Update on Wound Management in the Horse Annette M McCoy, DVM, MS, PhD, DACVS; University of Illinois College of Veterinary Medicine

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Elmer McBride
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1 Update n Wund Management in the Hrse Annette M McCy, DVM, MS, PhD, DACVS; University f Illinis Cllege f Veterinary Medicine Intrductin Wunds are amng the mst cmmn reasns fr equine patients t be seen by a veterinarian USDA survey f 3,349 equine peratins 9% f fals < 6 mnths f age and 4.7% f hrses > 6 mnths f age were affected by an injury, wund, r trauma; this was the mst cmmn health abnrmality in bth age grups. 18.6% f fals that died in the first 30 days did s as a result f nn-birth related injury, wund, r trauma. 23.9% f hrses 30 days t 6 mnths f age died as a result f injury, wund, r trauma. 16.0% f hrses ver 6 mnths f age died as a result f injury, wund, r trauma. Amng adult hrses, wunds/injuries were secnd nly t ld age as a leading cause f death. Mexic survey: skin wunds (abrasin, laceratin, abscess) reprted in 6.8% f a ppulatin f wrking hrses. General hrse ppulatin survey in the UK (2011) 40% f hrse wners reprted their hrse sustained an injury in the previus 12 mnths; 54% f injured hrses sustained ne r mre wunds (mst cmmn injury). Practitiner survey in New Zealand (2016) fund that wunds were the third mst cmmn reasn fr seeing a patient and the secnd mst cmmn cause f death r euthanasia. 25% f caselad was wund-related. Acrss surveys, mst cmmn wund lcatin was the distal limb. Likely underestimate true prevalence f wunds since many are treated by wners withut cnsulting a veterinarian. Physilgy f Wund Healing 3 phases f wund healing: acute inflammatry phase, prliferative phase, remdeling phase Tensile strength nly begins t return during remdeling phase Acute inflammatry phase characterized by recruitment f platelets/cltting factrs and leukcytes Terminatin f this phase is cmplex and prly understd Dysregulatin can lead t infectin, chrnic inflammatin, and/r excessive fibrsis Shuld last ~ 3 days pst-injury Exuberant granulatin tissue ccurs with a deficient but prtracted inflammatry phase Persistent hypxia frm cclusin f micrvessels within granulatin tissue Rapid and prlnged prliferatin f fibrblasts Deficient epithelializatin and cntractin Mainstays f treatment are debridement and bandaging Prliferative phase is characterized by the frmatin f granulatin tissue filling the defect, but minimal increase in tensile strength Granulatin tissue cmprised f macrphages, fibrblasts, and new bld vessels; replaces fibrin-cntaining clt and prvides a surface fr mesenchymal cell migratin

2 Epithelializatin begins 24-48h after injury, but des nt becme visibly evident until 4-6 days later (pink rim arund edge f wund) Will ccur faster in partial thickness wunds Rate much slwer in the distal limb than the flank New epithelium is very fragile Lasts frm ~ day 3 t day 14 pst-injury Remdeling phase includes wund cntractin (desirable) as well as cnversin f granulatin tissue t mature scar tissue (less desirable) During cntractin, dermis and epidermis are drawn in centripetally frm all sides f the wund; skin is nrmal in all respects (cmpared t scar tissue which is hairless and lacks nerves, glands, etc.); begins ~ 2 weeks after injury Myfibrblasts play a key rle 3 phases f cntractin Lag phase wund may get larger as the edges retract Rapid cntractin Slw cntractin Cntractin ends when the wund edges meet r when the skin tensin exceeds the strength f the myfibrblasts Lw numbers f myfibrblasts results in pr cntractin Better cntractin in areas with lser skin (i.e. trs) than tight skin (i.e. distal limb) Rapid gain f strength between 7-14 days pst-injury, but nly reach 20% f tensile strength by 3 weeks; 80% f riginal tensile strength by 1 year (scar tissue) Wund remdeling can ccur fr up t 2 years pst-injury Numerus cytkines and grwth factrs play a rle in wund repair Clny stimulating factrs Interferns Interleukins Tumr necrsis factr α Cnnective tissue grwth factr Epidermal grwth factr/transfrming grwth factr α Fibrblast grwth factr Insulin-like grwth factrs Keratincyte grwth factr Platelet-derived grwth factr Transfrming grwth factr β Vascular endthelial grwth factr Tendns and ligaments underg similar phases f wund repair, but at a much slwer rate than skin Wunds belw the crnary band cannt exhibit swelling, and d nt underg cntractin; epithelializatin ccurs via hf wall grwth frm the crnary band (prblematic if crnary band is invlved in wund then epithelium has t cme frm elsewhere and the hf may end up with an abnrmal appearance) Patient and wund factrs can affect wund healing Age, cncurrent mrbidities (i.e. malnutritin, dehydratin) Excessive trauma Chrnicity f wund Previus treatments (particularly thse with cyttxic effects) Lcatin (distal limb vs. bdy r head) Type f wund

