Cadaveric comparison of the accuracy of ultrasound-guided versus ‘blind’ perineural injection of the tibial nerve in horses

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Short communication

Cadaveric comparison of the accuracy of ultrasound-guided versus

‘ blind ’ perineural injection of the tibial nerve in horses

Maylin van der Laan

^a,b,

*, Els Raes

^a

, Maarten Oosterlinck

^b

aDepartmentofVeterinaryMedicalImagingandSmallAnimalOrthopedics,FacultyofVeterinaryMedicine,GhentUniversity,Salisburylaan133,9820 Merelbeke,Belgium

bDepartmentofSurgeryandAnaesthesiologyofDomesticAnimals,FacultyofVeterinaryMedicine,GhentUniversity,Salisburylaan133,9820,Merelbeke, Belgium

ARTICLE INFO

Articlehistory:

Accepted21December2020

Keywords:

Diagnosticanaesthesia Nerveblock

Lamenessexamination Orthopaedics Regionalanaesthesia

ABSTRACT

Duringdiagnosticevaluationofhindlimb lamenessinhorsesthetibialnerveblockis traditionally performedbased on anatomical reference points, but itcan be difﬁcult to achieve effectivelocal anaesthesiausingthisblindtechnique.Ultrasound(US)-guidedinjectioncouldincreasetheaccuracyof injection.Theaimofthisstudywastocomparetheaccuracyofbothtechniques.Twenty-onepairedsets ofcadaverhindlimbswereinjectedwith1mLmethyleneblueusingtheblindorUS-guidedtechnique.

Therewasnosigniﬁcantdifferenceinstainwidthandlengthandincolourednervelengthbetween techniques.However,thesuccessfulrateofnervestainingwas85.7%and47.6%fortheUS-guidedand blindtechnique,respectively(P=0.02;oddsratio6.6;95%conﬁdenceinterval,1.5–29.4).Thisstudy suggeststhattheUS-guidedtechniqueismoreaccuratethantheblindtechnique.However,inthetreated sample,asingleUS-guidedinjectiondidnotconsistentlyresultinnervestaining.

Nerve blocks are often used in the diagnostic evaluation of lamenessinhorses.Atibialnerveblockcanbeusedwhenmore distal nerve and/or intra-articular blocks have not resulted in improvementofthehindlimblameness(BassageandRoss,2011).

The tibial nerve emerges between the medial head of the gastrocnemius muscle and thesuperficial digital flexor muscle on the medial side of the crus. The nerve runs cranial tothe commoncalcanealtendonandiscontainedwithinthesuperficial caudal crural compartment limitedby thesuperficialand deep caudalcruralfasciae(Budrasetal.,2012;Denoixetal.,2020).

The blind technique consistsof injecting 15–20 mL of local anaestheticsolutionwitha20–22G,2.5cmneedleinthelateralor medialsideofthelimb,10cmproximaltothetubercalcaneiand1 cm cranialtothecommon calcanealtendon(Wheat and Jones, 1981;Dyson,1984;Skardaetal.,2009;BassageandRoss,2011).

Basedonthesizeofthetibialnerve,ithasbeenrecommendedto wait 20–30 minbeforeevaluatingtheresult(Bassageand Ross, 2011).However,theauthors’practicalexperiencesuggeststhatit canbedifﬁculttoachieveeffectivelocalanaesthesia,evenafter substantialwaitingtime andevenusinglargervolumesoflocal anaestheticsolution.

Ultrasound(US)-guidedinjectioncouldincreasetheaccuracyof injection,asstatedbyDenoixetal.(2020)albeitwithoutdirect comparisonbetweenblindandUS-guidedtechniques.Ultrasound- guidedinjectionallowsdepositionoflocalanaestheticsolutionas closeaspossibletothenerveandespeciallywithinthesuperﬁcial caudal crural compartment (Denoix et al., 2020). A detailed description of the US-guided technique is provided in the Appendix(SupplementaryItem1).Theaimofthisstudywasto comparetheaccuracyoftheconventionalblindtechniqueandthe US-guidedtechniquefor perineuralinjectionof thetibialnerve with methylene blue in cadaveric limbs of horses. It was hypothesised that the US-guided technique would result in superior accuracy compared tothe blind technique. Therefore, anexvivostudywasperformedon42cadaverhindlimbsfrom21 horseseuthanisedattheFacultyofVeterinaryMedicineofGhent Universityfor variousreasonsunrelatedtohindlimb pathology.

Researchethicscommitteeoversightwasnotrequiredasthestudy was performed using material collected during post-mortem examinations.Sex,ageand breedofthehorsesincludedinthis study werenot recorded. Hindlimbsweredisarticulated at the coxofemoraljointandstoredinarefrigerator(4C)inbatchesof twotothreehorses.Alllimbsweretestedwithinthreedaysof disarticulation.Paired hindlimbswererandomly assigned tobe injected using either the blind or US-guided technique, using simple randomisation by a random number list generated in spreadsheet software (Microsoft Excel). The limbswere placed

*Correspondingauthorat:HorsepracticedeWaert,Oud-heinenoordseweg18, 3274KDHeinenoord,TheNetherlands.

