Computed tomography evaluation of hip geometry restoration after total hip resurfacing

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Original

article

Computed

tomography

evaluation

of

hip

geometry

restoration

after

total

hip

resurfacing

A.

Arnould

a,b,∗

,

F.

Boureau

a,b

,

K.

Benad

a,b

,

G.

Pasquier

a,b

,

H.

Migaud

b,c

,

J.

Girard

b,c,d

a_{ServiceorthopédieD,centrehospitalierrégionaluniversitairedeLille,2,avenueOscar-Lambret,59037Lillecedex,France}

b_{UniversitéLille-NorddeFrance,59000Lille,France}

c_{ServiceorthopédieC,centrehospitalierrégionaluniversitairedeLille,2,avenueOscar-Lambret,59037Lillecedex,France}

d_{Domainemédecineetsport,facultédemédecinedeLille2,59037Lillecedex,France}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received22September2014 Accepted16April2015 Keywords: Biomechanicalreconstruction Hipresurfacing CTreconstruction Femoraloffset

a

b

s

t

r

a

c

t

Background: Anatomicreconstructionofthehipisamongthemainrequirementsforhiparthroplasty tobesuccessful.Resurfacingarthroplastymayimprovereplicationofthenativejointgeometrybuthas beenevaluatedonlyusingstandardradiographs.Wethereforeperformedacomputedtomography(CT) studytoassessrestorationofhipgeometryaftertotalhipresurfacing(HR),comparativelywiththe non-operatedside.

Hypothesis:HRdoesnotchangenativeextra-medullaryhipgeometrybymorethan5mmand/or5◦.

Patientsandmethods:CTwasusedtoevaluateunilateralHRin75patientswithameanageof52.2years (range,22–67years).Thenormalnon-operatedsideservedasthecontrolineachpatient.Meanfollow-up was2.5years(range,1.9–3.1years).Theprimaryevaluationcriteriawerefemoraloffset(FO)andfemoral neckanteversion(FNA)andthesecondarycriteriawerecupinclinationangle,cupanteversionangle,and lower-limblength.

Results:FOshowedanon-significantdecrease(mean,−2.2mm;range,−4.5to+3.7mm).FNAwas pre-served,withadifferenceoflessthan2◦_{atlastfollow-upversusthepreoperativevalue.Cupmeasurements}

showedameananteversionangleof24.8◦_{(0.9–48.6)andmeaninclinationangleof44.1}◦_{(32.1–56.3);}

correspondingvaluesforthenativeacetabulumwere38.9◦(20.5–54.8)and24.8◦(4.8–33.6).Theresidual lower-limblengthdiscrepancywaslessthan1mm(mean,−0.04mm[−1.2to+1.6mm]).Themeanangle betweenthefemoralimplantandthefemoralneckaxiswas5.4◦_ofvalgus.

Discussion:OurresultsshowthatHRaccuratelyrestoredthenativeextra-medullaryhipgeometry.

Levelofevidence:III,prospectivediagnosticcase-controlstudy.

©2015ElsevierMassonSAS.Allrightsreserved.

1. Introduction

Accuratebiomechanicalreconstructionofthehipisessential fortotalhiparthroplasty(THA)tobesuccessful[1],asgeometric parameterscorrelatewithjointandmusclefunction[2].Thus, fail-uretoreplicatethenativegeometrycancausealimporinstability ofthehip[3].Themanymethodssuggestedtorestorehip geome-tryincludepreoperativeplanning(usingtracingpaperordedicated computersoftware),navigation,andtheuseofmodularprostheses (e.g.,lateralizedfemoralstemsand/ormodularnecks)[4–6].In the-ory,hipresurfacing(HR)almostautomaticallyrestoresthenative hipanatomy[6]:incontrasttoTHA,HRpreservesthefemoralneck

∗ _{Correspondingauthorat:ServiceorthopédieD,centrehospitalierrégional}

uni-versitairedeLille,2,avenueOscar-Lambret,59037Lillecedex,France. Tel.:+33320446828;fax:+33320446607.

