Rev. bras. ortop. vol.52 número3

rev bras ortop.2017;52(3):242–250

SOCIEDADE BRASILEIRA DE ORTOPEDIA E TRAUMATOLOGIA

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

Review

Article

Patient-specific

instrumentation

in

total

knee

arthroplasty.

Should

we

adopt

it?

夽

Ana

Sofia

Teles

Rodrigues

_,

_Manuel

_António

_Pereira

_Gutierres

UniversidadedoPorto,FaculdadedeMedicina,DepartamentodeOrtopediaeTraumatologia,Porto,Portugal

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received9March2016 Accepted13June2016

Availableonline15September2016

Keywords:

Arthroplasty Replacement

Knee/instrumentation Patient-specificmodeling Kneeprosthesis

Prosthesisdesign

a

b

s

t

r

a

c

t

Totalkneearthroplasty(TKA)isasurgicalprocedureofparamountrelevancethatrestoresa substantialdegreeoffunctioninarthriticknees.Increasedconsiderationhasbeengivento theinfluenceoflimbalignmentonlongevityafterTKA,aserrorsincomponentplacement canbeassociatedwithinferiorfunctionandcompromisedlong-termperformance. Con-sequently,numerousstudiescomparingpatient-specificinstrumentation(PSI)tostandard instruments(SI)havebeenpublished.Patient-specificapproachesusepreoperativeimaging tocreatespecificmaterialsforeachpatient’sanatomyandweredesignedtoachieveahigher rateofsuccessinTKA,causingtheentireproceduretobemoreefficientandcost-effective. However,itisnotcleartowhatdegreethesestudiessupportthepotentialadvantagesof PSI.Thus,thepresentstudyaimed toreviewthecurrentevidencecomparingPSItoSI, concerningalignment,cost-effectiveness,andpostoperativefunctionalevaluation.

©2016PublishedbyElsevierEditoraLtda.onbehalfofSociedadeBrasileiradeOrtopedia eTraumatologia.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://

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

Instrumentac¸ão

personalizada

na

artroplastia

total

do

joelho.

Devemos

adotá-la?

Palavras-chave:

Artroplastia Substituic¸ão

Joelho/instrumentac¸ão

Modelagempersonalizada

Prótesedojoelho Desenhodeprótese

r

e

s

u

m

o

Aartroplastiatotaldojoelho(ATJ)éumprocedimentocirúrgicodefundamental relevân-cia que restaura boa parte da func¸ão de joelhos artríticos. Maior atenc¸ão tem sido

dada à influência do alinhamento do membro na longevidade após a ATJ, uma vez

queerros noposicionamentodos componentespodem estar associados àuma menor

func¸ãoecompromentimentododesempenhoalongoprazo.Consequentemente,vários

estudos compararam a instrumentac¸ão personalizada para cada paciente (IPP) com a instrumentac¸ãopadrão(IP).Asabordagenspersonalizadasusamimagenspré-operatórias paracriarmateriaisespecíficosparaaanatomiadecadapacienteeforamprojetadospara atingirumamaiortaxadesucessonaATJ,tornandotodooprocessomaiseficienteerentável. Noentanto,nãoestáclaroatéquepontotaisestudosrespaldamasvantagenspotenciaisda IPP.Assim,opresenteestudotevecomoobjetivoavaliarasevidênciasatuais,comparando

夽

WorkperformedintheUniversidadedoPorto,FaculdadedeMedicina,Porto,Portugal.

∗ _{Correspondingauthor.}

E-mail:a.sofiateles@gmail.com(A.S.Rodrigues).

http://dx.doi.org/10.1016/j.rboe.2016.06.008

rev bras ortop.2017;52(3):242–250

243

IPPeIPemrespeitoaoalinhamento,relac¸ãocusto-benefícioeavaliac¸ãofuncional pós-operatória.

©2016PublicadoporElsevierEditoraLtda.emnomedeSociedadeBrasileirade OrtopediaeTraumatologia.Este ´eumartigoOpenAccesssobumalicenc¸aCCBY-NC-ND

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Totalkneearthroplasty(TKA)isconsideredasuccessful

ortho-pedic procedure in the management ofdegenerative joint

disease based on the rate ofrevision. It representsone of

the most regularly performed musculoskeletal procedures,

restoring,inmostcases,asubstantialdegreeoffunctionin

arthritic knees. One can anticipate an increase in TKA in

thefuture, givenestimatedenlargementinpopulation size andlongevity.Therefore,perfectingsurgicaltechniqueisof

paramountrelevance,aserrorsincomponentplacementcan

beassociatedwithinferiorfunctionandcompromised long-termperformance.1,2

Forthepastfewyears,increasedconsiderationhasbeen

placedonthe influenceoflimbalignmentand component

position on longevity and outcomes after TKA,

review-ing the survivorship andpostoperative performanceofthe

procedure.3–5 _{Ithasbeen establishedthatneutral}

mechani-calalignmentiscriticalintheoverallsuccessofthesurgical

technique.2,6 _{Consequently, tibial and femoral component}

malalignmentremains a significant concern, as deviations

exceeding3◦_{ofvarus/valgusinthemechanicalaxishavebeen}

relatedwithpoorsurvivorship duetotheaccelerated wear resultantofabnormalstressesatthebearingsurfaces. Accord-ingly,tibialandfemoralcomponentsareneededtobeplaced

asprecisely as possibleand preventing malalignmentmay

provetobecost-effective.

