Rev. bras. ortop. vol.49 número2

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w w w . r b o . o r g . b r

Original

Article

Preoperative

planning

of

primary

total

hip

arthroplasty

using

conventional

radiographs

夽

,

夽夽

Edson

Hidenori

Miashiro

a,∗

,

Edson

Noboru

Fujiki

b

,

Eduardo

Nagashigue

Yamaguchi

b

,

Takeshi

Chikude

b

_,

_Luiz

_Henrique

_Silveira

_Rodrigues

b

_,

_Gustavo

_Martins

_Fontes

b

_,

Fausto

Boccatto

Rosa

b

a_Universidade_Estadual_de_Londrina,_Londrina,_PR,_Brazil

b_Orthopedics_Clinic,_Hospital_Estadual_Mário_Covas,_Faculdade_de_Medicina_do_ABC_(FMABC),_Santo_André,_SP,_Brazil

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received11October2012

Accepted5December2012

Availableonline2April2014

Keywords:

Hiparthroplasty

Planning

Hipradiography

a

b

s

t

r

a

c

t

Objective:theobjectiveofthisstudywastopresentananalogmethodforpreoperative

plan-ningofprimarytotalhiparthroplastyproceduresbasedonmeasuringthecomponentsby

overlayingthetransparenciesoftheprosthesisonthepreoperativeradiographsand

check-ingtheaccuracy,bothforpredictingthesizeoftheacetabularandfemoralcomponents

usedandforrestoringtheoffsetandcorrectingthedysmetria.

Methods:betweenMarch2005andJuly2009,56primarytotalhiparthroplastyprocedures

performedon56patientsattheMarioCovasStateHospitalinSantoAndréwereanalyzed.

Themeasurementsonthefemoralandacetabularcomponentsobtainedthroughplanning

werecomparedwiththosethatwereusedinthesurgery.Theoffsetsmeasuredthrough

thepreoperativeplanningwerecomparedwiththosemeasuredonthepostoperative

radio-graphs.Dysmetriawasevaluatedbeforeandaftertheoperation.

Results:accuracyof78.6%(p<0.001)inpredictingthesizeoftheacetabularcomponentand

82.2%(p<0.001)inpredictingthefemoralnailwasobserved.Theoffsetsmeasuredthrough

preoperativeplanningwerestatisticallysimilartotheoffsetsmeasuredonthepostoperative

radiographs.Aftertheoperation,weobservedabsoluteequalizationin48.2%ofthecases.

In87.5%,thedysmetriawaslessthanorequalto1cmandin69.6%,itwaslessthanorequal

to0.5cm.

Conclusions:theaccuracywas78.6%and82.2%,respectively,fortheacetabularandfemoral

components.Theoffsetsthatwereplannedpreoperativelywerestatisticallysimilartothose

measuredonpostoperativeradiographs.Wefoundabsoluteequalizationin48.2%ofthe

cases.

Ltda.Allrightsreserved.

夽

Pleasecitethisarticleas:MiashiroEH,FujikibEN,YamaguchibEN,ChikudebT,RodriguesbLHS,FontesbGM,etal.Planejamento

pré-operatóriodeartroplastiastotaisprimáriasdequadrilcomousoderadiografiasconvencionais.RevBrasOrtop.2014;49:140–148.

夽夽

WorkperformedatHospitalEstadualMárioCovas,FaculdadedeMedicinadoABC(FMABC),SantoAndré,SP,Brazil.

∗ _{Corresponding}_author.

E-mail:lhfmj@yahoo.com.br(E.H.Miashiro).

(2)

Planejamento

pré-operatório

de

artroplastias

totais

primárias

de

quadril

com

o

uso

de

radiografias

convencionais

Palavras-chave:

Artroplastiadequadril

Planejamento Quadril/radiografia

r

e

s

u

m

o

Objetivos:apresentarummétodoanalógicodeplanejamentopré-operatóriodeartroplastias

totaisprimáriasdequadrilbaseadonamedidadoscomponentespelasobreposic¸ãodas

transparênciasdaprótesesobrearadiografiapré-operatória.Everificaraacurácia,tantona

previsãodotamanhodocomponenteacetabularedocomponentefemoralusadocomona

restaurac¸ãodooffsetenacorrec¸ãodasdismetrias.

