TheRelationshipBetweenSuperficialDigitalFlexorTendonLesionsandAsymmetricFeetinEquine

Forelimbs

SJHHillAWCF

SubmittedinpartialfulfillmentoftherequirementsfortheawardoftheFellowshipoftheWorshipfulCompanyofFarriers

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AcknowledgementsTheauthorwouldliketothankthefollowingpeoplefortheirvaluedsupport,inspirationandencouragementduringthisstudy.A.Northrop.FacultyofScienceandTechnology,AngliaRuskinUniversity,EastRoad,Cambridge,CB11PT.R.BurtonM.A.(Hons)Cantab,M.Sc(Hons)10WestferryRoad.London.E148LSR.ShaveFWCF.Greenacre,CowGreen,Bacton,Stowmarket,Suffolk,IP144HJ.S.CurtisFWCFHonRCVS.TheForge,MoultonRoad,Newmarket,Suffolk,CB88DU.M.Tyler.BSc(Hons).34MainStreet.Belton-in-Rutland

iii

Summary

Reasons for performing this study: Formanyyears vets andhorseowners alike

havetriedto influencethetrimmingandshoeingtechniquesundertakenbyfarriers

inthebeliefthatashorttoewillhelpreducetheriskoftendoninjuries.Theauthor

however, foundthattendoninjuriesweremorecommoninthe limbwherethefoot

wassmallerandmoreupright.

Objectives:Theobjectivesweretomeasurethefootsizeoftheforefeetofhorsesthat

havesustainedsuperficialdigital flexor tendon (SDFT) injuries, and tomeasure the

forefeetofhorseswithinacontrolgroup.

Methods: The measurements of 25 horses with diagnosed SDFT injuries and a

control group of 25 horseswere used in this study, all of themeasurementswere

recorded. Measurements of the width at the widest part of the foot, the distance

betweentheheelsandthedistancefromthecentreoftoetothelastbearingsurface

of the lateralheelwererecorded.Disparitiesbetween thesizeof feetofeachhorse

and the relationship between this and SDFT injury were compared. Differences

between the injured group and a control groupwere statistically analysed using a

Kruskall-Wallistestofdifference.Associationsbetweenthesmallerfootandthefoot

thatwasinjuredwereinvestigatedusingaChi-squaredtest.

Results:Withinthe20horsesthatonlyhadinjurytotheSDFTinonelimb,16horses

hadSDFTcorelesioninjuriestothesmallerfoot,1hadapairoffeetand3horseshad

SDFTcorelesioninjurytothebiggerfoot.Therewasasignificantdifferencebetween

thecontrolandinjuredgroupsforpercentagedifferenceinfootlength(P<0.01)and

percentagedifferenceinthesumofallthedimensions(P<0.05).

Conclusion:Tendoninjuriesinthehorse’sforelimbhavebeenassociatedwithlong

toes.Thisstudydisprovesthattheoryandhighlightstheneedforfurtherresearchin

tothisarea.Thegreaterthedifferenceinfootsize,themorelikelyahorseisto

rupturetheSDFTandrupturesoftheSDFTaremorelikelytooccurinthelimbwith

thesmallerfoot.

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DeclarationI hereby declare that the work within this Fellowship thesis is my own. Anysourceshavebeendulyreferencedandanyillustrationsordiagramsthatarenotmyownareusedwiththepermissionoftheowner.

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Contents PageIntroduction 1Tendons 4SuperficialDigitalFlexorTendon 5TendonInjury 5CoreLesion 6AimsandObjectives 8 MethodsandMaterials 9TrimmingandMeasuringProtocol 10Datacollectionandanalysis 12Results 13Discussion 17Studylimitations 21FarrierConsiderations 22Conclusion 23Bibliography 24ManufacturersAddresses 27Appendix 28

Wordcount,4953.

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IntroductionAnecdotallyformanyyears,horseownersandveterinarysurgeonshavetriedto

influencethetrimmingandshoeingtechniques,undertakenbyfarrierstoreduce

thelengthoftoeinthebeliefthatthisreducesthepressureontheflexortendons

oftheforelimbandreducesthechanceofsustainingtendoninjury.However,the

term“longtoe”isinconsistentlydefined.Horsesthathavelargeflatfeetareoften

considered to have long toes. A horse with a lesser angle of dorsal hoof wall

(DHW)isoftendescribedashavingalongtoe,however,exactlythesamelength

toemaybedescribedasshortornormalsimplyduetoagreaterangleofDHW.

Toetoheelratioisthemajorfactorandahorsewithalowweakheelcangivethe

appearanceofthetoelookinglong.

Stashak(2008)hasstatedthatexcessivepasternslope,impropershoeing(short

shoeing,shoeingwithlongtoe/lowheel,alowhoofangle,toegrabsorclubfeet)

arepredisposingcausesof tendon injury.Historically, ithasbeenreportedthat

toesthataredescribedasbeingtoolongmustalwaysincreasethestrainonthe

back tendonsduring locomotion (Mattinson1922).Foreverycentimetreof toe

lengthinanaverageThoroughbredresultsin50kilogramsofforceactingonthe

tendons(Weller2016).However,incaseswherethehorsehasasymmetricfeet,

foot sizeandDHWangleappear tobemoresignificant factorsaffecting tendon

injury.Asymmetricfeetarecommoninlotsofhorsesanddonotalwaysmeana

horsehasaclubfoot.Asymmetricfeetaredefinedaspairsofopposingfeetthat

are not similar in appearance; one foot appears larger than the otherwith the

smallerfootoftenbeingmoreboxyinshape,withtheappearanceofbeingmore

upright. Personal experience shows that horses with SDFT lesions most

commonly have the injury to the limb with the smaller more upright foot.

