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Chapter17
SacralNerveStimulation
KlausE.Matzel

INDICATIONS/CONTRAINDICATIONS

Operativeinterventionforfecalincontinenceshouldonlybeconsidered whenconservativetreatmentsfailtoresultinadequatesymptomrelief.
Thespectrumofindicationsforsacralnervestimulation(SNS)/sacral neuromodulationiscontinuallyevolving.Sinceitsfirstuseforthe treatmentoffecalincontinencein1994,itsapplicationandacceptance havebroadened.Initialindicationswerelimitedtoaverydistinct population:patientspresentingwithfecalincontinenceandresidual functionofaweak,butstructurallyintact,striatedmuscularanal sphincterandpelvicfloor.However,thefollowingfindingswidenedthe spectrumofindications:
TheeffectofSNSisnotconfinedtothemuscleisrelevanttocontinence. Temporaryteststimulationislowrisk. Theresultofapositiveteststimulationishighlypredictiveoftheclinical
outcomeofchronictherapeuticstimulation.
Today,teststimulationisliberallyused,notonlyinestablished indicationsbutalsotoexplorepotentialnewindications,bothforspecific etiologiesleadingtoincontinenceandforotherpathologicalconditionsof thecolorectumresultinginfunctionaldisorder.Permanentstimulationis directedbytheclinicaleffectivenessofteststimulation.
Teststimulationisusedonapragmatictrial-and-errorbasisbecauseit isclinicallyefficientandminimallyinvasiveandbecausecurrentlyno otherreliableclinicalorphysiologicpredictorforapositiveoutcomeof chronicSNSwithapermanentneurostimulationdeviceexists.
Patientsareappropriateforteststimulationiftheyhaveexisting,evenif
residual,voluntaryanalsphinctericfunctionorexistingreflex sphinctericactivity,indicatinganerve–muscleconnection(confirmedby intactanocutaneousreflexactivity,reflexcontractionduringsneezingor coughing,oramuscleresponsetopudendalstimulationwiththeSt. Mark’selectrode).
ThelikelihoodofclinicallyefficientSNSislow,ifthecortical–spinal– neuralaxisiscompletelydisrupted;however,partialdisruptionofthe
corticospinalaxisdoesnotrepresentacontraindication.
Permanentstimulationwithafullyimplanteddeviceiscommonly indicatedifthetrialstimulationresultsin>50%symptomimprovement, usuallymeasuredasthenumberofincontinenceepisodesordayswith incontinentepisodesperobservedtimeperiod.
Inadditiontogeneralcontraindications(unfitforsurgeryorprone placement,bleedingdiathesis),contraindicationsforteststimulationand implantationofthepermanentdeviceincludethefollowing:
Pathologicconditionsofthesacrumpreventingadequateelectrode placement(suchascongenitalmalformations)
Skindisease(especiallyseptic)attheareaofimplantation MicturitiondisordersthatareconsideredcontraindicationsforSNS Pregnancy(ifanSNSdeviceisinplaceandactive,itshouldbe
deactivated) Psychologicalinstability,mentalinstability,orretardationthatwould
impedetheunderstandingandhandlingofthedeviceprogrammer Thepresenceofdevicesincompatiblewiththeimplanted
neurostimulator(cardiacpacemakerorimplantabledefibrillator) Theneedformagneticresonanceimaging(MRI)indiagnosingor
treatinganyothermedicalcondition(thecurrentgenerationof stimulationsystems(referringtoMedtronicInterstim)isonlyclassified asconditionallysafefor1.5TheadcoilMRI).
PREOPERATIVEPLANNING
Preoperativeplanningispragmaticandalgorithmic.Decisionmaking reliessolelyonthedocumentationofthepretreatmentbowelpatternand itschangeduringtemporarystimulation.Itishelpfultoknowwhether thepatientsretainvoluntarysphincter/pelvicfloorcontractionsorif reflexcontractioncanbeprovokedbyapin-pricktestorcoughingor sneezing.Thesemeasuresmayalsoserveasahelpfulreferenceof possiblemuscleactivityduetotargetnervestimulationthroughoutthe electrodepositioning.Ifboth—voluntaryandreflexfunctions—are missing,SNSislesspromising.
Successoftreatment(andthatofteststimulation)dependson appropriateelectrodeplacement;preoperativesacralimagingintwo planesidentifiesindividualvariancesinboneanatomyandsacral foraminaconfigurationandisespeciallyadvisableincasesofsuspected malformations.Preoperativebowelcleansingisnotnecessary,butrectal washoutishelpfultoreducegasintherectum,whichmayobstruct intraoperativefluoroscopicidentificationofrelevantbonystructuresand electrodepositioning.
