localization of pain in the equine foot emphasizing the ... · even though many foot problems...

Localization of Pain in the Equine FootEmphasizing the Physical Examination andAnalgesic Techniques

John Schumacher, DVM, MS, Diplomate ACVIM*;Debra R. Taylor, DVM, MS, Diplomate ACVIM†;Michael C. Schramme, DrMedVet, CertEO, PhD, Diplomate ECVS, ACVS; andJames Schumacher, DVM, MS, Diplomate ACVS

An astute clinician can gain insight into the location and cause of a horse’s lameness by carefullyexamining the feet. Even though many foot problems produce similar clinical signs, careful physicalexamination of the foot may provide clues as to which method of perineural or intrasynovial analgesiais likely to be the most helpful in localizing the source of pain. By using different techniques ofdigital analgesia, a clinician may be able to determine the structure within the foot that is the sourceof pain. As well as identifying a specific lesion that is the cause of pain and lameness, it is equallyimportant to identify poor foot conformation that may precipitate foot pain. Authors’ address-es: Equine Sports Medicine Program (John Schumacher) and Department of Clinical Sciences(Taylor), College of Veterinary Medicine, Auburn University, Auburn, AL 36849; Equine Clinic,National Veterinary School of Lyon, 69280 Marcy L’Etoile, France (Schramme); and Department ofLarge Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville,TN 37996 (James Schumacher); e-mail: [email protected]. *Corresponding author; †Present-ing author. © 2012 AAEP.

1. Introduction

Although the incidence of various causes of equinelameness may vary with breed and use of the horse,abnormalities of the foot are the most common cause oflameness in horses, and if a foot abnormality is not adirect cause of lameness, the abnormality may initiatelameness elsewhere in the musculoskeletal system.1–7

Because hoof conformation is closely correlated to theforces applied to the equine foot, physical examinationfor lameness should begin by visually inspecting thefoot.8 Visual examination is often followed by palpa-tion of the hoof/digit, by applying a hoof tester, by

examining the horse in motion, by administeringflexion and extension tests, then localization oflameness via diagnostic analgesia.

2. Visual Inspection of the Foot

Because many horses not experiencing lamenesshave distorted hoof capsules, it is important to dis-tinguish between functionally sound feet and feetwith hoof capsule distortion that is often associatedwith lameness.9 Constant observation of abnormalhooves may blind the clinician to hoof abnormalitiesthat may affect soundness.

138 2012 � Vol. 58 � AAEP PROCEEDINGS

IN-DEPTH: THE FOOT FROM EVERY ANGLE

NOTES

Orig. Op. OPERATOR: Session PROOF: PE’s: AA’s: 4/Color Figure(s) ARTNO:

1st disk, 2nd beb spencers 20 1-22,24,26 3328

SymmetryVisual evaluation of the distal portion of the limbrelies heavily on recognition of asymmetry betweenthe lateral and medial aspects of the same limb andbetween contralateral limbs. The human eye findssymmetry aesthetically more pleasing, and there-fore, asymmetry is often readily detected. Digitalasymmetry (laterality, high/low syndrome, mis-matched feet, mild club foot) may be acquired as aconsequence of decreased weight bearing caused byasymmetrical movement,3,10,11 asymmetrical ten-sion of tendons,9 and pain.12 The relatively over-loaded (i.e., initially more sound) foot acquires ashallower angle of the dorsal hoof wall, low or under-run heel (Fig. 1) and lower palmar angle (angle ofthe solar margin of the distal phalanx relative to theground surface), as well as a larger circumference ofthe solar margin and a wider hoof. In the relativelyunderloaded (i.e., lame or shorter-strided) limb, thefoot becomes more upright and narrow (Fig. 1) witha higher palmar angle.9 Once acquired, this asym-metry may remain even after the original lamenesshas resolved. Resolving the asymmetry requiresefforts toward restoring equality of load distributionbetween limbs. Although it is not always associ-ated with lameness, asymmetry of the equine hoofshould not be overlooked as an indication of previ-ous, impending, or chronic lameness.13 In onestudy, mismatched hoof angles occurred with equalprevalence in sound and lame horses, indicatingthat this type of asymmetry is not always associatedwith current lameness.14 We are not aware of anystudies that have assessed the consequences of mis-matched feet of mature, sound horses.

Coronary BandHair on the coronary band should lie flat against thehoof capsule; hair projecting horizontally (Fig. 2)may indicate excessive ground-reaction force on theassociated hoof wall and may be correlated to painwithin the foot. When viewing the foot from theside, a healthy coronary band should be nearlystraight with only a mild proximally directed arch(Fig. 3). The coronary band is dynamic, and itsshape can be affected by chronic overloading.15

A coronary band with a proximally directed arch atthe quarters is evidence of chronic overloading of thequarters (Fig. 4). A coronary band that bends dis-tally in the heel to become nearly vertical (Fig. 5) isan indication that the foot has a poorly developedheel. Asymmetry of the height of the coronaryband in the heel region on one side is commonlyknown as a “sheared heel”, which is defined as in-stability between medial and lateral bulbs of theheel15 and often a hoof capsule distortion resultingin proximal displacement of one quarter/heel bulb

Fig. 1. Asymmetric forefeet of the same horse are shown. Notethat the right front foot is more upright and the left front has ashallower angle of the dorsal hoof wall and an under-run heel.Photos courtesy of Pete Ramey.

Fig. 2. Note the coronary band hair in the quarter and heelregion of this foot projects horizontally. Farriers often refer tothis as “angry hair”. This usually indicates excessive ground-reaction force on the associated hoof wall and will often be seen onan upward arching coronary band.

Fig. 3. This is a relatively healthy hoof with a coronary bandangle that is within the proposed normal range. Coronary bandhair lies flat on the hoof wall, and there is only a slight arch to thecoronary band in the quarters. Note the straight hoof/pasternaxis and the near parallelism between the dorsal and palmar hoofwalls.

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relative to the contralateral side of the foot.16 Themedial heel bulb/quarter is more commonly dis-placed proximally because it is more common for thefoot to be offset laterally.9,17 This asymmetry of theheel region is important to note18 because it oftenindicates medial-lateral imbalance during loading9

and predisposes the horse to a spontaneous quartercrack on the side of the foot that has been displacedproximally.19 Sheared heels often have a “fissure”between the heel bulbs17 in which a chronicallymoist environment favors the development ofthrush.16 Sheared heels can be present withoutcausing lameness.15

The angle of the coronary band can be used toestimate the position of the distal phalanx withinthe hoof capsule. One study described the angle ofthe coronary band of apparently normal front feet tobe 23.5 � 3 degrees.8 We believe that the angle ofa normal coronary band is probably about 20 to 25degrees relative to the ground (Fig. 3). If the coro-nary band angle is �30 degrees, the horse is likely tohave a negative palmar/plantar angle (Fig. 6), and ifthe angle of the coronary band is �45 degrees, the

horse undoubtedly has a negative palmar angle.a,b,c

At the other extreme, a coronary band parallel toground (as viewed from the side) is indicative of ahigh palmar angle, which is often associated with aclub foot or distal rotation of the distal phalanx (Fig.7). The coronary band angle and the solar angle ofthe distal phalanx (palmar angle) are correlatedwith the distal interphalangeal joint moment arm(DIP MA) (DIP MA is alternate terminology for DIPtorque) and the force exerted by the deep digitalflexor tendon (DDFT) on the navicular bone.8 Thecalculation of internal distal limb forces duringstance phase has been described.20 The force appliedto the navicular bone before and after correctiveshoeing is calculated and depicted by the red arrowsof different size in Fig. 8. As the coronary bandangle increases or the solar angle of the distal pha-lanx (palmar angle) decreases, both the DIP MA andthe force exerted by the deep digital flexor tendon onthe navicular bone increase.8 In our opinion, assess-ing solar angle of the distal phalanx by examiningthe coronary band is easier in hind feet than in frontfeet. A hind foot with a negative solar angle (plan-tar angle) will have a growth ring pattern that iswider at the toe than at the heel and a line imaginedalong the coronary band slope and extended forwardwill strike the front leg above the carpus or even thechest or abdomen rather that at the carpus orbelow.21,c A distally directed arch in the coronaryband in the dorsal portion of the foot may indicateremodeling of the distal phalanx (Fig. 9).