3 Wund cntaminatin/infectin Mtin at wund site (disrupts healing tissue) Treatment chices can affect wund healing Timing/type f clsure Suture pattern/material Bandages/dressings Evaluatin f Wunds Wund assessment is the crucial first step in wund therapy wund repairs fail mre ften because f imprper assessment/preparatin than due t imprper therapy Basic principles: Thrugh histry Adequate restraint physical, chemical Lcal/reginal anesthesia Clipping after placing water-sluble gel in the wund Assessment depth, determinatin f which structures might be invlved If fracture is a cncern, place an apprpriate splint prir t radigraphic evaluatin Address life-threatening issues first excessive hemrrhage, shck, etc. Wunds f the head and neck Extensive bld supply and gd sft tissue supprt tend t bleed a lt Lts f imprtant structures may be invlved in the wund Heavy sedatin is ften necessary hrse may have abnrmal mentatin and/r be highly resistant t examinatin Thrugh evaluatin is imprtant because wunds can be much wrse than they lk n the surface Diagnstic imaging helps: radigraphs, ultrasund, CT, MRI Changes may be subtle r bvius Wunds ver bny surfaces Bld supply becmes an issue when there is nt adequate sft tissue t cver a wund, especially if peristeum is lst (e.g. deglving injury) Must debride edges and find alternative bld supply Injuries ver the cannn bne with lss f verlying tissue can be very difficult t manage prne t develpment f exuberant granulatin tissue Depending n riginal injury, sequestrum may frm leading t chrnic drainage/nn-healing wund Wunds f the thrax and abdmen Penetrating wunds may invlve the pleural r peritneal cavities Auscultatin, ultrasund, radilgy t help rule ut pneumthrax Abdmincentesis generally nrmal in the acute perid unless grss cntaminatin frm viscera is present Multiple layers t abdminal wall may shift, bscuring path f penetratin Enlarging a small skin wund may help t determine the invlvement f deeper layers Axillary wunds can result in pneummediastinum and/r pneumthrax; subcutaneus edema cmmn Wunds f the extremities Prximal limb has better bld supply and sft tissue supprt than distal limb Often easier t clse wunds prximally and they generally heal faster with fewer cmplicatins