That being said, two technological advancements,

aim-ing at improving the likelihood of achieving neutral TKA

alignment,haveemerged:computer-assistednavigationand

patient-specific instrumentation(PSI).7 _{Recently,numerous}

comparative studies and randomizedcontrolled trials that

compare patient-specific cutting blocks to conventional

instrumentshavebeenpublished.However,itisnotclearto whatdegreethesestudiessupportthepotentialadvantages ofPSI.8–10 _{Forthatreason,thepurposeofthepresentstudy}

istoperformareviewofthecurrentevidencecomparingPSI toSI,concerningalignment,cost-effectivenessand postop-erativefunctionalevaluation.Existinginformationconcerning

computer-assisted navigation will not be assessed in this

review.

Patient-specific

instrumentation

Aimingatenhancingtheoutcomesofthesurgery,the

man-ufacturing process for knee implants has improved over

theyears,involving,lately,patient-specificapproaches.The purposewastogetthemostaccuratepositioningforthe tib-ialandfemoralcomponents.3,11_{Thistechnologyemploysthe}

generationofapreoperativeimageofthe knee,along with hipandankleimagesfortheevaluationoftheoverall

align-mentofthelimb,mostcommonlycomputedtomography(CT)

ormagneticresonanceimaging(MRI).Computersoftwareis

usedtogenerateanidealthree-dimensional(3D)modelofthe patient’slowerlimbanatomy,allowingtheanatomical land-marksofthekneetobeeasilyidentified, andtocreatethe 3Dmodelsofthefemoralandtibialcomponentswithoptimal size,positionand alignment.Apreoperativeplan proposed withbonyresectionsisgeneratedandprovidedtothe operat-ingsurgeon,whoisthenabletoassessthe3Dplanningofthe kneeimplantwiththeproposedbonyresectionsandwiththe finalimplantsinplace.Atthispoint,thesurgeonisexpectedto approveorreviewthepreoperativeplan,adjustingasrequired bonyresection.Whenapproved,generallywithin3weeks,the manufacturerfabricatesacorrespondingsetofcustomcutting blocksindividualizedtothepatient’snativeanatomy.1,3_These

cuttingjigs are expectedto notonlydeterminethe proper coronal orientation, but also set the depth offemoral and tibialresection,anteroposteriorposition,rotation,andslope basedonthepreoperativeprototype.Alterationsin preoper-ative schedulingare inevitable withthe implementationof PSI:first,theplanningprocesshastobeanticipated,since,as mentionedabove,atleast3weeksarenecessarytofabricate

the cuttingblocks;second,the 3Dimagingstudies

manda-torypreoperativelywerenottypicallyperformedpreviously forconventionalTKA.Atlast,manufacturerandsurgeonmust cooperatefortheelaborationandapprovalofthepreoperative plan,ensuringthattheguidesareavailablebythetimeofthe procedure.7,12

Patient-specificinstrumentationwasdesignedtoachievea higherrateofsuccessinTKA,decreasingtheoddsofrevision.

The anticipated benefitsof this technology are numerous,

causingthe entireprocedure tobemoreefficientand cost-effective.7,13,14

First, being the patient-matched technology potentially

morepreciseandaccurate,withareductioninthe number

of outliers expected to be significant, neutral

postopera-tive alignment would be more reproducible with the use

of patient-specific jigs when compared to standard

align-menttechniques.12_{Second,thesurgeonhaspreoperativedata}

regardingthesizeandlocationofthebonyresections,along with implant sizing and rotation information. This way, it is possible to intraoperatively determine if the surgery is

proceeding as expected. Third, as fewer instruments trays

are requiredperprocedure, thesterilizationcostswouldbe reduced.12,15_{Fourth,amoreefficientsurgeryispredictedwith}

reductionofthetimeoftheprocedure,oncedifferentsteps havealreadybeenperformed,alsominimizingintraoperative decision making.11,12,16 _{Finally, by notrequiring the use of}

intramedullaryrodstodeterminealignment,PSIavoids vio-lationoftheintramedullarycanal,potentiallyenablingtothe incidenceoffatembolismandperioperativebloodloss.14,17

244

data to support its use. It remains controversial whether

advantagesovercome weaknesses.3,16,17 _{With the necessity}

ofapreoperativeCTscan,theradiationexposureincreases. Additionally,it isunclearif theanticipated costsreduction offsetthoseofthepreoperativestudiesandmanufacturingto fabricatethematerials.15,17_{Moreover,surgeriesmayneedto}

bedelayedduetothesubstantialamountoftimerequiredto obtainthesuitablepreoperativeimaging,formulatethe intra-operativeplan,andtofabricatethecuttingblocks.Lastly,the precisionofanatomiclandmarkinghasbeenfoundtobe cru-cialtothefinalaccuracyofthe technique.Deformitiesthat maymisrepresenttheexactnessoftheCTscanorMRI, possi-blywillleadtoacompromised3Dmodel.

