Comparative validation of the radiographic and tomographic measurement of patellar height

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Original

Article

Comparative

validation

of

the

radiographic

and

tomographic

measurement

of

patellar

height

夽

Marco

Antonio

Schueda

,

Diego

Costa

Astur

,

Gustavo

Gonc¸alves

Arliani

,

Gilberto

Hornburg

_,

_Ricardo

_Serpa

_,

_Walter

_Heinig

_Neto

_,

_Camila

_Cohen

_Kaleka

_,

Moisés

Cohen

a_{OrthopedistandcoordinatoroftheKneeSurgeryandArthroscopyPost-GraduationServiceofInstitutodeOrtopediaeTraumatologia}

(IOT)andTraumaSports,Joinville,SC,Brazil

b_{OrthopedistattheSportsTraumatologyCenteroftheOrthopedicsandTraumatologyDepartmentofEscolaPaulistadeMedicinada}

UniversidadeFederaldeSãoPaulo(Unifesp),SãoPaulo,SP,Brazil

c_{RadiologistattheImagingDiagnosticServiceofHospitalDonaHelena,Joinville,SC,Brazil}

d_{OrthopedistandPostgraduateStudentattheKneeSurgeryandArthroscopyServiceofIOTandTraumaSports,Joinville,SC,Brazil} e_{OrthopedistatFaculdadedeCiênciasMédicasdaSantaCasadeMisericórdia,SãoPaulo,SP,Brazil}

f_{FullProfessorandHeadoftheOrthopedicsandTraumatologyDepartmentofEscolaPaulistadeMedicinadaUnifesp,SãoPaulo,SP,}

Brazil

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Articlehistory:

Received8May2012 Accepted3August2012

Keywords:

Jointinstability Patella Radiography Tomography

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Objective:Toevaluateandvalidatetheradiographicmeasurementofpatellarheightwith computerizedtomographyscans.

Methods:Measuredthepatellarheightthroughthelateralradiographicimagesupportedby onefootandsagittaltomographicviewofthekneeinextension,flexionof20◦_,and quadri-cepscontractionof40patients(80knees),asymptomaticandnohistoryofkneeinjuries usingInsall–Salvatiindex.Therewere20adultfemalesand20adultmales.

Results:Theheightpatellarindexwashigherinwomenofallimagestaken,inproportion. Therewasnostatisticaldifferenceofpatellarheightindexbetweentheradiographicsand tomographicsimages.

Conclusion: TheInsall–Salvatiindexinfemaleswashigherinallcasesevaluated. Further-more,itispossibletomeasurethepatellarheightindexduringtomographicstudywithout distortingtheresultsobtained,usingtodefinethepresenceofpatellaaltaorpatellabaja.

©2013SociedadeBrasileiradeOrtopediaeTraumatologia.PublishedbyElsevierEditora Ltda.Allrightsreserved.

夽

StudyconductedatCentroDiagnosticoporImagemdoHospitalDonaHelena,Joinville,SC,Brazil.

∗ _{Correspondingauthorat:RuaBorgesLagoa783,5}◦_{andar,VilaClementino,CEP04038-032,SãoPaulo,SP,Brazil.} E-mail:[email protected](M.A.Schueda).

Validac¸ão

comparativa

da

medida

da

altura

patelar

radiográfica

e

tomográfica

Palavras-chave:

Instabilidadearticular Patela

Radiografia Tomografia

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e

s

u

m

o

Objetivo: Avaliarevalidaramedidadaalturapatelarradiográficaemexamestomográficos emextensão,flexãode20◦_{econtrac¸ãodoquadríceps.}

Métodos: Mensurac¸ão, com o uso do índice de Insall–Salvati, da altura patelar, por meioda imagemradiográficacomapoio monopodálicodeperfildojoelhoecorte sag-italde tomografiadojoelhoem extensão,flexão de20◦ _{econtrac¸ão doquadríceps,de} 40 indivíduos(20decadasexo,80 joelhos),adultos,assintomáticos esemhistórico de lesão.

Resultados: Oíndicedealturapatelarfoimaiornasmulheresemtodasasimagensfeitas, deformaproporcional.Nãoexistiudiferenc¸aestatísticadosvaloresdaalturapatelarentre oestudoradiográficoeotomográfico.

Conclusão: OvalordoíndicedeInsall–Salvatinosexo femininofoimaiorem todasas situac¸õesavaliadas.Alémdisso,épossívelmensurar,comométodousadoesemdistorc¸ões dosresultadosobtidos,ovalordaalturapatelarduranteoestudotomográficoparadefinir apresenc¸adepatelaaltaoubaixa.

