Sesamoid bone in the tendon of thesupinator muscle of dogs: incidence andcomparison of radiographic and computedtomographicfeaturesWordcount:8473

ManonDornyStudentnumber:01609678Supervisor:Dr.IngridGielenSupervisor:Prof.dr.WimVanDenBroeckSupervisor:Dr.AquilinoVillamonteChevalierAdissertationsubmittedtoGhentUniversity inpartial fulfilmentof therequirements for thedegreeofMasterofVeterinaryMedicineAcademicyear:2018-2019

GhentUniversity,itsemployeesand/orstudents,givenowarrantythattheinformationprovidedinthisthesisisaccurateorexhaustive,nor that the contentof this thesiswill not constituteor result inany infringementofthird-partyrights.GhentUniversity, itsemployeesand/orstudentsdonotacceptany liabilityorresponsibilityforanyusewhichmaybemadeofthecontentorinformationgiveninthethesis,norforanyreliancewhichmaybeplacedonanyadviceorinformationprovidedinthisthesis.

ACKNOWLEDGEMENTSIwould like to thank thepeople thathelpedmeaccomplish this thesisandhelpedmeachievemydegreeinveterinaryscience.

FirstofallIwouldliketothankDr.IngridGielen,Dr.AquilinoVillamonteChevalierandProf.Dr.WimVanDenBroeck. I thankthemall fortheirtimespend inhelpingmewithmyresearch,theirusefuladviceandtheirendlesspatience.Withouttheirhelp,Iwouldn’thavebeenabletoaccomplishthisthesis.

NextIwouldliketothankmyfamilyandfriendsfortheircontinuingsupportandmotivationduringthe lastyearsofvetschool.Myparentsandpartnerespecially, forall thementalbreakdownstheyhad to endure in periods of exams and deadlines. Thank you to my dad and father in law forproofreadingthisstudyandhelpingmeimprovemyEnglishwritingskills.

LastIwouldliketothankmysisterwhowasstudyingveterinarysciencewithme.Itwasatoughfewyears,welaughedtogether,criedtogether,butintheendwemadeittogether.

TABLEOFCONTENT

FRONTPAGE

CLAUSE

ACKNOWLEDGEMENTS

TABLEOFCONTENT

SUMMARY......................................................................................................................................5

1. Introduction....................................................................................................................................71.1. Anatomyoftheelbow..................................................................................................71.2. Elbowdysplasia...........................................................................................................10

Medialcoronoiddisease................................................................................10 Osteochondrosisofthemedialhumeralcondyle...........................................10 Ununitedanconealprocess............................................................................11 Elbowincongruity...........................................................................................12 Incompleteossificationofthehumeralcondyles...........................................12

1.3. Sesamoidbones..........................................................................................................122. Problemandaims.........................................................................................................................143. Materialandmethod....................................................................................................................144. Results...........................................................................................................................................155. Discussion.....................................................................................................................................166. Conclusion.....................................................................................................................................19

APPENDIX.....................................................................................................................................20

REFERENCES..................................................................................................................................21

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Summary

Sesamoidbonesarepresent indifferenttendonsandmuscles.Theydevelopinspotswithpressureor friction. This study focuses on the sesamoid bone in the supinator muscle of the dog. Thesupinatormuscleoriginatesonthelateralcollateralligamentoftheelbowandthelateralepicondyleofthehumerus.Sometimesthismusclecontainsasesamoidboneinitsorigin.Thissesamoidboneislocatedcraniolateraloftheheadoftheradiusandoccasionallytheyarticulate.Sesamoidbonescanbeimportantindiagnosingelbowdysplasia,astheycanbeconfusedforafragmentof,forexample,themedialcoronoidprocess.

InthisstudyX-raysandCTscansof100dogswerescoredby3observerswithdifferentdegreesofexperience.Ascoringsheetwasmadetoassesstheelbowsforasesamoidboneandelbowdysplasia.The incidence of the presence of a sesamoid bonewas evaluated on X-ray and CT. Interobserverstatistics were performed using the Cohen’s Kappa statistics and the association between thesesamoidboneandelbowdysplasiawasassessedusingChisquarestatistics.

OnX-raytheincidenceofasesamoidwasanaverageof8,33%ofthedogs.In43,52%ofthesedogsabilateralsesamoidbonewasobserved.OnCTasesamoidwasfoundin26%ofthedogs.In76,92%ofthesedogsabilateralsesamoidbonewasobserved.Anaverageof72%ofthesesamoidbonesweremissedonX-ray.Thesesamoidbonewasroundtoovalshapedwithadiameterof0,5-6,56mmx0,5-6,2 mm. The Kappa value for X-ray was 0,6910 (substantial agreement) and for CT 1,00 (perfectagreement). Therewas aweakpositive associationbetweenelbowdysplasia and appearanceof asesamoidboneinthesupinatormuscle(χ2=9,1474;p=0,002491).

CTisclearlysuperiortoX-rayforassessingthissesamoidbone.ForassessingtheX-raysexperienceisimportant, but for CT itmade no difference in this study. There is an association between elbowdysplasia and the appearance of a sesamoid bone, but further research is needed to assess thiscorrelation.

Samenvatting

Sesambeenderenkomenvooropverschillendeplaatseninhetlichaam.Zeontstaanopplaatsenwaarerdrukofwrijvingwordtuitgeoefend.Inditonderzoekwordtdefocusgelegdophetsesambeenindemusculussupinatorterhoogtevanhetellebooggewrichtvandehond.Indeaanhechtingvandezespieropdelateralecollateraalbandvandeelleboogendelateraleepicondylvandehumerusbevindtzichbij sommigehondeneensesambeen.Dit sesambeenbevindtzichcraniolateraalvanhethoofdvanderadiusenarticuleerthiersomsmee.Sesamsbeenderenkunnenbelangrijkzijn,aangezienzeverwardkunnenwordenmeteenfragmentvanbijvoorbeelddemedialeprocessuscoronoideus.