Métodos: entremarc¸ode2005e julhode 2009foramanalisadas56artroplastias totais

primáriasdequadrilfeitasem56pacientesnoHospitalEstadualMárioCovas.As

medi-dasdoscomponentesfemoraiseacetabularesobtidasnoplanejamentoforamcomparadas

comasqueforamusadasnacirurgia.Osoffsetmedidosnoplanejamentopré-operatório

foramcomparadoscomosmedidosnaradiografiapós-operatória.Adismetriafoiavaliada

nosmomentospréepós-operatórios.

Resultados: foi observadaumaacurácia de78,6%(p<0,001)naprevisão dotamanhodo

componenteacetabularede82,2%(p<0,001)naprevisãodahastefemoral.Osoffsetmedidos

noplanejamentopré-operatórioforamestatisticamentesemelhantesaosoffsetmedidosna

radiografiapós-operatória.Nopós-operatórioobservamosaequalizac¸ãoabsolutaem48,2%

doscasos.Em87,5%adismetriafoiigualaoumenordoque1cmeem69,6%foiigualaou

menordoque0,5cm.

Conclusões: aacuráciafoide78,6%e82,2%,respectivamente,paraoscomponentes

acetab-ularesefemorais.Osoffsetplanejadospré-operatórioforamestaticamentesemelhantes

aosmedidosnaradiografiapós-operatória.Verificamosequalizac¸ãoabsolutaem48,2%dos

casos.

EditoraLtda.Todososdireitosreservados.

Introduction

Preoperative planning for hip arthroplasty procedures was

initially poorly understood and used, since the designs

and sizes of the prostheses were very limited.1,2 _Today,

the variety of designs and the number of sizes of the

components have increased considerably, and total hip

arthroplasty has been transformed into a more complex

procedure.2

Preoperativeplanningmakesitpossibletoappropriately

choosethesizesofthecomponents,equalizethelimbsand

reducethedurationoftheoperation.2

Charnley1 _demonstrated _the_importance _of_preoperative

radiographicstudiesforchoosingthecorrectsizeofthe

pros-thesiscomponents,andalsoemphasizedtheimportanceof

restoringtheoffset.Thelatterisdirectlyrelatedtothestability

ofthearthroplasty.1,3–6

Dysmetriaisafrequentcomplicationoftotalhip

arthro-plasty.Itcauseslumbalgia,gait disordersand sciaticnerve

injuries.7–11

In this study, using conventional radiographs, we

present a preoperative planning method for primary

total hip arthroplasty based on measuring the

compo-nents through overlaying transparencies of the prosthesis

on the preoperative radiograph. The study had the

fol-lowing objectives: to assess the accuracy of predicting

the sizes of the acetabular and femoral components; to

analyze the restoration of the offset; and to correct the

dysmetria.

Material

and

methods

TheprojectforthisstudywasapprovedbytheEthics

Commit-teeoftheABCMedicalSchool,underthenumberCEP258/2007.

Between March2005and July2009,56primarytotal hip

arthroplastyproceduresperformedon56patientsatHospital

EstadualMárioCovaswereanalyzed.

Themeanagewas65years.Inall,37patients(66.1%)were

femaleand19(33.9%)weremale.Allthepatientshada

diag-nosisofarthrosis.

The inclusion criterion was the presence of unilateral

hiparthrosis.Theexclusioncriteriawerebilateralarthrosis;

moderate or severe acetabularprotrusion according to the

Sotelo-GarzaandCharnleyclassification;12_acetabular

dyspla-siagreater than CrowetypeI;13 _femoral_neck_fracture;_and

alterationsinotherjointsthatcauseddysmetria.

Allthearthroplastyproceduresweretotalandcemented,

andwereperformedusingaposteriorapproach.

