Equine Foot Surgery: A Joint Venture With the Farrier
Reprinted with permission from the American Association of Equine Practitioners. Originally printed in the 2010 AAEP Convention proceedings
Clifford M. Honnas, DVM, Diplomate ACVS; and Don Sustaire, CJF
Surgical invasion of the horny hoof capsule is oftenrequired to access lesions caused by infection, benigntumors, and penetrating injuries. Healing ofsurgical defects in the hoof wall or sole is oftenprotracted and necessitates some form of protectionduring the postoperative period to improve patientcomfort and to decrease environmental contaminationof the surgical site. Many of these surgicalconditions require a team approach between the veterinarianand the farrier to achieve optimal results.This paper will discuss a variety of foot conditionsfor which surgery is required to attempt resolutionand will also discuss farriery as an important componentof postoperative care.
2. Sequestrum Removal From the Distal Phalanx
The formation of a bone sequestrum involving thedistal phalanx generally occurs as a consequence ofthe introduction of environmental pathogens intothe soft tissues of the foot. Routine, long-standingfoot abscesses that fail to drain to the exterior of thehoof may on occasion result in the septic processsecondarily invading the adjacent bone. As the infectionbecomes established in the adjacent portionof the distal phalanx, the bone may lose its bloodsupply, resulting in development of a sequestrum.1Similarly, foreign bodies that penetrate the sole mayimpact the distal phalanx, causing a focal loss ofblood supply and formation of a sequestrum. Inaddition, blood supply alterations associated withlaminitis may result in sequestrum formation.1
The clinical signs that alert a practitioner or farrierto the possibility of a distal phalanx sequestruminclude a history of chronic lameness, recurrent purulentdrainage from the sole, and the presence of adraining tract that leads to bone. Radiographic evidenceof osteolysis or sequestration of a bone segmentis definitive for this condition (Fig.1). Occasionally, a sequestrum is not identified,but rather osteolysis that is evidenced by loss ofnormal bone density. Either of these radiographicpresentations (osteolysis or sequestrum) is evidencethat surgery is indicated. The infection generallyaffects the soft tissues of the sole, laminae, and hoofwall as well as the distal phalanx.1
Treatment is aimed at surgical debridement of theaffected bone and surrounding soft tissues. Thegoals of surgery are to provide drainage of purulentexudates, debride infected soft tissue, and removedevitalized bone.
Surgery can be performed with the horse anesthetizedor standing. The senior author typically debridesthe distal phalanx with the horse standing and sedated with the foot blocked. A tourniquetapplied around the fetlock to compress the digitalvessels against the proximal sesamoid bones willgreatly facilitate visualization during surgery (Fig.2). The cornified sole surrounding the drainingtract can be removed with a hoof knife, motorizedburr, or, in some instances, a scalpel.1 Currently,the senior author prefers to use a Forstner drill bitaon a cordless drill for penetration of the sole or walloverlying the sequestrum. This drill bit has asmall center point for starting the hole and drills aflat bottom hole (Fig. 3). It allows penetration ofthe wall or sole without drilling into the sensitivelaminae. Once the sole or wall has been penetrated,the laminae between the cornified sole anddistal phalanx is removed by sharp dissection with ascalpel or sharp curette and the draining tract followedto bone. Infected bone is softer than normalbone, which is removed with a large basket spoon curette. The soft tissue and bone are curetted tohealthy margins (Fig. 4).1
Postoperative care involves packing the surgicalsite loosely with sponges and bandaging the foot. A simple but effective bandage is made by placing ababy diaper on the bottom of the foot and securing itaround the pastern with the self-stick tabs. Thediaper is covered with cohesive tape,b and the cohesivetape is covered with strips of duct tape to preventthe bandage from wearing through to exposethe sole. This type of bandage will generally last2-3 days or more in stalled horses.1
The surgical site is inspected at 24- to 48-h intervals,and any questionable tissue is debrided. Systemicantibiotics are indicated in many cases;however, many horses recover without antibiotics.Non-steroidal anti-inflammatories (e.g., phenylbutazone,2.2-4.4 mg/kg, q 12 h) are indicated to minimizeinflammation and encourage weight bearing.1Application of a treatment plate either preoperativelyor postoperatively is helpful to improve patientcomfort and to simplify postoperative care (Fig.5). In most cases, healing is usually complete in8-12 wk. Once the sole has cornified, use of the treatment plate can be discontinued and a regularshoe applied.