Methods

A literature review was conducted related to the use of

PSIinTKAusingPubmeddatabase,onSeptember25,2015,

using the query “total knee arthroplasty/instrumentation”

AND(“patientspecific”OR“patientmatched”).Theliterature searchidentified100studies,whichwerethenlimitedto31 publishedbasedonthefollowinginclusioncriteria:(1)

com-parison ofpatients who underwent TKA withPSI tothose

whounderwentTKAwithconventionalinstrumentation;(2)

performedinvivo;(3)assessmentofpostoperativecoronal, sagittalorrotationalcomponentalignment,operativetime, cost and/orfunction scores. Review articles, editorials and techniquedescriptionswere excluded. Studiesthat didnot meetthecriteriaordidnotaddressthepurposeofthepresent reviewwereexcluded,aswerestudiespublishedinanother languagethanEnglishandbefore2010.Thebibliographiesof theselectedstudieswerenotsearchedadditionally.

Results

ThemainresultsaresummarizedinTable1.

Alignment

Achievingthemostpossibleaccuratealignmentatthe

com-pletion of TKA has been the upmost surgical goal for

the procedure, with numerous publications demonstrating

improvedsurvivorshipwiththisresult.Atleasttheoretically, patient-specific cutting blocks are believed to improve the accuracyoflimbalignmentbyguidingthecriticalbonecuts toward the hypothetically ideal position for each patient.

Despitemuchdebateontheusefulnessoftheinstruments,

therearestudiescomparing thevalueofthe new

mechan-icallyalignedPSIsystemtothatofstandardprocedurethat validatethesurgicalaccuracyofthetechniquetodate.

Fourrandomizedclinicaltrials(RTC)reportedresults sup-portingPSI.Withrespecttoachievingmechanicalalignment closertoneutral,Noble et al.12 _{favoredPSIover SI (1.7}◦ _vs

2.8◦_{; p=0.03). Chareancholvanich et al.}11 _{and Vundelinckx}

et al.3 _{reportedno difference inmechanicalalignment but}

thefirstonedidnoteanimprovementinfrontaltibial compo-nentalignmentwithPSIbeingclosertoneutral(89.8◦_versus

90.5◦_{;p=0.03),whilethesecondonefoundthatPSIwasmore}

accurateinreproducingthedesiredtibiaposteriorslope(2.9◦

versus 5.0◦_{; p=0.0008).Silva et al.}18 _{aimedatstudying the}

rotationalalignmentandtheauthorsassumedthatthereis asmallerchanceofinternalmalrotationofthetibial compo-nentwithPSI,havingthetraditionalinstrumentationhigher

dispersion and amplitude ofthe tibialcomponent rotation

around the neutral position. Numerousretrospective

stud-ies noted similar results, with significant improvement in extremitymechanicalalignmentafterPSI.2,6,7,19_AlsoRenson

etal.20 _{prospectivelyreportedmoreoutlierswithrespectto}

mechanicalaxiswithSI(p=0.043).Additionally,femoral com-ponentfrontalplaneposition19 _{androtationalalignmentof}

thefemoralcomponent7_{werealsoreportedtobeenhanced}

withPSI.

Althoughproponentsofpatient-matchedinstrumentation

contendthatitimprovesalignment,otherwell-designed com-parativetrialshaverevealed noimprovementinalignment.

TheseauthorswerenotabletoshowimprovementwithPSI,

but the customized techniquedid notend upbeing worse

thantraditionalinstrumentation.TheaccuracybetweenTKAs

performedwithPSIandthose donewithSIwasconsidered

comparable.ArandomizedcontrolledtrialconductedbyRoh etal.9_{showednosignificantdifferenceneitherinthemean}

alignmentinallparametersevaluated(mechanicalaxis,

sag-ittalandcoronalalignmentofeachcomponentandfemoral

component rotation) nor in the percentageof outliers. For Nunley etal.,16,21 _{inaretrospective study,bothgroupshad}

the mean coronal alignment measurements falling within

theacceptedrangesandthemeanHKAandequivalentthe

number of outliers. The same results are shared by other

authors.5,10,17,22,23

Atlast,someauthorsnotonlyconcludedthatno

improve-ment in alignment was achieved with the use of PSI, but

alsoreporteddecreasedalignmentaccuracy.Inarecent ran-domizedcontrolledtrial,Victorelal.1_{comparedconventional}

instrumentationwithpatient-specificguidesfromfour differ-ent implant suppliers: Signature® _{(Biomet Inc, Warsaw,IN,}

