Virginia Therapeutic Farriery

An In-Depth Look at Puncture Wounds to the Foot

Reprinted with permission from the American Association of Equine Practitioners. Originally printed in the 2010 AAEP Convention proceedings

W. Rich Redding, DVM, MS, Diplomate ACVS
Author's address: College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina 27606; e-mail: rich_redding@ncsu.edu. © 2010 AAEP.

1. Introduction

The horny hoof capsule of the foot is typically resistantto wounding, but under the right circumstances,sharp objects can penetrate the sole andfrog. The skin above the coronary band, however,is commonly involved in entrapment wounds, lacerations,and puncture wounds of the distal limb.Wounds to the solar surface of the foot most oftenoccur when the horse steps on a sharp object(s), suchas a nail. Puncture wounds have been classifiedaccording to the depth of penetration (superficialand deep) and location on the foot.1-3 Superficialwounds penetrate only the cornified tissue, whereasdeep wounds penetrate the germinal epithelium.However, wounds to the sole need only to penetrate1 cm to invade germinal epithelium, whereaswounds of the frog may need only 1.5 cm to invadevital structures. Fortunately, the most commonwound is a superficial wound of the solar surface ofthe foot. Deep wounds are much more serious andseparated into three types based on location. TypeI wounds penetrate to the sole and may damage thedistal phalanx (P3), whereas Type II wounds penetratethe frog and heel and can involve the deepdigital flexor tendon (DDFT), distal sesamoidean imparligament (DSIL), navicular bursa (NB), distalinterphalangeal joint (DIPJ), digital flexor tendon sheath (DFTS), and digital cushion (DC). Type IIIinjuries penetrate the coronary band and may causeseptic osteitis of P3, septic chondritis of the collateralcartilages of P3, or septic arthritis of the DIPJ.Because deep wounds have an increased risk forserious consequences, the need for early identificationof structural involvement and the institution ofaggressive medical treatment and early surgical interventioncannot be overemphasized. Assumingthat the wound is superficial may promote a delay inthe institution of the most appropriate treatmentand may be the difference between humane destructionand return to soundness. This paper will discussthe varied clinical presentation, diagnosticwork-up, and treatment options of puncture woundsto the foot.

2. Clinical Presentation and Diagnosis

Puncture wounds, whether superficial or deep, canfrequently create marked lameness. The degree oflameness may vary considerably depending on thedepth, location, and duration of the wound. Superficialwounds may have minimal lameness initiallybut become more severe several days later with thedevelopment of abscessation. In general, puncturewounds that invade the corium become quite painfulsoon after wounding. Progression to severe nonweight-bearing lameness occurs as the rigid hornyhoof capsule restricts the swelling associated withinflammatory response. Wounds that involvedeeper structures such as P3 or any of the synovialstructures such as the NB, DIP, DFTS, and/or theDDFT often become rapidly symptomatic. Unfortunately,the depth that these objects penetrate pastthe horny hoof capsule can be difficult to ascertain,and the severity of the clinical signs do little to helpdefine the structures that are involved. Recognizingwhen the wound occurred and where the woundis located can assist the clinician to choose the mostappropriate diagnostic and treatment strategy.A detailed history combined with a careful clinicalexamination is critical to direct the use of diagnosticimaging (radiography and ultrasonography) and assessthe need for clinical pathological analysis ofjoint/bursa/sheath fluid (should the potential for synovialsepsis exists). Magnetic resonance (MR)may be necessary to more accurately determine theextent of the injury.4

Fig. 1. Nail foreign body has penetrated the frog of this horse. A complete radiographic study of the foot with the nail in place is critical to determine depth and direction of penetration and give an indication as to what structures might be involved.

