (NMES) causes muscle con-tractions, which can compressvenous and lymphatic vessels.11 Thismechanical effect may assist in theresolution of posttraumatic andchronic edema.11 Repetitive contrac-tions may induce an increase invenous return12 and lymphaticflow,13 which may reduce edema.Thus, motor ES may affect the lymphdrainage or the interstitial hydro-static pressure components of fluidexchange, which can affect edemaformation and resolution.
Only a few studies have investigatedthe direct effect of motor ES onedema reduction in humans byassessing edema change as an out-come measure.14–17 One of the earli-est investigations advocating the useof motor ES in reducing joint swell-ing was by Crisler,14 who used an“Ultrafaradic Impulse Generator”device to “stimulate nerves and mus-cles by means of controlled electricshocks” in the treatment of patientswith acute strains and sprains. In 6of the 18 subjects, treated edemawas “grossly in evidence,” and areduction in swelling following a sin-gle treatment of ES of 5 minutesduration or less was reported. How-ever, no description was given as tohow the amount of swelling reduc-tion was measured.
Gould and associates15 reported astatistically significant difference inknee edema 4 weeks after openmeniscectomy between patientswho received voluntary isometricexercise training and patients whoreceived NMES treatment. Theauthors reported that, followingtreatment, 70% of the subjects in theES group had no swelling and that30% of those subjects had minimalswelling, as measured by circumfer-ence at the tibiofemoral joint space.All of the subjects in the voluntary
exercise group showed “visible ormoderate swelling” 4 weeks afterthe surgery.
Numerous studies have investigatedhow motor ES, by eliciting the mus-cle pump, may affect blood andlymph flow—the 2 main effectsthought to reduce edema. Studiesshowing positive effects of motor ESin increasing blood flow have beendone on both human18–20 and ani-mal21,22 models. The muscle pumpcan be elicited voluntarily or elec-trically and can lead to a reductionof edema by moving the fluid fromthe interstitial compartment to theblood vascular system. Faghri et al23
also suggested that electrically stim-ulated contractions activate the skele-tal muscle pump, thereby promotinglimb blood flow, and may be effec-tive in reducing venous pooling andedema. Lymph flow has been shownto increase during muscular exer-cise.24 The extrinsic forces caused bythe contracting muscles may increasethe lymph propulsion. In light of this,one of our previous investigationsdemonstrated that the increase in footand ankle volume that occurs withprolonged standing can be limitedwith the application of NMES to thelower leg muscles.25
The main aim of this study was totest the effects of motor-level bipha-sic ES applied to the gastrocnemiusand tibialis anterior muscles on ankleswelling in patients within 5 daysof an ankle sprain injury. The mainhypothesis was that 3 sessions ofNMES applied to the lower leg mus-cles would significantly reduce ankleswelling compared with no NMES.
MethodSubjectsThirty-four subjects within the agerange of 18 to 60 years with acuteankle sprain injury (occurring within5 days of the first scheduled test)were recruited within 12 monthsfrom the Minor Injuries Unit, Guy’s
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Hospital, London. Subjects who hada clinical diagnosis of a sprainedankle recorded in their medicalnotes were invited to participate inthe study. The severity of the ankleinjury was not documented in themedical notes in the form of anygrading or classification system. Sub-jects with diabetes, peripheral vascu-lar disease or any neurovascular def-icits or metal implants in the lowerleg, injury to the contralateral anklethat required surgical attention inthe previous year, or open woundsand subjects who were taking diuret-ics or wore pacemakers wereexcluded from the study. All subjectsgave written informed consent priorto testing.
Experimental ProtocolSubjects were assigned to 1 of 3treatment groups using concealedrandomization: (1) a group withNMES applied to the lower leg mus-cles, (2) a group with submotor ESapplied to the lower leg muscles, or(3) a group with electrodes set up onthe lower leg muscles with no ESapplied (sham ES group). Originally,the study had only groups 1 and 2 inorder to assess the effects of musclecontractions caused by NMES onreducing swelling. Therefore, theintention was to test a group thatreceived ES that caused muscle con-tractions (NMES) and compare theresults with a group of subjects whoreceived ES that did not cause visiblemuscle contractions (submotor ES).This latter group, therefore, wouldact as a placebo group with the sub-motor ES applied in a fashion thatwould not trigger electrophoresis,the theoretical basis for treatingswelling with submotor ES.26 How-ever, because it was not knownwhether the submotor ES couldaffect ankle volume, group 3 wasadded where no ES was applied butsubjects were prepared and mea-sured in the same way as the other 2groups (sham treatment).