E-mailaddress:maylin@live.nl(M.vanderLaan).

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withthelateralsidefacingdownandthelimbinsemi-extension;

theregionofinterestwasclippedpriortoinjection.Injectionwas performed 20 min after equilibration of the limb to room temperature.

For theblind technique,1 mL methylene blue was injected through a 21G, 2.5 cm hypodermic needle which was inserted approximately1cmdeep,atthemedialsideofthelimb,10cm proximaltothetubercalcaneiand1cmcranialtothecommon calcanealtendon(Skardaetal.,2009;Fig.1).Thistechniquewas performedbyaboard-certiﬁed(ECVS,ECVSMR)specialistoperator (MO)withextensiveclinicalexperienceofthisprocedure.Forthe US-guided technique, the region of interest was washed and subsequentlyrinsedwith70%denaturedethanol.Afterultrasono- graphicvisualisationofthetibialnerve(Fig.2)usingalinearprobe atfrequencyof7.5MHz(PhilipsCX50),a21G,2.5cmneedlewas insertedcranialtothenerveunderultrasoundguidanceand1mL methylene blue was injected. The US-guided technique was performed bya board-certiﬁed(ECVDI) specialistoperator (ER) withexpertiseinultrasound-guidedprocedures.

Fiveminafterperformingtheinjection, theskinmedial and proximaltothetarsuswasremovedtomeasurethelengthand widthofthemethylenebluestain(Fig.3).Subsequently,thetibial nervewasfurtherdissected,anditwasdeterminedwhetherthe nervewascolouredornot.Ifthenervewascoloured,thelengthof thenervecolouredbymethylenebluewasmeasured(Fig.4).Ifthe nerve wasnot coloured,thecolouredanatomical structure(e.g.

superﬁcial caudal crural fascia) was further dissected and measured(maximumdistribution,i.e.largestwidth(cranio-caudal direction) and length (proximo-distal direction) of the stain).

Moreover,itwasdeterminedifthestainwascaudal,cranial,medial orlateraltothenerveandthedistancebetweentheedgeofthe stainandthenervewasmeasured.Arulerwasusedforalllength

measurements.Theresearcherperformingthedissectionswasnot blindedtotheinjectiontechnique.

DataweretestedfornormalityusingKolmogorov–Smirnovand ShapiroWilktest,andWilcoxonsignedranktest(methyleneblue Fig.1.Illustrationoftheinjectionsite(bluedot)atthemedialsideofthehindlimb,

10cmproximaltothetubercalcaneiand1cmcranialtothecommoncalcaneal tendon.

Fig.2. Transverseultrasoundsectionofthecaudomedialpartofanequinecrus(+, tibialnerve; SDFT,superficial digitalflexortendon; DDFT,deep digitalflexor tendon).

Fig.3.Exampleofthemedialaspectofanequinecrusafterremovingtheskin(right isproximal;(1)tubercalcanei;(2)commoncalcanealtendon;(3)methyleneblue stain).

Fig.4. Exampleofthemedialaspectofanequinecrusafterremovingtheskinand dissectingthetibialnerve(rightisproximal;(1)tubercalcanei;(2)common calcanealtendon;(3)tibialnerve).

M.vanderLaan,E.RaesandM.Oosterlinck TheVeterinaryJournal269(2021)105603

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stainwidth),pairedStudent’st-test(methylenebluestainlength) andMann–WhitneyUtest(colourednervelength)wereusedto comparedatabetweentheUS-guidedandblindtechnique.Fisher’s exacttestwasusedtotestforassociationbetweenthetechnique usedandnervestainingresults,includingcalculationoftheodds ratioand95%conﬁdenceinterval(95%CI).Allstatisticaltestswere performedwithSPSSStatistics25(IBM),withstatisticalsigniﬁ- cance setat P<0.05. Data arepresented as mean standard deviation(SD)ormedian,interquartilerange.

Therewasnosignificantdifferenceinthestainlength(P=0.16) betweentheblind(6.182.07cm)andtheUS-guidedtechnique (7.041.61cm).Therewasalsonosignificantdifferenceinstain width(P=0.54)betweentheblind(1.5cm,1.2)andtheUS-guided technique(1.5cm,0.75).Nosignificantdifferencewasfoundinthe lengthofthecolourednerves(P=0.13)betweentheblind(4.5cm, 6.4) and the US-guided technique (6.75 cm, 4.5). However, injections resulting in coloured nerveswere significantly more oftenobservedwiththeUS-guidedtechnique(85.7%) thanwith theblindtechnique(47.6%;P=0.02;OR6.6;95%CI, 1.5–29.4).Inthe caseswithoutnervestaining,thedistancebetweenthenerveand themethylenebluestainwas0.1cmintheUS-guidedgroup(inall cases)and0.250.34cminthegroupusingtheblindtechnique.

Thiscouldnotbecomparedstatisticallybecauseofthelownumber of non-coloured nerves in the US-guided group (n = 3/21) compared withtheblindgroup(n=11/21).Dye depositiondid notindicateanypotentialrisksassociatedwitheithertechnique (e.g.intrasynovialdeposition).

