Rev. bras. ortop. vol.51 número3

rev bras ortop.2016;51(3):366–369

SOCIEDADE BRASILEIRA DE ORTOPEDIA E TRAUMATOLOGIA

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

Case

Report

Rare

anatomical

variation

of

the

musculocutaneous

nerve

–

case

report

夽

Sergio

Ricardo

Rios

Nascimento

_,

_Cristiane

_Regina

_Ruiz,

_Eduardo

_Pereira,

Lilian

Andrades,

Cristiano

Cirqueira

de

Souza

CentroUniversitárioSãoCamilo,SãoPaulo,SP,Brazil

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o

Articlehistory:

Received26June2015 Accepted17August2015 Availableonline27April2016

Keywords:

Arm/anatomy&histology Musculocutaneousnerve/anatomy &histology

Mediannerve/anatomy&histology Anatomicalvariation

Upperlimb

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Theclinicalandsurgicalimportanceofanatomicalknowledgeofthemusculocutaneous nerveanditsvariationsisduetothefactthatoneofthecomplicationsinmanyupper-limb surgicalproceduresinvolvesinjurytothisnerve.Duringroutinedissectionoftherightupper limbofamalecadaver,weobservedananatomicalvariationofthisnerve.The musculo-cutaneousnerveoriginatedinthelateralcordandcontinuedlaterally,passingunderthe coracobrachialismuscleandthencontinuinguntilitsfirstbranchtothebicepsbrachialis muscle.Justafterthis,itsuppliedanothertwobranches,i.e.thelateralcutaneousnerveof theforearmandabranchtothebrachialismuscle,andthenitjoinedthemediannerve.The mediannervefollowedthearmmediallytotheregionofthecubitalfossaandthengave risetotheanteriorintermediatenerveoftheforearm.Theunionbetweenthe musculocuta-neousnerveandthemediannerveoccurredapproximatelyatthemidpointofthearmand themediannerve.Giventhateitherourexampleisnotcoveredbytheclassificationsfound intheliteratureorthatitfitsintomorethanonevariationproposed,withoutusfinding somethingtrulysimilar,weconsiderthisvariationtoberare.

©2015SociedadeBrasileiradeOrtopediaeTraumatologia.PublishedbyElsevierEditora Ltda.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Rara

variac¸ão

anatômica

do

nervo

musculocutâneo

–

relato

de

caso

Palavras-chave:

Brac¸o/anatomiaehistologia Nervomusculocutâneo/anatomiae histologia

Nervomediano/anatomiae histologia

Variac¸ãoanatômica Membrosuperior

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Aimportânciaclínicaecirúrgicadoconhecimentoanatômicodonervomusculocutâneoe desuasvariac¸õesdeve-seaofatodequeumadascomplicac¸õesemdiversosprocedimentos cirúrgicosdomembrosuperiorenvolvesualesão.Emumadissecac¸ãoderotinadomembro superiordireitodeumcadávermasculinoobservamosumavariac¸ãoanatômicadessenervo. Onervomusculocutâneooriginou-senofascículolateral,seguiulateralmente,passousob omúsculocoracobraquialeseguiuatéseuprimeiroramoparaomúsculobícepsbraquial. Logoapósforneceumaisdoisramos,onervocutâneolateraldoantebrac¸oeumramoparao músculobraquial,eentãouniu-seaonervomediano.Onervomedianoseguiumedialmente

夽

StudycarriedoutatCentroUniversitárioSãoCamilo,LaboratoryofHumanAnatomy,SãoPaulo,SP,Brazil. ∗ _{Correspondingauthor.}

E-mail:[email protected](S.R.R.Nascimento).

http://dx.doi.org/10.1016/j.rboe.2015.08.019

rev bras ortop.2016;51(3):366–369

367

nobrac¸oatéaregiãodafossacubitaledeuentãoorigemaonervointermédioanteriordo antebrac¸o.Auniãodonervomusculocutâneocomonervomedianoaconteceu aproximada-mentenopontomédiodobrac¸oedonervomediano.Tendoemvistaqueasclassificac¸ões encontradasnaliteraturaounãoabrangemnossoexemploouomesmoseadequaamaisdo queumavariac¸ãoproposta,semquetenhamosencontradoalgumafielmentesemelhante, consideramosessavariac¸ãocomorara.

©2015SociedadeBrasileiradeOrtopediaeTraumatologia.PublicadoporElsevier EditoraLtda.Este ´eumartigoOpenAccesssobumalicenc¸aCCBY-NC-ND(http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Themusculocutaneousnerve(MCN)originatesfromthe lat-eralfasciculus(rootsC5–C7)whereitinitiallysendsabranch totheshoulderandthenperforatesthecoracobrachialis mus-cle,whichitinnervates,emergesbetweenthebicepsbrachii andbrachialismusclesandsendsamuscularbranchtoeach ofthese muscles. After supplyingall three muscles ofthe armanteriorcompartment,theMCNemergeslaterallytothe bicepsbrachiimuscletendon,asthelateralcutaneousnerve oftheforearmbecomestruly subcutaneouswhenit perfo-ratesthemusclefasciaproximaltothecubitalfossatoinitially followthecephalicveinandinthesubcutaneoustissueand, aftercrossingtheanteriorsurfaceoftheelbow,itcontinuesto supplytheskinofthelateralsideoftheforearm.1

Theclinical and surgical importance of the anatomical knowledgeofthisnerveanditsvariationsisduetothefact thatmanysurgicalproceduresintheupperlimbinvolve mobi-lizationordisplacementofthemusclesoftheanteriorarm compartmentand oneofthecomplicationsofthese proce-duresisMCNlesions.2

Therefore,wereportananatomicalvariationofthe muscu-locutaneousnerveobservedduringthedissectionofacadaver fromthehumananatomylaboratoryofouruniversity.