USA), TruMatch® _{(DePuyInc,Warsaw,IN,USA),Visionaire}®

(Smith&NephewInc,Memphis,TN,USA)andPatient-Specific Instruments®_{(ZimmerInc,Warsaw,IN,USA).TheuseofPSI}

didnotreducethenumberofoutliers.Actually,theauthors foundmoreoutliersinthesagittalandcoronalalignmentof the tibialcomponent (23%vs17%;p=0.002and15%vs3%;

p=0.03,respectively)withtheuseofPSI.Deviationsfrom tar-getalignmentamongPSIsubgroupsweresimilar,exceptfor sagittalalignmentofthefemoralcomponent,whichwas sig-nificantlybetterforthePSIsubgroupusingVisionaire®_system

(p=0.02)andhadfeweroutliers(p=0.001).Yet,thesame sys-temrevealedmoreoverallcoronalalignmentoutliers(p=0.04).

In anotherrecent RCTs,bothevaluating TruMatch® _(DePuy

Inc, Warsaw, IN,USA) system,Hamilton e Parks.15 _showed

improvedposteriortibialslopeinSIcases(p=0.001),whereas Woolsonetal.8_{reportedasignificantincreaseinthenumber}

ofoutliersforthesameparameterinthePSIgroup. Addition-ally,Kotelaetal.24_{foundanincreaseinthenumberofoutliers}

forcoronaltibialcomponentafterwithPSIhavingconducteda RCT.Similarly,Stronachetal.25_{retrospectivelyrevieweddata}

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Table1–SummaryofthedataregardingtheresultsofPSIstudies.

Study Studytype PSIsystem NumberofTKAs Results Outcomes

Abdeletal.4 _{RCT 20PSI Nodifferenceinearlyfunctional,}

quality-of-lifeorgaitoutcomes.

Functionalevaluation

20SI Barkeetal.22 _{Retrospective Visionaire}®_(Smith&

Nephew)

39PSI SIachievedaMAclosertoneutral.OT wasequivalent.

MA,OT

50SI

Barracketal.17 _{Retrospective Signature}®_{(Biomet) 100PSI EquivalentMAaccuracy,decreasedOT} andreducednumberofinstrumenttrays withPSI.

MA,OT,numberof instrumenttrays

100SI Barretetal.23 _Prospective

non-RCT

TruMatch®_{(DePuy) 66PSI ComparableMAandOTbetweengroups. MA,OT}

86SI

Boonenetal.14 _{RCT Signature}®_{(Biomet) 90PSI EquivalentMA,sagittalandcoronal} alignmentoffemurandtibia.PSI decreasedOTby5min.

MA,CFC,CTC,SFC,STC,OT

90SI Chareancholvanichetal.11 _{RCT Patient-Specific}

Instruments® (Zimmer)

40PSI NodifferenceinMA.Improvedaccuracy inCTC(89.8±1.2vs90.5±1.9,p=0.030) andfeweroutliersinSFCwithPSI (p=0.012).PSIdecreasedOTby5min.

MA,CFC,CTC,SFC,OT

40SI Daniilidisetal.6 _{Retrospective Visionaire}®_(Smith&

Nephew)

150PSI MAequivalent,withfeweroutlierswith PSI(9.3%vs.21.2%).

MA

156SI

Hamiltonetal.15 _{RCT TruMatch}®_{(DePuy) 26PSI NodifferenceinMA,CFC,CTCandSFC} withPSI.IncreasedposteriorslopeinSI (p<0.001).PSIrequiredfewerinstrument traysbutitwas4minlonger.

MA,CFC,CTC,SFC,STC,OT, numberofinstrumenttrays

26SI Heyseetal.7 _{Retrospective Visionaire}®_(Smith&

Nephew)

46PSI ReducedrateofFCRoutliersinPSIgroup comparedtoSI(2.2%vs22.9%,p=0.003).

FCR

48SI Ivieetal.19 _{Retrospective iTotal}®_G2

(ConforMIS)

100PSI MAandCFCmoreaccuratewithPSI,with feweroutliers(p=0.0016andp=0.032, respectively).NodifferenceinCTCandin sagittalalignmentbetweenthetwo groups.Nochangeswererequired.

MA,CFC,CTC,SFC,STC, needforapplyingchanges

100SI

Kotelaetal.24 _{RCT Signature}®_{(Biomet) 49PSI CTCshowedmoreoutliersinPSIgroup} (38.78%vs19.57%,p=0.0458).

