Rev. bras. ortop. vol.52 número2

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SOCIEDADE BRASILEIRA DE ORTOPEDIA E TRAUMATOLOGIA

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

Original

article

Anatomical

variations

of

pronator

teres

muscle:

predispositional

role

for

nerve

entrapment

夽

Edie

Benedito

Caetano

∗

_,

_Luiz

_Ângelo

_Vieira,

_Fábio

_Antonio

_Anversa

_Sprovieri,

Guilherme

Camargo

Petta,

Maurício

Tadeu

Nakasone,

Bárbara

Lívia

Correa

Serafim

PontifíciaUniversidadeCatólicadeSãoPaulo,FaculdadedeCiênciasMédicasedaSaúde,DisciplinadeOrtopediaeTraumatologia, Sorocaba,SP,Brazil

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Articlehistory:

Received15February2016 Accepted18April2016 Availableonline2March2017

Keywords: Pronation Mediannerve

Nervecompressionsyndromes

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Objective:Toassesstheanatomicalvariationsofthepronatorteresmuscle(PTM)andits implicationinthecompressionofthemediannerve,whichpassesthroughthehumeral andulnarheadsofthePTM.

Methods:Forthepresentstudy,100upperlimbsfromhumancadaversfromtheanatomy laboratoryweredissected.Forty-sixspecimensweremaleandfour,female,whoseaged rangedfrom28to77years;27werewhiteand23,non-white.Apilotstudyconsistingofsix handsfromthreefreshcadaverdissectionswasconductedtofamiliarizetheauthorswith thelocalanatomy;thesewerenotincludedinthepresentstudy.

Results:ThehumeralandulnarheadsofPTMwerepresentin86limbs.In72outofthe86 limbs,themediannervewaspositionedbetweenthetwoheadsofthePTM;in11,itpassed throughthemusclebellyofulnarheadofthePTM,andinthree,posteriorlytobothheads ofthePTM.Whenbothheadswerepresent,themediannervewasnotobservedaspassing throughthemusclebellyofthehumeralheadofPTM.In14outofthe100dissectedlimbs,the ulnarheadofthePTMwasnotobserved;inthissituation,themediannervewaspositioned posteriorlytothehumeralheadin11limbs,andpassedthroughthehumeralheadinthree. In17limbs,theulnarheadofPTMwaslittledeveloped,withafibrousbandoriginatingfrom theulnarcoronoidprocess,associatedwithadistalmusclecomponentneartheunionwith thehumeralhead.Infourlimbs,theulnarheadoftheMPRwasrepresentedbyafibrous band.Inbothlimbsofonecadaver,afibrousbandwasobservedbetweenthesupinator muscleandthehumeralheadofthePTM,passingovermediannerve.

Conclusion: Theresultssuggestthattheseanatomicalvariationsinrelationship median nerveandPTMarepotentialfactorsformediannervecompression,astheynarrowthe spacethroughwhichthemediannervepasses.

夽

StudyconductedatthePontifíciaUniversidadeCatólicadeSãoPaulo,FaculdadedeCiênciasMédicasedaSaúde,DisciplinadeOrtopedia eTraumatologia,Sorocaba,SP,Brazil.

∗ _{Corresponding}_author_.

E-mail:ediecaetano@uol.com.br(E.B.Caetano). http://dx.doi.org/10.1016/j.rboe.2017.02.003

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Variac¸ões

anatômicas

do

músculo

pronador

redondo

e

sua

importância

nas

síndromes

compressivas

Palavras-chave: Pronac¸ão Nervomediano

Síndromesdecompressão nervosa

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Objetivo: Analisarasvariaçõesanatômicasdomúsculopronadorredondo(MPR)esuas implicaçõesnacompressãodonervomediano,quepassaentreascabeçasumeraleulnar doMPR.

Método: Foramdissecados100membrossuperioresdecadáveresadultospertencentesao laboratóriodeanatomia;46cadávereseramdosexomasculinoequatrodofeminino.A idadevariouentre28e77anos;27eramdaetniabrancae23,nãobranca.Umestudopiloto queincluiutrêscadáveresfrescosfoifeito,parafamiliarizac¸ãodosautorescomaanatomia regional.Essesnãoforamincluídosnoestudo.

