Rev. bras. ortop. vol.52 número6

rev bras ortop.2017;52(6):731–734

SOCIEDADE BRASILEIRA DE ORTOPEDIA E TRAUMATOLOGIA

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

Case

Report

Accessory

muscle

of

the

flexor

digitorum

superficialis

and

its

clinical

implications

夽

Edie

Benedito

Caetano

,

João

José

Sabongi

Neto

,

Lucas

Augusto

Ayres

Ribas

,

Edson

Vinícius

Milanello

a_{DepartamentodeCirurgia,FaculdadedeCiênciasMédicasedaSaúdePontifícia,UniversidadeCatólicadeSãoPaulo,Sorocaba,SP,Brazil}

b_{ConjuntoHospitalardeSorocaba,Servic¸odeCirurgiadaMão,Sorocaba,SP,Brazil}

c_{FaculdadedeCiênciasMédicasedaSaúde,PontifíciaUniversidadeCatólicadeSãoPaulo,Sorocaba,SP,Brazil}

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Articlehistory:

Received8August2016 Accepted13September2016 Availableonline21October2017

Keywords:

Muscleskeletal/abnormalities Nervecompressionsyndromes Cadaver

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Anatomicalvariationsoftheflexordigitorumsuperficialis(FDS)muscleandtendonunitare frequentlyreportedbyanatomistsandclinicians.AnatomicalmusclevariationsoftheFDS anditstendonsmayincludevariationsofmusclebelly,presenceofaccessoryorduplicate tendons,abnormaltendonconnections, andabsence ofmuscleortendoncomponents. Suchvariations mayor maynot haveclinicalimplications.Thisreportpresentsa case notdescribedpreviously:aunilateralaccessorymuscleoftheflexordigitorumsuperficialis whichwasconnectedbyathicktendontotheflexordigitorumsuperficialismuscle;itwas directedproximallytotheinsertionofthemedialepicondyleofthehumerus,nexttothe superficialisheadofthepronatorteresmuscle.Thebellyoftheaccessorymusclewas pos-itionedanteriortothemedianandanteriorinterosseousnerve.Thisanatomicalvariation isknownastypeVintheclassificationofElliotetal.Theknowledgeoftheseanatomical variationshelpshandsurgeonsinterprettheclinicalexamination,particularlyinthe eval-uationofpatientswhohavesufferedtendoninjuriesorshowsignsofpossibleperipheral nerveentrapment.

©2017PublishedbyElsevierEditoraLtda.onbehalfofSociedadeBrasileiradeOrtopedia eTraumatologia.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Músculo

acessório

do

músculo

flexor

superficial

e

sua

implicac¸ão

clínica

Palavras-chave:

Músculoesquelético/anormalidades Síndromesdecompressãonervosa Cadáver

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Variac¸õesanatômicas(anomalias)daunidademusculotendíneadoflexorsuperficialdos dedos(FSD)têmsidorelatadascomfrequêncianaliteraturaemtratados,artigosclínicose anatômicos.Podemocorrervariac¸õesdocorpomuscular,presenc¸adetendõesacessóriosou duplicados,conexõesmusculotendinosasanormaiseausênciadocomponentemuscularou tendinoso.Essasvariac¸õespodemounãoterimplicac¸õesclínicas.Osautoresapresentam

夽

PaperdevelopedattheFaculdadedeCiênciasMédicasedaSaúde,PontifíciaUniversidadeCatólicadeSãoPaulo,Sorocaba,SP,Brazil. ∗ _{Correspondingauthor.}

E-mail:ediecaetano@uol.com.br(E.B.Caetano).

http://dx.doi.org/10.1016/j.rboe.2017.10.004

732

umcasonãodescritopreviamentedeummúsculoacessóriodomúsculoFSDunilateralque estavaconectadoatravésdeumtendãoespessoaomúsculoFSDedirigia-seproximalmente parainserir-senoepicôndilomedialdoúmeroaoladodacabec¸asuperficialdomúsculo pronadorredondo.Omúsculoflexorsuperficialacessórioposicionavaanteriormenteaos nervosmedianoeinterósseoanterior.Essavariac¸ãoseenquadranotipoV_{daclassificac¸ão}

deElliotetal.Oconhecimentodessasvariac¸õesanatômicasauxiliaocirurgiãodamãoa interpretaroexameclínico,emespecialnaavaliac¸ãodepacientesquesofreramlesões tendinosasouapresentamsinaisdepossíveiscompressãodealgumnervoperiférico.