Pelvicradiographswereperformedinanteroposterior(AP)

view,centeredonthepubicsymphysis,withthelowerlimbs

rotatedinternallyby15◦ _and_a_distance_of₁_m_between_the

bulboftheapparatusandthefilm;andinlateralviewcovering

theproximalone-thirdofthefemur.

Theacetabularcomponentwasmeasuredbyoverlayingthe

acetabulartransparencyontheAPradiographofthenormal

hip,inordertochoosethenumberthatfittedtheoutlineofthe

acetabulumbest.Theparametersusedweretheupperlateral

borderoftheacetabulum,theteardropandKöhler’siliosciatic

(3)

Fig.1–(A)Overlayingthetransparencyoftheacetabular componentonthenormalside.Thewhitearrowontheleft sideindicatestheupperlateralborderoftheacetabulum. Thewhitearrowontherightsideindicatestheteardrop. Thecenterofrotation(CR)ofthehipismarkedonthe transparencyandisindicatedbytheblackarrow.(B) Köhler’siliosciaticline.ThewhitearrowindicatesKöhler’s iliosciaticline.Thesizeoftheacetabularcomponent shouldnotgobeyondtheiliosciaticline.Theblackarrow indicatesthecenterofrotation.

determinedsuchthatitwouldnotgobeyondtheiliosciatic

line(Fig.1B).

Afterthecenterofrotation(CR)ofthenormalhiphadbeen

markedontheradiograph(Fig.1AandB),itwastransferred

tothesidetobeoperated.Totransferit,threereferencelines

wereusedasparameters:

LineH:goingalongthelowerlimitoftheteardrops(Fig.2A)

LineV1:goingalongthelateralborderoftheteardroponthe

normalsideandperpendicularlytotheintersectionwithline

H(Fig.2A)

LineV2:goingalongthelateralborderoftheteardroponthe

sidetobeoperatedandperpendicularlytotheintersection

withlineH(Fig.2A)

Fromthereferencelines,theCRwastransferredfromthe

normaltotheaffectedside.Wethendefinedfourdistances

measuredinmillimeters:

Fig.2–(A)ReferencelinesH,V1andV2.Thecenterof rotationismarkedonthenormalside,indicatedbyan arrow.Referencelines:thefirstgoesalongtheloweredge oftheteardrops(lineH);thesecondisperpendiculartoline Handgoesalongthelateraledgeoftheteardroponthe normalside(lineV1);thethirdisalsoperpendiculartoline Handgoesalongthelateraledgeoftheteardroponthe sidetobeoperated(lineV2).(B)TransferoftheCRfromthe rightside(normal)totheleftside.Distanceashouldbe equaltoa′_and_distance_b_should_be_equal_to_b′_.

Distancea:fromtheCRofthenormalsidetolineV1(Fig.2B);

Distanceb:fromtheCRofthenormalsidetolineH(Fig.2B);

Distancea′_: _same_length_as_distance_a,_starting_at_line_V2

(Fig.2B);

Distance b′_: _same _length_as _distance_b, _starting_at_line _H

(Fig.2B).

Theintersectionpointbetweenthedistancesa′_and_b′_was

theCRofthesidetobeoperated.

Thefemoraloffsetwasthedistancealongalinegoing

per-pendicularlyfromthecenterofrotationofthefemoralhead

totheintersectionwithalinegoingthroughthemiddleofthe

longaxisofthefemur.14

The offset of the prosthesis was the distance from a

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Fig.3–Offsetoftheprosthesis.

prosthesisheadtotheintersectionwithalinegoingthrough

themiddleofthemajorlongitudinalaxisofthefemoralnail

(Fig.3).

Tochoosethesizeofthe femoralcomponent,its

trans-parencywasoverlaidontheAPradiographonthesidetobe

operated(Fig.4).Thefemoralcomponentchosenwas

deter-minedtobetheonewithanoffsetclosesttothatofthenormal

side.

Thedysmetriacouldbeoneofthreetypes:atthecostofthe

femur,atthecostoftheacetabulumoratthecostofboththe

femurandtheacetabulum(mixedorcombined).15_To_identify

Fig.4–Measurementusingthetransparency.