©2013SociedadeBrasileiradeOrtopediaeTraumatologia.PublicadoporElsevier EditoraLtda.Todososdireitosreservados.

Introduction

Thepositionofthepatellainrelationtothefemurhasgreat clinicalimportanceanditisapredisposingfactorinthe etiol-ogyoffemoropatellarpainandinstability.1,2_{Definingwhether}

thejointbetweenthepatellaandthefemurisanatomically functionalisadeterminingfactortounderstandandtreatthis orthopedicsyndrome.

The change in patellar height is called patella alta when the patella is above its anatomical position and patellainferawhenthepatellaisbelowitsanatomical posi-tion.

This change in the vertical plane may result in other pathologiesoftheknee,suchasosteochondropathy,patellar luxationandinflammatoryprocessesthatcausepainandjoint effusion.3–5_{Thecorrectevaluationofitspositionisimportant}

forthealignmentstudyofthisjointanddiagnosisinpatients withanteriorkneepain.

Several methods have been described for patellar height measurement through lateral radiographic images of the knee.3,6–9 _{Thus, the radiographic study makes}

possible to determine whether the patella is incon-gruous in the vertical plane in relation to the femoral condyles.

Theuse of computed tomography (CT)for the study of patellaabnormalitieswasdescribedbytheFrenchschoolof Lyon.10 _{TheCT examinationallowsdeterminingvalueshat}

weredevelopedtodefinethepatellalateralizationinthe coro-nalplaneandtheshapeofthepatellarboneandcondyleswith thekneeindifferentdegreesofflexionandinmuscle contrac-tion.However,thistechniquedoesnotincludethestudyof patellarheight.

The aim of this study is to assess the agreement betweentomographicmeasurementsofpatellar heightand lateral knee radiographic images in randomly selected patients.

Materials

and

methods

This study was approved by the ethics committee of the current institution. Eighty knees of forty asymptomatic individuals, with no previous history of knee injury, were randomly recruited and examined by radiography and CT betweenDecember2009andAugust2010.

Thefollowingprotocolwasusedforeachassessedknee:

1 Lateralradiographyofthekneesupportedbyonefootonly and20degreesofflexion(Fig.1).

2 Computedtomographywithsagittalviewassessmentinfull extension,20degreesofflexionandquadricepscontraction (Fig.2).

TheradiographyandCTassessmentswereperformedby the same radiology technician, using standard positioning amongthestudyparticipants.

TheInsall–Salvatitechniquewaschosentomeasure patel-lar height in radiographic and CT assessments. For this purpose,thepatellartendonlengthandthepatellarlongest axisweremeasured.Theassociationbetweenthesevalues, respectively, resultsintheInsall–Salvatiindex. Thenormal valueofInsall–Salvatiindexinthelateralkneeradiographic measurementis1.02;values<0.8areconsideredpatellainfera, whereasvalues>1.2areconsideredpatellaalta.6

StatisticalanalysiswasperformedusingStudent’sttestto assessthedistributionofcontinuousvariablesandtoestimate thedifferencebetweentheobservedvalues.

Results

The40studyparticipants,20menand20women,wereaged 18–52years,withameanageof30.8years.

Fig.1–Lateralradiographicimageofthekneewithpatellar heightmeasurementusingtheInsall–Salvatitechnique.

20degreesofflexion(CTF)andinquadricepscontraction(CTC) ofthe 80evaluatedkneescanbeseeninTable1.Itcanbe observedthattherewasastatisticallysignificantdifference betweenpatellarheightmeasurementtechniquesand gen-deroftheassessedpatient(p<0.05).Regardingthesideofthe studiedknee,rightandleft,therewasnostatisticaldifference inpatellarheightevaluation(p>0.05).

Among the 40 patients, there was a statistical correla-tionbetweenCTandradiographicmeasurementsofpatellar

heightwiththekneeflexedat20degrees(ISF),inextension (ISE) and withcontractionofthe quadriceps(ISC)(p<0.05). Basedontheradiographicpatellarheightstudy(R),equations weredefinedtocorrelatetheexpectedvalueofthepatellar heightattheCT(Table2).

