Clinimetric properties of hip abduction strength measurements obtained using a handheld

19 Pages·2017·22.26 MB·English

RESEARCHARTICLE
Clinimetric properties of hip abduction
strength measurements obtained using a
handheld dynamometer in individuals with a
lower extremity amputation
RuudA.Leijendekkers1*,GerbenvanHinte1,AmyD.Sman1,J.BartStaal2,3,MariaW.
G.Nijhuis-vanderSanden1,2,4,ThomasJ.Hoogeboom2
1 DepartmentofOrthopaedics,PhysicalTherapy,RadboudUniversityMedicalCentre,Nijmegen,the
Netherlands,2 RadboudInstituteforHealthSciences,IQHealthcare,RadboudUniversityMedicalCentre,
a1111111111 Nijmegen,theNetherlands,3 ResearchgroupMusculoskeletalRehabilitation,HANUniversityofApplied
a1111111111 Sciences,Nijmegen,theNetherlands,4 DepartmentofRehabilitation,RadboudUniversityMedicalCentre,
a1111111111 Nijmegen,theNetherlands
a1111111111
*[email protected]
a1111111111
Abstract
OPENACCESS
Introduction
Citation:LeijendekkersRA,HinteGv,SmanAD,
StaalJB,Nijhuis-vanderSandenMWG, Suitablehandhelddynamometer(HHD)-techniquestotesthipabductionstrengthinindivid-
HoogeboomTJ(2017)Clinimetricpropertiesofhip ualswithalowerextremityamputation,irrespectiveoftheiramputationlevelareabsent.
abductionstrengthmeasurementsobtainedusing
TheaimofthisstudywastooptimiseaHHD-techniqueandtotestitsreproducibilityand
ahandhelddynamometerinindividualswitha
lowerextremityamputation.PLoSONE12(6): validity.
e0179887.https://doi.org/10.1371/journal.
pone.0179887 Methods
Editor:HagenAndruszkow,Universitatsklinikum Thisstudyinvolvedthreephases,inwhichtwotechniqueswereevaluated.BothHHD-tech-
Aachen,GERMANY
niquesusedalever-armof22centimetre.HHD-technique1usedabreak-technique.After
Received:February1,2017 obtainingwithin-sessiontest-retestreproducibility(phase1)weoptimisedtheHHD-tech-
Accepted:June6,2017 niquebyaddingafixation-beltandusingamake-technique(HHD-technique2).Wetested
thewithin-sessiontest-retestandinter-raterreproducibility(phase2)andthevalidity(phase
Published:June22,2017
3)ofHHD-technique2usinganisokineticdynamometer.Newcohortsofparticipantswere
Copyright:©2017Leijendekkersetal.Thisisan
recruitedforeachphase.
openaccessarticledistributedunderthetermsof
theCreativeCommonsAttributionLicense,which
permitsunrestricteduse,distribution,and Results
reproductioninanymedium,providedtheoriginal
Phase1:wetestedHHD-technique1in26participantswithalowerextremityamputation.It
authorandsourcearecredited.
wastest-retestreproducible(ICC3.1 :0.80–0.92,standarderrorofmeasurement
DataAvailabilityStatement:Allrelevantdataare agreement
(SEM):3.1–4.4Nmandsmallestdetectablechange(SDC):8.6–12.3Nm).Therewere
withinthepaperanditsSupportingInformation
files. questionsregardingthevalidityofthemeasurement,becausethemeanmuscletorqueof
theresiduallimbandsoundlimbweresimilar,whichisuncommon.Phase2:reproducibility
Funding:Theauthor(s)receivednospecific
fundingforthiswork. ofHHD-technique2wastestedin44participantswithalowerextremityamputation.Itwas
test-retestreproducible(ICC3.1 :0.96–0.97,SEM:3.9–4.7NmandSDC:10.9–12.9
Competinginterests:Theauthorshavedeclared agreement
thatnocompetinginterestsexist. Nm)butnotinter-raterreproducibledespitehavinggoodreliability(ICC3.1 :0.92,
agreement
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Hipabductionstrengthmeasurementtechnique
SEM:6.9–7.6NmandSDC:19.2–21.2Nm).Systematicbiasandbiasrelatedtothemagni-
tudeofthemuscletorquewassuspected.Phase3:theconcurrentvaliditywasestablished
in30healthyparticipants(r=0.84).Systematicbiasinmeasurementerrorwaspresent,
includingaconsistentoverestimationofthemuscletorqueof28%usingtheHHD.