Resultados:Em86membros,observou-seapresençadascabeçasumeraleulnardoMPR.Em 72dos86membros,onervomedianoestavaposicionadoentreascabeçasumeraleulnar doMPR;em11,esseencontrava-seatravésdamassamusculardacabeçaulnardoMPReem três,onervomedianoestavaposicionadoposteriormenteàsduascabeçasdoMPR.Noscasos emqueasduascabeçasdomúsculoestavampresentes,nãoseobservouonervomediano passandoatravésdamassamusculardacabeçaumeraldoMPR.Em14dos100membros dissecados,acabeçaulnardoMPRnãoestavapresente.Nessasituação,onervomediano posicionava-seposteriormenteàcabeçaumeralem11membroseatravésdacabeçaumeral emtrêsmembros.Em17membros,acabeçaulnarestavamuitopoucodesenvolvida,com conformaçãofibrosaemsuaorigemnoprocessocoronoidedaulna,associadaaum com-ponentemusculardistal,próximoasuauniãocomacabeçaumeral.Emquatromembros,a cabeçaulnardoMPRestavarepresentadaapenasporumabandafibrosa.Nosdoismembros deumcadáver,observou-seumaexpansãofibrosaquesaíadomúsculosupinadorparaa cabeçaumeraldoMPR,passandocomoumacintasobreonervomediano.

Conclusões: Essesresultadossugeremqueasvariaçõesanatômicasnarelaçãonervo medi-anoeMPRrepresentamfatorespotenciaisparacompressãonervosa,porestreitaroespaço noqualpassaonervomediano.

Introduction

Thereareseveralanatomicalstructuresthatcancompressthe mediannerveneartheelbowjoint.Fromproximaltodistal, thecompressionmaybecausedbytheStruthers’ligament1,2 withorwithoutthe supracondylarprocess ofthehumerus, byaponeuroticexpansionofthebicepsbrachiimuscle( Lacer-tusfibrosus),3,4_between_the_humeral_and_ulnar_heads_of_the pronatorteresmuscle(PTM),5,6_by_the_vascular_network_of_the region,7_and_by_the_arch_formed_by_the_two_insertions_of_the superficialflexormuscleofthefingers.8

Regardlessofthesesiteswherecompressionoccurs,this condition istermed pronator teres syndrome, because the compressionoccursmostfrequentlybetweenthetwoheads ofthismuscle.9–11_The_main_causes_are_the_anatomic varia-tionsofthePTM.Thenormalanatomicalpatterndescribed bytheclassicalanatomystudies12–14 _is_that_the_PTM_is con-stitutedbytwo heads. Thehumeralhead, moreextensive, originatesinthesupracondylarprocessofthehumerusand adjacencies.Theulnarheadoriginatesinthe coronoid pro-cessoftheulna.Thetwoportionsuniteforinsertionintothe diaphysisoftheradius,contouringtoit.Themediannerveis positionedbetweenthetwoheadsofthePTM.However,the

relationship between the median nerve and the humeral and ulnar heads of the PTM is subject to numerous variations.4,6,15,16 _This _study _aimed _to _analyze, _through anatomicaldissections,therelationshipbetweenthePTMand mediannerveandthuscontributetoabetterunderstanding ofthecausesofthepronatorteressyndrome.

Material

and

methods

One hundred upper limbs of 50 adult cadavers from the anatomydepartmentofthisinstitutionweredissectedforthis study,46cadaversweremaleandfourwerefemale.Theage rangedfrom28to77years;27werewhiteand23,non-white. Cadaverswhoseforearmsweredeformedbytraumas, malfor-mations,andscarswereexcluded.Apilotstudythatincluded threefreshcadaverswasconductedsothattheauthorscould familiarizethemselveswiththelocalanatomy.Thesewerenot includedinthisstudy.

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10cmproximaltotheintercondylarlineofthehumerus;at this location, it was positioned mediallyin relationto the brachialartery.Thedissectionproceededdistallyuntil reach-ingthebicipitalaponeurosis,whichwassectioned,allowing thevisualizationoftheproximalmarginofthePTM.The pres-enceofvariationsinthesurfaceheadandfibrousbandsatthe sitewasrecorded.Subsequently,thesuperficialheadofthe PTMwassectionedtransverselytoallowthevisualizationof thedeephead,whosepresentationwasvaried;itwasabsent in14ofthe100dissectedlimbs.Themediannervewasdistally dissecteduntilitpassedthroughthearchformedbythe prox-imalinsertionsoftheflexordigitorumsuperficialismuscles. Inalldissectedlimbs,thefirstbranchofthemediannervein theforearmwasalwaystowardsthesuperficialheadofthe PTM.Allforearmmusclesweredissected;theirinnervation, thepresenceofcommunicationamongtheforearmnerves (Martin-Gruber anastomosis), the relationship between the mediannerveandthebicipitalaponeurosis,andthe relation-shipofthemedianandanteriorinterosseousnerveswiththe archoforiginofthethreeheadsoftheflexordigitorum super-ficialismusclewereanalyzed.Theanatomicalvariationswere annotatedandphotographed.AKeller2.5Xmagnifyingglass wasusedformagnification.Thisstudywasapprovedbythe hospital’sethicscommitteeundertheCAAENo.1.356.351.