Research has shown that the smaller foot is more vulnerable, indicating that

horsesare less likely to suffer catastrophicmusculoskeletal injury (CMI) in the

footwith a greater solar surface area (Kane 1998).More recently, it has been

reported thatWarmblood horses with asymmetric forefeet are likely to retire

fromcompetitionearlierthanhorseswithsymmetricalfeet,especiallyinthecase

ofjumpinghorses(Ducro2009).Kummer(2005)foundthat70%ofWarmblood

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horses(n=40)hadasignificantlylargerleftfootanddistalphalanxthantheright.

Itwasnoted thatall thehorses in this studywereclinically soundand the feet

showednoabnormalityordistortion,suggestingthatasymmetryisasignificant

occurrence.Inastudyofflexuraldeformityinapopulationof373Thoroughbred

foals, 75% of club feetwere found to be on the right front (Curtis 2012). Any

asymmetry in hoof spread measurements may suggest unequal loading of the

limbs,whichinturnmaycontributetoinjuriesandreducedperformance(Wilson

2009).Loadcanbederivedasthehorse’sbodyweightmovingovertheweight-

bearinglimb,causingthephalangealjointstoextend.

With reference to the relation of shoeing practice to the various tendons,

reducingthelengthoftoeisproventoreducethepeakstraininthedeepdigital

flexortendon(DDFT)atthepointofbreakover(Balch1995).Thishasverylittle

effectonthestrainplacedonthesuperficialdigitalflexortendon(SDFT);infact

raisingahorse’sheelsandcreatingabrokenforwardhoofpasternaxisincreases

fetlock drop which in turn increases the pressure on the SDFT but reduces

pressureintheDDFT(Lawson2007).Abrokenbackhoofpasternaxis(HPA)has

theoppositeeffectandreducespressureontheSDFT,butincreasespressureon

theDDFT(Riemersma1996).Longtoes/flatfeetareoftenassociatedwithhaving

abrokenbackHPA.

The forelimb SDFT is far more likely to be injured than any other tendinous

structures in the equine limb, with approximately 90% of tendon injuries in

racehorsesoccurringtothistendon(Ely2004;Ely2009).Thegroundsurfaceof

thehoofshouldbeatrightanglestotheloadbearingline,failuretoachievethis

canhaveasignificantaffectonthewaybothfootandlimbareplaced,whichin

turn will affect the foot flight of the limb (Colles 2010). Williams & Deacon

(1999) stated that 95% of all horses have some form of foot imbalancewhich

predisposesthemtoinjury.

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Tendoninjuryhasbeenfoundtobethemostcommonreasonforretirement in

racingthoroughbreds.SignsofSDFTinjuryhavebeenfoundin24%(n=263)of

national hunt horses that were assessed by ultrasound scan (Avella 2009)

Additionally, the riskof tendon injury increaseswith age (Avella2009;Thorpe

2010).Whiletendoninjuriesoccurringtohorsesinotherdisciplinesarelesswell

reported,asmallnumberofstudieshaveshownasignificantriskofinjurytothe

SDFT, suspensory ligament (SL) when compared to injuries occurring in the

DDFTdependingonthedisciplineundertaken(Murrayetal.,2006;Singeretal.,

2008).

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TendonsTendons are longitudinally arranged collagen fibres that act as a tensile

communication between muscle and bone to facilitate locomotion as seen in

(Figure 1). They are composed of dense connective tissue arranged in parallel

densely packed bundles. Peritendon surrounds these bundles and epitendon

surrounds the entire tendon unit. Both of these connective tissues carry the

bloodsupplytotheinternalstructuresofthetendon.

Figure1.Lateralviewshowingtendonsandligamentsofthelowerlimb(www.novobrace.com)

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TheSuperficialDigitalFlexorTendon(SDFT)TheSDFToriginates fromthesuperficialdigital flexormuscle,whichoriginates

from themedial epicondyle of the humerus, with the superior check ligament

attachingittotheradiusproximaltothecarpus.Proximaltothefetlock,theSDFT

formsaringthroughwhichtheDDFTpassesthroughcalledthemanicaflexoria.

The SDFT continues dorsally where it bifurcates to pass abaxially around the

DDFT to insert on the distal-dorsal surface of the proximal phalanx and the

proximal-dorsal surface of the middle phalanx. The SDFT, along with the

suspensoryligament(SL),playsamajorroleintheenergyrecyclingsystemofthe

forelimb. As the fetlock descends, the kinetic energy created is stored

temporarily as strain energy in the SDFT. Elastic recoil converts most of the

stored energy back to kinetic energy as the foot leaves the ground (Alexander

1988).Thisallowsefficientlocomotion.5-10%ofstoredstrainenergyisreleased

as heat (Ker 1981, Riermersma 1985). The SDFT has a similar function to the

Achilles tendon in humans and is unique in its ability to store energy. It can

stretchand recoilup to16%witheach strideat gallop, functioning close to its

mechanical limit (Stephens 1989). In comparison, the maximum strain of the

commondigitalextensortendonhasbeenestimatedat2.5%(Birch2008).

TendonInjuryTendon injuries are a breakdown in the matrix that holds the collagen fibres

together. Such breakdown in the matrix causes the tendon fibres to rupture.

There are several potential causes of tendon injuries. The majority of tendon

injuries are thought to occur due to an accumulation of micro-damage over a

number of loading cycles, rather than being caused by an acute injury (Riley

2008).Asahorsegetsolder,theelasticitywithintendonsisreduced,whichalso

increasestheriskoftendoninjury(Thorpe2015).