InditonderzoekwerdenradiografieënenCTscansvandeellebogenvan100hondenbekekendoor3onderzoekers met verschillend niveau van expertise. Een scoreblad werd ingevuld m.b.t.aanwezigheidvanhetsesambeenenelleboogdysplasie.Erwerdnagegaaninhoeveelpercentvandehonden een dergelijk sesambeen voorkwam op RX en CT. Interobserver statistiekwerd toegepasta.d.h.v.Cohen’sKappastatistiek.Daarnaastheeftmenookgekekennaaraanwezigheidvanelleboogdysplasieenofereenverbandwasmetaanwezigheidvanhetsesambeen(χ2statistiek).

Bijgemiddeld8,33%vandehondenwerdeensesambeengevondenopRX.Gemiddeld43,52%vandeze honden had bilateraal een sesambeen. Op CT werd in 26% van de honden een sesambeengevonden.Daarhadden76,92%vandehondenbilateraaleensesambeen.Erwerdengemiddeld72%van de sesambeenderen gemist op RX. Het sesambeen was rond tot ovaal van vorm met eendiametervan0,5-6,56mmx0,5-6,2mm.DeKappawaardevoorRXwas0,6910(voldoendetotgoede

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overeenstemming) en voor CT 1,00 (perfecte overeenstemming). Er bleek een zwakke positieveassociatie tussen aanwezigheid van het sesambeen en aanwezigheid van elleboog dysplasie (χ2 =9,1474;p=0,002491).

CT is dus duidelijk superieur t.o.v. RX om dit sesambeen te beoordelen. Op RX is ervaring eenpluspuntomditsesambeentekunnenonderscheiden,maaropCTisergeenonderscheidopvlakvanervaring. Het sesambeen is gecorreleerd met aanwezigheid van elleboog dysplasie, maar verderonderzoekisnodigomdezecorrelatietebeoordelen.

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1.Introduction

1.1.Anatomyoftheelbow

Theelbowisajointconsistingof3bones,thehumerus,theradiusandtheulna(Fig1).Thehumerusisalongbonethatendsdistallyinthehumeralcondyle.Thehumeralcondyleconsistsoftwoparts,themedialtrochleahumeriandthelateralcapitulumhumeri.Thecapitulumhumeriarticulateswiththeheadof the radius.The trochleahumeriarticulateswith the trochlearnotchof theulnaandaportionofthefoveaoftheradius.Caudallyonthehumeralcondyletheolecranonfossa is located.Thisisthefossafittedfortheolecranonoftheulnawhenthelegisinextension.Onthecranialsideofthehumeralcondyleistheradialfossa.Theheadoftheradiusfitsinthatfossawhentheelbowisinflexion.Bothofthesefossaecommunicatewitheachotherthroughtheforamensupratrochleare.Onthemedialandthelateralsideofthehumeralcondylesaretheepicondyles.Thesestructuresaremainly insertionpoints fordifferentmusclesand ligaments.Theradius isalsoa longbonethat liesparallel to theulna. Itarticulatesproximallywiththehumerus,butalsowiththeulna, formingthehumeroradial and the proximal radioulnar joint. The radius is shorter than the ulna and its mostimportantfunctionisattachmentofmuscles.Themostproximalpartoftheradiusiscalledtheheadoftheradius.Ontheradialheadthereisanindentation,thearticularfovea.Thispartarticulateswiththecapitulumhumeri.Theradiusarticulateswiththeradialnotchoftheulnathroughthearticularcircumference,anosseousbandontheradialhead.Theulnaisalsoalongbone.Itstrochlearnotcharticulatesproximallywiththehumeraltrochleaformingthehumeroulnarjoint.Thetrochlearnotchis a round shaped indentationon the cranial sideof theolecranon.Proximally the trochlearnotchendsintheanconealprocess.Theulnaarticulateswiththeproximalradiusthroughtheradialnotch.Thisradialnotchisformedbytheprocessuscoronoideusmedialisandlateralisthatarelocatedatthedistalpartofthetrochlearnotch.Themedialcoronoidprocess is largerthanthelateralone(EvansanddeLahunta,2013;Trosteletal.,2003).

Fig. 1:A: Lateral view right distal humerus and proximal radius and ulna.B: Cranialviewrightdistalhumerusandproximalulnaandradius.(From:Trosteletal.,2003)

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Theelbowjointconsistsof3joints,thehumeroradialjoint,thehumeroulnarjointandtheproximalradioulnar joint (Fig2).Thehumeroradial joint is formedbythehumeral trochleaandthefoveaofthe radius. The humeroradial joint consists of the trochlea humeri and the trochlear notch of theulna. The incisura radii and the articular circumferenceof the radius form theproximal radioulnarjoint. There isone capsule surrounding the three joints. The collateral ligamentsand theanconealprocessrestrictthemovementoftheelbowjoint.Thelateralcollateralligamentinsertsonthelateralepicondyleofthehumerusanddividesintwoligamentsthatendontheneckoftheradiusandtheannularligament.Themedialcollateralligamentattachestothemedialepicondyleofthehumerus,divides in two ligaments and ends on the proximal radius and ulna. The annular ligament of theradiusgoesaroundtheradiusandinsertsonthemedialandlateralcoronoidprocessesoftheulna.Thisligamentholdstheradiusclosetotheulna(EvansanddeLahunta,2013;Trosteletal.,2003).

Fig.2:A:Cranialviewoftheleftelbowjoint.B:Sagittalviewoftheproximalradiusandulna.(From:Trosteletal.,2003)

Like every joint the elbow has extensor and flexormuscles (Fig 3). The extensormuscles are themusculus triceps brachii, the anconeal muscle and the musculus tensor fasciae antebrachii. Thetriceps brachiimuscle is thebiggestmuscle consisting of four heads, the caput longum, the caputlaterale,thecaputmedialeandthecaputaccesorium.Thefourheadsallinsertonthetuberolecrani.The longheadattacheson thedistolateralborderof thescapula.The lateralheadattacheson thetricipital linebetween the tuberositadeltoideus and the tuberositas teresminor. Themedial headattachesonthetuberculumminorandtheaccessoryheadattachesontheproximocaudalpartoftheneckofthehumerus.Theanconealmuscleisasmallmusclethatattachesonthelateralepicondylarcrest,thelateralepicondyleandpartofthemedialepicondyle.Itinsertsonthelateralsurfaceoftheproximalendoftheulna.Themusculustensorfasciaeantebrachiialsoinsertsonthetuberolecrani,butalsoontheantebrachialfascia,anditarisesfromthecaudalborderofthescapula(Liebichetal.,2009;EvansanddeLahunta,2013).

