artrite, tenosynovitis e infeçao

Vet Clin Equine 22 (2006) 363–388

Septic Arthritis, Tenosynovitis,and Infections of Hoof Structures

Joel Lugo, DVM, MS, Earl M. Gaughan, DVM*J.T. Vaughan Large Animal Hospital, Department of Clinical Sciences,

College of Veterinary Medicine, Auburn University, Auburn, AL 36849, USA

Infection of synovial compartments and the structures within a horse’sfoot can be devastating to soundness, athletic careers, and even life for af-fected animals. Joint and tendon sheath sepsis disrupts normal function inthe short term because of associated pain and inflammation. If unsuccess-fully treated, long-term function is affected because of degenerative joint dis-ease and fibrous tissue restriction of tendon and joint capsule motion.Unfortunately, these infections are quite common as a result of the anatomyand exposed nature of the distal limbs of horses. Early diagnosis and aggres-sive treatment can often result in satisfactory and normal return to functionand athleticism, however.

Pathogenesis

An accurate medical history is essential to understand completely theetiopathogenesis of a case of septic synovitis. Signalment information canoften give some insight into how an organism likely arrived in a synovialcompartment. Younger foals typically are affected with septic synovitis, pri-marily septic arthritis, after systemic distribution of bacteria from a site dis-tant to the affected joint. Foals with a primary nidus of infection are knownto develop septic arthritis secondary to bacteremia. The most common sitesof primary infection seeding joints seem to be the lungs and umbilical rem-nant tissues [1]. Therefore, it is wise to investigate thoroughly these tissuesand the systemic health of a foal diagnosed with septic arthritis [1]. Themost common avenue of bacterial delivery to synovial compartments ofadult horses is through a wound.

* Corresponding author.

E-mail address: [email protected] (E.M. Gaughan).

0749-0739/06/$ - see front matter � 2006 Elsevier Inc. All rights reserved.

doi:10.1016/j.cveq.2006.03.005 vetequine.theclinics.com

mailto:[email protected]

364 LUGO & GAUGHAN

A thorough examination of any traumatic injury to the distal limb ofa horse is essential for early detection of synovial contamination. Lacera-tions and puncture wounds are the most common avenues of bacterial de-livery to a synovial structure. Therefore, when these types of wounds arenear to or associated with a joint or tendon sheath, close inspection is re-quired to determine the tissues involved. Wounds that lacerate or abradethe skin and subcutaneous tissues overlying synovial compartments can befrustrating to assess completely immediately after wounding. Occasionally,delayed contamination of a synovial compartment can occur if the capsuleis damaged, such that necrosis and sloughing of overlying capsular tissue oc-curs over several days after wounding. Although rare, this type of synovialexposure should not be overlooked with wounds that disrupt superficial tis-sues over a joint or tendon sheath.

Diagnosis

The physical examination of a horse suspected of having septic synovitisshould be thorough and should evaluate all appropriate body systems andtissues. Lameness resulting from septic synovitis is expected to be severe.With infection that is contained within a closed synovial compartment,the pressure and inflammation of the septic process can result in grade4 to 5 (toe touching to non–weight-bearing) lameness. This is common sec-ondary to puncture wounds and small synovial penetrations from otherwounds. Severe lameness is also observed as an open synovial wound healsby second intention before the septic process has resolved. This particularsituation may follow a misleading presentation. Horses with open jointsand tendon sheaths may be comfortable if the synovial compartment isdraining. Horses may also be comfortable if they are receiving higher dosesof phenylbutazone. The observed lameness may be completely attributableto the wound and the tissue disruption rather than to the infection untilthe contaminated structure begins to close and entrap the septic inflamedfluid. Thus, it is possible that a horse with septic synovitis may not initiallydemonstrate the more severe grades of lameness commonly associated withthis disease. This can be true for several days after injury.

Careful local examination of wounded or suspected infected tissues is in-dicated. Palpation of affected joints and tendon sheaths typically revealsswelling, which can be edema in perisynovial tissues and effusion withinthe synovial compartment. Other classic signs of inflammation are also nor-mally present. Regional heat is often palpable, and erythema can be detectedwhen hair is removed. Palpation and assessment of range of motion are of-ten associated with an avoidance response indicating pain.

When suspected synovial sepsis is associated with a wound, careful clean-ing is important in the acute stages. Restraint appropriate for close manip-ulative examination is essential. This typically requires sedation and often

365SEPTIC ARTHRITIS, TENOSYNOVITIS, AND HOOF INFECTIONS

local anesthesia. At times, general anesthesia may be necessary to facilitatea complete assessment of tissue injury and contamination. Xylazine with bu-torphanol or detomidine is usually sufficient for sedation, and regional localanesthesia can make the examination easier. Sterile lavage solutions are rec-ommended for wound cleaning to avoid any complicating factors fromother sources of contamination. Clean tap water can also be helpful if thelimb has marked gross contamination. Aggressive wound cleansing and re-moval of foreign material should be completed. The addition of disinfec-tants at this stage of evaluation is often used but may not be necessary.The removal of gross contaminants is most important to allow deeper as-sessment of the wound and underlying synovial structures. Manual palpa-tion with a sterile gloved hand or the fingers can help to assess the depthof a wound as well as to identify intrasynovial tissue exposure. With appro-priate restraint and local anesthesia, a wounded limb can be assessed withthe horse standing in a weight-bearing position and with the affected limbheld in the examiner’s hand as palpation and manipulations are completed.Whenever an open synovial compartment is confirmed, aggressive treatmentshould be initiated. If any doubt exists, other diagnostic measures should bepursued and the suspect synovial structure considered infected until provenotherwise. One such method is to use a sterile surgical probe as an extensionof the fingers. Malleable probes can be used to investigate punctures, smallerwounds, and the depths of larger wounds inaccessible to sterile fingers. Ifuncertainty remains when using a probe, radiographs can be made witha probe in place to determine the location of the probe and the likely tissuesinvolved in a wound.

Perhaps the most convincing evidence that a synovial compartment hasbeen opened after wounding is to place a sterile solution in the synovialspace and confirm communication with the wound. This is accomplishedin the same manner as routine synoviocentesis. The greatest challenge afterwounding is to identify a location for needle placement that is sterile anddoes not increase the risk of synovial contamination. A site of unwoundednormal skin over the ‘‘opposite’’ side of a joint from a wound is preferred.This is often difficult to identify and may depend on the timing after occur-rence of the injury. With delay of hours to days, a wound site can becomeswollen and the subcutaneous space contaminated, such that passing a hypo-dermic needle could result in synovial contamination of an otherwise normaljoint or tendon sheath. This should obviously be avoided and efforts concen-trated on resolving the cellulitis before synoviocentesis is performed in theregion. During this period, the synovial space should otherwise be treatedas if infected, with administration of systemic antimicrobials and anti-inflammatory medications.

