Rev. Bras. Anestesiol. vol.65 número3

RevBrasAnestesiol.2015;65(3):177---179

REVISTA

BRASILEIRA

DE

ANESTESIOLOGIA

www.sba.com.br

SCIENTIFIC

ARTICLE

Anatomical

basis

for

sciatic

nerve

block

at

the

knee

level

夽

Fabiano

Timbó

Barbosa

,

Tatiana

Rosa

Bezerra

Wanderley

Barbosa

,

Rafael

Martins

da

Cunha

_,

_Amanda

_Karine

_Barros

_Rodrigues

_,

Fernando

Wagner

da

Silva

Ramos

_,

_Célio

_Fernando

_de

_{Sousa-Rodrigues}

a_{UniversidadeFederaldeAlagoas(UFAL),Maceió,AL,Brazil} b_{CentroUniversitárioUnisebInterativo,Maceió,AL,Brazil} c_{HospitalUnimedMaceió,Maceió,AL,Brazil}

d_{DepartamentodeAnatomia,UniversidadeEstadualdeCiênciasdaSaúdedeAlagoas(Uncisal),Maceió,AL,Brazil}

Received9January2014;accepted10March2014 Availableonline18March2015

KEYWORDS

Anatomy; Anesthesia, administration; Sciaticnerve

Abstract

Backgroundandobjectives: Recently,administrationofsciaticnerve blockhasbeen revised duetothepotentialbenefitforpostoperativeanalgesiaandpatientsatisfactionaftertheadvent ofultrasound.Theaimofthisstudywastodescribetheanatomicalrelationsofthesciaticnerve inthepoplitealfossatodeterminetheoptimaldistancetheneedlemustbepositionedinorder torealizethesciaticnerveblockanteriortoitsbifurcationintothetibialandcommonfibular nerve.

Method: Thestudywasconductedbydissectionofhumancadavers’poplitealfossa,fixedin

10% formalin,from theLaboratory ofHuman AnatomyandMorphology Departmentsofthe

UniversidadeFederaldeAlagoasandUniversidadedeCiênciasdaSaúdedeAlagoas.Accessto thesciaticnervewasobtained.

Results:44poplitealfossawereanalyzed.Thebifurcationofthesciaticnerveinrelationto theapexofthefossawasobserved.Therewasbifurcationin:67.96%belowtheapex,15.90% abovetheapex,11.36%neartheapex,and4.78%intheglutealregion.

Conclusions: The sciaticnervebifurcation toitsbranches occurs atvarious levels, andthe chancetosucceedwhentheneedleisplacedbetween5and7cmabovethepoplitealis95.22%. © 2014SociedadeBrasileirade Anestesiologia.Publishedby ElsevierEditoraLtda.Allrights reserved.

夽

Researchplace:UniversidadeFederaldeAlagoas,Maceió,AL,Brazil. ∗_{Correspondingauthor.}

E-mail:fabianotimbo@yahoo.com.br(F.T.Barbosa).

http://dx.doi.org/10.1016/j.bjane.2014.03.010

178 F.T.Barbosaetal.

PALAVRAS-CHAVE

Anatomia;

Anestesia,conduc¸ão; Nervoisquiático

Basesanatômicasparaobloqueioanestésicodonervoisquiáticononíveldojoelho

Resumo

Justificativaeobjetivos: Recentemente afeitura de bloqueio do nervo isquiático tem sido revistadevidoaopotencialbenéficoparaanalgesiapós-operatóriaesatisfac¸ãodospacientes apósoadventodaultrassonografia.Oobjetivodesteestudofoidescreverasrelac¸ões anatômi-casdonervoisquiáticonafossapoplíteaparadeterminaradistânciaidealemqueaagulha deveserposicionadaparaafeituradobloqueioanestésicodonervoisquiáticoanteriorasua bifurcac¸ãoemnervotibialefibularcomum.

