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A preliminary investigation into the effects of active interferential current therapy and placebo on pressure pain sensitivity: a random crossover placebo controlled study

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A preliminary investigation into the effects of active interferential current therapy and placebo on pressure pain sensitivity: a random crossover placebo controlled study
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  Physiotherapy97(2011)291–301 A   preliminaryinvestigationintotheeffectsof    activeinterferentialcurrenttherapy   andplaceboonpressurepainsensitivity:a   randomcrossoverplacebocontrolledstudy JorgeFuentesC a , b , ∗ ,   SusanArmijo-Olivo b , c ,DavidJ.Magee b ,DouglasP.Gross b a  Departmentof    PhysicalTherapy,CatholicUniversityofMaule,Talca,Chile b FacultyofRehabilitationMedicine,DepartmentofPhysicalTherapy,UniversityofAlberta,Canada c  AlbertaResearchCentreforHealthEvidence(ARCHE)FacultyofMedicineandDentistry,UniversityofAlberta,Canada AbstractObjective   (1)   Todetermine   the   effect   of    active   and   placebo   interferential   current   on   muscle   painsensitivity   using   an   experimental   mechanicallyinduced   pain   model.   (2)   To   evaluate   the   predictive   role   of    expectations,   gender,   baseline   muscle   pain   sensitivity,   and   intervention   order   onplacebo   response. Design   Randomized   placebo   controlled   cross-over   trial. Setting   University   research   laboratory. Participants   Forty   healthyvolunteers   (20   females,   20   males). Interventions   Active   interferential   current,   placebo   (sham)   interferential   current,   and   no   treatment/control   were   applied   to   the   lumbar   areaon   different   days. Main   outcomes   measures   Pressure   painthresholds   andplacebo   response. Results   The   two-way   ANOVA   withrepeated   measures   analysis   determined   asignificant   interaction   between   condition   and   time   ( P   =   0.002).Pairwise   comparisons   found   differences   between   active   interferential   and   the   control   condition   at   15   minutes   into   treatment   (mean   differ-ence   =   0.890   kg/cm 2 ,   95%   CI   0.023   to   1.757,   P   =0.043)   and   at30   minutes   into   treatment   (mean   difference   =   0.910   kg/cm 2 ,95%   CI   0.078to   1.742,   P   =   0.028).   The   increase   in   pressure   painthresholds   betweenthe   active   interferential   and   the   control   condition   (1.12kg/cm 2 )was   clinically   meaningful.   Logistic   regression   analysis   showed   that   the   condition   sequence   order   was   the   only   variable   that   predictedplacebo   response   (odds   ratio   9.7;   P   =0.028).   Ifasubject   started   the   sequence   receiving   placebo   treatment   first,   the   odds   of    respondingto   placebo   would   beapproximately   10   timeshigher   (i.e.   90%   probability   of    being   aplacebo   responder)   than   that   of    starting   withan   activetreatment. Conclusions   Active   interferential   wasmore   efficient   than   control   condition   in   decreasing   muscle   painsensitivity.   Placebo   interferential   wasnot   significantly   different   from   control.   Treatment   sequence   demonstrated   astrong   association   with   placebo   response.   These   findings   haveimplications   for   future   research   characterizing   and   identifying   placebo   responders   in   physiotherapy.©   2011   Chartered   Society   of    Physiotherapy.Published   by   Elsevier   Ltd.   All   rightsreserved. Keywords: Interferentialcurrent;Placeboeffect;Placebopredictors;PPT;Musclepainsensitivity;Clinicalsignificance Introduction Interferential   therapy   isthetranscutaneous   application   of alternatingmedium-frequency   amplitude   modulated   electri-calcurrent   at   lowfrequency   (0–250Hz)   [1–3].Interferential ∗ Correspondingauthor.DepartmentofPhysicalTherapy,CatholicUni-versityofMaule,Talca,Chile.Tel.:+17804361012;fax:   +17804921626.  E-mailaddress:  jorgef@ualberta.ca(J.   FuentesC). therapy   iswidely   used   by   clinicians   toprovidepain-relief    foravarietyof    conditions   and   patient   populations   [4–8].The   application   of    thismodalityhasbeenshown   todecreasepain   in   the   shortterm   in   kneeosteoarthritis   [9–12]postoperative   knee   pain   [13],   and   fibromyalgia   [14].   