resonance imaging analysis of the meniscus in the knee-flexed position: An openmagnetic Medial meniscus posterior root tear induces pathological posteriorextrusion ScienceDirect

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Original article

Medial meniscus posterior root tear induces pathological posterior extrusion of the meniscus in the knee-flexed position: An open magnetic resonance imaging analysis

S. Masuda , T. Furumatsu

, Y. Okazaki , Y. Kodama , T. Hino , Y. Kamatsuki , S. Miyazawa , T. Ozaki

DepartmentofOrthopaedicSurgery,OkayamaUniversityGraduateSchoolofMedicine,Dentistry,andPharmaceuticalSciences,2-5-1Shikatacho,Kitaku, Okayama700-8558,Japan

a r t i c l e i n f o

Articlehistory:

Received22November2017 Accepted1^stFebruary2018

Keywords:

Medialmeniscus Roottear Meniscusmobility Extrusion

Magneticresonanceimaging

a b s t r a c t

Background: Amedialmeniscusposteriorroottear(MMPRT)isdefinedasaninjurytotheposterior meniscalinsertiononthetibia.InMMPRT,themedialmeniscus(MM)hoopfunctionisdamaged,and theMMundergoesamedialextrusionintotheinteriorfromthesuperiorarticularsurfaceofthetibia.

However,thedetailsofMMpositionandmovementduringkneejointmovementareunclearinMMPRT cases.ThepresentstudyaimstoevaluateMMpositionandmovementviamagneticresonanceimaging (MRI)examinationoftheMMposteriorextrusion(MMPE)atkneeflexionanglesof10^◦and90^◦.We hypothesizedthat,duringkneeflexion,theMMwillshifttotheposteriorandtheposteriorextrusion willincreasecomparedtothatwhenthekneeisextended.

Materialsandmethods:Twenty-fourpatientswerediagnosedwithsymptomaticMMPRTonopenMRI examination.PreoperativeMMPE,anteroposteriorinterval(API)oftheMM,andMMmedialextrusion (MMME)atkneeflexionanglesof10^◦and90^◦weremeasured.

Results: Forpatients with MMPRT, the MMPEincreased from −4.77±1.43mmto 3.79±1.17mm (p<0.001)whenthekneeflexionangleincreasedfrom10^◦to90^◦.Further,flexingthekneefrom10^◦ to90^◦decreasedtheAPIoftheMMfrom20.19±4.22mmto16.41±5.14mm(p<0.001).MMMEshowed nosignificantchangebetweenkneeflexionanglesof10^◦and90^◦.

Discussion:Thisstudydemonstratedthat,incasesofMMPRT,theMMPEclearlyincreaseswhentheknee isflexedto90^◦,whileMMMEdoesnotchange.OurresultssuggestthatopenMRIexaminationcanbe usedtoevaluatethedynamicpositionoftheposteriorMMbyscanningthekneeasitflexesto90^◦. Levelofevidence:IV:retrospectivecohortstudy.

©2018ElsevierMassonSAS.Allrightsreserved.

1. Introduction

Amedial meniscusposteriorroot tear(MMPRT)isan injury totheposteriormeniscalinsertiononthetibia.AnMMPRTleads toabnormalkneejointkinematics[1]and cancompromisethe circumferential kneeintegrity. Therefore, axial loads cannot be transferred to hoop stress [2]. Medial meniscus (MM) under- goesradialdisplacement,whichisdefinedasMMextrusion.MM extrusionhasbeendescribed asanimportantrisk factorinthe progression ofkneeosteoarthritis,as it isinvolved in thethin- ningofarticularcartilage,jointspacenarrowing,andspontaneous

∗ Correspondingauthor.

E-mailaddress:[email protected](T.Furumatsu).

osteonecrosisoftheknee[3,4].Further,thesuccessrateofconser- vativemedicaltreatmentsorpartialmeniscectomiesinMMPRTis notfavorable;presently,meniscalrepairproceduresusingthepull- outmethodorthesutureanchormethodarerecommended[5–8].

However,theseproceduresarecontroversialandrequirefurther validation.Incasesofmedialextrusion,meniscusrepairdoesnot leadtocompleteresolution.