Theflexormusclesarethemusculusbrachialis,themusculusextensorcarpiradialisandthemusculusbicepsbrachii.Themusculusbicepsbrachiiattachesonthetuberculumsupraglenoidales.Whenthismusclecrossesovertheelbowjointthemusclesplits intwotendons.Oneofthesetendonsinserts

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ontheulnartuberosityandtheotherontheradialtuberosity.Themusculusbrachialisattachesontheproximal part of the sulcusmusculus brachialis. It endson the tendonof themusculus bicepsbrachii that insertson the radial tuberosityand italsoendson theulnar tuberosity.Themusculusextensorcarpiradialisattachesonthelateralepicondylarcrestofthehumerus.Atthedistalthirdoftheradiusitsplitsintwotendons.OneofthesetendonsinsertsonasmalltuberosityonmetacarpalIIandtheotheronmetacarpalIII.

Apartfromextensionandflexionoftheelbowitisalsopossibletosupinateandpronatetheelbow.Themost importantmuscles for these functions are the supinatormuscle and the brachioradialismuscleforsupinationandthepronatorteresmuscleforpronation(Fig.3;Trosteletal.,2003;Evansandde Lahunta, 2013). The supinatormuscleoriginates from the lateral collateral ligamentof theelbowandthebaseofthelateralepicondyleofthehumerus(Barone,2000).Itendsontheproximalquarter of the craniomedial part of the radius (Barone, 2000; Evans and de Lahunta, 2013). Themusculusbrachioradialisisalsocalledthemusculussupinatorlongus.Itattachesontheproximalend

Fig.3:Musclesofthebrachiumandantebrachium.A:Lateralaspect.;B:Lateralaspectwith lateralheadofthe triceps removed.;C:Medial aspectwithmusculus biceps brachii removed.;D: Caudolateral aspect.;E:Antebrachialmuscles,craniolateralaspect(From:EvansanddeLahunta,2013).

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of the lateralepicondylar crestof thehumerusandendson the radiusbetween the thirdand thedistal fourth of the radius. Themusculus pronator teres attaches on themedial epicondyle of thehumerusandendsonthemedialborderoftheradius(EvansanddeLahunta,2013).

1.2.Elbowdysplasia

Elbow diseases are often seen in rapidly growing large breed dogs but also in other less specificbreeds (LaFond et al., 2002; Samoy et al., 2011). Common elbow diseases are medial coronoiddisease, osteochondrosis of the elbow, ununited anconeal process, articular cartilage injury andelbow incongruity (Kirberger and Fourie, 1998; Samoy et al., 2011). These diseases are commonlyreferred to as elbow dysplasia. Other less common diseases like incomplete ossification of thehumeralcondylesaresometimesincludedintheelbowdysplasiacomplex(Dallagoetal.,2015).Theincidence of elbow dysplasia ranges from 0% to 70% depending on the breed (Hazewinkel et al.,1995;Flückiger,2002).

Medialcoronoiddisease

Medial coronoid disease (MCD) is a common disease in young, large breed dogs (Villamonte-Chevalieretal.,2015;Dallagoetal.,2015). Itdescribesthechangesthatcanoccur in thecartilageand subchondral bone of the medial coronoid process. Lesions associated with medial coronoiddisease are chondromalacia, fissures, non-displaced fragments, displaced fragments and erosion(Dallago et al., 2015). The exact cause of medial coronoid disease has not been determined yet.There are genes coding for elbow dysplasia, but also other factors like obesity, trauma and othercauses are considered (Morgan et al., 2000; Temwichitr et al., 2010; Guthrie and Pidduck, 1990).Anotherpossiblecauseformedialcoronoiddiseaseiselbowincongruity.Duetothemalalignmentofthe jointsurfaces, theweightbearingthroughthemedialsideofthe jointcanbealtered.Elevatedloadingofthemedialcoronoidprocesscanthenleadtolesionsandfracturesofthemedialcoronoidprocess(GemmillandClements,2007;Danielsonetal.,2006).

Mostdogswithmedialcoronoiddiseasearelame.Othersymptomsareexorotationoftheaffectedlegs,moderatejointdistension,crepitationduringmovementanddecreasedrangeofmotionoftheelbow joint. The first symptoms usually occur at 4 to 6 months old. In some cases they occurbetween6 to8monthsorevenafter6years (Temwichitretal.,2010).Traditionally,adiagnosis ismade with radiographs. The best views for visualizing the medial coronoid process are themediolateral and the craniocaudal medial oblique (Cr15L-CdMO) radiographs (Hazewinkel andVoorhout,1986;Wosaretal.,1999).Anotherdiagnostic tool thatcanbeused formedialcoronoiddiseaseiscomputedtomography.Basedonthehighsensitivityandspecificityithasbeenconsideredthat CT is the preferred non-invasive technique to assess medial coronoid disease lesions of thecanineelbowjoint(Villamonte-Chevalieretal.,2015).

Osteochondrosisofthemedialhumeralcondyle

Osteochondrosisdevelopsmostlikelyduetoaproblemintheendochondralossification(DemkoandMcLaughlin,2005;Samoyetal.,2011).Duringtheendochondralossificationthecartilageisgraduallyreplacedbybone.Sometimesthisprocess is interruptedonafocalareaonthebone. Intheelbowjoint this usually occurs on the medial humeral condyle. This results in a weaker degenerativecartilaginous spot that ismore prone to lesions during normalweight bearing. If the cartilaginousarea is damaged, a flap is formed and degradation products will go into the joint causinginflammation. The formation of the flap is called osteochondritis dissecans. The flap can stayattachedtotheboneorcandetachandformajointmice.Usuallythisflapdoesnotmineralizeandstayscartilaginous(DemkoandMcLaughlin,2005).