Inaddition,clinically   meaningful   effects   at   3   and   6monthsfollow-uphave   beenreported   in   patients   with   frozen   shoulder[15],and   low   back    pain   [16,17].   In   contrast,   no   hypoalgesiceffectshave   been   demonstrated   in   shoulderpain   [18,19]. 0031-9406/$–seefrontmatter©2011CharteredSocietyofPhysiotherapy.PublishedbyElsevierLtd.Allrightsreserved.doi:10.1016/j.physio.2011.01.001  292  J.   FuentesCetal./Physiotherapy97(2011)291–301 Pressure   algometry   is   themostcommon   modalityused   to   apply   a   uniform   rate   of    pressure   for   inducingmechanicpain   [20–23].   Among   thevariousexogenousexperimentalpain   models   (i.e.   electrical,   mechanical,   chem-ical),   the   mechanically   induced   pain   modelisbelievedtoassessdeep   tissue   (i.e.   muscle)   reflecting   its   sensitivity   topain[24,25]Pressure   pain   sensitivity,   evaluated   using   thepressure   painthreshold   is   the   mostcommonly   used   method   forquantitativeanalysisof    localmuscle   pain   and   tenderness.   The   assessmentofpressure   pain   thresholds   has   been   extensively   used   in   bothclinical   [23,26,27],   and   experimental   conditions   [22,28,29]toassess   muscle   pain   sensitivity   and   to   evaluatetheefficacyoftherapeutic   interventionsand   pain   relieving   modalities   inpatients   aswell   as   healthysubjects.   In   addition,treatment-inducedchanges   in   pressure   painthresholds   observed   inlaboratorysettings   are   believedto   correlatewell   with   changesin   the   clinical   status   of    pain,   and   as   such,algometry   and   themeasurement   of    the   pressurepain   thresholds   isconsidered   ausefulexperimental   model[21]Placeboeffect   represents   thecontextual   and   psychoso-cialaspect   ofevery   treatment   surrounding   thepatient[30].Despite   the   growing   interest   in   studying   its   effect,   the   placebostill   remains   arelatively   unexploredarea   of    study   in   phys-iotherapy.Results   of    a   literature   search   including   PEDro,MEDLINE,Scopus,   and   Embase   (1966–2009),   found   onlyone   study   [31]   investigatingthe   direct   measure   of    the   placeboeffect   of    interferential   therapy   by   comparing   placebo   inter-ferential   therapy   againstnointervention.   Authors   reportedthatplacebo   interferential   therapy   wasbetter   at   modulatingexperimentalischemicpain   compared   to   control   [31]   how-ever   a   degree   of    caution   isrequired   when   interpreting   theseresultsdueto   the   small   samplesize   included( n   =   12)andothermethodological   issues.Thus,additional   research   isclearly   needed   to   assesstheeffectof    placebo   as   apain   modulatorincontrolled   condi-tions.It   is   unclear   ifthereaction   to   placebo   interferentialtherapy   obtained   in   experimental   ischemicpain   iscompa-rableto   other   models   ofexperimental   pain.   Forexample,ofinterest   would   be   to   determine   the   magnitude   of    placebointerferential   therapy   in   amechanically   induced   pain   modelin   healthysubjects.Similarly,   althoughevidence   suggests   that   patient   expec-tationshaveasignificant   impact   onoutcomes   [32,33],informationregardingtherole   of    gender,   treatment   sequenceorder   (i.e.   receiving   placebo   or   activeinterferential   therapyfirst),expectations,   and   muscle   pain   sensitivityas   determi-nantsof    placebo   analgesia   in   physiotherapyinterventions   isstill   lacking.Therefore,   theprimary   objective   of    this   study   wastodetermine   themagnitude   of    the   placebo   interferentialtherapy   effect   onmusclepain   sensitivity   in   anexperi-mentallyinduced   mechanical   pain   in   healthysubjects.   Wealsoaimed   to   identify   thepotentialpredictors   of    placeboresponsein   subjects   responding   the   placebo   interferentialtherapy.A   secondary   objective   wasto   determine   the   hypoal-gesiceffect   of    active   interferential   therapy   on   muscle   painsensitivity. Methods  Research   design This   study   wasa   randomized   placebo   controlled   cross-over   trial   design. Subjects Aconveniencesample   of    40healthystudents   and   staff fromthe   University   of    Alberta   wasrecruitedconsisting   of    20females   and   20   males.   