Before arriving at the testing labo-ratory, subjects were randomly as-signed, in groups of 3, to 1 of the 3groups, using a die protocol. Uponarrival at the testing laboratory, themedical history and history of thepresent complaint were documentedfor all subjects. From this information,patient eligibility for participation inthe study was determined. Subjectsthen completed an adapted HughstonClinic Subjective Rating Scale for AnkleDisorders. We modified the adaptedHughston Clinic Subjective Rating Scalefor Ankle Disorders from a similarquestionnaire used for knee disor-ders.27 Its validity and reliability inpatients with ankle injuries havenot been tested.
Height and body mass were mea-sured, and then, with the subjectspositioned supine, ankle girth wasassessed with the figure-of-eight tapemeasurement technique.28,29 Blindedbilateral girth measurements weretaken before treatment at all 3 testsessions to allow for a comparison ingirth between both sides, to assesswhether swelling was present in theinjured leg before treatment com-
menced, and to allow clinicians whodo not have access to volumetry toevaluate the results relative to theirpatients.
Before the electrodes were appliedto each subject’s leg, 2 volumetricmeasurements were taken for bothankles. To be able to test all subjectson consecutive days, 2 differentassessors were involved in assessingankle-foot volume. Although not allsubjects were assessed by the sameresearcher, the same researcherassessed volume for each subject ineach of the 3 test sessions. Reliabilitytesting of the volumetric measure-ments was performed for the 2testers on 20 uninjured ankles thatwere tested on 2 separate days. The2 volume assessors were blinded tothe group allocation of the subjects.Ankle-foot volume was assessed witheach subject in the sitting position(Fig. 1).
The volumeter was filled with tepidwater (temperature ranged from 20°to 35°C), and the excess water thatflowed out of the overflow spoutwas collected in a jug. Once the
Figure 1.Subject positioning during volumetric testing.
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excess water had flowed to less thanone drip a second, the water wasdiscarded from the collecting jug,the spout was dried, and a dry,empty jug was placed underneaththe overflow spout. The subject satwith one leg on either side of thevolumeter and then was asked togently place the leg that was beingtested into the volumeter until theplantar aspect of the foot was flat onthe bottom of the volumeter and thelower leg was as far back into thevolumeter as possible, without actu-ally touching the back of the volume-ter. The ankle was in a neutral posi-tion, and the knee joint was atapproximately 90 degrees of flexion.
As the leg was placed into the volu-meter, the displaced water was col-lected in the jug below the overflowspout. The subject was asked toremain still until the excess waterhad flowed to a rate of less than onedrop of water a second. Once all thedisplaced water had been collected,the jug was carefully removed andweighed. This measurement was
converted from grams to millilitersusing the conversion 1 g�1 mL.30
The subject then was allowed toremove the leg from the volumeter.The same jug was used in each trialto collect the displaced water andwas dried before and after each trial.The leg also was dried before eachtrial. This procedure was repeated,and the arithmetic mean was calcu-lated to represent the ankle-footvolume.
Upon completion of the volumetricmeasurements, the leg was dried and4 electrodes were secured to eachsubject’s skin over the tibialis ante-rior muscle and the gastrocnemiusmuscle heads of the injured leg forsimultaneous ES over these muscles.The subject was positioned supine,and the injured leg was elevatedabove heart level and supportedover a stool. The leg was secured tothe stool with a strap placed at thelevel of the ankle. In an attempt tominimize ankle joint movement, thesubject was asked to place the footup against a stable cabinet. The sub-
ject also was secured to the plinthwith a strap around the level of thepelvis.
Four 10-cm-diameter Carbonflexdisk electrodes* were applied to thelower leg muscles of the injured legof all subjects. They were made ofconductive carbonized rubber andsecured with a standard crepe ban-dage to the subject’s lower leg witha water-soaked sponge separatingthe skin and the electrodes. Two elec-trodes were placed over the musclebelly of the gastrocnemius muscle,and 2 electrodes were placed over thetibialis anterior muscle of the injuredlimb. The sensations that would likelybe felt were explained to the subjectswho were allocated to receive eitherNMES or submotor ES.
For ES, the HEALTHFIT dual-channelP4-Microstim stimulator† was used.The 2 electrodes on each musclewere connected to a separate chan-nel of the stimulator. The ES wascharacterized by a low-voltage, rect-angular waveform having modulatedpatterns of frequency and pulseduration (Fig. 2). The 30-minute ESpattern used for the subjects in theNMES and submotor ES groups had atotal of 360 cycles, with each cyclelasting 5 seconds. Each cycle con-sisted of 400 pulses having differentcombinations of pulse-to-pulse inter-vals and duration values. The calcu-lated average frequency of ES was80 Hz, but the actual ES was deliv-ered in packets (bursts) causingshort-lasting muscle contractionsevery 1.25 seconds (0.8 Hz) for thesubjects in the NMES group. Duringeach burst, the pulse duration variedfrom 60 to 240 microseconds, andthe pulse-to-pulse interval was 8 milli-seconds (125 Hz).