E-mailaddress:[email protected](A.Arnould).

andthereforedoesnotinducelateralizationofthefemur, lengthen-ingofthelimb,orchangesinthecentreofrotationofthefemoral head[7].AlthoughrestorationofhipanatomyafterHRhasbeen evaluated,onlystandardradiographshavebeenusedtomeasure thegeometricparameters[6].Standardradiographslackprecision andcannotprovideinformationaboutanteversion[2].

Wethereforeconductedaprospectivestudyusingcomputed tomography(CT)toassesshipgeometryafterHRcomparativelyto thenon-operatednormalside.WehypothesisedthatHRrestored nativeextra-medullaryhipgeometrywithlessthan5mmand/or 5◦differenceversusthenon-operatedside.

2. Patientsandmethods 2.1. Patients

Aprospectivenon-randomisedstudyofpatientsmanagedbya singlesurgeonwasperformed.Inclusioncriteriawereasfollows:

http://dx.doi.org/10.1016/j.otsr.2015.04.004

Fig.1.Measurementoncomputedtomographyimagesofcupinclinationinthecoronalplane,astheanglesubtendedbythetransversecupaxisandtheinter-teardropline.

adultwhounderwentunilateralHRduringthefirsthalfof2010, normal contralateral hip (no degenerative disease or surgery), preoperative limblength discrepancy absent orless than1cm, absenceofpost-traumaticlesionsofthespineandpelvis,absence ofnegative-anglehipdysplasia, andnormal kidneyfunction. In all patients, the prosthesis used was the Conserve® Plus Total ResurfacingHipSystem(WrightMedicalTechnology,Arlington,TN, USA),withanacetabularcomponentshapedasatruncated hemi-sphereandacoverageangleof170◦.Allpatientssignedaninformed consentdocumentbeforestudyinclusion.

There were 75patients –46males (61.3%) and 29females (38.7%)–with a mean age of 52.2years (range, 22–67), a mean body weight of 80.1_±17kg (95% confidence interval [95%CI], 67–92),andameanbodymassindexof26.2±4.6kg/m2_(95%CI,

23–28). Among them, 32 (42.7%) had HR on the left side. The reasons for HR were primary hip osteoarthritis, n=34 (45%); osteoarthritis complicating femoro-acetabular impinge-ment,n=23(31%),osteoarthritiscomplicatinghipdysplasia,n=10 (13%);osteoarthritiscomplicatingacetabularprotrusion,n=3(4%), avascularnecrosisofthefemoralhead,n=2(3%);polyepiphyseal dysplasia,n=1,osteoarthritiscomplicatingosteochondromatosis,

n=1;andresidualabnormalitiesafterfemoralepiphysiolysis,n=1. Meanpostoperativefollow-upwas2.5years(range,1.9–3.1).

2.2. Operativetechnique

AllHRprocedureswereperformedunderlaminarflow,bya sin-glesurgeon(JG),afterpreoperativeplanningaimedatreplicating thenativegeometryofthehip(centreofrotation,femoraloffset [FO],andlower-limblength[LLL][8]).Apostero-lateralapproach wasusedandthefemurwastreatedfirst[8].Theacetabularcup waspress-fitintheanatomicposition,i.e.,paralleltothe trans-verseligamentandtotheacetabulumclearedofanyosteophytes. ThispositionwassoughtregardlessofthereasonforHR.An ante-rioroverhangof1mmwasmaintainedtoeliminateallriskofcup impingementonthepsoasmuscle.Thefemoralinstrumentation allowedchangesinfemoralcomponentpositioninallthreeplanes. Thefemoralcomponent wasimplantedin theneutral position, inthesagittalplaneof theneckand inslightvalgusrelativeto thecoronalplane.Theabsenceofnotchingof thefemoralneck waschecked.Meansizeswere57.3mm(52–66)forthecupand 51.4mm(46–60)forthefemoralcomponent.

