method for tendon graft in porcine tibia – using an interference screw plus staple 夽

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SOCIEDADE BRASILEIRA DE ORTOPEDIA E TRAUMATOLOGIA

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

Original Article

Biomechanical analysis of a double ﬁxation

method for tendon graft in porcine tibia – using an interference screw plus staple ^夽

Luis Antônio de Ridder Bauer

^a

, Hermes Augusto Agottani Alberti

^a

, Vitor Gustavo de Paiva Corotti

^a

, Ana Paula Gebert de Oliveira Franco

^b^,∗

, Edmar Stieven Filho

^a

, Luiz Antônio Munhoz da Cunha

^a

aUniversidadeFederaldoParaná(UFPR),Curitiba,PR,Brazil

bUniversidadeTecnológicaFederaldoParaná(UTFPR),Curitiba,PR,Brazil

a r t i c l e i n f o

Articlehistory:

Received21February2017 Accepted19May2017 Availableonline27July2018

Keywords:

Anteriorcruciateligament Tibia

Orthopedicﬁxationdevices Biomechanicalphenomena Tendons

a bs t r a c t

Objective:Theaimofthestudywastocomparethemechanicalbehaviorofinterference screwtibialﬁxationvs.screw-plus-stapletibialﬁxationinananimalmodel.

Methods:Thirty-sixpieces ofswine kneespecimenswereselectedanddividedintotwo groups:Group1,tibialﬁxationwithinterferencescrew(n=17),andGroup2,ﬁxationwith interferencescrewandstaple(n=19).Themodelsweresubmittedtoasinglecycleoftension testing.Thefollowingvariablesweremeasured:graftcross-sectionalarea,failurepointon 10mm(F10),yieldload(Fy),andstiffness.

Results:Themeanvaluesofgraftcross-sectionalarea,F10,Fy,andstiffnessdidnotpresent signiﬁcantdifferencesbetweenthegroups.

Conclusion:Theadditionofasecondstaple-typeligamentﬁxationdevice,complementing theinterferencescrew,didnotincreasethemechanicalsafetyofthesystem.

creativecommons.org/licenses/by-nc-nd/4.0/).

Análisebiomecânicadaduplaﬁxac¸ãodeenxertotendinosoemtíbia porcina–usodeparafusodeinterferênciaeagrafe

Palavras-chave:

Ligamentocruzadoanterior Tíbia

Dispositivosdeﬁxac¸ãoortopédica

r e su m o

Objetivo:Compararocomportamentomecânicodaﬁxac¸ãotibialcomparafusodeinterfer- ênciaversusparafusodeinterferênciacomagrafe,emmodeloanimal.

Métodos:Foramselecionadas36peçasdejoelhosuínoedivididasemdoisgrupos:Grupo 1,fixaçãotibialcomparafusodeinterferência(n=17)eGrupo2,fixaçãocomparafusode interferênciaeagrafe(n=19).Osmodelosforamsubmetidosatestedecicloúnicodetração.

夽StudyconductedatUniversidadeFederaldoParaná(UFPR),Curitiba,PR,Brazil.

∗ Correspondingauthor.

E-mail:[email protected](A.P.Franco).

https://doi.org/10.1016/j.rboe.2018.07.003

2255-4971/©2018PublishedbyElsevierEditoraLtda.onbehalfofSociedadeBrasileiradeOrtopediaeTraumatologia.Thisisanopen accessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

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Fenômenosbiomecânicos Tendões

Forammensuradasasseguintesvariáveis:medidadaáreadesec¸ãotransversaldoenxerto, pontodefalhanos10mm(F10),yieldload(Fy)erigidez.

Resultados: Osvaloresmédiosdeáreadeseçãotransversaldoenxerto,F10,Fy,erigideznão apresentaramdiferençassignificativasentreosgrupos.

Conclusão:Aadiçãodeumsegundodispositivodefixaçãoligamentartibialtipoagrafe,com- plementaraoparafusodeinterferência,nãoaumentouasegurançamecânicadosistema.

Introduction

Theanteriorcruciateligament(ACL)isoneofthefourmost important ligaments of the knee. Together with the pos- teriorcruciate ligament,tibialcollateral,and posterolateral ligaments,it helps maintainthe knee stableby notallow- ingabnormalmovementsbetweenthefemurandthetibia.