©2017PublicadoporElsevierEditoraLtda.emnomedeSociedadeBrasileirade OrtopediaeTraumatologia.Este ´eumartigoOpenAccesssobumalicenc¸aCCBY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

Theflexordigitorumsuperficialis(FDS)muscleisthelargest muscleintheforearm.Itformsanintermediatemusclelayer betweenthesuperficialanddeepmusclegroups.Themedian nerve and the ulnar artery enter the forearm as it passes between its radialand humeral-ulnar heads. However,the relationshipofthemediannervetothetwoheadsoftheflexor digitorumsuperficialismayshowanatomicalvariations.

Theupperlimbmay haveduplicateandaccessory mus-cles,as well asanomalous muscles. Anatomical variations of the flexor digitorum superficialis and its tendons are not uncommon: variations of the muscle belly, abnormal musculotendinous connections, absence of the tendinous component, particularly of the little finger, have been described inclinical and anatomicalstudies.1,2 _These

vari-ations may or may not have clinical implications. The knowledgeof these anatomical variationshelps hand sur-geonstointerprettheclinicalexamination,especiallyinthe evaluation of patients who experienced tendon lesions or showsignsofpossiblecompressionofanyperipheralnerve.

Elliotetal.3 _{discussthedevelopmentofflexordigitorum}

superficialisfromamphibianstohumans;theyreviewedmore than30articles,andclassifiedthevariationsintofivetypes. TypeI:connectionbetweenthetendonsofthemuscleitself. TypeII:connectionbetweentheFDSmuscletendonsandthe flexorretinaculum.TypeIII:digastricsuperficialflexormuscle. TypeIV:distalextensionofthemusclebellyoftheFDS.Type V:anatomicalvariationsoftheFDSmuscleintheforearm.

Case

report

Wepresentacasethathasnotbeenpreviouslyreportedofa unilateralsuperficialflexoraccessorymuscleidentifiedduring routineanatomicaldissectionsmadebyresidentsandmedical studentsoftheOrthopedicsandTraumatologyDepartment. The study is registered in the Research Ethics Committee underno.1.025.516.Thepurposeofaseriesof100dissections wastorecordanatomicalvariationsintheupperlimb focus-ing on the presenceof anomalous nerve communications (e.g.,MartinGruber’sanastomosis),anatomicalvariationsof muscles and its tendons(e.g., Gantzer muscle), aswell as theperipheralnerves,andtoanalyzethepossibilityofthese variations being responsible for pathologies, especially for

compressive syndromes. The dissection of each limb was madethroughamedianincisionthroughouttheforearm, mid-dleandlowerthirdofthearm;twoflaps,includingtheskin andthesubcutaneoustissue,werereflectedtotheradialand ulnar sides, respectively; thesame wasdone inrelationto the forearmfascia, withtheentiremusculaturethus being exposed.Inoneoftheselimbsweidentifiedthisrare vari-ationdescribed.Itwasfroma57-year-oldmalecadaver.We donothaveanysignificantindividualclinicalhistory.There was noevidenceofany surgicalprocedure inthearm and forearm.Thelongpalmarismusclewaslackingbilaterally.All otherforearmmuscleswerepresentandshowednovariation. Thecontralateralforearmwasanatomicallynormal,except fortheabsenceofthelongpalmarismuscle.Theanomalous musclewasconnectedtotheflexordigitorumsuperficialis.It consistedoftwomusclebelliesseparatedbyanintermediate tendon,directedproximallytoinsertitselfontothemedial humerusepicondylenexttothesuperficialheadofthe prona-torteresmuscle.Theaccessorysuperficialflexormusclewas positionedanteriortothemedialandanterior interosseous nerves. The anomalous muscle was dissected away from theotherstructuresandstudiedindetail.Themuscle mea-surements were made and the forearm was photographed (Figs.1and2).Themaximumthicknessoftheaccessory mus-cle was2.5cmand the length9cm. Themuscle (FDS) and its accessorymusclereceivedinnervationfrom themedian nerve.