If an appropriate site can be identified, the overlying skin should be asep-tically prepared and a hypodermic needle (21- to 14-gauge) placed in the sus-pected joint or tendon sheath. If at all possible, an aliquot of synovial fluidshould be obtained from any synovial space under suspicion. This is often

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not possible, because the synovial fluid may be drained from an open struc-ture and is not available for aspiration. If synovial fluid can be obtained,however, a nucleated cell count and measurement of total solids can beused to confirm infection. Synovial fluid can also be quickly assessed for to-tal protein content with a refractometer. Total protein concentrations of 3.5mg/dL or greater (normal %2.5 mg/dL) have been associated with septic sy-novial fluid. Total protein concentrations of 4.0 mg/dL or greater have beenconsidered to indicate sepsis with more sensitivity than total synovial whiteblood cell counts [2]. Joint and tendon sheath fluid white blood cell countsgreater than 30,000 cells/mL are typically associated with synovial sepsis.Some cases may present with lower cell counts if substantial deposits of fi-brinous material are present, however. Absolute proof of synovial sepsis isdependent on locating and identifying a microorganism from the tissues inquestion. Therefore, cytologic identification of bacteria in synovial fluid andwithin synovial white blood cells is of great assistance. Culture and identifi-cation of the infecting microorganism(s) represent the ultimate confirmationof sepsis and are also tremendously helpful in orienting appropriate therapy.Positive culture and sensitivity results are substantially enhanced by placingsynovial fluid in blood culture media and incubating for 24 hours beforeplating samples versus directly plating synovial fluid [1]. Blood culture incu-bation of infected synovial fluid samples can increase the odds of obtaininga positive culture from 40% to 80% compared with culturing synovial fluiddirectly onto agar plates [1]. Most often, there is a minimal period of empiricantimicrobial treatment while synovial fluid cultures are pending.

After synovial fluid has been obtained, a volume of sterile irrigation fluid(balanced polyionic fluid or saline) sufficient to distend the synovial com-partment should be injected under pressure. Placing an intravenous exten-sion set on the needle can assist with this procedure by accommodatingfor some motion on the part of the horse. If the injected fluid distends thesynovial compartment without communication with the wound site, thejoint or tendon sheath can be assumed to be closed at the time of examina-tion. Again, it should be recalled that this assessment can change with timein rare cases. If the injected fluid becomes evident at the wound site (appearsas drips of fluid under pressure), it must be interpreted that the synovialcompartment is open, contaminated, and, for treatment purposes, infected(Fig. 1). This technique has been the most useful for acute-phase interpreta-tion and assessment of wounds near joints and tendon sheaths in relation topenetration of the synovial space. Careful observation is often required todetect the exit of injected fluid.

Imaging techniques can be used to assess wounds associated with jointsand tendon sheaths further. Plain radiography can occasionally reveal evi-dence of an open synovial compartment. The presence of gas densities inthese spaces is not normal and can be interpreted as air that has entereda joint space. Care must be exercised if radiographs are made after synovio-centesis, because air can be present and lead to false interpretation. It seems


that this radiographic sign is rare, and it may be more likely in large spacesthan in smaller joints and tendon sheaths.

Positive-contrast radiography has great potential to assist in obtaining anearly diagnosis of synovial cavity communication with a wound site. Positive-contrast material can be administered in two ways. It can be injected intoa wound to determine if the underlying synovial space is opened. Alter-nately, the contrast media can be placed directly into a suspected joint,bursa, or tendon sheath, and communication between the wound trackand synovial structure can be determined. Perhaps the most common useof positive-contrast material is its direct injection into a tract or injectionvia a small catheter placed in a tract (fistula). This is more useful with apuncture or small exit wound than with wide laceration trauma. The resultingfistulogram can provide useful information as to the depth and direction ofa wound and whether or not the wound communicates with the suspectedsynovial compartment. A 14- or 16-gauge intravenous catheter or smallanimal urinary catheter can work well to access this type of wound tract forinjection of contrast material. A volume sufficient to allow backflow fromthe catheter is usually enough for a diagnostic study. Radiographs shouldbe taken as soon as possible after injection, and any excess contrast materialshould be cleaned from the hair and skin before exposure so as to avoid arti-facts and poor images. Any evidence of communication between the woundand synovial structure should be taken seriously as an indication to institutetreatment of septic synovitis (Fig. 2).

Radiographs can reveal other abnormalities indirectly associated withseptic disease of synovial structures. Soft tissue swelling, loss of joint space,and lysis or erosion of periarticular bone may be seen on radiographs of

Fig. 1. Sterile polyionic fluid injected into a joint distant from a wound egresses from the

wound site, indicating an open contaminated synovial compartment.

368 LUGO & GAUGHAN

infected joints. Signs of septic osteitis or osteomyelitis of bone associatedwith joints are perhaps the most consistent radiographic signs from surveyfilms that infectious synovitis is present [1]. Septic tenosynovitis alone israrely associated with specific findings from survey films.

Ultrasonography of joint spaces and tendon sheaths can provide usefulinformation. Normal synovial fluid has a uniform anechoic appearance.The dark image is typically clear of echogenic material. With sepsis, synovialfluid can appear to contain echogenic particles and strands of material. Thisis likely consistent with the accumulation of fibrin, inflammatory debris, andforeign material. The absence of this flocculent material does not rule outa septic process when infection is highly considered for an affected jointor tendon sheath.

Nuclear scintigraphy is not commonly used in the diagnosis of septic sy-novitis. Some rare cases that do not demonstrate typical signs may benefitfrom scintigraphy. Vascular and soft tissue phase scintigraphy may offersome advantage for horses with unusual presentations by demonstrating in-creased uptake of radiopharmaceutic agent at sites of inflammatory change.Perhaps nuclear scintigraphy could be used to monitor an affected horse astissues respond to treatment; however, final resolution remains in question.A return to a normal baseline image may indicate resolution of inflamma-tion and, likely, the infectious component of the disease as well.

The growing presence and use of three-dimensional imaging of equinelimbs may have an impact on the diagnosis of synovial diseases. Soft tissueabnormalities may be better visualized with MRI, and subtle bone lesionsmay be more readily identified with CT. To date, no distinct advantage ofthese imaging modalities over radiography and ultrasonography for diagno-sis of septic arthritis and tenosynovitis in horses has been described. Injuryand abnormalities of the navicular region, including the navicular bursa,

Fig. 2. Positive-contrast material injected into an open tract indicates an open digital tendon

sheath.


have been recently characterized using MRI, however, and there seems to bepromise of gaining more insight into the nature of these injuries in the horseusing this type of imaging [3].

An early accurate assessment and diagnosis of septic synovitis are neces-sary to achieve a successful outcome. Whether considering a foal with hema-togenous origin septic arthritis or an adult horse with an infected synovialstructure secondary to wounding, time is an essential factor influencing finalsuccess. The described diagnostic efforts are indicated and recommended. Inthe absence of these, or if indications are not absolutely convincing, it is wiseto consider a suspect joint, tendon sheath, or bursa as infected until provenotherwise and to institute aggressive treatment as soon as possible. Delay indoing so can be costly to tissue disruption, destruction, soundness, and pos-sibly life. Open synovial compartments seem to respond much better to ag-gressive treatment before the establishment of frank sepsis. It is possible toprevent infection after wounding if these aggressive treatment efforts are ini-tiated as soon as possible. Again, an early and accurate diagnosis is the key.