Conclusion
HHD-technique2isatest-retestreproducibleandvalidmeasuringtechniqueThetechnique
maybefurtheroptimisedbytheuseofanexternaldevicetostabilisetheHHD.
Introduction
Lowerextremitymusclestrengthtrainingisanimportantelementofrehabilitationpro-
grammesforindividualswithalowerextremityamputation[1–6].Theimportanceissup-
portedbythefollowingfindings:1)strengthofthemusclesofthehipjointintheresiduallimb
isdecreasedupto35%relativetohealthysubjectsandupto28%comparedtothesoundlimb
[7,8];2)muscleatrophyoftheresiduallimbispresentupto73%comparedtothesoundlimb
[9];3)decreasedandasymmetricmusclestrengthisassociatedwithlowergaitspeedandan
asymmetricgaitpattern[10–13]4)decreasedstrengthofthemusclesofthehipjointisassoci-
atedwithloweractivitylevels[7].Reliable,validandresponsivemeasurementinstrumentsare
neededtomeasuremusclestrength.Thisisimportanttobeabletodeterminetheintensityof
strengthtrainingandtoevaluatetheeffectivenessofarehabilitationprogramme.
Inscientificresearchvariousinstrumentsareusedtoevaluatelowerextremitymuscle
strengthinindividualswithalowerextremityamputation,suchasisokineticdynamometers
[4,7,8,14],anOpticalTestingofIsometricMoments(OpTIMo)device[13],10-repetitionmax-
imumtestsonresistancemachines[1]andhandhelddynamometers(HHD)[3,15].Fordaily
clinicalpracticeameasurementhastobelowincost,non-time-consuming,portableandeasy
touse,whichisonlythecaseforHHDmeasurements[16].Clinimetricpropertiesformuscle
strengthmeasurementobtainedwithaHHDaremainlyestablishedinable-bodiedpersons,
butarelackingforindividualswithalowerextremityamputation[16].
VariousmeasurementtechniquestoevaluatehipabductionstrengthusingaHHDare
describedinthecurrentliterature[17–27].Noneofthesemeasurementtechniquesissuitable
forindividualswithatransfemoralamputationbecauseofthepositioningoftheHHDinrela-
tiontotheabsenceofakneeoranklejoint.Themainvariationsinexecutionarecharacterised
by:1)theparticipants’position(side-lyingorsupineposition),2)thepositionoftheHHD
(slightlyproximaltotheedgeofthelateralfemoralcondyleorthelateralmalleolus,respec-
tively),3)theuseofadditionalfixation-belts,4)thetypeofresistancetechniqueused(‘break-
technique’or‘make-technique’),5)theuseofadditionalportabledevicestostabilisetheHHD
[17–27].
Theaimofthiscross-sectionalstudywastooptimiseahipabductionstrengthmeasurement
techniqueforindividualswithalowerextremityamputation,irrespectiveoftheirlevelof
amputation,andtotestitsreproducibilityandvalidity.TheoptimisationoftheHHDmeasure-
menttechniqueinthisstudyinvolvedthreephases(Fig1),inwhichtwotechniqueswereeval-
uated.InbothHHD-techniquesthemusclestrengthoftheparticipantwasassessedinsupine
position,agravityneutralisedposition[22],topreventmeasurementbiasduetoweightdiffer-
encesbetweentheresiduallimbandsoundlimb.Additionally,measurementvariationis
reducedbytestinginasupinepositioncomparedtotestinginaside-lyingposition[24].A
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Hipabductionstrengthmeasurementtechnique
Fig1.Flowchartstudy.
https://doi.org/10.1371/journal.pone.0179887.g001
newcohortofparticipantswasrecruitedforeachphaseofthestudy(Fig1).TheCOSMIN
Checklistwasfollowedforthepreparationofthemanuscript[28].
