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UniversityofIowaUniversityofIowaIowaResearchOnlineIowaResearchOnlineThesesandDissertationsSummer2013DevelopmentofanovelbalanceassessmenttoolanditsDevelopmentofanovelbalanceassessmenttoolanditsvalidationinthestudyofpatientswithsymptomaticspinalvalidationinthestudyofpatientswithsymptomaticspinaldeformitydeformityMonicaPaliwalUniversityofIowaFollowthisandadditionalworksat:https://ir.
uiowa.
edu/etdPartoftheBiomedicalEngineeringandBioengineeringCommonsCopyright2013MonicaPaliwalThisthesisisavailableatIowaResearchOnline:https://ir.
uiowa.
edu/etd/4891RecommendedCitationRecommendedCitationPaliwal,Monica.
"Developmentofanovelbalanceassessmenttoolanditsvalidationinthestudyofpatientswithsymptomaticspinaldeformity.
"MS(MasterofScience)thesis,UniversityofIowa,2013.
https://doi.
org/10.
17077/etd.
z69tz6syFollowthisandadditionalworksat:https://ir.
uiowa.
edu/etdPartoftheBiomedicalEngineeringandBioengineeringCommonsDEVELOPMENTOFANOVELBALANCEASSESSMENTTOOLANDITSVALIDATIONINTHESTUDYOFPATIENTSWITHSYMPTOMATICSPINALDEFORMITYbyMonicaPaliwalAthesissubmittedinpartialfulfillmentoftherequirementsfortheMasterofSciencedegreeinBiomedicalEngineeringintheGraduateCollegeofTheUniversityofIowaAugust2013ThesisSupervisors:AssociateProfessorSergioMendozaProfessorNicoleGroslandGraduateCollegeTheUniversityofIowaIowaCity,IowaCERTIFICATEOFAPPROVALMASTER'STHESISThisistocertifythattheMaster'sthesisofMonicaPaliwalhasbeenapprovedbytheExaminingCommitteeforthethesisrequirementfortheMasterofSciencedegreeinBiomedicalEngineeringattheAugust2013graduation.
ThesisCommittee:SergioMendoza,ThesisSupervisorNicoleGrosland,ThesisSupervisorDavidWilderLauraFreyLawTae-HongLimiiTomyparentsandmybrotheriiiACKNOWLEDGEMENTSIwouldliketotakethisopportunitytothankeveryonewhoassistedmethroughoutthedevelopmentandexecutionofthisproject.
IamthankfultoDr.
SergioMendozaforbeingmyadvisor.
Hisconstantmotivationandguidancehashelpedmeenhancemyknowledgeandunderstanding.
IwouldliketoacknowledgeDr.
ChristopherGravesforhisassistanceinthedevelopmentofthedataacquisitionsoftware.
IappreciatethehelpofMs.
RachelNashinrecruitingsubjectsforthisstudy.
IwouldliketothankDr.
DavidWilderforhisguidanceinthedevelopmentofthepointloadingdevice.
IamthankfultoDr.
LauraFreyLawforherinvaluableinputinthecalibrationprocedure.
IwouldalsoliketothankDr.
NicoleGroslandandDr.
AsgharBhattifortheirvaluableassistanceandguidanceindifferenttechnicalaspectsoftheproject.
Finally,Iwouldliketothankmyparents.
Theyhavebeenaconstantsourceofinspirationandencouragement.
Iamdeeplythankfultomyfriendsfortheirlovingsupportthroughoutmystrugglesandtheirappreciationonmyaccomplishments.
ivTABLEOFCONTENTSLISTOFTABLES…viLISTOFFIGURES…viiCHAPTER1:INTRODUCTION…1StatementoftheProblem…1PosturalStabilityandBalance1AssessmentofBalance…2Aims…3BalanceinPatientswithSpinalDeformity…4SpecificHypotheses…6CHAPTER2:LITERATUREREVIEW…7PosturalInstability…7BalanceAssessmentScales…8ForcePlateTechnologyandWiiBalanceBoard…9SpinaldeformitiesandSagittalImbalance…10CompensatoryMechanisms…11ConeofBalance…12ArmPositionforLateralRadiographAcquisition…12CHAPTER3:MATERIALSANDMETHODS…18DataAcquisition…18Calibration…19PointLoadingDevice…19CalibrationProcedure…20SignalProcessingandOutputParameters…23ClinicalStudy…25Subjects…25Trials…26Analysis…26StatisticalAnalysis…27CHAPTER4:RESULTS…34Calibration…34RepresentativePlot…35ComparisonofPathLengthamongPatientsandControls………………36ComparisonofVelocityamongPatientsandControls…36CHAPTER5:DISCUSSION…49vClinicalTestingandValidation…50RepresentativePlot…50ComparisonofSwayParametersinPatientGroupsandControl.
.
51SignificanceofStudyingBalanceinSpinalDeformities……….
.
53LimitationsandFuturework…53LimitationsofWBB…53ValidityoftheSwayParameters…54APPENDIXA:ACRONYMS…55APPENDIXB:MATLABCODE…56REFERENCES…59viLISTOFTABLESTable1.
Subjectgroups…25viiLISTOFFIGURESFigure1.
Sagittalbalance-A.
BalancedB.
Imbalanced…14Figure2.
Compensatorymechanisms[Source-CBarreyetal.
2011]3015Figure3.
Pelvicretroversion[Source-Mendoza-LattesS.
etal2010]33………….
.
16Figure4.
Coneofbalance[Source-DuboussetJ1994]1317Figure5.
Screenshotofcustomgraphicuserinterface(GUI)28Figure6.
Pointloadingcalibrationdevice…29Figure7.
Calibrationofgroundreactionforce…29Figure8.
COP(X,Y)Calibrationsetup…30Figure9.
PowerspectraldensityoftheCOPsignal…31Figure10.
Rawdata,filtereddataanddown-sampleddata…32Figure11.
FeetpositioningontheWBB…32Figure12.
Standingposition-handsonsides(30sec)33Figure13.
Correlationbetweenthebottom-leftsensorforcewithappliedforce……39Figure14.
Correlationbetweenthebottom-rightsensorforcewithappliedforce…39Figure15.
Correlationbetweenthetop-rightsensorforcewithappliedforce…….