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The exact etiology for this interruption is unknown. It ismost likely amultifactorial complex thatincludesgenetics,rapidgrowth,overnutrition,trauma,ischemia,hormonalinfluencesandsoon.Thiscouldexplainwhyitisseenmorefrequentlyinyoung,rapidlygrowing,largebreed,maledogswithahighnutritionintake(DemkoandMcLaughlin,2005;Samoyetal.,2011).Osteochondrosisdissecansisoftenpresentwithafragmentedcoronoidprocess.Inatleast12%ofthecasesosteochondrosisofthemedialhumeralcondyleoccurstogetherwithafragmentedcoronoidprocess(BurtonandOwen,2008).

Clinical signs are lameness, uni- or bilateral, pain and stiffness. The lameness gets worse throughexercise and gets betterwith rest. The range ofmotion can be reduced due to pain (Demko andMcLaughlin,2005).

Again, radiographs are a good diagnostic tool. Osteochondrosis of themedial humeral condyle isvisibleontheextendedandflexedmediolateralviewandthecraniocaudalviewfrom5to6monthsof age (Kirberger and Fourie, 1998; Demko andMcLaughlin, 2005). It is seen as flattening of thesubchondral bone of the humeral condyle. Sometimes a small concave indentation is also visible(KirbergerandFourie,1998;BurtonandOwen,2008;Samoyetal.,2011).Sometimes the lesion issurroundedbysclerosisandosteoarthriticchangescanbepresentinthejoint.Thearthrosislesionsare less severe than in cases with medial coronoid disease, but a combination of these twopathologies results in the most severe arthrosis (Kirberger and Fourie, 1998). Osteochondrosisdissecans isalsovisibleoncomputedtomography. It isvisualizedasasclerotic rimaroundanareawithlesseropacityonthemedialhumeralcondyle(Samoyetal.,2011).

Ununitedanconealprocess

Ununited anconeal process is a condition where there is no radiographic fusion between theanconealprocessandtheproximalulnaafter20weeksofage.Theanconealprocesscangrowasanextensionoftheproximalulnargrowthcentreoritcanhaveitsownossificationcentre(LenehanandVanSickle,1985;Samoyetal.,2011).Aseparateossificationcentreisdescribedinsomebreedslikethe German Shepherd, Grey Hounds, Saint Bernard, Weimeraner, Vizsla, Afgan, English pointer,Bassett,Dachshund,GoldenRetriever,Labradorretriever,DobermanPinscherandPitBull(LenehanandVanSickle,1985;Frazhoetal,2010).Normally,fusionwiththeulnamustbecompleteattheageof20to24weeks (LenehanandVanSickle,1985;Sjöströmetal.,1995;Samoyetal.,2011). If theunion is not complete at that age, it will not occur spontaneously. This doesn’t mean that theanconealprocessiscompletelyloose.Itcanbeattachedtotheulnabyabridgeoffibrocartilageorfibroustissuethatisn’tvisibleonradiographs(Sjöströmetal.,1995).

Dogs are usually presented with front limb lameness at 5 to 9months of age (Lenehan and VanSickle,1985;Sjöströmetal.,1995).Although,therearecaseswithclinicalsignsoutsideofthatagerange (Samoy et al., 2011). Lameness can be uni- or bilateral and usually increases with exercise(LenehanandVanSickle,1985;Samoyetal.,2011).Swellingandpainofthejointcanoccurduetoinflammation(Sjöströmetal.,1995).Withflexionorextensioncrepitationispresentandtherangeofmotion is decreased due to pain and osteoarthritis (Sjöström et al., 1995; Samoy et al., 2011).Osteoarthritisofthejoint iscausedbyinstabilityofthejointduetotheununitedanconealprocess(Sjöströmetal.,1995).

Thisconditioncanbediagnosedonamediolateralradiographoftheflexedelbow.Thereisafracturelinevisiblebetween theanconealprocessand theproximalulnaor the fragmentcanbedisplacedproximally.CTcanbeusedtogetmoreinsightonthedisplacementofthefragmentsandtoassessotherpathologicalchangesofthejoint(Samoyetal.,2011).

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Elbowincongruity

Elbowincongruitymeansthatthealignmentoftheradius,theulnaand/orthehumerusisdisturbed(Burton and Owen, 2008). There are two types of elbow incongruity described. The first type iscausedbyanunderdevelopedradiusorulna.Ifoneofthesebonesistooshort,thejointsurfacewillnotbesmoothandaligned,but therewillbea stepbetween the lateral coronoidprocessand theproximalradius.Thesecondtypeisanincongruitybetweenthetrochlearnotchoftheulnaandthehumeral trochlea. If the trochlear notch grows at a slower rate than the humeral trochlea, thetrochlearnotchwillbetoosmalltocoverthehumeraltrochlearesultinginincongruity(KirbergerandFourie,1998;Samoyetal.,2011).

Elbowincongruityisoftenseenwithotherpathology,forexamplemedialcoronoiddisease,ununitedanconealprocessorosteochondrosisdissecans(KirbergerandFourie,1998;Samoyetal.,2011).Thiscanbeduetothefactthattheloadingofthebonesischangedduetotheincongruity.Thistheoryissupported by data from studies of Bernesemountain dogs (Ubbink et al., 1999). Thismeans it isdifficult to link elbow incongruity to lameness, because the lameness could also be explained byother pathologies (Samoy et al., 2011). Some studies also indicate that some degree of elbowincongruityisnormalindogs(BurtonandOwen,2008).

Elbowincongruitycanbediagnosedusingtheextendedmediolateralandcraniocaudalradiographs.Radiographicalchangesareastepbetweendelateralcoronoidprocessoftheulnaandtheproximalradius, thehumeruscanbedisplacedcranially, thehumeroulnarand thehumeroradial joint spacecanbeincreasedandthetrochlearnotchcanbemoreellipticofshape(KirbergerandFourie,1998;Samoy et al., 2011). Computed tomography can also be a tool in diagnosis of elbow incongruity(GemmillandClements,2007).