Phase1:Test-retestreproducibilityofHHD-technique1
Methods
Theaimofthisphasewastodeterminethewithin-sessiontest-retestreproducibilityofHHD-
technique1;abreak-techniquewithouttheuseofanadditionalfixation-beltorportabledevice
tostabilisetheHHD.Wechosenottouseanyadditionaltoolsinordertomakethetestas
practicalaspossibleandtoimproveeasyimplementationindailyclinicalpractice.
Participants. Allconsecutiveindividualswithin3months,withalowerextremityampu-
tationwhofollowedarehabilitationprograminourcentreorhadaregularfollow-upwereeli-
gibleforthestudy(Fig1).Awritteninformedconsentwasobtainedfromallparticipantsprior
totheassessment.ThestudywasconductedaccordingtotheprinciplesoftheDeclarationof
Helsinki(64thversion,19-10-2013).Theprotocolofthisphaseofthisstudy(registration
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Hipabductionstrengthmeasurementtechnique
number2012/547)wasapprovedbytheEthicsCommitteesoftheRadbouduniversitymedical
centre.TheindividualdisplayedinFig2hasgivenwritteninformedconsent(asoutlinedin
PLOSconsentform)topublishthisimage.
Studyprocedure. Thetest-retestmusclestrengthassessmentwasperformedbyaphysio-
therapystudent(RvE)followingtrainingfromanexperiencedphysiotherapist(RL).Apilot
wasperformedwherethreeindividualsweretestedusingthemeasurementtechniqueto
ensurestandardisationoftheprocedure.Both,thetestandretestassessmentwereperformed
consecutivelyinonesessiononthesameday.Bothassessmentsstartedwithmusclestrength
testingoftheleftlimbfollowedbytherightlimb.Theparticipantswereofferedsufficienttime
(atleast1minute)torestbeforethemusclestrengthtestofeachlimbandbetweentheassess-
ments.Themusclestrengthvaluewasnotvisiblefortheraterduringthetestasthescreenof
theHHDwaspositioneddownwards(Fig2A),todecreasethechanceofmeasurementbias.
Testingprocedure. Participantswerepositionedinsupinepositiononatreatmenttable,
whichwascoveredwithanadditionalanti-slipmattopreventsliding(Fig2A).Thepartici-
pantsheldtheirarmsbytheirchestandthelowerlimbswereinneutralposition(limbsshoul-
der-widthapart).Theraterplacedamarkingontheskintoindicatethepointwheretheforce
wouldbeapplied.Thismarkwasusedforboththetestandthere-test.Thepointwasmarked
20centimetre(cm)distalofthemostprominentaspectofthegreatertrochanter.Whenpartic-
ipantshadashorterresiduallimb,thelever-armwasadjustedandnoted.Musclestrengthwas
obtainedinNewton(N)usingthebreak-techniquewithaportableHHD(MicroFET2TM,
HogganScientificLLC.,SaltLakeCity,Utah,UnitedStates)includinga4cmwidetransducer
pad.Inthisprocedure,theraterappliedaresistancethatwassufficienttocounteracttheforce
generatedbytheparticipant,afterwhichtheratergraduallyovercametheparticipants’force
andstoppedthemomentthelimbgaveway.Thelever-armtothecentreofthepad(22cm)
wasusedtocalculatethehipabductiontorquevalueinNewtonmetre(Nm).
Followingawarming-upofonesubmaximalcontraction,allparticipantsperformedthree
maximalcontractionsfor3to5secondswitha1-minuterestintervalforeachlimb[22,24].
Thehighestscoreofthethreemaximalcontractionswasusedforanalysis[24].Duringall
strengthmeasurements,verbalencouragementwasgiven[22].