.
.
40Figure16.
Correlationbetweenthetop-leftsensorforcewithappliedforce……….
40Figure17.
Linearityerrorforonefullcycleofloading41Figure18.
Hysteresiscurveforonefullcycleofloadingandunloading………….
.
.
42Figure19.
Graphrepresentingmeasuredforce(a.
u.
)vs.
outputforce(lbs)……….
.
.
43Figure20.
GraphbetweentheKnownXvs.
thecalibratedvalueofX(Xc)………44Figure21.
GraphbetweentheKnownYvs.
thecalibratedvalueofY(Yc)…………45Figure22.
Representativegraphbetweenacontrolandapatient…46viiiFigure23.
Graphcomparingpathlengthbetweencontrolandpatientgroups…….
.
.
47Figure24.
Graphcomparingswayvelocitybetweencontrolandpatientgroups….
.
.
481CHAPTER1:INTRODUCTIONStatementoftheProblemPosturalStabilityandBalanceBalanceisdefinedastheabilityofhumanbodytomaintaincenterofgravitywithinthebaseofsupporttopreventfalling1.
Maintenanceofbalancerequirescoordinationbetweensensorineuralandmusculoskeletalsystems.
Anumberofmedicalconditionscanimpairfunctionofanyofthesesystemsandtherebypredisposeindividualstoposturalinstability,lossofbalanceandfalling.
Aging,obesity,vestibulardeficits,neurologicconditions,abnormalspinalcurvatures,peripheralneuropathiesetc.
areknowntoaffectbalance.
Thereisahighprevalenceoffallsamongtheelderly.
Fallsinolderadultsareamajorcauseofdeath,fracturesandtraumaticbraininjuriesthataffectqualityoflifeandindependentliving.
Fallsresultingfromposturalinstabilityandimpairedbalanceputconsiderableeconomicburdenonhealthcaresystemandisamajorpublichealthissue2.
Obesitychangesthemassdistributionbetweenbodysegmentsandisassociatedwithpoorposturalcontrol.
Higherbodymassindex(BMI)resultsininstabilityinmedio-lateralandanterior-posteriordirections.
Obeseolderadultshavehigherprevalenceoffallsascomparedtotheirnormalweightcounterparts3.
Neurologicdisorderssuchasmultiplesclerosis4,parkinson'sdisease,cerebralpalsyetc.
aresignificantlyassociatedwithanincreasedinstabilityandfallrisk.
Arthritisandinjurytolowerlimbssuchasanklesprainsandotherorthopedicpathologiesareknowntocontributetobalanceproblems.
Spinaldeformitiesshiftthelocationofcenterofgravityinanterior-posterioror2medio-lateraldirections,therebychallengingthebalancesystem.
Therefore,evaluationofposturalinstabilityandassessmentofbalanceisofcriticalvalueinclinicalpractice.
AssessmentofBalanceAnumberofbalancemeasurementscaleshavebeendeveloped.
Scalesbasedonself-reportedquestionnairesregardingfallhistory,activitylevelsetc.
,othersbasedonfunctionalevaluationsuchasRombergtest,Forwardreachingtest,Timedupandgo,PerformanceorientedMobilityAssessment(POMA),Bergbalanceetc.
arecommonlyusedinclinicalpractice5,6,7.
Thesetestsareaccessibleinvariousclinicalsettingsandeconomicallyfeasibleintermsoftime,cost,laborandequipment.
Althoughfunctionaltestsareadvantageousbecauseoftheirpracticality,simplicityandinexpensivenature,thesedonotprovideinformationandcannotidentifyminorchangesordamagesinbalancecontrolsystem.
Onlyafewscaleshavebeenshowntohavesignificantassociationswithincreasedfallrisks.
Thereisnotenoughsupportingevidenceinfavorofanyspecificbalancemeasurementscaleinassessingtheriskoffallfromtheoutcomescoreofthescale.
Moreover,theresultsofthebalancetestscandifferdependinguponthediagnostictestused8.
Forceplatesareconsideredgold-standardforassessmentofbalance.
Centerofpressure(COP)isthelocationofthegroundreactionforcethatcanberecordedthroughforceplates.
Itisanaccurateandreliablemeasureofbalanceandstability.
Forceplatesprovideinformationaboutthemedio-lateralandanteriorposteriordisplacementsofCOPsignal.
COPcanbeusedtostudytheeffectofsensorineuralandmuscularsystemsincontrolofbalance.
AnalysisofCOPsignalcanprovideinsightintheuseofdifferent3strategiesformaintainingbalance.
OutputparameterssuchasCOPpathlengthandareaaredirectmeasuresofposturalstability.
Despiteitsadvantages,forceplatetechnologyisseldomusedoutsidelaboratoriesandresearchenvironmentsbecauseofitsexpensiveinstrumentationandoperationalcomplexity.
Also,theprocessofoperationistimeconsumingandrequiresatrainedtechnicianforitsuseandinterpretationofresults.
Thesefactorslimititsavailabilityandusebycliniciansandtherapists.
AWiiBalanceBoard(WBB)isanaccessorytotheNintendoWiigameconsole.
ItconsistsoffourpressuretransducersandcanbeprogrammedtoperformasaforceplatebycapturingCOPsignal.
Itisaninexpensive,widelyavailableandportabledevice.
Itsvalidityandreliabilityinassessmentofstandingbalanceagainstlaboratorygradeforceplatformshasbeentestedinliterature9.
Excellenttest-retestreliabilityandintra-classcorrelationcoefficienthasbeenreported.
Henceitcanbeusedasanalternativeconsumerlevelforceplate9,10.
ThepurposeofthisprojectwastoprogramaWBBtotrackCOPsignalusingdataacquisitionsoftware(LabView)andtodevelopanintegrated,graphicaluserinterface(GUI)basedsystemthatcanbeusedtoassessbalanceintheclinicalsetting.
AimsThestudyconsistedofthefollowingfouraims.
1.
Developuserfriendlysoftwarethatfunctionstocapture,processanddisplayCOPsignalfromtheWBB.
42.
DevelopacalibrationprotocolandtesttheperformanceofWBBintermsoflinearityandhysteresis.
3.