Hoof Wall

The normal healthy hoof wall should be smooth,have a light sheen, and be free of flares, cracks, andprominent growth rings. Formation of growthrings has been reviewed by Rooney.22 Growthrings are horizontal ridges of the hoof capsule thatare formed by tubular horn distortion that occurswhen perfusion of the coronary corium is altered by

Fig. 5. Note that in the heel, the coronary band of this hoofbends downward to become nearly vertical.

Fig. 4. Note the upward arch in the coronary band in the quarters of these hooves. The arch is an indication of overloading of thehoof wall in the region distal to the arch which causes the coronary band to displace proximally. In the picture on the right, note thata hoof crack in the quarter (red arrow) has occurred in the same tubular horn that is associated with the upward arch of the coronaryband (white arrow). Both abnormalities indicate that the hoof wall in this region has been under excessive ground reaction forcecausing it to deform (upward arch) and fail (crack).



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changes in diet, exercise, or by systemic disease.Wall growth is generally inversely related to hoofloading.15,23 When growth of the wall becomes re-tarded as the result of uneven circulation, altera-tions in growth ring width are evident at theproximal margin of the hoof capsule (Fig. 10). Webelieve that narrow growth rings in some areas in-dicate that circulation of the coronary corium hasbeen decreased in that region (Fig. 11). A region ofthe hoof with narrowed growth rings (suggestingaltered/uneven circulation) has most likely been re-ceiving nonuniform or excessive ground-reactionforce because wall growth is generally inversely re-lated to load.23 A hoof that exhibits growth ringsthat are narrower in some regions (Fig. 11) probablyhas chronic overload of the hoof wall in the region ofnarrow rings. Narrow growth rings are commonlyseen in the toe region of horses with chronic lamin-itis because the dorsal region of the corium is usu-ally the area most poorly perfused, a result ofcompression of dorsal coronary corium, solar plexus,and dorsal laminar vessels caused by rotation of thedistal phalanx.24 In our experience, narrow growthrings are often found in the medial quarter of theforefeet of athletic horses presented for lameness

evaluation. The coronary band of these horses isusually displaced proximally similar to the coronaryband of horses with sheared heels and is probablycaused by similar unequal distribution of verticalforces,17 which may be accentuated by conformationor mediolateral imbalance. For horses with proxi-mal displacement of the coronary band in eitherregion, lameness may resolve after administeringonly the medial portion of an abaxial sesamoid nerveblock, suggesting that abnormally localized forces onthe hoof wall may be a source of pain.

The presence of hoof wall flares or cracks is oftencaused by chronic, excessive overloading of the hoofwall in the region where these defects arefound.16,19,25 Cracks in the quarter are more likelyto be a cause of lameness than cracks in other re-gions because the quarter is thinner than other re-gions, making a quarter crack more likely to involvethe dermal layers of the hoof.25 Horizontal cracks(Fig. 12) are usually the result of a disruption ofproduction of horn caused by coronary band traumaor when subsolar infection opens (“gravels out”) atthe coronary band. These cracks are seldom acause of lameness.25

Fig. 6. Observation of the steep coronary band angle (29 degrees) of this horse correctly predicted that the plantar angle would bezero or negative in his right rear foot. Also note the broken hoof/pastern axis that is frequently associated with this conformation.The third image is an overlay of the radiograph over the photo of the distal limb created using Adobe Photoshop® software.

Fig. 7. Observation of a coronary band nearly parallel with the ground prompted a correct prediction that the palmar angle of thishorse’s front foot would be relatively high [i.e.,14 degrees (middle image)]. The third image is an overlay of the radiograph over thephoto of the distal limb created using Adobe Photoshop® software.



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FrogThe frog is highly dynamic, and its morphologychanges relative to current hoof demands and ter-rain.26 The width of a healthy frog should equal50% to 66% of its length.17,27,28 The frog of ahealthy hoof has sufficient depth at its dorsal aspectto reach the bearing surface.29,30 If this portion of

the frog does not engage the ground, fibrocartilage inthe palmar portion of the foot develops poorly oratrophies.30 The central sulcus should be wide andshallow so that the index finger or ring finger fitseasily into it (Figs. 13A–F). Contracture of the cen-tral sulcus is commonly observed. Contraction ofthe central sulcus can create an anaerobic environ-

Torque � 500 kg � 0.06 cm � sine 35° � 17.1 m.kg

Fnav � 2[FDDFT) � cos (�/2)]20; where � � 123

Fnav � 2[10 N/kg � cos (123/2)]

Fnav � 2[10 N/kg � 0.477]

Fnav � 9.54 N/kg

Torque � 500 kg � 0.06 cm � sine 27° � 13.5 m.kg

Fnav � 2[FDDFT � cos (�/2)]20; where ��125

Fnav � 2[10 N/kg � cos (125/2)]

Fnav � 2[10 N/kg � 0.462]

Fnav � 9.24 N/kg

Fig. 8. These images represent radiographic overlay of the same foot before (A) and after (B) a shoeing change/reset. Note that thecoronary band angle has decreased from 24 to 20 degrees, the palmar angle has increased from 1 to 8 degrees, and the pastern-distalphalanx axis has been straightened by 8 degrees by the reset. The torque on the distal interphalangeal joint at stance (Torque �Force (500 kg) � radius (0.06 cm) � sine of the angle) is decreased by this shoeing change/reset. The force exerted by the DDFT onthe navicular bone (Fnav) (as represented by the size of the red arrows) has also decreased in magnitude after the change/reset. Theseimages were created using Adobe Photoshop® software by Dewey R. Wilhite from original images supplied by DRT; technicalassistance on calculations was provided by Randy Luikart, CJF.

Fig. 9. The photo on the left shows a coronary band “dipping” lower at the dorsal hoof wall (black arrow) than in the quarters (redarrow) in a horse with chronic laminitis. The radiograph of the same foot shows substantial bone remodeling. The solar margin ofP3 has acquired the shape of a “banana,” and there is a “ski tip” at the dorsal rim.



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ment that is ideal for development of thrush (Figs.14A–F).26 When the frog tissue entrapped by thecontracted sulcus becomes infected, the dermis atthe deepest aspect of the sulcus often becomeseroded. The horse may exhibit lameness and showsignificant signs of pain when the sulcus is cleanedwith a hoof pick. The pain caused by thrush in thecentral sulcus may cause some horses to land toefirst to avoid loading the inflamed soft tissues of theheel. Landing toe-first may cause the heel to con-tract and atrophy more, perpetuating the infectionand lameness.