ThetreatmentofACLinjuryisoftensurgical.Intheabsence of an ACL, the practice of some sports becomes inadvis- able,asfrequentsprainsmayoccurduetoinstabilityandits complications.¹ Theindicationofsurgicalreconstructionof theACLisduetothepresenceofsymptoms,especiallyinsta- bility.Thismethod oftreatment presents betterresultsfor sportspractice.²

In the United States, the most commonly used graft for ACL reconstruction is the knee flexor tendons, more specificallythe tendonsofthe gracilisand semitendinosus muscles.Thisgraftisalsocalledquadrupledgrafts,because ithasfourbundles,twofromthegracilisandtwofromthe semitendinosus.³Itsmainadvantagesarelowmorbidityatthe donorsite,lowerratesofquadricepsmuscleatrophy,andless painfulrehabilitation. Asadisadvantage ofthistechnique, someauthorsquestiontherigidityoftendonfixationtothe bone.⁴

InmostcasesofACLreconstruction,thetibiaissecured with interference screws, which was the first device spe- ciallydesignedforthistypeofsurgery.⁵Thisisolatedmethod may not be sufficient for tibial fixation since the tibial cancellous bone has a lower density than its femoral equivalent.⁶ This finding is more frequently observed in elderlypatientsorinthosewithdiseasesthataffectboneden- sity.Inthesecases,anadditionalfixationmayberequired.⁷ Another possible advantage of a secondary fixation is the fact that the patient is authorized to undergo a more aggressiveinitialrehabilitation,withless musclemassand proprioception loss, due to the increase in fixation resistance.

Thethreefrequentoptionsforadditionaltibialattachment tothe screware staples,ascrewpost,and ascrewwith a washer. Theuse ofscrew posts orscrews withwashers is affordableandpresentgoodresults.⁸Thedisadvantageisthat, insomecases,itcangeneratepainintheregionunderthe screwhead.Thisincidenceofpaincanreach48%ofthecases.⁸ Thestapleisaﬁxationmethodthathastheadvantageof being positionedatthe same levelas the bonestructures, reducingthechancesofdiscomfortforthepatient.Thesta- plecanbeusedasasupplementtotheinterferencescrew,but

onlyafewstudiesintheliteraturehaveassessedthemechan- icalbehaviorofthesupplementaryﬁxationwithstaplesinthe tibia.^7,9,10

Thisstudy isaimedatcomparing, inan animal model, the mechanicalbehavioroftibialﬁxationoftheﬂexorten- dongraftswithaninterferencescrewvs.aninterferencescrew plusastaple.

Material and methods

The test specimens were mounted with swine tibiae and bovinetendons.^11,12Theyweredividedintotwogroups:Group (1)controlgroup,inwhichthegraftwassecuredwithinterfer- encescrews;Group(2)doubleﬁxationgroup,inwhichthegraft wassecuredwithinterferencescrewandstaples.

Thetendonswereharvestedinaslaughterhouse,andthe peritendinoustissueswereremoved.Asthetendonanatomy isY-shaped,theyweredissectedtoformtwotendonsegments.

ThetwoendsoftheseparatedtendonsweresuturedwithNo.

5polyesterthread.

Tendons were harvestedinpairs,formeasurementina perforated ruler, with millimeter holes, in order to create quadrupledgrafts.Onlygraftswithamaximumdiameterof 9mmwereincludedinthestudy.

Toaccuratelygaugethearea,thegraftswereimmersedin typeIIJeltratealginate(Dentsply,York,PA,UnitedStates)ina 20-cm-long,5-cm-widebox.Afterafewseconds,thealginate pastebecomesgelatinousandcreatesacast.Thiscastwas sectionedtransverselyinto10-mm-thickblocks.¹³

Sectionsfromtheresultingtemplatewerescannedat600 dpi resolution using anHP J5780^® digitizer; the Image-Pro Plus^®softwarewasusedtogeneratecross-sectionalareamea- surementsofthetemplatesfromthescannedimages(Fig.1).

Theareaofeachquadrupledgraftwasobtainedbyadding themeanareaofitsfourextremities.