2.3. Assessmentmethods

FOandFNAweretheprimaryevaluationcriteria.Thesecondary evaluationcriteriaweretheinclinationanglesofthecupandbony acetabulum,theanteversionanglesofthecupandbony acetabu-lum,andLLL.

Helical CT with metal artefact suppression was performed. Imageswereacquiredfromtheuppermostpointoftheiliaccrests tothelessertrochanters;slicesthroughthefemoralcondyleswere obtainedalso.CTfindingswereanalysedrelative totheanterior pelvic plane (APP, Lewinnek reference plane) [9]. Cup inclina-tioninthecoronalplanewasmeasuredbetweenthetransverse axisof the cup and theinter-teardrop line(Fig.1). The native neck-shaftangle(CC’D)wasmeasuredonthenormal contralat-eralhipbetweentheaxisof theneck(CC’)and theaxisofthe shaft(C’D).Thestem-shaftangleoftheimplant(C’C”D)was mea-sured between the axis of the shaft (C’D) and the axis of the femoralstem(C’C”)(Fig.2aandb).FOontheoperatedand non-operatedsideswasdeterminedasdescribedbyMcGroryetal.[10]. Onthenormalnon-operatedside,versionandinclinationofthe acetabulum wererecorded (Fig. 3a).Prostheticcup anteversion wasassessedastheanglebetweenthetransversecupaxisand thesagittalplane,intheaxialplane(Fig.3b).Femoralneck ver-sionwasmeasuredrelativetotheposterior bicondylarplaneof thefemur.Thehead-neckratiowascomputedasthefemoral-head diameterdividedbythefemoral-neckdiameter,measuredinthe planethroughthemiddleofthefemoralhead.LLLdiscrepancywas assessedbydeterminingthelengthoftheperpendicularsegments joiningthelinethroughthemiddlesofthelessertrochantersto theCTteardroponeachside,inthecoronalplane.Thisdistance wasmeasuredonbothsidestoassessanyLLLchangesinducedby HR.

All measurements were taken by an independent observer, who had no role in the surgical procedures and who used image-processing software (OSIRIX, OsiriXFoundation, Geneva, Switzerland) to obtain three-dimensional multi-planar recon-struction(MPR).Thisimagereconstructionsoftwarehas0.3-mm precisionandgoodreproducibilitywithaninterclasscorrelation coefficient>0.9[11].

Atlast follow-up, thefollowing clinicaldatawere recorded: Oxfordhipscore[12],Merle d’Aubigné-Postel(MAP)score[13], HarrisHipScore(HHS)[14],Devaneactivityscore[15],andUCLA activityscore[16].

Fig.2. aandbMeasurementofthenativeneck-shaftangle(CC’D,subtendedbytheneckaxisCC’andtheshaftaxisC’D)andprostheticneck-shaftangle(C’C”D,subtended bythestemaxisC’C”andtheshaftaxisC’D).

2.4. Statisticalmethods

Thestatisticalanalysiswasperformedbythemethodological supportplatformofthepublichealthdepartmentattheLille teach-ing hospital,Lille, France.Sample size wasestimated based on theprimaryevaluation criterion(FO within5mmof thenative value±2.5mm).Assumingastandarddeviationof4.7forFO,with thealpharisksetat0.05andpowerat80%,weneededtoinclude 56patients.

Descriptivestatisticswerecomputedforthequantitative meas-uresofimplant positionand ofnon-operated hipgeometry.To comparethetwosides,Student’sttestwaschosenfor paramet-ricdata (C’C”Dangle,FO, neck version relative to theposterior bicondylarplane,andoverallversion)andWilcoxon’stestfor non-parametricdata(LLLdiscrepancy, head-neckratio,neckversion relativetothecoronalplane,prostheticheaddiametervs.native headdiameter,cupversionvs.acetabularversion,andinclination ofthecupvs.inclinationoftheacetabulum).Hipgeometry parame-tersontheoperatedandnon-operatedsideswerecomparedusing Student’sttestforparametricdataandthepairedWilcoxontest fornon-parametricdata.ValuesofP<0.05wereconsidered signif-icant.