Treatment

The aim in treating septic arthritis and tenosynovitis is eradication of thebacterial load, removal of any foreign material, elimination of inflammatorymediators and free radicals, pain relief, and restoration of the normal syno-vial environment so as to promote tissue healing. These objectives areachieved by appropriate administration of antimicrobial drugs, joint lavage,surgical debridement, anti-inflammatory drugs, and a postinfection rehabil-itation program. Early recognition and aggressive treatment are essential toeliminate infection and obtain a successful outcome.

Antimicrobial drugs

Judicious use of antimicrobial drugs for the management of infected orcontaminated synovial structures requires knowledge of the most likely or-ganisms responsible for the infection and an understanding of the mecha-nism of action and spectrum of activity for each antimicrobial. Forexample, injuries to equine joints are more likely to have a mixed bacterialpopulation consisting of Enterobacter spp, Streptococcus spp, Staphylococ-cus spp, Pseudomonas spp, and anaerobes [2]. Septic arthritis after surgeryor intra-articular injection is mainly caused by Staphylococcus spp [4]. Thegoal of therapy is to achieve antimicrobial concentrations above the mini-mum inhibitory concentration (MIC) in the infected tissue without produc-ing toxic effects to the animal [1]. Efficacy of an antimicrobial depends onthe physiochemical properties of the drug and the biologic properties ofthe target bacteria. Factors at the site of infection, such as pH, bacterialload, phases of bacterial growth, and the presence or absence of oxygen,influence the activity of the antimicrobial [5].

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Antimicrobials are classified by their pharmacologic properties intoconcentration-dependent and time-dependent categories [5]. This is clinicallyimportant when administering antimicrobials by local methods, such as in-travenous or intraosseous regional perfusion or intra-articular medication,in which concentration-dependent drugs are more beneficial. With concen-tration-dependent drugs, the higher the concentrations achieved in the tis-sue, the greater is the killing effect [5]. Otherwise, time-dependentantimicrobials do not have a greater killing effect by increasing the concen-tration in the tissue. In general, aminoglycosides, fluoroquinolones, andmetronidazole are considered concentration-dependent, whereas b-lactams,macrolides, and vancomycin are considered time-dependent [5].

The route of antimicrobial administration is important. Combinations ofsystemic and local administration of antimicrobials are recommended forthe treatment of horses with septic arthritis and tenosynovitis [1]. Intrave-nous administration of broad-spectrum antimicrobials must be initiated assoon as the diagnosis of a septic condition is presumed after obtaining a sam-ple for culture. The intravenous route provides a faster onset of action andmaximizes penetration of a drug into the synovial structures compared withthe oral or intramuscular route [5]. Systemic antimicrobial therapy is partic-ularly necessary for foals with septic arthritis so as to treat bacteremia andprevent hematogenous dissemination of the causative organism to other tis-sues. Selection of an antimicrobial depends on its efficacy against the con-taminating organism, safety for the animal, and expense of the drug. Theclinician should administer broad-spectrum antimicrobials initially andthen make adjustments according to clinical progression, culture, and anti-microbial sensitivity. Broad-spectrum coverage is important, because syno-vial fluid cultures are positive in only 40% to 64% of horses suspected ofhaving an infected synovial structure [6]. Furthermore, in many cases, otherinfecting organisms may not be isolated by culture but remain present, in-fecting the synovial structure. This is particularly important in synovial in-fections caused by penetrating wounds, where mixed bacterial infections arecommon [2].

Traditionally, the most common antimicrobials used to treat horses withseptic arthritis or tenosynovitis are a b-lactam agent (eg, sodium or potas-sium penicillin, cephazolin) combined with an aminoglycoside (eg, gentami-cin, amikacin). When administered systemically, these antimicrobialsdistribute well into extracellular fluid, reaching high concentrations in syno-vial fluid [7–10]. This antimicrobial combination is a good initial choice, be-cause the antimicrobial spectrum is effective for the most common isolatescausing musculoskeletal infections in horses [4,11]. Other antimicrobialsthat have been clinically effective or have been shown to enter the synovialfluid at therapeutic concentrations in clinically normal joints include tetra-cycline, trimethoprim-sulfonamide combinations, metronidazole, ticarcillinsodium, ceftiofur sodium, and vancomycin [1,12]. It is important to avoidthe routine use of ticarcillin and vancomycin, however, and to use them


only as a last resort. This is necessary to prevent the development of moreresistance by the bacteria.

Aminoglycosides are still considered the drugs of choice for treatment oforthopedic infections in horses. The duration of sustained antimicrobial ef-fectiveness is concentration dependent and has an excellent post-antimicro-bial effect, which refers to the ability to suppress bacterial growth afterexposure to the antimicrobial [5]. The larger the drug tissue and serum con-centration, the greater is the bactericidal effect. A single daily dose of gen-tamicin (6.6 mg/kg administered intravenously) is more beneficial than theconventional thrice-daily dosing (2.2 mg/kg administered intravenously ev-ery 8 hours) [13]. Godber and colleagues [13] demonstrated that a singledaily dose of gentamicin reached the targeted antimicrobial tissue concen-tration, prolonged the post-antimicrobial effect, and lowered the risk fornephrotoxicity in normal adult horses. Nevertheless, the pharmacokineticproperties of aminoglycosides are altered in hypoxic neonatal foals [14].Therefore, in neonates, serum aminoglycoside peak and trough concentra-tions should be measured to adjust the dose and dose interval [14]. Althoughaminoglycosides have been good antimicrobials for treating musculoskeletalinfections in horses, the emergence of multiple antimicrobial-resistant or-ganisms has created great concern in human and veterinary medicine [15].Methicillin-resistant Staphylococcus aureus has been isolated in orthopedicinfections in horses. The antimicrobial spectrum of S aureus has revealed re-sistance to most aminoglycosides, including amikacin and gentamicin [15].Therefore, judicious use of antimicrobials and evaluation of new antimicro-bial alternatives are required for future success in treating equine synovialsepsis.