Asingleoverstraincancauseatendontoruptureandsuchoverstraincanoccur

asaresultofunevengroundcreatinghyper-extensionof the fetlockorslipping

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due to the fact thatahorse isperformingclose to itsmechanical limit (Stashak

2008).Adirecttraumawhilstthetendonisloadedcanalsocausedamage.Muscle

fatiguecanresultinreducedneuromuscularcontrolandthiscancauseinstability

of tendons (Kai. 1999)and therefore increase the riskofoverstrain.TheDDFT

helpsstabilisethefetlockjointbutismoresusceptibletomusclefatiguethanthe

SDFT.ThisinstabilitycancausefurtherstraintotheSDFT.Higherincidencesof

injuryarereportedonfirmersurfaces(Williams2001).Studieshaveshownthat

when horses are racing, the inside leg in relation to the bend is slightlymore

pronetoinjury(Rooney1981).

CoreLesionsCorelesionsaremostaccuratelydiagnosedusingultrasoundexamination(Figure

2).Initialassessmentnormallydemonstratesexcessiveheatandthickeningofthe

tendononpalpation.Themostcommonsiteofinjuryisinthemiddlethirdofthe

metacarpusregion(Figure3).Thisareaisnarrowerthantheproximalanddistal

parts of the SDFT with more restricted blood supply, it is also proven to

degenerate more with age and use than other areas within the tendon

(Patterson-Kane 1998). Peripheral tendon injuries can occur and are often

accompaniedbyskincontusions,suchinjuriescanoftenbetestedbypullingthe

skin away in the affected area and by pinching the skin to see if there is a

reaction.Thiscanaidinconfirmingwhetherthereisdirecttraumaornot.

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Figure2.UltrasoundscanshowingacorelesioninjurytotheSDFT.(©TownandCountryVets)

Figure3.SDFTlesioninthemidthirdofmetacarpalregion.(©S.Hill)

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The coreof the SDFT can reach temperatures of 45°C after sevenminutes at a

gallop, which is 10°C higher than the temperature of the peripheral surface

(Stashak2008).Prolongedexposure toheat cancauseexcessivedamage to the

cellsthatcreatetheextracellularmatrixbetweenthecollagenfibres,causingthe

coreof the tendon to rupture (Thorpe2010).At temperaturesabove45°C, cell

survival drops dramatically and at 51°C, less than 5% of cells survive (Birch

1997).Poorbloodsupplyinatendoncontributestoanincreaseintemperature;

in addition, theheat is dissipated relatively slowly (Thorpe2010). Poorblood

supplyalsogreatlyreducesthespeedofthehealingprocess.Thereisaneedto

understandmoreaboutsusceptibilitytocorelesionsintheSDFT,duetoitshigh

prevalenceintheriddenhorse.

AimsandobjectivesTheaimofthisstudywastotestthehypothesesthat1)lesionstotheSDFTare

related to asymmetric feet; and 2)where there are disparities in foot size the

smallerfootisontheaffectedlimb.

Theobjectivesweretomeasurethefootsizeoftheforefeetofhorsesthathave

sustainedSDFTinjuries;tomeasuretheforefeetofhorseswithinacontrolgroup,

and to compare the size difference between the feet of each horse. These

measurementswere to be statistically analysed in order to identify differences

between the control and injured groups, in order to explore the relationship

betweenthesmallerfootandtheaffectedlimbandtotestwhetherthelimbwith

thesmallerfootwasmoresusceptibletoSDFTinjury.

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Methods&MaterialsSelectionofSDFTlesionhorsesAllhorsesthatwereselectedwithSDFTlesions,wereownedbycustomersofthe

author.AllhorseswithasuperficialSDFTinjurywerediagnosedandconfirmed

with ultrasound scans by a veterinary surgeon. All injuries were core lesion

injuriesintheforelimbsandnotdirecttraumainjuries.

SelectionofcontrolgrouphorsesThecontrolgroupwasa selectionof convenience, comprisingof (n=25)horses

that weremeasured using the samemethods as described below. The control

group consisted of the first (n=25) horses that the author was granted

permissiontoincludewithinthestudy.Horseswereofmixedbreedandtypeand

usedforvarioustypesofwork.Writtenpermissionwasgrantedfromtheowners

ofallthehorsesusedinthestudy.Therewasnoethicalconcernwiththisstudy

asnochangewasmadetothewayhorseswereshodortreated.

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TrimmingandmeasuringprotocolAllhorsesweretrimmedandmeasuredbytheauthortoavoidinconsistency.The

frogsweretrimmedsymmetricallytogaugetheheelheightofeachfootandthe

hoofproportions.Anyexfoliatingsolewasremovedandthehoofwallbarsand

heelsweretrimmedtoachievealevelplane,correctHPAandsymmetrical

proportionswherepossible,readytoreceiveashoe,shodinleisurehorsestyle.

Thisoftenmeantreducingtheheelheightmoreonthesmallermoreuprightfoot.

Dorsalwallflaresweredressedtotryandachievesymmetrywherepossibleand

equalwallthicknessaroundthetoe.Thebearingborderofthehoofcapsulewas

trimmedperpendiculartothelongaxisoftheflexortendons.Noroundingofthe

distalborderofthehoofwascarriedoutpriortomeasuring.Theauthor

measuredthewidestpartofeachfoot(Figure4),thewidthbetweentheheels

(Figure5)andthedistancefromthecentreoftoetothelateralheel(Figure6)in

millimeters(mm)usingabrassrule4.Theangleofthedorsalhoofwall(Figure7)

wasalsorecordedusingabrasshoofgauge3whilethefootwasnon-weight

bearing.