Results

In86dissectedlimbs,thehumeralandulnarheadsofthePTM werewellindividualized,consistingoftwodistinctmuscular portionsthatjoinedtoinsertthroughanenlargedtendon, con-touringtoandinsertinginthemiddlethirdofthediaphysisof theradius(Fig.1).In72ofthe86limbs,themediannervewas positionedbetweenthehumeralandulnarheadsofthePTM (Fig.1).In11limbs(fourbilaterally),itwaspositionedthrough themuscularmassoftheulnarheadofthePTM(Fig.2).In threeforearms(onebilaterally),themediannervewas pos-itionedposteriorlytothetwoheadsofthePTM(Fig.3).When bothheadsofthemusclewerepresent,nocasesofthemedian nervepassingthroughthemusclemassofthehumeralheadof thePTMwereobserved.In14ofthe100limbs,theulnarhead ofthePTMwasabsent.Inthissituation,themediannervewas positionedposteriorlytothehumeralheadin11limbs(Fig.4) andthroughthehumeralheadinthreelimbs(Fig.5).

Thehumeralheadwaslargerthantheulnarhead(Fig.1). Apoorlydevelopedulnarheadwasobservedin17limbs,with afibrousconformationinitsorigininthecoronoidprocessof theulna,associatedwithadistalmuscularcomponent,close toitsunionwiththehumeralhead(Fig.6).Theulnarheadof thePTMwasrepresentedbyafibrousbandnotassociatedwith amuscularcomponentinonlyfourlimbs(Fig.7A).Onboth limbsofasinglecorpse,afibrousexpansionextendingfrom thesupinatormuscletothehumeralheadofthePTM,passing asabandoverthemediannerve,wasobserved(Fig.7B).In fivelimbs,theulnarheadwasinsertedalongsidetheGantzer muscle,inthecoronoidprocessoftheulna.Ineightlimbs,a highinsertionofthehumeralheadPTMrangingfrom2.8to 3.5cmproximaltothemedialepicondylewasobserved(Fig.7A andB;Table1).

Median nerve

Ulnar head

Humeral head

Ulnar head

Fig.1–In86limbs,thehumeralandulnarheadsofthePR

musclewerewellindividualized.

Median nerve

Ulnar head

Ulnar head Humeral head

Humeral head

Fig.2–Inninelimbs(threebilaterally),themediannerve

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Table1–EvaluationofthehumeralandulnarheadsofPTMandtheirrelationshipswiththemediannervein100 dissectedlimbs.

Pronatorteres Locationofthemediannerve Percentage %Total

Humeralandulnar headspresent

BetweenthetwoheadsofthePTM 72 86

PosteriorlytothetwoheadsofthePTM 3

ThroughtheulnarheadofthePTM 11

ThroughthehumeralheadofthePTM 0

Absentulnarhead ThroughthehumeralheadofthePTM 3 14

PosteriorlytothehumeralheadofthePTM 11

Absenthumeralhead Notrecorded 0 0

Total 100 100

Discussion

In 86 of the 100 dissected limbs (86%), the humeral and ulnarheadsofthePTMwerepresent,whichisinagreement withtheresultsreportedbyStabilleetal.6_(83.5%),_Jamieson andAnson15 _(81%), _and_Hollinshead17 _(91%)._Other _authors observeddifferentpercentages:HoferandHofer,18_56%,_and Nebot-Cegarraetal.,19_68%._In₇₄_of_these₈₆_limbs,_the_median nervewaspositionedbetweenthehumeralandulnarheadsof thePTM;in11,themediannervepassedthroughthe muscu-latureoftheulnarheadofthePTM.Inthreelimbs,themedian nervewaspositionedposteriorlytobothPTMheads.Incases inwhichbothheadsofthe PTMwere present,nocasesof themediannervepassingthroughthemuscularmassofthe humeralheadofthePTMwereobserved.

Median nerve

Median nerve Humeral head

Humeral head

Ulnar head

Fig.3–Inthreeforearms(onebilaterally),themediannerve

waspositionedposteriorlytothetwoheadsofthePTM.