The relationship of the untrimmed frog to the soleindicates the position of the distal phalanx withinthe hoof capsule (i.e., the palmar angle).31 For in-stance, if the apex of the frog is deeply recessed andthe frog appears to be angling toward the coronaryband at the toe, the distal phalanx is probably sim-ilarly positioned, having a negative palmar angle.31

Fig. 10. Examination of the hoof surface can give an indication of its overall health and growth rate during previous weeks to months.In the image on the left, the dry and scaly hoof surface can be an indication of retarded hoof growth. Note that the dorsal aspect ofthis hoof (black arrow) has a slightly wider growth ring and a more normal, smooth surface. The narrower growth ring (red arrow)is associated with the dry and scaly side of the hoof.

Fig. 11. Note the divergent growth rings, in the foot in the image on the left, that are commonly found in horses with chroniclaminitis. The middle image shows narrow growth rings in the medial quarter of a horse with chronic laminitis. The image on theright shows smooth new growth that resembles an “earthworm” (black bracket) proximal to an invaginated growth ring (black openarrow). The red bracket shows a region that was previously thinned to help stimulate the upper new growth. The upper new growth(black bracket) is a positive prognostic sign of improved hoof perfusion compared with the recent past.

Fig. 12. A horizontal hoof crack is usually the result of disrup-tion of the production of horn caused by coronary band trauma orwhen a subsolar infection opens (“gravels out”) at the coronaryband.



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Collateral Grooves or SulciThe depth of the collateral grooves may provide anaccurate anatomical reference for predicting the re-lationship between the internal and external struc-tures of the foot and the bearing surface because thedepth of the collateral grooves is not altered by anymethod of hoof care,32 whereas the plane of the frogcan be altered by a hoof knife.33 Foot structurethat can be predicted based on characteristics of the

collateral grooves includes depth of sole, distance ofthe distal phalanx from the bearing surface, and thepalmar/plantar angle. Based on dissection studiesof the foot, there appears to be a constant relation-ship between the collateral grooves and hoof con-formation/structure.a,b The collateral groovesapparently run parallel to and a fixed distance (10to 11 mm) from the solar surface of the distal pha-lanx in the dorsal half of the foot and the same

Fig. 13. Images A, B, and C show hooves with open central sulci in which the index or ring finger would easily fit. D, E, and F depictthe appearance of open central sulci as viewed from the palmar aspect. There is no narrow space (fissure) in these heels that couldharbor thrush-causing organisms.

Fig. 14. The central sulci of hooves shown in images A, B, and C are narrow and deep and may be a site of pain causing lameness.D, E, and F when viewed from the palmar aspect, a contracted central sulcus (white arrows) may have slightly different appearanceson horses with weight-bearing versus non–weight-bearing frogs. This is a good example of learning to appreciate the distortions inthe “space” around the foot.9 The contracted sulcus is a common site of thrush and can become a source of pain. Pain often can beelicited by gently probing a contracted sulcus with a hoof pick. Figure 14F is a pretreatment picture of the same foot shown in Figure13f.



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distance from the collateral cartilages in the palmarhalf of the foot. In the healthy foot with adequatedepth of sole, the collateral groove at the apex of thefrog is 10 to 20 mm from the ground.33 This indi-cates that the distal phalanx is positioned an ade-quate distance from the ground, because the concaveaspect of the distal phalanx is positioned 10 to 11mm proximal to the deepest part of the collateralgroovea,b (Figs. 15 and 16). We are currently con-ducting studies to validate these observations.

The orientation of the dorsal aspect (front half) ofthe collateral groove in relation to the ground planeparallels the position of the distal phalanx in thehoof capsule. Collateral grooves of some horseshave a stair-step or undulating shape where thegroove dips or curves to become substantially deeperin the heel region (Fig. 17). We believe that collat-eral grooves that exhibit this type of conformationare an indication of poor development of the internalstructures of the heel. A foot that has collateralgrooves with this deep curvature in the heel regionshould be examined radiographically to confirm dig-ital alignment and orientation of the distal phalanx

to the ground (palmar angle). Horses with a nega-tive palmar/plantar angle typically have a long toe-low heel conformation and a shallow digital cushion.For horses with this type of conformation, the com-bined thickness of the frog and digital cushion is lessthan 2 inches9 and the heel bulbs can be easilydistracted.30 Many lame horses with negativeplantar angles do not block sound to the foot becausethis conformation may be associated with pain in thehock, suspensory ligament, and lumbar region.5–7,d

HeelsDuring examination of the foot, the “heel base” of thehoof capsule, the collateral cartilages, and the digi-tal cushion should be evaluated. The “heel base” ofthe hoof capsule includes the hoof wall, the buttress,angle of the sole, and the bars.34 The heel tubulesshould be straight and have an angle of incidencewith the weight-bearing surface similar to the tu-bules in the toe region. Ideally, the most palmarextent of the bearing surface of the heel tubuleswould be at the base of the frog and very near avertical line drawn thru the middle of the third

Fig. 15. This image was rendered in Autodesk ® 3dsMax®. Original 3D data were derived from dicom images using MaterialiseMimics Software®. The hoof capsule is partially translucent in this image so that internal structures can be visualized. Point Aindicates the deepest aspect of the collateral grooves at the apex of the frog. Point B indicates the point on the solar surface of thedistal phalanx that is directly proximal to the deepest aspect of the collateral grooves at the apex of the frog (point A). The consistentdistance (10 to 11 mm) between these two points allows the clinician to predict distal phalanx orientation. The collateral groove depth(point A to the ground plane) in this foot is sufficient to allow space for adequate sole depth in the toe region. If one imagines movingthe ground plane proximally so that the distance from the ground plane to point A is zero mm, it becomes clear that sole depthdecreases as collateral groove depth decreases. Image created by Dr. Ray Wilhite, Department of Anatomy and Physiology, CVM,Auburn University.



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metacarpal/metatarsal bones. Many podiatristsdescribe under-run heels as those that are �5 de-grees lower than the toe angle.18 O’Grady, how-ever, emphasized the relationship of the foot to themetacarpal/metatarsal bones when determining ifthe heels are under-run.33 He considered heels po-sitioned well forward of the line drawn through themiddle of the third metacarpal/metatarsal bones tobe under-run.33 Under-run heels that grow for-ward toward the widest part of the foot often col-lapse under the weight of the horse, causing heeltubules to run nearly ground parallel. The barsand the angle of the sole may be crushed and de-formed as a consequence of the severely under-runheel. One author (D.R.T.) has observed that horses

with under-run or collapsed heels generally havethin (less than 2 inches9) digital cushions that areeasily deformed with finger pressure.

Solar Proportionality

When viewing the solar aspect of a healthy hoof, theground surface should be approximately as wide asit is long (Fig. 18).28 This creates a relative propor-tion from the front of the foot to the palmar aspectthat is related to alignment of the center of articu-lation (of the distal interphalangeal joint) in themiddle of the foot, or when shod, the middle of theshoe.35 The normal solar surface of the foot may bewider laterally than medially.28,32

Fig. 16. The image on the left depicts point A as the deepest point of the collateral grooves at the apex of the frog. The hoof capsulehas been made partially translucent in the image on the right so that point B can be visualized on the solar surface of the distalphalanx. Image created by Dr. Ray Wilhite, Department of Anatomy and Physiology, CVM, Auburn University.