Calculatebalanceparameters:PathLength,SwayAreaandSwayVelocities.
4.
Clinicaltestingofthesoftware:Prospectivecohortstudy,comparingbalanceparametersbetweenaknownbalancedeficitpopulation-spinaldeformitypatientsvs.
age,BMIandsexmatchedcontrols.
BalanceinPatientswithSpinalDeformitySpinaldeformitiesencompassavarietyofconditionsthataffectthenormalspino-pelvicalignmentincoronalorsagittalplaneorlongitudinalaxis(rotationaldeformity).
Commonpresentingsymptomsincludeprogressivedeformity,paininbackandlowerextremities11.
Thecenterofbalanceinsagittalplanedeformitypatientsiswidelystudiedradio-graphicallyusingsagittalverticalalignment(SVA).
Themeasurementsareperformedradio-graphicallybydroppingaplumblinefromCervical7vertebra,andmeasuringthehorizontaldistancefromthecenteroftheplumb-linetotheposterior-superiorcornerofSacral1vertebra.
Avarietyofchangesinthespine,pelvisandlowerextremitiesareobservedinpatientstocompensateforanteriorshiftinthegravityline.
Afewcompensatorymechanismsreportedinliteraturearereductionofthoracickyphosis,hyper-extensionofspinalsegments,retrolisthesisinspine,pelvicretroversion,andkneeflexionandankleextensioninlowerlimbs12.
Thesemechanismsappearprogressivelytocorrectincreasingimbalanceandbringtheaxisofgravityinphysiologicposition.
5JeanDubousset,firstintroducedtheconceptof'coneofbalance',referringtoastableregionofstandingposture,deviatingoutsidetheconeposechallengestobalancemechanisms13.
Theabilityofthehumanbodytomaintainthecenterofgravity(COG)withintheconeofeconomywithminimalenergyexpenditureresultsfromacomplexinteractionofsupra-andinfra-pelvicalignmentparameters.
Ofmanyspineandpelvicradiographicalignmentparameters,multiplestudiesshowthattrunkimbalancecorrelateswithpoorqualitylifeoutcomesscoresandprogressivelyworseninglowbackpain14,15,16.
TrunkimbalanceismeasuredbytheSVA(SagittalVerticalAlignment).
Thesecorrelationsdonotexplainsymptomsforeverycase,andtherearenotableexamplesofpatientswithseveredeformityandminimalfunctionalloss,aswellasotherswithnot-so-severedeformityandseverefunctionalloss14.
Thewayindividualpatientstackletrunkimbalancemaybevariableandmaydependonotherconstitutionalfactorssuchasage,baselinecardiovascularconditioning,andBMI.
TheaimofthisstudyistovalidateWBBbasednovelevaluationtoolforthestudyofadultspinaldeformitybyexaminingbalanceparametersincomparisonwithhealthycontrolpopulation.
Changesinposturalstabilityduetopresenceandseverityofsagittalimbalance(SVA)inrelationwithcompensatorymechanism-pelvicretroversionareanalyzed.
Oneofthefunctionsofspineinthebodyistotransferloadsfromupperbodytopelvisandlowerextremitiesinordertomaintainanuprightstandingposture.
Presenceofspino-pelvicmisalignmentwouldproducesomedegreeofposturalinstability.
ItishypothesizedthatalthoughcompensatorymechanismsmaycorrectforpositiveSVA,6assumingtheseposturesputshighenergydemandsonthemusculoskeletalsystemresultinginfatigue,painandposturalinstability.
Patientswithlowbackpainhaveademonstrablelargerposturalswaywithsmallerthoraco-lumbarmovements.
Thisrepresentsarigidposturalcontrolstrategy,maybeaprotectivemechanism,basedontheincreasinguseofanklebalancingstrategies17,18,19.
Inpatientswithtrunkimbalance,theparaspinalmusclesareatincreasedmechanicaldemand,andmaythusmimictherigidposturalcontrolstrategiesdescribedforlowbackpainpatients.
Similarly,thiswouldalsoreflectinincreasedposturalsway.
SpecificHypothesesH1=Pathlength,swayvelocityandswayareawillbehigherforpatientsthanincontrols.
Ithasbeentheorizedthatmechanismstocompensateforanatomicalsagittalplaneimbalanceinpatientsresultinposturesthatputhighmusculoskeletalloadsanddemandhigh-energyexpendituretomaintainthesepostures,consequentlyfatiguingthemusculatureandaggravatingpain.
H2=Pathlength,swayvelocityandswayareawillincreaseingroupswithprogressivesagittalimbalanceandpresenceofcompensatorymechanisms.
7CHAPTER2:LITERATUREREVIEWPosturalInstabilityMaintenanceofanerectpostureduringquietstandingrequiresacontinuouslyactingcontrolmechanismtopreventfromfalling.
Humanbalancecontrolduringquietstandinghasbeendescribedasaninvertedpendulumabouttheanklejoint1.
Maintenanceofbalancedependsonproprioceptionthroughsensoryandmotorsystems;posturalcontrolrequiresthecoordinationbetweenmusculoskeletalelementsofthebody.
Anumberofpathologiesareknowntoaffectthebalancesystem.
Variousstudieshavereportedthataging,neurologicdisorders,obesity,lowerlimbosteoarthritis,injury,abnormalspinalcurvaturesetc.
canresultinsignificantposturalinstability.
Agingisassociatedwithpoorneuromuscularcontrolandhighprevalenceofosteoarthritis10.
Fallsintheelderlyisapublichealthissue.
In2010,directmedicalcostsoffallswereestimatedtobe$30.
0billion.
Fallsinolderadultsareamajorcauseofdeath,fracturesandtraumaticbraininjuriesthataffectqualityoflifeandindependentliving20.
Prevalenceofobesityisgrowingrapidly.
In2009-2010,CDCreportedthatmorethanone-thirdoftheUSadultsareobese21.
Obesityisassociatedwithpoorposturalcontrol.
Higherbodymassindex(BMI)havebeenshowntoresultininstabilityinmedio-lateralandanterior-posteriordirections22,23.
Obeseolderadultshavehigherprevalenceoffalls(27%vs.
15%)ascomparedtotheirnormalweightcounterparts3.