Enrofloxacin is used for horses with refractory septic arthritis and osteo-myelitis or when long-term administration of antimicrobials is required. Theuse of enrofloxacin is considered extralabel because enrofloxacin is not cur-rently approved for use in horses. It has been widely used, however, becauseof its broad-spectrum bactericidal effect, relatively safety, and ease of ad-ministration [16]. Similar to aminoglycosides, enrofloxacin is a concentration-dependent antimicrobial drug and has a good post-antimicrobial effect [5].A single daily intravenous dose of 5.5 mg/kg or oral dose of 7.5 mg/kgadministered every 24 hours or 4.0 mg/kg administered every 12 hourspenetrates tissues adequately and would attain concentrations high enoughin the tissue fluids to treat infections caused by susceptible bacteria [17]. Astudy evaluating the effects of injectable enrofloxacin demonstrated thatlong-term administration using 5.5 mg/kg administered intravenouslyonce daily was safe in adult horses [16]. Enrofloxacin is not recommendedfor use in foals because it may cause cartilage lesions and lameness in neo-nates [18,19]. Furthermore, enrofloxacin inhibits cell proliferation, inducesmorphologic changes, decreases total monosaccharide content, and alterssmall proteoglycan synthesis at the glycosylation level in equine tendoncell cultures [20]. These effects are more pronounced in juvenile tendon cells

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than in adult equine tendon cells [20]. Therefore, the use of fluoroquinolonesis not without risk. Tendonitis and spontaneous tendon rupture have beenreported in people during or after therapy with fluoroquinolones [20]. Theoral route of administration is preferable in horses requiring long-term an-timicrobial administration because of the relative ease of administrationcompared with the intravenous route. An oral gel formulation made fromthe injectable cattle product was shown to produce blood levels sufficientto resolve infections caused by a variety of common equine pathogens anddid not cause any detrimental effect in normal adult horses [21].

Imipenem-cilastin, cefotaxime, and amoxicillin have been studied as po-tential alternatives for the treatment of septic arthritis in horses [22,23]. Ce-fotaxime is a third-generation cephalosporin. It has a broad spectrum ofactivity, having bactericidal activity against many gram-positive andgram-negative aerobic bacteria. Based on a pharmacokinetic study, a doseof 25 mg/kg administered every 6 hours reached therapeutic concentrationswithin 30 minutes of intravenous administration for cefotaxime-susceptibleorganisms in the synovial fluid of horses [22]. Because the drug concentra-tion falls below the targeted MIC (!1 mg/mL) 6 hours after injection, ad-ministration every 6 to 8 hours was recommended [22]. Amoxicillin isa class of penicillin with a better gram-negative spectrum [23]. Errecaldeand coworkers [23] investigated the pharmacokinetics of amoxicillin ata dose of 40 mg/kg administered intravenously in normal horses and horseswith experimental arthritis. The rate of penetration from serum to synovialfluid was greater in arthritic animals compared with normal animals, indi-cating better penetration in these cases. In contrast, the rate of disappear-ance from synovial fluid was more rapid in normal horses compared witharthritic horses, indicating persistence of the drug in the diseased joint[23]. Pharmacokinetic studies of imipenem-cilastin indicated that a dose of10 to 20 mg/kg administered by slow intravenous infusion every 6 hoursachieve antimicrobial concentrations that are effective for most susceptiblepathogens and do not cause any adverse effects in normal horses [24].

Oral antimicrobial administration is generally preferred when long-termadministration is required. Oral administration is not recommended in theacute phase of infection, because gastrointestinal tract absorption may beerratic; thus, serum and tissue concentrations may be lower than needed.Exceptions include the use of metronidazole tablets for the treatment of an-aerobic infections, especially for treatment of Bacteroides fragilis infections.We routinely prescribe oral antimicrobials, such as trimethoprim-sulfonamide combinations or enrofloxacin, for 10 to 14 days after resolutionof clinical signs and discharge from the hospital.

Nonsteroidal anti-inflammatory drugs

When bacteria invade synovial structures, a severe inflammatory re-sponse develops. Inflammatory mediators, free radicals, and destructive


enzymes released by the inflamed synovium and neutrophils induce a viciouscycle of inflammation and tissue destruction [1]. Breakdown products of theinflammatory cells, such metalloproteinases, oxygen free radicals, and cyto-kines, in turn, cause synovitis and cartilage degradation, leading to joint ef-fusion, severe lameness, and, eventually, osteoarthritis [25]. Nonsteroidalanti-inflammatory drugs (NSAIDs) may help to diminish the inflammatoryprocess, minimize cartilage destruction, and provide analgesia, which is im-portant for these horses to prevent support limb laminitis. Phenylbutazone(4.4–8.8 mg/kg administered once daily), ketoprofen (2.2 mg/kg adminis-tered two or three times a day), and flunixin meglumine (1.1 mg/kg admin-istered two times daily) are commonly used to reduce synovial inflammationin horses [26]. These drugs can suppress induced synovial membrane prosta-glandin E2 (PGE2) production without detrimental effects on synovial mem-brane viability and function [27]. In experimentally induced synovitis inhorses, phenylbutazone was more effective than ketoprofen for reducinglameness, joint temperature, synovial fluid volume, and synovial fluidPGE2 [28]. Selective cyclooxygenase 2 inhibitors are currently under inves-tigation and seem promising at reducing the toxic side effects observedwith the currently used NSAIDs [27,29].

Administration of intravenous dimethyl sulfoxide (DMSO) solution hasbeen advocated by one of the authors (EMG) as an adjunctive therapy toreduce synovial inflammation. DMSO is a free radical scavenger, it is anti-septic and analgesic, and it may inhibit chemotaxis of inflammatory media-tors [30]. In addition, some evidence suggests that DMSO can boost theeffects of other drugs [31]. The most commonly used dose is 0.25 to 1 g/kgof body weight administered intravenously up to a 10% solution, witha maximum duration of treatment of 5 days [32]. This dose is safe in awakeand anesthetized horses, but higher DMSO concentrations (O10% solu-tion) can cause hemolysis and should be avoided [32]. Hyaluronan (HA)and polysulfated glycosaminoglycans may also be used to alleviate signsof synovial inflammation in horses with induced nonseptic synovitis andmay have beneficial effects in horses with septic joints [33]. One study of in-fected joints in horses demonstrated that a single intra-articular injection ofHA after joint lavage significantly reduced lameness, joint circumference,synovial fluid white blood cells (WBCs), and proteoglycan loss from articu-lar cartilage [34]. In another study, intrathecal administration of sodiumhyaluronate in a collagenase-induced tendonitis model demonstrated somebeneficial effect in tendon healing and prevention of adhesion formation[35]. The intra-articular use of these drugs in the acute stage of infectionshould be avoided, however, because the immunosuppressive propertiesmay enhance the risk of infection recurrence [36]. Until the risk of infectionafter administration via the local and systemic routes is investigated further,these drugs should be used after signs of infection have resolved. Theauthors usually recommend a series of systemic injections (HA or polysul-fated glycosaminoglycans) 3 to 4 weeks after discharge from the hospital.

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Our clinical impression is that these agents can be used to help resolve thesynovitis and capsulitis that occurs after infection and can help to preventadhesion formation in the case of septic tenosynovitis.

