Endoscopy of the Digital Flexor Tendon Sheath in Horses

An arthroscopic procedure for examination of the digital flexor tendons and tendon sheath was developed in 16 equine limbs and 12 horses. Distension of the tendon sheath and insertion of the arthroscope was accomplished through a cul-de-sac on the palmar or plantar surface of the tendon sheath 1 to 2 cm palmar or plantar to the digital neurovascular structures and between the annular ligament and proximal digital annular ligament. A single arthroscope entry point allowed examination of all regions of the tendon sheath cavity and most surfaces of the digital flexor tendons within the sheath. Distal to the fetlock, surgical procedures could be performed through additional entry portals on the lateral, medial, or palmar surfaces of the tendon sheath. The palmar digital vessels and nerves were avoided by palmar placement of the instrument incisions and insertion of a needle before incising the skin. The fetlock canal and proximal regions of the tendon sheath were examined by redirecting the arthroscope. Flexion of the fetlock aided passage of the arthroscope into the proximal tendon sheath regions. Evaluation of the palmar surface of the superficial digital flexor tendon was limited by the midline attachment of the tendon sheath, otherwise the surfaces of the tendons and tendon sheath could be examined with 25 degrees and 70 degrees arthroscopes. The tendon sheath was more tightly invested to the tendons in the proximal regions, limiting the arthroscope movements and second instrument access.     

Vascular Supply of the Tendon of the Equine Deep Digital Flexor Muscle Within the Digital Sheath

The vascular and microvascular anatomy of the equine deep digital flexor tendon (DDFT) within the digital sheath was studied by injecting the vasculature with either colored latex or barium sulphate for radiographic, microangiographic, histologic, and computed tomographic (CT) evaluation. Consecutive 4-mm thick two-dimensional CT slice data were reconstructed to 3-dimen-sional volumetric images to enhance spatial evaluation of the blood supply. Gross dissection and angiographic studies identified three major vascular sources. Above the fetlock, the DDFT was supplied by either a branch of the medial palmar artery (Arteriae digitalis palmaris communis II) or a branch of the medial palmar digital artery (A. digitalis [palmaris propria III] medialis). Below the fetlock, the DDFT was supplied by branches from the lateral and medial palmar branches to the proximal phalanx (Ramus palmaris phalangis proximalis). The most distal aspect of the tendon received small branches from the medial and lateral palmar digital arteries. Using histology and microangiography we observed an extensive and uniform intratendinous vascular network above and below the fetlock, with a relatively avascular region of tendon palmar to the fetlock. The most distal 2.0 to 2.5 cm of the tendon within the sheath was heavily infiltrated with fibrocartilage along its dorsal aspect.     

Treatment of a Cyst-Like Synovial Hernia Associated with the Digital Flexor Tendon Sheath of a 17-Year-Old Pony

The aim of this study is to describe the successful treatment of a synovial hernia associated with the digital flexor tendon sheath (DFTS) in a 17-year-old pony. The pony presented with left forelimb lameness and multiple unusual swellings of the palmar and plantar aspect of the fetlock. The lameness was isolated to a swelling in close proximity to the DFTS of the left forelimb using diagnostic analgesia, and on diagnostic imaging, the swelling was found to be associated with the DFTS. The hernia resolved after percutaneous drainage and intralesional corticosteroids and atropine and pressure bandaging. Reports of synovial hernias in the horse associated with the DFTS are rare. This difference should be considered when presented with cases exhibiting similar clinical signs.     