Fig. 17. Note that the collateral groove of this hind foot of a 4 year-old Thoroughbred racehorse is deeper at the apex of the frog (redarrow) than it is at mid frog (white arrow), which indicates that the position of the palmar aspect of the palmar processes of the distalphalanx is lower than the dorsal rim (i.e., the foot has a negative plantar angle). Also note that the collateral groove curves inwardto be deepest under the heel region (blue arrow). This conformation of the collateral groove indicates a “weak” or “underdevelopedheel.” Horses with this collateral groove conformation usually have thin digital cushions and heel bulbs that are easily distracted.The lateral radiograph of the same foot confirms the presence of a negative plantar angle and a broken hoof/pastern axis (even thoughthe slight obliquity in this radiograph makes it difficult to determine the exact plantar angle, the plantar angle is definitely less thanzero). Photos courtesy of HoofSolutions™.



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SoleThe healthy sole tends to be callused and between 10to 15 mm thick33 beneath the distal rim or tip of thedistal phalanx. The sole must be at least 10 mmthick to protect the distal phalanx from trauma as-sociated with impact.9,33 A ruler calibrated in mil-limeters can be placed within the collateral groove tomeasure the distance between the deepest part ofthe groove and the plane of the outer perimeter ofthe sole (Fig. 19). We believe this measurementpredicts the height at which the distal phalanx issuspended above the bearing surface of the foot andcan be used to predict solar depth. It is not uncom-mon to find horses in which the depth of the collat-eral grooves measured at the apex of the frog isessentially zero millimeters from the ground (i.e., nospace). This may indicate that at the apex of the

frog (which is normally about 2 cm behind the tip ordistal rim of the distal phalanx in the nonlaminiticfoot), the bone on the midline is only 10 mm proxi-mal to the bearing surface. Considering that thedistal phalanx is concave, the sole of these horsesbecomes thinner from the apex of the frog peripher-ally toward the tip or distal rim of the distal pha-lanx. As an example of this, one of the authors(D.R.T.) has observed that flat-soled horses thathave zero collateral groove depth at the apex of thefrog, generally have less than 7 mm of solar depth atthe tip or distal rim of the distal phalanx (Fig.19A).33a The distal rim of the distal phalanx is pre-disposed to trauma when the sole is less than 10mm.9,33 Over time, the traumatized distal phalanxremodels and takes on a rounded appearance on thelateral radiographic projection (Fig. 20B). Afterthis happens, solar depth may appear to be closer tonormal when measured, but this is due to boneresorption. Feet with shallow collateral groovesare predisposed to solar bruising, subsolar infection,remodeling of the distal phalanx, and even rim frac-tures of the distal phalanx due to lack of solar depthand/or concavity of the sole. The opposite situationis true of feet with deep collateral grooves at theapex of the frog. These feet have sufficient solardepth and/or solar concavity to elevate and protectthe distal phalanx from the trauma associated withimpact.

3. Digital Palpation of the Foot

The examiner should be thoroughly familiar withthe normal anatomical features of the digit and in-cidental variations to appreciate any deviation fromthe normal as determined by digital palpation.When a finding is suspicious, the region of the limbin question should be compared with that of thecontralateral limb. A methodical digital examina-tion of the distal portion of the limb proceeds fromdistal to proximal, first with the limb weight-bear-ing, then with the limb lifted, always looking forswellings, defects, variations in temperature, andother irregularities. Examination by palpationstarts with assessment of the temperature of thehoof wall, the coronary band and the heel bulbs byusing the palm or the back of the hand. The handcan detect temperature differences in tissue of 1°to 1.5°C.36 Elevated temperature of a foot mayindicate the presence of inflammation, subsolarinfection, or the prodromal stages of laminitis.Decreased temperature of the coronary band mayindicate poor perfusion of the coronary corium asoften occurs with subacute-chronic laminitis oncethe lamina have failed and coronary corium is beingcrushed by weight bearing against the unstable hoofcapsule or severe, mediolateral imbalance in whichcase the corium will be cooler on the overloaded sideof the foot. Some clinicians and hoof-care profes-sionals use inexpensive infrared thermometers toincrease their ability to objectively evaluate temper-ature of the hoof and coronary band, but efficacy of

Fig. 18. This foot very closely approximates the desired dimen-sions of a healthy foot. The white line, which represents thewidth of the weight-bearing surface, is the same length as the redline, which represents the length of the weight-bearing surface.

Fig. 19. The ruler is placed into the deepest aspect of the collat-eral groove at the apex of the frog. The depth of this space inrelation to the outer perimeter of sole is measured. In the imageon the left the depth is measured to be 15 mm, indicating that thedistal phalanx is adequately protected by sole. The photo on theright depicts a hoof with very shallow collateral groove depth(near zero), indicating that the distal phalanx is inadequatelyprotected by sole. (See radiograph of similar foot in Fig. 20A.)Photos courtesy of Pete Ramey.



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these instruments used for this purpose has notbeen studied.

The coronary band of a healthy hoof should feelthick and spongy2 and should have no evidence of a“ledge” where a finger can be placed behind theproximal aspect of the hoof capsule (Fig. 21). A

prominent ledge or depression in the coronary bandindicates that the distal phalanx is located deeperthan normal within the hoof capsule. Horses withthis palpable abnormality at the dorsal aspect of thecoronary band usually have excessive distance be-tween the coronary band and the extensor process.2

In our experience, a palpable depression in the cor-onary band is usually accompanied by other digitalabnormalities that can be found during physical ex-amination, such as a thin, flat, sole with a shallowcollateral groove at the apex of the frog, a narrow,contracted frog (which may have a contracted cen-tral sulcus), a narrow heel, and a narrow distancebetween the collateral cartilages. The dorsal as-pect of the coronary band and the region immedi-ately proximal to it should be palpated for effusionin the dorsal pouch of the DIP joint. Effusion in thedorsal pouch is an indication of synovitis, which isclaimed to be a significant cause of foot pain in someperformance horses.4,37,38 Effusion in the DIPjoint, however, can also be a nonspecific finding be-cause it can be caused by mechanical stress/forcesand often it is not associated with lameness. Dis-tension of the DIP joint is also occasionally observedin horses with navicular disease.39

Heel

In recent years, inadequate development of fibrocar-tilage in the palmar/plantar portion of the foot hasbeen recognized as a precursor to tissue injury andlameness.30,40 Horses with underdeveloped heelstypically have poorly formed digital cushions andthin collateral cartilages. These structures deter-mine the overall conformation of the palmar/plantarportion of the foot. It remains to be determined ifheel development is a static state associated withgenetically determined conformation or a conforma-tion that can be altered by physical stimulation;possibly either or both factors may be involved.Clinicians should gain an appreciation for variationin the consistency and overall size of the digitalcushion and collateral cartilages. The digital cush-ion can be palpated between a thumb placed be-tween collateral cartilages and the fingertips placedon the frog (Fig. 22). A sense of “normal” can belearned by palpating the digital cushions of soundhorses with “good feet” and comparing those find-ings with those of horses with poorly conformedfeet.30,40,41 The depth of the combined tissues ofnormal digital cushion and frog should be 2 inches.9

Horses with underdeveloped digital cushions or“flimsy” collateral cartilages2 typically have under-run heels that can be easily moved up and downindependently or they may have contracted heelsand thin, non–weight-bearing frogs.30,33 The feetof the hind limbs are far less likely to have under-developed heels, and these feet can be comparedwith the front feet to get a sense of heel develop-ment.33 The authors and othersa,e have observedthat horses that have been chronically stalled, how-