Forimplantationofthepermanentdevice,thepositionofthe implantablepulsegenerator(INS)shouldbediscussedwiththepatient andmarkedpreoperatively.Thepatientshouldbeabletoreachitwith thehandheldprogrammertoactivateanddeactivateitortochange stimulationamplitudeinapresetrange.Interferencewithpersonal habitsorclothingshouldbeavoided.

SURGERY

Concept
PermanentSNSisindicatediftrialstimulationresultsinsymptomrelief. Usually,a50%reductioninthenumberofincontinentepisodesordays withincontinenceora50%reductioninthevalidatedClevelandClinic Florida-FecalIncontinenceScore(CCF-FIS)isconsideredadequate.The trialshouldbelongenoughtoconfirmthesechanges;generally2weeks issufficient.
TheSNSprocedureconsistsofthreesteps:
Inthefirstdiagnosticstage,acutepercutaneousnerveevaluation(PNE), theaccessibilityofthenerve/sthroughthesacralforamen,andthe
feasibilityofelectrodeplacementaredetermined. PNEassessestherelevanceofeachsacralspinalnervetoanal
sphinctericcontractionandanalcanalclosure/pelvicfloorcontraction. Thisinformationcanhelpperformthefollowing:
sphinctericmusclesandthepatient’sabilitytomakefullvoluntaryuse ofthem
demonstrateindividualdifferencesofthesomatomotor/somatosensory innervation
sphinctericnervesupply
Intheseconddiagnosticstep,thetherapeuticpotentialofstimulationis assessedbytemporarilystimulatingthesacralnerveidentifiedduring
acutetesting.Asatherapeutictrial,itservestoselectpatientswhomay benefitfrompermanentneurostimulation.Twotechniquesareused:one withtemporaryelectrodes,whichareremovedafterteststimulation;the otheronewithanelectrode,whichcanbeusedforpermanent stimulationifteststimulationisclinicallybeneficial.
Inthethirdstep,theaimistopermanentlyimprovesymptomswith continuouslow-frequencystimulation.
PNEandpermanentimplantationcanbeperformedunderlocalor generalanesthesia.
Ifgeneralanesthesiaisused,musclerelaxantsshouldbeavoided.They
suppressthemotorreactionwhenthesacralnervesarestimulatedand complicatetheidentificationoftheoptimalpositionfortheelectrode.
Iflocalanesthesiaisused,accidentalblockadeoftherelevantsacral spinalnervesshouldbeavoidedbecausethetechniqueofelectrode
placementdependsonaconductingnerve.
Anatomy
Technically,themostimportantpartoftheprocedureatallstages—acute testing,subchronicteststimulation,andpermanentimplantation—isthe appropriateplacementoftheelectrode.Theaimistopositionthe electrodeclosetothetargetnerve.Itshouldbepositionedclosetothe exitofthesacralspinalnervesthroughtheventralopeningofthesacral foramen,atthesitewherethenervesenterthepelviccavityandproximal totheformationofthesacralplexus.Itshouldbeplacedparalleltothe targetnerve.
p.124
p.125
Distinct,palpable,bonyanatomiclandmarkshelpidentifythesacral foramina.Mostcommonly,S3isusedforstimulation;duringthe procedure,itisalsousedasareferencesitefororientationtoplace electrodesonS4orS2.
Thefollowinglandmarkshelpidentifytheforamina(Fig.17-1):
Thespinalprocessesmarkthemidline.Variationscanoccur,mostly distally.
TheS3foramenlevelislocatedmedialtotheupperedgeofthegreater sciaticnotch.
TheS3foramenlevel(upperedge)correspondstohalfthedistance betweentheupperedgeofthesacrum(lumbar–sacraljunction)andthe
tipofthecoccyx. TheS4levelcorrespondswiththesacralcrest.Soft-tissuecoverageis
leastatS4level. Theforaminaarelocated1–2cmfromthemidline,whichismarkedby
thepalpablespinalprocesses.(Thearrangementoftheforaminarelative tothemidlinemayvaryfromparalleltoamoreV-shapedpattern.)
FIGURE17-1Sacrumwithlandmarksforpalpation.
Thedistancebetweenthelevelsofthesacralforaminaisapproximately
1.5cm.Thetechniqueofelectrodeimplantationevolvedovertime.Today, theprocedureisperformedwiththeuseoffluorscopy(MedtronicInc, Minneapolis,MN).
NeurostimulationDevicesforSNS:MainComponents
TestStimulationLead,MedtronicModel3057:Unipolarlead designedtobeimplantedadjacenttothesacralnervefortemporary
stimulation. InterStimTinedLead,MedtronicModel3889:Aquadripolarin-
lineleadcontainingfourcylindricalelectrodesequalinlengthand spacedequidistantly.Theleadhastinesandmarkerbands.Thetines anchorthelead,andthemarkerbandsindicateleaddepthandtine deploymentduringpercutaneousimplantationwithaleadintroducer. Theelectrodecomeswithaseparatecurved,softerstylet.Thepacked stifferstyletinthetinedleadelectrodeshouldbereplacedwiththe curvedstyletfortheprocedure.