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Figure4.Widestpartofthefoot(©S.Hill)Figure5.Widthbetweentheheels(©S.Hill)

Figure6.DistancefromthecentreoftoeFigure7.Angleofdorsalhoofwall(DHW)(©S.Hill)

tothelateralheel.(©S.Hill)

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DatacollectionandanalysisThemeasurements were recorded using separate forms for each horse taking

note of thehorse’s age, breed and type ofwork thehorsewasused for,which

limb/limbswereaffectedandwhenandhowtheinjuryhappened(ifknown).The

measurementswere recorded in Excel1. The limbwith the tendon injurywas

recorded,togetherwiththeageofthehorseatthetimeofinjuryandthetypeof

work being undertaken. Photoswere recorded to demonstrate the findings for

eitherfootand/ortendon.

The threemeasurements of each foot (width of foot,width between heels and

distancefromtoetolateralheel)werealladdedtogethertogiveasinglenumber

inorder to compare sizedifferencebetween feet. Calculationswere converted

intoapercentage toallow fordirectcomparisonsbetweensubjects.Thebigger

footwassaidtobe%biggerthanthesmallerfoot.Thedatawasanalysedusing

Minitab2totestforanystatisticalassociationsanddifferences.

StatisticalanalysisThe datawas checked for normality and itwas found to be non-parametric; it

wasnotnormal.DatawasanalysedusingaKruskal-Wallistesttoidentifyifthere

wereanysignificantdifferencesbetweenthehoofmorphologyoftheinjuredand

control groups. Additionally, data was analysed to investigate significant

associationsbetweenleftorrightsmallerfootagainstwhethertheinjurywason

thesmallerfoot.ThetestthatwasusedforthiswasaChi-Squaredtest.

QualitativeObservationsHorseswerevisuallyassessedbothstaticallyanddynamically.Thehorse’slower

limbwasassessedwhilstnon-weightbearingtoobserveanylimbdeviations.The

author noted the conformation of each limb and foot comparatively within

bilateral pairs.Themovementof eachhorsewas assessedvisually atwalk and

recordedusingCoachesEye5softwaretoevaluatethefootflightofeachlimb.

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Results

Hoofmorphology;differencesbetweenthesmallerandlargerfoot

Within the groupwith the SDFT injury, (n=18) horses had a smaller right fore

(RF), (n=6) had a smaller left fore (LF) and (n=1) were measured to have an

evenlysizedpairoffeet,(n=25intotal).Withinthecontrolgroup,(n=12)horses

hadasmallerRF,(n=12)horseshadasmallerLF,and(n=1)hadanevenlysized

pairoffeet.Thefindingswithintheinjuredgroupfoundthat72%ofhorseshada

smallerrightfore.(Figure8)

Whencompared, (n=12)horseshada core lesion injury in theSDFT in theRF,

(n=8)intheLFand(n=5)hadSDFTcorelesioninjuryinbothforelimbs.Within

the(n=20)horsesthatonlyhadinjurytotheSDFTinonelimb,(n=16)horseshad

SDFTcoretendoninjuriestothesmallerfoot,(n=1)hadapairoffeetand(n=3)

horseshadSDFTcorelesiontothebiggerfoot.(Figure9)

24.0%

48.0%

72.0%

48.0%

4.0% 4.0%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Tendon Control

%left/right/pairsm

allerfoot

Pair

Right

Left

Figure8.Thepercentage(%)ofleftandrightsmallerfootorpairintheSDFTinjuredgroup(Tendon)andthecontrolgroup(Control).

14

Using a Kruskal-Wallis test of difference, there were no significant differences

betweenthecontroland injuredgroups forpercentagedifference in footwidth

(P=0.65)orpercentagedifferenceinheelwidth(P=0.80).Therewashowever,a

significant difference between the control and injured groups for percentage

differenceinfootlength(P=0.006)(Figure10),andpercentagedifferenceinthe

sumofallthedimensions(P=0.049)(Figure11).

Smaller64%

Bigger12%

Both20%

Pair4%

2

Figure9.Thenumberofhorses,bypercentage(%),withaSDFTinjuryinthesmallerorbiggerfootedlimb,SDFTinjurytobothlimbs,orifthehorsehadapairoffeet.

1

f

15

Figure9.Percentagedifferenceinthefootlengthbetweenthesmallerandlargerfoot,comparingthecontrolandinjuredgroups;therewasaverysignificantdifferencebetweencontrolandinjuredhorses(P<0.01).

Figure10.Percentagedifferenceinthesumofallfootdimensionsbetweenthesmallerandlargerfoot,comparingthecontrolandtheinjuredgroups;therewasasignificantdifferencebetweenthecontrolandinjuredhorses(P<0.05).

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AssociationbetweeninjuryandsmallerfootThesmallerfootwasidentifiedasbeingeithertheleftortherightfoot.Onehorse

wasidentifiedashavingfeetofthesamesizeandthishorsewasnotincludedin

thisanalysis.Therefore,96%(n=24)ofthehorseswitha limbinjurypresented

either the leftor theright footassmaller.Fromthissample,25%(n=6)havea

smallerleftfootand75%(n=18)werefoundtohaveasmallerrightfoot.There

werearelativelyhighpercentageofhorsesthatdemonstratedinjuryinthelimb

that was the smaller foot (67%, n=16). A Chi-Squared test was carried out to

investigatetheassociationbetweenthelimbtheinjurywaspresentedonandthe

smaller foot. Therewas a significant association (P=0.008) found between the

smallerfootandthecorrespondinglimbthattheinjurywason(Figure12).