EVALUATION OF THE EQUINE DIGITAL FLEXOR TENDON SHEATH USING DIAGNOSTIC ULTRASOUND AND CONTRAST RADIOGRAPHY

This study was designed to evaluate the normal anatomy of the digital flexor tendon sheath using contrast radiography and diagnostic ultrasound. Iodinated contrast medium was injected into eight cadaver limbs and the limbs immediately frozen. Lateromedial and dorsopalmar/plantar radiographs were made. These limps were then cut transversely and proximal to distal radiographs of each slab were made. This cross sectional contrast methodology allowed the visualization of the relative size and shape of the superficial and deep digital flexor tendons as well as the potential space taken by effusions of the digital flexor tendon sheath.
The second part of the study used twelve live animals with normal digital flexor tendon sheaths. Ultrasonographic measurement of the structures of the digital flexor tendon sheath at each level were compiled. This documented the ability of diagnostic ultrasound to image: 1) the superficial and deep digital flexor tendons, 2) the proximal and distal ring of the manica flexoria , 3) the straight and oblique sesamoidean ligaments, and 4) the mesotendinous attachments to the superficial and deep flexor tendons. Iodinated contrast medium was then injected into the digital flexor tendon sheath and the ultrasonography repeated. These images were compared with those obtained from contrast radiography and prosections of twenty normal limbs. The iodinated contrast medium enhanced sonographic imaging of the structures of the digital tendon sheath, particularly the abaxial borders of the superficial digital flexor tendon branches and the mesotendinous attachments to the superficial and deep digital flexor tendons.     

Endoscopically Assisted Annular Ligament Release in Horses

An endoscopically assisted technique for internally dividing the palmar or plantar annular ligament was developed in six cadaver limb specimens and two anesthetized horses. Under arthroscopic view, a slotted cannula was inserted into the digital sheath through a stab wound proximal to the annular ligament and advanced through the fetlock canal superficial to the flexor tendons with the slot oriented toward the fibers of the annular ligament. Division of the annular ligament by 90-degree tipped open and guarded blades was observed and verified by direct arthroscopic view. At necropsy, complete division of the annular ligament without iatrogenic damage to the neurovascular structures was confirmed by dissection. Annular ligament division was performed in seven horses with complex tenosynovitis conditions. Tenoscopic examination and removal of tendon and digital sheath adhesions, masses, and bands was followed by endoscopically assisted annular ligament transection. At follow-up, five horses were sound athletes without recurrent digital sheath problems, one horse had residual lameness, and one horse was still convalescing.     

Dynamic flexion/extension and non‐weight bearing ultrasonography is helpful for identifying manica flexoria tears in horses

Lesions of the manica flexoria are a tenoscopic finding in horses with digital flexor tendon sheath tenosynovitis. This retrospective case series study describes the ultrasonographic findings in seven horses admitted for digital flexor tendon sheath swelling associated with lameness and tenoscopic confirmation of a manica flexoria tear. Six horses had a partial manica flexoria tear, one a complete rupture. The ultrasonographic examination included a static examination on the weight and non‐weight bearing limb and a dynamic limb assessment during flexion and extension. The main ultrasonographic finding at the static weight bearing examination in horses with a partial tear was an asymmetrical appearance of the manica flexoria at the level of the junction with the lateral border of the superficial digital flexor tendon, or an incomplete visualization of the manica flexoria in case of complete rupture. The split edges of the completed ruptured manica flexoria were seen floating in the synovial fluid at the examination in flexion. In six of seven cases, the superficial digital flexor tendon slid abnormally relative to the deep digital flexor tendon, during flexion/extension movements, with medial displacement of the superficial digital flexor tendon, appearance of an anechoic gap between the flexor tendons or reduced superficial digital flexor tendon sliding. Because ultrasonographic diagnosis of the manica flexoria tear is considered challenging, detection of these ultrasonographic features is helpful to increase the likelihood of identifying manica flexoria tears prior to tenoscopy. Authors recommend static ultrasonographic examination of the manica flexoria using a flexed limb position and dynamic ultrasonographic examination using flexion and extension positioning for horses with suspected digital sheath injury.     

Proximal Digital Annular Ligament Desmotomy in Horses: A Cadaveric Study

Proximal digital annular ligament (PDAL) desmitis occurs in horses for which PDAL desmotomy is the only reported treatment. The presented work aims to develop a technique for safely performing PDAL desmotomy in horses. Twenty hind limbs and 13 forelimbs, harvested from horses dead or euthanized for reasons unrelated to any structure in the pastern region, were used. All horses were free of disease at the level of their PDAL. Proximal digital annular ligament desmotomy was performed using a minimally invasive approach to the digital flexor tendon sheath between the palmar (plantar) annular ligament and the PDAL, using a medial or a lateral access. Limbs were immediately dissected after the procedure to assess the completeness of the PDAL desmotomy and any possible damage to surrounding structures. The PDAL was successfully transected in all limbs except one. Damage to the surrounding tissue included transection of the palmar digital nerve (n = 1), longitudinal tear of the superficial digital flexor tendon (n = 3), and transection of the ligament of the ergot (n = 21). A medial approach was found to be safer than a lateral approach. In conclusion, PDAL desmotomy can be performed in a safe, repeatable, and technically easy way. This is, to our knowledge, the first report of a standardized technique for performing a PDAL desmotomy in the horse.     