Many horses point the affected limb and preferentiallyload the unaffected area(s) of the foot whenwalking. Increased digital pulses are common, andin some cases, the digital pulse may be increasedonly on the affected side. Increased heat may bepalpable at the coronary band and/or over the hoofcapsule in the affected limb. With chronicity, theremay be swelling of the pastern, and a non-septiceffusion within the digital flexor sheath can developbecause of a sympathetic flare associated with theinflammatory response within the foot. Hoof-testerapplication, early after wounding, may reveal pinpointsensitivity, but over time, a painful reactionmay be elicited over the entire sole region. Visualinspection of the foot will often reveal the source ofthe lameness and should begin by cleaning of thehoof wall, sole, and frog. If the offending objectremains in the foot (especially radio-opaque material),an attempt to obtain a set of radiographs canallow the clinician to measure the depth of penetrationand evaluate which structures may be involved(Fig. 1). Paring the sole with a hoof knife or raspingthe hoof wall may reveal the puncture wound ora black tract or crack in the solar surface. Afterthe surface of the foot is cleaned and the wound isidentified, a sterile preparation of the foot with anantiseptic detergent and alcohol rinse should be performed.This will allow further exploration of thewound without fear of contaminating the surroundingnormal tissue. Probing of the wound with asterile probe or teat canula can be helpful to determinethe depth and direction of the wound. Radiographstaken with the probe/canula in place canmore accurately assess depth and direction and thestructures affected. When an obvious crack orblack tract is found, then exploration may lead to anabscess. A small looped hoof knife or a bone curette(#2) is useful to explore these areas and establishdrainage. Locating the entry site of wounds to thefrog may prove difficult, because the elastic tissues of the frog tend to close over the wound. Aftercleaning the foot, if a wound is not apparent, thenhoof testers should be applied in a methodical mannerto find point sensitivity suggestive of the puncturesite. Sharp debridement of the wound isnecessary to remove necrotic tissue as well as anyforeign material that is present in the wound. Thedepth of the sharp dissection is determined by theappearance of the tract and is guided by placementof a sterile probe.

Radiography is indicated in all cases to identifythe presence of concurrent bony involvement such asfractures, osteitis, and later sequestrum formation.Gas shadows, debris, and radio-opaque foreign bodiesmay be seen, and this may indicate the depth anddirection of the puncture. More advanced radiographicdiagnostic techniques such as contrastfistulography or contrast arthrography may be necessaryto evaluate a poorly defined wound and tomore carefully assess the specific structures (especiallysynovial) that may be involved. The techniqueand indications for these procedures will bediscussed later in the paper. Osteitis and sequestrumformation may take weeks to manifest radiographically,and therefore, follow-up radiographs may be indicated if the wound is not healing appropriately.Diagnostic ultrasonography has alsoproven particularly helpful to define the extent ofdamage incurred during wounding, either from apuncture or laceration of the distal limb. Use ofdiagnostic ultrasound can be helpful to assesswounds to the foot but is limited to windows providedby the skin at the coronary and softer tissue ofthe frog. Given this limitation, diagnostic ultrasoundhas been helpful to identify tendon damageand synovial distention as well as assess the characterof the synovial fluid of the DIPJ, NB, andDFTS. An increase in cellularity and fibrin contentin the synovial fluid increases its echogenicity.The presence of gas shadows suggests either an openjoint space or the presence of gas-producing organismsin the joint fluid. In addition, shadowing artifactsmay be visible ultrasonographically, which issuggestive of foreign material such as wood splinterscommonly seen in coronary-band wounds. The specificuse of diagnostic ultrasound will be discussedwhere appropriate later in the paper.

Clinical pathological evaluation of the synovialfluid of the NB, DIPJ, and/or DFTS is often necessaryto confirm synovial sepsis. With the needle inposition in the joint, it can be beneficial to injectsterile balanced electrolyte solution in a volume significantto generate substantial fluid pressurewithin the joint. A positive fluid-pressure studyevidenced by visualizing fluid escaping from thewound is strongly suggestive that the integrity ofthe synovial capsule has been compromised. Thesynovial structure(s) should be considered contaminatedand potentially septic. Early diagnosis andaggressive treatment are critical to effectively treatwounds that invade the NB, DIPJ, DFTS, andDDFT, and therefore, it warrants these diagnosticprocedures. Wounds to the coronary band are managedsimilarly with joint-fluid recovery and a fluidpressurestudy performed on the DIPJ (if the woundis dorsal) and DFTS (if the wound is palmar/plantar),and they should be carefully assessed for aforeign body, particularly wood splinters. Reconstructionof these wounds should be attemptedwhere possible.