* Bloomex International Inc, 295 Molnar Dr,Elmwood Park, NJ 07407.† Valmed SA, Sion, Switzerland.
Figure 2.Diagram of the electrical stimulation pattern used.
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Over this burst pattern, there wassuperimposed another pattern of ES.This pattern had a repeat cycle of 5seconds and a frequency of pulsesvarying from 45 to 120 Hz, withsimultaneous variation of pulse dura-tion from 60 to 140 microseconds.The last phase of the cycle startedabout 77 seconds after the unit wasswitched on. The frequency rangedfrom 2.68 to 83.33 Hz, with a pulseduration ranging from 40 to 180microseconds. This unit was batteryoperated and was tested on theresearcher before each applicationto ensure that the batteries were inworking order.
For subjects in the NMES group, theintensity of ES was increased to thesubjects’ maximum level of toler-ance and was adjusted as necessarythroughout the 30-minute test period.For subjects in the submotor ES group,the unit was switched on and theintensity was increased until a flickerof muscle contraction was seen in thestimulated muscles. At this stage, theintensity was reduced very slightlyuntil the flicker of contraction disap-peared. Subjects should still have hadsome cutaneous sensation of the elec-trical current occurring under andaround the electrode pads. At the endof 30 minutes of ES, the maximumstimulation level reached for eachmuscle was recorded. Subjects in thesham ES group were positioned in thesame manner as subjects in the other 2groups with the electrodes attached,but no ES was applied. The unit wasswitched on until the subjects heardthe initial alarm, and then the exam-iner switched off the unit. The sub-jects had been advised that theyshould not feel any sensation duringthe next 30 minutes. After 30 minutesof being in this position the subjects’bilateral foot and ankle volume wasremeasured.
Two volumetric measurements ofthe injured ankle were taken firstfollowed by 2 measurements of the
uninjured ankle. The subjects thenwere rescheduled to attend the sec-ond and third sessions as soon aspossible, usually on consecutivedays. When subjects attended fortheir subsequent tests, they wereasked several questions regardingwhether they had taken any moreanalgesics or anti-inflammatories andwhether any other treatments (eg,physical therapy, ice) had beenapplied to the ankle since the previ-ous session. When subjects attendedfor their last session, they also wereasked to complete the adaptedHughston Clinic Subjective RatingScale for Ankle Disorders after theposttest ankle volume measure-ments were taken. The distancesfrom the left-hand anchors in theadapted Hughston Clinic SubjectiveRating Scale for Ankle Disorderswere measured by the volume asses-sors who were blinded to the treat-ment groups of the patients. Threefurther questions were asked tomonitor their ankle injury on thesubsequent test days: how they felttheir ankle condition had changedsince the previous session (ie,improved, worsened, no different),how great they felt any change was(using a visual analog scale), andwhether they had done any differentactivities since the last session. Thedata collected for these 3 questionswere not used in this study.
Data AnalysisThe data collected were subject age,height, body mass, bilateral anklevolume before and after interventionfor all 3 test sessions, figure-of-eightgirth measurements, and adaptedHughston Clinic Subjective RatingScale for Ankle Disorders scores.
Prior to comparing outcomes in thegroups, an analysis was performedto evaluate whether the groupswere similar with respect to factorsthat might affect outcome otherthan the study treatment given. Thecomparability of the subjects in the 3
groups at baseline was assessed byanalyzing the age, height, and bodymass data (all normally distributed)using a one-way analysis of vari-ance (ANOVA) test. To ensure thatthe subjects were not significantlymore swollen or perceived them-selves to be more limited in onegroup compared with another, theinjured ankle volume, swelling vol-ume (injured-uninjured ankle vol-ume), injured ankle girth measure-ments, ankle girth differences (injured-uninjured ankle girth), and adaptedHughston Clinic Subjective RatingScale for Ankle Disorders scores as re-corded on the first test session beforeintervention were analyzed for all sub-jects in the 3 groups. Tests of nor-mality indicated that the ankle vol-umes, ankle girth measurements, andadapted Hughston Clinic SubjectiveRating Scale for Ankle Disordersscores were normally distributed, socomparability among the 3 groupsat baseline was assessed with anANOVA test.