New surgical approach to the plantar fetlock joint through the digital flexor tendon sheath wall and suspensory ligament apparatus in cases of concurrent septic synovitis in two cattle

A new surgical approach to the infected fetlock joint is described in two cattle suffering from septic tenosynovitis of the lateral digital flexor tendon sheaths of the right lateral hind-digits with concurrent septic serofibrinous arthritis of the adjoining fetlock joints, caused by penetrating wounds. In both patients, the infected sheaths were opened and the superficial and deep digital flexor tendons were removed. Intraoperatively, a small entry through the fetlock joint capsule was detected, directly distal to the lateral proximal sesamoid bone. The tract was surgically enlarged and a second approach into the plantar fetlock joint pouch was created proximally by making a 3 cm long and 0.5 cm wide incision between the two lateral suspensory ligament branches. This allowed easy access to the plantar joint pouch, removal of fibrin clots and an effective joint lavage using 5L of sterile saline solution. The incisions of the fetlock joint capsules remained unsutured and were drained using soft polyurethane foam to preclude premature closure. The tendon sheath wounds remained unsutured. In both patients, the digital flexor tendon sheath and the fetlock joint were lavaged daily for the following three days. The infection was eliminated in both cattle and both fully recovered without residual lameness.     

Comparison of conventional and alternative arthroscopic approaches to the palmar/plantar pouch of the equine distal interphalangeal joint

Reasons for performing the study: The conventional arthroscopic approach to the palmar/plantar aspect of the distal interphalangeal joint (DIPJ) may result in the inadvertent penetration of the digital flexor tendon sheath (DFTS) and the navicular bursa (NB). This iatrogenic communication would be undesirable subsequent to arthroscopic lavage of a septic DIPJ. Hypothesis: A lateral/medial approach to the palmar/plantar aspect of the DIPJ will result in a significantly lower rate of inadvertent penetration of the DFTS and NB, whilst still providing adequate intra‐articular evaluation. Methods: The conventional palmar/plantar approach or a novel lateral/medial approach to the DIPJ was performed on cadaver fore‐ and hindlimbs (30 limbs/approach). Subsequently, India ink was injected into the dorsal pouch of the DIPJ, and the DFTS (n = 60) and NB (n = 20) were examined for the presence/absence of ink. In addition, observations of the number of attempts made to access the joint, evidence of iatrogenic intra‐articular trauma and occurrence of incomplete visualisation of the palmar/plantar pouch were recorded. Results: With the conventional approach, DFTS penetration was noted in 18/30 (60%) of the limbs, compared to 1/30 (3.3%) with the lateral/medial approach (P≤0.001). NB penetration was seen in 5/10 limbs with the palmar/plantar approach compared to 0/10 with the lateral/medial approach (P = 0.01). No significant differences were found between the approaches in the number of attempts made to access the joint, the incidence of iatrogenic intra‐articular trauma, or the occurrence of incomplete visibility of the palmar/plantar pouch. Conclusions: The novel lateral/medial approach to the DIPJ significantly decreases the risk of inadvertent penetration of the DFTS and NB. Potential relevance: The novel lateral/medial approach to the DIPJ is an effective technique to gain access to the palmar/plantar pouches, and is particularly advantageous for arthroscopic lavage of a septic DIPJ.     

Intrathecal deep digital flexor tenectomy for treatment of septic tendonitis/tenosynovitis in four horses

Objective: To describe partial removal of the intrathecal component of the deep digital flexor tendon (DDFT) in horses with chronic septic DDF tendonitis and tenosynovitis unresponsive to conventional therapy, and to report long‐term outcome. Study Design: Case series. Animals: Horses (n=4). Methods: Four horses with chronic septic DDF tendonitis and tenosynovitis were treated by surgical tenectomy of the intrathecal component of the DDFT, followed by stabilization in casts and subsequent corrective shoeing. All horses were previously managed unsuccessfully with combinations of conventional therapy consisting of systemic antibiotics, through and through tendon sheath lavage/open drainage, regional limb perfusions, tenoscopy with debridement and transection of the palmar/plantar annular ligament, and intrathecal antibiotics. Results: Time from initial injury/diagnosis to tenectomy ranged from 10 to 210 days. Mean hospitalization time after surgery was 82 days. Long‐term follow‐up (>1.5 years; mean, 3.8 years) was available. All 4 horses were able to walk comfortably at pasture and were used as broodmares. Conclusions: Intrathecal tenectomy is a viable surgical procedure for treatment of chronic septic tenosynovitis of the digital sheath that is complicated by septic tendonitis of the DDFT.     

