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  • Author or Editor: Stephen E. Weisbrode x
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Objective—To determine the effects of phenylbutazone (PBZ) on bone activity and bone formation in horses.

Animals—12 healthy 1- to 2-year-old horses.

Procedures—Biopsy was performed to obtain unicortical bone specimens from 1 tibia on day 0 and from the contralateral tibia on day 14. Fluorochromic markers were administered IV 2 days prior to and on days 0, 10, 15, and 25 after biopsy was performed. Six horses received PBZ (4.4 mg/kg of body weight, PO, q 12 h) and 6 horses were used as controls. All horses were euthanatized on day 30 and tissues from biopsy sites, with adjacent cortical bone, were collected. Osteonal density and activity, mineral apposition rate (MAR), and percentage of mineralized tissue filling the biopsy-induced defects in cortical bone were assessed. Serum samples from all horses were analyzed for bone-specific alkaline phosphatase activity and concentration of PBZ.

Results—MAR was significantly decreased in horses treated with PBZ. Regional acceleratory phenomenon was observed in cortical bone in both groups but was significantly decreased in horses treated with PBZ. Osteonal activity was similar at all time points in all horses. In control horses, percentage of mineralized tissue filling the cortical defects was significantly greater in defects present for 30 days, compared with defects present for 14 days. Differences in percentage of mineralized tissue were not detected in horses treated with PBZ.

Conclusions and Clinical Relevance—PBZ decreased MAR in cortical bone and appeared to decrease healing rate of cortical defects in horses. (Am J Vet Res 2000;61:537–543)

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in American Journal of Veterinary Research


Objective—To evaluate the effects of triamcinolone acetonide (TA), sodium hyaluronate (HA), amikacin sulfate (AS), and mepivacaine hydrochloride (MC) on articular cartilage morphology and matrix composition in lipopolysaccharide (LPS)-challenged and unchallenged equine articular cartilage explants.

Sample Population—96 articular cartilage explants from 4 femoropatellar joints of 2 adult horses.

Procedures—Articular cartilage explants were challenged with LPS (100 ng/mL) or unchallenged for 48 hours, then treated with TA, HA, AS, and MC alone or in combination for 96 hours or left untreated. Cartilage extracts were analyzed for glycosaminoglycan (GAG) content by dimethyl-methylene blue assay (ng/mg of dry wt). Histomorphometric quantification of total lacunae, empty lacunae, and lacunae with pyknotic nuclei was recorded for superficial, middle, and deep cartilage zones.

Results—LPS induced a significant increase in pyknotic nuclei and empty lacunae. Treatment with TA or HA significantly decreased empty lacunae (TA and HA), compared with groups without TA or HA, and significantly decreased empty lacunae of LPS-challenged explants, compared with untreated explants. Treatment with AS or MC significantly increased empty lacunae in unchallenged explants, and these effects were attenuated by TA. Treatment with MC significantly increased empty lacunae and pyknotic nuclei and, in combination with LPS, could not be attenuated by TA. Content of GAG did not differ between unchallenged and LPS-challenged explants or among treatments.

Conclusions and Clinical Relevance—Treatment with TA or HA supported chondrocyte morphology in culture and protected chondrocytes from toxic effects exerted by LPS, AS, and MC.

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in American Journal of Veterinary Research


Objective—To determine whether human parathyroid hormone (hPTH) gene in collagen matrix could safely promote bone formation in diaphyseal or subchondral bones of horses.

Animals—8 clinically normal adult horses.

Procedure—Amount, rate, and quality of bone healing for 13 weeks were determined by use of radiography, quantitative computed tomography, and histomorphometric analysis. Diaphyseal cortex and subchondral bone defects of metacarpi were filled with hPTH1-34 gene-activated matrix (GAM) or remained untreated. Joints were assessed on the basis of circumference, synovial fluid analysis, pain on flexion, lameness, and gross and histologic examination.

Results—Bone volume index was greater for cortical defects treated with hPTH1-34 GAM, compared with untreated defects. Bone production in cortical defects treated with hPTH1-34 GAM positively correlated with native bone formation in untreated defects. In contrast, less bone was detected in hPTH1-34 GAM-treated subchondral bone defects, compared with untreated defects, and histology confirmed poorer healing and residual collagen sponge.

Conclusions and Clinical Relevance—Use of hPTH1-34 GAM induced greater total bone, specifically periosteal bone, after 13 weeks of healing in cortical defects of horses. The hPTH1-34 GAM impeded healing of subchondral bone but was biocompatible with joint tissues. Promotion of periosteal bone formation may be beneficial for healing of cortical fractures in horses, but the delay in onset of bone formation may negate benefits. The hPTH1-34 GAM used in this study should not be placed in articular subchondral bone defects, but contact with articular surfaces is unlikely to cause short-term adverse effects. (Am J Vet Res 2004;65:1223–1232)

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in American Journal of Veterinary Research


Objective—To identify patterns and correlations of gross, histologic, and gene expression characteristics of articular cartilage from horses with osteoarthritis.

Animals—10 clinically normal horses and 11 horses with osteoarthritis of the metacarpal condyles.

Procedures—Metacarpophalangeal joints were opened and digitally photographed, and gross lesions were scored and quantified. Representative cartilage specimens were stained for histologic scoring. Total RNA from dorsal and palmar articular surfaces was processed on an equine gene expression microarray.

Results—Histologic scores were greater in both regions of osteoarthritic joints, compared with corresponding regions in control joints. Cartilage from the palmar aspect of diseased joints had the highest histologic scores of osteoarthritic sites or of either region in control joints. A different set of genes for dorsal and palmar osteoarthritis was identified for high and low gene expression. Articular cartilage from the dorsal region had surface fraying and greater expression of genes coding for collagen matrix components and proteins with anti-apoptotic function, compared with control specimens. Articular cartilage from the palmar region had greater fraying, deep fissures, and less expression of genes coding for glycosaminoglycan matrix formation and proteins with anti-apoptotic function, compared with cartilage from disease-free joints and the dorsal aspect of affected joints.

Conclusions and Clinical Relevance—Metacarpal condyles of horses with naturally occurring osteoarthritis had an identifiable and regional gene expression signature with typical morphologic features.

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in American Journal of Veterinary Research


Objective—To provide long-term follow-up information for a series of dogs and cats with invasive and noninvasive thymomas treated by excision alone.

Design—Retrospective case series.

Animals—9 cats and 11 dogs with thymoma.

Procedures—Medical records were reviewed. The following factors were analyzed for their effect on prognosis: age of dog or cat, invasiveness of the tumor, percentage of lymphocytes in the mass (percentage lymphocyte composition) on histologic evaluation, and mitotic index of the mass.

Results—All patients were treated with excision of the tumor alone. Median overall survival time for the cats was 1,825 days, with a 1-year survival rate of 89% and a 3-year survival rate of 74%. Median overall survival time for the dogs was 790 days, with a 1-year survival rate of 64% and a 3-year survival rate of 42%. Recurrence of thymoma was observed in 2 cats and 1 dog, and a second surgery was performed in each, with subsequent survival times of 5, 3, and 4 years following the first surgery. Percentage lymphocyte composition of the mass was the only factor that was significantly correlated with survival time; animals with a high percentage of lymphocytes lived longer.

Conclusions and Clinical Relevance—Results of this study indicated that most cats and dogs with thymomas did well after excision. Even cats and dogs with invasive masses that survived the surgery and the few cats and dogs with recurrent thymomas or paraneoplastic syndromes had a good long-term outcome. Excision should be considered an effective treatment option for dogs and cats with thymomas.

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in Journal of the American Veterinary Medical Association