Magneticresonanceimaging(MRI)iseffectivefordiagnosing MMPRT[9–11].Untilnow,thecharacteristicindicationsofMMPRT havebeenreportedtoincluderadialtearsigns,ghostsigns,cleft signs,andgiraffenecksigns[12].Further,MRI examinationcan showmedialmeniscusmedialextrusion(MMME),thoughthisis notafindingspecifictoMMPRT[12,13].Whensubstantialmeniscal extrusionisidentified,itishighlylikelythatoneoftheselesions ispresent, resultinginthedisruptionofmeniscalstability [14];

https://doi.org/10.1016/j.otsr.2018.02.012

1877-0568/©2018ElsevierMassonSAS.Allrightsreserved.

however,someacuteroottearscanoccurwithoutanyextrusion.

Sunget al.comparedtheincidenceof spontaneousosteonecro- sisbetweenpatientswithMMPRTsandthosewithMMposterior horizontaltears;theincidenceofosteonecrosisandtheextentof meniscalextrusionweresignificantlygreater inthekneeswith MMPRTs[15].MeniscalextrusionafteranMMPRToftenleadsto clinicalsignssuchasearlyjointspacenarrowing,swiftprogression ofarthritis,andvariousdeformitiesoftheknee[16].

Eveninanormalknee,theMMisknowntomovetotheposte- riorasthekneeflexes[13].Duringkneeflexion,theposteriorhorn ofthemedial meniscuswillincrease peakcontactpressure and decreasecontactareainthemedialcompartmentoftheknee[17].

However,therehasbeennodynamicevaluationoftheMMincases ofMMPRT.Thismeansthat,incasesofMMPRT,thepositionand movementoftheMMduringkneemovementareunclear,includ- ingthepositionoftheMMwhenthekneeflexesto90^◦,orhow exactlytheMMmovesasthekneeflexes.InMMPRT,theposterior rootconnectingtheMMposteriorhorntothetibiaistorn.Basedon this,wehypothesizedthat,duringkneeflexion,theMMwillshiftto theposteriorandtheposteriorextrusionwillincreasecomparedto thatwhenthekneeisextended.Theaimofthepresentstudywas toevaluateMMposteriorextrusion(MMPE)ofakneeafflictedwith MMPRTduringkneeflexionanglesof10^◦and90^◦usingopenMRI examination.

2. Materialsandmethods 2.1. Patients

Twenty-fourpatients(19womenand5men;meanage,60.3 years)whounderwentsurgicaltreatmentsforMMPRTbetween March2016andJanuary2018wereincluded(Table1).Allpatients werediagnosedwithMMPRTonMRIandsurgicalfindings.We excludedpatientswithotherMMinjuriesandanteriorcruciatelig- amentinjuries.PatientshadKellgren–Lawrencegrade0,1,or2.

MMPRTsincludedbothacute(<3months)(n=11)andchronic(3 months)(n=13)tearsafterpainfulpoppingevents[18].Typesof MMPRTweredeterminedbyarthroscopicexaminationsaccording tothemeniscalroottearclassification.Arthroscopicpulloutrepair wasperformedinallpatients.

2.2. AssessmentsofMRimages

OpenMRIwasperformedusingtheOasis1.2T(HitachiMed- ical,Chiba,Japan)withacoilunderthe10^◦and90^◦knee-flexed positionsina non-weight-bearingconditionandlateralposition (affectedkneedownonthetable).StandardsequencesoftheOasis includedasagittalprotondensity-weightedsequence(repetition time[TR]/echotime[TE]:1718/12)usingadrivenequilibriumpulse witha90^◦flipangleandcoronalT2-weightedmulti-echosequence (TR/TE:4600/84)witha90^◦flipangle.Theslicethicknesswas4mm witha0-mmgap.Thefieldofviewwas16cmwithanacquisition matrixsizeof320(phase)×416(frequency)[19].Measurementsof

Table1

Demographicsandclinicalcharacteristics.