Penetrating objects are commonly contaminatedwith dirt, rust, and manure. This material isdriven deep into the wound. The superficial aspectof the wound frequently seals quickly. Without adequatedrainage, an anaerobic environment developsand can promote the growth of anaerobicbacteria. Abscessation formation is common andwill require drainage. Although this abscessationcan easily be drained, one organism of particularconcern that can be deposited in the tissue is Clostridiumtetani, which causes tetanus. This diseaseis not often treated successfully, and therefore, it isbetter prevented by vaccination. Adequate protectioncan be achieved by vaccination with tetanustoxoid; however, a booster of toxoid should be givenin the event of a puncture wound to the foot. Unvaccinated horses should receive both a tetanus toxoidand a tetanus antitoxin as soon after woundingas possible.

Farriers may be asked to deal with puncturewounds to the foot. Superficial wounds carry agood prognosis and can have dramatic resolution oflameness within 24-48 h, whereas deeper woundsrequire surgical debridement. Superficial woundsand infections are effectively treated by establishingdrainage, soaking the foot in an Epsom-salt solution,poulticing the foot until drainage has ceased, andprotecting the foot until the hoof-capsule defect hashealed. Because of the serious complications thatcan occur with the deeper wounds mentioned earlierin this paper, it is this author's opinion that a veterinarianshould be involved when dermal tissuehas been affected and debridement of this tissue isnecessary. Any delay in the initiation of the appropriatetreatment can have serious consequences.Debridement may be painful and necessitates theuse of diagnostic analgesia at the level of the palmardigital or abaxial sesamoid nerves. In addition, theprocedure may cause hemorrhage, which can beminimized when a tourniquet is applied. Regionalperfusions are becoming more frequently used toincrease the concentration of antibiotics in the foot,and they require a veterinarian to perform. Medicationssuch as antibiotics and anti-inflammatorydrugs may be indicated and will need a veterinarian'sprescription. If a farrier were to treat an establishedinfection in the hoof, it could be perceivedas practicing veterinary medicine, and the farriercould be held liable

Fig. 2. (A) Radiographic appearance of septic pedal osteitis. (B) Septic pedal osteitis with sequestra formation.

3. Septic Pedal Osteitis and Sequestrum

Puncture wounds to the sole of the foot can introducebacteria and debris to the solar surface of theP3 and frequently produce a septic pedal osteitis.Septic pedal osteitis involves bone lysis of P3 andoften has the presence of purulent exudate (whichdifferentiates this condition from non-septic pedalosteitis).5 In addition, chronic soft-tissue infection(e.g., subsolar abscess from a previous puncture) canalso extend into the bone. Septic pedal osteitis canalso occur as a sequela of chronic laminitis. Theconcurrent presence of periosteal trauma, bacterialcontaminations, and poor vascularity of fracturefragments result in an increased incidence of sequestrumformation and osteitis in P3.

Clinical examination is similar to other puncturewounds and frequently reveals a draining tract thatleads to P3. Occasionally, a horse that is on systemicantibiotics and anti-inflammatories will notmanifest significant lameness and drainage untilthe medications/antibiotics are discontinued. However,radiographs should show the affected area todetermine the presence of an osteitis and/or sequestrum(Fig. 2). If necessary, a fistulogram can beperformed to evaluate the tract for a foreign bodyand/or to assess the amount of undermined sole. A venogram may be performed to assess blood flowto the affected area.

Surgical drainage and debridement of the infectedbone and necrotic soft tissue is necessary for thewound to heal. Wounds to the sole can be safelyexplored and debrided with the horse standing.The horse should be placed on systemic antibioticsand anti-inflammatories before surgery. An area ofsole 1-2 cm in diameter should be removed aroundthe puncture site so that the tract can be completelyexplored, unless radiographs suggest that the osteitis/sequestrum is determined to be larger. Thesurgical approach should follow the draining tract (ifpresent) and allow adequate exposure of all affectedtissue for the removal and effective ventral drainageof exudate. Complete resection of the drainingtract is important. If there is no draining tract,then a radiograph with radio-opaque markers can be placed on the sole, and a radiograph can be taken tomap out the approach to the affected bone. A tourniquetplaced at the fetlock and proximal sesamoidbones should be used to minimize bleeding and allowthe surgeon to distinguish between normal and abnormaltissue. A regional perfusion with antibioticscan also be performed after tourniquet placementand before beginning surgery. Wounds that penetratethe solar corium should have the affected coriumremoved by sharp dissection. Abnormal boneshould be removed by curettage. Culture of theinfected bone should determine the appropriate antibiotictherapy, although a mixed growth of severalbacterial species can be expected. Removal of allinfected/affected material is important for resolutionof the drainage.