Affected horses have an excellent prognosis forreturn to athletic function unless laminitis is theunderlying cause of the distal phalangeal infection.1
A keratoma is a benign, keratin-containing soft tissuemass that develops between the hoof wall anddistal phalanx.2 The occurrence of a keratoma atthe sole has also been reported; however, this locationis uncommon.3 The etiology of keratoma formationis unknown but may be a response to chronicirritation.2
The clinical signs are those of a progressively developinglameness that becomes more pronouncedas the keratoma gradually enlarges and createspressure between the hoof wall and distal phalanx.The lameness may be intermittent. As the keratomaenlarges, disruption of the external hoof architecturemay become apparent as evidenced by abulge in the hoof wall or inward deviation of whiteline.1
The diagnosis is definitively confirmed when radiographyof the foot shows a semicircular or circularradiolucent defect at the margin of the distal phalanx.This radiographic lesion is the result of theexpanding keratoma causing focal bone resorption.The bone margin surrounding keratoma is smoothand not sclerotic, which differentriates a keratomafrom infection.1
Surgery is indicated when the lameness is confirmedto originate in the foot with diagnostic blocks,and the characteristic radiographic lesion is identified.The keratoma is approached by resecting thehoof capsule overlying the mass. The most difficultaspect of surgery is targeting the precise location toenter the hoof wall if deformities in the hoof wall donot delineate the location. This is best accomplishedby taping radiopaque markers to the hoofwall and obtaining sequential radiographs to ascertainthe location. A cordless drill and Forstner bitare used to remove the hoof wall overlying the keratoma.This method is less invasive than the hoofwall resection technique previously used, and bothpreserve the stability of the hoof wall during theconvalescent period.1
Surgery can be performed in the anesthetizedhorse or standing using local anesthesia. The seniorauthor prefers the standing approach for mosthorses unless their temperament precludes thischoice. Again, a tourniquet at the level of the fetlockis used to reduce hemorrhage and aidvisualization.1
Postoperatively, a foot bandage is applied andchanged at 3- to 4-day intervals until the surgicaldefect in the hoof wall has cornified. Once granulationtissue has covered the exposed bone, astringentssuch as merthiolate (thiamersol) or iodine (2-7%) are applied to dry the tissue and enhancecornification. Phenylbutazone is administered as needed in the postoperative period. Antibiotics aregenerally unnecessary because infection does nottypically accompany the keratoma.1
The prognosis for resolution of lameness and returnto intended use is excellent. The hoof wallentry site usually grows down in 6-12 mo, resultingin a normal-appearing foot.1
4. Necrosis of the Collateral Cartilage
Infection and necrosis of a collateral cartilage can beseen as a sequelae to lacerations, foot abscesses,puncture wounds, gravel (chronic ascending infectionunder hoof wall), hoof cracks, and blunt trauma(over reach injuries, kicking inanimate objects), resultingin avascular necrosis.1
Affected horses become lame as abscesses formwithin the cartilage. The lameness is often intermittent,ranging from mild when the abscesses aredraining to the exterior to severe when the drainingtracts seal for a period of time. As the infectionbecomes established, marked soft tissue swellingover the affected cartilage becomes apparent. Purulentdrainage from the cartilage may or may notbe present at the initial examination, depending onthe patency of the draining tract.1
The diagnosis is made by observation of drainingtracts proximal to the coronary band over the affectedcartilage, or in some cases, marked swelling ofthe cartilage accompanied by severe lameness withoutaccompanying drainage. Radiographs obtainedwith a flexible metal probe in the tract or afterinfusion of contrast media into the tract will helpdetermine the depth of the tract and confirm involvementof the cartilage. Importantly, if the abscesseswithin the cartilage are draining atpresentation, the horse may not be very lame. Thisshould not delay surgery because lameness will recurwhen the draining tracts seal again. Becausethe cartilage is relatively avascular, antibiotics andinfusion of caustic agents into the draining tractsare usually ineffective in resolving the infection.1Colonizing the draining tracts with medical grademaggotsc (maggot debridement therapy) is onetreatment option that may have merit. The idea isthat the maggots will eat necrotic tissue and therebypreclude the necessity of surgery if successful.The authors do not have any personal experiencewith this treatment option.