Statisticalanalysis. Participantcharacteristicsincludingsex,age,levelofamputationand
thelengthoftheresiduallimbweredescribed[29].Theresiduallimblength(cm)wasmea-
suredfromcrotchtothemostdistalendoftheresiduallimb.Thetorquevalues(Nm)werecal-
culatedforboththeresiduallimbandthesoundlimb.Thedifferenceinmuscletorque(Nm)
betweenthetestandtheretestwascalculated.Categoricaldatawerepresentedasexactnum-
bersandpercentageswerecalculatedforthevariouslevels.Forthecontinuousdata,means
andstandarddeviationswerecalculated.
Reproducibility(test-retest)wasdividedinreliabilityandagreementparameters[30].
Reliabilitywastestedusingtheintraclasscorrelationcoefficient(ICC).ICC’swerecalculated
usingatwo-waymixedeffectmodel(ICC3.1 ).with95%confidenceintervals(CI).The
agreement
InterpretationofICCvalueswasbasedonguidelinesofferedbyByrt[31]:0.01–0.20poorreli-
ability,0.21–0.51slightreliability,0.41–0.60fairreliability,0.61–0.80goodreliability,0.81–
0.92verygoodreliability,and0.93–1.00excellentreliability.Standarderrorofmeasurement
(SEM )andthesmallestdetectablechange(SDC )werecalculatedtoassess
agreement agreement
agreement.Bothareexpressedintheunitofthemeasurement(Nm).TheSEMwascalculated
p p
asSEM = σ2 = (σ2 +σ2 )[32].Thevarianceduetosystematicdifferences
agreement error o residual
betweentheobservers(σ2 )andtheresidualvariance(σ2 )wereobtainedfromthevar-
o residual p
companalysis[32].TheSEM wasusedtocalculatetheSDC =1.96(cid:3) n(cid:3)
agreement agreement
SEM[30].Inthisformula‘n’referstothenumberofmeasurements,whichistwoinourstudy
[30].Additionally,theSEM%andSDC%werecalculatedasoutcomesindependentofthe
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Fig2.Assessmentset-up.A:Handhelddynamometer-technique1;B:Handhelddynamometer-technique2,
indefaultsupineposition.
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unitofmeasurement.TheSEM%andSDC%werecalculatedbydividingtheSEMandthe
SDC,respectively,bytheaveragetorquevalueofthetestandtheretestandthenmultiplying
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Table1. Participantcharacteristics.
Participantcharacteristics Phase1 Phase2 Phase3
HHD-technique1 HHD-technique2
Groupa Groupb
n=26 n=44 n=30 n=7
Sex(male),n(%) 20 (77) 28 (64) 18 (60) 4 (57)
Age(yrs),mean(SD) 51.7 (15.0) 53.9 (12.7) 33.1 (15.6) 22.0 (1.9)
Amputationlevel
-Transfemoralamputation,n(%) 18 (69) 35 (80) NA NA
Lengthresiduallimb(cm),mean(SD) 21.4 (3.7) 21.1 (4.4) NA NA
-Throughkneeamputation,n(%) 1 (4) 1 (2) NA NA
-Transtibialamputation,n(%) 7 (27) 7 (16) NA NA
-Footamputation,n(%) NA 1 (2) NA NA
HHD:handhelddynamometer;Yrs:Years;cm:Centimetre;SD:Standarddeviation
https://doi.org/10.1371/journal.pone.0179887.t001
by100[21,23].ABland-Altmanplotwasconstructedtodetermineiftherewasbiasinmea-
surementerror[33,34].Thisplotshowstheraterdifferenceagainstthemeanmuscletorque.
Theplotvisualisestherelationshipbetweenthemeasurementerrorandtheobservedvalue
includingthepresenceofsystematicbiasandbiasrelatedtothemagnitudeofhipabduction
strength[34].The95%limitsofagreement(95%LoA)wereshownintheplot(meandiffer-
ence±1.96SDofthedifference).AllanalyseswereperformedusingIBMSPSSStatisticsv22
(SPSSInc.,Chicago,Illinois,UnitedStates).Inallcases,twosidedp-values<0.05wereconsid-
eredtobestatisticallysignificant.