Discussion

Patellofemoralmisalignmentgeneratesanabnormalcontact betweenthesestructures,developingintoanoverloadofthe articularsurfaceandtheforcesontheextensormechanism,11

predisposingtopatellarluxation,chondromalaciaand knee osteoarthritis.12 _{These pathologies often cause knee pain.}

Moststudiesofanteriorkneepaincausalfactorshavesought to associate theseabnormalities with patellar tilt and dis-placement,themorphologyofthefemoraltrochlea13,14 _and

thetibiofemoralfrontalplanealignment.15,16

Therearealsochangesinthesagittalplane,involvingthe patellaaltaandthepatellainfera.Patellaaltaisconsidereda clinicalentityassociatedwithpainandpatellofemoral insta-bility, as a consequenceof decreasedbone stability of the patellawiththefemur.11_{However,patellarheight}

measure-ment isdemonstrated andanalyzedbylateralradiographic imageswiththerelaxedquadricepsmuscle.Thecontraction ofthismusclecauseselevationandlateralizationofthepatella andinfluencespainsymptomsandsignsofinstabilityinthe affectedknee.11,17

Severalmethodshavebeendescribedformeasurementof patellarheight.InsallandSalvati6_{werethefirsttodescribe}

a specific method to establish patellar height and associ-ated the patellar tendon length with the greatest patellar lengthonradiographs.Bierdertand Albrecht18_usedMRIto

evaluate patellar height and correlated the patella to the femur. Forthis purpose,theyusedcartilaginous landmarks and thus eliminated the bone variation, which is possi-bly the largest source of error in accurate patellar height measurement.19,20

The results of this study show that the Insall–Salvati method can be applied to CT with sagittal view in

Table1–MeanmeasurementofpatellarheightusingtheInsall–Salvatimethodforradiographicassessment(R)andCT inextension(CTE),20degreesofflexion(CTF)andquadricepscontraction(CTC)betweenmenandwomen.Itcanbe observedthatthereweresignificantdifferencesbetweenthegendersinallassessments(p<0.05).

Imagingassessment Male Female

Mean SD Mean SD pvalue

Patellarheightvalue

R 1.07 0.15 1.2 0.17 <0.05

CTE 0.95 0.14 1.04 0.18 <0.05

CTC 1.04 0.14 1.17 0.19 <0.05

CTF 1.03 0.14 1.16 0.18 <0.05

SD=standarddeviation.

Table2–FormulasdevelopedtoobtainthepatellarheightvalueusingtheInsall–SalvatiindexonCTinextension(ISE), 20degreesofflexion(ISF)andquadricepscontraction(ISC)inthepresenceoftheInsall–Salvatiindexobtainedatthe radiographicassessment(R)supportedbyonefootonly,inmaleandfemalepatients.

Patellarheightconversionequations

Male Female

Extension ISE=0.11+0.78×R ISE=0.03+0.84×R

20degreesofflexion ISF=0.12+0.85×R ISF=0.02+0.95×R

Quadricepscontraction ISC=0.14+0.84×R ISC=0.02+0.96×R

extension, as well as with 20 degrees of flexion and in contraction.6 _{This index was higher in female individuals}

for all measurements. This difference is probably due to thesmallersizeofthepatella infemales,asmentioned in otherstudies.21–24_{Redziniaketal.}25_{suggestedintheirstudy}

that the Insall–Salvati index measurement in men ranges from 0.9 to 1.1 and in women, from 0.94 to 1.18, which shows that this index is higher in women. Miller et al.26

foundno suchdifference betweenmenand womenin his study.

The results obtained when comparing patellar height measurement through radiography and CT showed a sig-nificant correlation. Considering that CT has been used as the main complementary resource in the assessment of pathologies caused by patellofemoral misalignment,3,27

patellar height measurement, together with the imaging study used by the Lyon protocol8 _{helps its}

understand-ing in different situations without compromising the results obtained, as there was no statistical difference betweenthedifferent positionsstudiedinradiographsand CT scans. Thus, regardless of the measurement being made through radiographic or tomographic assessment, patellar height can be obtained by the index measure-ment.

AcriticismofthestudyisthatonlytheInsall–Salvatiindex wascorrelated,asthisindexisnotunanimouslyacceptedin theliteratureforpatellarheightevaluation.

Conclusion

TheInsall–Salvatiindexinfemaleswashigherinallassessed situations.Furthermore,itispossibletomeasure,withthe methodusedandwithoutdistortionoftheresults,thevalue ofpatellarheightduringthetomographicstudytodefinethe presenceofthepatellaaltaorpatellainfera.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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