Elution of antimicrobials from a cross-linked dextran gel: In vivo quantification.

REASONS FOR PERFORMING STUDY: Use of a novel, biodegradable, antimicrobial-impregnated gel provides an alternative method of local treatment of infections in horses. OBJECTIVES: To determine in vivo elution of antimicrobial medications from antimicrobial-impregnated cross-linked dextran gel and to evaluate the effect on wound healing when implanted subcutaneously in horses. METHODS: Amikacin-, vancomycin- or amikacin/clindamycin-impregnated gel was placed subcutaneously in 11 horses' necks, using 6 replicates with a 3 month washout between experiments. Capillary ultrafiltration probes for collection of interstitial fluid were placed 0 cm and 1.5 cm from the gel-filled incisions. Samples were collected at 0, 4, 8 and 12 h, and on Days 1-10. Blood was collected on Days 0, 1 and 7. Amikacin and vancomycin samples were analysed via fluorescence polarisation immunoassay, and clindamycin samples via high-performance liquid chromatography. Histology of biopsy samples was performed at the completion of the study. Differences in mean histomorphological scores between groups were assessed using Wilcoxon's signed ranks test. RESULTS: Maximum antimicrobial concentrations were detected at 4 h (amikacin), and 8 h (vancomycin, and amikacin and clindamycin from the combination gel). Mean ± s.d. peak concentrations for amikacin, vancomycin, amikacin (amikacin/clindamycin) and clindamycin were 6133 ± 1461, 7286 ± 2769, 3948 ± 317 and 985 ± 960, respectively. Median number of days for which antimicrobial concentration remained above minimum inhibitory concentration for target microorganisms at implantation was ≥10 days for vancomycin, 9 days (± 1) for amikacin and 8 days (± 1) for clindamycin. Mean plasma amikacin and vancomycin concentrations were lower than detectable limits; mean serum clindamycin concentrations were 0.52 µg/ml and 0.63 µg/ml at 24 h and 7 days, respectively. There were no significant differences in histomorphological scores between treatment and control incisions (P≥0.22). CONCLUSIONS AND POTENTIAL RELEVANCE: Cross-linked dextran gel is a safe, effective alternative local antimicrobial delivery method.

Evaluation of a novel post operative treatment for sinonasal disease in the horse (1996-2007).

REASONS FOR PERFORMING STUDY: Results of surgical treatment of sinonasal disease in horses have been reported previously; however, this paper describes the outcome of horses in which a specific post operative treatment protocol was used. OBJECTIVES: The objectives of the study were to determine: 1) short- and long-term outcome; 2) complications; and 3) recurrence rates of different disease processes, when horses were treated with a specific treatment protocol. METHODS: Medical records of horses presented for surgical treatment of sinonasal disease from 1996-2007 were reviewed. Results and duration of surgical exploration were recorded. Post operatively, the sinus flaps were re-opened with the horses standing and sedated. Number of horses requiring further treatment (debridement and/or lavage), median number of post operative days when the flap was re-opened, median number of times the flap was opened and median duration of hospitalisation were recorded. Short- and long-term survival and complication rates were determined. RESULTS: Ninety-one horses were included in the study. The sinus flaps were re-opened with the horses standing a median of 3 days post operatively. Thirty-nine horses (43%) required further treatment at this time and 89 horses (97%) survived to discharge. Incision infection was the most common complication encountered (29%). No horse required a blood transfusion. Recurrence rates were 5% for paranasal sinus cysts, 12% for progressive ethmoid haematoma and 50% for neoplasia. CONCLUSIONS: Rapid removal of the primary lesion followed by packing the sinuses and re-evaluating in the standing horse in a more controlled environment offers a safe and effective means to thoroughly assess and treat sinonasal disease. POTENTIAL RELEVANCE: Surgical time, intraoperative haemorrhage, long-term complications and recurrence rates of paranasal sinus diseases treated via frontonasal or maxillary sinus flap may be reduced using this technique.

Histological evaluation of the equine larynx after unilateral laser-assisted ventriculocordectomy.