Regional perfusion

Regional perfusion can be used to achieve high local concentrations ofantimicrobials in a selected region of the limb, particularly in areas of ische-mic tissue [37]. The antimicrobial is injected into a superficial vein proximalto the site of infection (intravenous; Fig. 3) or into the medullary cavity ofa bone in a similar location (intraosseous). For both techniques, a tourniquetis placed proximal and distal to the site of infection so as to occlude the su-perficial venous system. As the perfusate is infused, it distends the venoussystem, allowing the antimicrobial to diffuse into the tissues. Experimentaland clinical investigations have demonstrated the beneficial value of thesetechniques as adjunctive therapy for orthopedic infections in horses [38]. Lo-cal antimicrobial concentrations can reach 25 to 100 times the MIC for mostcommon equine pathogens [37–41]. This suggests that administration ofconcentration-dependent antimicrobials, such as aminoglycosides, by re-gional perfusion should have an excellent bactericidal effect and should im-prove treatment efficacy. A high ratio of peak concentration (Cmax) to MICis associated with a greater bactericidal effect and a longer post-antimicrobialeffect [5]. Amikacin and gentamicin are usually the drugs of choice toinfuse by regional perfusion [37–40]. Other antimicrobials agents thathave been anecdotally used include potassium penicillin, ampicillin, cefotax-ime, ceftiofur, chloramphenicol, and enrofloxacin. The use of enrofloxacin,which is another concentration-dependent antimicrobial, for regional perfu-sion is currently under investigation; however, until further results are re-ported, it should be used with caution. A single dose of enrofloxacin of1.5 mg/kg diluted in saline (60 mL) and regionally perfused into the cephalicvein achieved concentrations 10 times the MIC for the most common

Fig. 3. Intravenous regional limb perfusion in a 4-week-old foal with septic arthritis. The foal is

in lateral recumbency; tourniquets are placed above or below the hock, and a catheter is placed

in the saphenous vein for perfusion.


organisms causing equine orthopedic infections in the midcarpal synovialfluid, bone marrow, and interstitial tissue of the third metacarpal bone.A higher dose or extravasation of the antimicrobial solution caused mild tomoderate perivascular cellulitis, however. Fluoroquinolones at high concen-trations are toxic to chondrocytes [19].

The decision to use the intravenous or intraosseous route of administra-tion depends on the target tissue to be treated (joint versus bone), the pres-ence of periarticular edema, access to a peripheral vein, availability ofequipment, and the clinician’s preference. Both procedures can be per-formed with a horse standing or under general anesthesia. Two studieshave been published comparing the pharmacokinetic effects of amikacin de-livered by intraosseous or intravenous infusion [39,40]. One study comparedthe two techniques using an infusion of amikacin (500 mg) in the digital veinor medullary cavity of the third metacarpal bone [39]. No significant differ-ences were found with the time to Cmax or elimination half-life betweenmethods in synovial fluid samples in the distal interphalangeal joint, meta-carpophalangeal joint, or digital flexor tendon sheath [39]. Each techniquecan produce a mean Cmax ranging from 5 to 50 times that of the recommen-ded serum Cmax for therapeutic efficacy. The second study compared the twotechniques of regional perfusion for delivery of antimicrobials in the tibio-tarsal joint [40]. Results of this study demonstrated that intravenous infu-sion of amikacin at a rate of 1 g diluted in sterile saline (60 mL) producedthe highest concentration of amikacin in the tibiotarsal joint comparedwith intraosseous infusion, which was performed in the distal portion ofthe tibia (mean � standard error [SE]: 701.8 � 366.8 mg/mL versus 203.8 �64.5 mg/mL, respectively) [40]. Our opinion is that intravenous administrationis technically easier and faster to perform, special equipment is not required,and the vein can be catheterized at a location distal to the surgical site. Nev-ertheless, when there is severe soft tissue swelling or edema or when veins arenot easily accessed, intraosseous perfusion is probably the best choice. Sig-nificantly higher concentrations of antimicrobials can be achieved with in-tra-articular administration than those obtained with regional intravenousor intraosseous perfusion [41]. Therefore, intra-articular administration ofantimicrobials may be more effective for the treatment of septic synovitis.For further discussion on regional perfusion, the reader is referred to thearticle by Cruz and colleagues in this issue.

Technique for intravenous regional perfusion

In most of the initial studies on regional perfusion, the procedure wasperformed with the horse under general anesthesia [37,38,42]; however,the technique can be readily performed with the horse standing. The horseis sedated with a combination of detomidine and butorphanol, and a tourni-quet is placed proximal and distal to the targeted area and infusion site. Forperfusion of the distal limb (distal metacarpus or tarsus to foot), the digital

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vein is used. The cephalic vein in the forelimb or the saphenous vein in thehind limb can be used to perfuse the region distal to the distal third of theradius or tibia, including the carpus and tarsus, respectively. Any other su-perficial vein that is exposed after the tourniquet is in place can be used,however (see Fig. 1). After aseptic preparation of the site, a 23-gauge butter-fly catheter is inserted into the selected vein and the antimicrobial solution isslowly infused over 5 to 15 minutes. For larger vessels, such as the cephalicor saphenous vein, a 20-gauge, 1-in intravenous catheter can be placed. Thecatheter can be used to prevent extravasation of the drug during perfusionand the associated complications. After infusion, the catheter is removed,pressure is applied for a few minutes over the venipuncture site, and thetourniquet is maintained in place for 30 minutes. The procedure is repeatedevery 24 hours for 3 to 5 days or as needed. We have used intravenous re-gional perfusion as the only route for antimicrobial administration inseveral horses affected with septic arthritis after open injuries to joints.Resolution of the infection was achieved. Regional perfusion was per-formed every 24 to 36 hours for a total of seven times with amikacin orenrofloxacin.

Technique for intraosseous perfusion

This technique can be performed with the horse standing or under gen-eral anesthesia [43]. After the horse is sedated and restrained in stocks,the site is clipped and prepared as for aseptic surgery. Regional nerve blocksand local infiltration of anesthetic drugs are used to desensitize the region.A 1-cm stab incision is made through the skin, subcutaneous tissue, andperiosteum on the most readily accessible aspect of the bone. The soft tissueis retracted, and a 3.2- to 4.0-mm (3.2 mm in foals) unicortical hole is drilledthrough the cortex. A special cannulated screw is then inserted after tappingthe hole to the specific screw diameter. The cannulated screw is not alwaysnecessary, however, because infusion can be performed by introducing themale end of a catheter extension set into the unicortical hole. Regional per-fusion is performed as described for the intravenous technique. After theprocedure, the skin over the cortical hole or cannulated screw is suturedand bandaged.

Intrasynovial antimicrobials

Intra-articular administration of antimicrobials is an effective and inex-pensive method for treating septic arthritis. Advantages of intra-articularadministration include achievement of high concentrations of the drug inthe synovial structure, the ability to use cost-prohibitive drugs in smalldoses, and the reduction of systemic toxic effects. Administration of a single150-mg dose of gentamicin or ceftiofur provides high and sustained concen-trations above the MIC (%2 mg/mL) for the most common equine bacterial


pathogens for at least 24 hours [44,45]. A recent investigation compared in-tra-articular and bone gentamicin concentrations after intra-articular andintravenous regional limb perfusion in horses [41,45]. The Cmax of gentamicinin synovial fluid was significantly higher (800 times) with intra-articularadministration than with regional perfusion and remained 6 times higher 24hours after treatment. The bone gentamicin concentration remained higherthan the MIC for only 8 hours using both techniques, and no significant dif-ference was observed between methods [41].