In addition to comparing the groupsfor their baseline status, they alsowere evaluated for other treatments(eg, analgesic or anti-inflammatorymedication, other physical therapytreatment, ice) that occurred duringthe period between the first and lasttests. The percentage of subjectswho were taking analgesic medica-tion and the percentage of subjectswho sought other treatment duringthe study were calculated and areshown in Table 1.
Test-retest reliability was analyzedfor the 2 volume assessors on a totalof 20 uninjured ankle volumes.Least significant difference (LSD) testand intraclass correlation coefficient(ICC[3,k]) values were calculated.The LSD value represents the levelbelow which the observed value willbe attributable to measurementerror.
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The outcome measures used in thisstudy were the pretreatment andposttreatment changes for: (1) meaninjured ankle volume, (2) meanswelling volume, (3) mean injuredankle girth, and (4) mean ankle girthdifference measured at each test ses-sion and adapted Hughston ClinicSubjective Rating Scale for Ankle Dis-orders scores obtained during thefirst and third test sessions.
Kolmogorov-Smirnov tests of nor-mality indicated that the volume,girth, and questionnaire data werenormally distributed. However, dueto the small sample size and theshape of the histograms (asymmetri-cal and skewed), the nonparametricKruskall-Wallis test for k indepen-dent samples was used to test forstatistically significant differencesamong the 3 groups for all of thesevariables.
To analyze differences among the 3test sessions (over time) for each ofthe 3 groups, the nonparametricFriedman test for k related samplesfor the volume and girth data wasused. Because the adapted HughstonClinic Subjective Rating Scale forAnkle Disorders was completed onlyduring the first and third sessions,the nonparametric Wilcoxon testwas used to assess for differencesbetween the first- and third-session
(over time) questionnaire scores foreach group.
Data analyses were performed usingSPSS for Windows 10.1‡ and Excel§
packages. Unless otherwise stated, acriterion level of P �.05 was usedfor all analyses.
ResultsThe subject characteristics of the 3groups at baseline are shown inTable 2. Height and injured and un-injured ankle girth measurementswere statistically different at base-line. The Tukey Honestly SignificantDifference post hoc analysis showedthe difference to be between thesham ES and submotor ES groups.The characteristics of each group forthe other possible confounding vari-ables are displayed in Table 1.
Descriptive data for the adaptedHughston Clinic Subjective RatingScale for Ankle Disorders are shownin Table 3. Kruskall-Wallis analysesshowed no statistically significantdifferences among groups for thechange in adapted Hughston ClinicSubjective Rating Scale for Ankle Dis-orders scores between the first andthird test sessions (P�.05). A Wil-
coxon signed ranks test showed astatistically significant differencebetween the first and third sessionscores for the adapted HughstonClinic Subjective Rating Scale forAnkle Disorders within the 3 groups(P �.05).
The descriptive data for meaninjured ankle volume are shown inTable 4 and displayed in Figure 3.Kruskall-Wallis analysis of the meaninjured ankle volume changes ineach test session showed no signifi-cant differences among the 3groups. Analyses for comparisons ofmean injured ankle volume changebetween test sessions (over time)performed with the Friedman testshowed no significant differencesfrom one test session to the nextfor all 3 groups (NMES group:�2�1.273, P�.529; submotor ESgroup: �2�1.636, P�.441; sham ESgroup: �2�3.167, P�.205). No sta-tistically significant differences werefound in any of the 3 groups whenthe pretest injured ankle volume atsession 1 and the posttest injuredankle volume at session 3 were com-pared (P�.017, Bonferroni adjustedlevel).
Table 5 summarizes the means(�SD) of the swelling volumes foreach group at each test session.Kruskall-Wallis analysis of the mean
‡ SPSS Inc, 233 S Wacker Dr, Chicago, IL60606.§ Microsoft Corp, One Microsoft Way, Red-mond, WA 98052-6399.
Table 1.Comparisons of Possible Confounding Factors Among the 3 Groupsa
NMES Group(n�11)
Submotor ESGroup (n�11)
Sham ES Group(n�12)
Mean period between injury and test 1 (d) 3.3 3.5 3.5
Mean period between test 1 and test 3 (d) 3.4 2.9 2.5
No. of subjects with prior history of ankle injury 5 (45%) 4 (36%) 7 (58%)
No. of subjects taking analgesics or NSAIDmedication during study
8 (72%) 8 (72%) 7 (58%)
No. of subjects receiving additional treatmentduring study (ie, ice, formal physical therapyb)
3 (27%) 8 (72%) 6 (50%)
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation, NSAID�nonsteroidal anti-inflammatory drug.b Formal physical therapy treatment that was reported included soft tissue mobilization techniques and ultrasound. No compression therapy modalities werereported.