3. Results

Alltheclinicalparametersevaluatedinourstudyimproved sig-nificantly(Table1).Table2reportstheCTfindings.ThemeanFO decreasewas₋2.2mm(₋4.5to+3.7mm),whichwasnot statis-ticallysignificant(P=0.2).Thedifferenceinfemoralanteversion relativetothenormalsidewaslessthan2◦(P=0.3).Cupinclination

wasnotsignificantlydifferentfrominclinationoftheacetabulum onthenormalside.Incontrast,meancupanteversionwas signif-icantlygreaterthanmeananteversionoftheacetabulumonthe normalside(P=0.001):24.8◦ (15◦ to30◦ for92.7%ofcups)and 19◦,respectively.Meancupinclinationwas44.1◦(<50◦for94.9% ofcups),comparedto38.9◦forthecontralateralnativeacetabula. ThedifferenceinLLLontheoperatedsideversusthenon-operated sidewassmall(mean,−0.04mm[−1.2to+1.6mm]).Theposition ofthefemoralimplantrelativetothefemoralneckaxiswasin5.6◦ ofvalgus.Noneofthefemoralimplantswasinvarusrelativetothe nativefemoralneck.

4. Discussion

HR restores native hip geometry, as shown by our CT studydemonstratingaccuratereplicationofgeometricparameters within5mmand5◦(FO,LLL,andfemoralneckanteversion).

Nevertheless,severallimitationsofourstudymustbe acknowl-edged.WedidnotincludeconsecutivepatientsundergoingHR,as weconfinedourstudytopatientswhosecontralateralhipwas nor-mal.However,anormalcontralateralhipwasneededtoobtaindata onthenativehipgeometryofeachpatient.Thesamplewas rela-tivelysmall(n=75)butwaslargerthanthesampleneededtoobtain 80%statisticalpowerand,therefore,allowedareliableanalysisof hipreconstruction.Wechosetheanteriorpelvicplaneasthe refer-enceforanalysingourdata.Thisplanewasusedinmostpublished studiesofhipimplantposition,afactthatallowscomparisonsofour findingstothoseobtainedbyothers.Nevertheless,theorientation ofthisplanevarieswidely[17].

Thedataaremean±SD(range).

a_{Statisticallysignificantdifferences.}

Table2

Descriptiveanalysisofhipgeometryparametersdeterminedbycomputedtomographyonthesidetreatedwithtotalhipresurfacingandonthenon-operatednormalside. Operatedside Non-operatedside Pvalue C’C”Dangle(◦) 137.3±5.7(127/151) 131.9±5.2(120/143) 0.4 LLLdiscrepancy(mm) −0.05±0.5(−1.2/1.6) −0.05±0.5(−1.2/1.6) 0.6

Femoraloffset(mm) 39.4±4.7(29/52) 41.6±5(32/54) 0.2

Head-neckratio(mm) 2±0.2(1.6/2.5) 1.8±0.1(1.5/2.1) 0.5 Versionneck/coronalplane(◦_{) 7.2±11.2(−17.8/30.4) 10.2±12.2(−19.4/38.7) 0.1} Diameterofprostheticheadvs.nativehead 51.4±3.7(46/60) 49.7±3.8(38/54) 0.3 Versionneck/posteriorbicondylarplane(◦_{) 16.7±7.1(0/41.4) 15.1±7.7(−1.1/33.2) 0.3} Versioncupvs.acetabulum(◦) 24.8±11.1(0.9/48.6) 19.1±5.8(4.8/33.6) 0.001a Overallversion(cuporacetabulumandfemur) 28.2±15.7(−7.5/62.9) 35.8±9.1(11.8/59.3) 0.07 Cupinclinationvs.acetabulum(◦_{) 44.1±5.5(32.1/56.3) 38.9±4.4(20.5/54.8) 0.3}

Thedataaremean±SD(range).CC’D:neck-shaftangle.

a_{Statisticallysignificantdifferences.}

Fig.3.aandbMeasurementoncomputedtomographyimagesofanteversionof thenativeacetabulum(a)andoftheresurfacingcup(b),astheanglessubtended bythetransverseaxisofthecup(oroftheacetabulumidentifiedbasedonitstwo horns)andthesagittalplane.