Neurologicdisorderssuchasmultiplesclerosis4,parkinson'sdisease,cerebralpalsyaresignificantlyassociatedwithanincreasedinstabilityandfallrisk.
Spinaldeformitiesshiftthepositionofcenterofgravityinanterior-posteriorormedio-lateraldirections,therebychallenge8balancesystem24.
Since,balanceisaffectedasaresultofnumerousdiseaseprocessesofsuchwide-spreadoccurrence,evaluationofposturalinstabilityandassessmentofbalanceisimportant.
BalanceAssessmentScalesBalanceassessmentscalesdevelopedandwidelyusedinclinicsandrehabilitationcentersareoftenbasedonfunctionalperformanceoftheindividuals.
FewofthewidelyusedscalesthatarefoundaretheBergBalanceScale(Berg),theClinicalTestofSensoryInteractionandBalance(CTSIB),theFunctionalReachTest,theTinettiBalanceTestofthePerformance-OrientedAssessmentofMobilityProblems(Tinetti),theTimed"UpandGo"Test(TU>),PhysicalPerformanceTest(PPT),tandemstand,tandemwalk,oneleggedstanceetc.
Functionaltestsrequirethesubjecttoperformafewdaytodaytasksandassignascoretothetaskdependingonthetimetakentoperformthetaskorthelevelofdifficultyexperienced.
Thesetestsareusuallyeasytorun,costeffective,timeefficient,anddonotrequiremuchinstruments.
Thesecanbeadministeredinmostlyanyclinicalsettingbyanytherapist.
Duetothesereasons,functionalassessmenttestsarewidelyused.
However,thesetestshaveanumberoflimitations.
Thesetestsarehighlysubjective,oftendependingonself-reportedvalues.
Thevalidityandreliability,sensitivityandspecificityofthetestsarevariable.
Therecanbevariabilityinthetestresultdependingupontheselectionofthediagnostictestandselectedcutpoints.
Onlyafewscalessuchastandemstand,tandemwalk,oneleggedstanceetc.
havebeenshowntohavesignificantcorrelationwithfallrisk.
Noonescalehasbeenidentifiedtobebetteroverothersinquantifyingbalanceandassessingfallrisks8.
Thesetestsdonoprovide9informationaboutforcedistribution,whichunderlyingsysteminvolvedinbalancecontrolisdamagedorwhichmusclegroupsareinvolvedinmaintenanceofbalance.
ForcePlatetechnologyandWiiBalanceBoardGenerally,commerciallyavailable,laboratorygradeforceplatesarerecognizedasanoutstandingtoolforassessingbalanceduetotheirabilitytoaccuratelymeasureCOP.
COPsignalgivesthepointlocationofthegroundreactionforce.
ForceplatesprovidetheCOPdisplacementorexcursioninanterior-posteriorandmedio-lateraldirections.
COPsignalistheonlymajormeasureofbalancethatgivestheinformationaboutthecenterandmaintenanceofbalancefromthebiomechanicalpointofview.
Duringquietstanding,inordertoassumeasteadyposture,theCOPshouldliewithinthebaseofsupport,(i.
e.
theperimeterofthefeet).
ControlofCOPsignalintheanterior-posteriordirectionisbyanklemuscleswhilethemedio-lateralcontrolrequiresactivationofthehipmuscles.
TheCOPexcursions,asprovidedbytheforceplates,canbeanalyzedtoprovideinformationaboutactivityofdifferentmusclegroups.
Thesignalcanbeprocessedtoprovideoutputmeasuresofbalancesuchaspathlength,swayvelocityandareatoprovidedetailedpictureofinstability.
ResearchersinthepasthavealsousedthefrequencydomainanalysisoftheCOPsignaltostudybalance25.
However,therearelimitationstotheuseofsuchforceplatesoutsideresearchenvironments.
Highcost,non-portability,customsetupandtrainingrequiredforitsoperationhinderitswidespreaduse.
TheWBBhasbeenrecognizedasatoolthatcanbeprogrammedtomimicthefunctionofforceplatebasedtechnologybycapturingtheCOPsignal9,10.
Ithasbeenshowntohaveexcellentaccuracyandreliabilitywhencomparedwithtraditionalforce10platestodeterminecenterofpressureinbalancestudies9,10.
Thedeviceiswidelyavailable,costslessthan$100,isnotbulkyandthusisportable.
Clarketal.
9studiedtheperformanceoftheWBBagainstalab-gradeKistlerforceplate.
Thestudyrecruitedthirtyhealthyindividualswithoutanylowerlimbpathology.
ThesubjectswereaskedtostandontheWBBandforceplateinfourdifferentconditions:(1)singleleg,(2)doubleleg,(3)eyesopenand(4)eyesclosed.
Theoutputmeasure,pathlengthwasdefinedasthetotaldistancetravelledbytheCOPsignal.
TheWBBwasshowntoproducegoodtest–retestreliabilityforCOPpathlengthasstudiedbywithindeviceintraclasscorrelationcoefficients(ICC=0.
77–0.
89).
ThestudyconcludedthataWBBisavalidtoolforthestudyofstandingbalanceandcanbeusedasaconsumerlevelalternativetotheforceplate.
Historically,studyofbalanceinspinaldeformitypatientshasbeendoneviauseofradiography.
Sagittalplanedeformity,compensatorymechanismsforthecorrectionofimbalance,studyofbalanceusingradiographicparametersanditslimitationsunderscoringtheneedtostudybalanceusingCOPareintroducedinthefollowingsection.
SpinaldeformitiesandSagittalImbalanceTheprevalenceofspinaldeformityinindividualsovertheageof60yearsvariesbetween39%26,27and68%26,28.
Spinaldeformitiesencompassavarietyofconditionsthatalternormalanatomicalalignmentofspinein3D,i.
e.
coronalorsagittalplanesuchasscoliosis,kyphosis,spondylolisthesis,iatrogenicflatbacketc.
Adultidiopathicscoliosismaybecausedbyarthritisandprocessofaging,howevercasesofcongenitaland11adolescentscoliosisarealsofound.
Commonpresentingsymptomsincludeprogressivedeformity,paininbackandlowerextremities.
Sagittalverticalalignment(SVA)iswidelyusedtostudysagittalplanedeformities.
