The reliability of the anterior pelvic plane for computer navigated acetabular component placement during total hip arthroplasty: Prospective study with the EOS imaging system

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Original

article

The

reliability

of

the

anterior

pelvic

plane

for

computer

navigated

acetabular

component

placement

during

total

hip

arthroplasty:

Prospective

study

with

the

EOS

imaging

system

O.

Barbier

,

W.

Skalli

,

L.

Mainard

,

D.

Mainard

,

Computer

Assisted

Orthopedic

Surgery–France

(CAOS-France)

a_{Servicedechirurgieorthopédique,hôpitalcentral,29,avenuedeLattre-de-Tassigny,54000Nancy,France}

b_{Laboratoiredebiomécanique,écolenationalesupérieuredesartsetmétiersParistech,boulevarddel’Hôpital,75013Paris,France} c_{Servicedechirurgieorthopédique,hôpitald’instructiondesArmées-Bégin,69,avenuedeParis,94160Saint-Mandé,France} d_{Servicederadiologie,hôpitalBrabois,rueduMorvan,54511Vandœuvre-lès-Nancy,France}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Accepted1st_July2014 Keywords:

Totalhiparthroplasty EOS

Navigation Anteriorpelvicplane

a

b

s

t

r

a

c

t

Introduction:Computernavigatedtotalhiparthroplastyismostlybasedontheuseoftheanteriorpelvic plane(APP)asareference.EOSisanewimagingsystemthatprovidesthree-dimensionalanalysisofthe pelvisinafunctionalpositionwithalowdoseofradiation.Theaimofthisstudywastoevaluatethe reliabilityoftheAPPforplacementofthecupduringcomputernavigatedTHAusingEOS.

Hypothesis:ThereliabilityoftheAPPislimitedfortheplacementoftheacetabularcupduringcomputer navigatedTHA.

Materialsandmethods:ThiswasaprospectivemonocentricstudyusingtheEOSimagingsystem eval-uating44patientsinthestandingpositionthreemonthsaftercomputernavigatedTHA(OrthopilotTM_). ReproducibilityofEOSmeasurementswereanalyzedusingSterEOSsoftwareandthereliabilityofthe navigationdataforthepositionofthecupwereassessed.

Results:IntraandinterobserverreproducibilityofthemeasurementsoftheorientationofthecupbyEOS weregoodwithcorrelationcoefficientsabove93%and95%andconfidenceintervalsoflessthan±5◦. Meancupinclinationandanteversionwere41.3◦_and20.9◦_and44.3◦_and29.5◦_{respectivelyin} opera-tivelyandpost-operatively.Thedifferencesbetweenmeasurementsofoperativecupinclinationusing computerassistednavigationandthepost-operativeEOSmeasurementsweresignificant(P<0.05)with acorrelationcoefficientoflessthan40%.

Discussion:OurstudyconfirmsthelackofprecisionoftheAPPasareferenceforpositioningofthe acetab-ularcomponent,especiallyinrelationtoanteversion.AlthoughformanyyearstheAPPwasconsideredto beaglobalreference,infact,itissubjecttosignificantinter-individualvariationsandvariationsduring changesinposition.Thesefactors,associatedwiththedifficultyofdeterminingthepreoperativeAPP, explainthelackofreliabilityofthisreference.PreoperativeevaluationoftheorientationofAPPbyEOS anditsintegrationintothenavigationsystemcouldhelptheoperatorpositionthesecomponents.

Levelofevidence:LevelIIIProspectivediagnosticcasecontrolledstudy.

©2014ElsevierMassonSAS.Allrightsreserved.

1. Introduction

Theuseofcomputernavigationoptimisesthepositionofthe cupduringtotalhiparthroplasty (THA)toimprove biomechan-ics,reducetheriskofdislocationandearlycomponentwear.The anteriorpelvicplane(APP),usedasaplaneofreferencefor nav-igation,isananatomicalreferencethatcannotbesuperimposed

∗ _{Correspondingauthor.}

E-mailaddress:[email protected](O.Barbier).

on the vertical plane in clinical practice [1–6] and has signif-icant inter-individual variations and variations, depending on the patient’s position[5,6].EOS is a recent imaging technique, based onthe workof Georges Charpak, Nobel Prizein physics in 1992 [7,8], which provides a static and/or functional 3-D image of the skeleton. A reconstruction of the entire body in a functional position is obtained from two digital orthogonal 2-D imagesobtainedsimultaneously,witha lowlevel of radia-tion [7–10].Our hypothesis wasthat the reliability of theAPP waslimited forpositioningthe cupduringcomputernavigated THA.

http://dx.doi.org/10.1016/j.otsr.2014.07.003

Theaimsofthisstudywere:(1)tovalidatethereproducibility oftheEOSimagingsystemformeasuringcuporientationand(2)to usetheEOSsystemtoanalyzethereliabilityoftheAPPforoperative cupplacement.