After surgery, a sterile bandage is maintainedduring recovery and changed daily to effectivelyremove excess drainage. Daily inspection of thesurgery site is helpful to determine if further debridementis necessary. After 5-7 days, a treatmentplate may be placed on the foot to assist indaily bandage changes. Maggot debridement is anon-traumatic, minimally invasive method to removenecrotic tissue from an extensive foot infection.This therapy is often used in conjunction withand after light surgical debridement. Maggot therapydecreases healing time in postsurgical coffinbonedebridements and is useful in treating chronic,reoccurring non-healing foot ulcers, canker, quittor(necrosis of collateral cartilage), chronic soft-tissueabscess, and osteomyelitis.6

The prognosis for soundness depends on the causeof the infection, its duration, and the adequacy ofsurgical debridement. One report evaluated thatup to 25% of the coffin bone can be removed andpotentially become sound.7

Fig. 3. A sterile probe has been placed in a puncture wound of the frog and shows that the wound is not deep enough to involve the NB, DIPJ, or DFTS.
Fig. 4. Contrast fistulogram of a puncture wound to the dorsal hoof wall, which shows that the wound extends to the laminar corium.
Fig. 5. Contrast arthrogram of a normal DIPJ in a horse with a puncture wound to the frog. There is no contrast material leaking from the joint. This is an indication that the original puncture wound did not penetrate the DIPJ, but joint-fluid analysis is still indicated.

4. Penetrating Injuries to the Navicular Area

Penetrating injuries to the frog can extend to theDDFT and depending on the direction, can extendinto the NB, DIPJ, and/or DFTS. These injuriesare considered potentially career-ending and evenlife-threatening, because sepsis within any of thesesynovial structures carries a guarded to poor prognosis.Sepsis of any synovial structure requires immediateand aggressive treatment. Therefore,because wounds to this area have the potential toinvolve these synovial structures, careful evaluationfor synovial involvement is warranted. If a radioopaqueforeign body is still in place, survey radiographsmay help determine the depth ofpenetration. A complete set of survey radiographsis necessary to evaluate the depth and direction ofthe foreign body as well as the involvement of thesoft tissues and bones of the foot (see previous discussion).At least two radiographs taken in orthogonalplanes with the probe in place are necessary todefine the correct depth and direction of the penetration.If the object has been removed before examination,then careful scrutiny of the foot may reveal the puncture site. A sterile metal probe canbe used to evaluate the course and extent of thewound (Fig. 3). Contrast fistulography and contrastarthrography/bursagraphy are radiographictechniques that can be used to further define thewounds' involvement with the DDF and the synovialstructures. Contrast fistulography is useful to assessthe depth and direction of the tract by placing acatheter into the wound and injecting contrast materialunder pressure. The path that the contrasttravels typically follows the path of the puncturewound (Fig. 4). Contrast arthrography/bursagraphyis performed by injecting contrast materialinto the DIPJ, NB, or DFTS independently to showsynovial-membrane integrity (Fig. 5). If the woundhas breached one of these synovial structures, thecontrast material may be seen to leak from the synovialspace into the subcutaneous tissues and thetract.

Diagnostic ultrasound can be useful in assessingwounds that involve the frog. Careful evaluationwith the probe on the frog may show gas shadowspresent in the soft tissues of the foot, NB, or coffinjoint and should be considered confirmation of penetrationand probable contamination. Diagnosticultrasound can also be used in conjunction withprobe or needle placement, because a metal contentfrom each creates a shadowing artifact that can bevisualized and followed in real time to determine theinvolvement of key structures. In addition, sequentialultrasonographic examinations may beused to assess the response to therapy as evidencedby changes seen in the character and quantity of thesynovial fluid. Placement of a closed-suction drainat the distal-most extent of the sheath may be assistedby the use of ultrasound. This is particularlyimportant to evaluate the effectiveness of a closedsuctionapparatus in collecting the accumulatingfluid formed within the DFTS.