MA,CFCCTC,SFC,STC

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Table1–(Continued₎

Study Studytype PSIsystem NumberofTKAs Results Outcomes

Marimuthetal.10 _{Retrospective Visionaire}®_(Smith& Nephew)

115PSI Nodifferencesintheevaluated parameters.Similarnumberofoutliers.

MA,CFC,CTC,SFC,STC, FCR

185SI

Ngetal.2 _{Retrospective Signature}®_{(Biomet) 105PSI OverallMAsimilar,butfeweroutliers} withPSI(9%vs22%,p=0.018);CFC(90.7 vs91.3,p<0.001)andCTC(89.9vs90.4,

p=0.005)closertoneutralinPSIgroup comparedtoSI.

MA,CFC,CTC

55SI Nobleetal.12 _{RCT Visionaire}®_(Smith&

Nephew)

15PSI MAclosertoneutralwithPSI(1.7vs2.8,

p=0.03).PSIshowedreductioninOT (7min)andnumberofinstrumenttrays needed.

MA,CFC,CTC,OT,number ofinstrumenttrays

14SI

Nunleyetal.16 _{Retrospective Signature}®_{(Biomet) 57PSI Equivalentnumbersofoutlierswith} respecttoMA.DecreasedOTby12min afterPSI.

MA,OT

57SI

Nunleyetal.21 _{Retrospective Signature}®_{(Biomet) 50PSI Equivalentnumbersofoutlierswith} respecttoMA.

MA

50SI Rensonetal.20 _{Prospectivecase}

series

Signature®_{(Biomet) 71PSI FeweroutliersinMAwithPSIcompared} toSI(13%vs29%,p=0.043).DecreasedOT timeby9minandthenumberof instrumenttraysbysixtrayswithPSI.

MA,CFC,CTC,SFC,STC,OT, numberofinstrumenttrays

60SI

Rohetal.9 _{RCT Signature}®_{(Biomet) 42PSI Nodifferencegroupswithrespecttoall} evaluatedparameters.Equivalentnumber ofoutliers.OTwas13minlongerwithPSI andPSIhadtobeabortedin16%ofknees.

MA,CFC,CTC,SFC,STC, FCR,OT,needforapplying changes

48SI Silvaetal.18 _Prospective

randomized

Signature®_{(Biomet) 23PSI NosignificantdifferenceinFCRandTCR} betweengroups,butlessdispersionand amplitudeofTCRaroundtheneutral positionwithPSI.

FCR,TCR

22SI

Stronachetal.25 _{Retrospective Signature}®_{(Biomet) 58PSI NoimprovementinalignmentwithPSI.} Worseningofaccuracyofthetibialslope withPSI(38%vs61%,p=0.01).Equivalent OT.

MA,CFC,CTC,SFC,STC,OT

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Table1–(Continued₎

Study Studytype PSIsystem NumberofTKAs Results Outcomes

Stronachetal.26 _{Retrospective Signature}®_{(Biomet) 66PSI EquivalentOTbutmultiplechanges} requiredintraoperativelywithPSI (2.4changes/knee).

OT,needforapplying changes

62SI Tibeskuetal.13 _{Activity-based}

costingmodel

Visionaire®_(Smith& Nephew)

IncreasedefficacyinOTandutilizationof instrumenttrayswithPSI.PSIis economicallyeffective.

OT,numberofinstrument trays

Victoretal.1 _{RCT Signature}®_{(Biomet) 61PSI NosignificantdifferencesbetweenPSI} andSIwithrespecttocomponent alignment.PSIhadmoreoutliersthanSI inCTC(14.6%vs3.1%,p=0.03)andSTC (21.3%vs3.1%,p=0.002).Visionaire® subgrouphadmoreoverallcoronal alignmentoutliers(p=0.04)butfewerSFC outliers(p=0.001).PSIwasabandonedin 22%ofpatientsandmodifiedin28%of patients.

MA,CFC,CTC,SFC,STC, FCR,needforapplying changes

TruMatch®_{(DePuy) 64SI} Visionaire®_(Smith&

Nephew) Patient-Specific Instruments® (Zimmer)

Vundelinckxetal.3 _{RCT Visionaire}®_(Smith& Nephew)

31PSI EquivalentMA.ImprovedSTCwithPSI (2.9±2.39vs5.0±2.14,p=0.0008).No differenceinpain,patientsatisfaction,or functionaloutcomes(KOOS,Lysholm score).

MA,STC,functional evaluation

31SI

Woolsonetal.8 _{RCT TruMatch}®_{(DePuy) 22PSI IncreasednumberofoutliersinPSIgroup} withrespecttotibialslope(32%vs8%,

p=0.032).Nosignificantdifferencewith regardtoOTorKneeSocietyratingor functionscore.