Itisacceptedasanimportantandreliablepredictorofhealthstatusintheadultswithspinaldeformity14.
Itismeasuredradio-graphicallybydroppingaplumblinefromthecenterofC7vertebra,andmeasuringthehorizontaldistancefromthecenteroftheplumb-linetotheposteriorcornerofS1endplate28.
Figure1showsSVAmeasurementinabalancedandanimbalancedspine.
NotethattheimbalancedspineismarkedbypositiveSVA.
Glassman14,15foundasignificantcorrelationbetweenpositiveSVAanddecreasedqualityoflifeinpatientswithsymptomaticspinaldeformity.
CompensatoryMechanismsSagittalplanedeformitiesresultinginpositivesagittalimbalancehinderinassuminganerectstandingposture.
Avarietyofchangesinthespine,pelvisandlowerextremitiesareobservedinpatientstocompensateforanteriorshiftingravityline.
Afewcompensatorymechanismsreportedinliteraturearereductionofthoracickyphosis,byhyper-extensionofspinalsegmentsproximaltothespinaldeformity,retrolisthesisinspine,hipextension,andkneeflexionandankleextension30.
Thesemechanismsappearprogressivelytocorrectincreasingimbalanceandbringtheaxisofgravityinphysiologicposition31.
Figure2showsthevariouscompensatorymechanismsatthespine,pelvicorlowerlimblevelthatmaybepresentinpatientswithpositivesagittalimbalance.
Pelvicretroversionisthebackwardtiltofthepelvisoverthefemoralheads.
Itisthefirstmechanismtosetintocorrectforsagittalimbalance31.
Figure3ashowsaseverelyimbalancedspinewithpositiveSVA;Figure3bshowstheuseofpelvic12retroversiontocorrectimbalance.
Pelvictilt(PT)isdefinedastheanglesubtendedbytheverticalaxisoriginatingfromthecenterofthefemoralheadandthemidpointofthesacralendplate.
Itisapositionalparameterthatmeasuresthecompensationbypelvicrotation32.
ConeofBalanceJeanDuboussetfirstintroducedtheconceptof'coneofbalance',referringtoastableregionofstandingposture,wheretheenergyexpenditureforstanceisminimized.
Deviationsfromthisconeposechallengestobalancemechanisms13.
Figure4illustratesthe'coneofbalance'.
Inhumans,two-thirdsofthebodymassislocatedattwo-thirdsheightabovetheground.
Theabilityofthehumanbodytomaintainthecenterofgravity(COG)withintheconeofeconomywithminimalenergyexpenditureresultsfromacomplexinteractionofsupra-andinfra-pelvicalignmentparameters.
Theseparametersareinfluencedbytheflexibilityofthespineandjointsofthelowerextremities,neuro-muscularcontrol,strength,endurance,andbodyhabitus.
Itbecomesevidentthattheimpactofspinaldeformityonstanceismulti-factorial,andthuscannotbeexclusivelycorrelatedtostaticalignmentparameters.
Thuscenterofpressuremeasurementsbecomeparticularlyrelevantinthestudyofthefactorsthatinfluenceordeterminesymptomsinpatientswithspinaldeformity.
ArmPositionforLateralRadiographAcquisitionInnormalstance,weusuallyplaceourhandsonthesidesofourthighs.
Acquisitionoflateralradiographicimagesforstudyofthespinerequiresclearingofthehumerusfromtheproximalthoracicspineforvisualizationpurposes.
Armscrossedon13chest,elbowsflexedatvariousangles,armssupportedonthewall,fistsonclavicleetc.
arecommonlyusedpositionsindifferentinstitutions.
AnumberofstudiesaimedatevaluatingtheeffectofarmpositiononthoracolumbarspinalalignmentandSVA,attemptingtoidentifyanoptimal,functionalarmpositionarefoundinliterature.
ResultsofthesestudiesindicatedthatsomepositionsmaybebetterthanothersintermsofvarianceinSVAreadings;howevernoneofthepositionsrepresentedafunctionalstandingposition34,35,36,37.
Radiographyisaffectedbypositioningprotocolandthusnotareliableinevaluatingsagittalprofileandbalance.
Inadditiontothis,radiographyhasadegreeofinter-observerandintra-observervariance,representsspino-pelvicalignmentonlyasingleframeoftimeanddoesnotofferinformationonfootpositionorforcedistribution.
Althoughspine-pelvicparametersobtainedbyradiographicmeasurementsarewidelyusedinpractice,optimalwaytostudyglobalbalanceisusingforceplatesandassessingcenterofpressure(COP).
ThereiscontroversyovertheaccuracyofradiographicmeasurementsinrepresentingtruecenterofbalanceascomparedtoCOPonforceplates38,39.
14Figure1.
Sagittalbalance-A.
BalancedB.
Imbalanced15Figure2.
Compensatorymechanisms[Source-CBarreyetal.
2011]3016Figure3.
Pelvicretroversion[Source-Mendoza-LattesS.
etal2010]3317Figure4.
Coneofbalance[Source-DuboussetJ1994]1318CHAPTER3:MATERIALSANDMETHODSDataAcquisitionAWBBhasfourstraingaugetypetransducersateachcornerthatdetectandconvertforceintoelectricalsignal.
TheWBBhasinbuiltcircuitryconsistingofananalogtodigitalconvertorandaBCM2045chipforBluetoothconnectionwithanycomputer.
Customdataacquisitionsoftwarehadbeendevelopedusingastandardsoftwaretoolkit(LabView)tocapturetheforceoutputsfromeachsensorandisavailableasopensource40.
Buildingupontheopensourcecode,additionalsoftwarewaswrittentocalculateverticalgroundreactionforceandlocationoftheCOPcoordinates(X,Y)usingthefollowingequations.
Where-Fz:Totalgroundreactionforce,FTL:ForcefromTop-Leftsensor,FBL:ForcefromBottom-Leftsensor,FTR:ForcefromTop-Rightsensor,FBR:ForcefromBottom-Rightsensor.
NotethatthecoordinatesoftheCOP(X,Y)wererecordedintermsofforces.
However,thecalibrationoflocationofCOP(X,Y)wasperformedlatertoderiveX,Yinunitsofdistances.