4 Invlvement f deeper structures is a majr cncern: synvial structures, tendns/ligaments Mvement impairs healing Wunds are ften highly cntaminated The best way t determine if a synvial structure cmmunicates with a wund is t put a needle int it distant frm the wund and pressurize with sterile saline Leave amikacin behind Invlvement f synvial structures always cmplicates wund care and frequently decreases prgnsis Fr tendn laceratins, prgnsis depends greatly n the depth f the laceratin which structures are damaged? Penetrating wunds f the ft ( street nail ) Depending n length and rientatin f the penetrating bject, can invlve many different structures Cffin jint, navicular bursa, navicular bne, third phalanx, digital cushin, deep digital flexr tendn, ligaments f the navicular bne Can be difficult t evaluate the track, especially in the frg leave the freign bdy in until evaluatin if pssible Flush in bth directins if cncerned abut cmmunicatin with synvial structures Cntrast radigraphy may help t determine invlvement f jint/bursa Assessment f chrnic wunds aimed at determining underlying cause(s) and may invlve diagnstic imaging, culture f surface and deep tissues Optins fr Wund Clsure Primary clsure Always desirable reduces healing time and scarring allwing earlier return t use, reduces risk f additinal cntaminatin/infectin, requires less aftercare and thus reduces expenses Sharp debridement f wund edges when pssible, fllwed by irrigatin New glves and instruments after debridement, befre clsure If the skin is questinable, leave it can always be remved later Suture patterns Appsitinal r everting preferred Interrupted suture pattern preferred Tensin-relieving sutures (r ther tensin relieving techniques) in cmbinatin with appsitinal patterns Suture material Generally nn-absrbable in the skin hlds strength fr lnger Deeper layers use absrbable suture clse dead space whenever pssible (place drains if needed) Tensin-relieving sutures ften with larger suture Mnfilament vs multifilament ften persnal preference; may prefer mnfilament if cncerned abut cntaminatin/infectin Delayed clsure Suturing delayed t allw reductin f bacterial cntaminatin (e.g. via debridement) and/r reductin f swelling/edema Delayed primary clsure ccurs befre frmatin f granulatin tissue within 4 days f injury

5 Delayed secndary clsure ccurs after frmatin f granulatin tissue nly used fr chrnic r infected wunds Secnd intentin Relies n wund cntractin and epithelializatin Cases with severe tissue lss May be left uncvered if n the bdy, upper limbs, etc. clean daily until filled in with granulatin tissue Petrleum jelly belw the wund t help prevent serum scald Distal limb wunds at risk fr develping exuberant granulatin tissue Bandage +/- external captatin as apprpriate Antimicrbials? Mst justified in cases f synvial invlvement, existing infectin, expected nging cntaminatin. Tpical Therapy Optins Many, many wund dressings n the market (Table 3.1 in Stashak & Theret Equine Wund Management, 2 nd Ed cntains an extensive list) Dressings are classified as adherent, hydrphilic, nn-adherent, absrbent/nnabsrbent, r bilgic Further classified as active/passive, cclusive/semi-cclusive, unprcessed/prcessed, etc. Wet-t-dry r hypertnic dressings can be used fr mechanical debridement Occlusive synthetic dressings are used t prmte mist wund healing and prmte autlytic debridement, which seems t be selective fr necrtic tissue Hydrphilic (highly absrbent) dressings are best used during the inflammatry phase and may prmte the frmatin f granulatin tissue Semi-cclusive synthetic dressings may be used t absrb exudate; best used after epithelializatin has begun (may prmte exuberant granulatin tissue) Antimicrbial dressings shuld be used judiciusly, but can be useful in highly cntaminated wunds Bilgic dressings prmte wund cntractin and epithelializatin, may prvide grwth factrs that supprt healing Many ther tpical treatments intments, grwth factrs, stem cells, etc. have been tried with mixed results Recent research: Tpical xygen therapy (Tracey et al., 2014) n significant difference in healing between treated and untreated Hneybee lactic acid bacteria (Olfssn et al., 2016) seemed t prmte healing in chrnically infected wunds (n=7) Silver sdium zircnium phsphate plyurethane fam wund dressing (Kelleher et al., 2015) mre rapid healing ver the first 30 days in treated hrses, but n difference in verall time t healing between treated and untreated Intravenus reginal limb perfusin with amikacin (Edwards-Milewski et al., 2016) did nt negatively affect time t healing in treated hrses Autlgus stem cells (Breckx et al., 2015) wunds clsed significantly faster than untreated cntrls; similar effects nted fr allgenic stem cells Manuka hney gel (Bischfberger et al., 2016) led t mre rganized granulatin tissue bed and decreased inflammatin in treated wunds (nly went ut t day 10 after wund frmatin) Activated prtein C (Bischfberger et al., 2015) - n significant difference in healing between treated and untreated

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