Swinetibiae were obtainedfromanimals ofLarge White breedweighingbetween100and120kg.Fortyspecimenswere selectedandpurchasedinaslaughterhouseforhumancon- sumption.

Thesurgical procedurebegan withaconventional tibial guidetopositionaKirschnerwire,whichservedasaguide fordrillingthe9-mmtunnelwithacannulateddrill.Thetun- nelwascreated initsoriginalinsertion;its exitwasplaced betweentheintercondylareminences,inthesuperiorartic- ularsurface.Thedrillfollowedtheguidewireonthemedial aspectofthetibia,approximately2cmmedialtotheanterior tibialtuberosity.

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Fig.1–ImageacquiredbythescannerinImage-ProPlussoftware.

Fig.2–Thornystaple.

In17specimens,thegraftwassecuredonlywitha9-mm diametertitaniuminterferencescrew(Group1).InGroup2,a thornystaplewasused(Fig.2)inassociationtotheinterfer- encescrewtosecurethegraft(Fig.3).

Afterthesurgicalprocedure,thespecimenswereembed- dedinepoxyresin134inrigidPVCmoldswiththedimensions of60mmdiameter,75mmlength,and3.3mmthickness.The epoxyresinwasmanipulatedataratioof1:4,i.e.,25%catalyst and75%resin.Thetotalcuringtimeof60minwasrespected.

In order to maintain the specimens upright during the simultaneousﬁllingofsixcastswithresin,asupportdevice wasconstructedwithMDFsheets(15-mmthick),abrushed steelbar(12.7×500mm),andwoodscrews(5×30mm).The heightfrom the base tothe support bar was 230mm; the externallengthofthegraft,500mm;andtheexternalwidth, 180mm.

Afterbeingembeddedinresin,thesamplesweremounted inaﬁxationandalignmentdevicefortheassay.Thisdevice consistsofan angled precisionvise withjawsdesigned to allowtheattachmentofcylindricalbodies.Theconﬁguration oftheviseallowedagoodvisualalignmentbetweenthetrac- tionaxisandthegrafttunnel.

Fig.3–Fixationwithinterferencescrewandstaple.

Thejawsofthe visewere madeofAISI1045steel,with wedgecreasesinclinedat20^◦,whichallowedtiltingthex-axis from20^◦to65^◦.

Thetendontractionsleevewasmadeofthesamematerial astheviseandconsistsofthreecomponents:aﬁxationscrew intheloadcell,theU-shapedbody,andan8-mmdiameterpin onwhichthetendonwaslooped.

Duringallmanipulation,storage,andﬁxationprocedures and mechanical testing,the tibiaeand tendons were kept moist withanisotonicsalinesolutiontoavoiddehydration andalterationoftheirmechanicalcharacteristics.

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Table1–Resultsofthemeanvaluesoftheforceatthe 10mmdisplacementpoint(F10),yieldload(Fy),rigidity (R10andRy),andtension(10andy)forGroups1and2, andstatisticalsigniﬁcance(p).

Group1 Group2 p

F10(N) 324.7±12A 333.1±78A 0.4

Fy(N) 304.6±13B 251±144B 0.12

R10(N/mm) 31.5±12C 32.4±8C 0.39

Ry(N/mm) 38.4±14D 40.3±12D 0.33

10(MPa) 9.3±4E 10.2±2E 0.19

y(Mpa) 8.9±5F 7.7±4F 0.21

Note:Differentcapitallettersrepresentstatisticallysigniﬁcantdif- ferencesintheline.

Thetendons were placedinan EMIC DL10000 traction machine,equippedwithdisplacementtransducersandanS- typeloadcell(EMIC-CCE5KN),withamaximumnominalload of500Kgfandresolutionof0.1Kgf.Thegraftwasmaintained at50mmfrom the tibia, simulatingthe surgicalcondition.

Theﬁxationofthetendonloopsonthesleeveandofthetest specimenonthe jawswasmadethrough visualalignment oftheaxisofrotationofthemachineandtheaxispassing throughthegrafttunnelintheﬁxationdevice.