Fig. 20. (A), This foot has near zero collateral groove depth atthe apex of the frog (point A). Note that inadequate sole depth (6mm) is found under the rim of the distal phalanx. (Anatomicallocation of points A and B are also shown in Figs. 15 and16.) Also note the gas shadows that the collateral grooves createin the heel area (red arrows). This is the radiographic appear-ance of a foot with the “stair-step” or undulating shape of thecollateral grooves that we believe to be associated with a “weak”or “underdeveloped heel.” The heel bulbs of this horse wereeasily distracted with digital pressure and the digital cushionwhen palpated was soft and thin. Also compare this foot with thefoot in Fig. 17, which also has “undulating” collateral grooves, yetto a greater extent, whereby the shallowest point is at mid-frog,indicating that the distal phalanx of that foot has a negativeplantar angle. Horses with negative plantar angles usuallyhave adequate sole depth under the dorsal rim of the distalphalanx but may have inadequate solar protection under thepalmar processes. (B), The distal phalanx in this radiographhas severe bone remodeling as the result of chronic laminitis andthin soles. If the distal phalanx was normally shaped, it proba-bly would penetrate the sole; instead, bone has been remodeled bythe chronic trauma and suboptimal perfusion. Also note thatthe collateral groove depth of this horse is quite shallow (esti-mated to be less than 3 mm), and the gas shadow of the collateralgrooves in the heel region is the similar to the foot in A.



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ever, are likely to have poorly developed heels in thehind feet.

Horses with poorly developed heels may be pre-disposed to injury of the navicular bone and DDFTfor several reasons: (1) they tend to have low pal-mar/plantar angles, which increases the force ex-erted by the deep flexor tendon on the navicularbone,8 (2) horses with poorly developed heels tend toland toe first, with the deep digital flexor tendon/muscle unit contracting as the heel descends caus-ing abnormally high compressive forces on thenavicular bone, which in turn causes disease of thisstructure and increased strain in the DDFT duringlocomotion,42 (3) poorly developed feet have 15 timesfewer vascular channels in the collateral cartilages

than are found in “good feet.”29 Feet with fewervascular channels may contain less blood to act as ahemodynamic energy dissipation mechanism.

The palpable enlargements on the middle pha-lanx at the attachments of the medial and lateralcollateral ligaments of the DIP joint, which aresituated approximately at 10 and 2 o’clock aroundthe circumference of the coronary band (with 12o’clock being at the dorsal aspect of the sagittalplane of the foot), should be symmetrical. Severedamage to these ligaments may result in soft tis-sue swelling, and palpation of these sites mayelicit signs of pain from the horse, but evidence ofdisease of these collateral ligaments is often notpalpable.43

The thickness, density, and pliability of the collat-eral cartilages should be compared between lateraland medial cartilages and between cartilages of leftand right feet.2 Poor quality of the collateral carti-lages may indicate the heel as a source of pain, andpalpation of this tissue also helps to determine thepliability of the hoof. Extremely stiff and inflexiblecollateral cartilages are often found in an uprightfoot, whereas “flimsy” cartilages are commonlyfound in feet with a collapsed heel and narrow con-vex frog.2 This distance between the cartilagesshould be assessed as well. One author (D.R.T.)has observed that horses with suboptimal heel de-velopment (especially Quarter Horses with narrowfrogs, with/without heel pain) often have a verysmall distance between the cartilages (�1 fingerwidth).

Extensive ossification of one or both collateralcartilages may be observed in horses with diseaseof a collateral ligament of the DIP joint, trauma tothe distal phalanx, trauma to the cartilage itself,or trauma to the ligaments that join the collateralcartilages to the middle (chondrocoronal ligament)and distal (chondroungular ligament) phalanges

Fig. 21. The coronary bands in these pictures that have a prominent “ledge” due to excessive distance between the coronary band andthe extensor process of the distal phalanx. Horses with these ledges are called “sinkers” when the ledge occurs because of laminitis(left image). The authors have observed that some sound horses can have excessive distance between the coronary band and extensorprocess and may have similar yet more subtle indications of “prominence” of the proximal aspect of the capsule as seen in the figureon the right where the top of the capsule can easily be palpated.

Fig. 22. The digital cushion should be palpated to become famil-iar with the variations in depth and density that exist betweenhorses. The digital cushion should have a density similar to atennis ball or a “well-done” steak. The frog and digital cushionshould have a combined depth of approximately 2 inches. Photocourtesy of Pete Ramey.



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or the navicular bone (chondrosesamoideanligament).44

4. Hoof Testers

The use of hoof testers may enable the examiner tofind or rule out the presence of pain associated withthe hoof wall, sole, dermal tissues, and digital cush-ion, but false-negative and false-positive findingsobtained using the hoof tester are common. De-formability of the sole as the hoof tester is appliedmay give an indication of sole thickness. Causes offalse-positive findings with the hoof tester are re-flexes that occur when the horse is startled or an-noyed by the pressure applied to the foot. Manyhorses with chronic foot pain do not react to testersbecause the hoof capsule has deformed to protect thepainful region. In the authors’ experience, manyhorses with severe foot pain do not react to applica-tion of a hoof tester such as those with a subsolarabscess, laminitis, or fracture of the distal phalanx,perhaps because pain is already near maximal.The knowledge of abnormal sensitivity in the dorsalor palmar aspect of the sole of the foot is especiallyimportant when considering the differential diagno-sis of structures desensitized by various diagnosticanesthetic techniques in the foot. The use of hooftesters for identification of navicular pain is contro-versial but is generally considered to be unreli-able.14,45 The degree of response to application ofhoof testers is determined by the size of the testers,the size of the foot, the thickness of the sole, thedemeanor of the horse, the amount of pressure ap-plied by the examiner, and finally, by the presence ofdisease. It is important to develop a sense for whatare normal variations between horses. Responsesshould be compared carefully between contralateralfeet. In one study, examination using a hoof testerhad a sensitivity of 45%, a specificity of 50%, apositive predictive value of 50%, and an accuracy of48% for the identification of navicular pain.14 Inanother study, only 11% of horses with naviculardisease reacted to hoof testers applied over the mid-dle third of the frog.45 Another important use ofhoot testers is to assess the deformability or integ-rity of the structures of the hoof capsule; for exam-ple, sole depth can readily be evaluated by howmuch it deforms with application of hoof testers.

5. Physiological Stress Tests

Flexion tests of the distal portion of the lower limbhave been used for many years to attempt to localizepain in the distal portion of the limb. Flexion testsof the distal portion of the lower limb exacerbatelameness of horses with disease of the proximal anddistal interphalangeal joints, proximal and distalsesamoid bones, disease of a digital flexor tendon orsuspensory ligament, as well as the metacarpopha-langeal joint, which cannot be excluded from thetest.13 In addition, the response to a flexion test ofthe distal portion of the lower limb is subjectivebecause response depends on the force and time

applied.46,47 One study found the optimal force fora flexion test to be 100 N for 1 minute.46 A slightlypositive response to flexion (100 N/1 min) in horseswith no other clinical signs or clinical or radio-graphic signs of disease of the distal portion of thelimb had no clinical significance.46 Other investi-gators showed that most clinically sound horses re-act slightly to a flexion test of the distal portion ofthe limb and that a positive response to the flexiontest increased significantly with age.48 This obser-vation and the lack of long-term consistency of thetest cast doubt on the presumption that a positiveflexion test indicates subclinical joint disease andquestion the possible value of the test as a predictorof future, joint-related problems.48 Temporarylameness that occurs after flexing the distal portionof the lower limb is more likely to be clinically sig-nificant if the response differs markedly betweencontralateral limbs.