In clinical cases, antimicrobials are usually injected through a hypodermicneedle into a joint or tendon sheath each day for 3 to 5 days or are injectedat the end of a joint lavage procedure. Recently, equine clinicians have ad-vocated the use of an indwelling catheter, intravenous administration sets,or specialized pumps to administer antimicrobials into a joint more fre-quently (two to three times per day) or continuously [46–48]. Lescun andcolleagues [47] developed a method for continuous infusion of gentamicininto the tarsocrural joint by using an infusion catheter. The infusion catheterconsists of flow control tubing connected to a balloon infuser (Flow ControlTubing; Mila International, Erlanger, Kentucky) by the use of an extensionset with a T-shaped connector. Most of the catheters functioned well for the5-day infusion period, and continuous intra-articular infusion of gentamicin(0.17 � 0.02 mg/kg/h) resulted in antimicrobial concentrations greater than100 times the MIC of 2 to 4 mg/mL [47]. Complications with the infusionmethod occurred in 7 of 24 horses and were primarily associated with failureof the infuser balloon and blockage of the catheter [47]. In a second part ofthe study, investigators evaluated the effects of continuous infusion of gen-tamicin on synovial membrane and articular cartilage [46]. Continuous infu-sion of gentamicin produced mild but transient inflammatory changes in thearticular cartilage and synovium [46].

Intra-articular administration of antimicrobials and joint lavage may beall that is necessary to resolve septic arthritis in adult horses, but this is notrecommended in foals. Systemic administration of antimicrobials is essentialto treat bacteremia and prevent the hematogenous dissemination of organ-isms. Appropriate antimicrobial selection can lead to a dramatic response ineliminating the infection. Aminoglycosides, particularly gentamicin andamikacin, are routinely chosen because of their efficacy against the mostcommon equine pathogens. Many other antimicrobials have been used totreat septic joints; however, it is essential that antimicrobials be evaluatedfor potential inflammatory effects on the synovium and articular cartilagebefore their clinical use. High tissue concentrations of some antimicrobials(eg, enrofloxacin) may damage the synovium and are toxic to chondrocytes[19]. The addition of antiseptic solutions to lavage fluids used to treat in-fected synovial structures was not more effective than lavage with a balancedelectrolyte solution alone [49,50]. Furthermore, the use of chlorhexidine andpovidone iodine (R0.1% solution) is too irritating to the joint and tendonsheaths for safe use [51–53].

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Repositol antimicrobials

Another effective method for local antimicrobial delivery is the use ofantimicrobial-impregnated nonbiodegradable implants [54]. The most com-mon nonbiodegradable matrix implant is polymethylmethacrylate (PMMA),which is a type of bone cement. Antimicrobials are incorporated evenlywithin the matrix and are released by diffusion. These types of implantsare characterized by rapid release of the antimicrobial in the first 24 hours,followed by slow and prolonged release thereafter [54]. Numerous studieshave reported that heat-stable antimicrobials (stable up to 100�C) areeluted from the PMMA in concentrations that exceed the MIC of themost common equine bacterial pathogens [54]. In horses, PMMA impreg-nated with gentamicin sulfate, tobramycin sulfate, amikacin sulfate, andcefazolin has been used successfully in the treatment of open fracturesand joint infections [55]. In another report, gentamicin-impregnatedPMMA beads were used in the treatment of 12 horses with septic synovitis[56]. Selected cases had been refractory to standard treatments (lavage, de-bridement, joint drainage, and systemic antimicrobials) or had evidence ofosteomyelitis adjacent to a synovial cavity [56]. Eleven of the 12 horsessurvived, and 6 returned to full athletic use [56]. Recently, the same au-thors reported the use of gentamicin-impregnated PMMA beads for thetreatment of infections involving the tarsometatarsal and distal intertarsaljoints in 11 horses [57]. After a 7- to 8-mm tract was drilled through thejoint to stimulate ankylosis [57], 5 to 10 beads were placed into the tractdrilled across the affected joint and were left in place for 14 days [57].In this report, 81% of these horses survived and 7 returned to athleticuse [57]. In our experience, antimicrobial-impregnated PMMA beads arebetter to use when horses have developed chronic refractory septic arthritisor osteomyelitis or when ankylosis of a joint can be stimulated (eg, distaltarsal joint). It is important to recognize that implantation of beads canproduce a marked inflammatory reaction and cartilage erosion that canlead to progressive joint damage [58]. Another disadvantage is thatPMMA beads are nonbiodegradable and a second operation is necessaryto remove the implants from the joint. In some clinical cases, however,PMMA beads have been left in place for years with no obvious problem.

Antimicrobial-impregnated PMMA beads can be prepared in the surgicalroom at the time of implantation or ahead of time and sterilized with ethyl-ene oxide [54]. Beads can be fabricated by hand or by injecting the materialinto a mold. The PMMA hardens within 5 to 10 minutes. When it becomeslike clay, the material is made into beads or cylinders and is implanted intothe joint through an arthrotomy. Usually, antimicrobial powder or liquid(1–2 g) is mixed with the PMMA polymer (1:10 or 1:5 ratio) and shapedas desired [54]. Different studies have found that the addition of more anti-microbial powder or the type of antimicrobial used can alter the mechanicalstrength of the implant [59,60]. In the treatment of septic joints, mechanical


strength is not an issue, however, and high concentrations can be used ifthere is no effect on polymerization. The beads can be placed on suture ma-terial or surgical wire to facilitate implantation and retrieval from the surgi-cal site. Factors that influence the antimicrobial Cmax and the length of timeconcentrations remain above the MIC after impregnated PMMA bead im-plantation depend on the brand of the PMMA polymer, the amount of an-timicrobial mixed, the elution properties of the antimicrobial used(aminoglycosides O ceftiofur), and the amount of fluid flowing past the im-plants [54]. Antimicrobial elution is related to surface area; therefore, morerapid elution of the antimicrobial occurs from small rough beads than fromlarge smooth beads, because smaller beads have a larger surface area pervolume [59]. Several antimicrobials elute from PMMA, including gentami-cin, amikacin, ceftiofur, fluoroquinolones, metronidazole, and clindamycin[59,61]. Elution of metronidazole is dependent on the dose, and combina-tions of metronidazole and gentamicin sulfate in PMMA resulted in higherrates of elution compared with elution of metronidazole or amikacin alone[61]. Unfortunately, tetracycline and chloramphenicol do not tolerate thepolymerization process [59]. If the infection does not resolve, implantationof new PMMA beads with the same or different antimicrobials every 7 to10 days should be considered.