After ﬁxation of the porcine knee to the machine, a constant80-Ntraction forcewas appliedfor2minforpre- tensioning and system accommodation.¹⁴ Thereafter, the tractionforcewasreturnedto10N.Atthatmoment,thesin- gletractiontestwasinitiatedataspeedof30mm/min.The testwas interrupted after10mm ofdisplacement. F₁₀ was deﬁnedastheforcemeasurementatthepointof10mmof displacement.¹⁵

Theforce and displacement data were providedby the EMICmachine’s software(TESC)and exported toMicrosoft Excel^®software.

The ﬁrst point at which the chart line stopped being straightwasalsorecorded,asitisthepointwherethetendon deformityhasceasedtobeelastic(withacapacitytoreturnto theoriginalstate)andhasbecomeplastic.¹⁶Thisparameter iscalledtheyieldloadandisrepresentedinthisstudyasFy.⁷ ForcertainF10andFy,thesecantmodewasusedtomea- sure the slope of the line, which translates into stiffness measurements(R₁₀andRy).

TheF₁₀andF_yvaluesofeachgroupweredividedbythearea ofthegrafttestedtomeasuretension,andarerepresentedas 10andy.

Student’st-testwasusedtoobtainthep-valuetoassessthe statisticalsigniﬁcanceofthedifferencebetweenthegroups.

Valueswereconsideredsigniﬁcantwhenp<0.05.

Results

Themean areavalueforGroup1was37±10mm²,and for Group2,32±4mm²;nostatisticallysigniﬁcantdifferencewas observedbetweenthegroups(p>0.05).

Whencomparingbothgroups,nostatisticallysigniﬁcant differencewas observedregardingF10 and Fy failure loads, stiffnessmeasurements(R₁₀ andRy),andstrengthandten- sion;theresultsareshowninTable1.

Discussion

Themoststudieddoublefixationmethodsusescrewposts, anchors, and staples.Atheoreticaladvantageofthestaple overtheothersisthatitactsdirectlyonthetendon.Thiscan leadtoamoreefficientmechanicalactionwhencompared with anchors and screw posts,which are secured through wires.Despitethistypeofmechanicalaction,inthepresent study,nosignificantdifferenceswerefoundbetweenthegroup inwhichthetibialfixationwasmadeonlywithinterference screwsandthegroupwithinterferencescrewsassociatedwith staples.IntheclassicstudybyKurosakaetal.,⁵betterresults werefoundinthetensilestrengthofcadavergraftssecured withinterferencescrewswhencomparedwithstaples;itcan behypothesizedthattheinterferencescrewalreadyreaches themechanicallimitofthetendonandthatthecomplemen- taryfixationisnolongerabletoincreaseresistance.Inturn,in thestudybyGerichetal.,¹⁷maximumstrengthvaluesrang- ing from506to758Nwereobservedinthegroupinwhich fixationwasmadewithinterferencescrewsand558Nforthe group withstaples.Therigiditycalculated fora175N-load wassignificantlyhigherinthestaplefixationgroup.Animpor- tantlimitationwhencomparingthepresentresultswiththose observedbyKurosakaetal.⁵andGerichetal.¹⁷isthatthey analyzedsinglefixationsinthepatellartendon;inthepresent study,onegrouphadcombinedfixation,andinbothgroups, thefixationwasmadeoveratendongraft.

ForthetestswithACLreconstructionfixationdevices,the idealwouldbetohavemusculoskeletaltissueofyounghuman donors,sincetheACLreconstructionprocedureisindicated inphysicallyactivepatients.²Theshortageofyoungcadaver tissueleadstothehuntforsimilarsubstitutes,asthemainfac- torinfixationdurabilityisbonequality.Oneofthemostused optionsistheswineknee,becauseithasasimilaranatomy, despitethefactthatitscancellousboneismoreresistant.¹² Theidealanimalmodelforsimulationofhumankneeflex- orsisthebovinedigitaltendon,whosemechanicalbehavior isverysimilartothatofthehumankneeflexortendon.¹¹The present studywasaimedatcomparing theeffectivenessof differentfixationdevicesusingtheanimaltissuemodelsbest suitedfortheinvestigation.However,theabsolutedatashould notbeextrapolatedtohumanbeings.