Numberofpatients 24

Gender,men/women 5/19

Roottearclassification Type1/2/3/4/5

1/20/0/3/0 Kellgren-Lawrencegrade

Grade0/I/II/III/IV

3/14/7/0/0

Age(years) 60.3±9.7

Height(m) 1.56±0.07

Bodyweight(kg) 65.9±13.3

Dataofage,height,andbodyweightaredisplayedasmean±standarddeviation.

theMMwereperformedusingasimpleMRI-basedmeniscalsizing techniqueonthesagittalandcoronalviewsatkneeflexionanglesof 10^◦and90^◦(Fig.1).First,kneeflexionwassetwiththefemoraland tibialaxialanglesat10^◦and90^◦;then,scoutviewsweretaken.Axial imagingvisualizedthecross-sectionwherebothmenisci–theMM andlateralmeniscus–werevisualizedinthesameslice.Theaxial imagingofthedistalpartofthefemurwasusedtosettheposterior condylaraxis(PCA),andareferencelinewasdrawnperpendicu- lartoit.Thereferencelinedefinedthesagittalcross-sectionthat passedthroughthecenteroftheMM’stransversediameterasthe measuredcross-sectionfortheMMPE.TheMMPEwasmeasured usingalinepassingorthogonallythroughthemedialtibialplateau, thedistancefromtheposterioredgeofthetibia(excludingosteo- phytes)totheposterioredgeoftheMM.Usingtheposterioredgeof thetibiaasthestandard,extrusionstowardtheposteriorfromthe tibialedgewasnotedaspositivevalue,andabsenceofextrusionas negativevalue(Fig.2).Additionally,wesetthedistancebetween theanteriorandposteriorMMfreeedge(inneredge)whentheknee wasflexedat10^◦and90^◦astheanteroposteriorinterval(API)ofthe MMandmeasuredeach.TheabsoluteMMMEwasmeasuredfrom theosteophyte-excludedoutermarginofthemedialtibialplateau totheouteredgeoftheMM[20].

2.3. Statisticalanalysis

Datawerepresentedasmeans±standarddeviation.Differences betweengroupswerecomparedusingtheMann-WhitneyUtest.

PowerandstatisticalanalyseswereperformedusingEZR-WINsoft- ware.Statisticalsignificancewassettop<0.05.Thesamplesizewas estimatedforaminimalstatisticalpowerof80%(␣=0.05).Allsam- plesizeandpowercalculationswerecompletedusingtheEZR-WIN software.

3. Results

Therewas noMMPE in 10^◦ kneeflexion (−4.77±1.43mm).

At 90^◦ knee flexion, the MMPE significantly increased to 3.79±1.17mm (Table2; p<0.001) Theglobal AP mobility was 8.56±2mm.

At10^◦,theAPIwas20.19±4.22mm,while,at90^◦,itsignificantly decreasedto16.41±5.14mm(Table2;p<0.001).

InMMPRT,MMMEwas2.80±0.66mmat10^◦kneeflexionand 2.55±0.56mmat90^◦(Table2;p=0.052).

4. Discussion

Themostimportantfindingofthepresentstudyisthat,incases ofMMPRT,theMMPEbecomesgreaterwhentheangleofkneeflex- ionincreasesto90^◦.Incontrast,theMMMEremainsunaffectedby theangleofkneeflexion.Ourhypothesisisconfirmed.

WhenMMPRToccurs,theposterioredgeoftheMMwasfound tomovetotheposterioramean8.56±2.00mm.Thisdistanceof MMmovementtotheposteriorincasesofMMPRTisclearlygreater thanthedistancetheMMposterioredgeofnormalkneesmoved duringflexion.

In anormal meniscus,MM posterior movementin thenon- weight-bearingkneeisreportedtoreach3.8mmattheposterior hornwith3.3mmofradialdisplacement.Conversely,MMposterior movementintheweight-bearingkneeis3.9mmandradialmove- mentis3.6mm[21].Inacadavericstudy,duringkneeflexion,the posteriormovementoftheMMwas5.1mm[22].Comparedwith thatinpreviousresearch,theMMposteriormovementwasmuch greaterincasesofMMPRT:8.56±2mm.BecauseMMPEincreases asthekneeflexesfrom10^◦to90^◦,theposteriormovementofthe MMisthoughttoincreaseaswell.ThoseexperiencingMMPRThave

Fig.1.MRI-basedmeasurements.Kneeflexionwassetwiththefemoralandtibialaxialangleat10^◦(A)and90^◦(B),respectively.Wesettheposteriorcondylaraxis(PCA,C), andareferencelinewasdrawnperpendiculartoit(D).Thereferencelinedefinedthesagittalcross-sectionthatpassedthroughthecenteroftheMM’stransversediameter.