Método: Otrabalhofoifeitopormeiodedissecc¸ãodefossapoplíteadecadávereshumanos,

fixadosemformola10%,provenientesdoLaboratóriodeAnatomiaHumanadosdepartamentos

deMorfologiadaUniversidadeFederaldeAlagoasedaUniversidadedeCiênciasdaSaúdede

Alagoas.Obteve-seacessoaonervoisquiático.

Resultados: Foramanalisadas44fossaspoplíteas.Observou-seabifurcac¸ãodonervoisquiático emrelac¸ãoaoápicedafossa.Houvebifurcac¸ãoem67,96%abaixodoápice,15,90%acimado ápice,11,36%próximaaoápicee4,78%naregiãoglútea.

Conclusões:Abifurcac¸ãodonervoisquiáticoemseusramosocorreemváriosníveiseachance deseobtersucessoquandoaagulhaéusadaentre5e7cmacimadafossapoplíteaéde95,22%. ©2014SociedadeBrasileiradeAnestesiologia.PublicadoporElsevierEditoraLtda.Todosos direitosreservados.

Introduction

Thepoplitealsciaticnerveblock(PSNB)wasfirstdescribed in 1923, but its infrequent use in clinical practice may be justified by the difficulty in accessing the nerve in thisregion,highincidenceof unwantedsideeffects,such as dysesthesia, and technical difficulty in the blockade.1 Recently,the PSNB hasbeen revised dueto thepotential benefit for postoperative analgesia and patient satisfac-tion because of the use of nerve stimulator.2 _{The use of} ultrasound to help the PSNB technique has also encour-agedprofessionalstoseektheadvantagesandbenefitswhen theyperformthisblockademoreoften.3_Themain disadvan-tageof SPSNBis littleornoblockingaction insaphenous nerve.3

Sciaticnerveisderivedfromthefibersofspinalsegments L4-S3.4 _{Two nerve trunks originatingfrom this nervemay} be distinguished, which are the tibial and comumfibular nerves.5 _{The sciatic nerve block in the area abovethese} nervesbifurcationprovidesanesthesiabelowthekneelevel, exceptforthemedialaspectoftheleg,whichisinnervated bythesaphenousnerve.4

Completelowerlimbblockaderequiressaphenousnerve anesthetic block. Saphenous nerve block (SNB) may be performed above the knee, at the knee level, below the knee, and just above the medial malleolus.6 _{The SNB} success rate varies according to its level of blockade with local anesthetic, and at the knee level it can be 40%.7

Theobjectiveofthisstudywastodescribethe anatom-ical relationships of sciatic nerve in the popliteal fossa to determine the optimal distance the needle should be positionedto perform the anesthetic block of the sciatic nervebeforeitsbifurcationintotibialandcommonfibular nerves.

Method

Cadavers fromtheMorphologyDepartmentof theFederal UniversityofAlagoasandtheUniversityofHealthSciencesof Alagoaswereused.ThematerialcomprisedadultBrazilian cadaversofbothsexes,withunknownages,whodiedfrom differentcausesandwerefixedwith10%formalin.

Material for dissection, pins, and mechanical caliper (Metrica®_{)wereusedtoobtainthedata.}

Thecadaverwasplacedinpronepositiononthe dissec-tion table to be dissected. Then the popliteal fossa was demarcated, whose limits are the superolateral with the bicepsfemorismuscle,thesuperomedialwiththe semimem-branosusandsemitendinosusmuscles,theinferomedialand theinferolateralwiththerespectiveheadsofthe gastroc-nemius muscle. Subsequently, a longitudinal incision was madeinthecenterofthepoplitealfossa,followedbytwo transverseincisions.Aftertheskinandsubcutaneoustissue removal,accesstothepoplitealfossawasachieved,andthe dissectionoffatandlocalfasciawasperformed,preserving the nerve in its original position.When the sciatic nerve wasalreadybifurcatedatthefossalevel,theincisionwas extendedupwardsinsearchforthesiteofitsbifurcation.