Oneoftheparametersofthestudywasthefailureofthe systemat10mmofdisplacement(F10)sinceitisrecognized that 10mm of anterior tibial translation indicates clinical instabilityand therapeuticfailure.¹⁵ThevaluesofF10were similar totheyieldload(Fy), whichisthemostcommonly usedparameterincurrentstudies.¹⁸

TheuseoftheF10failurepoint,i.e.,anincreaseofthegraft lengthby10mm,couldbeanadditionalvariabletobecol- lectedinbiomechanicalstudies.Althoughthisoccursbelow the 445N threshold,defined as a minimumacceptable for rehabilitationofACLreconstructionsurgery,itisbelievedthat ligamentinsufficiencyisalreadydefinedatthispoint.¹⁹Thus, evenifthereisalinearforcevs.displacementbehavior,aforce measurementoflessthan445Natthepointof10mmwould meanaprobablefailure,evenifthecurvedoesnotdemon- strateyieldload.Thishypothesismotivatedtheadoptionof thisparameter.¹⁹

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Studies evaluatingadditional tibialfixation withstaples had force values at the point of failure similar to those observedinthe present study.Onestudy showed afailure forceof254Nforscrewfixationand197Nforscrewandstaple (p=0.24).⁷Otherstudiesevaluatingtibialfixationalsofound similarvalues,usingothermethodsofadditionalfixation.^20,21 Bothrigidity parameters(R10 and Ry)showed nosignifi- cantdifference betweenthe groups.Apossibleexplanation for this lack of significance is that the values observed may representthe plasticlimit ofthe graft.Therefore, the additionofanother fixationdevicedidnotincreasesystem resistance.Thishypothesisisstrengthenedbythefactthat the F10 and Fy values were similar. Another factor is the high density of porcine cancellous bone, which may have increased screw effectiveness. Therefore, the screw as an isolated fixation device may have been sufficient to bring the tendon to its plastic deformation, making additional attachmentsirrelevantfromthemechanicalstandpoint.^10,12 However,anotherstudyobservedagreaterclinicalstabilityin thegroupwithadditionalfixationwithstaplestwoyearsafter surgery.⁹

In the two studies in which fixation stiffness was compared, the absolute values were substantially higher than those found in this study, although not statistically significant.^7,9 Apossibleexplanationisthatsuchdifferences mayhaveoccurredduetopriorcyclicaltesting.Inbothstudies, acyclictestwasperformedpriortotraction,whichcouldhave ledtoaccommodationofthefixationsystem,providingamore immediateresponsetothetensioningofthesystem,which wouldbetranslatedasgreaterstiffness.Thesedatamaysug- gestacyclicpretensioningpriortograftfixation,whichmay increasestiffness;theliteraturepresentdivergentopinionsof poorscientificquality,beingunabletoprovethisbehavior.^22–24 InGroup1,theinfluenceofthecross-sectionalareawas suppressedbythe stresscalculation(10 andy). Anaccu- ratemeasurementofthegraftareaiscriticalincorrectingthis bias.Studiesthatmeasuregraft areaonlythroughaperfo- ratedruler,whichhasasharpincreaseateachtesthole,can impactthe reliabilityofthe values.Alginate castmeasure- mentmeetstheprecisionrequirements,inadditiontobeingof lowcost.

Thepresentstudyhassomelimitations,suchasthesmall samplesize,thefactthatnocyclictestswereperformed,that animalmodelswereused,andthatthemodelshadnofemur.

Thestudywasaimedatperforminganisolatedevaluationof thetibialfixation,andthepresenceofafemurcouldgenerate abias.Grafttractionwasmadeinthesamelineasthetibial tunnel,simulatingtheworstpossiblescenario.^5,25–27 Future studies,whichconsidertheabovelimitations,arenecessaryto determinethemechanicalefficacyoftheextra-tunnelstaple associatedwithaninterferencescrewinthetibialfixationof quadrupledflexortendongrafts.

Conclusion

Thepresentstudyfailedtodemonstrateagreaterefficacyof thedoublefixationofquadrupledflexortendonsusinginter- ferencescrewandstaplewhencomparedwithfixationmade withaninterferencescrewalone.

Conﬂicts of interest

Theauthorsdeclarenoconﬂictsofinterest.

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