(D)Radialtearsign(arrowhead).(E)and(F)indicatethemeasurementofMMPEwiththekneeflexed10^◦and90^◦,respectively.

injuredtheposteriorrootconnectingtheMMposteriorhorntothe tibia.Therefore,whenkneeflexionincreasesto90^◦,theMMmoves posteriorlyandextrudesbeyondtheposteriortibialedge,resulting inMMPE.Further,inapreviousstudy,thedistancebetweenthe anteriorandposteriorhornoftheMMis25.88±3.33mmincadav- ericknees[23].IncasesofMMPRT,theAPIdecreasesastheangle ofkneeflexionincreasesto90^◦.Duetothis,thecontactpressure onthetibiofemoralcontactareaincreaseswhenthekneeisflexed at90^◦ in individualswithMMPRT.Based onthesefindings,we surmisethatthecontactpressurefromthekneejointcartilageata kneeflexionangleof90^◦mustbemuchgreaterinindividualswith MMPRT.

StaticevaluationoftheMMhasbeenpossibleviaMRIexam- ination.However,MRI examinationof theMMduring dynamic

activity,suchaskneeflexion,isdifficult.Therehavebeenocca- sionalstudiesonMRIexaminationofthekneeduringflexion,but almostallofthemexaminedcadaverknees;onlyafewstudieshave evaluatedthekneesperformingdynamicmovementsinlivingpar- ticipants[4,20,22].Computedtomographyscanninghasbeenused notonlytoevaluatebone,butalsodynamickneeflexion.How- ever,itisnotrelevantforsofttissuestructuressuchastheMM.The presentstudyusedopenMRIexaminationtodynamicallyevaluate theMMandMMPE.

PreviousresearchhaslinkedMMMEtoosteoarthritisprogres- sion in theknee [24]. MMMEis not only observed in cases of MMPRT,butalsoathighratesinotherformsofMMtearing.

Thereareseverallimitationsofthis study.First,thenumber ofcasesstudiedissmall.Second,theMMPEofnormalkneeswas

Fig.2. MRI-basedmeasurements.Sagittalimagesofthekneeflexedat10^◦(A)and90^◦(B).Anteroposteriorinterval,API(double-headedarrows,dottedlines).Medialmeniscus posteriorextrusion,MMPE(arrows).Posteriormarginsofthemedialtibialplateau(solidlines)andMM(dashedlines).

Table2

Measurementofmagneticresonanceimaging.

10^◦ofkneeflexion 90^◦ofkneeflexion p-value MMPE(mm) −4.77±1.43 3.79±1.17 <0.001

API(mm) 20.19±4.22 16.41±5.14 <0.001

MMME(mm) 2.80±0.66 2.55±0.56 0.052

MMPE:medialmeniscusposteriorextrusion;API:anteroposteriorinterval;MMME:

medialmeniscusmedialextrusion.Dataaredisplayedasmean±standarddeviation.

under-evaluatedusingopenMRIexamination.Thekneejointsof middle-agedandolderpatientscommonlyshowinjurytotheMM tosomedegree,andnormalMMcasesarefew[25–27].So,itis difficulttoobtainperfectnormalcontrol.Anotherreasonforthis limitationwasthelimitednumberof facilitieswhereopenMRI examinationwaspossible.Third,MRI examinationsofknees at 10^◦and90^◦offlexionarenotevaluationsofdynamicMMmove- mentusingperfectlymatchedsagittalsections.Normally,thetibia undergoesinternal rotation astheknee flexes[28].In cases of MMPRT,theMMposteriorrootistorn,whichmeansthattheMM’s functionasasecondarystabilizerisalsoreduced,leadingtothe increasedpossibilitythat thetibiawill rotate externallyduring knee flexion [29]. Fourth, we only evaluated the non-weight- bearingmeniscusbyopenMRI.Themeniscusintheweight-bearing conditionwasnotassessed.

5. Conclusions

WhenakneepresentinganMMPRTisflexedto90^◦,MMMEdoes notchange,buttheposteriorMMmovesexcessivelytotheposte- rior,causinganotableMMPE.Ourresultssuggestthatusingopen MRIexaminationtoobservetheconditionandpositionoftheMM whenkneeflexionisat90^◦canassistinevaluatingtheeffectsof therapiesaddressingthiscondition.

Funding

Nofundingsourceswereprovidedforthisstudy.

Disclosureofinterest

Theauthorsdeclarethattheyhavenocompetinginterest.

AppendixA. Supplementarydata

Supplementarydataassociatedwiththisarticlecanbefound,in theonlineversion,athttps://doi.org/10.1016/j.otsr.2018.02.012.

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