An extension/flexion test of the DIP joint and na-vicular apparatus is performed by placing a 15- to20-degree wooden wedge beneath the foot so thateither the toe or heel is elevated for a period of 1minute or more. Alternatively, the foot can beplaced on one end of a plank, the other end of whichis gradually elevated by the examiner to produce asimilar effect. Elevation of the toe increases strainin the DDFT, navicular suspensory ligaments, andthe impar ligament, and increases the compressiveforce on the navicular bone. Nevertheless, in onestudy, toe elevation tests had a sensitivity of only55% and a specificity of only 42% for the presence ofnavicular pain.14 Elevation of the heel reducesstrain in the DDFT, impar ligament, and navicularsuspensory ligaments but directly increases impactpressure on the heels. Despite this, Turner14 foundthat the heel elevation test had a sensitivity of 76%and a specificity of 26% for the presence of navicularpain. One author (M.S.) has observed that manyhorses with lesions of the DDFT (as identified onMRI) experience worsening of lameness after theheel is elevated.

6. Surface for Observing Lameness

As a general rule, pain originating in the distalportion of the limb causes a supporting limb lame-ness (or impact lameness), as opposed to a swinginglimb lameness (or propulsion lameness), character-ized by the exaggerated downward motion of thehead and neck when the sound (i.e., contralateral)limb strikes the ground. Lameness caused by painin the distal portion of the limb tends to be worsewhen the horse is trotted on hard ground than whenthe horse is trotted on soft ground. Lamenesscaused by pain in the distal portion of the limb isoften more noticeable when the horse trots in acircle, especially when the lame limb is on theinside.





7. Significance of Physical Examination of the Hoof

Many of the observations described above are thoseof the authors and other clinicians and have notbeen validated by scientific investigation. We hopethat these observations will be subjected to scientificscrutiny to determine their predictive value in de-termining disease of the foot.

8. Localizing Pain Within the Foot Using Nerve andJoint Blocks

Choice of Local AnestheticAlthough many clients expect the source of paincausing lameness to be identified during a singleexamination, identifying the source of pain within afoot may require multiple examinations using a dif-ferent technique of perineural or intra-articular an-algesia at each examination. When multipleexaminations are anticipated, the choice of local an-esthetic solution may be important. Use of 2% li-docaine in such cases may allow for closer intervalsbetween examinations because the analgesic effectof lidocaine is shorter than that of other commonlyused local anesthetic agents, such as mepivacaine.The length of analgesic effect of lidocaine or mepi-vacaine is not well documented, perhaps because thelength of analgesic effect may depend on the degreeof pain causing lameness.49 Some authors claimthe analgesic effect of perineurally administered li-docaine to last 90 to 180 minutes and that of mepi-vacaine to last 120 to 180 minutes.49,50 Accordingto Wyn-Jones,51 however, the length of analgesiceffects of these drugs is less. Wyn-Jones claimedthat lidocaine, when administered perineurally, hasan analgesic effect of only 30 to 45 minutes and thatmepivacaine, when administered perineurally, hasan analgesic effect of only 90 to 120 minutes.51

Andreen et al52 found that the analgesic effect ofmepivacaine administered into the middle carpaljoint of horses lasted only 55 minutes when treatinghorses for endotoxin-induced synovitis of the middlecarpal joint. Lidocaine is more irritating to tissuethan is mepivacaine,53 which may make it less de-sirable for use in the distal portion of the limb.Because lidocaine is more inflammatory than ismepivacaine, the authors prefer to use mepivacainewhen anesthetizing joints of the distal portion of thelimb. Intrasynovial use of 2% lidocaine may also beundesirable because lidocaine has been shown invitro to be significantly more chondrocytotoxic thanis 2% mepivacaine.54 Perineural administration of2% or 3% ketamine HCl in isotonic saline solution orbicarbonate solution at the base of the proximalsesamoid bones produced 15 to 25 minutes of anal-gesia in an experimental model,55,56 indicating thatthis short-acting drug may prove useful as a localanesthetic agent for lameness examination whenmultiple techniques of local analgesia are antici-pated. The authors, however, are unaware of re-ports concerning the clinical value of ketamine HCLfor regional analgesia in the horse.

The Palmar Digital Nerve Block

A positive response to anesthesia of the palmar dig-ital nerves of lame horses was once believed to lo-calize pain to the palmar third or half of the foot,including the palmar aspect of the DIP joint,whereas the dorsal branches of the palmar digitalnerves were thought to innervate the remainder ofthe foot.57,58 These beliefs were obviously the re-sult of misinterpretation of desensitization of thepalmar portion of the coronary band that occursafter a palmar digital nerve block and desensitiza-tion of the entire coronary band that occurs after anabaxial sesamoid nerve block or a pastern ringblock, each of which anesthetizes the dorsalbranches of the palmar digital nerve. Many clini-cians believed that the palmar digital nerves shouldbe anesthetized near or distal to the proximal mar-gin of the collateral cartilages to avoid anesthesia ofthe dorsal branches of the palmar digital nerve andhence desensitization of the entire foot.51,59 Easteret al60 found, however, that anesthesia of the palmardigital nerves just proximal to the bulbs of the heelalleviated lameness caused by endotoxin-inducedpain in the DIP joint, indicating that the palmardigital nerves alone innervate the entire DIP joint.According to the study by Easter60 and results of anearlier anatomic study by Sack,61 the dorsalbranches of the palmar digital nerve are unlikely tocontribute much more than sensory innervation tothe dorsal aspect of the coronary band and dorsallaminae of the foot.

A more important reason for depositing local an-esthetic solution as far distally in the pastern aspossible when performing a palmar digital nerveblock is that more proximal deposition of local anes-thetic solution increases the likelihood of desensitiz-ing the proximal interphalangeal (PIP) joint.62

When a 0.5 � 16-mm (25-gauge, five-eighths inch)needle is inserted over the palmar digital nerve onecentimeter proximal to the proximal edge of thecartilage of the foot and directed distally, local an-esthetic solution is probably deposited at or slightlydistal to the level of the palmar border of the PIPjoint, because the height of the collateral cartilage inrelation to the level of the palmar region of the PIPjoint is probably similar for most horses.62 The like-lihood of inadvertently desensitizing the PIP joint(and thus misinterpreting the result of a palmardigital nerve block) increases when reassessment ofgait after the nerve block is delayed.62

The first reevaluation of lameness can begin 5minutes after administering regional analgesia inthe distal portion of the limb.51,63 Wyn-Jones ad-vised prompt assessment of gait after regional anal-gesia of the distal portion of the limb because rapiddiffusion of anesthetic solution could anesthetizeother nerve branches, thus confusing results of theexamination51 Nagy et al62,65 found that radiopaquecontrast medium deposited perineurally in the lowerportion of the limb traveled a substantial distance





proximally along the neurovascular bundle within10 minutes after administration (Fig. 23). Deposi-tion of local anesthetic solution outside the fascia(Fig. 23) surrounding the neurovascular bundle hasbeen offered as an explanation for the delay in de-sensitization of a region that sometimes occurs afteradministration of regional analgesia.64 A clinicianprobably would have no idea if a delay in resolutionof lameness after a nerve block was due to proximalmigration of local anesthetic solution with eventualinadvertent desensitization of a more proximal,painful lesion or, instead due to deposition of localanesthetic solution outside fascia surrounding theneurovascular bundle.