rev bras ortop.2017;52(6):731–734

733

Fig.2–(A)Accessoryflexordigitorumsuperficialis (anatomicalvariation),mediallyreflected.(B)Intermediate tendon.(C)Superficialheadofthepronatorteres(medially reflected).(D)Flexordigitorumsuperficialis.(E)Median nerve.

Discussion

Anatomical variations of the flexor digitorum superficialis muscles are not uncommon; they may mimic soft tissue tumorsor causenerve compression.Theanatomical varia-tionsthathavebeendescribedmostfrequentlyoccurinthe palm ofthe hand.4,5 _{In amphibians, the superficial flexors}

arisefromthepalmofthehandandduringthecourseof evo-lutionthesemusclesmovetotheforearm.6_{Itispossiblethat}

thepresenceofthemusclebellyinthehandrepresentsthe persistenceofanintermediatestageofevolution.7,8

Themusclecomponentoftheflexordigitorumsuperficialis mayoccasionallyextendintothecarpaltunnelandmaybe identifiedduring surgeryfordecompression ofthe median nerveinthecarpaltunnel.Duringthefingerflexion-extension movementthe tendonsmovewithinthe carpaltunneland mayfrequentlycauseintermittentsymptomsduringdigital flexion.9,10

Elliotetal.3_{reportedacaseofanatomicalvariationtypeV,}

statingthatthiswasararevariation.Duringthesurgical pro-cedure,theyidentifiedasmallmuscleattachedbyatendonto theflexordigitorumsuperficialismuscleofthemiddlefinger, 8cmproximaltothewristfold;thissmallmusclecrossedthe mediannerveanteriorly,andwasattachedtothedeepsurface ofthetransversecarpusligament;itwassuperficialtothe nor-malsuperficialflexortendonsandtothemediannerve;this variationisconsideredunlikelyasbeingthecauseofmedian nervecompression.Theydescribedanothersurgicalcase(type I)inwhichtherewasasmallanomalousmuscleattachedto thetendonoftheflexordigitorumsuperficialisproximallyand distallytotheindexfingerinthepalmofthehand;during digitalflexion,thisanomalousmusclepenetratedthecarpal tunnelthusincreasingthecontentofthetunnel,whichcan causeintermittentsymptoms.Theydescribedathirdcaseof typeIVinwhichtheflexormusclebellyoftheindexfinger extendedtotheinteriorofthecarpaltunnelandincreasedits content.

TheliteraturereportsothercaseswithtypeVanatomical variation.ThefirstwasreportedbyMainland.1_Incadaveric

dissection,he observeda variationof the flexordigitorum

superficialis,inwhichthetendonsoftheringandsmallfingers wereconnectedtothreemuscles;twowereintheforearm,the longpalmarismusclewasabsent.ThesecondcaseoftypeV wasreported byFigueiredo andHooper11_{;inthiscasethey}

found,duringasurgicalprocedure,ananomalousmusclein theforearm,whichcausedtheflexionoftheproximal inter-phalangealjointoftheindexfingerwhenpulled;themedian nerve wassituatedsuperficiallytothis muscleinthe fore-armandwrist;theystatedthatthelimitedsurgicalincision didnotallowbetterexploration.Themostemblematiccase oftype(V)wasdescribedbyFromont.12_{Duringdissectionof}