Fig.5–Normalhips.Line1goesalongthelowerlimitof thesciatictuberosities.Line2goesalongtheupperlateral edgeoftheacetabula.Line3goesthroughthemidpointof thelessertrochanters.Thethreelinesareparallel.

dysmetria, theparametersusedwerethreelinesontheAP

radiographofthepelvis,centeredonthepubicsymphysis:15

Line1:determinedbytracingoutastraightlinethroughthe

mostdistalpointsofthesciatictuberosities;

Line2:determinedbytracingoutastraightlinealongthe

upperlateraledgeoftheacetabula;

Line3:determinedbytracingoutastraightlinethroughthe

midpointsofthelessertrochanters.

Innormalhips,thethreelinesareparallel(Fig.5).

Tomeasurethedysmetria,theparametersusedwereline

H,going along the lower limitofthe teardrops, and line3

(Fig.6).

Thepelviswiththeacetabularcomponentchosen,the

cal-culatedCRandthefemurtobeoperatedweredrawnusing

Dysmetria = a–b

(5)

Fig.7–Thewhitearrowindicatesthedrawingofthepelvis withtheacetabularcomponent.Theblackarrowindicates thedrawingofthefemur.

tracingpaperoverlainontheAPradiograph(Fig.7).The

draw-ingofthepelviswasthenoverlainonthedrawingofthefemur,

and bothof thesewere placedon the transparency ofthe

femoralcomponent(Fig.8).

Theleveloftheosteotomyofthefemoralneckfor

equaliz-ingthelimbswasdefinedbyslidingthedrawingsacrossthe

femoraltransparency.Forthis,lines1,2and3hadtobekept

parallel(Fig.8).

Thechi-squaretestwasappliedtoascertaintheaccuracy

ofthepredictionsfortheacetabularandfemoralcomponents.

TheMann–Whitneytestwasappliedtocomparetheplanned

offsetmeasurementswiththoseobtainedonthe

postopera-tiveradiograph.

Dysmetriawasanalyzedaftertheoperation.

Weused the Statistical Package for the Social Sciences

(SPSS),version17.0,toobtainresultsofastatisticalnature.

Results

Accuracy of 78.6% (p<0.001) in predicting the size of the

acetabularcomponent was observed (Table 1). Accuracyof

82.2% (p<0.001) in predicting the femoral nail was found

(Table2).

Fig.8–Preoperativeplanning.Lines1,2and3areparallel.

Theoffsetsmeasuredinthepreoperativeplanning were

statisticallysimilartotheoffsetsmeasuredonpostoperative

radiographs,withp=0.630(Table3).

ThemeandisplacementoftheCRwas4mminthe

hori-zontalaxisand6mmintheverticalaxis.

Themeanpreoperativedysmetriawas1.6cm,witharange

from0.0to3.9cm(Table4).Aftertheoperation,weobserved

that the limbs had been equalized in 27 patients (48.3%),

stretchedin18(32.1%)andshortenedin11(19.6%).Themean

postoperativedysmetriawas0.4cm,witharangefrom0.0to

2.1cm(Table5).Weobservedthatthepostoperativedysmetria

waslessthanorequalto1.0cmin87.5%ofthepatientsand

lessthanorequalto0.5cmin69.6%.

Withregardtothefemoralnail,itwasobservedtobe

pos-itioned neutrallyin43 hips(76.7%),withvalgusrotationin

three(5.4%)andwithvarusrotationin10(17.9%).

Theanalysisofthemeaninclinationoftheacetabular

com-ponentinthefrontalplaneshowedthatthiswas42◦_,_with_a

rangefrom30◦_to₅₈◦_.

Thevariationsintheoffsetonpostoperativeradiographs

in relation to what was planned were statistically similar

(p=0.123),withregardtoneutral,varusandvalguspositions

ofthefemoralnail.

The correlation betweenvariations inthe postoperative

offsetvaluesrelativetowhatwasplannedandtheinclination

oftheacetabularcomponentwasnotstatisticallysignificant

(p=0.657).