Septic tenosynovitis in horses: 25 cases (1983-1989).

The medical records of 25 horses with septic tenosynovitis treated over 7 years (1983 to 1989) were reviewed to determine clinical features of the disease and response to treatment. The median age of horses with septic tenosynovitis was 5 years (range, 1 month to 21 years). Fourteen fore limbs and 11 hind limbs were affected. Sepsis was located in the sheath of the digital flexor tendons of 22 horses. Sepsis was located in the sheath of the extensor carpi radialis tendon (1 horse), sheath of the long digital extensor tendon (1 horse), or sheath of the common digital extensor tendon (1 horse) in the remaining horses. Nine horses received only medical treatment, using a combination of broad-spectrum parenterally administered antimicrobial drugs (8 of 9 horses), nonsteroidal anti-inflammatory drugs (8 of 9 horses), or irrigation of the wound (4 of 9 horses). Fourteen horses were treated surgically with either transection of the palmar/plantar annular ligament of the metacarpo/metatarsophalangeal joint (5 of 14 horses), lavage of the sheath after insertion of drains into the sheath (7 of 14 horses), or both (2 of 14 horses). All horses treated surgically were concurrently treated parenterally with broad-spectrum antimicrobial drugs and nonsteroidal anti-inflammatory drugs. Two horses with septic tenosynovitis were not treated and were euthanatized at the owners' request. Five horses were euthanatized before discharge from the hospital. Two horses (both treated medically) were lost to follow-up. Follow-up information was obtained for 18 horses, 6 to 55 months after discharge from the hospital.(ABSTRACT TRUNCATED AT 250 WORDS)     

Surgical Approach for Removal of Nonarticular Base Sesamoid Fragments of the Proximal Sesamoid Bones in Horses

Objectives— To describe a surgical approach for the removal of nonarticular base sesamoid fragments in performance horses and to report the outcome. Study Design— Retrospective study. Animals— Horses (n=11), 7 months to 10 years of age, with lameness because of nonarticular base sesamoid fragments. Methods— Lameness was localized to the metacarpophalangeal/metatarsophalangeal region by clinical examination or response to diagnostic local anesthesia. Radiographs confirmed the diagnosis of a nonarticular base sesamoid fragment. Surgical removal was performed with an incision over the base of the affected sesamoid through the digital flexor tendon sheath. After identifying the fragment with the aid of needles, a small vertical incision was made in the straight distal sesamoidean ligament (SDSL) and the fragment was freed from its attachments and removed. Six months convalescence and rehabilitation was prescribed for all horses. Results— Eleven horses had 16 nonarticular fragments of the base of the proximal sesamoid bones. Eleven (69%) fragments occurred in the forelimbs with the right front (82%) and medial sesamoid (73%) more commonly affected. Horses were treated by surgical fragment removal. In horses with follow‐up, 9 of 10 returned to their intended use. Conclusions— Surgical removal of nonarticular base sesamoid fragments can be accomplished through a palmar/plantar approach through the digital flexor tendon sheath and SDSL. This “keyhole” approach minimizes damage to the distal sesamoidean ligament attachments to the sesamoid base and allows some horses to return to their intended use. Clinical Relevance— Surgical removal of nonarticular base sesamoid fragments should be considered in horses with performance‐limiting lameness as a result of the fragment.     