thehandofacadaver,thepresenceoffouranomalousflexor digitorumsuperficialismuscleswasidentified,whicharosein theretinaculumoftheflexorsandwereinsertedinthebaseof themiddlephalanxofthefourfingersandactedasflexorsof theproximalinterphalangealjoint;thenormalflexor digito-rumsuperficialismusclelocatedintheforearmhadonlytwo tendons,oneforthemiddlefingerandtheotherforthering finger.Inthecontralaterallimb,theflexordigitorum superfi-cialismusclehadonlytwotendonsforthemiddleandring fingers,whichwereinsertedintotheflexorretinaculum. Yesi-ladaetal.13_{reportedthatduringthesurgicalprocedurethey}

observedacaseoftypeVanomaly;therewasasingle,well developedmuscleextendingtothepalmofthehandwithout the presenceoftendons;tractioninthe musclecausedthe flexionoftheproximalinterphalangealjointoftheindex, mid-dle,ringandsmallfingers;thepalmarlongmusclewasabsent. Stilland Kleinert8_{identified, duringsurgicalprocedures,}

twocases(typeIV)inwhichthemusclecomponentextended distally to the carpal tunnel and were described as “aber-rantmuscles”;theyreportedthatduringtheflexion-extension movementsofthefingersthesemusclesenterand exitthe carpaltunnelandmaycausesymptomsofmediannerve com-pression.

EliasandSchulter-Ellis14_{reportedthesurgicalcaseofan18}

yearoldmalepatientinwhichtheyrecordedtheexistenceof digastricmuscle(typeIII)thatwasinsertedatthebaseofthe middlephalanxoftheindexfinger,hadaproximalpathand passedunderthecarpaltunnel;however,asitwasasurgical case,itcouldnotbeexploredproximally.Theyreporteda sec-ondsurgicalcaseinwhichthemuscleinsertedintothesiteof theflexordigitorumsuperficialisoftheindexfinger,andthe musclecomponentpassedthroughthecarpaltunneltoward theforearm.

StillandKleinert8_{reportedsimilarcasesofTypeIIanomaly}

inwhichtheanomalousmusclearoseintheflexor retinacu-lumandwasattachedtothetendonoftheflexordigitorum superficialisinthedistalpartofthepalm.Hammer-Villar14

reportedasimilarcase(TypeII)inwhichtheanomalous mus-clearoseinthethenarregion,andwasattachedatthebase of the middle phalanx of the index finger. Wesser et al.7

describedthepresenceofanatavisticFDSmuscleoriginating in the palmar aponeurosisand the transverse carpal liga-ment,andinsertedintothebaseofthemiddlephalanxofthe indexandmiddlefingers.Alltheseauthorsagreethatthese anatomicalvariationsareatavistic,occurasaconsequence oftheinterruptionofsomestageofdevelopmentasinthe amphibians.

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Fig.3–ByanalogywithGantzer(A)muscle,alsocalled accessorytotheflexorpollicislongus(B),whichisfrequent becauseitoccursin68%ofthelimbs,wecallthisrare muscleasaccessoryoftheflexordigitorumsuperficialis. (C)Mediannerve.(D)Anteriorinterosseousnerve.

consideredthatmostofthedescribedanatomicalvariations were identifiedinthe palmofthe hand,and onthe distal thirdof the forearm duringsurgical procedures of decom-pressionofthecarpaltunnel,andinthesecasestheincision waslimited.Wehaddoubtsaboutthedenominationofthis anatomicalvariationwereported.Wecouldcallit“digastric flexordigitorumsuperficialismuscle”,becausetheanatomical nominaconsiders thattwo musclebellies joinedbya ten-donshouldbecalled thisway. TheGantzermuscle (Fig.3) presentin68%oftheforearmsisalsocalledaccessorymuscle oftheflexorpollicislongusmusclebecauseitisasmall mus-clethatjoinstheflexorpollicislongusmuscletothemedial epicondyleofthehumerusortothecoronoidprocessofthe ulnaand adjacencies;thus,duetothesimilarity and anal-ogy,itwastermed“accessorymuscleoftheflexordigitorum superficialis”.Itcouldevenbeconsideredasavariationofthe humeralinsertionofthe“proximallyexpandedflexor super-ficialismuscle”withthepresenceofanintermediatetendon. Inanycase,wedidnotrecordtheanatomicalvariationthat wehavedescribedinthemainclassicalmanualsofanatomy andinourresearch.Wedonothavetheclinicalhistoryofthis cadaver,butweidentifiedthattheaccessoryflexormuscleof theFDSwasanteriorlysituatedtotheanteriormedianand interosseousnerves,andcouldpotentiallybethecauseofthe compressivesyndromeoftheanteriorinterosseousnerveor ofthepronatorteressyndrome.