Localization of pain to either the medial or lateralaspect of the foot may be possible by anesthetizingthe medial and lateral palmar digital nerves at dif-ferent times. Some causes of lameness, such asnavicular disease or disease of the DIP joint, wouldbe highly unlikely to be the cause of lameness ifdesensitization of one side of the foot resolves lame-ness, whereas uniaxial diseases such as a nonarticu-lar palmar process fracture of the distal phalanx,unilateral solar or hoof wall disease, and severesheared heels would be more likely causes of lame-ness. Some uniaxial diseases such as desmitis of acollateral ligament or a subsolar abscess, however,may require analgesia of both palmar digital nervesto significantly resolve lameness.

Intra-Articular Analgesia of the DIP JointIntra-articular analgesia of the DIP joint using 5 to10 mL of local anesthetic solution, like the palmar

digital nerve block, has limited value in localizingpain within the foot. Local anesthetic solution ad-ministered into the DIP joint desensitizes thatjoint,66 the navicular bursa,67 the navicularbone14,68,69 and its suspensory ligaments,70 the toeregion of the sole,71,72 and, for most horses, thatportion of the deep digital flexor tendon that resideswithin the foot.73 When a large volume of localanesthetic solution (e.g., 10 mL) is administered, theheel region of the sole is also desensitized.72

Not all horses that are lame because of pain in theDIP joint (or any joint) respond positively to intra-articular analgesia. Intra-articular analgesia mayrelieve pain caused by disease of periosteum andcapsular soft tissue, but when joint disease involvessubchondral bone, pain may not resolve with intra-articular analgesia.74,75 Because subchondral boneis innervated by nerves that enter the bone marrowvia the nutrient foramen, anesthesia of nerves prox-imal to branches that enter the nutrient foramenmay be necessary to resolve joint pain and lameness(Fig. 24). Perineural anesthesia of the palmar dig-ital nerves proximal to the origin of the branchesthat enter the nutrient foramen of the middle pha-lanx may be necessary to resolve lameness causedby subchondral bone pain in the middle phalanx incases of osteoarthritis of the DIP joint (low ringbone).

Although local anesthetic solution administeredinto the DIP joint has been shown to diffuse to thenavicular bursa and navicular bone,76,77 we believethat the most likely explanation for desensitizationof the navicular bone and its supporting ligamentswhen local anesthetic solution is administered intothe DIP joint is anesthesia of subsynovial nerves

Fig. 23. Radiopaque contrast medium deposited perineurally(white arrow) in the lower portion of the limb may travel asubstantial distance proximally along the neurovascular bundlewithin minutes after administration.56 Deposition of local anes-thetic solution outside the fascia surrounding the neurovascularbundle (black arrowhead) has been offered as an explanation forthe delay in desensitization of a region that sometimes occursafter administration of regional analgesia.56

Fig. 24. Intra-articular or regional anesthesia (needles B and C)may fail to resolve lameness in some horses with joint disease ifpain originates from subchondral bone. Because subchondralbone is innervated by nerves that enter the bone marrow via thenutrient foramen, anesthesia of nerves proximal to branches(needle A) that enter the nutrient foramen may be necessary toresolve joint pain and lameness.



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that supply sensory fibers to the navicular bone andits suspensory ligaments70 and anesthesia of thepalmar digital nerves where they lie in close prox-imity to the palmar pouch of the DIP joint (Fig.25).67,78 Schumacher et al72 found that anestheticsolution administered into the DIP joint desensitizesthe toe region of the sole and, occasionally, desensi-tizes the palmar aspect of the coronary band, find-ings that support the theory that analgesia of theDIP joint also anesthetizes the palmar digitalnerves. We believe that local anesthetic solutionwithin the DIP joint anesthetizes the palmar digitalnerves at a site proximal to that which suppliesinnervation to the navicular bone and its associatedstructures. If this theory is correct, failure to ame-liorate lameness after intra-articular analgesia ofthe DIP joint would probably exclude diseases of thenavicular bone or bursa or toe region of the sole as acause of lameness. However, this theory makes itdifficult to explain the report of Dyson and Kidd69

that describes 21% of lame horses that failed torespond to intra-articular analgesia of the DIP jointbut improved significantly after intrabursal anal-gesia of the navicular bursa, unless that grouprepresented horses with atypical neuroanatomy.Turner, reporting results of a study of 80 horseswith foot pain, concluded that navicular disease canbe excluded as a cause of lameness if gait is notimproved after analgesia of the DIP joint.14 If a

large volume (e.g., 10 mL) of local anesthetic solu-tion is administered into the DIP joint without ame-lioration of lameness, pain in the heel region of thesole also could probably be eliminated as a cause oflameness.72

Intra-Bursal Analgesia of the Navicular BursaSignificant amelioration of lameness after adminis-tering local anesthetic solution into the navicularbursa indicates disease of the bursa, the navicularbone, and/or its supporting ligaments,69 solar toepain71,72 or disease of the portion of the DDFT in thefoot.79,80 Even though analgesia of the DIP jointresults in analgesia of the navicular bone68 orbursa,67 analgesia of the navicular bursa does notresult in analgesia of the DIP joint.69,79,81,82 Anal-gesia of the navicular bursa may help to differenti-ate pain associated with disease of the DIP jointfrom pain associated with disease of the navicularbone and associated structures. Clinical14,79 andexperimental82 observations indicate that a positiveresponse to intra-articular analgesia of the DIP jointand a negative response to intra-bursal analgesia ofthe navicular bursa indicate pain within the DIPjoint as the cause of lameness. This clinical obser-vation is valid if solar pain as a cause of lamenesscan be eliminated with hoof testers.71,72 One pos-sible explanation for the observation that analgesiaof the DIP joint causes analgesia of the navicularbursa but analgesia of the navicular bursa does notcause analgesia of the DIP joint is that the site ofdirect contact between the palmar pouch of the DIPjoint and the palmar digital nerves is located prox-imal to the origin of the deep branches that inner-vate the DIP joint and the navicular bursa, whereasthe site of direct contact between the navicularbursa and the palmar digital nerves is located distalto these branches (Fig. 26).

Some clinicians once assumed that improvementin lameness observed within 10 minutes after injec-tion of the DIP joint with local anesthetic solutionindicates that lameness is caused by pain in the DIPjoint alone and that improvement observed morethan 10 minutes after injection is caused by diffu-sion of local anesthetic solution into the navicularbursa or around the nerves providing sensory inner-vation to the navicular bone and its associated struc-tures.81,83,84 This assumption appears to be invalidbecause a positive response to intra-articular anal-gesia of the DIP joint has been observed to occurwithin 5 to 8 minutes of injection in a majority ofhorses with navicular disease or experimentally-in-duced navicular bursal pain.67,79 Based on resultsof his neuroanatomical studies, Bowker concludedthat much of the navicular apparatus, the insertionof the distal sesamoidean impar ligament, and theinsertion of the DDFT are anesthetized within 7 to 9minutes of intra-synovial analgesia of the DIPjoint.3 Results of experimental studies indicatethat the effect of intra-articular analgesia of the DIPjoint or of intrabursal analgesia of the navicular

Fig. 25. A possible explanation for desensitization of the navic-ular bone and its supporting ligaments when local anestheticsolution is administered into the DIP joint is anesthesia of thepalmar digital nerves, where they lie in close proximity to thepalmar pouch of the coffin joint. In this radiograph of a cadaverlimb (also seen in Fig. 22), radiopaque solution is seen within theneurovascular bundle of the palmar digital nerve. The DIPjoint, which was injected with a mixture of 10 mL of radiopaquesolution and air, displaces the palmar digital nerve (arrows),which lies in close proximity to its palmar pouch (black arrow-head).