This   sample   size   waschosen   basedon apriori   samplesize   calculations   using   α =   0.05,   powerof    80%and   aneffect   size   of    0.25   for   arepeated   measuresanalysis[34].Specific   inclusion   criteriaconsisted   of    healthysub- jectsbetween   theages   of    18   and   50years,   taking   noanalgesic   medication,   and   subjects   without   previous   expe-rience   in   electrotherapy.   Exclusion   criteria   wereany   painfulmusculoskeletal   condition   or   any   contraindications   to   elec-trotherapy.   All   subjects   acknowledgedtheirunderstandingand   willingness   to   participate   by   providing   signed   consent.Everysubjectwas   reimbursed   CAD$40   for   their   participa-tion   in   thestudy.Approval   of    thisstudy   wasobtained   fromtheUniversity   of    Alberta   HealthResearch   Ethics   Committee.  Interventiondescription Both   active   and   placebo   interferential   therapy   treatmentsweredelivered   with   acalibrated   Intellect   Legend   Stim   electri-calstimulator   (Chattanooga   Group   Inc.,   Hixson,   TN,   USA).Parameters   for   the   active   interferential   therapy   treatmentincludedacarrier   frequency   of    4000   Hzthat   wasnot   mod-ulated   (AMF   =   0Hz).   Thirty   minutes   of    stimulation   wasappliedusing   four   electrodes   placed   overthelumbar   (L 1 )andsacral   (S 2 )areas   (see   Fig.1),with   theright   erectorspinaemuscle   targeted   as   central   area   of    stimulation   (4   cmto   therightof    thespinous   process   of    L 4  level)   [22].   Thecurrentintensity   forthe   treatment   wasat   asensory   level[13,22,35–37]. Placeboapplication   and    control   condition The   placebo   treatment   included   sham   interferential   ther-apy.Thirty   minutes   of    shamapplication   wasdelivered   inthesamefashion   as   per   theactive   interferential   therapy   treatment,exceptthat   thelead   wiresof    theequipment   were   disconnectedfromthejack    of    their   output   channels.   Thus,   the   subjectsreceivedno   currentoutput.   The    jack    of    the   output   channelswascovered   during   the   procedure.   Duringtheapplicationtheinvestigator’sinstructions   were   as   follows:   ‘Iam   goingto   apply   atherapeutic   currentcalled   subthreshold   electrical   J.FuentesCetal./Physiotherapy97(2011)291–301 293 stimulation   which   you   might   or   might   notbeable   to   perceivebeneath   the   electrodes.   It   isstill   unknown   ifthis   new   type   of stimulationis   better   thanthe   standard   stimulation’.   Subjectswere   facing   the   equipment   screen   which   displayed   visual   andoutput   signals.Thecontrol   condition   consisted   of    no   application   of interferentialtherapy   or   placebo   treatment.   To   keep   theinvestigatorresponsible   forthepressure   pain   threshold   mea-surements   blinded,   theelectrodes   werepositioned   inthe   samearrangementas   used   fortheactive   and   placebo   interferentialtherapy   applications   for30   minutes.   However,   subjects   weretoldthat   no   treatment   was   delivered. Placebo   responder  Aplacebo   responder   was   considered   a   subjectwith   anincreasein   his/her   pressure   pain   threshold   of    ≥ 1.1kg/cm 2 asa   result   of    theinterferential   therapy   placebo   intervention.Thiscriterion   wasbased   onpreviouscalculations   of    clinicalsignificance   for   thisoutcome[22,38] Primaryoutcome    –pressurepainthreshold  Pressure   pain   sensitivity   wasevaluated   through   thepres-sure   pain   threshold,   or   theminimum   pressurethat   inducespainor   discomfort   [39].   In   thisstudy,a   mechanical   algometerwasused   todetermine   themuscle   pain   sensitivity   in   the   lum-bararea.   Pressure   pain   threshold   measurements   have   beenshowntohave   good   orexcellent   inter-rater   reliability   (ICC0.74–0.90)   [40]   and   intra-raterreliability   (ICC   0.75–0.99)[20,23,25,41].Atrained   physiotherapistassessor   (JF)   measured   pressurepainthresholds   by   applying   acalibrated   mechanical   algome-ter(Wagner   Instruments,   Greenwich,   CT   06836-1217)   at   aconstant   rateof    forceof    1   kg/cm 2 seconds.   The   algometer   wasappliedperpendicularly   overtheright   erector   spinae   mus- Fig.1.Fourcarbonrubberelectrodesplacedover   lumbar(L 1 )andsacral(S 2 )areas.Mechanicalalgometerappliedperpendicularlyovertherighterectorspinaemuscletargetedasthecentralareaofstimulation(4cmtotherightofthespinousprocessofL 4 ). cle,   landmarked   for   reproducibility,   4   cmto   theright   of    thespinous   process   of    L 4  (seeFig.   