REASONS FOR PERFORMING STUDY: Trans-endoscopic laser surgery, such as unilateral laser-assisted ventriculocordectomy (LVC), has gained popularity in the treatment of RLN because a laryngotomy incision or general anaesthesia are not required. However, removal of the vocal fold and ventricle takes considerable laser energy and could cause collateral tissue damage, including injury to the adjacent laryngeal cartilages. OBJECTIVES: To document the histological effects of laser surgery on laryngeal tissues in horses that have undergone LVC for the treatment of laryngeal hemiplegia (LH). METHODS: Six horses were used: 4 with experimentally induced LH that had subsequently undergone LVC 6 months prior to euthanasia; and, 2 horses were used as controls. One of the control horses with naturally occurring LH was used to study the effect of neuropathy alone, whereas the other was subjected to euthanasia immediately following LVC to evaluate the acute effect of laser surgery. Using a band saw, each larynx was sectioned transversely at 5 mm intervals and evaluated histologically. RESULTS: Acutely, LVC caused thermal damage to adjacent soft tissues but did not affect the histology of the laryngeal cartilages. Six months after LVC, laryngeal cartilages were histologically normal and there was squamous metaplasia of the repaired laryngeal mucosa, resulting in restitution of the mucosal integrity. CONCLUSIONS: Using a diode laser in contact fashion at 20 W, LVC can be used to remove the laryngeal vocal fold and ventricle without causing laryngeal cartilage damage. POTENTIAL RELEVANCE: Laryngeal chondritis is an unlikely consequence of LVC.

Effects of unilateral laser-assisted ventriculocordectomy in horses with laryngeal hemiplegia.

REASONS FOR PERFORMING STUDY: Recent studies have evaluated surgical techniques aimed at reducing noise and improving airway function in horses with recurrent laryngeal neuropathy (RLN). These techniques require general anaesthesia and are invasive. A minimally invasive transnasal surgical technique for treatment of RLN that may be employed in the standing, sedated horse would be advantageous. OBJECTIVE: To determine whether unilateral laser-assisted ventriculocordectomy (LVC) improves upper airway function and reduces noise during inhalation in exercising horses with laryngeal hemiplegia (LH). METHODS: Six Standardbred horses were used; respiratory sound and inspiratory transupper airway pressure (Pui) measured before and after induction of LH, and 60, 90 and 120 days after LVC. Inspiratory sound level (SL) and the sound intensities of formants 1, 2 and 3 (Fl, F2 and F3, respectively), were measured using computer-based sound analysis programmes. In addition, upper airway endoscopy was performed at each time interval, at rest and during treadmill exercise. RESULTS: In LH-affected horses, Pui, SL and the sound intensity of F2 and F3 were increased significantly from baseline values. At 60 days after LVC, Pui and SL had returned to baseline, and F2 and F3 values had improved partially compared to LH values. At 90 and 120 days, however, SL increased again to LH levels. CONCLUSIONS: LVC decreases LH-associated airway obstruction by 60 days after surgery, and reduces inspiratory noise but not as effectively as bilateral ventriculocordectomy. POTENTIAL RELEVANCE: LVC may be recommended as a treatment of LH, where reduction of upper airway obstruction and respiratory noise is desired and the owner wishes to avoid risks associated with a laryngotomy incision or general anaesthesia.

Prevention of ischaemia-induced small intestinal adhesions in foals.

REASONS FOR PERFORMING STUDY: Treatments addressing variously theorised pathophysiological mechanisms of small intestinal adhesions have been reported. This study applied those classes of treatments to the most clinically relevant aetiology of post operative adhesions. HYPOTHESIS: Treatments addressing the pathophysiology of ischaemia-reperfusion induced adhesions would accordingly reduce the incidence of adhesions from this model. METHODS: Four classes of treatments were administered for 72 h to 16 foals subjected to complete ischaemia followed by reperfusion to create peritoneal adhesions. These groups were: 1) FPG group--flunixin meglumine (1.1 mg/kg bwt i.v., divided q.i.d.), potassium penicillin G (22,000 iu/kg bwt i.v., q.i.d.) and gentamicin (2.2 mg/kg bwt i.v., t.i.d.); 2) HEP group--heparin (80 iu/kg bwt subcut., b.i.d.); 3) DMSO group--dimethylsulphoxide (DMSO) (20 mg/kg bwt [diluted in 500 ml normal saline] i.v., b.i.d.); and 4) SCMC group--sodium carboxymethylcellulose (500 ml 3% sterile solution intraperitoneally, administered only at the beginning of surgery). RESULTS: Post operative intestinal obstruction did not occur in any foal. After 10 days, necropsy revealed bowel-to-bowel adhesions in none of the FPG or DMSO groups, in 2/4 of the SCMC group, in 3/4 of the HEP group and 5/6 foals subjected to the procedure without treatment (UIR group). CONCLUSIONS: Inhibition of the inflammation associated with ischaemia and reperfusion in foals treated with FPG or DMSO decreased small intestinal adhesions in foals. POTENTIAL RELEVANCE: Although anti-inflammatory therapy was shown to eliminate bowel-bowel adhesions in this controlled study, it must be remembered that clinical cases are without control. These therapies are advised to improve the result but are unlikely to eliminate the problem.