Case

report

During a routine dissection of the right upper limb of a male cadaver that belonged to the anatomy laboratory collection,weobservedananatomicalvariationofthe mus-culocutaneousmuscle. Thecorpse,previouslypreserved in formaldehydeandthroughtheglycerinationmethodof Gia-comini, was dissected. All the subcutaneous tissue and superficialfascia wereremoved.Subsequently, thebrachial plexus,startingfromitsfasciculus,waspaintedwithyellow fabricpaint.ThetrajectoryoftheMCNwasanalyzedand mea-suredfromitsorigininthelateral,uptoitsunionwiththe mediannerve,whichwasalsomeasuredfromitsorigininthe medialandlateralfasciculus,tothecubitalfossaregion.An AbsoluteDigimatic®_{digitalcaliperofMitutoyoSulAmericana}

Ltdawasusedforthemeasurements.

Inourspecimen,theMCNoriginatedinthelateral fascicu-lus,whichprovidesacomponentfortheoriginofthemedian nerve.TheMCNfollowedlaterallyfor47.38mm,passedunder thecoracobrachialismusclefor32.73mmtothenemergeon theothersideofthismuscleand thenfollowfor55.38mm

up toits first branchto thebiceps brachii muscle.Then it coursedfor29.56mmlongerandprovidedtwomorebranches: thelateral cutaneousnerveoftheforearmandabranchto thebrachialmuscle. Subsequently,it followedfor29.34mm longer andjoinedthemediannerve,whichwas145.90mm

1 2

4

4

5 9

10 11

10

BBM

CBM

BM 5

3

Fig.1–Photographoftheanatomicalvariationofthe

musculocutaneousmuscleintherightupperlimb.1,lateral

fasciculus;2,posteriorfasciculus;3,medialfasciculus;4,

musculocutaneousnerve;5,mediannerve;9,muscular

branchofthebicepsbrachii;10,lateralcutaneousnerveof

theforearm;11,muscularbranchtothebrachial.CBM,

coracobrachialismuscle;BBM,bicepsbrachiimuscle;BM,

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BBM

BM

10

11

5

4 9

5

Fig.2–Photographoftheanatomicalvariationofthe

musculocutaneousmuscleintherightupperlimb.4,

musculocutaneousnerve;5,mediannerve;9,muscular

branchofthebicepsbrachii;10,lateralcutaneousnerveof

theforearm;11,muscularbranchtothebrachial.BBM,

bicepsbrachiimuscle;BM,brachialmuscle.

longsinceits originup toits unionwiththe musculocuta-neousnerve.Themediannervefollowedmediallyalongthe armfor158.41mmtotheregionofthecubitalfossaandthen gaveorigintotheanteriorintermediatenerveofforearm.The unionofthemusculocutaneousnervewiththemediannerve occurredatapproximatelythemidpointofthearmandthe mediannerve(Figs.1–3).

Discussion

TheanatomicalassociationsofMCNhavebeenstudiedover thepastfewyearsaimingtopreventlesionsduringsurgical procedures2_{andthesevariationsofteninvolve} communica-tionbetweenthemusculocutaneousandthemediannerves throughoneormoreofthecommunicatingbranches.3–8_The MCNcan also send anindependent branch tothe coraco-brachialismuscleinsteadofperforating,remainingparallelto themediannervebyavariabledistanceuntilitpassesunder thebicepsbrachii,orsomeofthemediannervefibersmay followforsomelengthintheMCNbeforejoiningitsowntrunk, ortheMCNcansendmuscularbranchestothepronatorteres muscleorinnervatethedorsumofthethumbintheabsence oftheradialnervesuperficialbranch.1

Consideringthelargenumberofvariationsfoundinthe lit-erature,therehavebeenattemptstoclassifysuchvariations. Themostoftenusedclassificationcriteriainthecomparisons ofthevariationpatternoftheMCNandMNistheone pro-posedbyLeMinor,whichdescribesfivetypesofvariation.9,10 Ourexampledidnotfitinanyofthefivetypesdescribedby theauthor.AnotherclassificationistheonebyVenieratosand Anangnostopolou,3_{thatindicatesthreetypesofpossible} vari-ations.Inthiscase,ourvariationfitsintotwoproposedtypes: TypeII,inwhichtheunionoftheMCNwiththeMNoccurs distallytothecoracobrachialismuscle,andTypeIII,inwhich neitherthenervenorthecommunicantbranchperforatethe coracobrachialismuscle.9,10

SomeauthorsclassifythevariationsintheMCNtakinginto accountthe number ofcommunicatingbranches andtheir height.3–8_{Inourfinding,theanastomosisoftheMCNoccurs}

1

3

7

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9

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11

12

6

4

5

CBM

BBM

BM

5

5

3

2

1

Fig.3–Schematicillustrationoftheanatomicalvariationof

themusculocutaneousnerveintherightupperlimb.1,

lateralfasciculus;2,posteriorfasciculus;3,medial

fasciculus;4,musculocutaneousnerve;5,mediannerve;6,

ulnarnerve;7,medialcutaneousnerveoftheforearm;8,

medialcutaneousnerveofthearm;9,muscularbranchof

thebicepsbrachii;10,lateralcutaneousnerveofthe

forearm;11,muscularbranchtothebrachial;12,anterior

interosseousnerve.CBM,coracobrachialismuscle;BBM,

bicepsbrachiimuscle;BM,brachialmuscle.

afterthemuscularbranchtothebrachialmuscle.Considering thattheclassificationsfoundintheliteratureeitherdonot includeourexampleoritfitsmorethanoneproposed varia-tion,withoutourhavingfoundanothertrulysimilarone,we considerthisvariationasrare.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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