MA,CFC,CTC,STC,FCR, OT,functionalevaluation

26SI Yaffeetal.5 _{Retrospective Patient-Specific}

Instruments® (Zimmer)

44PSI NodifferenceinMA,SFCorSTC.No differenceinpain,motion,KneeSociety kneescores;PSIhadhigherKneeSociety functionscorespre-andpostoperatively

MA,SFC,STC,functional evaluation

40SI

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Cost-effectiveness

Another source of conflict associated with the

implemen-tation of PSI is whether this technique will reveal itself cost-effectiveornot.ConsideringitwasconsensualthatPSI

iscomparabletoSI,equivalentoutcomeswithmore

expen-sivetechnologydonotfitintothecurrentcost-effectiveness paradigm.Multiplefactorsplayasubstantialroleintheoverall efficiencyandeconomicsofTKA.Theadvantagesclaimedby supportersofPSIinthesurgerytime,thenumberof

instru-ment trays used and the need for applying changes may

supportacumulativedecreaseinresourceuse.Currently,TKA representsalargeexpenseinthehealthbudgetandany reduc-tionintheexpensesitcarriesisofparticularinterestinrespect tothepresenthealtheconomicclimate.

Operative

time

DecreasedsurgicaltimewithPSIhasbeendescribed,allowing increasedoverallprocedureefficiencyandcost-effectiveness ofTKA.Still,itwasnotunanimouslyobserved.

ThereareavailabledatafromRCTssupportingareduction

ofthe operatingtimeusingPSIsystem. Chareancholvanich

etal.11_{randomized80patientstoundergoTKAwithPSIorSI}

andreportedthatthisnewtechnologyreducedskin-to-skin operativetimebyamean5.1min(p=0.019).Additionally, com-parableresultswerereportedbyBoonenetal.,14_havingthePSI

surgerytaken5minlessthantheprocedurewithSI(p<0.001) andNobleetal.12_{(PSItook6.7minless;p=0.048).Also}

Ren-sonetal.,20_{inaprospectivestudy,showedthetimeofsurgery}

woulddecreasewithPSI.

Usinganactivity-basedcostmodel,Tibeskuetal.13_found

thatPSIcuttingblocksallowedamoreefficientuseoftime intheoperatingroom,leadingtoincreasedrevenuesforthe hospital.Theauthorsobservedadecreaseof10minincutting timeand20mininthepreparationoftheoperatingroom,per procedure.Theexplanationisgivenbytheuseoftheimplant guideasawaytoreducetimefordeterminationofthesize oftheimplantduringaprocedure.Byallowingthesurgeries toendearlier,theauthorsassumeitwouldenablethe hos-pitaltocarryoutadditionalprocedures.Moreover,the cost savingswasmatchedwiththeadditionalcostassociatedwith thenewtechnology.Theoverallcostswerealmostidentical, withPSIcostingjust59D _{more,indicatinghowthe}

theoreti-calincreasedefficiencyoftheprocedureconductedwithPSI mayoffsetitsextracosts,especiallyaftersurgeonsgainmore experience.

Onthecontrary,afterhavingperformedafinancialanalysis incorporatingthecostofpreoperativeimagingandthecutting guide,aswellassparedoperatingroomtimeandinstrument processing,Barracketal.17_{showedthatPSIwasactuallymore}

expensive than SI. As a resultof diminished surgerytime

and sterilization costs,a totalsavingof$322per casewas reportedwiththeuse ofPSI.Nonetheless, thecustom cut-tingguidewasestimatedtocost$950andpreoperativeMRI waspredictedtovaryfrom$400to$1250,basedoninsurance.

Itwasconcludedthatanysavingsbornebyoperatingroom

timegainedandinstrumentprocessingwereoverwhelmedby

theoverheadcostsdemandedbyPSI.AlsothreeRCTsfailedto showdecreasedoperativetimewithPSI.Theprimaryoutcome measuredbyHamiltoneParks15_{wastotalsurgicaltime}

cal-culatedfrominitialskinincisiontoendofclosure.52patients wererandomizedtoeitherPSIorconventionalTKA.Whilethe PSIgrouptookanaverageof61:47min,themeantimeforSI groupwas57:27min(p=0.006),withthemostofthetime dif-ferenceoccurringduringfemoralpreparation.Similarly,Roh et al.9_{counted59.4minforPSIcomparedto46.6minforSI}

(p<0.001).Atlast,Woolsonetal.8_{alsofailedtoshowany}

differ-encebetweengroups.Comparableresultswerealsoobserved byotherauthors.22,25,26

Number

of

instrument

trays

PSI isalsoexpectedtodecreasethe number of

instrumen-tation trays used, given the abolition of steps such as IM alignmentguideplacement.Thecostsassociatedwith main-tenance,storageandsterilizationcouldpotentiallydecrease after fewer trays are needed to be opened. Noble et al.12

recorded the number of instrument trays opened for each

caseanddemonstratedasignificantreductioninthenumber ofinstrumenttraysused(mean4.3vsmean7.5;p<0.0001). Similarly,HamiltoneParks.15_{reportedasignificantlyhigher}

numberofsurgicalinstrumenttraysusedintheSIcases, com-paredwiththetraysrequiredforthePSI(mean7.3vsmean 2.5;p<0.001).Additionalauthorsanalyzedthissamevariable andunanimouslysupportedtheclaimthatPSIdoesresultina decreasednumberofinstrumenttrays.16,17,20_Tibeskuetal.13

intheiractivity-basedcostinganalysis,observedthatPSIledto utilizationof4traysless,whichwasestimatedtocorrespond to1400trayslessannually,comparedtoSI.Thisdecreasewas anticipatedtoresultinpotentialcostsavingsof160D_per

pro-cedure.