Serosal injury in the equine jejunum and ascending colon after ischemia-reperfusion or intraluminal distention and decompression.

OBJECTIVE: To document morphologic changes that occur in equine intestinal serosa after experimentally induced ischemia and subsequent reperfusion (jejunum, ascending colon) or after intraluminal distention and decompression (jejunum). STUDY DESIGN: Morphologic effects of ischemia-reperfusion or intraluminal distention-decompression determined on the serosal layer of the equine jejunum. The large colon serosa was evaluated after ischemia-reperfusion injury. ANIMALS OR SAMPLE POPULATION: Seven adult horses. METHODS: After induction of general anesthesia and ventral median celiotomy, ischemia was created by arteriovenous (AVO) and lumen occlusion of a 20-cm segment of jejunum and ascending colon for 70 minutes, followed by a 60-minute reperfusion period. Intraluminal distention (25 cm H2O) was created in a second 20-cm jejunal segment and maintained within the abdomen for 120 minutes, followed by a 120-minute decompression period. Seromuscular biopsies were obtained upon entering the abdomen and after the ischemic and reperfusion periods, and after the distention and decompression periods along with corresponding control seromuscular biopsies. Samples were processed and examined by light microscopy, transmission electron, and scanning electron microscopy. RESULTS: Ischemia and reperfusion, and intraluminal distention and decompression, resulted in severe morphologic changes in the seromuscular layer of equine jejunum. A similar period of ischemia-reperfusion caused minimal changes in the ascending colon serosa. CONCLUSION: Adult equine jejunum sustains more serosal damage than the ascending colon after similar periods of ischemia-reperfusion injury. Intraluminal distention and subsequent decompression causes serosal damage in the equine jejunum. CLINICAL RELEVANCE: The small intestine is more susceptible to seromuscular layer damage than the ascending colon.

Arthroscopic removal of patellar fracture fragments in horses: five cases (1989-1998).

OBJECTIVE: To evaluate the use of arthroscopy as the primary method for removal of large patellar fracture fragments. DESIGN: Retrospective study. ANIMALS: 5 performance horses of various breeds with patellar fractures. PROCEDURE: Clinical signs of lameness, external evidence of injury, and radiography were used to diagnose and determine fracture orientation. Arthroscopy of the stifle joint was performed on the affected limb with the horse positioned in dorsal recumbency and under general anesthesia. Progress after surgery was determined by evaluating medical records and via telephone conversations with owners. RESULTS: 4 of 5 horses had fractures of the medial aspect of the patella and 1 horse had a fracture of the lateral aspect of the patella. There were no postoperative complications with the joint or the arthroscopic portal incisions. Recovery periods ranged from 3 to 5 months. All horses recovered completely from surgery, and performed at the same or higher level of competition as before arthroscopy. CONCLUSIONS AND CLINICAL RELEVANCE: Femoropatellar joint arthroscopy is a favorable means by which evaluation of the stifle joint and removal of large fracture fragments can be achieved with negligible postoperative complications.

Metacarpophalangeal joint synovial pad fibrotic proliferation in 63 horses.