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changes in swelling volume in eachtest session showed no significantdifferences among the 3 groups. AFriedman test analysis of the changein swelling volume changes showedno statistical significance from onetest session to the next (over time)for each group (NMES group:�2�2.364, P�.307; submotor ESgroup: �2�1.636, P�.441; sham ESgroup: �2�0.167, P�.920).
The results for the injured anklegirth measurements are shown inTable 6. Kruskal-Wallis analysisshowed a statistically significant dif-ference among the 3 groups for theinjured ankle girth measurementstaken at test sessions 1 and 2. Overthe 3 test sessions, a Friedman testanalysis showed a significant differ-ence for the NMES injured anklegirth measurements (�2�14.558,P�.001). No statistically significantdifferences were found for theinjured ankle girth data over time inthe submotor ES group or the shamES group.
The mean girth differences areshown in Table 7. Kruskal-Wallisanalysis showed no statistically sig-nificant differences among the 3groups for the girth differences mea-sured at the 3 test sessions. The girthdifferences were significantly differ-ent between sessions for the NMESgroup (P�.040). There were no sta-tistically significant differences over
time for the girth differences in thesubmotor ES group or the sham ESgroup (P�.05).
The ratings of the 2 volume assessorshad very high reliability, with an ICC(3,k) of .999 each and an LSD testvalue ranging from 12 to 15 mL. Thisfinding indicates that any volumechanges of less than 15 mL can be
Table 2.Subject Characteristics at Baseline (Mean�SD) With Test for Statistically Significant Differences Among Groupsa
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation.b Significant difference P�.05.c Range of possible scores for the adapted Hughston Clinic Subjective Rating Scale for Ankle Disorders score is 0 to 100, with 0 representing a score for afully functioning ankle.
Table 3.Mean (�SD) Scores for the Adapted Hughston Clinic Subjective Rating Scale forAnkle Disordersa (95% Confidence Intervals Are Shown in Italics)b
NMES Group(n�11)
Submotor ESGroup(n�11)
Sham ESGroup(n�12)
Score for session 1 65 (13)(56 to 74)
70 (10)(63 to 77)
63 (12)(55 to 71)
Score for session 3 42 (20)(29 to 55)
45 (17)(34 to 56)
46 (16)(36 to 56)
Change in scores fromsession 1 to session 3
23 (14)c
(14 to 32)25 (21)c
(11 to 39)17 (15)c
(7 to 27)
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation. Range of possible scores forthe adapted Hughston Clinic Subjective Rating Scale for Ankle Disorders is 0 to 100, with 0representing a score for a fully functioning ankle.b Confidence intervals are approximate due to the asymmetrical shape of the histograms.c Significant difference P �.05.
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attributed to measurement errorrather than a real change resultingfrom the intervention. An ICC(3,k)of .99 has been reported for thefigure-of-eight tape measurementtechnique with an LSD value withinthe range of 0.53 and 0.73 cm.31 TheLSD test value of the assessors was0.57 cm, which agrees with the find-ings of other researchers.
DiscussionAlthough a significant difference inadapted Hughston Clinic SubjectiveRating Scale for Ankle Disordersscores was found in the final sessioncompared with the first session in all3 groups, no significant difference
was found among the 3 groups. Thisfinding suggests that the NMESgroup did not provide any advantageover the control groups in returningthe subjects to their self-assessedpreinjury functional status.
Statistical differences were found forinjured ankle girth among the 3groups at sessions 1 and 2 and forthe injured ankle girth and girth dif-ferences in the NMES group over the3 sessions; however, these findingsmay not be meaningful becausethere was a statistically significantdifference in ankle girth measure-ments taken at baseline among the 3groups (Tab. 2). As there also was an
unexpected, but significant, differ-ence with the uninjured ankle girthmeasurements, it is possible thatsubjects in the sham ES group hadsmaller limbs than subjects in theother 2 groups. However, this differ-ence was not found for the baselineankle volume measurements. Thiscould be because the volumeter ismore accurate than the tape mea-sure at recording volume or morelikely because the small sample sizeproduced this spurious result. Theunexpected difference in subjects’height among the 3 groups at base-line further supports the argumentthat the small sample size is a limita-tion of the study.