Surgical Anatomy for Desmotomy of the Accessory Ligament of the Superficial Digital Flexor Tendon (Proximal Check Ligament) in Horses

Dissections were performed to study the surgical anatomy for desmotomy of the accessory ligament of the superficial digital flexor tendon (proximal check ligament [PCL]). The surgical approach was initiated by incising the skin cranial to the cephalic vein and caudal to the distal radius. A palpable foramen in the antebrachial fascia that transmits a branch of the cephalic vein was used to advance deeper dissection. After the antebrachial fascia was incised, the fan-shaped PCL was exposed by retracting the en-sheathed tendon of the flexor carpi radialis muscle caudally. Desmotomy was performed gradually to avoid severing branches of the palmar carpal rete that pervade the ligament. Complete transection was evidenced by visualization of the membranous roof of the carpal canal distally, the muscle belly of the radial head of the deep digital flexor centrally, and loose areolar connective tissue along the caudal radius proximally. The vessels of the palmar carpal rete were visible coursing between the severed edges of the PCL. This report highlights relevant anatomic landmarks to facilitate an accurate desmotomy.     

Mineralization can be an incidental ultrasonographic finding in equine tendons and ligaments

Tendon/ligament mineralization is recognized in horses but information regarding its clinical significance is limited. The aims of this observational study were to report the structures most commonly affected by ultrasonographically detectable mineralization and, for these, determine frequency of diagnosis and key clinical features. Cases presented at our hospital in April 1999–April 2013 and September 2014–November 2015 were included: a total of 27 horses (22 retrospective, five prospective). Mineralizations were most common in deep digital flexor tendons (10) and suspensory ligament branches (eight), representing 10% and 7% (estimated), respectively, of horses diagnosed with injuries to these structures during the study. Two deep digital flexor tendon and three suspensory ligament branch cases showed bilateral mineralization. Deep digital flexor tendon mineralization was restricted to the digital flexor tendon sheath, most commonly in the proximal sheath (±sesamoidean canal), and seven of 10 cases involved hindlimbs. Suspensory ligament branch mineralization was visible in the same ultrasound window as the proximal sesamoid bones in 10/11 limbs and six of eight cases involved forelimbs. Previous corticosteroid medication was a feature of one deep digital flexor tendon and one suspensory ligament branch case. Mineralization was associated with lameness in some but not all limbs. Mineralized foci within the deep digital flexor tendon preceded hypoechoic lesion formation in two limbs. Of the cases with deep digital flexor tendon or suspensory ligament branch injury only, one of three and two of three cases, respectively, became sound. Findings indicated that tendon/ligament mineralization can be associated with lameness in some horses, but can also be an incidental finding.     

Chronic eosinophilic granulomatous tenosynovitis in a Quarter Horse mare

A 5-year-old Quarter Horse mare was presented to the Michigan State University Equine Surgery Service for evaluation of a right hind metatarsophalangeal joint injury. On presentation, the horse was a grade 4/5 lame. Radiographs and ultrasonography showed peritendinous ossification/mineralisation of soft tissue structures and digital flexor tenosynovitis with profound intracapsular mineralisation. A digital flexor tendon sheath tenoscopy was performed with a plantar annular ligament desmotomy and a manica flexoria ligament tenotomy. During surgery, a significant amount of tan granular material was found within the digital tendon sheath. Approximately 80% of this material was removed, and a sample was sent for histopathology. The horse was diagnosed with eosinophilic granulomatous tenosynovitis. Long-term follow-up revealed improvement with four treatments of intralesional triamcinolone given 2–4 weeks apart. The horse became serviceably sound (grade 1/5) and was beginning light work under the saddle approximately 5 months post-tenoscopy.     

MUSCULOSKELETAL LESIONS AND LAMENESS IN 121 HORSES WITH CARPAL SHEATH EFFUSION (1999–2010)

Equine carpal sheath effusion has multiple etiologies. The purpose of this retrospective study was to describe the prevalence of distinct musculoskeletal lesions lameness in a sample of horses with a clinical diagnosis of carpal sheath effusion. A total of 121 horses met inclusion criteria. Seventy‐four percent (89/121) of horses were lame at presentation; middle‐aged (9–18 years, 80%) and older (> 18 years, 85%) horses were lame more frequently than young horses (< 9 years, 44%). Ninety‐three percent (113/121) were diagnosed with osseous and/or soft tissue abnormalities. Of these 113 horses, 10 exhibited osseous abnormalities, whereas 111 were diagnosed with soft tissue lesions. Eighty‐four percent (93/111) of the soft tissue injuries extended from the caudodistal antebrachium to the palmar metacarpus. The superficial digital flexor tendon (98/111; 88%) and accessory ligament of the superficial digital flexor tendon (64/111; 58%) were the most commonly injured structures, with both structures affected in 41 (41/111; 37%) horses. Injuries within the caudodistal antebrachium included the superficial digital flexor musculotendinous junction (66), the accessory ligament of the superficial digital flexor tendon (64), and deep digital flexor muscle (21), in isolation or in combination with other structures. Increased echogenicity in the medial superficial digital flexor musculotendinous junction was detected in 40 horses and was significantly associated with increasing age (middle‐aged, 19/40; old, 18/40). Findings from this study indicated that age should be taken into consideration for horses presented with carpal sheath effusion and that adjacent structures within the caudodistal antebrachium should be included in evaluations.     