1).The   erector   spinae   musclewaschosen   because   it   haspreviously   been   used   in   clinical[42,43],and   experimental   settings   [20,22].   Excellent   intra-examiner   reliability   hasbeenreported   [20,44]   and   normativevaluesare   available   for   thisarea   [44].   The   force   recordedbythealgometer   was   theminimum   amount   of    pressurethatevoked   thefirst   sensation   ofpain   [21,44]. Generalprocedure Allsubjects   received   both   interferential   therapy   interven-tions(i.e.   activeand   placebo)   plusthe   controlcondition   onseparate   days.   The   sequence   order   of    treatment   wasrandom-izedusing   acomputerized   table   of    random   numbers.   Toavoidacarryover   effect,   treatments   were   applied   with   awashoutperiodof    at   least   one   day   of    rest   between[22,45,46].A   trainedphysiotherapist(SAO)applied   theinterferential   therapy   treat-ments.The   subjects   wereblind   to   the   interferential   therapyinterventions.   The   investigator(JF)   in   chargeof    measuringpressurepainthresholds   was   blindto   the   conditions   and   tothestatistical   analysis   of    data.Duringthe   first   visit,   subjects   weretold   that   they   wouldreceivetwointerferential   therapytreatments   (i.e.   activeorplacebo)based   ondifferent   stimulation   parameters   or   theycould   receive   thecontrol   condition   for30   minutes   accordingtothe   randomization   order.On   the   second   and   third   visits,   subjects   received   theotherconditions   as   perthe   randomization   procedure   (Fig.   2).Beforeconducting   the   pressure   pain   threshold   assessment,subjectswereinstructed   in   theapplication   of    thealgometerandgivena   demonstration.   They   thenunderwent   a   prac-ticetestof    pressure   pain   threshold   measurements   usingthedominant   forearm   until   the   subjectfelt   theyunderstoodthesensation   and   whattheywere   being   asked   to   doandfeel.Duringtheprocedure   of    assessing   pressure   pain   thresh-olds,patients   wereinstructed   to   differentiate   the   pressurefroma   feeling   of    ‘being   pressed’   to   ‘initial   pain   recognition(threshold)’   [39].   Subjects   were   asked   to   say‘stop’   as   soonastheyfelta   clear   sensation   of    pain,   distinct   from   pressure   ordiscomfort.   The   forcerecorded   wastheamount   of    pressurethatevoked   pain   (pressure   pain   threshold).Pressurepain   threshold   measurements   were   taken   onfourdifferentoccasions   during   the   experimental   procedureforeach   of    the   threeconditions;   M1(10   minutes   pre-treatment),   M2   (time0),   M3(15minutes   into   treatment),M4(30   minute-end   of    treatment)(see   Fig.   3).   On   eachocca-sion,twoconsecutivepressure   pain   threshold   measurementsperformed60   seconds   apart   were   collected   and   averaged.  Expectancy   ofpain   relief    measurements Beforeand   after   the   application   of    thethree   conditions,subjects   were   askedto   rate   theirexpectations   of    pain   relief.The   Credibility   and   Expectancy   Questionnaire   (CEQ)   was  294  J.   FuentesCetal./Physiotherapy97(2011)291–301   Session 1 Time Session 1 Time Session 1 PPT measurement M1 -10 min   PPT measurement M1 -10 min PPT measurement M1 PPT measurement M2 -1min   PPT measurement M2 -1 min PPT measurement M2 Active IFT 0 min   Placebo IFT 0 min Control PPT measurement M3   15 min   PPT measurement M3 15 min PPT measurement M3PPT measurement M4   30 min   PPT measurement M4 30 min PPT measurement M4 Exit 35 min  Exit 35 min Exit One day apart One day apart One day apart Session 2 Crossover Placebo IFT or Control Session 2 Crossover Active IFT or Control Session 2 Crossover Active IFT or Placebo IFT One day apart One day apart One day apart Session 3 Crossover Placebo IFT or Control Session 3 Crossover Active IFT or Control Session 3 Crossover Active IFT or Placebo IFT Subject who met the inclusion criteria Randomization order Fig.2.Schematicsequenceofthestudyprocedure. -10 0 15 30  10 min pre-treatment Time 0 15 min into treatment End of treatment Pretest value M1 Pretest value M2 Test value M3 Test value M4 Fig.3.Theexperimentalprocedure.Descriptionofthe   recordingsofpressurepainthresholdsatdifferenttimeintervalsduringthestudyfortheactive,placeboandcontrolconditions.   