Results
Weincluded26participants(20men)withalowerextremityamputation(Table1).The
meanageofthisgroupwas52years(range:24–80years).Wedidnothavetoadjustthede-
faultlever-armof22cminanyoftheincludedparticipants(n=18)withatransfemoral
amputation.
Thetest-retestreproducibilityofHHD-technique1issummarisedinTable2.Wefound
fairtoverygoodreliability(ICC3.1 :0.80,95%CI:0.58–0.91)fortheresiduallimband
agreement
verygoodtoexcellentreliability(ICC3.1 :0.92,95%CI:0.83–0.97)forthesoundlimb.
agreement
TheSEMwas5.4Nmand3.1NmandtheSDCwas15.1Nmand8.6Nmintheresiduallimb
Table2. Phase1:Test-retestreproducibilityHHD-technique1.
Testedlimb Test(Nm) Retest Difftest-retest 95%LoA ICC3.1 (95% SEM SEM% SDC SDC%
agreement agreement
(Nm) (Nm) (Nm) CI)
agreement
mean mean(SD) mean(SD) (Nm) (Nm)
(SD)
Residuallimb 57.5 60.8(12.9) -3.3(7.1) -17.2;10.6 0.80(0.58–0.91)* 5.4 7.4 15.1 25.5
(n=26) (11.0)
Soundlimb 56.5 58.0(11.0) -1.4(4.2) -9.6;6.8 0.92(0.83–0.97)* 3.1 5.4 8.6 15.0
(n=26) (11.0)
HHD:handhelddynamometer;Nm:Newtonmetre;SD:Standarddeviation;Diff:Difference;LoA:limitsofagreement;ICC:Intraclasscorrelationcoefficient;
CI:Confidenceinterval;SEM:Standarderrorofmeasurement;SDC:Smallestdetectablechange
%:Percentage
*:p<0.001
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Hipabductionstrengthmeasurementtechnique
Fig3.Bland–Altmanplotsforwithin-raterdifferencesandtheirrelationtothemagnitudeofhip
abductionstrengthmeasuredwithHHD-technique1.Nm:Newtonmetre;Thesolidlinerepresentsthe
meandifference(systematicbias)andthedashedlinesillustratethe95%limitsofagreement(mean
difference±1.96SDofthedifference).
https://doi.org/10.1371/journal.pone.0179887.g003
andthesoundlimb,respectively.TheSEM%was9.1%and5.4%andtheSDC%was25.5%
and15.0%intheresiduallimbandthesoundlimb,respectively.The95%LoAwas-17.2to
10.6Nmand-9.6to6.8Nmfortheresiduallimbandthesoundlimb,respectively(Table2
andFig3).
Interpretationoftheresults. ThereproducibilityofHHD-technique1seemedgoodand
nowithin-raterbiaswaspresent,buttheresultsquestionedtheinternalvalidityofthemea-
surement.Themeanhipabductiontorqueoftheresiduallimbandsoundlimbwerealmost
similar(Table2),whichdidnotcorrespondentwithourobservationsduringwalking.Further-
more,theseresultswereunexpectedasnopreviousresearchreportedonthese[7,8].Inthe
residuallimb,Ryseretal.[8]foundadeficitof28%inthehipabductormuscletorqueand
Kowaletal.[7]foundadeficitof15%inthehipextensormuscletorquecomparedtothe
soundlimb.Weidentifiedtwopossibleconfounderswhichcouldhaveinfluencedthevalidity:
1)inconsistentparticipants’fixationonthetablebecauseofdifferencesbetweenparticipants’
capacitytofixatethemselvesonthetablewitharesiduallimborasoundlimb,and2)therela-
tivehighmusclestrengthvaluesduetotheuseoftheshort-lever-arm(22cm)andthebreak-
technique[20].Highmusclestrengthvaluescanalsoinfluencetheparticipants’fixationonthe
tableandmayhaveledtobiasedresultsbecausethestrengthoftheraterwillmorelikelyinflu-
encetheoutcome[35].Becauseofthesefindingsandpossibleconfoundersweadjustedthe
HHD-techniqueforthenextphase,resultinginHHD-technique2.