Incompleteossificationofthehumeralcondyles

Incompleteossificationofthehumeralcondyles(IOHC)isuncommonindogs(RobinandMarcellin-Little,2001). It ismostly seen ingrowing, largebreeddogsandspaniels,but it canalsobe seen itotherbreedslikePugs,RottweilersandLabradorRetrievers(RobinandMarcellin-Little,2001;Gielenetal.2018).Itiscausedbythenon-fusionofthemedialandthelateralhumeralcondyle.Thisresultsina lesion likea fissureora fracturebetween thehumeral condyles.Sometimes these lesionscanreachuptothesupratrochlearforamen(Gielenetal.,2018).Normallythefusioniscompleteattheageof8to12weeks.Dogswith IOHCarepredisposedforcondylarfractures(RobinandMarcellin-Little, 2001;Moores, 2006). These fractures can occur without any trauma. It can happen duringnormalmovement,butsincethelesionbetweenthecondylesweakensthebone, itfracturesmoreeasily.ThisconditioncanbediagnosedonradiographsorCT.CTispreferredbecauseonradiographsIOHC can be missed due to superposition of bony structures (Gielen et al., 2018). The preferredradiograph for this condition is theCr15M-CdLOview,but IOHC lesionscaneasilybemissed if thebeamis5degreesoffset(Rovestietal.,1998).

1.3.Sesamoidbones

Sesamoidbonesaresmallnoduleslocatedincertaintendonsorjointcapsules.Theydevelopwherethereisfrictionbuttheycanalsobeformedprenatally(EvansanddeLahunta,2013).AccordingtoEvans and de Lahunta (2013), sesamoid bones have 3 important functions: protect tendons frombonyprominences,increasesurfaceforattachmentoftendonsandchangethedirectionofpull.Upto44sesamoidbonescanbeshown in theappendicularskeletonofadog (EvansanddeLahunta,2013). They are located in the elbow, the stifle, the tarsus, the carpus, themetacarpophalangealjoints,themetatarsophalangealjointsandinterphalangealjoints(AllanandDavies,2018;Evansand

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deLahunta,2013).Notallsesamoidbonescanbeidentifiedonradiographs,assometimessesamoidbones are still cartilaginous at the age of the dog when radiographs are taken. In some dogssesamoid bones are unilaterally present orabsent. For example, the intraarticulartarsometatarsalsesamoidhasanincidenceof27%, whereas the lateral plantartarsometatarsalsesamoidhasanincidenceof50% (Allan and Davies, 2018). The biggestsesamoid bone is the patella in the m.quadriceps femoris, which is present in alldogs(Frandsonetal.,2009).Sesamoidbonesare also present in other species and inhumans.Dependingonthespeciesalargerorlowernumberofsesamoidbonesarepresentincomparisonwithdogs.

In some dogs the elbow contains onesesamoid bone, the sesamoid bone in theoriginof thesupinatormuscle.Themusculussupinator isasmallmusclethat is locatedonthe craniolateral side of the elbow (Fig. 3;Evans and de Lahunta, 2013). It originatesfrom the lateral collateral ligament of theelbowand thebaseof the lateralepicondyleof the humerus (Barone, 2000). From itsorigin them.supinatorcrossesover the jointcapsuleof theelbowand the radius to inserton theproximalquarterofthecraniomedialpartoftheradius(Barone,2000;EvansanddeLahunta,2013).Themusculussupinator iscoveredby themusculusextensorcarpi radialisand thecommondigitalextensormuscle(Liebichetal,2009).Itsfunctionis,likeitsnamesuggests,thesupinationofthepaw(EvansanddeLahunta,2013).

Insomedogsasesamoidbonecanbefoundinthetendonoforiginofthesupinatormuscle(Fig4).Radiologicalsurveysoftheelbowfoundasesamoidboneassociatedwiththeelbowin9,4%,to31%oftheexamineddogs(Woodetal.,1985).Thissmallbonearticulateswiththelateralaspectoftheheadoftheradius(EvansanddeLahunta,2013). If it ispresent, it isusuallybilateral (Woodetal.,1985). Why this sesamoid bone is only present in 9,4% to 31% of the dogs and not in others isunknown.

OnradiographsandCTscansthesesamoidbonecanbeseenasasmallcirculartooval,welldefinedbonewith a dense uniformmineralization. The sizecan vary from 0,5mm to 5,0mm indiameter(Woodetal.,1985).Tovisualizethesesamoidboneitisrecommendedtouseacraniocaudalmedial-to-lateral oblique radiograph or CT (Wood et al., 1985). The main advantage of CT is avoidingsuperpositionofoverlyingstructures(Buzug,2008).

The sesamoid bone in the supinator muscle is important since it can be mistaken for otherpathologies, like medial coronoid disease. Fragmented medial coronoid process is the mostdiagnosedformofelbowdysplasiaingrowingdogs(Temwichitretal.,2010).

Fig4.Localisationofthesesamoidboneinthetendonoforiginofthesupinatormuscle(From:EvansanddeLahunta,2013).

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2.Problemandaims

In this study datawere collected from 100 dogs retrospectively from the patient database of theDepartment of Veterinary Medical Imaging and Small Animal Orthopaedics of Ghent University.Inclusion criteria were bilateral radiographic and CT assessment of the elbow joints of 50 dogswithoutand50dogswithelbowdisease.TheincidenceofthepresenceofthesesamoidbonewillbeevaluatedbothonradiographsandonCTimages.Thehypothesisisthatalargernumberofsesamoidboneswill be identified on CT images in comparisonwith radiographs. Evaluating the radiographsand CT images will give an insight in when and why this bone will easily be mistaken for otherpathologies.Asecondaimistoevaluateifthepresenceofthesesamoidbonecanbecorrelatedwithelbow pathology likemedial coronoid disease. Additionally, the detection of a sesamoid bone onradiographs and the sensitivity of this finding is most probable dependent on the training andexperienceleveloftheobserver.Thehypothesisisthatthedetectionofthesesamoidboneandthesensitivitywouldincreasewiththelevelofpractice.