Thefollowingdistancesweremeasured:fromthefossa apextothesciaticnerveemergencypoint,fromthenerve emergency point to the tibial and common fibular nerve bifurcation, fromthe bifurcationto theend of superolat-erallimit,andfromthedepths ofsciaticnervesurfaceto thepoplitealsheathandbicepsfemorismuscle.

Results

Anatomicalbasisforsciaticnerveblock 179

Regarding nerve bifurcation in relation tothe apexof poplitealfossa, itwasobserved thatthere wasa bifurca-tionbelow the apexin 67.96%;above theapex in15.90% withmeandistanceof1.72cm,greaterdistanceof3.40cm, and shorter distance of 0.55cm;and next tothe apexin 11.36%. The sciatic nerve was already bifurcated at the glutealregionin4.78%.

Regarding nerveemergence in relation to the apexof poplitealfossa,itwasobservedthatthenerveemergedat the same level of the apexin 56.81%, below the apexin 42.86%withameandistanceof1.67cm,longerdistanceof 3.60cm,andshorterdistanceof0.80cm.Tibialandcommon fibularnervesemergedseparatelyin2.36%.

Regardingthepoplitealfossalimits,itwasobservedthat the superomedial limit had an average length of 5.78cm withagreaterlengthof10cmandashorterlengthof2.5cm. The superolateral limit had an average of 5.98cmwith a greater length of 11cm and a shorter length of 2.25cm. The inferior limit hadan average lengthof 4.06cm,with agreaterlengthof8.80cmandashorterlengthof1.70cm. Regardingthedistancefromthesciaticnervesheaththat coatsthepoplitealvessels,theaveragewas1.35cm,witha greaterdistanceof2.60cmandshorterdistanceof1.35cm. Regardingthedistancefromthesciaticnervetothelong head of the biceps femoris muscle,the average distance was1.23cm,withagreaterdistanceof3cmandashorter distanceof0.40cm.

Discussion

Thereareseveralapproachestosciaticnerveblock,suchas posterior,anterior,lateral,andpopliteal,butthepopliteal approachhasbeenassociatedwithagoodscoreofpatient satisfaction.3_{Ablockadeofsensoryandsympatheticfibers} may occur, so that PSNB can be indicated not only for paincontrolduringanesthesiabutalsoforanalgesiainfoot traumaorpaincausedbyburns.3

Knowledgeofperipheralnervesanditsanatomical rela-tionships facilitates its location during the execution of anesthetic techniques, reduces the rate of complications associatedwithanesthesia,andincreasesthefrequencyof successfulblockades.8

This studyobservedtheanatomicalrelationshipsofthe sciaticandsaphenousnerves anddidnotaimtostudy the anesthetictechniquesandtypeofanesthetics,aswellasits quantityandconcentration.

The popliteal sciaticnerve block isknown aspopliteal block, in which a needle is inserted between 5 and 7cm abovethefossaapexandadvancedtowardthenerve.4_The

needleshouldbeinsertednearthemain trunkbeforethis nervebifurcationintothetibialandcommonfibularnerves.4 Thechanceofaneedletobenearthesciaticnervebefore itsbifurcationintoothernerveswheninserted5---7cmabove thefossais95.22%,regardingthebifurcationinrelationto theapexofpoplitealfossa.

Arandomizedclinicaltrialthatevaluatedthe effective-ness of sciatic nerve block at the knee level found that the injection of anesthetics in two points would have a highersuccessrate,butatthetimeofthisstudytheuseof ultrasoundinanesthesiahadnot beenwidely publicized.9 Anatomicalstudiesmaycontributetoimprovetheblockade techniquesusingultrasoundandthuscontributetoincrease effectiveness,withahigherscoreofpatientsatisfaction.

The sciatic nerve bifurcation in itsbranches occurs at variouslevels,andthechance tosucceed is 95.22%when theneedleisplacedbetween5and7cmabovethepopliteal fossa.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

References

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