2. Materialsandmethods

2.1. Patients

Thiswasa prospective,non-randomizedstudyofa cohortof patientswhounderwentcomputerassistedTHAforprimaryhip arthritis during the 12-months inclusion period. Patients with a history of hipsurgery or presenting withhipdysplasia were excluded.All patients wereoperated onby the same surgeon. TheinterventionwasperformedbyaHardinge-typemini-invasive anterolateralapproach[1]inlateraldecubituspositionat45◦,with theOrthopilotTM_{(BBraun,Melsungen,Germany)navigation}

sys-tem.TheAPPwasusedastheplaneofreferencefornavigation.A press-fitcup(PlasmacupTM_{,BBraun,Melsungen,Germany)anda}

cementlessstraightstem(ExciaTM_{,BBraun,Melsungen,Germany)}

wereusedfor each patient.Thegoal foracetabular component positioningduringtheinterventionwas15◦±10◦anteversionand 40◦±10◦inclination.Thefinalpositionofnavigatedcupplacement wasnoted.Allpatientsunderwentthesamepost-operative reha-bilitationprotocol.

2.2. Methodofassessment

Allpatientsunderwentfollow-upbyEOSimagingat3months post-operative.TheprotocoldescribedbyLazennecetal.[6]and Chaibietal.[10]wasused:standingwiththefeetapart.Quality criteriadescribedbyLazennecetal.[6]andChaibietal.[10]were usedtovalidate thetests.Cup orientation measurementswere obtainedfrom clinically validated sterEOS (EOS imaging, Paris, France)software[6,10].Cupinclinationonthefrontalplanewas definedastheanglebetweenthecupaxisandthehorizontal refer-encelineontheAPview[6,10]andcupanteversiononthesagittal planeastheanglebetweenthecupaxisandthereference horizon-tallineonthelateralview[6,10].

2.3. Statisticalanalysis

ThestatisticalanalysiswasperformedwithNumbers09TM

Ver-sion4.3(AppleInc,Cuppertino,CAUSA)software.Repeatability (intraobserverreliability)andreproducibility(interobserver reli-ability)oftheEOSTM_{systemwerecalculatedforthefirst10cases.}

Twomeasurementswereperformedbytwoindependentobservers (asurgeonanda radiologist)andtwo successivemeasurements wereperformedat1-monthintervalbythesameobserverforthe 10firstpatients.Themeandifferences(d),thestandarddeviation (SD)andthe95%confidenceinterval(CI95%)(equivalentto2×SD) were calculated to analyze the data. The correlations between measurementsand betweenobserverswereevaluatedbylinear regressionforpairedsamplesandthePearson’sinterclass correla-tioncoefficient(ICC)betweenthedifferentseries.AnICCofmore than0.8wasconsideredtobegoodandconfirmedreliabilityof measurements.Reliabilitybetweenmeasurementswasevaluated accordingtotheBlandandAltman[11]methodbygraphically rep-resentingthedifferencebetweenthe2measurements(performed bythesameobserveror2independentobservers)inrelationtothe meanmeasurement.

Quantitativedatawereanalyzedbydeterminingthemean(M), themeandifferencesand thestandard deviation(SD).Alackof statistically significant variation in cup orientation angles was confirmedby apairedt-testand bycalculatingthePearsonICC

Fig.1.Overallresultsoftheinter-andintraobserverstudyofEOSmeasurements ofcupinclination(1.1)andanteversion(1.2).

betweenthedifferentseriesofoperativeandpost-operative mea-surementstoevaluatecupinclinationandanteversionvariationfor allpatients.Anindividualanalysisofvariationsinoperativeand post-operativedatawasalsoperformedusingtheBlandand Alt-manmethodbygraphicallyrepresentingthedifferencebetween thetwovaluesinrelationtothemeanvalue[11].

Thestudyprotocolwasvalidatedbythelocalethicscommittee andpatientswereinformedofthestudyprotocol.

3. Results

Forty-fourpatientswithprimaryhiparthritiswereincludedin thestudy.Therewere11menand33women,meanage64years old (range=40–83,SD±14.6) mean body mass index 27kg/m2

(range=18–41,SD±6).