Medical records, radiographs, and sonograms of 63 horses with metacarpophalangeal joint synovial pad proliferation were examined retrospectively. All horses had lameness, joint effusion, or both signs associated with one or both metacarpophalangeal joints. Bony remodeling and concavity of the distodorsal aspect of the third metacarpal bone (Mc3) just proximal to the metacarpal condyles was identified by radiography in 71 joints (93%); 24 joints (32%) had radiographic evidence of a chip fracture located at the proximal dorsal aspect of the proximal phalanx. Fifty-four joints (71%) were examined by ultrasound. The mean +/- SD sagittal thickness of the synovial pad was 11.3 +/- 2.8 mm. Seventy-nine percent of the horses had single joint involvement with equal distribution, between the right and left forelimbs. Sixty-eight joints in 55 horses were treated by arthroscopic surgery. Sixty joints (88%) had debridement of chondral or osteochondral fragmentation from the dorsal surface of Mc3 beneath the synovial pad and 30 joints (44%) had a bone chip fracture removed from the medial or lateral proximal dorsal eminence of the proximal phalanx. Complete or partial excision of both medial and lateral synovial pads was completed in 42 joints. Only the medial synovial pad was excised or trimmed in 21 joints, and 5 joints had only the lateral pad removed. Eight joints in eight horses were treated by stall rest, administration of intra-articular medication and systemic nonsteroidal anti-inflammatory drugs. Follow-up information was obtained for 50 horses treated surgically and for eight horses treated medically. Forty-three (86%) that had surgery returned to racing; 34 (68%) raced at an equivalent or better level than before surgery. Three (38%) of the medically treated horses returned to racing; only one horse raced better than the preinjury level. Horses that returned to racing at a similar or equal level of performance were significantly younger in age than horses returning at a lower level or not racing (P < or = .05). Overall, horses with synovial pad proliferation treated by arthroscopic surgery had a good prognosis for return to racing at a level equal or better than before injury.

Large colon resection for treatment of lymphosarcoma in two horses.

With the exception of lipoma, neoplasia of the gastrointestinal tract is rare in horses. Lymphosarcoma is the most common neoplasm of the hematopoietic system in horses. In horses with lymphosarcoma of the large colon, clinical signs may include intermittent signs of mild abdominal pain, weight loss, pyrexia, and pelvic flexure impaction caused by impingement of the colonic lumen by the mass. Peritoneal fluid analysis may be normal or have a high total protein concentration. If signs of metastasis are not evident, resection of the large colon affected by the mass may prolong survival.

Radiographic and arthroscopic findings associated with subchondral lucency of the distal radial carpal bone in 71 horses.

Case records and radiographs of 71 horses with subchondral lucency, without radiographic evidence of fracture, located on the distal radial carpal bone were examined retrospectively. All horses had lameness and/or joint effusion referable to the carpus. Distal radial carpal bone subchondral lucency was found as a solitary lesion or as a lesion concurrent and symmetric to a contralateral distal radial carpal bone chip fracture. The lesion appeared radiographically as a lucency or shadow on the distal dorsal margin of the radial carpal bone and was most evident on the flexed lateromedial and dorsolateral-palmaromedial oblique projections. Sixty-four joints in 55 horses underwent arthroscopic surgery. Surgical findings included osteochondral fragmentation in 44 joints, cartilage fragmentation with subchondral bone softening in 17 joints and cartilage fraying in 3 joints. Corresponding third carpal bone lesions were observed in 18 joints and moderate to severe synovitis was present in 24 joints. Carpal bone subchondral radiolucency without a fracture fragment observed on radiographs indicated cartilage and bone damage. In some cases, small chip fractures (1-2 mm) were present within the cartilage debris examined at surgery, yet were not radiographically visible. Follow-up information was obtained on 50 of the operated horses and 14 nonoperated horses. Forty (80%) of the surgically treated horses returned to racing, with 34 (68%) of these horses (20 of 26 with subchondral lucency as a solitary lesion) racing at a level of competition equal to or better than the pre-injury level. Of the 14 horses which were not operated, 6 (42%) returned to racing of which only 2 (14%) raced at the same pre-injury level of competition. Radiographic evidence of radial or intermediate carpal bone subchondral lucency is an indication of cartilage and bone damage which is best treated with arthroscopic surgery.

Microvascular permeability and endothelial cell morphology associated with low-flow ischemia/reperfusion injury in the equine jejunum.