Discussion

During the 1970s, only limited numbers of implants were

placed.2,16 _Today, _there _are _several _different _designs_and _a

large number of sizes available,17 _which _makes _planning

essential.2,16 _However,_few_studies_have_evaluated_the

accu-racyofcomponentsizepredictions.2,6,16,18,19

Webeganthisinvestigationwiththeaimofevaluatingthe

methodusedinourinstitution.

Today,planningmethodsusingdigitalradiographsexist.

These enable high precision,6,20 _as _demonstrated _by _Eggli

etal.,6_who_observed_accuracy_of_around_90%_in_component

predictions.

InBrazil,digitalradiographsarestillnotusedroutinely.The

methoddescribedinourstudy waslessprecise,butcanbe

appliedtoconventionalradiographswithoutadditionalcost

fortheprocedure.

Inoursample,weobservedthattheaccuracywas78.6%for

theacetabularcomponentsand82.2%forthefemoral

com-ponents. These values were similar to those presentedby

Paniegoetal.,2_who_found_accuracies_of_83%_for_the

acetab-ularcomponentsand76%forthefemoralcomponents;andto

thosereportedbyGonzálezDellaValleetal.,16_who_observed

accuraciesof83%and78%,respectively,fortheacetabularand

femoralcomponents.Bothoftheauthorgroupsusedplanning

methodswithconventionalradiographs.

Itisdifficulttopredicttheexactmagnificationin

conven-tionalradiographs.Forthisreason,inordertominimizethe

possibledeviations,westandardizedproductionofthe

(6)

Table1–Frequencyandpercentagedistributionoftheacetabularcomponentsusedatthetwoobservationtimes.

Acetabularcomponent planned

Acetabularcomponentused Total

44 48 50 52

44 18 0 0 0 18

32.10% 0.00% 0.00% 0.00% 32.10%

48 0 20 0 0 20

0.00% 35.70% 0.00% 0.00% 35.70%

50 0 1 3 0 4

0.00% 1.80% 5.40% 0.00% 7.10%

52 0 5 1 3 9

0.00% 8.90% 1.80% 5.40% 16.10%

54 0 0 0 3 3

0.00% 0.00% 0.00% 5.40% 5.40%

56 0 0 1 1 2

0.00% 0.00% 1.80% 1.80% 3.60%

Total 18 26 5 7 56

32.10% 46.40% 8.90% 12.50% 100.00%

Source:HospitalEstadualMárioCovas.

Table2–Frequencyandpercentagedistributionofthefemoralnailsusedatthetwoobservationtimes.

Femoralcomponent planned

Femoralcomponentused Total

10.5 12 13.5 15 35.5 37.5

10.5 8 0 0 0 0 0 8

14.30% 0.00% 0.00% 0.00% 0.00% 0.00% 14.30%

12 3 15 0 0 0 0 18

5.40% 26.80% 0.00% 0.00% 0.00% 0.00% 32.10%

13.5 0 0 1 0 0 0 1

0.00% 0.00% 1.80% 0.00% 0.00% 0.00% 1.80%

15 0 1 1 1 0 0 3

0.00% 1.80% 1.80% 1.80% 0.00% 0.00% 5.40%

16.5 0 0 0 1 0 0 1

0.00% 0.00% 0.00% 1.80% 0.00% 0.00% 1.80%

35.5 0 0 0 0 15 1 16

0.00% 0.00% 0.00% 0.00% 26.80% 1.80% 28.60%

37.5 0 0 0 0 2 6 8

0.00% 0.00% 0.00% 0.00% 3.60% 10.70% 14.30%

44 0 0 0 0 0 1 1

0.00% 0.00% 0.00% 0.00% 0.00% 1.80% 1.80%

Total 11 16 2 2 17 8 56

19.60% 28.60% 3.60% 3.60% 30.40% 14.30% 100.00%

Arthroplasty procedures aim to restore the hip biome-chanicstonormalconditions,throughchoosingappropriate prosthesissizes, so as toavoid intraoperativeand postop-erativecomplicationsandconsequentlyincreaseprosthesis longevity.