Table 4.Mean (�SD) Volume (in Milliliters) of Injured and Uninjured Ankles in the 3 Groups With Kruskall-Wallis Test for StatisticallySignificant Differences Among Groupsa (95% Confidence Intervals for the Injured Ankle Are Shown in Italics)b
Change in volume from first to lasttest (pretest 1–posttest 3)
Injured ankle 8 (65) 24 (57) �28 (38)
Uninjured ankle �14 (41) 28 (47) �11 (27)
Pretest–posttest volume in session 1
Injured ankle �20 (28)(�40 to �2)
�8 (40)(�35 to 17)
�32 (28)(�51 to �13)
�2�3.239, P�.198
Uninjured ankle 5 (33) �16 (31) �2 (27)
Pretest–posttest volume in session 2
Injured ankle �27 (12)(�35 to �19)
�10 (31)(�31 to 11)
�19 (15)(�29 to �9)
�2�3.039, P�.219
Uninjured ankle 14 (29) �3 (18) 3 (12)
Pretest–posttest volume in session 3
Injured ankle �27 (21)(�41 to �13)
�6 (29)(�25 to 13)
�21 (31)(�41 to �1)
�2�3.630, P�.163
Uninjured ankle �1 (18) �9 (28) �6 (23)
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation. For difference scores, negative values indicate an increase in volume, and positivevalues indicate a decrease in volume.b Confidence intervals are approximate due to the asymmetrical shape of the histograms.
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Arguably the most likely conclusionfrom these results is general innature: that submotor and motor ES,as used in this study, are not effec-tive in decreasing ankle-foot swellingin the early period after an anklesprain. In particular, given that thestudy was designed to evaluate theeffectiveness of NMES, the evidencehere is strongest in regard to its inef-fectiveness, and this was surprisinggiven the previously demonstratedability of the stimulator used in thisinvestigation to decrease ankle-footvolume changes caused by pro-longed standing.25
Other interpretations, however,should be considered before makinga strong conclusion, and one possi-ble interpretation of these findings isthat NMES is effective, but was notfound to be effective in this studybecause of the small sample size,especially given the large standarddeviations found. Consequently, apower analysis of the injured anklevolume change was undertaken todetermine the chance of a type IIerror occurring, and the power
(2-sided, P �.05) was 0.325 for thedifference between the NMES andsham ES groups and 0.672 for thedifference between the submotor ESand sham ES groups. The low powerof this study, therefore, should betaken into consideration when inter-preting the statistically nonsignifi-
cant findings. A small effect size(�0.18) also was found when thechange scores for volume, girth andHughston Clinic Subjective RatingScale for Ankle Disorders score wereanalyzed.
Figure 3.Injured ankle volume (mean�SD, in milliliters) at the beginning of each session.NMES�neuromuscular electrical stimulation, ES�electrical stimulation.
Table 5.Mean (�SD) Swelling Volumes (Injured Ankle-Uninjured Ankle Volume) at Each Test Session (in Milliliters) With Kruskall-WallisTest for Statistically Significant Differences Among Groupsa (95% Confidence Intervals Are Shown in Italics)b
Change in swelling volume, session 3 �26 (37)(�51 to �1)
3 (39)(�23 to 29)
�15 (47)(�45 to 15)
�2�2.848, P�.241
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation. For changes in swelling volumes, negative values indicate an increase in volume,and positive values indicate a decrease in volume.b Confidence intervals are approximate due to the asymmetrical shape of the histograms.
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Table 6.Mean (�SD) Injured and Uninjured Ankle Girth Measurements (in Centimeters) With Kruskall-Wallis Test for StatisticallySignificant Differences Among Groupsa (95% Confidence Intervals for the Injured Ankle Are Shown in Italics)b
NMES Group(n�11)
Submotor ESGroup(n�11)
Sham ES Group(n�12)
SignificanceLevel
Ankle girth, session 1
Injured ankle 58.0 (4.7)(54.8 to 61.2)
59.5 (5.7)(55.7 to 63.3)
54.0 (4.5)(51.1 to 56.9)
�2�7.033, P�.030c
Uninjured ankle 56.1 (4.2) 57.5 (4.9) 53.4 (4.6)
Ankle girth, session 2
Injured ankle 57.7 (4.3)(54.8 to 60.6)
58.8 (5.8)(54.9 to 62.7)
54.0 (4.7)(51.0 to 57.0)
�2�6.191, P�.045c
Uninjured ankle 55.7 (4.1) 57.5 (4.8) 53.4 (4.4)
Ankle girth, session 3
Injured ankle 56.7 (4.6)(53.6 to 59.8)
58.2 (6.2)(53.0 to 62.4)
54.3 (4.4)(51.5 to 57.1)
�2�3.042, P�.218
Uninjured ankle 55.5 (4.3) 57.1 (5.6) 53.3 (4.3)
Difference in ankle girthfrom test 1 to test 3
Injured ankle 1.2 (0.6) 1.3 (1.4) �0.3 (1.2)
Uninjured ankle 0.5 (0.6) 0.4 (1.1) 0.1 (0.9)
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation.b Confidence intervals are approximate due to the asymmetrical shape of the histograms.c Significant difference P �.05.