J.FuentesCetal./Physiotherapy97(2011)291–301 295 6.06.57.07.58.08.59.09.510.0M1 (?10 min)   M2 (0 min)   M3 (15 min)   M4 (30 min)    P   r   e   s   s   u   r   e   P   a   i   n   T    h   r   e   s    h   o    l    d   s   K   g    /   C   m   2 Timeline of the experimental procedure Active IFT   Control IFTPlacebo IFT Fig.4.Averagepressurepainthresholds(kg/cm 2 seconds)duringthetimelineoftheexperimentalprocedureforthethreeconditions(activeIFT,placeboIFTandcontrol).Resultsareshownasmean ±   SEM. usedfor   thispurpose   [47].   The   CEQ   is   considered   to   beavalid   and   reliable   [47]   tool   to   measure   the   expectancyconstruct. Dataanalysis A   two-way   ANOVA   design   withrepeated   measures   wasusedto   evaluate   differences   in   pressure   pain   threshold   val-uesacross   measurement   times   amongthe   conditions(i.e.activeinterferential   therapy,   placebo   interferential   therapy,and   control).   A   Bonferroni’s   post   hoc   testwas   used   to   adjustformultiple   comparisons   during   pairwise   comparisons.   Thestandard   error   ofmeasurement   valuewas   calculated   to   deter-mineclinical   importance   of    the   difference   in   thepressure   painthreshold   measurements   [48].Toidentify   thepredictors   ofplacebo   analgesia,   amultiplelogisticregression   analysis   wasperformed.   The   outcome   forthisanalysis   was   whether   or   not   thesubjectwasa   placeboresponder   (yes/no   =   dichotomous   variable)   based   on   thepre-vious   established   criterion   ( ≥ 1.1   kg/cm 2 ).   The   predictorsusedin   this   model   were   gender   (female/male),   pre-treatmentmuscle   pain   sensitivityvalues   (continuous   variable),   levelsofexpectations   for   pain   relieffortheplacebo   interferen-tialtherapy   (continuous   variable)and   interferential   therapyorderof    treatment   sequence   (categorical   variable   with   3cat-egories:starting   withplacebo   interferential   current,   startingwithactive   interferential   current,   or   starting   withcontrol).Theadjusted   oddsratios   werereported   for   each   of    theout-comesanalyzed.   The   level   of    significance   was   set   at   α =   0.05.Data   analysis   wasperformed   blinded   sinceeach   subject   andcondition   wascoded   by   anindependent   assistantnot   involvedinthe   trial.   The   computer   programs   SPSS   version   17.0   andSTATA   version   10   were   usedfor   allanalyses   (SPSSInc.   233S.Wacker   Drive,   Illinois,   USA,   StataCorp   LP   4905LakewayDriveCollege   Station,   Texas   77845,   USA). Results Subjects A   total   of40   healthyvolunteers,   mean   age   29.9years(SD   =6.88,   range   =   19–47   years),   height   170.6   mt(SD   =   8.26),   weight   74.4   kg   (SD   =   14.49)   wereassessed   forthisstudy.   No   subjects   were   excluded.Regardingthetreatment   sequence,   15,   11   and   14   sub- jectsreceived   the   active   interferential   therapy,   thecontrolcondition,and   theplacebo   interferential   therapy   as   first   inter-ventionrespectively.  Maineffectsof    interferential   therapy   onmuscle    painsensitivity Nostatistically   significant   differencesamong   thethreeconditions(i.e.   activeinterferential   therapy,   placebo   inter-ferential   therapy,   and   control)   regardlesstime   of    evaluationforan   increase   in   pressure   pain   threshold   were   found   (meandifferencebetween   activeinterferential   therapy   and   placebointerferential   therapy=   0.079   kg/cm 2 ,   P =   1.0,   [95%   CI   0.700to0.857   mean   difference   between   active   interferential   ther-apyand   control   =0.461   kg/cm 2 ,   P =   0.385,   [95%   CI0.281to1.203];   mean   difference   betweenplacebo   interferentialtherapyandcontrol=   − 0.382   kg/cm 2 ,   P =   0.254,   [95%   CI − 0.922   to   0.158]).  Interaction   between   time   and    interferential   therapyapplicationson   muscle    pain   sensitivity The   two-way   ANOVA   determined   that   there   wasasignificantinteractionbetween   condition   and   time   of    eval-uation( P   =   0.002).   In   addition,therewas   a   significant   maineffect   for   time( P   <   0.001)(Fig.   4).Pairwise   comparisonsfound   differencesbetween   the   activeinterferential   therapy
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