Microvascular permeability of the jejunum of clinically normal equids and microvascular permeability associated with 60 minutes of ischemia (25% baseline blood flow) and subsequent reperfusion were investigated. Eight adult horses were randomly allotted to 2 equal groups: normal and ischemic/reperfusion injury. Lymphatic flow rates, mesenteric blood flow, and lymph and plasma protein concentrations were determined at 15-minute intervals throughout the study. Microvascular permeability was determined by estimates of the osmotic reflection coefficient, which was determined when the ratio of lymphatic protein to plasma protein concentration reached a constant minimal value as lymph flow rate increased (filtration-independent lymph flow rate), which occurred at venous pressure of 30 mm of Hg. Full-thickness jejunal biopsy specimens were obtained at the beginning and end of each experiment, and were prepared for light microscopy to estimate tissue volume (edema) and for transmission electron microscopy to evaluate capillary endothelial cell morphology. The osmotic reflection coefficient for normal equine jejunum was 0.19 +/- 0.06, and increased significantly (P < or = 0.0001) to 0.48 +/- 0.05 after the ischemia/reperfusion period. Microscopic evaluation revealed a significant increase (P < or = 0.0001) in submucosal and serosal volume and capillary endothelial cell damage in horses that underwent ischemia/reperfusion injury. Results indicate that ischemia/reperfusion of the equine jejunum caused a significant increase in microvascular permeability.

Progression of femoropatellar osteochondrosis in nine young horses. Clinical, radiographic and arthroscopic findings.

The clinical and radiographic progression, and arthroscopic findings for nine young horses (< 1 year of age) with femoropatellar osteochondrosis (OCD) are presented. Horses had a 2 to 12 week history of bilateral (8 horses) or unilateral (1 horse) hindlimb lameness. The most consistent clinical signs included femoropatellar joint distention and bilateral hindlimb lameness. At the onset of clinical signs, radiographic lesions were not present (4 horses) or subtle (5 horses), but were easily identified on radiographs taken 4 to 24 weeks later. Arthroscopic surgery was delayed until radiographic changes became obvious. Surgical findings in 20 femoropatellar joints were most commonly osteochondral "flaps" located on the proximal lateral trochlear ridge of the femur and were larger than had been indicated by the radiographs. Eight horses were being used for their intended purpose, which was racing (3 horses were racing and 3 were in race training), dressage (1 horse) or pleasure riding (1 horse). One horse required a second surgery when similar lesions developed on the opposite stifle, and was euthanatized 2 months later because of persistent lameness. One clinical signs are observed, osteochondrosis lesions of the distal femur can progress in foals younger than 9 months of age and the full extent of the radiographic lesion may take several weeks to develop.

Evaluation of the microcirculation of the equine small intestine after intraluminal distention and subsequent decompression.

Effects of intraluminal distention (25 cm of H2O, 120 minutes) and subsequent decompression (60 minutes) on intramural vascular patterns of the small intestine was evaluated in 7 anesthetized horses. Intraluminal distention (25 cm of H2O, 120 minutes) was created in 2 jejunal segments in each horse. Experimental and control segments were removed either immediately after the experimental period or after 60 minutes of decompression. The vascular system of experimental and control jejunal segments was lavaged with NaCl, then was injected with a blue-colored radiopaque medium for microangiography or with a diluted methyl methacrylate for scanning electron microscopy of microcorrosion vascular casts. After angiographic evaluation, tissue sections were prepared for light microscopic evaluation to assess vascular filling and tissue morphology. The distended segments had short villi, which were separated by expanded crypts, and had mesothelial cell loss, neutrophil infiltration, and edema in the seromuscular layer. The number of perfused vessels was significantly (P < 0.05) decreased in the seromuscular layer and, to a lesser extent, in the mucosal layer of the distended segments, compared with controls. After decompression, the morphologic lesions progressed in mucosal and serosal layers and the number of observed vessels increased in all intramural layers; however, vascular density did not return to the predistention state. These results identify altered intramural vascular patterns in the equine jejunum during luminal distention and subsequent decompression.

Evaluation of the microcirculation of the equine jejunum and ascending colon after ischemia and reperfusion.