Intra-andinterobservervariabilityforpost-operativecup ori-entationevaluatedbytheEOSsystemaresummarizedinTable1 andFig.1.Thedifferencesinsuccessivemeasurementsto deter-mine intra-and interobserver variability were not significantly differentfromzero,showingthattherewerenosystematic mea-surementerrors.Therewasgoodagreementforanteversionvalues andinclinationobtainedbyeachoperatorandthesameoperator, withcorrelationcoefficientsofmorethan93%.UsingaCIof95%, randomerrorsforeachoftheparameterswaslessthan±5◦,witha widedistributionofanteversionasshownbytheBlandandAltman graphicanalysis(Fig.2).

Theresultsofthedirectpairedcomparisonof operativeand post-operativeanglesobtainedbycomputernavigationandEOS respectively are summarized in Fig. 3 and Table 2. Agreement betweenthetwomeasurementswaspoorwithacorrelation coef-ficientoflessthan40%.Thedirectpairedt-testshowedasignificant differenceinoperativeand post-operativevalues (Table2).The BlandandAltmangraphicanalysisshowedsignificantdispersion inrelationtothemeanmeasurement,especiallyforanteversion (Fig.4).

4. Discussion

ThisisthefirststudyusingtheEOSsystemtoassessthe reliabil-ityoftheAPPasareferenceforcupplacementduringcomputer assistedTHA.Althoughcertainauthorshaveanalyzedcupposition afterTHAusingX-raysorCT-scan,thesemeasurementsare impre-ciseorinexactbecausepelvictiltvariesdependingonthepatient andhis/herposition[4,6,10–16].

Table1

Intra-andinterobserverstudyofvariabilitywithEOS.

Repeatability Reproducibility

d 2SD ICC P-value d 2SD ICC P-value

Inclination 0.29 1.34 0.93 0.44 −0.19 1.60 0.94 0.26

Anterversion −0.47 4.84 0.93 0.35 −0.16 5.08 0.94 0.31

d:meandifferences;2DS:twostandarddeviations(c95%confidenceintervalofdifferences);P-valueoftheStudentt-test(observereffectforrepeatabilityandrepetition effectofthemeasurementsforreproducibility);ICC:Pearson’sinterclasscorrelationcoefficient.

Table2

DirectpairedcomparisonsofmeasurementsofcupanglesobtainedoperativelyduringcomputernavigatedTHAandpost-operativelybyEOS.

Inclination Anteversion

Navigation EOS Difference Navigation EOS Difference

M 41.32 44.36 −3.0 20.91 29.52 −8.6

DS 2.66 5.34 5.1 6.7 10.19 9.8

P-value 0.0013 0.000004

ICC 0.38 0.36

M:mean,DS:standarddeviation;P-value:studentt-testofpairedseries;ICC:Pearsoninterclasscorrelationcoefficient.

Fig.2.Graphicrepresentationofthedifferencebetweenthemeasurementsandthe meanmeasurementsaccordingtoBlandandAltmanforcupinclination(2.1)and anteversion(2.2).

The first step was to confirm that the EOS system reliably measuredcuporientation.Ourresultsconfirmedthoseinthe lit-eratureandshowedgoodinter-andintraobserverreproducibility ofEOSmeasurements.Journéetal.[12]measuredacetabularcup inclinationand anteversion ondrybone withEOS and founda repeatabilityof±1.4◦and±2.3◦respectivelyandareproducibility of±1.6◦and±2.5◦respectivelywithaCIof95%.Billaudetal.[16], evaluatedametalbackcupandfoundadifferenceof1.7◦±1.4◦ forinclinationand1.5◦_±2.9◦foranteversionbetweenEOSand CT-scanresultsrespectively,andaninterobservererrorof2.6◦±1.4◦ forinclinationand2.5◦±1.4◦foranteversionrespectively.Kalteis etal.[5]showedthattheprecisionofacetabularcupinclinationand anteversionmeasuredonplainX-rayswas±3◦and±10◦, respec-tively,whileitwasapproximately2◦withCT-scan.Lazennecetal. [6]confirmedtheseresultsanddidnotfindanysystematic intra-andinterobservererrorsinthestandingorsittingpositionswith a 95% CI between±3.83◦ and±6.27◦ for acetabularparameters respectively.Thus,althoughCT-scanisstillconsideredtobethe “goldstandard”forthemeasurementofcuporientation,radiation limitsitsuse.EOSisthereforeaninterestingandreliable alterna-tive,whichismoreprecisethanconventionalX-rayandwithless radiation.