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bursa on lameness should be assessed soon afterinjection (i.e., within 5 to 10 minutes) because afterthis time, structures desensitized by diffusion of lo-cal anesthetic solution become uncertain.71,72,82

Analgesia of the Digital Flexor Tendon SheathPain induced in the toe and heel regions of the sole,pain associated with synovitis of the DIP joint, andpain associated with synovitis of the navicular bursaare not significantly attenuated by intrathecal anal-gesia of the DDFT sheath.85 It is logical, therefore,to assume that intra-synovial analgesia of the digi-tal flexor tendon sheath does not anesthetize thepalmar digital nerves but rather desensitizes onlystructures that are contained within or border onthe sheath itself (e.g., the superficial and DDFTs,the straight and oblique distal sesamoidean liga-ments, the annular ligaments of the fetlock andpastern). An abaxial sesamoid nerve block abol-ished or improved lameness localized to the foot inall of 46 horses found to have a significant lesion inthe digital portion of the DDFT using MRI.73 Apalmar digital nerve block (PDNB), analgesia of theDIP joint, or analgesia of the navicular bursa, how-ever, each ameliorated lameness in about two-thirdsof these horses.

Because lameness caused by disease of the DDFTwithin the foot may fail to improve significantlyafter analgesia of the palmar digital nerves, the

coffin joint, or the navicular bursa, we believe that aportion of the DDFT receives its sensory supply frommore proximal deep branches of the medial and lat-eral palmar digital nerves that enter the digitalflexor tendon sheath. Improvement of lameness inhorses with lesions of the DDFT within the foot afterintrathecal analgesia of the digital flexor tendonsheath has been described.86 Because the palmardigital nerves are not anesthetized by blocking thedigital flexor tendon sheath,85,87 it has been sug-gested that blocking the digital flexor tendon sheathdirectly may be a technique that can be used todiagnose deep digital flexor tendonitis within thefoot without the use of magnetic resonance imag-ing.87 Performing intrathecal analgesia of the dig-ital flexor tendon sheath on horses with lamenessthat is unchanged after anesthesia of the palmardigital nerves but resolves after an abaxial sesamoidnerve block may be useful. Resolution of lamenessafter intrathecal analgesia of the digital flexor ten-don sheath justifies suspicion of a lesion within thedigital portion of the DDFT or other structures con-tained within the digital flexor tendon sheath.

References and Footnotes1. Moyer WA, Carter GK. Examination of the equine foot. In:

Floyd AE, Mansmann RA, editors. Equine Podiatry. St. Louis:Elsevier Saunders; 2007:112–127.

2. Turner TA. Examination of the equine foot. Vet Clin NorthAm Equine Pract 2003;19:309–332.

3. Bowker RM. Innervation of the equine foot: Its importanceto the horse and to the clinician. In: Floyd AE, MansmannRA, editors. Equine Podiatry. St. Louis: Saunders Elsevier;2007:74–89.

4. Goodman NL. The racing Quarter Horse. In: Ross MW,Dyson SJ, editors. Diagnosis and Management of Lamenessin the Horse. 2nd edition. St. Louis: Elsevier Saunders;2011:1051–1056.

5. Dyson S. Diagnosis and management of common suspen-sory lesions in the forelimbs and hindlimbs of sport horses.Clin Tech in Equine Pract 2007;6:179–188.

6. Mansmann RA, James S, Blikslager AT. Long toes in thehind feet and pain in the gluteal region: an observationstudy of 77 horses. J Equine Vet Sci 2010;30:720–726.

7. Redden RF. Clinical and radiographic examination of theequine foot, in Proceedings. Am Assoc Equine Pract 2003;49:169–185.

8. Eliashar E, McGuigan MP, Wilson AM. Relationship of footconformation and force applied to the navicular bone of soundhorses at the trot. Equine Vet J 2004;36:431–435.

9. Redden RF. Hoof capsule distortion: understanding themechanisms as a basis for rational management. Vet ClinNorth Am Equine Pract 2003;19:443–462.

10. Ridgway K. Low heel/high heel syndrome. In: Ramey P,editor. Care and Rehabilitation of the Equine Foot. Lake-mont, GA: Hoof Rehabilitation Publishing LLC; 2011:368–380.

11. Ramey R. Club foot. In: Ramey P, editor. Care and Reha-bilitation of the Equine Foot. Lakemont, GA: Hoof Rehabili-tation Publishing LLC; 2011:382–389.

12. Verschooten F. Locomotory system of the purchase exami-nation in the horse. Equine Pract 1992;8:9–16.

13. Ross MW. Movement. In: Ross MW, Dyson SJ, editors. Di-agnosis and Management of Lameness in the Horse. 2nd edi-tion. St. Louis: Elsevier Saunders; 2011:64–80.

14. Turner TA. Predictive value of diagnostic tests for navicularpain, in Proceedings. Am Assoc Equine Pract 1996;42:201–204.

Fig. 26. This diagrammatic picture of the foot explains a possi-ble reason for the observation that analgesia of the DIP jointcauses analgesia of the navicular bursa but analgesia of thenavicular bursa does not cause analgesia of the DIP joint. Thereason may be that the site of direct contact between the palmarpouch of the DIP joint and the palmar digital nerves is locatedproximal to the origin of the deep branches that innervate theDIP joint and the navicular bursa, whereas the site of directcontact between the navicular bursa and the palmar digitalnerves is located distal to these branches. The arrow points tobranches of the palmar digital nerve that supply the navicularapparatus.81 Courtesy of Dr. Amy Bentz, Academic VeterinarySolutions LLC.



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15. Parks AH. Foot balance conformation and lameness. In:Ross MW, Dyson SJ, editors. Diagnosis and Management ofLameness in the Horse. 2nd edition. St. Louis: ElsevierSaunders; 2011:282–293.

16. Dabareiner RM, Moyer WA, Carter GK. Trauma to the soleand wall In: Ross MW, editor. Diagnosis and Managementof Lameness in the Horse. 2nd edition. St. Louis: ElsevierSaunders; 2011:309–319.

17. O’Grady SE. How to manage sheared heels, in Proceedings.Am Assoc Equine Pract 2005;51:451–456.

18. Turner TA. The use of hoof measurements for the objectiveassessment of hoof balance, in Proceedings. Am Assoc EquinePract 1992;38:389–395.

19. O’Grady SE, Castelijns HH. Sheared heels and the correla-tion to spontaneous quarter cracks. Equine Vet Educ 2011;23:262–269.

20. Buchner HHF. Distal limb internal dynamics: joint mo-ments, tendon forces, and lessons for orthopedic shoeing, inProceedings. Am Assoc Equine Pract 2005;51:134–148.

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localization of pain in the equine foot emphasizing the ... · even though many foot problems...

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