AGraphicaluserinterfaceasshowninFigure5,wasdesignedcomprisingoffeaturessuchasdisplayofCOPsignalinrealtime,specificationofdatarecordingtime,19androutinesforsavingthedata.
DatawassavedinExcelformatandexportedtoMatLabforsignalprocessingandanalysis.
CalibrationPointLoadingDeviceTheprocessofcalibrationrequirespointloadingonthesurfaceoftheWBB.
Fewpointloadingmechanismsdevelopedforthispurposecanbefoundintheliterature.
BobbertandSchamhardt41usedasturdywoodenboardsupportedonaballstylusatonecornerforpointloading.
Weightswereloadedonthewoodenboardwhiletheboardwaskeptlevelbysupportingothercornersoutsidetheperipheryofforceplate.
Collinsetal.
employedaninstrumentedpoleforcalibratingforceplates.
Thepolehadaloadingplateatoneendtoputweights,conicaltipatthebasetoensureaxialloading.
Motiontrackingmarkersandaloadcellwereappliedtothepoletomonitorthe3Dorientationofthepoleandaxialforcerespectively42.
Inthisproject,tocalibrateWBB,apointloadingdevicewasdesigned.
Theworkingprincipleisthatthecenterofgravityofanequilateraltrianglepassesthroughitscentroid.
Thedeviceconsistsofanannulardiscsupportedonthreeconicalstainlesssteelpegs,withahollowverticalpoletoslidedowndiscweightsandacrylicsee-throughglasswithacross-wireinthemiddle.
[D.
G.
Wilder,personalcommunication,2012].
Figure6showsthepointloadingcalibrationdevice.
Consequently,thethreepegsestablishedtheverticesofanequilateraltrianglewithitscentroidcoincidingwiththecenterofthecross-wire.
Discweightscanbealignedontopofoneanotherduringloadingbyslidingthemdowntheverticalpole.
Theweights20restonannulardisc,whichisinturnsupportedbythepegs.
Thesupportreactionfromthegroundwillbeequallydistributedamongthethreepegs.
Thetipsoftheconicalpegswereroundedto1mminradius,toavoiddiggingorscratchingoftheWBBsurface.
CalibrationProcedureDataacquisitionsoftwarewasprogrammedtoreportforcesfromallforcesensors(top-rightTR,top-leftTL,bottom-rightBRandbottom-leftBL),groundreactionforceandCOPdisplacementinmedio-lateral(X)andanterior-posterior(Y)directions.
CalibrationoftheWBBwasatwo-stepprocessinvolving(1)calibrationofthegroundreactionforceand(2)calibrationofthelocationofCOP(X,Y).
I.
CalibrationofGroundReactionForceProtocol:Thefollowingstepswereperformedonallcornersoftheboard,ateachsensorindividually:1.
Afullcycleofloadingandunloadingofpointloadsof12N,34N,56N,78N,101N,123N,167N,212N,256Nwereappliedonthesensor(Figure.
9).
2.
Datawascollectedforthreeseconds.
ForcesfromeachsensorFTR,FTL,FBRandFBLwererecordedforeachtrial.
TotalgroundreactionforceFZwascalculatedas:FZ=FTR+FTL+FBR+FBL3.
Linearityofeachsensorwasstudiedbyregressionanalysisbetweenappliedloadandrecordedsensorforce.
4.
CalibrationfactorC,definedastheslopeofknownversusrecordedforceswascalculatedas.
215.
Percentfullscaleoutput(%FSO)hysteresiserror(%e(h))wascalculatedforeachcycleofloading,expressedas:()(||)Whereyup–outputduringupscaleloading,ydown–outputduringdownscaleloading,ymax–maximumoutput,ymin–minimumoutput.
Themaximumerrorofthefourcycleswasreported.
6.
%FSOlinearityerror(%e(l))wascalculatedforeachcycleofloadingas:()(||)WhereyL–Bestlinearregressionoutput,ytrue–Trueoutput,ymax–maximumoutput,ymin–minimumoutput.
Themaximumerrorofthefourcycleswasreported.
Figure7showstheloadingoftheweightsontheWBBsensorforthecalibrationofgroundreactionforce.
II.
CalibrationOfCenterofPressureLocationThecoordinatesofCOP(X,Y)onaforceplateaccordingtoKistler43isgivenbythefollowingequations:()()Where,Z=verticaldistancebetweenworkingplaneandX,Yplaneofforceplatform,Fx=TotalforceinXdirection,Fy=TotalforceinYdirection,22Fz:Totalverticalforce,FTL:Forcefromtop-leftsensor,FBL:Forcefrombottom-leftsensor,FTR:Forcefromtop-rightsensor,FBR:Forcefrombottom-rightsensor,CalX=halfthedistancebetweenthesensorsalongtheXaxisCalY=halfthedistancebetweenthesensorsalongtheYaxis.
TheWBBsensorscannotdetectforcesinthehorizontaldirections(FxandFy),henceadjustmentsintheCOP(X,Y)calculationsweremadetoaccountforlackofsensitivityinWBBtoshearforces.
ThefollowingprocedurewasperformedtoaccuratelydeterminethevaluesofCalXandCalYfortheWBB.
Agridof2cmby2cmwasplottedonthesurfaceoftheWBB.
Sixteendifferentpoints,fourpointsineachquadrantontheWBBwereselectedastrialpoints.
Loadsof12N,34N,56N,78N,101N,123N,167N,212N,256Nwereappliedoneachtrialpoint.
Atotalof144trialswereperformed.
Forcesfromeachsensor,totalgroundreactionforce,COP(X)andCOP(Y)locationsdatawererecordedfor3seconds.
Figure8showsthepointloadingdeviceplacedatX=-2cm,Y=2cmpointonthe2cmby2cmgridplottedonthesurfaceoftheWBB.
Duetotherectangulargeometryoftheboard,themedio-lateral(X)axisoftheboardislongerthantheanterior-posterior(Y)axis.
Hence,CalXandCalYwerecalculatedseparatelyasgivenbelow:()()ThecalibratedvaluesofX(Xc)andY(Yc)aregivenas:23()()()()Where,andCorrelationplotsbetweenKnownXvs.
XcandKnownYvs.
Ycwereproduced.