Intramural vascular patterns of the jejunum and colon were evaluated during ischemic strangulation obstruction (ISO, 70 minutes) and subsequent reperfusion (60 minutes) in 7 adult anesthetized horses. Microvasculature of experimental and control segments was described by comparison of results from microangiography, light microscopy, and scanning electron microscopy of vascular replicas. Experimental and control segments with isolated vascular arcades were removed either immediately after the experimental period or after 60 minutes of reperfusion. Blood was flushed from the vascular system by use of isotonic NaCl, and the segments were divided. Half of each segment was perfused with a modified radiopaque medium for microangiographic evaluation, and half was perfused with dilute methyl-methacrylate to create a vascular replica to be studied by scanning electron microscopy. Microangiographic section also were evaluated for histologic changes. Microvasculature of jejunal control segments and all colon segments was similar to described normal microvasculature of the equine jejunum and ascending colon. In jejunal ISO segments, intramural perfusion was redistributed away from the mucosa. In the villi, the central arteriole was short and convoluted and the subepithelial capillaries were not filled. The submucosal vessels and crypt capillaries were congested, compared with those of controls, and the serosal vessels were not filled in the ischemic segments. Histologic grade II-III mucosal lesion was seen in jejunal ISO segments. Reperfused jejunal segments had a transmural hyperemic response, and previously unfilled capillaries were observed in all intestinal layers. After reperfusion, the mucosal lesion progressed to grade III-IV and a cellular infiltrate and edema formation were observed in the serosa. The intramural vasculature of the ischemic and reperfused colon remain unchanged. Minimal histologic damage was observed in the colon after 70 minutes of ISO or after 60 minutes of reperfusion.

Removal of a fracture fragment from the palmar aspect of the intermediate carpal bone in a horse.

A 10-year-old Dutch Warmblood gelding sustained a fracture of the palmar tuberosity of the intermediate carpal bone 2 weeks prior to admission. The dorsolateral-palmaromedial oblique and flexed lateromedial radiographic views revealed the fracture line. The palmar fracture fragment from the intermediate carpal bone was removed by arthrotomy of the palmar intercarpal joint, which was approached through the carpal canal. Twenty months after surgery, the horse was show jumping without evidence of lameness.

Healing of full-thickness cartilage compared with full-thickness cartilage and subchondral bone defects in the equine third carpal bone.

The effect of lesion depth on the quality of third carpal bone cartilage repair was examined. A 1-cm diameter articular defect penetrating the calcified cartilage in one limb and the subchondral bone plate in the opposite limb was created in the radial facet of the third carpal bones. Clinical and xeroradiographic examinations were performed every 4 weeks until 4 months (3 horses) and 6 months (3 horses) after surgery. The synovial membrane, non-opposing articular surfaces and articular defects were examined grossly, histologically and histochemically. Grossly, deeper defects contained thicker, whiter tissue, but both joints contained generalised degenerative changes. Defects extending through calcified cartilage were filled deeply by fibrocartilage and superficially by fibrous connective tissue. Defects extending through subchondral bone were consistently filled with hyaline-like cartilage in the depths of the lesion, fibrocartilage in the intermediate layer and fibrous connective tissue superficially. The results indicate that subchondral bone is the source of hyaline-like cartilage repair tissue and suggest that quality of healing of cartilage defects may be improved by penetrating the subchondral bone plate. It also appears that the synovitis associated with the procedure must be controlled before the procedure can be advocated for treatment of clinical cases.

Comparison of two grafting methods in 4.0-mm drill defects in the third metacarpal bone of horses.

In 6 horses, bilateral metacarpal vertical series of three 4.0-mm unicortical drill holes were made. At random, one of each series of 3 holes was filled using a sternal 4.0-mm cancellous bone cylinder or a slurry of cancellous bone injected into the hole or left as an empty control. All horses had lateral metacarpal xeroradiographs at monthly intervals. Three horses (6 metacarpi) were examined post mortem after 4 months and 3 others after 6 months. Immediate through 4-month post-operative xeroradiographs demonstrated increased density in the holes with cancellous cylinders and no difference could be seen between the untreated controls and holes injected with slurry. From 5 months, no radiographic difference could be seen between the treatment groups. No consistent histological difference between treatment groups could be detected. In conclusion, no justification for clinical grafting of 4.0-mm unicortical dorsal metacarpal drill holes could be found.