Fig.4. Graphicrepresentation ofthe difference betweenoperative computer navigatedmeasurementsandpost-operativeEOSresultscomparedtomean mea-surementsaccordingtoBlandandAltmanforcupanteversion(4.1)andinclination (4.2).

Second,thisstudyshowedthatthereliabilityoftheAPPwas limitedasareferenceforoperativecuporientationespeciallyin relationtoanteversion. Thislack of precisionhasalready been reportedintheliterature[17–20].Therearethreepossible explana-tionsforthis.First,theoperativedeterminationofAPPorientation isdifficultbecausethepercutaneouspalpationofboneanatomy landmarks(pubisandiliacspine)isimprecise.Wolfetal.[17]used akinematicmodeltoshowthatanerrorof4mmwhen identify-ingtheselandmarkswouldresultina2◦errorininclinationand 7◦ in anteversionin thefinal cupposition,whiletheminimum thicknessofthesofttissuesbetweenthesurfaceoftheskinand thebonewasapproximately8mmattheiliacspineand13mmat thepubis,forameanunderestimationofanteversionof4.4◦. Sec-ond,computernavigationusestheAPPasalocalpelvicreference. Thisreference,whichwasconsideredtobeexactformanyyears andtobegloballyhorizontalinthesupinepositionandverticalin thestandingposition,wasalsoconsideredtobesuperimposable upontheGalileanreferenceframeusedtoperformTHA.Indeed, initially,theAPPwasconsideredtobeindependentofgenderand age[18,19]andstablebetweentheseatedandstandingposition andafterTHA[19].However,studieshavenowshownthattheAPP is,infact,notverticalbuthasaposteriortiltofapproximately4◦, morethan5◦in38%ofcasesandeven10◦in13%ofcases,andthese aresignificantinter-individualvariations[17–20].Finallythe posi-tionofthepelvisisdynamic,notstatic,duringchangesinposition anddailyactivitiesandthisvariation,whichisnotpredictable,is between−2◦and−5.4◦ofpelvicextension[4,20–25].TheAPPused asareferencecouldbeweightedinrelationtothepelvictiltinthe standingposition,assuggestedbyWolfetal.[17].Althoughthis authoraddedtheestimated4◦todetermineAPPorientation dur-ingsurgery,thevariationofthepositionofthepelvisbetweenthe preoperativestanding(X-rayorEOS)orsupine(CT-scan)positions andtheoperative lateraldecubitus positionmakesthis estima-tionrandom.Thefinalpossibleexplanationisthatthevariation incuporientationcomparedtotheAPPmaybetheresultofa mod-ificationinpelvicparametersbeforeandafterTHA,asshownby

Nishiharaetal.[21] andBabischetal.[4],andthisvariation in pelvictiltduringcupinsertionmustbetakenintoconsideration sothattheorientationisnotthesameforallpatients.McCollum etal.[24]alsosuggestedadjustingcuppositiontoanteroposterior pelvictilttoreducetheriskofdislocationafterTHAbecauseof thewiderange(−37◦–44◦)ofpreoperativevaluesofpelvictiltin patientsinthesupineposition.Lembecketal.[26]measured varia-tionsinfunctionalanteversionofthecupinrelationtovariationsin pelvictiltanddefinedthenotionoffunctionalacetabular antever-siontoobtainabalancebetweenstabilityandmobility.According toLazennecetal.[6]andLembecketal.[26],avariationin poste-riorpelvictiltof1◦resultsinanincreaseinfunctionalanteversion ofthecupof0.7◦.Philippotetal.[25],emphasizedthenecessity oftakingintoaccountsagittalbalanceofthespineandthepelvis duringTHAanddefinedanewreference,thepelvi-Lewinnekangle whichisapproximately12◦,constantwhatevertheposition,and whichtheyincludedinthenavigationprotocol.

5. Conclusion

Pelvictilt,functionalanteversion andthelackofprecisionin identifyingtheAPParethecauseofpoorreliabilityofthis refer-enceforacetabularcupposition.Preoperativeevaluationofthese parametersmustbeimprovedtoimproveaccuracyincup posi-tioning.FurtherresearchusingEOSshouldhelpprovidespecific individualdataforpreoperativeplanningofcomponentplacement aswellasachieveoperativegoalsbyintegratingthisinformation intocomputernavigatedTHA.

Disclosureofinterest

Theauthorshavenotsuppliedtheirdeclarationofconflictof interest.

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