ThePTMulnarheadwasabsentin14% ofthedissected limbs.InthestudybyStabilleetal.,6_it_was_observed_in_15%; inthatbyHollinshead,17_in_9%,_and_in_that_by_{Nebot-Cegarra} et al.,19 _in_21.7%._Kaplan20 _and _Zancolli21 _reported_that_the absenceoftheulnarheadisfrequent.TestutandLatarjet12 andChiarugi14_also_observed_this_absence,_but_did_not_record howoftenthisanatomicalvariationmayoccur.

Testut and Latarjet12 _and _Le _Double _and _Anatole22 describedthatatendonsegmentmayreplacetheulnarhead ofthePTM;Spinner23_considers_that_this_variation_occurs fre-quently.Stabilleetal.6_observed_the_ulnar_head_represented_by afibrousbandin9%ofthecases.Inthepresentstudy,17limbs hadapoorlydevelopedulnarhead,withafibrouscomponent initsproximalportioninthecoronoidprocessoftheulna,but

Humeral head

Median nerve

Fig.4–AbsenceoftheulnarheadofthePTM.Inthis

situation,themediannervewaspositionedposteriorlyto

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Median nerve

Humeral head

Fig.5–AbsenceoftheulnarheadofthePTM.Inthis

situation,themediannervepassedthroughthehumeral

headinthreelimbs.

associatedwithamuscularcomponentinthedistalportion, beforejoiningthehumeralhead.Inonlyfourlimbs,theulnar headofthePTMwasrepresentedbyafibrousband,not asso-ciatedwithamuscularcomponent.Inagreementwithallthe studiesanalyzed,nocasesofabsenthumeralheadofthePTM wereobserved.

Testutand Latarjet12 _and _Le _Double _and _Anatole22 _also describedthatthehumeralandulnarheadofthePTMmaybe completelyseparate,withdistalinsertionsatdifferentsites. Inthepresentstudy,inagreementwithStabilleetal.,6_in_the 86limbsinwhichbothheadswerepresent,thesewereunited beforetheirinsertionintothemiddle-thirdoftheradial dia-physis.

Barret,24_in₂₀₀_dissected_cases,_observed_in_one_of_them anadditionalportionofthehumeralhead,termingitthethird headofthePTM.HealsoreportedthatBuchananhadobserved athirdheadofthePTM, whichoriginatedfrom the supra-condylarprocessofthehumerus.Caetanoetal.2_published_a caseinwhichtherewasmediannervecompressioncausedby theinsertionofthehumeralheadofthePTMin supracondy-larhumeralprocess.Inthepresentstudy,theinsertionofthe humeralhead(2.8–3.5cm)proximaltothemedialepicondyle ofthehumeruswasobservedineightcases.

Thepositioning ofthe mediannerveposteriorly toboth headsofthePTM,describedbyJamiesonandAnson15_in_6% oflimbsandbyDiDioandDangelo16_in_2.5%,_was_observed_in threeforearms(3%)inthepresentstudy.

Median nerve

Median nerve Ulnar head

Ulnar head

Humeral head

Fig.6–In11limbs,apoorlydevelopedulnarheadwas

observed,withafibrousconformationinitsorigininthe

coronoidprocessoftheulna,associatedwithadistal

muscularcomponent,closetoitsunionwiththehumeral

head.

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Humeral head Supinator muscle Fibrous band Humeral head Ulnar head

A

B

Median nerve

Fig.7–(A)Infourlimbs,theulnarheadofthePTMwas

representedbyafibrousbandnotassociatedwithamuscle

component;(B)intwolimbs,afibrousexpansionextended

fromthesupinatormuscletothehumeralheadofthePTM,

passingasabandoverthemediannerve.

Surgeons should be aware ofthe anatomical variations thatcanbeobservedintheelbowregion,astheychangethe positionofthenoblestructures,puttingthematriskduring arthroscopicproceduresandopensurgicalapproachesinthe region.

Conclusion

Theanatomicalvariationsofthehumeraland ulnarheads ofthe PTM inrelation totheir constitution and frequency canalterthepositioningofthemediannerve.Themost fre-quentlyobservedvariationwasabsenceoftheulnarhead.In thepresenceoffibrousbands,especiallywhenthe median nerveextendsclosetothecoronoidprocessoftheulnawhere theulnarheadofthePTMhasafibrousconstitution,nerve compressioncanoccurduetoanarrowingofthenerve pas-sagespace.Itisclearthatthepassageofthenervethrough themusclemassofthePTMisnotonlyaplacewithgreater potentialtocausepronatorteressyndrome,butalsoaltersthe normalcourseofthemediannerve.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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