Phase2:Test-retestandinter-raterreproducibilityofHHD-
technique2
Methods
Theaimofthisphaseofthestudywastodeterminethewithin-sessiontest-retestandinter-
raterreproducibilityofHHD-technique2.WiththisHHD-techniquewestrivedtogather
internallyvalidoutcomesbydecreasingthetorquevaluesandincreasingtheparticipants’fixa-
tiononthetable(Fig2B).Therefore,wechangedtotheuseofamake-techniqueandtheuseof
additionalfixation-belt.Apotentialadvantageofusingthemake-techniqueisthatitreduces
theinfluenceofthestrengthoftheraterontheoutcomes,whereasabreak-techniqueproduces
highertorquevalues[36,37].
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Participants. Allconsecutiveindividualswithin30months,withalowerextremityampu-
tationwhowereinvitedforapre-operativeassessmentforabone-anchoredprosthesis
betweenMay2014andOctober2016wereeligibleforthispartofthestudy(Fig1)[38].Awrit-
teninformedconsentwasobtainedfromallparticipantspriortotheassessment.Thestudy
wasconductedaccordingtotheprinciplesoftheDeclarationofHelsinki(64thversion,19-10-
2013).Theprotocolofthisphaseofthisstudy(registrationnumber2014/196)wasapproved
bytheEthicsCommitteesoftheRadbouduniversitymedicalcentre.
Studyprocedure. First,thetest-retestassessmentswereperformedbythefirstauthor
(RL).Second,anexperiencedcolleague(GvH)performedanadditionalassessmenttotestthe
inter-raterreproducibility.Allassessmentswereperformedconsecutivelyinonesessionon
thesameday.Allassessmentsstartedwithmusclestrengthtestingoftheleftlimbfollowedby
therightlimb.Theparticipantswereofferedsufficienttime(atleast1minute)torestbefore
themusclestrengthtestofeachlimbandbetweentheassessments.Themusclestrengthvalue
wasnotvisiblefortheratersduringthetestasthescreenoftheHHDwaspositioneddown-
wards(Fig2B),todecreasethechanceofmeasurementbias.
Testingprocedure. ThetestingprocedureofHHD-technique2wassimilartoHHD-tech-
nique1,withtheexceptionofthefollowing:1)amake-techniquewasusedand2)anaddi-
tionalfixation-beltatthelevelofthepelvistofixatetheparticipantonthetablewasusedto
preventsliding(Fig2B).ThiskindoffixationhaspreviouslybeendescribedbyPuaetal.[22].
Themake-techniqueinvolvedaresistance,appliedbytherater,thatwassufficienttocounter-
acttheforcegeneratedbytheparticipant.Theparticipantwasinstructedtograduallyincrease
theforceaimingatamaximalcontractionafter3to5seconds.
Statisticalanalysis. Participantcharacteristicswerecalculatedandpresentedinthesame
wayasdescribedinphase1ofthestudy.Thetorquevalues(Nm)ofboththeresiduallimband
thesoundlimbwerecalculated.Thedifferenceinmuscletorque(Nm)withinthetest-retest
andwithintheinter-raterassessmentwascalculated.ICC’swerecalculatedusingatwo-way
mixedeffectsmodel(ICC3.1 )with95%CIforthetest-retestreliabilityandusinga
agreement
two-wayrandomeffectsmodel(ICC2.1 )fortheinter-raterreliability[32,34].The
agreement
sameparametersofagreementcalculateinphase1(SEM ,SDC ,SEM%and
agreement agreement
SDC%)werecalculatedinthisphase,forboththetest-retestandtheinter-raterreproducibil-
ity.Thepresenceofbiasinmeasurementerrorwasassessedusingthe95%LoA.Allanalyses
wereperformedusingIBMSPSSStatisticsv22(SPSSInc.,Chicago,Illinois,UnitedStates).In
allcases,twosidedp-values<0.05wereconsideredtobestatisticallysignificant.