Because PMMA impregnated with antimicrobials has been effectivein eliminating infection, there have been multiple investigations to developbiodegradable matrix implants. The main advantage of this type of deliverysystem is that the entire volume of antimicrobial can be slowly releasedwhile the material degrades. Themost commonmaterials investigated includecollagen, plaster of Paris, hydroxyapatite, polylactide-polyglycolide, andpolypropylene fumarate cross-linked with a methylmethacrylate monomer(a type of bone cement) [54]. Many of these materials are still under investiga-tion and are not yet being used in clinical studies. In addition, biocompatibilitystudies need to be performed in vitro and in vivo before placement ofthese biodegradable implants into joints. Potentially dangerous release oflarge amounts of antimicrobials or induction of a severe inflammatory re-sponse may occur during degradation of these implants [54]. Cook and co-workers [62] investigated the use of a biodegradable drug delivery system(50:50 DL-lactide-glycolide copolymers and poly(DL) lactide impregnatedwith gentamicin) for the release of gentamicin in synovial explants fromthe cadavers of four adult horses. This investigator concluded that gentami-cin released at high concentrations for 10 days resulted in the elimination ofinfection, with no adverse effect on synovial HA production or synovialmorphology and viability [62]. The only available in vivo study on biodegrad-able implants in horses was reported by Summerhays and colleagues[63] in 2002. Gentamicin-impregnated collagen sponges were used to treateight horses with traumatically induced synovial sepsis. The antimicrobial-impregnated collagen sponges were introduced into the joints through thearthroscopic cannula after arthroscopy and joint lavage. Seven of the eight

380 LUGO & GAUGHAN

horses respondedwell to treatment, were sound at follow-up, andhadno long-term effect secondary to implantation of the collagen sponges [56]. Presently,gentamicin-impregnated collagen sponges are only available in Europe andare not approved for use in the United States. The use of biodegradable im-plants is an area of extensive research, and their use is likely to increase inthe near future. For further discussion on repositol antimicrobials, the readeris referred to the article by Cruz and colleagues in this issue.

Lavage

Synovial lavage and drainage are essential in horses with septic joints andtendon sheaths. The goals of joint lavage are removal of debris and foreignmaterial, debridement of contaminated or devitalized tissue, and eliminationof inflammatory mediators [12,25]. A number of techniques have been de-scribed, including through-and-through lavage via hypodermic needles,open incisions with or without drains, and lavage under arthroscopic guid-ance. The decision to use any of these techniques is based on the cause(induced by trauma versus hematogenous spread), duration of the infection,and severity of clinical signs. In acute cases and for joints that do not havemultiple compartments, through-and-through needle lavage may be effectivein eliminating infection. If infection is well established, there are large fibrinclots in the joint, or the joint has multiple compartments (eg, stifle, hock),however, the lavage fluid may totally bypass the infected area and the infec-tion persists. Joint lavage through needles can be performed with a standinghorse using sedation and local anesthesia, although it is usually easier andmore effective with the horse under general anesthesia. Three to 5 L of fluidis recommended for routine lavage. After the lavage procedure, antimicro-bials are injected into the joint and the limb is bandaged to reduce inflam-mation and to protect the surgical sites. Systemic anti-inflammatory drugsshould be administered as well.

Arthroscopic surgery is a valuable tool in the management of synovialcontamination and infection. Arthroscopy offers several advantages, includ-ing improved visibility; lavage of a larger area of the synovial structure; andidentification and removal of foreign material, fibrin, and devitalized tissue.The benefits of arthroscopic exploration and lavage of contaminated jointswere demonstrated in a retrospective study by Wright and colleagues [64]. Inthat report, 41 of 121 affected horses that had arthroscopic surgery hadintra-articular foreign material that was identified during surgery and waspredicted to be present before surgery in only 6 of those horses [64]. Further-more, osteochondral lesions were identified in 51 horses and recognizedbefore surgery in only 25 cases [64]. Tenoscopic-assisted lavage and debride-ment are effective for the treatment of open injuries of the digital flexor ten-don sheath [65]. At the conclusion of arthroscopy or tenoscopy, theinstrument portals can be primarily closed or enlarged for continueddecompression and drainage of the synovial compartment.


The fluid of choice for synovial lavage is a sterile balanced electrolyte so-lution [1]. The addition of antiseptics, such as chlorhexidine or povidoneiodine, into the lavage solution causes irritation to the joints and has notproven to be more effective than a balanced electrolyte solution alone [50].The addition of DMSO to lavage solutions has been used by many equine cli-nicians. Lavage or intra-articular administration of DMSO (10% up to 40%solution) has been used experimentally and clinically to treat septic arthritis inhorses [1]. As previously mentioned, the free radical scavenging and anti-in-flammatory properties of DMSOmay help in decreasing the inflammation in-side a joint. One of the authors (EMG) routinely addsDMSO as a 1% to 10%solution to the lavage fluid. Nevertheless, a recent in vitro study demonstratedthat exposure of DMSO to cartilage explants at concentrations greater than5% suppresses equine articular cartilage metabolism (decreases proteoglycansynthesis and lactate metabolism) in normal joints [66]. In another study,daily exposure of 10% DMSO to equine cartilage explants resulted in detri-mental effects on cartilage proteoglycan synthesis and caused chondrocytedeath in a time-dependent manner (O3 days of exposure) in normal joints[67]. This effect has not been demonstrated in cases of synovial sepsis.

In chronic or refractory caseswith established inflammation, open incisionsare recommended for decompression and removal of inflammatory debris[68]. An arthrotomy permits extensive lavage and constant joint drainage byleaving the incision open.Arthrotomies are typically performed under generalanesthesia.Oneor two3- to 5-cm incisions canbemade into a joint at locationsthat allow adequate drainage of fluid and removal of fibrin [68]. Arthrotomyincisions can be left open and protected by a sterile bandage, which should bechanged daily. For sites that are difficult to bandage, such as the stifle region,a stent bandage can be sutured in place. Once an infection resolves, the inci-sions can be closed. Complications include premature closure of an incisionsite or, in contrast, the formation of exuberant granulation tissue attributableto chronic infection [69]. Arthrotomy was more effective for treating experi-mentally induced septic arthritis than arthroscopy and synovectomy becauseit provided better drainage [69].

After surgical drainage is established and initial lavage and debridementare performed, daily assessment and medical management are essential forsuccessful treatment. In horses with an established infection, daily lavageand intra-articular administration of antimicrobials are typically performeduntil lameness and synovial fluid cytology improve. The decision to repeatthe joint lavage is based on clinical examination of the patient. If drainageceases, joint distention occurs, lameness recurs, or the synovial fluid nucle-ated cell count remains high (O30,000 cells/mL), the joint should be re-treated with local therapy and lavage, and this should be repeated untilcomplete resolution of the infection. If clinical improvement occurs, joint la-vage can be discontinued, followed by discontinuation of local antimicrobialtherapy. In some instances, a single lavage procedure may clear the infec-tion; however, the need for multiple lavage procedures is more typical.

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Rehabilitation

Capsulitis and articular degeneration can be detrimental consequences ofseptic arthritis in horses [49]. Furthermore, infection of the digital tendonsheath can result in severe adhesion formation and fibrosis, which canlead to chronic pain or mechanical lameness [1,35]. After elimination ofan infection, physical therapy and medical management of the patient arecritical to return a joint or tendon sheath to full athletic potential and min-imize damage to the synovium and articular cartilage or to prevent the for-mation of adhesions.