ArandomisedtrialcomparingTHAandHR[6]basedon radio-graphsofthereconstructedhipsshowedthatHRwasassociated withbetterrestorationofLLLandFOandwithdecreased variabil-ityofthecorrection.FOwasrestoredwithin±4mmin57%ofcases

afterHRcomparedtoonly25%afterTHA(P<0.001); correspond-ingproportionsforLLLrestorationwithin4mmwere86%and60%, respectively(P<0.001).Similarly,inaretrospectivecomparisonof THAandHR[18],restorationofFOandLLLwassignificantlybetter afterHR(meanvariationinFO,1.3mmafterHRvs.3.5mmafter THA;correspondingvalues forLL,4.9mmand 11.9mm, respec-tively).InanothercomparisonofTHA(n=50)andHR(n=40)[19]

performedduringthesameperiodbythesamesurgeon, restora-tionofFOandLLwasmorereliablewithHR.Ourresultssupport thesefindingsbyshowingthatHRaccuratelyreplicatesthenative hipgeometry.However,inallpreviousstudies,hipgeometrywas assessedusingstandardradiographs,whichareknowntoperform lesswellthanCTinthisindication,particularlyformeasuringFO andanteversion[20,21].Thus,anoriginalfeatureofourstudyis thatanatomichipreconstructionwasassessedbasedonCT,i.e., onmoreaccuratedatathanthoseobtainedbystandard radiogra-phy.

Thefemoralcomponent wasin 5.4◦ of valgusrelative tothe femoralneckinourstudy.Thispositioninslightvalgusconverts shearforces(whichcanpromoteimplantloosening)into compres-sionforces[22].Beauléetal.[23]recommended7.8◦ofvalgusto decreasetheriskoffailedfemoralcomponentfixation.Thefemoral implantshouldnotbeinvarus,asthispositionincreasesnotonly theriskofvarustiltingoftheimplant,butalsotheriskofthinning ofthecervicalcortex,whichcanresultinafemoralneckfracture

[24].

Meancupinclinationinourstudywaslessthan45◦(44.1◦).This positionmaybeoptimalinHR withametal-on-metalimplant, inordertopromote lubricationandgoodfunction[23].Marked inclinationcanresultinedgeloading,whichbreaksupthe lubri-cationfilm,therebypromotingasepticcuplooseningbyincreasing thelooseningmoment[25,26].Inaddition,cupinclinationgreater than 55◦ is nearly always associated with the risk of adverse reactionstometaldebris.Thesameappliestothesagittalplane. Retroversion of the cup can result in anterior cam impinge-ment of the cup on the anterior femoral neck, which would be expected to result in subluxation and increased metal ion shedding [27].Great care shouldtherefore be taken toremain withinthesafetyzone(inclination<45◦ andanteversion15–30◦)

5. Conclusion

Ourresultsshowthat,withtheexceptionofacetabular ante-version,HRmorecloselyreplicatesthenativehipgeometrythan doesTHA.Anteversionof thecupwasgreaterthan anteversion ofthenativebonyacetabulum, butthis positioncomplieswith currentrecommendationsforacetabularcomponentpositioning duringHR.

Disclosureofinterest

AlexandreArnould,FlorianBoureau,andKevinBenaddeclare thattheyhavenoconflictsofinterestconcerningthisarticle.

Henri Migaud declares that he has no conflicts of interest concerningthis articlebutreportsworkingasaneducationand researchconsultantforZimmerandTornier.

Gilles Pasquier declares that he hasno conflicts of interest concerningthis articlebutreportsworkingasaneducationand researchconsultantforZimmer.

JulienGirarddeclaresthathehasnoconflictsofinterest con-cerning this article but reports working as an education and researchconsultantforSmith&NephewandforMicroport. References

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