Tenosynovitis of the digital flexor tendon sheath and annular ligament constriction syndrome caused by longitudinal tears in the deep digital flexor tendon: a clinical and surgical report of 17 cases in warmblood horses

REASONS FOR PERFORMING STUDY: Inflammation of the digital flexor tendon sheaths is a chronic and nebulous condition often unresponsive to medical and surgical treatment. OBJECTIVES: To evaluate the incidence of longitudinal tears (LT) as the underlying cause of chronic tenosynovitis and annular ligament constriction syndrome (ALCS) in warmblood horses. METHODS: The records of 25 horses with chronic tenosynovitis and ALCS in which tenoscopical inspection of the digital flexor tendon sheath (DFTS) was performed between 1999-2000 were reviewed. Of 25 horses, 17 were diagnosed with an LT in the deep digital flexor tendon (DDFT). All horses had a history of distension of the DFTS and/or signs of an ALCS. All cases presented typical signs of a chronic inflamed DFTS on ultrasonography and 11 horses showed ultrasonographic changes (echogenic material or an irregular outlining) at the lateral or medial border of the DDFT. The diagnosis of LTs of the DDFT was established in all cases by tenoscopy. Surgical treatment consisted of removal of the torn collagen fibrils using a mechanical resector and decompressing the fetlock canal by a transection of the palmar annular ligament (PAL) using a hook knife under tenoscopic control. RESULTS: Ten horses became sound and resumed their previous level of work, 3 horses remained lame, 4 horses returned to previous level of work but needed intrasynovial treatment of the DFTS and reduced competition frequency to remain sound. CONCLUSIONS: Horses presented with chronic inflamed DFTS and/or ALCS might suffer from LTs in the DDFT; however, the diagnosis cannot be established with absolute certainty using only ultrasonography. Longitudinal tears should be suspected if ultrasonographic changes are present lateral or medial to the border of the DDFT but tenoscopical examination of the tendon sheath is essential to establish an accurate diagnosis and an effective treatment. POTENTIAL RELEVANCE: The presence of these LTs might explain why some cases of chronic tenosynovitis of the digital flexor tendon sheath and/or ALCS do not respond on surgical transection of the PAL alone without tenoscopy.     

Computed tomographic contrast tenography of the digital flexor tendon sheath of the equine hindlimb

Pre‐surgical investigation of digital flexor tendon sheath pathology remains challenging with current standard imaging techniques. The aim of this prospective, anatomical, pilot study was to describe the anatomy of the equine hind limb digital flexor tendon sheath using a combination of computed tomography (CT) and computed tomographic contrast tenography in clinically normal cadaver limbs. Ten pairs of hind limbs with no external abnormalities were examined from the level of the tarsometatarsal joint distally. Limbs initially underwent non‐contrast CT examination using 120 kVp, 300 mAs, and 1.5 mm slice thickness. Sixty millilitres of ioversol iodinated contrast media and saline (final concentration 100 mg/ml) were injected using a basilar sesamoidean approach. The computed tomographic contrast tenography examination was then repeated, before dissection of the specimens to compare gross and imaging findings. The combined CT and computed tomographic contrast tenography examinations provided excellent anatomical detail of intra‐thecal structures. The borders of the superficial and deep digital flexor tendons, and the manica flexoria were consistently identifiable in all limbs. Detailed anatomy including that of the mesotenons, two of which are previously undescribed, and the plantar annular ligament were also consistently identifiable. Dissection of all 10 pairs of limbs revealed there to be no pathology, in accordance with the imaging findings. In conclusion, the combination of CT and computed tomographic contrast tenography may be useful adjunctive diagnostic techniques to define digital flexor tendon sheath pathology prior to surgical exploration in horses.