Need

for

applying

changes

OneofthetheoreticaladvantagesofPSIisdecreasedoperative timethroughminimizationofintraoperativedecisionmaking

andinstrumenthandling.Numerouspreoperativestepsmust

becompletedmeticulouslyfortheresultantguidestobe pre-cise.Theaccuracyofthepreoperativeplanaccompanyingthe PSIwasalsocalledintoquestionbydifferentauthors.

Recently,Ivieetal.,19_{inaretrospectivestudy,reportedall}

thesurgeriestohaveproceededwithoutrequiringadditional surgeoninterventionorachangefromthepreoperative surgi-calplan,notbeingnecessaryanyconversiontoconventional TKA. This is in contrast to other investigations that have

shown frequent surgeon-directed changes during PSITKA.

According toVictoret al.,1 _{inarandomizedstudy withthe}

inclusion offour different PSI systems, the custom

instru-mentsprocedure hadtobemodifiedin28%ofthepatients

and abandonedinmorethan 20%.Themostcommon

rea-son for modifyingthe use ofthe PSI was the necessityto

changethesize.AlsoRohetal.9_{soughttoevaluatethe}

reli-ability ofPSI by intraoperatively investigatingwhether the surgerycouldbecompletedwithPSIalone.Actually,in8knees (16%),theprocedurecouldnotaccuratelybecompletedand

rev bras ortop.2017;52(3):242–250

249

Stronachetal.26_{showedthatonly23%ofthefemoraland47%}

ofthetibialimplantedcomponentsizewasproperlypredicted byPSI.

Postoperative

functional

evaluation

Itisnoticeablealackofpublishedstudiesonthefunctional resultsandgaitparametersofpatientsthathaveundergone PSITKA.Especiallyafterthepopularizationofminimally inva-sivesurgicaltechniques,eventhoughlong-termsurvivorship ispertinent,early painreliefand improvedfunctional

out-comeshavebecomeincreasinglyimportanttopatientsand

surgeons.Itremains unknownwhetherPSI improves

func-tion and pain-related outcomes and gait. For that reason,

someauthorsdecidedtoappropriatelymeasurethese param-eters,inordertodeterminewhethertheycouldpotentiallybe improvedwithPSI.

Four ofthe selected studies addressed these questions,

resulting in conclusions substantially consensual.

Vun-delinckxet al.3 _{conducted a study with a mean follow-up}

oflittlemorethan6months,randomizing62 patients,and reportedthatPSIdonotconferanyfunctiongainscompared tothetraditionalTKA.ThePSIdidnotshowitselfofgreater valuewithrespecttopostoperativepain(measuredusingthe visualanalogscale),patientsatisfaction,functionaloutcome,

basedonLysholmscoreand KneeinjuryandOsteoarthritis

OutcomeScore(KOOS),andgaitparameters.

Similarly,Abdel et al.4 _{performeda randomizedclinical}

trialwith40 patients, evaluatingsubjective andobjectively

functionalandgaitoutcomes,preoperativelyand3months

postoperatively,usingpatient-reportedoutcomescores(new KneeSocietyScore(KSS),KOOSandSF-12)andgait parame-ters.At3monthspostoperatively,almostallfunctionalscores wereincreasedinbothgroupscomparedwithpreoperatively. However,therewere nostatisticalsignificantdifferences in postoperativefunctionalscoresbetweengroupsandthesame

occurred concerning the analyzed gait parameters. Hence,

theauthorsagreedthatnobenefitinpainorearlyfunction

and nocomparative improvementin gaitparameters were

conferredbyPSIwhencomparedwithconventionalTKA,as

assessedbytheKSS,KOOSandSF-12andcomprehensivegait analysis.

Yaffeetal.5_{alsofailedtoshowadifferenceinKSSorpain}

scoreimprovementbetweenPSIandconventionaljigs,aftera 6monthfollow-upof122patients.Still,PSIdidshowa

signif-icantlyhigherKneeSocietyfunctionsubscoreimprovement

from thepreoperativeperiodtothe 6-monthpostoperative

period, when compared to conventional instrumentation.