Aseptic collection of a joint-fluid sample at a siteremote from the wound is recommended in all cases.An increase in total cell count (>30-40,000 cells/µl)with a predominance of neutrophils and an elevatedtotal protein concentration (≥3 g/dl) are good indicatorsof sepsis. Gram staining of the joint fluidmay show free bacteria in the joint fluid. The fluidshould be submitted for bacterial culture and antibioticsensitivity testing. Samples of synovial fluidfrom the coffin joint, DFTS, and NB should be obtained.Even if one or more of these structures iscontaminated, the prognosis is improved by earlydiagnosis and immediate and aggressive medicaland surgical therapy.

Medical therapy includes broad-spectrum systemicantibiotics, appropriate surgical debridement (both endoscopicallyand of the wound), copious lavage of thesynovial structure, regional perfusion of antibiotics,and intra-articular antimicrobial medication.

The diagnostic findings dictate which surgicalprocedure is performed. With wounds involving the frog that are not thought to involve a synovialstructure, the cornified tissue overlying the puncturesite should be removed, and the tract should beexplored to its limit. A probe or the injection of newmethylene blue dye into the tract can be used toguide dissection. Wounds thought to involve any ofthe synovial structures of the foot should be approachedendoscopically for debridement and lavage.This procedure must be performed undergeneral anesthesia. At the same time, regionalperfusion with an appropriate antibiotic can be performed.Endoscopic examination of these synovialstructures has been described elsewhere.8 In additionto endoscopic debridement and lavage, the siteof wounding is debrided by sharp dissection, and alldevitalized tissue is resected. After completion ofthe procedure, an antibiotic is injected into the affectedsynovial structure.

Fig. 6. Streetnail procedure has been performed on this horse, and the window through the frog to the DDFT can be seen.

In years past, infections of the NB have beenmanaged by a procedure termed a “streetnail” surgery.This procedure involves creating a funnelshapedwindow in the frog with a layer by layerdissection through the DC to expose the DDFT.In the process, all devitalized tissue around thepuncture wound is debrided (Fig. 6). If the puncturewound seems to continue through the DDFT,then a longitudinal incision that separates the tendonfibers is made in the DDFT to allow exposure tothe NB. Any portion of the tendon that appearsnecrotic or devitalized is resected. The NB isopened and lavaged. Careful placement of the windowthrough the DDFT over the flexor cortex of the navicular bone is critical to avoid entering the coffinjoint distal to the navicular bone (through the imparligament) and the palmar/plantar pouch of the coffinjoint or the DFTS proximal to the navicular bone.The flexor tendon sheath and coffin joint should bedistended to determine if there has been inadvertentpenetration of either structure.

Postoperative care is a very critical aspect of thisstreetnail procedure. Lavage of the bursa/joint/sheath and both regional perfusion and intra-articular/intrathecal antibiotics should be performeddaily for 3 days and then every other day for 3 daysuntil clinical improvement is seen. The surgicalwounds and the dissected frog wound should bemaintained under a sterile bandage and changeddaily until the discharge begins to diminish. Convalescenceafter the streetnail procedure is muchlonger than for horses treated using endoscopic lavageof the NB. The streetnail wound will takesubstantially longer to fill in and will require muchmore frequent and intense postoperative care. Forthose horses that require a streetnail procedure, acancellous bone graft can be packed into the woundto promote the obliteration of dead space, preventascending contamination, and provide a scaffoldinginto which cells can migrate during wound healing.

Fig. 7. Needle placement into the bursa for aspiration of fluid for culture and sensitivity as well as for a through and through lavage.

When financial constraints limit more involvedtherapy, transcutaneous lavage of the NB, with ingress/egress of fluid and antibiotic through an 18-gauge, 3.5-in spinal needle, can be attempted (Fig. 7). However, it is important to impress on the clientthat this procedure is likely to be effective onlyin early cases with minimal contamination, andeven then, the success rate is much lower than forsurgical exploration and lavage.