Table 7.Mean (�SD) Ankle Girth Differences (Injured Ankle Girth-Uninjured Ankle Girth) (in Centimeters) With Kruskall-Wallis Test forStatistically Significant Differences Among Groupsa (95% Confidence Intervals Are Shown in Italics)b
NMES Group(n�11)
Submotor ESGroup(n�11)
Sham ES Group(n�12)
SignificanceLevel
Girth difference at test 1 1.9 (2.1)(0.5 to 3.3)
2.0 (2.0)(0.7 to 3.3)
1.1 (1.2)(0.3 to 1.9)
�2�1.290, P�.525
Girth difference at test 2 2.1 (2.0)(0.8 to 3.4)
1.7 (1.1)(1.0 to 2.4)
1.0 (1.8)(�0.1 to 2.1)
�2�1.361, P�.506
Girth difference at test 3 1.2 (1.7)(0.1 to 2.3)
1.1 (1.1)(0.4 to 1.8)
1.5 (1.4)(0.6 to 2.4)
�2�0.496, P�.780
Change in girth differencesfrom test 1 to test 3
0.7 (1.0) 0.9 (1.6) �0.4 (1.1)
a NMES�neuromuscular electrical stimulation, ES�electrical stimulation.b Confidence intervals are approximate due to the asymmetrical shape of the histograms.
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It is also possible that NMES is effec-tive but not in the manner used inthis study or not on this sample. Thisallows the opportunity to considerhow the NMES treatment strategymight have been altered in order toincrease its effectiveness. The studydesign, ES parameters, and treatmentduration used in this study differedfrom those of other studies in whichthe researchers advocated the use ofNMES in reducing edema,14–17 whichmay have influenced the apparent in-effectiveness of NMES in reducingedema. The studies by Crisler14 andLake17 were descriptions of clinicalresults of NMES treatment that theyhad applied in practice, rather than arandomized trial. Furthermore, Crislerreported the use of an Ultrafaradic M-4Impulse Generator on 400 cases ofvarious sprains and strains withoutidentifying the positioning of the elec-trodes in the different regions.
Gould et al15 applied the NMES moreintensely than that used in the cur-rent study. They applied the ES for 16hours a day for 2 weeks followingopen meniscectomy and reported“several hundred contractions perday.” This is very different from the30-minute treatment session for 3 daysthat was used in this study. The otherstudy that advocated the use of NMESin reducing edema was by Griffin etal,16 who applied a single 30-minutesession of ES that had a pulse fre-quency of 8 pps (pulse duration wasnot specified) to produce minimal vis-ible contractions. Therefore, the inten-sity of treatment was lower than thatused in our study, and only one treat-ment session was given. All of thesevariations in treatment durations, ESparameters, and design methodologycontribute to the conflicting resultsfor the efficacy of NMES in edemareduction. Future work should evalu-ate whether different treatment inten-sities, durations (number and durationof sessions), frequencies (sessionsover time), current parameters, targetmuscle groups and electrode position-
ing, type of contraction (static versusdynamic), and periods of interventionrelative to the injury (ie, more or lessacute stage) affect treatment effective-ness.
It is possible that NMES, as used inthis study on this sample, is effectivein reducing swelling, but its effec-tiveness remains undetected. Theeffectiveness of NMES can be de-duced if the sample in this study wasnot representative of individualsrecovering from ankle sprain or thetest tools used in this study were nogood. We suspect that the formerexplanation is not valid. In regard tothe latter explanation, a variety ofmeasures covering outcomes thatwe think clinicians and patientsconsider important were used tomitigate this problem. We know ofno other measure of the main out-come, foot-ankle volume, that ismore accurate than the volumetricmethod used in this study. The accu-racy of the volumetric method alsomay have been reflected in the differ-ences found among groups at baselinefor the ankle girth measurements butnot for the volume measurements.Finally, the possibility exists that theinclusion of the foot in this analysismay have hidden changes in ankle vol-ume. If that were the case, then thevolume changes in the ankle, whichhave been shown to affect the sur-rounding neuromuscular system32 andare suspected to be more critical thanfoot volume changes, may have re-sponded differently in the 3 groups.