0

2

4

6

8

10

12

Smallerleftfoot Smallerrightfoot

Num

berofhorses

Injuryinleftlimb

Injuryinrightlimb

Injuryinbothlimbs

Figure11.Frequencyoftherelationshipbetweenthesmallerfootandtheinjuredlimb.Therewasasignificantassociationbetweenthesmallerfootandthelimbtheinjurywason(P<0.01).

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Discussion Theaimofthisstudywastotestthefollowinghypotheses.

1) SDFT lesions are related to uneven feet; this was proven. After testing, the

percentagedifferencebetweenpairsof feetwassignificantlygreaterwithinthe

groupwiththeSDFTinjurycomparedtothepercentagedifferenceofthecontrol

group(p<0.05).

2)Wheretherearedisparitiesinfootsize,thesmallerfootisontheaffectedlimb.

This was also proven and the results were highly significant. The greatest

differencewithinpairsoffeetwasfoundtobeinthedistancefromtoetolateral

heel(P<0.01).Thiswasalsothemeasurementthattheauthorfeltwasincreased

in lengthof the smaller footdue to the trimmingprotocol.Theauthorbelieves

that without the prior intervention of standard farriery, these measurements

wouldhavedisplayedevengreatersignificance.

Theseresultssuggestthatthegreaterthedifferenceinfootsize,themorelikelya

horseistohaveaSDFTcorelesioninjury.Theseresultsalsodemonstratedthata

horseismorelikelytohaveacorelesionintheSDFTinthelimbwiththesmaller

foot.

The number of horses with a smaller right fore within the injured group was

similarto(Kummer2005)whereitwasfoundthat70%ofhorseshadasmaller

rightforeandCurtis(2012)alsofoundthat75%offoalsstudiedhadaclubfoot

on the right fore.However the control group showed equal numbers of horses

withsmallerleftandrightfeet.

Kane(1998)showedthatcatastrophicmuscularinjuries(CMI)werelesslikelyto

occurinlimbswherethegroundsurfaceareaandfootwidthweregreater.CMI

was not categorized solely as SDFT injuries but also included SL damage and

DDFT injuries. Nevertheless Kane’s results support the findings of the present

study.

Wilson(2009)suggeststhatafootwithalesserDHWangleisoftensubjectedto

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greater loading. The author observed that flatter feetwith a lesserDHWangle

have a greater hoof spread than that in smallermore upright feet. The author

believesthatafootwithmorehoofspreadhasgreatershock-absorbingabilities

thatwillreducetheamountofvibrationandpeakstressessentthroughthelimb.

AlthoughtheangleoftheDHWwasmeasuredandrecorded,statisticaltesting

wasnotundertaken.Theauthorconsideredthedifficultyinachievingastraight

DHWwhentrimmingmoreuprightfeet,duetothenaturalDHWconcavityoften

associatedwithsuchfootconformation.MeasuringtheDHWangleafter

trimmingoftenreducedthedifferencebetweenpairsoffeetintheattemptto

achievecorrectHPA.Moleman(2005)foundhoofgaugestobeaninaccurate

methodofmeasuringhoofwallangle(HWA)whencomparedtotheuseof

radiographs,suggestingthatviewingafootlaterallywithouttheuseof

radiographsmaybemisleadinginassessinghoofconformation.Horseswithlong

toesoftenhaveabrokenbackHPA.Riesmersma(1996)statesthatloweringthe

heelsofthefootandthuscreatingapossiblebrokenbackHPAincreasesstrainon

theDDFTbutreducesstrainontheSDFT.Thismechanicalalterationinlimb

balancewouldmovethefetlockdorsally,thusreducingthetensionontheSDFT

asitpassesoverthemetacarpal-phalangealarticulation(fetlockjoint),butwould

haveanoppositeeffectontheDDFTasthedistalinterphalangealarticulation

(coffinjoint)wouldmovecaudally.Thissupportstheauthor’sfindingsthatfeet

withlongertoesarelesslikelytosufferSDFTinjuries,whereasamoreupright

footwould.Horseswithasymmetricfeetwouldappeartohavemoreheeltotrim

offthemoreuprightfootwhenbeingshod/trimmedeachtimeinorderto

achievecorrectlimbalignment,thiscouldbecausedbyanunderlying

predispositionsuchaslimblengthdisparityorflexuralcontractionwhichcan

causeafocalpointofload.Thisincreaseinheelheightbetweenshoeingcycles

willcausethefetlockjointtodropandinturnincreasethestrainontheSDFT.

Movingthepointofbreakoverback,towardsthecentreofrotationofthedistal

interphalangealjointreducesthelengthofthemomentarm,reducingthestrain

ontheDDFT(Balch.O1995).Theamountofforceappliedtothestructuresofthe

backofthelimbhasnotchanged,soreducingthestrainontheDDFTwillinturn

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increasethepressureontheotherstructures(SDFT&SL).

To date most studies concerning tendon injuries and catastrophic muscular

injuries have assessedbiomechanics on a sagittal plane rather than a 3Dview.

Fewhavetakenintoconsiderationthemediallateralandortorquemovement.

When viewed from in front at awalk, the author noticed that horseswho had

asymmetricfeethaddifferentlimbconformationandfootflightfromeachother.