Surgery is indicated based on the presence of aswollen cartilage with draining tracts. Severeswelling accompanied by severe lameness in the absenceof drainage would warrant an ultrasoundevaluation of the cartilage and consideration of surgicalexploration. Treatment is aimed at excisionof the affected portions of cartilage and overlyingsoft tissue and establishing ventral drainage. Thesurgery is accomplished with the horse in lateralrecumbency. As with other foot procedures, a tourniquetis applied at the level of the fetlock to enhancevisualization during surgery. In addition,regional perfusion of the distal limb with antibiotics can be performed while the tourniquet is in place.Only the infected portions of the collateral cartilageneed to be excised. During the surgical procedure,the foot is extended in an attempt to tense the palmarpouch of the distal interphalangeal joint andretract it from the deeper areas of dissection. Thesenior author prefers to access the proximal portionof cartilage above the coronary band through acurved incision based proximally. This techniquepreserves skin for primary closure and allows easieraccess to portions of the cartilage that will be accessedthrough the hoof wall later in the procedure.The skin flap is reflected proximally, and all accessiblediseased proximal cartilage is removed. Diseasedcartilage beneath and distal to coronary bandis accessed and removed through a hole drilled inthe hoof wall. The tissue and cartilage between thetrephine hole and proximal incision is removed bysharp dissection to allow ventral drainage. If thediseased tissue extends axially toward the joint, theintegrity of the joint can be assessed via arthrocentesisand distention of distal interphalangeal joint ata site remote from the surgical incision. At thecompletion of surgery, the skin incision is sutured,and the trephine hole is packed loosely with gauzesponges. The foot is bandaged until the skin incisionis healed and the hole in the hoof wall is cornified.Systemic antibiotics are generally indicatedfor 7-10 days. Additionally, regional perfusion ofthe distal limb should be considered in cases wherediseased tissue extends down to the region of thedistal interphalangeal joint in a location that wouldrisk penetration of the joint capsule with overzealousdebridement.1
Considerations for the farrier include patching thehoof wall once the surgical entry site has cornifiedcompletely. Care should be taken to ensure thepatch does not provide an environment to trap bacteriaand induce the development of an abscess beneaththe repair.
The prognosis is good after complete resection ofthe diseased cartilage and soft tissue. Incompleteresection, however, may be complicated by recurrenceof clinical signs and necessitate re-operation.1
5. Hoof Wall Resection
Indications for removal of hoof wall are commonlyencountered in equine practice and can be accomplishedin several ways. Currently, the most commoncondition where hoof wall removal is indicatedas part of the therapy is the structural damage andseparation at the stratum medium and stratum lamellatum,commonly known as "white line disease." 1 The term "white line disease" is amisnomer because the white line is anatomicallydefined as the junction of the hoof wall and sole.However, "white line disease" is the most commonterm used to describe the separation of hoof wallproximal to the white line. White line diseaseseems to be a progressive deterioration of the attachmentof the hoof wall that appears to be the result of keratolytic agents that have yet to be definitivelyidentified (Fig. 6).1 This loss of attachment canoccur in hooves that appear healthy on the surfaceand have no known injury or disease. It is notuncommon for an outwardly appearing normal hoofwall to have a significant amount of hoof wall unattached.This occurrence led to the early descriptionsof "hollow hoof."1 Farriers often recognize theoccurrence of unattached wall before significantdamage has been done. These early cases are easilytreated with removal of the diseased tissue andapplication of an astringent/antiseptic. If, however,the hoof wall separation is extensive, removalof the affected and undermined hoof wall is the mosteffective way to resolve the condition. It is commonfor the hoof wall to grow back completely normal andwell attached. Hoof wall removal can also be useful in dealing with extensively infected and unstablehoof cracks. Removal of the diseased and underminedhoof wall can allow better resolution of theinfection and facilitate treatment of the underlyingsensitive tissues.1