Ourresultsconﬁrmthatwhenthetibialnerveisapproachedin anisolatedlimbpositionedonatablegeneratingoptimalaccess conditions, using the US-guided technique produces a more predictable result than not using it, based on the signiﬁcantly higher proportion of coloured nerves with the US-guided technique.Theoddsratioshowedanimportantdifference buta low precision (95%CI,1.5–29.4),which isa consequenceofthe smallsamplesize.Inthethreecasesinwhichthenervewasnot colouredaftertheUS-guidedtechnique,themethylenebluewas just1mmdistanttothenervewhenmeasuredatdissection,under thedeepcruralfascia(Fig.5)whichprecludeddistributionofthe methyleneblue.Asimilarobservationwasmadeformostcasesin whichthenervewasnotcolouredaftertheblindtechnique,but interestingly, in two of those cases, the methylene blue was injected in the perineural fat but without reaching the nerve (Fig.6).Althoughthesamplesizewastoosmalltoallowstatistical comparison of this variable between groups, it illustrates the

possiblecontributionofthefasciaandperineuralfatininhibition ofthedistributionofthemethyleneblue.

Performing the US-guided technique safely on a live horse withoutsedation canbe challenging, becauseof theadditional equipmentandpersonnelrequiredasrecentlydescribedbyDenoix et al. (2020). In that report,it was recommendedto havetwo peoplerestrainingthehorseandtwooperators,eachpositionedon onesideoftheinjectedleg.Denoixetal.(2020)useda1.5cm25G hypodermicneedleanda6–10MHzmicroconvexprobetoinject 5–8mLoflocalanaestheticsolutionbothcranialandcaudaltothe tibial nerve, whereas in the present study, we only injected craniallyandusedaverysmallvolumeofmethyleneblue(1mL)to assessaccuracyofinjection.WiththeincreasedaccuracyoftheUS- guidedtechnique,asmallervolumeofanaestheticsolutionmaybe sufﬁcient for obtaining a successful block of the tibial nerve, althoughthisrequiresfurtherinvestigationinvivo.

Twodifferentoperators(onespecialistclinicianexperiencedin using the blind technique and one experienced in US-guided injections)wereusedforthetwotechniques,toavoidthatoperator preferenceorexperiencewithonetechniquewouldcreatebiasin theresults. Theoretically,it wouldhavebeenpreferabletohave onesingleoperatorwithnopreferenceand equalexperiencein blind and US-guided injection techniques, but this was not consideredachievableforthepresentstudy.

Inthepresentstudy,alinearprobewithafrequencyof7.5MHz wasused,whichallowedsufficientdetailtovisualisethenerveon thesecadaverlimbs.However,amicroconvexprobemaybeeasier tohandleonalivehorse.Moreover,ahigherfrequencywouldhave resultedinabetterresolutionandincombinationwiththedepth ofthenervetobestained,thismayhaveaffectedthesuccessofthe US-guided technique.It is therefore recommendedto optimize visualisationofthesuperficialand deepcaudal cruralfasciaeto ensurecorrectinjection.Regardingtheneedlelength,therather superficialdepthofthetibialnervedidnotrequirefullinsertionof the2.5cmneedleintheblindtechnique,howeverintheUS-guided technique,entryangleandprobewidthmustalsobeconsidered and a 1.5 cm needle asused by Denoixetal. (2020) might be insufficientwhenusingalinearprobe.

Inconclusion, this studyconﬁrmsthat underoptimalaccess conditions,theUS-guidedtechniqueforthetibialnerveblockmay bemoreaccuratethantheblindtechnique.However,evenunder ultrasoundguidance,asingleinjectiondidnotconsistentlyresult innervestainingduetopuncturingthedeepcaudalcruralfascia.

Thismaybeovercomebyusingahighertransducerfrequencyand/

Fig.5.ExampleofaspecimeninwhichthenervewasnotcolouredaftertheUS- guidedtechnique,withthemethyleneblueinjected1mmtoodeep,underthedeep cruralfasciawhichprecludeddiffusionofthemethyleneblue(rightisproximal;(1) tubercalcanei;(2)commoncalcanealtendon;(3)tibialnerve;(4)methyleneblue stain).

Fig.6. Exampleofaspecimeninwhichthenervewasnotcolouredaftertheblind technique;withthemethyleneblueinjectedintheperineuralfatbutwithout reachingthenerve(rightisproximal;(1)commoncalcanealtendon;(2)tibial nerve;(3)methylenebluestain).

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or byinjecting cranialand caudaltothenerve asdescribed by Denoixetal.(2020).

Conﬂictofinterest Nonedeclared.

Acknowledgements

WethankthetechnicalstaffoftheDepartmentofPathology, Bacteriology and Poultry Diseases of the Faculty of Veterinary Medicine of Ghent Universityof theirhelp with collectingthe specimens.

AppendixA.Supplementarydata

Supplementarymaterialrelatedtothisarticlecanbefound,inthe onlineversion,atdoi:https://doi.org/10.1016/j.tvjl.2020.105603.

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