The limb with the smaller more upright foot displayed a greater degree of

verticalaxisrotation,offsetkneeand/orfoot,hadatendencytolandlateralheel

first and then shifted the load on to the medial heel. The smaller foot often

displayedmedial/lateralasymmetryasaresultofunevenloading.

Load is when the horse’s bodyweight moves over the weight-bearing limb

causing the phalangeal joints to extend. Even loading is when the

metacarpophalangeal joint (fetlock) descends equally between the bulbs of the

heels.Unevenloadingcausesthefetlocktodescendoveroneheelmorethanthe

other.Ahorsethat lands lateral firstusuallycauses the fetlocktodescendover

themedial heel more. The effect of this is that the fetlock descends in an arc

rather than a vertical plane; this in turn causes a torqueor spiral effect as the

limb is being loaded. The foot flight of a limb that lands lateral first has a

tendencytowinginandthenmovelaterallyjustbeforethefootisplacedonthe

floor, this is the horse trying to achieve level footfall.When the limb does not

travel ina straight line frombreakover to footplacement, agreaterdistance is

travelled and therefore more energy is used. Energy cannot be created or

destroyed;itcanonlybechangedfromoneformtoanother.Sciencedefinesheat

as the flowofenergy fromawarmobject toacoolerobject.Heatenergy is the

result ofmovement; extramovementwillmanifest as heat [temperature] (Ker

1981).Thiswill also causemore fatigue to the structures involved.Ker (1981)

suggeststhat7%ofenergyislostwitheachcycle.

Somehorsesmayappear to land level,but in factdonot loadequally,with the

fetlockdescendingoveroneheelmorethantheother.Horsesthatdonotlandor

load evenly do not recycle the kinetic energy efficiently. Energy is transferred

20

intoheat,whichwillweakenastructuremakingitmoresusceptibletoinjury.The

hotter the tendon becomes, the less chance of cell survival within the matrix

holding the collagen fibres together, allowing the tendon to rupture. Further

researchisneededtotestwhetherthereismoreheatwithinthetendononthe

moreuprightlimbwhilstahorseisatwork.

Williams (2001) states that horses aremore likely to suffer injuries on harder

ground.Hardergroundislesssympathetictoanyimbalanceandunevenloading

inahorse’slimb,thereforecausingmorevibrationthatmanifestsasheat.Rooney

(1981)foundthathorsesinracingweremorelikelytobreakdownontheinside

leg and it is the author’s view that Rooney’s findings are the result of greater

imbalanceandgreater loadingon that leg.The inside leg ismore likely to land

lateral first whilst on the turn. Any imbalance of a limb is exaggerated on the

inside leg due to the fact that the horse is leaning on that side in order to go

roundthebend.

Duringthisstudytheauthorfoundthatinthe5horsesthathadSDFTinjuriesto

bothlimbs,theseverityofdamagethatcouldbepalpatedwithinthetendonof

thesmallerfootedlimbwasfargreater.Thissupportedthefindingsthatthe

greaterdamageoccurredtothesmallerfootedlimb.

The author observed that out of the (n=25) horseswith SDFT injuries, (n=13)

had asymmetric feet prior to injury. However, through experience, the author

believedthatallofthehorseswouldhavehadasymmetricfeetfromayoungage

andthatinjurywasnotthecauseofasymmetryduetonon-weightbearingonthe

injuredlimb.

21

StudyLimitations

Theauthortookhoofwallangle(HWA)measurementsofallthefeet.However,it

was felt that trimming protocol reduced the difference between the hoof wall

anglesduetothefacttheheelheightwasreducedmoreinthesmallerfoot.This

also increased the lengthof thehorse’s foot,whichwouldnegatively affect the

resultsbyincreasingthetotalsumofmeasurementsandthereforereducingthe

chanceofshowingwhichisthesmallerfoot.Thesmaller,moreuprightfootwas

often found to have a dorsal dipmaking it difficult to achieve a level plane on

whichthehoofgaugecanrest.

Althoughevery carewas takenby theauthorwhenmeasuring thehorses’ feet,

humanerrorwillalwaysbeafactor.Ifthestudywereconductedagaintheauthor

felttheuseofimageanalysissoftwarewouldenablethesurfaceareaofthesole

tobemeasuredmoreaccurately,providingabettercomparisoninfootsize.

22

Farrierconsideration.AFarriershouldobserveahorse’sbalancebothstaticallyanddynamicallybefore

trimming a horse’s foot. The requirements of each individual limb need to be

considered inorder toallowthe footand limbto land, loadandpushoff in the

most efficientway tominimisemuscle and tendon fatigue. Rarely do both feet

need trimming in the same manner. More attention is needed to the medial-

lateralbalancetoachievelevelfootfallandloading,thiscanonlybeachievedby

watchingthehorsewalk.

Ifahorse’s foot isnotsymmetrical then it isnotbearingweightevenlyandthe

farrierand/orveterinarysurgeonneedstoconsiderwhyandwhere,theuneven

loading is coming from. Reducing the height of heels to restore correct hoof

proportionsaimingtoachievedorsal/palmersymmetrywithinthehoofcapsule

and a correct HPA, this will often result in the heel height in the smaller foot

being trimmedmore.Reducing thedorsalhoofwall thickness in the toe region

doesnotchangetheangleofthepedalbone.Itonlygivestheimpressionthatthe

horse’sfootisanatomicallycorrectandcanleadtoweakeningtheintegrityofthe

hoof capsule. Positioning the shoe to support the limb as it loads will help to

distribute the forces more evenly and therefore reduce the chance of injury.