There have been numerous methods described forremoval of hoof wall with each having their applicationand respective advantages and disadvantages.Probably the most widely used method involves theuse of a motorized tool, such as a dremel and tungstencarbide bits to remove the hoof wall or create agroove to separate diseased from normal hoof wall.1
The advantage of using a motorized burr is that itallows controlled and precise removal of tissue.The biggest disadvantage is that it can be quite slowwhen removal of large areas of hoof is necessary.If removal of large amounts of hoof wall is indicated, a pair of half round nippers from GE Forge can beused to do the "rough" work, and the more precise"edges" can be touched up with the motorized burr.1
Therapeutic shoeing is usually indicated to providestability to the foot and reduce pain. Aftersubstantial hoof wall resection, instability of thedistal phalanx may ensue, resulting in ventral rotationof the bone. This is best managed by applicationof a heart bar shoe or other appliance to attemptstabilization of the distal phalanx. After hoof wallis removed, depending on the extent of the resection,it is usually indicated to keep the hoof wall bandageduntil the exposed tissue is adequately cornifiedand lameness has resolved. After the tissuesare adequately cornified and firm to the touch, applicationof a composite reconstruction may be consideredif needed.1
Something that has proven useful in the treatmentof hooves after removing the hoof wall is theuse of a sugar and betadine paste. The hypertonicitycombined with the antiseptic povidone-iodinedoes a nice job of drying out the underlying tissueswithout the use of more harsh astringents. Afterthe tissues have shrunk and dried, the bandages canbe removed, and either iodine or thiamersol can beused to further harden the cornifying tissues.1
6. Subsolar Abscesses
Subsolar abscesses are probably the most frequentcondition affecting the foot of the horse for whichinvasion of the hoof capsule is required. Affectedhorses often present with a severe lameness, and thehorse owner is often concerned that the horse has afracture or other malady resulting in the presentinglameness.1 An increase in the strength of the digitalpulse will be palpable as a result of the inflammationwithin the foot. Hoof tester examinationmay identify a focal area of sensitivity (such as overa nail hole); however, most commonly the pain identifiedis generalized over much of the sole. Perineuralanesthesia of the palmar digital nerves justproximal to the collateral cartilages will often resolvethe majority of the lameness; however, on occasion,anesthesia of these nerves at the level of theproximal sesamoid bones is necessary, particularlywhen the abscess is in the toe region.1 Occasionally,the pain from the abscess is not overcome by desensitizing(blocking) the foot, further confounding thediagnosis.
Careful examination of the bottom of the foot willoften allow identification of a tract or crack that willlead to the abscess. Often paring of the sole with ahoof knife is necessary to identify black areas thatmay lead to the abscess. When a crack or blackarea is identified, careful exploration is necessary toidentify if the abscess is beneath that area. A smalllooped hoof knife or a #2 curette is useful to explorethese areas that may potentially lead to the abscess.The crack or black area is followed by removing asmall amount of hoof material until the crack orblack area disappears or until the abscess is openedup. Often, a grayish-colored fluid will escape orooze from the abscess entry site once the abscess ispenetrated. The authors prefer to make justenough of an entry site that will allow the fluid todrain from the abscess cavity. A large hole is generallyunnecessary; however, small holes can plugand result in recurrence of clinical signs. Largeabscesses with significant undermining of the solemay need to be debrided more aggressively.1
Aftercare is routine and involves placing the footin a bandage to keep dirt and debris from pluggingthe drainage hole.
Surgery of the equine foot is often perceived to bequite difficult because of the hoof capsule. Knowledgeof the specific disease entities that require surgicalintervention and an in-depth understanding ofthe anatomy of the tissues beneath the hoof capsuleis a prerequisite to successful surgical treatment.A close working relationship between the veterinarianand farrier needs to be established to produceoptimal results.
References and Footnotes