AveragepercentageerrorbetweenKnownandcalibratedvaluesofCOP(X,Y)wascalculatedas:||||SignalProcessingandOutputParametersCustomsoftwarewaswritteninMatLabforsignalprocessingandcalculationofoutputparameters.
COPdatawasimportedandpowerspectralanalysisusingFastFourierTransform(FFT)wasdonetofindnoisefrequencycomponentinthesignals.
Figure9showsthepowerspectraldensityoftheCOPsignal.
ThepeakinthegraphcorrespondstothefrequencyoftheCOPsignal.
Thecut-offfrequencyforthelowpassfilterwaschosentobe5Hztofilterouthigherfrequencynoise.
Azero-phaselag,eighthorderlowpassButterworthfilterwithacut-offfrequencyof5Hzwasdesignedtofilterthedata.
Ideally,thesamplingrateofdatacollectionbytheWBBis60Hz.
However,duetovariousreasonssuchaspoorqualityofthesensors,weakblue-toothconnectionthenumberofsamplescollectedpersecondmayvary.
TheaveragesamplingrateoftheWBBusedinthisstudywasfoundtobe54Hz.
Thedatawerethendownsampledto45HzusingsignalprocessinginMatLab.
Figure10showsa30secondlongrawCOPdata,24filtereddataanddownsampleddataversustimeframes.
Notethatthenumbersofframeswerereducedto1330from1620whenthesignalwasdown-sampledto45Hzfrom54Hz.
Followingoutputparameterswerecalculated:1.
Pathlength44–Pathlengthisthetotalvectordistancetravelledbythecenterofpressureduringatrial.
ThepathlengthinXandPathlengthinYwerealsocalculatedtoprovideinformationonthedirectionofmajorsway(medio-lateraloranterior-posterior).
2.
Swayarea(95%confidenceregion)44–Itmeasurestheareaoftheellipseformedby95%oftheX,Ycoordinatesaroundtheirmeanvaluesduringaspecifiedtimeunit.
Itisgivenas:()√()where-sxxandsyy-standarddeviationsinxandy,sxy-Covariancebetweenxandy,=3;n>120.
3.
RootMeanSquareVelocityinXandYandtotalRMSvelocity.
∑∑√()25ClinicalStudySubjectsNinety–sevenpatientswithspinaldeformities(namely,adultidiopathicscoliosis,kyphosis,spondylolithesisandiatrogenicflatback)wererecruitedfromtheOrthopaedicSpineClinic.
Patientsweresubdividedintofourgroupsbasedontheirsagittalimbalance(SVA)andPelvicTilt(PT)32.
Thirtyhealthyageandgendermatchedvolunteerswererecruited.
Individualswithhistoryofscoliosis,majorspineorlowerlimbinjuriesorsurgeries,diabetes,strokes,polio,neuromuscularorneurologicaldiseaseswereexcludedfromthestudy.
Controlsubjectswereincludedonlyiftheyreportedtobeabletowalkat-least5blocksunassisted.
Thefollowingtableliststhesubjectgroups,numberofsubjectsineachgroupandmeanageandBMI:S.
N.
SubjectGroupsNumberofsubjects(female,male)Age(years)Mean±S.
D.
BMI()Mean±S.
D.
1LowSVA(25)26(22females,4males)58±1626.
8±5.
03HighSVA(>5cm),LowPT(5cm),HighPT(>25)34(27females,7males)65±1030.
3±7.
05Controls30(24females,6males)55±1028.
6±5.
4Table1.
SubjectgroupsDemographicdatasuchasweight,height,ageandgenderwererecorded.
26Standingradiographsinthesagittalplanewerecollectedonthedayofdatacollection.
Radiographicparameters:SVA,definedasthedistancebetweenaplumb-linedroppedfromthecenteroftheC7vertebraandtheposteriorborderofthesacralendplatewasmeasured.
PT,definedastheanglesubtendedbytheverticalaxisoriginatingfromthecenterofthefemoralheadandthemidpointofthesacralendplatewasalsomeasured.
Subjectswereaskedtostandonagraphpaperwiththeirfeetparallelandcomfortabledistance,usuallyshoulder'swidthapart.
Distancebetweentheheelsanddistancebetweentoeandheelwererecorded.
TheWBBwasplacedsixinchesinfrontofawall.
Halftheheel-heeldistancewasmarkedontheXaxis,andhalfthetoetoheeldistancewasmarkedontheYaxisoftheboard.
Symmetricplacementoffeetaboutthemedio-lateralandanterior-posterioraxesoftheboardwasassured.
Figure11showsthepositioningofasubject'sfeetontheWBB.
TrialsSubjectswerepositionedontheboardandaskedtokeeptheirkneeslockedinextension,whilerestingtheirarmsonthesides(Neutralposition)asillustratedintheFigure12.
COPdisplacementdatainmedio-lateralandanterior-posteriordirectionswererecordedfor30seconds.
AnalysisThedatawasfilteredthroughan8thorderlowpassButterworthfilteratacutofffrequencyof5Hzanddown-sampledto45Hz.
TheCOPpathlength,RMSswayvelocity(medio-lateral[X]andanterior-posterior[Y]),RMSTotalswayvelocityand95%confidenceellipseareawerecalculated.
27StatisticalAnalysisAone-wayANOVAwasperformedtoassessthedifferencesmeanpathlength,swayvelocityand95%swayareabetweenthecontrolsandthefourpatientgroupsatasignificancelevelof0.
05.
28Figure5.
Screenshotofcustomgraphicuserinterface(GUI)29Figure6.
PointloadingcalibrationdeviceFigure7.
Calibrationofgroundreactionforce30Figure8.
COP(X,Y)calibrationsetup31Figure9.
PowerspectraldensityoftheCOPsignal32Figure10.
Rawdata,filtereddataanddown-sampleddataFigure11.
FeetpositioningontheWBB33Figure12.
Standingposition-handsonsides(30sec)34CHAPTER4:RESULTSCalibrationRegressionanalysisbetweenappliedforceandrecordedforcefromeachsensorshowedthatwithincreasingmagnitudeofappliedforce,therewasalinearincreaseinforcedetectedbythesensor.
Figure13showslinearcorrelationbetweenthebottom-leftsensorforceFBLversustheappliedforce.