BringingthepointofbreakoverbackwillreducepeakforceontheDDFTbutmay

increasetheforceonotherstructures,whichareknowntohaveahigherinstance

ofinjurywhencomparedtotheDDFT.

23

ConclusionTheconclusionsdrawnfromthisstudyare:

1)Thehistoricalopinionthattendoninjuriesinthehorse’sforelimbare

associatedwithlongtoesisincorrectwhenrelatingtotheinjurytotheSDFT.The

SDFTisreportedtobethetendoninvolvedinover90%oftendoninjuries.

2)Modernshoeingtechniquesareundertakeninthebeliefthatreducingthetoe

lengthorbymovingthebreakoverpointback,reducesthechanceofinjurytothe

flexortendons,thismayaidinthepreventionofDDFTinjuries,butcanalso

exacerbatethechanceofinjuryoccurringintheSDFT.Wherehorseshave

asymmetricfeet,thelimbwiththesmallerfootismorelikelytosustainaSDFT

injury.

3)Horseswithlargerdifferenceinhoofsizewithinpairsoffeetaremore

susceptibletotendoninjury.

4)Conformationforsoundnessisoftenoverlookedwithfashionableexaggerated

movementtakingpriorityinthebreedersmind.Thiscomesatacostas

asymmetryinhorse’sfeetandlimbsareproventoreduceahorse’sworkinglife.

ConformationisamajorfactortothecauseofSDFTinjuries;moreattentionis

neededwhenbreedinghorses.Thisstudyhighlightstheneedforfurtherresearch

inthisarea.

24

BibliographyAlexander,R.,McN.ElasticMechanismsinAnimalMovement.CambridgeUniversityPress,1988.Avella.C.S,Ely.E.R,Verheyen.K.L,Wood.J.L,Smith.R.K."UltrasonicassessmentofthesuperficialdigitaflextendonsofNationalHuntracehorsesintrainingovertworacingseasons."EqineVeterinaryJournal41(2009):449-454.Balch.O,White.K,Butler.D,Metcalf.S,."Hoofbalanceandlamenessimpropertoelength,hoofangleandmediallateralbalance."Educ.pratc.vet.17(1995):1275-1283.Birch,H.L.,Worboys,S.,Eissa,S.,Jackson,B.Strassbourg,S.andClegg,P.D."Matrixmetabolismratediffersinfunctionallydistincttendons."MatrixBiol.27(2008):182-189.Birch.H.L,Wilson.A.M,Goodship.A.E."theeffectofexercised-inducedlocalisedhyoerthermiaontendoncellsurviial."Thejounalofexperimentalbiology.200(1997):1703-1708.Colles.C,Ware.R.ThePrinciplesofFarriery.London:J.A.Allen,2010.Curtis.S.J,Rosbotham.J.D,Reilly.J.D."TheIncidenceofAcquiredFlexuralDeformityandUnilateralClubFoot(unevenfeet)inThoroughbredFoals."CongressonEquineMedicineandSurgery.Geneva,2012.Ducro.B.J,Gorissen.B,vanEldik.P,Back.W."InfluenceoffootconformationondurationofcompetativelifeinaDutchWarmbloodhorsepopulation."EquineVeterinaryJournal,no.41(2)(2009):144-148.Ely,E.R.,Avella,C.S.,Price,J.S.,Smith,R.K.,Wood,J.L.,Verheyen,K.L.,."Descriptiveepidemiologyoffracture,tendonandsuspensoryligamentinjuriesinNationalHuntracehorsesintraining."EquineVet.J41(2009):372-378.Ely,E.R.,Verheyen,K.L.,Wood,J.L."FracturesandtendoninjuriesinnationalhunthorsesintrainingintheUK:apilotstudy."EquineVet.J36(2004):365-367.Kai.M,Takahashi.T,Aoki.O,Oki.H."InfuenceonroughtracksurfacesoncomponentsofverticalforcesincanteringThoroughbredhorses."EquineVeterinaryJournal30(1999):214-217.Kane,.A.J,Stover,.S.M,Gardner.I.A,Bock.K.B,Case,J.T,Johnson.B.J.,Anderson.M.L,Barr.B.C,Daft.B.M,Kinde.H,Larochelle.D,Moore.J,Mysore.J,Stolz.J,Woods.L,Read.D.H,Ardans.A.A."Hoofsize,shape,andbalanceaspossibleriskfactorsforcatastrophicmusculoskeletalinjuryofthoroughbredracehorses."AJVR59,no.12(December1998):1545-1542.