3.Materialsandmethod

Studydesign

Data of 100 dogs were collected retrospectively from the patient database of the department ofVeterinaryMedical ImagingandSmallAnimalOrthopaedicsofGhentUniversity,Belgium. InclusioncriteriawerebilateralradiographicandCTassessmentoftheelbowjointsof50dogswithoutand50dogswithelbowdisease.Thecasesdatefrom2007to2018.Allthecaseswereassessedandscoredby3observers,2radiologistsexperiencedinscoringradiographsandCTimagesofelbowsand1non-experienced veterinary student. The scoring sheet included presence of a sesamoid bone,dimensions of the sesamoid bone, arthrosis, ununited processus anconeus, medial coronoideusdisease,osteochondrosisandincompleteossificationofthehumeruscondyles.ToassesstheimagesproperlyaDICOMviewersoftwarewasused(RadiantDICOMviewer,OsiriX).

Radiographictechnique

Dogs were sedated using dexmedetomidine (0,005mg/kg of body weight). Three standardradiographs were taken of each elbow, a lateral extension, a lateral flexion and a craniocaudalradiograph,usingadigitalradiographysystem,EDR6(digitalradiographicsystem)EKLINdevicefromCanon (Canonmedical systems). For the lateral viewsdogswereplaced in lateral position, on theside of the leg that needed to be X-rayed. The upper limbwas pulled caudally and the headwaspulledback to prevent superposition. Ideally the angle betweenhumerus andulna is 120° for theextendedviewand less than45° for the flexedview.TheX-raybeamneeds tobecenteredonthemedialepicondyle.Thiswasdoneforboth legs.Forthecraniocaudalviewthedogswereplaced insternalpositionwithitslegsextendedcranially.Theheadwaspulledbacktopreventsuperposition.The X-ray beamwas centered on the joint-space distal to themedial epicondyle of the humerus.BothlegswereX-rayedinthisposition.

Computedtomographictechnique

Dogsweresedatedusingdexmedetomidine(0,005mg/kgofbodyweight)andintubated.Anesthesiawas inducedusingPropofol (bolusof2mg/kgofbodyweight)andmaintainedusing Isofluraneand100% oxygen. The dogs were positioned in left lateral decubitus with the thoracic legs extendedcranially.Theheadofthedogwaspulledbackandlaterallytopreventsuperpositionandartefacts.CT imageswereobtainedwithafour-slicescanner(LightSpeed,GEmedicalsystems)using120kVp,140mA and 25cm field of view parameters. Adjacent transverse views of 1.3mm thickness were

15

made from the proximal aspect of the olecranon to 2cm distal of the elbow joint using a bonealgorithm(DeRyckeetal.,2002).

Statisticalanalysis

Statistical analysis was used to calculate if there is a significant association between having asesamoid bone and having elbow dysplasia. The Chi square (χ2) test was used with a 2 x 2contingencytableofoccurrenceofsesamoidboneandoccurrenceofelbowdysplasia.Thistestwasperformed with and without the Yates correction. Also the Phi and the Cramer’s V value werecalculated.ForinterobservervariabilityoftheparameterforpresenceofasesamoidbonetheKappatestwasused.TheunweightedKappatestwasusedsincethereisnoneedforaweightedKappatest.TheweightedKappatestdistinguishesbetweenthemagnitudesofdisagreement.Thepresenceofasesamoidboneisnotingrades,it’spresentorit’snot,meaningthatthemagnitudeofdisagreementisnotapplicapleonthisstudy.ThevaluesoftheKappatestwere:0,01-0,20:slightagreement;0,21-0,40:Fairagreement;0,41-0,60:Moderateagreement;0,61-0,80:Substantialagreement;0,81-1,00:Almostperfectagreement(LandisandKoch,1977).Statisticalanalyseswereperformedwithhelpofastatisticalprogram(SPSS).

4.Results

Therewere100dogsincludedinthisstudy.ThemajorityofthesedogswereGoldenRetrievers(n=42) and LabradorRetrievers (n = 34). Apart from thosebreedstherewere16otherbreeds includedandonedogofunknownbreed (Table 1). Therewere 40 female and 60male dogs. Theaverageagewas1yearand8monthswiththeyoungestbeing4monthsandtheoldest7yearsand8months.

Interobserver variability was calculated for presence of thesesamoid bone. The Kappa value for sesamoid bones on X-raywas 0,6910 meaning that there was a substantial agreementbetweenthe3observers.TheKappavalue for sesamoidboneson CT was 1,00,meaning that there was a perfect agreementbetween the 3 observers. Thismeans that the averages of thepercentages of the 3 observers can be used withoutcompromisingtheoutcomeofthisstudy.

ForthepercentagesofsesamoidbonesonX-raytheaveragesofthe 3 observers were calculated. For CT no averages wereneededsincethe3observers foundthesamesesamoidbones.OnX-rayasesamoidbonecraniolateraloftheheadoftheradiuswas observed in an average of 8,33% of the dogs. 43,52% ofthesedogswasobservedashavingbilateralsesamoidbones.OnCTthe3observers foundasesamoidbone in26%of thedogs.76,92% of these dogs were observed as having a bilateralsesamoidbone.Anaverageof72%ofthesesamoidbonesweremissedonX-ray. Itwasassumedthatnosesamoidbonesweremissed on CT. Still, it might be possible that the 3 observersmissedthesamesesamoidbone.Theexactresultsofeveryobserverarefoundintheappendix.

Breed NumberGoldenretriever 42LabradorRetriever 34CavalierKingCharlesSpaniel 4BerneseMountainDog 3GermanShepherd 2Malinois 2CaneCorso 1WhiteSwissShepherd 1AmericanStaffordshireTerrier 1Bordeauxdog 1Boxer 1BorderCollie 1AustralianShepherd 1EnglishSpringerSpaniel 1EnglishCockerSpaniel 1Labione 1Stabyhoun 1BrittanyDog 1Unknown 1TOTAL 100Table 1. List of breeds and number ofdogsineachbreedincludedinthisstudy.