R2=0.
999wasfound.
Figure14showslinearcorrelationbetweenthebottom-rightsensorforceFBRversustheappliedforce.
LinearregressionequationrevealedR2=0.
999.
Figure15showslinearcorrelationbetweenthetop-leftsensorforceFTLversustheappliedforce.
R2=0.
999wasfound.
Figure16showslinearcorrelationbetweenthetop-rightsensorforceFTRversustheappliedforce.
R2=0.
999wasfound.
Linearityerrorin%FSOwascalculatedforeachfullcycleperformedonfoursensors.
MaximumofthefourcycleswascalculatedandwasfoundtobeBrandoff,J.
,Casden,A.
C.
,Kuflik,P.
,&Neuwirth,M.
G.
(2009).
Sagittalplanedeformityintheadultpatient.
TheJournaloftheAmericanAcademyofOrthopaedicSurgeons,17(6),378–388.
27.
BoulayC,TardieuC,HecquetJ,etal:Sagittalalignmentofspineandpelvisregulatedbypelvicincidence:Standardvaluesandpredictionoflordosis.
EurSpineJ2006;15:415-422.
28.
Roussouly,P.
,Gollogly,S.
,Noseda,O.
,Berthonnaud,E.
,&Dimnet,J.
(2006).
TheverticalprojectionofthesumofthegroundreactiveforcesofastandingpatientisnotthesameastheC7plumbline:aradiographicstudyofthesagittalalignmentof153asymptomaticvolunteers.
Spine,31(11),E320–5.
29.
Mac-Thiong,J.
-M.
,Transfeldt,E.
E.
,Mehbod,A.
A.
,Perra,J.
H.
,Denis,F.
,Garvey,T.
A.
,Lonstein,J.
E.
,etal.
(2009).
Canc7plumblineandgravitylinepredicthealthrelatedqualityoflifeinadultscoliosisSpine,34(15),E519–27.
30.
BarreyC,RoussoulyP,PerrinG,LeHuecJC.
Sagittalbalancedisordersinseveredegenerativespine.
CanweidentifythecompensatorymechanismsEurSpineJ.
2011Sep;20Suppl5:626-33.
31.
LeHuecJC,CharoskyS,BarreyC,RigalJ,AunobleS.
Sagittalimbalancecascadeforsimpledegenerativespineandconsequences:algorithmofdecisionforappropriatetreatment.
EurSpineJ.
2011Sep;20Suppl5:699-703.
32.
LafageV,SchwabF,PatelA,HawkinsonN,FarcyJP.
Pelvictiltandtruncalinclination:twokeyradiographicparametersinthesettingofadultswithspinaldeformity.
Spine(PhilaPa1976).
2009Aug1;34(17):E599-606.
33.
Mendoza-LattesS,RiesZ,GaoY,WeinsteinSL.
Naturalhistoryofspinopelvicalignmentdiffersfromsymptomaticdeformityofthespine.
Spine(PhilaPa1976).
2010Jul15;35(16):E792-8.
34.
MarksM,StanfordC,MaharA,NewtonP.
Standinglateralradiographicpositioningdoesnotrepresentcustomarystandingbalance.
Spine(PhilaPa1976).
2003Jun1;28(11):1176-82.
35.
MarksM,StanfordC,NewtonP.
Whichlateralradiographicpositioningtechniqueprovidesthemostreliableandfunctionalrepresentationofapatient'ssagittalbalanceSpine(PhilaPa1976).
2009Apr20;34(9):949-54.
36.
FaroFD,MarksMC,PawelekJ,NewtonPO.
Evaluationofafunctionalpositionforlateralradiographacquisitioninadolescentidiopathicscoliosis.
Spine(PhilaPa1976).
2004Oct15;29(20):2284-9.
37.
AotaY,SaitoT,UesugiM,IshidaK,ShinodaK,MizumaK.
Doesthefists-on-claviclespositionrepresentafunctionalstandingpositionSpine(PhilaPa1976).
2009Apr15;34(8):808-12.
doi:10.
1097/BRS.
0b013e31819e2191.
6238.
RoussoulyP,GolloglyS,NosedaO,BerthonnaudE,DimnetJ.
TheverticalprojectionofthesumofthegroundreactiveforcesofastandingpatientisnotthesameastheC7plumbline:aradiographicstudyofthesagittalalignmentof153asymptomaticvolunteers.
Spine(PhilaPa1976).
2006May15;31(11):E320-5.
39.
ZainaF,PizzettiP,DonzelliS,NegriniF,NegriniS.
WhyX-raysarenotreliabletoassesssagittalprofile:acrosssectionalstudy.
StudHealthTechnolInform.
2012;176:268-72.
40.
NationalInstrumentsforums.
http://forums.
ni.
com/t5/LabVIEW/Use-Wii-Balance-Board-in-LabVIEW/td-p/710740.
41.
BobbertMF,SchamhardtHC.
Accuracyofdeterminingthepointofforceapplicationwithpiezoelectricforceplates.
JournalofBiomechanics1990;23(7):705-710.
42.
CollinsSH,AdamczykPG,FerrisDP,KuoAD.
Asimplemethodforcalibratingforceplatesandforcetreadmillsusinganinstrumentedpole.
GaitPosture.
2009Jan;29(1):59-64.
doi:10.
1016/j.
gaitpost.
2008.
06.
010.
Epub2008Aug27.
43.
Kistler.
1984MulticomponentmeasuringforceplateforBiomechanicsandIndustrytype9287,KistlerSwitzerland.
44.
StinsJF,LedebtA,EmckC,vanDokkumEH,BeekPJ.
Patternsofposturalswayinhighanxiouschildren.
BehavBrainFunct.
2009Oct2;5:42.
doi:10.
1186/1744-9081-5-42.
45.
NachemsonA.
Theloadonlumbardiscsindifferentpositionsofthebody.
ClinOrthopRelatRes.
1966Mar-Apr;45:107-22.
46.
LafageV,SchwabF,SkalliW,HawkinsonN,GageyPM,OndraS,FarcyJP.
Standingbalanceandsagittalplanespinaldeformity:analysisofspinopelvicandgravitylineparameters.
Spine(PhilaPa1976).
2008Jun15;33(14):1572-8.