25

Ker.R.F."Dynamictensilepropertiesoftheplantaristendonofsheep."JournalofExperimentalBiology93(1981):283-302.Kummer,M,Hans,G,Isabel,I,Jorg,A,Christoph,L."TheeffectoftrimmingonradiographicmeasurementsonthefrontfeetofnormalWarmbloodhorses."TheVeterinaryJournal.,2005:notKnown.Lawson.S.E.M,Chateau.H,Pourcelot.P,Denoix.J.M."Weffectsoftoeandheelelevationoncalculatedtendonstrainsinthehorseandtheinfluenceoftheproximalinterphalangealjoint."j.Anot210(2007):583-591.Mattinson,A.B.Huntingsartofhorse-shoeing.Forth.London:Bailliere,TindallandCox,1922.Moleman.M,vanHeel.M.C.V,vandenBeltA.J.M,Back.W."Accuracyofhoofanglemeasurementdevicesincomparisonwithdigitallyanalysedradiographs."EquineVeterinaryEducation17(2005):319-322.Murray,R.C.,Dyson,S.J.,Tranquille,C.,andAdams,V."Associationoftypeofsportandperformancelevelandanatomicalsiteoforthopaedicinjurydiagnosis."EquineVet.J38(2006):411-416.Patterson-Kane,J.C.,Wilson,A.M.,Firth,E.C.,etal."Exerciserelatedalterationincrimpmorphologyinthecentralregionsofsuperficialdigitalflexortendonsfromyoungthoroughbreds:acontrolledstudy."EquineVetJ.30(1998):61-64.Riemersma,D.J.,vandenBogert,A.J.,Jansen,M.O.,etal."Influenceofshoeingongroundreactionforcesandtendonstrainsintheforelimbofponies."EquineVetJ.28(1996):126-132.RiermersmaD.J.,SchamhardtH.C."Invitromechanicalpropertiesofequinetendonsinrelationtocrosssectionalareaandcollagencontent."ResearchVeterinaryScience39(1985):263-270.Riley,G."Tendinopthy-frombasicsciencetotreatment."Nat.Clin.Pract.Rheumatol.4(2008):82-89.Rooney,J.R.,Genovese,A."SurveyandanalysisofbowedtendoninThoroughbredracehorses."EquineVeterinaryJ.1(1981):49-53.Singer,E.R.,Barnes,J.,Saxby,F.,andMurray,J.K."Injuriesintheeventhorse:trainingvscompetition."Vet.J.175(2008):76-81.Stashak,T.S.itarget.com,br.89,2008.http://www.itarget.com.br/newclients/abraveq2012/down/2012/abr_ne09_pal_ted5.pdf(accessed1225,2015).

26

Stephens,P.R.,Nunmaker,D.M.andButterweck,D.M."ApplicationofaHall-effecttransducerformeasurementoftendonstrainsinhorses."Am.J.VetRes,no.50(1989):1089-1095.Thorpe,C.T.,Clegg,P.D.,Birch,H.L."Areviewoftendoninjury:Whyistheequinesuperficialdigitalflexortendonmostatrisk?"Equinevet.J,no.42(2)(2010):174-180.Thorpe,C.T.,Spiesz,E.M.,Chaudhry,S.,Screes,H.R.C.,Clegg,P.D."Scienceinbrief:Recentadvancesintounderstandingtendonfunctionandinjuryrisk."EquineVeterinaryJ.47,no.2(2015):137-140.Weller,R."WhyBonesBreakandTendonsRupture."Americanfarriersjournal,may2016.Williams,R.B.,Haskins,L.S.,Hammond,C.J.,etal."Racehorseinjuries,clinicalproblemsandfatalitiesrecordedonBritishracecoursesfromflatracingandNationalHuntracingduring1996,1997,and1998."EquineVet.J33(2001):478-486.Williams.G,Deacon.M.NoFootNoHorse.Buckingham:Kenilworthpress,1999.Wilson.G.H,McDonald.K,O"Connell.M.J."Skeletalforelimbmeasurementsandhoofspreadinrelationtoasemmetryinbilateralforelimbofhorses."EquineVeterinaryJournal.41(2009):238-241.

27

ManufacturersAddresses

1.Excel2007(version12);MicrosoftCorp,OneMicrosoftWay,Redmond,

WA98052-6399,USA.

2.Minitab17,MinitabLtd.;ProgressWay,BinleyIndustrialEstate,Coventry,

CV32TE,UK.

3.Brass hoof gauge. Anvil Brand Shoe Co. 500 S. Spencer St. P.O. Box 198.LEXINGTON,IL61753,UNITEDSTATES4.BrassRule. JimBlurton Ltd. RoseHill. Kingswood. Forden.Welshpool.Wales.UK.5.CoachesEye,TechSmithCorporation,2405WoodlakeDrive,Okemos,

Michigan,48864-5910UNITEDSTATES

28

Appendices

Consentletter

Recipient Address Stephen Hill AWCF xxxxxxxxxxxxxxx Home Farm xxxxxxxxxxxxxxx Belton xxxxxxxxxxxxxxx Rutland xxxxxxxxxxxxxxx LE15 9JT xxxxxxxxxxxxxxx 10 September 2015 Dear XXXX,

I am currently developing a case study in which I am examining the correlation of asymmetric feet and tendon injuries in the forelimbs of horses.

Therefore I intend to invite owners of horses with tendon injuries to be included in this study.

With regard to my request to include your horse as part of a case study approach to my Fellowship of the Worshipful Company of Farriers dissertation, I have put together the following details.

Details of study:

1. The names of horses and owners will be withheld to ensure anonymity and confidentiality.

2. All information and photographs/recording material will be securely stored.

3. The use of photographs and video recordings will be utilised as a means of examining the premise of my thesis. These materials may have to be utilised as part of a thesis presentation to confirm my findings.

4. A copy of the dissertation/case study will be made available to the owner.

5. It is my intention that parts of the paper will be submitted for inclusion in appropriate publications.

If you are satisfied with the terms as laid out in this letter and consent to your horse participating in this study, please sign and date below.

29

Yours sincerely,

Stephen Hill

Owner signature:

Date of signature:

30

Email from Novobrace giving permission to use their image. Hello Stephen, Yes, you may use images on our site for your thesis; please give credit to www.novobrace.com as warranted. Have a good week and good luck on your exams. Sincerely, Dee Fife Equinext, LLC +1 859.421.0032 Consent email from Town and Country Veterinary Centre. I can confirm that I have consented for Stephen Hill to print and present images I have provided of the cases he has worked on. John Abbott BVM&S CertEM(IntMed) Dipl. ECEIM MRCVS Town and Country veterinary centre Le16 9HE Sent from my iPhone