In an earlier study,25 the motor ESmethod used in the present studywas found to be effective in limitingthe increase in ankle-foot volumethat occurs in prolonged standing.This finding raises the question as towhy a positive finding occurred inonly one of these studies. To addressthis question, one should first con-sider the differences between the 2studies. The studies mainly differedin the type of sample evaluated
(uninjured versus injured subjects),the position of the subjects duringthe ES (standing versus supine lyingwith legs elevated), and the numberof sessions in which the treatmentwas evaluated (1 versus 3). Of these3 methodological differences, wesuspect that the type of sample stud-ied is the most likely cause for theineffectiveness of NMES found in ourstudy. The subjects evaluated in ourstudy had swelling resulting from amusculoskeletal injury (ie, a sprainedligament). Such an injury would tendto cause swelling of an inflammatorynature where an increase in capillarypermeability would produce an accu-mulation of interstitial fluid causingswelling.
It is more likely that the swellingproduced by prolonged motionlessstanding in the earlier study wouldhave been venous in nature andcaused by an increase in the venouspressure. Because NMES reducesexcess fluid primarily by simulationof the musculo-venous pump, whichwould lower the increased venouspressure,33 it may be possible thatthis mechanism would be moreeffective in reducing swelling pro-duced by raised venous pressurerather than increased capillary per-meability. The pressure of restrain-ing the limb to the stool in our studyalso may have affected the lymphaticand venous return in the leg. This, inturn, could have affected the amountof limb swelling reduction and con-tributed to the nonsignificant differ-ences of edema reduction withNMES.
Swelling that has been produced byincreased capillary permeability, asin the case of musculoskeletal injury,also may respond better to submotorES rather than NMES, as supportedby the animal studies conducted byMendel and Fish.34 They performeda series of studies using high-voltagecathodal ES (120 pps, 10% belowvisible contractions) on frog and rat
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models and found that up to four30-minute treatment sessions witheither 30- or 60-minute rest periodsbetween treatments curbed edemaformation for up to 24 hours afterinjury. Their findings support thetheory put forth by Reed35 that sub-motor ES may have reduced micro-vessel permeability, which could af-fect the amount of fluid accumulatingin the interstitial spaces.
Another possible theory suggestedas to how cathodal ES may help todecrease swelling is by a electro-phoretic phenomenon where nega-tively charged current repels nega-tively charged serum proteins, which,in turn, causes a fluid shift and re-duces edema.26 However, Karnes etal36 also used anodal current in theirexperiments and found that, althoughit did not curb edema formation, itwas not exacerbated either, thus sug-gesting that the electrophoretic effectis not likely to be the main means ofhow submotor ES controls edema.The submotor ES parameters used byMendel and colleagues34,36 were notapplied in our study. However, it isnot known exactly how submotor ESworks to reduce edema, and thereforeit may have affected some of thechanges that occurred in the submo-tor ES group.
An interesting trend observable inthis study was the consistent in-crease in injured ankle-foot volumeduring the “treatment” sessions in all3 groups as exemplified in Table 4.When swelling volume was analyzed(Tab. 5), the change in swelling wasgreater at the end of “treatment”for the NMES and sham ES groupsfor all 3 sessions and for the submo-tor ES group for the second session.This finding indicates an increase ininjured-side swelling or a decrease inuninjured-side volume. The latter isreasonable because it is expectedthat placing the leg in the nondepen-dent position for prolonged periodswould decrease the ankle-foot vol-
ume, although we did not find statis-tically significant differences be-tween sitting and supine lying inuninjured individuals in a previousstudy37 and there was not a consis-tent decrease in uninjured ankle vol-ume in this study (Tab. 4). The in-crease in volume of the injured sideis much more difficult to explain.One explanation is that the motor ESwas acting as an irritant to the tissuescausing an increase in swelling, butthis was countered by the increasein swelling in the sham ES group.
ConclusionUsing the present study design, nodifferences were found between theNMES and submotor or sham ESgroups in ankle-foot volumes in theearly period after ankle sprain. Thislittle researched area requires addi-tional, larger studies that consideralterations in the treatment protocolgiven the variety of NMES approachesthat can be taken when this treatmentis given.
Dr Man and Dr Morrissey provided concept/idea/research design, writing, data analysis,project management, and institutional liai-sons. Dr Man provided data collection, fundprocurement, and facilities/equipment. DrCywinski provided the stimulators for thestudy and reviewed the manuscript.
This article was received August 9, 2005, andwas accepted August 18, 2006.
DOI: 10.2522/ptj.20050244
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