Enhancedcomponentrotationandpositioningandimproved

component size accuracy may be the explanation for the

results.However,asthisisaretrospectivecase-controlstudy,

there was not randomization of the patients, introducing

potentialbias. Infact, PSI group hadhigher preoperatively

knee scores, function scores and pain scores than

man-ual instrumentationgroup. Consequently, firm conclusions

fromthis findingremain elusiveduetotheaffected ability ofthe authors todrawdefinitiveconclusionsfrom the raw postoperativelyscores,eventhoughthegroupsaresimilarin bodymassindex,gender,ageandpreoperativediagnosis.

Morerecently,Woolsonetal.,8_{inaRCT,reportedno}

signif-icantdifferencewithregardtoKneeSocietyratingorfunction score.

Discussion

In order to gain acceptance into modern practice, new

technology must demonstrate either (1) increased efficacy

comparedtoexistingtechnologyor(2)equivalentoutcomes withreducedcost.

On the basis of their data, some authors showed

results that sustain of the value of customized cutting

blocks.2,7,12,13,19,20 _{Onecan expectthat this technologywill}

assistinrestoringthemechanicalaxiswithaccuracy poten-tiallybetterthanconventionalinstrumentation.Infact,allthe selectedstudiesshowednoinferiormechanicalandfemoral

component alignment withPSI. Onlythe tibial component

revealedcontroversialresults.

However,differentexampleshaveshowndeficientguide

fit intraoperatively in which conventional instrumentation

was preferred rather than accepting the potential risk of

anundesirableresection.1,9,26_{Thispresurgicalprocessadds}

complexity,time,expense,andmultiplestepstotheTKA pro-cess.Anerrormadeintheinitialstepsoftheprocesswilllead tocontinuedreproductionofthaterror.Thisraisesaconcern thatthepreoperativelyproposedimplantsizeandalignment fromPSImaynotbeanaccuratereflectionofpatientanatomy and,therefore,unreliable.Surgeonsmustbecautiousagainst

blind approval of PSI technology without supportive data.

Additionally, some authors claim that more intraoperative

decision-makingwasrequiredbyPSI,preventingittoreduce operativetime.9,15_{Accordingly,nodifferenceinsurgerytime}

between thegroups wasestablished.This mayresultfrom

additionaltimetakentoevaluateeachstep,regularlyrepeated resectionsandrejectedblindacceptanceoftheproposedcuts, preventingtheauthorsfromimmediatelymakethecutsafter placingthesurgicalguides,whichcouldcompromisethe accu-racyofthecomponentssizeandposition.Nonethelessseveral authorsbelievethePSIcuttingjigstoachievelargerprogresses insurgerytimewithmoreexperience,asthestudieswereled duringtheearlylearningcurveforhigh-volumesurgeonswho haveperformedseveralthousandTKAsusingSI.1,2,16_Lackof

expertisewiththePSImaybeenoughtobiastheresults. Sur-geonsareexpectedtoimprovethetechniqueandbeableto makefeweradjustments,reducingthesurgicaltimewithPSI, asthevolumeofperformancesincreases.

Final

remarks

Thevalueofanymedicaltechnologydependsonwhetheror

notitimprovesclinicaloutcomesandPSIoffersnumerous the-oreticaladvantagesthatmakeitanattractivealternativefor TKA.Asthistechnologystillremainsarelativelynewconcept, itisnotsurprisingthat,despiteitsincrease,thebodyof liter-atureremainslimited.Regardlessofwhetherthistechnology isfoundtobeacceptableinthefuture,thetruthisthat dif-ferent studiesassumedbothtechniquesare abletorestore

limbalignment andplace thecomponents withequivalent

250

supportthisinnovativetechnique, PSIhasnotconsistently beenshowntobecost-effectiveortoofferanyclinical ben-efitwithregardtofunctionalscoresassessed.Theextensive numberofanglesthatcanbemeasuredtoevaluatetheefficacy ofPSIalsomakesthecomparisonbetweendifferentstudies difficult.Additionally,ispossiblethatasix-monthfollow-up periodmaynotbesensitiveenoughtodetectPSI’seffecton

functionaloutcomesandcomponentsurvivorship.

PSImayhaveasmallandspecificroleincertaincases,such aswhentheuseofanIMorextra-medullaryrodwithmounted cuttingblock is impossible,for example after severe post-traumaticsequelsofdistalfemoralorproximaltibialfractures orforpatientswithIMhardwareorextra-articulardeformities, butadditionaljustifyingdataisvitalprioritsroutineuse.

Itispossiblethatmorepreciseconclusionsmayemerge.

Thatbeingsaid,additionalRCTsshouldbeconducted

com-paringtheclinicaloutcomesofPSItothetraditionaltechnique

with a longer postoperative follow-up period and a larger

samplebefore definitive conclusionsare made, concerning

functionalefficacyofthistechnologyandthepotential appli-cabilityofPSItospecialsituations.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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