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Thesesamoidbonewasroundtoovalshapedwithadiameterof0,5-6,56mmx0,5-6,2mm.OnX-raythesesamoidboneshadauniformmineralizationandthebordersweresmoothandwelldefined.AmedullaandcortexwerevisibleonCT.Figure5showsanX-rayandCTscanofadogwithasesamoidboneinthesupinatormuscle.

Anaverageof57%ofthedogshadelbowdysplasiainoneorbothelbows.Anaverageof29,67%oftheseaffectedelbowscontainedasesamoidbone.Afterstatisticalanalysistherewasa44%chancetohaveelbowdysplasiawithoutasesamoidboneanda70%chancetohaveelbowdysplasiawithasesamoid bone. Statistical analysis, using a chi-square test, showed that there was a significantcorrelationbetweenelbowdysplasiaandasesamoidbone in thesupinatormuscle.Thechisquarevaluewas9,1474withap-valueof0,002491(significantatp<0,05).ThePhiandCramer’sVvalueswere0,214.

5.Discussion

Inthisresearchasesamoidboneinthesupinatormuscleoftheelbowwasdetectedin8,33%ofthedogs on X-ray and 26% of the dogs on CT.Other surveyswhich only studied radiographs found asesamoid bone in 9,4%, 11% and 31% of the dogs (Grondalen, 1982a; Grondalen, 1982b;Wood,1985).Thelatterradiographedtheintactelbowsfirst,dissectedthesupinatormusclefromthebonystructuresandradiographedthedissectedsupinatormuscleagain.ThiscanexplainwhythestudybyWood(1985)foundapercentageofsesamoidbonesclosertothepercentagethisstudydetectedonCTscan.Bydissectingthesupinatormusclefromthebonystructure,superpositionisbypassed.Theother 2 surveys only assessed intact elbows on X-ray, which can explain why the percentages ofsesamoidbonesdetectedinthosesurveysareclosertothepercentageofsesamoidbonesfoundonradiographsinthisstudy.

ThehypothesisthatahighernumberofsesamoidboneswouldbedetectedonCTscansappearstobeconfirmed.Themostprobablereasonissuperpositionofoverlyingstructuresonradiographs.Thisis visualized on figure 6. The sesamoid bone is located craniolateral to the head of the radius. Toproperly see the sesamoid bone the radiographs should be craniomedial to caudolateral oblique,because this view reduces superposition of the radial head on the sesamoid bone (Boroffka and

Fig.5.X-rayandCTscanoftherightelbowofthesamedog.

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Kirberger, 2015). In a standard radiographic survey of the elbow of a dog this radiograph isn’tincluded.Itisevenadvisedtopronatetheelbow15°totakethecraniocaudalradiograph(Flückiger,2010).Bypronatingtheelbow,itbecomesacraniolateral15°caudomedialobliqueview.Thisviewisbetter to assess the elbow for medial coronoid disease, since the craniomedial structures areprojectedonthecassette(Rauetal.,2011).Thesesamoidboneislocatedonthecraniolateralsideofthe elbow, intending that on this radiograph it is difficult to visualize the sesamoid bone in thesupinator muscle. On the pronated craniocaudal radiograph the sesamoid bone of the supinatormuscle is often superposed on the radial head and difficult to notice. On CT images there is nosuperposition, which makes it easier to visualize the sesamoid bone. Still it is important to lookcloselyasthesesamoidbonecanbeverysmallandissometimesonlydetectableon1CTimage.ThiswayitcaneasilybemissedifaCTscanisassessedtooquickly.

Woodetal.(1985)foundthatinmostcasesthesesamoidboneisbilateral.Inthisstudyanaverageof43,52%ofthedogswereobservedwithabilateralsesamoidboneonX-ray.OnCTthispercentageincreasedto76,92%.Thisagaincanbeexplainedbysuperposition.SometimesthesesamoidbonesarebilateralbutonlyoneofthetwoisvisibleonX-rayduetosmalldifferencesinangleoftheX-raybeam with the consequent superposition. This means that the percentages of uni- and bilateralsesamoidbonesonCTaremorerepresentativethanthepercentagesfoundonX-ray.ConcludingasWoodetal.(1985)stated,mostdogsthathaveasesamoidboneinthesupinatormusclehavethembilaterally.

Thereweresomedifferencesbetweenthe3observers.Theexperiencedradiologistsfound13and14sesamoid bones on X-ray. The non-experienced observer found 11 sesamoid bones. This can beexplained by experience. Rau et al. (2011) studied the differences between experienced andinexperienced observers in diagnosing medial coronoid disease on X-ray, CT and arthroscopy.Radiography is considered inferior to CT for diagnosingmedial coronoid disease. Rau et al. (2011)concludedthatexperiencedobserverscouldhaveaspecificityonX-rayalmostashighasonCTfordiagnosingmedial coronoiddisease. Inexperiencedobserversmissa lotonX-raybecauseacertain

Fig.6.X-rayandCTscanoftherightelbowofthesamedog.OnX-raythereisnosesamoidbonevisiblecraniolateraloftheheadoftheradius(blackcircle),yetCTshowsthatthereisasesamoidbonepresent.

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amountofexperienceisneededtoproperlyassessX-raysoftheelbow(Rauetal.2011).Theelbowisacomplexjointwithmultiplejointsindifferentplanesandalotofbonyprotrusions,whichmakesitadifficult joint to evaluate (Masonet al., 2002).Another studybyBurtonet al. (2008) assessed thereliability of radiological assessment of ulnar trochlear notch sclerosis in dysplastic canine elbows.The radiographs were scored by orthopeadic surgeons and diagnostic imaging specialists.InterobserveragreementwasassessedusingtheKappastatistictestandresultedinfairagreement.This indicatesagain that interpretingX-raysof theelbow isnoteasyandcanbediscussible.Theseresultscanexplaintheloweramountofsesamoidbonesobservedbythenon-experiencedobserverinthisstudy.OntheCTscansthe3observerssawthesamenumberofsesamoidbones.CTscansareeasier to assess because there is no superpositionof overlying structures. Still basic knowledgeofanatomyandinterpretingCTscansisneededtoproperlyassessCTstudies.