Results
Weincluded44participants(28men)withalowerextremityamputation(Table1).Themean
ageofthisgroupwas54years(range:27–78years).In3outof35participantswithatransfe-
moralamputationwehadtoadjustthedefaultlever-armfrom22cmto18cm.
Thetest-retestreproducibilityofHHD-technique2issummarisedinTable3.Thetest-
retestreliabilitywasexcellentforboththeresiduallimb(ICC3.1 :0.96,95%CI:0.93–
agreement
0.98)andthesoundlimb(ICC3.1 :0.97,95%CI:0.94–0.99).TheSEMwas4.7Nmand
agreement
3.9NmandtheSDCwas12.9Nmand10.9Nmintheresiduallimbandthesoundlimb,
respectively.TheSEM%was8.3%and5.7%andtheSDC%was22.7%and16.0%intheresid-
uallimbandthesoundlimb,respectively.The95%LoAwas-14.1to10.9Nmand-12.4to7.6
Nmfortheresiduallimbandthesoundlimb,respectively(Table3andFig4).
Theinter-raterreproducibilityofHHD-technique2issummarisedinTable4.Theinter-
raterreliabilitywasfairtoexcellentfortheresiduallimb(ICC2.1 :0.92,95%CI:0.59–
agreement
0.97)andverygoodtoexcellentforthesoundlimb(ICC2.1 :0.92,95%CI:0.84–0.96).
agreement
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Table3. Phase2:Test-retestreproducibilityHHD-technique2.
Testedlimb Test(Nm) Retest Difftest-retest 95%LoA ICC3.1 (95% SEM SEM% SDC SDC%
agreement agreement
(Nm) (Nm) (Nm) CI)
agreement
mean mean(SD) mean(SD) (Nm) (Nm)
(SD)
Residuallimb 56.1 57.8(23.3) -1.6(6.4) -14.1;10.9 0.96(0.93–0.98)* 4.7 8.3 12.9 22.7
(n=44) (22.9)
Soundlimb 67.0 69.4(24.6) -2.4(5.1) -12.4;7.6 0.97(0.94–0.99)* 3.9 5.7 10.9 16.0
(n=44) (24.5)
HHD:handhelddynamometer;Nm:Newtonmetre;SD:Standarddeviation;Diff:Difference;LoA:limitsofagreement;ICC:Intraclasscorrelationcoefficient;
CI:Confidenceinterval;SEM:Standarderrorofmeasurement;SDC:Smallestdetectablechange
%:Percentage
*:p<0.001
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TheSEMwas6.9Nmand7.6NmandtheSDCwas19.2Nmand21.2Nmintheresiduallimb
andthesoundlimb,respectively.TheSEM%was11.6%and11.0%andtheSDC%was32.8%
and30.8%intheresiduallimbandthesoundlimb,respectively.The95%LoAwas-20.9to7.3
Nmand-23.9to16.5Nmfortheresiduallimbandthesoundlimb,respectively(Table4and
Fig4).
Themeasurementsofbothrater1asrater2identifiedanasymmetryinmuscletorque
betweenthetwolimbs.Themuscletorqueoftheresiduallimbwas11to16%lowerthanthe
muscletorqueofthesoundlimb.
Interpretationoftheresults. Thetest-retestreproducibilityofHHD-technique2was
good.Thereliabilityhadincreased(ICC3.1 :0.96–0.97versusICC3.1 :0.80–
agreement agreement
0.92)andtheSEMwassimilar(3.9–4.7Nmversus3.1–5.4Nm),comparedtoHHD-technique
1(Tables2and3).TheSDCoftheresiduallimbwasbetter(12.9Nmversus15.1Nm)andthe
SDCofthesoundlimbwasslightlyworse(10.9Nmversus8.6Nm),relativetoHHD-tech-
nique1.Nowithin-raterbiaswasfound,butthereweresuspicionsforsystematicbiasandbias
relatedtothemagnitudeofthemuscletorquewithintheinter-ratertest,inparticularforthe
testoftheresiduallimb.Onaverage,thevaluesofthesecondraterwerehigherthanthose
fromthefirstrater.Thedifferencebetweenratersincreasedwhenthesubjectsexhibitedlarger
hipabductionstrength(Fig4).