Theimportanceoftheoffsetisrelatedtothefunctioningof theabductormusculature:1,4,5,21_through_planning,_it_is

possi-bletorestoreit.1,3–6,21,22_Its_restoration_is_related_to_the_stability

ofthearthroplasty.1,3,6,21_The_offsets_measured_in_the

preop-erative planningin oursamplewere statisticallysimilarto

Table3–Descriptionofandcomparisonbetweentheoffsetsplannedandused.

Pairofvariables n Mean Standard deviation

Minimum Maximum 25th

percentile

Median 75th

percentile

Significance (p)

Offsetplanned(mm) 56 39.7 5.4 30.0 55.0 35.0 38.5 42.0 0.630

Offsetused(mm) 56 40.3 6.4 30.0 57.0 35.0 39.0 45.0

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Table4–Descriptionoftheaffectedlowerlimbbeforetheoperation.

Lengthofaffectedlower limbbeforethe operation(cm)

n Mean Standard

deviation

percentile

Median 75th

percentile

Shortened 53 1.7 0.9 0.4 3.9 1.0 1.5 2.3

Equalized 3 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Total 56 1.6 0.9 0.0 3.9 0.9 1.5 2.2

Table5–Descriptionoftheaffectedlowerlimbaftertheoperation.

Lengthofaffectedlower limbbeforethe operation(cm)

n Mean Standard

deviation

percentile

Median 75th

percentile

Shortened 11 0.9 0.7 0.3 2.1 0.4 0.8 1.7

Stretched 18 0.7 0.3 0.4 1.5 0.5 0.6 1.0

Equalized 27 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Total 56 0.4 0.5 0.0 2.1 0.0 0.3 0.6

thosemeasuredonpostoperativeradiographs.Thisisrelated totheaccuracyof82.2%inpredictingthesizeofthefemoral nails,whichhadfixedoffsetvalues.Therefore,ifthesizeof thefemoralcomponentiscorrect,thereisagreaterlikelihood ofachievingtheplannedoffset.

In1988,Yoderetal.23_observed_greater_rates_of_loosening

ofthefemoralcomponentwhentheacetabularcomponent

wasplacedaboveandlaterallytothecenterofrotation.In

1996,Pagnanoetal.24_observed_greater_rates_of_loosening_of

theacetabularandfemoralcomponentswhenthe

acetabu-larcomponentwasplacedabovethecenterofrotation,even

withoutlateraldisplacement.Inoursample,meanvariations

fromtheplannedcenterofrotationwere4mminthe

hori-zontalaxisand6mmintheverticalaxis.Thesewerecloseto

whatwaspresentedbyPaniegoetal.,2_who_observed_that_96%

ofthecentersofrotationwereplacedwithdisplacementof

lessthan4mmfromtheplannedcenterofrotation.Itseems

tousthat thechangesinpositionofthe centerofrotation

aredifficulttomeasure,sincetheycanvarygreatlywiththe

magnificationofconventionalradiographs,giventhatthese

changesaremeasuredinmillimeters.Yoderetal.23_observed

that measurements of4–5mmare very imprecise on

con-ventionalradiographs,whichexplainsthegreateraccuracyof

planningwhendigitalradiographsareused.

Insituationsinwhichtheacetabulumpresentslossofbone

stockordysplasia,placementoftheacetabularcomponentat

thecenter ofidealrotationismoredifficult,sinceinthese

casesadditionalcoveragewithgraftsfromthefemoralhead

maybeneeded.Thesecaseswereexcludedfromourstudy,

sincetheycouldhaveledtobiasintheanalysison

displace-mentofthecenterofrotation.

Dysmetria is a common complication following hip

arthroplasty.7–9 _Its_correction_can_be_envisaged_through

pre-operativeplanning1,3,6,21_and_also_during_the_operation.8_The

operatedside oftenbecomes stretched.7 _Dysmetria _greater

than1cmhasbeencorrelated withlumbalgia.9 _Our_results

wereinferiortothosepresentedbyEgglietal.,6_who_observed

dysmetriaoflessthan5mmin94%ofthecases.Inour

sam-ple,weobservedabsoluteequalizationin48.2%ofthecases.