Theexcisionoftheseanomalousmusclesiscontroversial andeachcaseshouldbeanalyzedindividually.Wesseretal.7

considerthatsurgeryisnotnecessary,becausethese anatomi-calvariationsmaybepartofthefunctionalunitthatmakesthe

digitalflexion,andmaycausesomefunctionalimpairment. Vichare4_{alsodoesnotresecttheseanomalousmusclesifthere}

are no painful symptoms or nerve compression. Elias and Schulter-Ellis14_{recordedthepresenceofthesevariationsin}

ninecasesandallwereoperatedon.Kostakogluetal.2_prefer

surgerybecause theyconsider thattheseabnormalities are potentiallypainfulorcausecompressionsyndromes.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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1.MainlandD.Anuncommonabnormalityoftheflexor digitorumsublimismuscle.JAnat.1927;62Pt1:86–9.

2.Kostako ˘gluN,BormanH,Kec¸ikA.Anomalousflexor

digitorumsuperficialismusclebelly:anunusualcaseofmass inthepalm.BrJPlastSurg.1997;50(8):654–6.

3.ElliotD,KhandwalaAR,KulkarniM.Anomaliesoftheflexor digitorumsuperficialismuscle.JHandSurgBr.

1999;24(5):570–4.

4.VichareNA.Anomalousmusclebellyoftheflexordigitorum superficialis.Reportofacase.JBoneJointSurgBr.

1970;52(4):757–9.

5.SpinnerM.Injuriestothemajorbranchesofperipheral nervesoftheforearm.2nded.Philadelphia:W.B.Saunders; 1978.

6.WesserDR,CalostypisF,HoffmanS.Theevolutionary significanceofanaberrantflexorsuperficialismuscleinthe humanpalm.JBoneJointSurgAm.1969;51(2):396–8.

7.StillJMJr,KleinertHE.Anomalousmusclesandnerve entrapmentinthewristandhand.PlastReconstrSurg. 1973;52(4):394–400.

8.TanzerRC.Thecarpal-tunnelsyndrome;aclinicaland anatomicalstudy.JBoneJointSurgAm.1959;41(4):626–34.

9.BaruchA,HassA.Anomalyofthemediannerve.JHandSurg Am.1977;2(4):331–2.

10.FigueiredoUM,HooperG.Abnormalcourseofthemedian nerveassociatedwithananomalousbellyofflexordigitorum superficialis.Hand.1980;12(3):273–4.

11.FromontNI.Anomaliesmusculairesmultiplesdelamain, absencedufle´chisseurpropreduponce;absencedesmuscles del’e ´minencethenar;lombricauxsupple ´mentaires.BullSoc AnatParis.1895;70:395–401.

12.YesiladaAK,TatlıdedeHS,C¸akmakE,KıyakMV,Kılınc¸L. Anomalouslargeuniquemusclebellyofflexordigitorum superficialisandtheabsenceofPalmarislongusinthe forearm.JPlastReconstrAesthetSurg.2013;66(1):137–9.

13.EliasLS,Schulter-EllisFP.Anomalousflexorsuperficialis indicis:twocasereportsandliteraturereview.JHandSurg Am.1985;10(2):296–9.