In an early report, horses with NB sepsis treatedwith appropriate surgical debridement within 4days after injury had a reasonably good prognosis.Another author has reported good success with arthroscopicexploration of the NB in lieu of the moreaggressive streetnail procedure. Cases involving ahindlimb are more likely to return to previous activitiesthan those involving a forelimb. When theDDFT is involved, the prognosis is more guarded.The most common and serious mistake made in themanagement of these cases is the initial use of aconservative approach.

5. Lacerations and Penetrating Injuries That Involve the DIPJ

Septic processes involving the DIPJ usually resultfrom traumatic injuries to the foot, most often alaceration that involves the dorsal aspect of the coronaryband. Puncture wounds to the frog can penetratethe DDFT, NB, and DIPJ, creating a septicbursa and joint. Diagnosis and treatment of synovialsepsis was discussed in the previous section onpenetrating injuries to the navicular area. The differencesin diagnosis and management of a lacerationthat involves the DIPJ will be discussed here.

An accurate history should be obtained to determinethe time lapse since the injury, any knowledgeof the wounding incident (for example, what causedthe wound), the amount and character of drainagefrom the wound, and the degree of lameness that thehorse has manifested since injury. Information about how the wound has been treated, particularlythe use of any medications, is extremely important.Lacerations that involve the DIPJ (and any joint, forthat matter) can be surprisingly comfortable if thejoint is draining and currently being treated withantibiotics and non-steroidal anti-inflammatories.Recognizing the location of the wound and the increasedrisk for damaging the joint capsule in thedorsal aspect of the foot should lead the clinician toperform diagnostic procedures that can confirm orrefute joint-capsule involvement.

Radiographic examination of lacerations of thecoronary band area with sepsis of the DIPJ mayshow evidence of joint-space widening because offluid accumulation and occasional gas shadows inthe joint space (suggesting that the joint is open orhas a gas-producing organism). However, this radiographicfinding can be inconsistent; particularly,if the joint is open, there is little accumulation offluid. In addition to fractures, osteochondral fragmentsor radio-opaque foreign material may be apparentin the joint, but more often, they are close tothe puncture/wound. Osteomyelitis may be evidentin chronic cases. Contrast arthrography mayhelp document joint involvement, although arthrocentesis,joint-fluid analysis, and a fluid-pressurestudy may be more useful than arthrography.

Diagnostic ultrasound can be useful to identifysynovial distention and assess the character of thesynovial fluid. Demonstration of a large fluidpocket can be quite useful for ultrasound guidance ofneedle placement into the pocket, increasing thechance of joint-fluid recovery. An increase in cellularityand fibrin content in the synovial fluid increasesits echogenicity. The presence of gasshadows suggests either an open joint space or thepresence of gas-producing organisms in the jointfluid. The puncture site/wound itself should beevaluated ultrasonographically to get an appreciationof the soft-tissue structures involved and if foreignmaterial is still present within the wound.Sterile preparation of the wound with the applicationof sterile lube into the wound will allow a morecomplete ultrasound examination of the woundedarea. A sterile sleeve/glove placed over the transducercan allow placement of the probe directly overand/or into the wound to more carefully examine thespecific structures that are involved. In addition,ultrasonographic diagnosis of periarticular involvementof tendon and ligament injury can significantlyaffect the prognosis.

While placing a needle for sample collection, it isadvisable to assess the integrity of the joint capsuleby injecting sterile balanced electrolyte solution(BES) into the joint. The fluid should be injectedunder pressure, and the wound should be assessedfor fluid leakage. Sometimes it is necessary to havethe horse walk a short distance to visualize fluidbeing expressed from the wound. Fluid seen exitingthe wound is evidence of capsular disruption.As discussed in the previous section, confirmation of joint contamination indicates the need for aggressivemedical and surgical therapy.