In87.5%,thedysmetriawaslessthanorequalto10mmand

in69.6%itwaslessthanorequalto5mm.However,itneeds

tobetakenintoconsiderationthatthestudybyEgglietal.6

wasconductedusingdigitalradiographs.

Dolhain etal.5 _reported_that_varus _or_valgus_positioning

of the femoraland acetabular components influenced the

offset of the arthroplasty. In our sample, the relationship

betweenthevaluesofincreased,decreasedandequalized

off-setachievedaftertheoperationthroughputtingthefemoral

component into a varus, valgus or neutral position was

analyzed.Itwasobservedthattherewerenostatistically

sig-nificantdifferencesbetweenthecategoriesofthevariableof

femoralnailposition(p=0.123).Thefemoralnailwasplacedin

aneutralpositionin76.7%ofthecases,invarusin17.9%and

invalgusin5.4%.However,inthecasesinwhichweobserved

valgusorvaruspositioning,thesewereslighterrorsthatdid

notgiverisetoanysignificantvariationsinoffset.

Going againstwhat wasobservedbyDolhainet al.,5 _we

foundfromoursamplethatthevariationsinoffsetwerenot

relatedtothevariationsininclinationoftheacetabular

com-ponent.

Dobzyniacetal.25_determined_that_the_ideal_for_the_femoral

componentwastopositionthenailinneutralinthefrontal

plane,with20◦_to₃₀◦_of_anteversion_and_neutral_position._For

theacetabularcomponent,itshouldbe45◦_of_abduction_and

20◦_to₃₀◦_of_anteversion._Lewinneck_et_al.11_defined_a_safety

zonefortheacetabularcomponentcomprisinganinclination

of30◦_to₅₀◦_,_in_the_frontal_plane,_and_anteversion_of₅◦_to₂₅◦_.

Inoursample,theacetabularcomponentwaspositionedwith

ameaninclinationinthefrontalplaneof42◦_,_with_a_range

from30◦_to₅₈◦_.

Toobtaingreaterprecisioninpositioningprosthesis

com-ponents,computer-aidednavigationsystemsweredeveloped,

thus enabling lower variationinpositioning theacetabular

(8)

costisstillhighinBrazil.Inourstudy,themeaninclinationof

theacetabularcomponentinthefrontalplanewas42◦_,_with_a

rangefrom32◦_to₅₈◦_._This_variation_was_greater_than_what_has

beenpresentedusingcomputer-aidednavigationsystems.

The preoperative planning enabled greater precision in

choosingthesizesoftheacetabularandfemoralcomponents

andfacilitatedcorrectionofthedysmetria.Itmadeit

possi-bletopredictintraoperativedifficultiessuchastheneedfor

femoralheadbonegraftingforadditionalgraft coverage in

casesofacetabulardysplasia,theneedforinsituosteotomy

ofthefemoralneckincasesofsevereacetabularprotrusion

andtheneedforsmallcomponentsinshortpatients.Itmade

itpossibletochooseafemoralcomponentforrestoringthe

offset,andtodeterminetheidealcenterofrotationonthe

affectedside.

Conclusions

a) Weobservedaccuracyof78.5%and82.2%,respectively,for

theacetabularandfemoralcomponents;

b) The offsets measured during the preoperative planning

werestatisticallysimilartothosemeasuredonthe

post-operativeradiographs;

c) Therewasabsoluteequalizationin48.2%ofthecases.In

87.5%,thedysmetriawaslessthanorequalto1cmandin

69.6%itwaslessthanorequalto0.5cm.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgements

Weare gratefulforcollaborationfrom ProfessorsGiancarlo

Polesello, Sérgio Mainine, Alberto Miyazaki and Joel

Mura-chovski,whoseopinionswerefundamentalindrawingupthis

study.

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