Wefoundamuscletorquedeficitupto16%intheresiduallimbcomparedtothesound
limb.Thisisinlinewithpreviousresearch,wheredeficitsof15to28%aredescribed[7,8].
BasedontheseresultsweweremoreconfidentthattheinternalvalidityofHHD-technique2
wassuperiortoHHD-technique1.TotesttheinternalvalidityofHHD-technique2,phase3
ofthisstudywasconducted.
Phase3:ConcurrentvalidityofHHD-technique2
Methods
TheaimofthisphasewastodeterminetheconcurrentvalidityofHHD-technique2usingan
isokineticdynamometer.IntheHHDassessmentthedefaultparticipants’positionwasa
supineposition,agravityneutralisedposition[22],topreventmeasurementbiasduetodiffer-
entweightoftheresiduallimbandsoundlimb.Thedefaultpositionforparticipantsduring
theisokineticdynamometerassessmentwasaside-lyingposition.Thiscouldnotbechanged,
thereforethisphaseofthestudyinvolvedtwoparts(Fig1):1)assessmentoftheconcurrent
validityofHHD-technique2insupinepositionand2)assessmentofthehipabduction
PLOSONE|https://doi.org/10.1371/journal.pone.0179887 June22,2017 9/19
Hipabductionstrengthmeasurementtechnique
Fig4.Bland–Altmanplotsforwithin-raterandbetween-raterdifferencesandtheirrelationtothe
magnitudeofhipabductionstrengthmeasuredwithHHD-technique2.Nm:Newtonmetre;Thesolidline
representsthemeandifference(systematicbias)andthedashedlinesillustratethe95%limitsofagreement
(meandifference±1.96SDofthedifference).
https://doi.org/10.1371/journal.pone.0179887.g004
strengthusingHHD-technique2inside-lyingposition.Theaimofthesecondpartwastorule
outbiasresultingfromoftheparticipants’positiononthetable.
Participants. ThisphaseofthestudywasconductedattheHANUniversityofApplied
Sciences.AllphysiotherapystudentsoftheHANandtheirrelativeswereeligibleforthispart
ofthestudy.Theywererecruitedwithinatimeperiodofthreemonthsusingposters,leaflets
andsocialmedia.Allincludedparticipantswereassessedinsupineposition(groupa).
Table4. Phase2:Inter-raterreproducibilityHHD-technique2.
Testedlimb Tester Tester2 Difftest-retest 95%LoA ICC2.1 (95% SEM SEM% SDC SDC%
agreement agreement
(Nm) (Nm) (Nm) (Nm) CI)
agreement
mean(SD) mean(SD) mean(SD) (Nm) (Nm)
Residuallimb 56.1(22.9) 62.9(26.1) -6.8(7.2) -20.9;7.3 0.92(0.59–0.97)* 6.9 11.6 19.2 32.3
(n=44)
Soundlimb 67.0(24.5) 70.7(27.9) -3.7(10.3) -23.9;16.5 0.92(0.84–0.96)* 7.6 11.0 21.2 30.8
(n=44)
HHD:handhelddynamometer;Nm:Newtonmetre;SD:Standarddeviation;Diff:Difference;LoA:limitsofagreement;ICC:Intraclasscorrelationcoefficient;
CI:Confidenceinterval;SEM:Standarderrorofmeasurement;SDC:Smallestdetectablechange
%:Percentage
*:p<0.001
https://doi.org/10.1371/journal.pone.0179887.t004
PLOSONE|https://doi.org/10.1371/journal.pone.0179887 June22,2017 10/19