Arthroscopy has been reported for the treatmentof septic joints and has proven to be a very usefuladjunct in the treatment of joint sepsis by allowingvolume flushing of the joint and extensive debridementof the affected synovial membrane. Arthroscopyallows a more complete evaluation of the jointand extensive debridement of the affected synovialtissue, especially with motorized instrumentation.Osteochondral fragments and areas of osteomyelitisare more effectively managed with arthroscopictechniques. Arthroscopic techniques are describedin detail in a number of surgical texts. Arthrotomyincisions have been used in the past to treat contaminatedjoints but have proven inferior to arthroscopybecause of the limited visualization and ability todebride the joint. However, enlargement of the arthroscopyportals to make arthrotomy incisions maybe indicated in grossly contaminated wounds to allowconstant drainage of septic fluid but also toprovide easy placement of a teat canula or catheterfor volume flushing in the standing animal. Injoints with large-volume redundant joint capsule(necessary for a wide range of motion) like the DIPJ,placement of antibiotic impregnated polymethylmethacrylate(AI-PMMA) beads or cylinders may beused to increase the local delivery of antibiotics.

A recent report evaluated the use of endoscopiclavage in the treatment of septic joints, tendonsheaths, and bursae. Endoscopic portals and traumaticwounds were closed primarily after lavage.Follow-up information on the 118 patients revealeda 90% survival rate, with return to athletic functionin 81% of horses.9 In this population of cases, itwas the early institution of treatment that allowedthis protocol to be successful. This approach is unlikelyto be successful in horses with more chronicwounds that contain large amounts of fibrin andgross contamination.

Long-term survival in chronic cases of septic arthritisis considered poor (only around 40% in onestudy).10,11 Ankylosis can occasionally and may ultimatelyresult in pasture soundness. Use of cancellousbone grafts can help encourage ankylosis ifthat is the goal.

6. Infection of the Collateral Cartilages

Lacerations, punctures wounds, abscesses, and occasionally,hoof-wall cracks can involve the collateralcartilages of the foot. Wounds that involve thecollateral cartilage may cause cartilage necrosis,which may lead to chronic infection of the cartilage.Infection of the collateral cartilage(s) of the foot iscalled quittor and is most common in draft breeds.A chronic non-healing wound or abscessation withintermittent purulent discharge from the infectedcartilage is the usual clinical presentation. The diagnosisis based on the clinical signs of swelling anddrainage from the affected cartilage. The primarydifferential diagnosis is chronic foot abscess. However,the drainage site for quittor usually is abovethe coronary band, whereas most submural abscesses(gravel) drain from the coronary band.Lameness can be severe, especially when pressureincreases from the accumulation of purulent materialin the infected structures. As with foot abscesses,after drainage occurs, the lameness seemsto diminish.

The collateral cartilages have a poor blood supply,and therefore, healing of these tissues is slow.Furthermore, because most of the cartilage lieswithin the hoof capsule, it is difficult to establisheffective drainage. Thus, quittor is a surgical disease.The treatment of choice is surgical excision ofall infected tissue and establishment of adequateventral drainage in conjunction with broad-spectrumantimicrobials. The wound should be cultured,but it is likely to grow a mixed population ofbacteria. The surgeon can culture the infected cartilagewhen removed at surgery, which will give amore accurate culture and sensitivity.

A proximally based curved incision is made toaccess the infected cartilage. Meticulous dissectionis necessary, because the palmar pouch of the DIPJis located just axial to the collateral cartilages.Honnas et al.12 recommend placing the foot in tractionto place tension on the joint capsule, therebyretracting it away from the area of dissection.12Surgical dissection can also be assisted by injectingnew methylene blue into the draining tract to clearlyidentify the affected tissue. Complete removal ofall diseased cartilage may necessitate removal of aportion of the proximal hoof wall, which can be performedwith a Dremel tool or trephine, while takingcare to preserve the germinal tissue of the coronaryband.

After the dissection is complete, the DIPJ shouldbe distended with sterile BES, and the woundshould be assessed for fluid leakage that would indicateloss of integrity in the joint capsule. If theDIPJ capsule is breeched, then the prognosis is decreased,and the joint should be treated as if contaminated.If the joint capsule can be closed, thenan attempt should be made to do so. If closure isnot possible, the wound should be treated as an openarthrotomy, as described for septic arthritis. Theskin incision is closed primarily, if possible.