InterStimImplantableNeurostimulator,MedtronicModel
3058:Aneurostimulatorproducingelectricalpulsesforstimulation
withavarietyofparameters,modes,andpolarities.Theimplantable neurostimulatorconnectsdirectlywiththeelectrodewithonescrew.
N’VisionClinicianProgrammer,MedtronicModel8840:Used byphysicianswithan8870ApplicationCard(software)toprogramand
communicateviatelemetrywithanInterStimorInterStimII neurostimulator.
iConPatientProgrammer,MedtronicModel3037:Tousewith theInterStimII(3058)neurostimulator.Thishandheldunitallowsthe
patienttoturntheneurostimulatoronoroff,changepresetprograms, adjusttheamplitudewithinpresetlimits,andcheckthestatusofthe neurostimulatorandprogrammerbatteries.
p.125
p.126
PatientPositioning
Thepatientispositionedprone(iffluoroscopywithlateralimagingofthe sacrumisusedonanX-ray-capableoperatingtable).
Thepelvisiselevatedandsupported;lumbarlordosisshouldbereduced asmuchaspossible.
Thelegsandfeetarefixed,butshouldbemovable,asconcomitant movementsoftheipsilaterallegandfootduringstimulationmayaid
electrodeplacement(Fig.17-2). Thebuttocksaretapedtoallowvisualaccesstotheanusandthe
perineum.Tapingshouldnotbesotightastocounteractstimulation­inducedcontractionoftheanusandthepelvicfloor,whichcanbe delicate.
Theoperativefield(sacrumandbuttock)isdrapedandsterilized. Visualizationofmotorresponsesoftheanusandtheperianalarea,as
wellasthefeet,shouldbeensured.
FIGURE17-2Patientpositioning:pelvicfloor,anus,and
feetshouldbevisible.Lordosisshouldbeflattened.
Perioperativeantibioticprophylaxisisadvisedforimplantationof permanentdevices.
PreinterventionalImagingandMarking
Referencestoanatomicallandmarksaremarkedontheskin:Themedial edgesoftheforaminaareidentifiedwithfluoroscopyandmarkedonthe skinonbothsideswithverticallinesandthelowerendoftheiliosacral jointsandmarkedwithahorizontallineresultinginan“H”sign(Fig.17-
3).
FIGURE17-3Imagingofthesecrum:medialedgesofthe
foraminaandlowerendsoftheiliosacraljunctionmarked resultinginan“H”-sign.A.X-rayandB.onskin.
AcutePercutaneousNerveEvaluation
Foracutepercutaneousnerveevaluation(APNE),needleelectrodes (MedtronicModel041828or041829ForamenNeedles),notisolatedat thetipandthetop,areinsertedintothedorsalsacralforaminaofthe potentiallyrelevantnerve—mostcommonlyS3,butalsoS4.Placementis guidedbysacralbonylandmarks,the“H”signandsupportedand confirmedbyfluoroscopy.
Identificationofthesacralforamina:Adistinctsensationof enteringthedorsalopeningoftheforamen,perforatingrigid
ligamentousstructures(ascomparedwithhittingtheperiosteumofthe sacrum),isexperienced.
Needleelectrodepositioning:Theangleofinsertionshouldbeacute tominimizetheriskofnerveorvasculardamage,whichis60degreesat
theleveloftheskin(Fig.17-4).Astheneedlehastocrossthesofttissue beforeenteringtheforamen,itsentrancepointshouldbecephaladtothe positionoftheforamen.Theneedleshouldideallybeinsertedatthe angleofthefusionplaneofthesacrumandstrictlyintheverticallineof thecentralbodyaxis(theuprightofthe“H”sign).Theentryintothe foramenshouldbetheuppermedialcorneroftheforamen.
Optimizingpositioning:Oncetheforamenisentered,theneedle electrodeshouldbemovedinaventraldirection(orback)with
intermittentstimulationofgraduatedamplitude(beginningwithlow amplitudes).Gentlemovementsinmillimeterstepswithintermittent stimulationwillhelpoptimizepositioning.Markersontheneedle electrodeindicatethedepthofplacement.
Responsetostimulation:Amotorresponseofthepelvicfloorand theanus(ifgeneralanesthesia)orasensoryresponse(iflocal
anesthesia)optimizesthepositioningoftheneedleelectrode.
FIGURE17-4Acuteneedleelectrodeinsertion:oblique
entryintotheforamen.Tipattheventralopeningofthe foramen.
Althoughtheeffectofstimulationonthepelvicfloorandthelower extremityactivitymayvaryamongindividuals,thefollowingmotor responsesaregenerallytypical:
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