Physical therapy

Early passive range-of-motion exercises should be initiated as soon as aninfection is eliminated. This is particularly important after a tendon sheathinfection so as to minimize the formation of adhesions. Passive joint flexionmay improve circulation, reduce edema, improve the range of motion of thejoint, and break down fibrinous adhesions. Exercise should be restricted,however, so as to minimize damage to affected articular cartilage. Aftera joint infection has resolved, several weeks of stall rest and passive jointmotion are suggested. A progressively increasing exercise program, thelength of which depends on the severity of the infection and damage tothe synovial structures, should then be instituted. It is difficult to convinceowners and trainers to rest a horse for 4 to 6 months. Rest is essential forhealing of affected cartilage, subchondral bone, or tendon. For horseswith mild infection and articular damage, we usually recommend 4 weeksof stall rest, followed by 4 weeks of stall rest and hand walking, followedby 4 weeks of turnout or swimming. For horses with severe infections, weusually recommend 3 to 4 months of stall rest with passive joint motion.If available, swimming physiotherapy can provide excellent exercise andpassive joint motion. Otherwise, horses affected with septic tendon sheathsundergo a more intensive controlled exercise program minimizing theamount of total stall confinement and gradually increasing the amount ofexercise. Walking exercise is recommended as soon as an affected horse iscomfortable enough to walk freely and willingly.

Pharmaceutic management

Intra-articular administration of HA, polysulfated glycosaminoglycans,or corticosteroids is not routinely used during the acute stage of infection,but these pharmaceutic agents can be of benefit after resolution of the infec-tion. The anti-inflammatory and chondroprotective properties of theseagents may be beneficial during the healing process of the synovial compart-ment and may help to reduce the capsulitis or adhesion formation usuallyobserved after joint or tendon sheath infections. One of the authors (JL) rec-ommends intra-articular medication with HA and corticosteroids 6 weeks


after resolution of the infection. More research in this area is necessary toincrease the number of horses that can return to full athletic performanceafter synovial infections.

Hoof structures

Wounding of the coffin joint can and should be approached as for otherjoints. The other, almost unique, synovial structure within the equine foot isthe navicular bursa. The navicular bursa is structured and responds simi-larly to joint and tendon sheath tissues in that it is a synovial compartment.The main difference is the relatively isolated and protected location of thenavicular bursa. The navicular bursal location renders it difficult to reachand assess for potential contamination.

The navicular bursa is most commonly wounded by puncture from thesolar surface of the foot. The bursa can also be opened from heel bulb lac-erations that wound deeply into the heel region; however, this is far lesscommon than puncture trauma. The nature of puncture wounds canmake certain diagnosis of navicular involvement difficult. The keratinizedtissue of the sole and frog is quite elastic and may not reveal the exact loca-tion of acute puncture wounds. It is recommended that radiographic imagesbe made of any foot with a penetrating foreign body while the foreign bodyis in place. It is helpful for a veterinarian to be able to evaluate a foot beforea nail or other foreign body has been removed. At least two radiographicprojections are necessary to assess the location of the foreign body. Withmore chronic cases, purulent exudate and/or distortion of the solar tissuescan make identification of a tract easier. Positive-contrast studies of pene-trating tracts or bursal tissues can also be helpful in diagnosing septic bur-sitis. As with other synovial structures, early diagnosis is the key to success.Delays of greater than 24 hours seem to result in more challenging treatmentrequirements and a decreasing prognosis for soundness as treatment delaysincrease.

The basic tenets of treatment are the same as for septic synovitis in anyother location. The challenging location of the navicular bursa makes phys-ical treatment difficult. Traditionally, the ‘‘street nail’’ procedure has beenused to open the palmar or plantar aspect of the navicular bursa for drain-age, debridement, and lavage. This procedure is effective, although modifi-cations to the procedure also seem to accomplish the same goalssuccessfully. Reviews of septic navicular bursitis have indicated a poor prog-nosis for success of the street nail procedure [70]. This may be attributable toa number of factors, however, including the dimensions of the open ventralapproach. When only the soft tissue structures of the foot and navicularbursa are involved, the traditional street nail approach can be abbreviatedto expand the wound site for drainage and lavage. This can reduce the mag-nitude of the soft tissue disruption and perhaps improve clinical results. Thearthroscopic approach for navicular bursa lavage has been described [71].

384 LUGO & GAUGHAN

This seems to be a serviceable procedure for lavage and some visual inspec-tion of the bursal anatomy. Some cases require continuous drainage for res-olution of the septic process, however. It has been demonstrated fromclinical cases that open drainage can be beneficial and can also providea ready portal for repeated lavage.

Deep penetrating trauma that does not involve the synovial structures ofthe foot can reach the distal phalanx. Subsolar abscesses that are refractoryto routine care and deep puncture wounds should be considered candidatesfor developing septic pedal osteitis. This can be a difficult diagnosis in theearly stages; however, with time and loss of bone, radiographic assessmentcan be used to assess bone involvement accurately. Local lysis and loss ofuniform osseous density as seen on a 60� dorsoventral projection of the dis-tal phalanx are the diagnostic signs for septic pedal osteitis (Fig. 4).

Treatment of septic pedal osteitis should be based on removal of the dis-eased bone. It is unlikely that systemic, regional, or local antimicrobial ther-apy alone can resolve the septic process in the distal phalanx. The locallyinvolved bone may be devitalized and antimicrobial penetration limited,such that clinical signs can abate during antimicrobial use only to returnwhen antimicrobials are discontinued. Debridement of the infected bone isnecessary. This can be accomplished from a solar approach or throughthe hoof wall. The ventral approach has some advantages in that ventraldrainage is achieved and the solar aspect of the foot can be fit to a treatmentplate shoe for easy access and wound management. Debridement of the dis-tal phalanx can be performed under general anesthesia or with local anesthe-sia and standing restraint. A distal limb tourniquet is highly recommendedto maintain visibility of the surgical site. Debridement can be performedwith a curette or powered instruments. An interface between diseased and

Fig. 4. The local lysis of bone is consistent with septic pedal osteitis.


normal bone is typically apparent based on color and texture. Debridementcan be stopped once hard and lighter colored bone is exposed. A treatmentplate shoe is usually placed to allow repeated wound cleaning after surgery.The treatment plate is recommended until second-intention healing and ke-ratinization of the solar tissues are complete. The prognosis for futuresoundness is good if the insertion of the deep digital flexor tendon andthe distal interphalangeal joint are not affected [72].

Summary

Septic arthritis, tenosynovitis, bursitis, and septic diseases of the distallimbs of horses can be successfully treated, and affected horses can returnto athletic work. These results are most likely after early accurate diagnosisand aggressive targeted treatment. In some instances, protracted rehabilita-tion programs may also be required. If treatment is not pursued aggressivelythrough diagnostic and therapeutic efforts, affected horses can have debili-tating and life-threatening complications. Therefore, timing and earlysuccess with treatment are essential to return a horse to normal.

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