The prognosis is guarded, because it can be difficultto remove all of the infected tissue. The incisionis at risk of dehiscence, which can complicatethose cases where the coffin joint was invaded whileattempting to remove the affected tissue. If thecoffin joint is invaded, then treatment becomesmuch more aggressive and must address the principlespreviously discussed.

7. IV Regional Perfusion for Septic Processes in the Digit

Infection can be a serious complication in woundsinvolving the foot. Foot infections can be difficult totreat, because they often are polymicrobial; additionally, the organisms may be resistant to multiple commonlyused antibiotics, and the infected area may bepoorly vascularized (owing to its inherent structureand/or because swelling of the infected soft tissueswithin the rigid hoof capsule impedes vascular flow).Infection is enhanced in the presence of damaged tissue,hematoma formation, avascular bone, or foreignmaterial (including soil and fecal matter).

Sepsis, vascular compromise, and a drop in pH asa consequence of inflammation and ischemia mayprevent adequate delivery or activity of antibioticsin the infected tissue. Furthermore, vascular compromiseincreases the risk of sequestrum formation,which can promote bacterial proliferation.

IV regional perfusion (IVRP) involves the deliveryof an antibiotic to a selected region of the limbthrough the venous system. The infused volume isdelivered under pressure to ensure distribution ofthe fluid to all vascular spaces in the region distal tothe tourniquet. Retention of the antibiotic in thevenous space for several minutes allows diffusioninto surrounding tissues that may otherwise haveinadequate blood flow. During IVRP of the distallimb, it is possible to achieve antibiotic concentrationsin the tissues that are 25-50 times the minimuminhibitory concentration required to kill mostpathogenic bacteria.13 Thus, with this technique,it is possible to achieve therapeutic concentrations ofantibiotic, even in necrotic tissue.

Fig. 8. Placement of a tourniquet at the level of the sesamoid can be effective for surgery or regional perfusion of the digit.

8. Technique

Regional perfusion of the digit can be performed inthe standing horse.14 The skin over the medialor lateral digital vein is aseptically prepared. Acatheter is aseptically placed in the digital vein;most clinicians use a 20-gauge catheter placed in thelateral digital vein. A tourniquet or Esmarch'sbandage is applied to the fetlock (Fig. 8). An extensionset is attached to the catheter, and infusion isbegun. Ideally, the antibiotic chosen is determinedby culture and sensitivity results. Frequently,however, the results are not available when thefirst perfusion is performed. The clinician must,therefore, rely on clinical judgment and select anappropriate antibiotic based on the most likely organism(s) involved. The antibiotics most commonlyused for IVRP include amikacin (0.5-1.0 g),gentamicin (1 g), potassium penicillin (10 millionunits), timentin (1 g), and cephazolin (1-2 g). Regardlessof the antibiotic selected, the amount to bedelivered (e.g., 1 g amikacin) is diluted in 20 ml ofsterile BES. The antibiotic solution is infused over30-60 s, but the tourniquet is left in place for a totalof 20-30 min before it is removed.

IVRP can be performed as a single treatment orrepeated as often as necessary until clinical improvementis seen or the patency of the digital veins becomescompromised. The most common complicationwith IVRP is injury to the vasculature and soft tissues,either from catheterization or perivascular leakage ofthe solution and subsequent local reaction.

9. Intraosseous Infusion

Intraosseous regional perfusion is an alternative toIVRP. It has the advantage of avoiding the repeateduse of regional vessels. With this technique,the antibiotic solution is infused into the intraosseousspace. After aseptic skin preparation, local anesthesia,and a stab incision through the skin andperiosteum, a 4-mm diameter hole is drilled throughthe cortex of the bone adjacent to the septic process.An intraosseous infusion needle or the male adaptorof an IV extension set is wedged into the hole, andthe antibiotic solution is infused into the medullarycavity. Unfortunately, the bones of the digit can bedifficult to access for this procedure.

References

  1. Richardson GL, Pascoe LR, Meagher D. Puncture wounds of the foot in horses: diagnosis and treatment. Compend Cont Educ Pract Vet 1986;8:S379-S387.
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