Itwas also suggested that the sesamoid bone could bemistaken formedial coronoid disease. AnexampleofapatientofthisstudyisvisualizedinFigure7.Onthelateromedialradiographthereisasmallbonyopacitylocatedcranialtothemedialcoronoidprocessandsuperposedontheradialhead(black arrow). Inexperienced observers assessing these radiographs might think that this is afragmentofthemedialcoronoidprocess.WhilelookingattheCTscansthereisnofragmentofthemedialcoronoidprocess(whitearrow).Thecoronoidprocessisintact,butatthelateralsideoftheradial head a sesamoid bone is present (black arrowhead). The bony opacity on the radiograph ismostlikelythatsamesesamoidbone.

Thechi square test showed that there isa significant correlationbetweenpresenceofa sesamoidboneandelbowdysplasia(χ2=9,1474;p=0,002491).ThePhiandCramer’sVvalueswere0,214.Thissuggests that the correlation between the two variables is weak. Further research might beinteresting to assess how both variables are correlated. Important to notice is that correlationdoesn’tnecessarilymeansthatthereiscausationasothervariablespossiblyinfluencethismatter.It

Fig7.A:Lateromedialradiographoftheleftelbow.Theblackarrowmarksabonyopacity;B:CTscanofleftelbowofsamedog.Thewhitearrowmarkstheintactmedialcoronoidprocess;C:CTscanoftheleftelbowofthesamedog.Theblackarrowheadmarksthesesamoidboneinthesupinatormuscle.

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wasalsonottakenintoaccountthattwosesamoidbonescouldbefromthesamedog.Thestatisticaltestwasperformedonindividualelbowsandnotperdog.Sincemostdogshavebilateralsesamoidbones,thiscanalsoinfluencetheresultsofthesestatistics.Althoughapossibleexplanationforthiscorrelation can be as Wilson et al. (2014) described for the biceps brachii and medial coronoiddisease.Apossibleunderlyingcauseformedialcoronoiddiseaseinvolvestransverse-planeradioulnarincongruity. This theory states that the incongruity is amplified by the contraction of the bicepsbrachii. Contraction of the biceps brachii results in elbow supination and flexion. This rotationalmovementcan inducedamage to theaxialmarginof themedial coronoidprocesswhen it collideswiththeradialhead.Thiscaneventuallyleadtomedialcoronoiddisease(Hulseetal.,2010;Wilsonetal.,2014).Itmightbepossiblethatthesesamoidboneinthesupinatormusclehasthesamekindofeffectonthestructuresoftheelbowjoint. If thesesamoidbonecollideswithastructureoftheelbowduringcertainmovements, it canmaketheelbowmorepronetoarthrosisandotherelbowdysplasialesions.

Inanotherstudytheproximalepiphysealplateoftheradiuswasclosedinalldogswithasesamoidbone (Woodetal., 1985). Thisepiphysealplate closesaround8 to12monthsofage (Kealyetal.,2011).Wood(1985)suggestedthattheremightbeacorrelationbetweenappearanceofasesamoidboneandage, but statistical analysis of thedata showed that therewasno significant increase infrequencyofsesamoidbonesinmaturedogs(Woodetal.,1985).Inthisrecentstudytherewere4dogs with a sesamoid bone but with the epiphyseal plates not fully closed. This shows that asesamoidbonecanbepresenteveniftheproximalepiphysealplateoftheradiusisnotclosedyet.Apossibleexplanationforthelackofsesamoidbonesinyoungdogsmightbethatthesesamoidboneisnotfullyossifiedyet.Sesamoidbonescanstillbecartilaginousattheageofthedogatwhichtheradiographs are taken (Allan and Davies, 2018). Cartilage is not visible on X-ray, so cartilaginoussesamoid bones are not yet visible on radiographs. It could be interesting to take radiographs ofyoungdogstoassessthemforasesamoidboneinthesupinatormuscleandre-evaluatethesedogsafteracertainagetoseeifmoredogshavesesamoidbonesatahigherage.

6.Conclusion

Thisstudy isaretrospectivestudyandthereforehas its limitations. Itmaynotbeapplicabletotheentire population of dogs, since the cases were not selected entirely randomly. Inclusion criteriawere X-rays and CT scans of both elbowsmeaning that not all healthy dogs and dogswith elbowdisease were included in this study. Still some valuable results were found. CT is the superiortechnique to assess the presence of this sesamoid bone. 26% of the dogs in this study have asesamoid bone in one or both elbows and most of them have them bilateral. For radiographicalinterpretation of elbows experience is important, unlike for CT. For CT the 3 observers found thesameamountofsesamoidbones,meaningthatexperienceislessimportantforinterpretationofCT.Still knowledge of elbow anatomy is needed. A positive correlation was found between elbowdysplasiaandpresenceof the sesamoidbone,but this correlationwasaweakcorrelation.Furtherresearchmightbeinterestingtoseehowbothvariablesarecorrelatedandifothervariablesmightplayaroleinthis.

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Appendix

Table 1. Difference between X-ray and CT. Observer 1 and 2 are experienced in radiographicalexaminationofelbows,observer3isnon-experienced.

Obs.1 Obs.2 Obs.3 Average

Total dogs with sesamoid on X-ray (100dogs)

-unilateral

-bilateral

9%

-44,44%

-55,56%

8%

-62,5%

-37,5%

8%

-62,5%

-37,5%

8,33%

-56,48%

-43,52%

TotalamountofsesamoidbonesonX-ray(200elbows)

14/200(7%)

13/200(6,5%)

11/200(5,5%)

12,67/200(6,3%)

Total dogs with sesamoid on CT (100dogs)

-unilateral

-bilateral

26%

-23,08%

-76,92%

26%

-23,08%

-76,92%

26%

-23,08%

-76,92%

26%

-23,08%

-76,92%

Total amount of sesamoid bones on CT(200elbows)

46/200(23%)

46/200(23%)

46/200(23%)

46/200(23%)

MissedsesamoidsonX-ray 32/46(70%)

33/46(72%) 35/46(76%) 33,33/46(72%)

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