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  • Author or Editor: C. Wayne McIlwraith x
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Using biodegradable pins, sternal cartilage autografts were fixed into osteochondral defects of the distal radial carpal bone in ten 2 to 3-year-old horses. The defects measured 1 cm2 at the surface and were 4 mm deep. Control osteochondral defects of contralateral carpi were not grafted. After confinement for 7 weeks, horses were walked 1 hour daily on a walker for an additional 9 weeks. Horses were euthanatized at 16 weeks. Half of the repair tissue was processed for histologic and histochemical (H&E and safranin-O fast green) examinations. The other half was used for the following biochemical analyses: type-I and type-II collagen contents, total glycosaminoglycan content, and galactosamine-to-glucosamine ratio. On histologic examination, the repair tissue in the grafted defects consisted of hyaline-like cartilage. Repair tissue in the nongrafted defects consisted of fibrocartilaginous tissue, with fibrous tissue in surface layers. On biochemical analysis, repair tissue of grafted defects was composed predominantly of type-II collagen; repair tissue of nongrafted defects was composed of type-I collagen. Total glycosaminoglycan content of repair tissue of grafted defects was similar to that of normal articular cartilage. Total glycosaminoglycan content of nongrafted defects was 62% of that of normal articular cartilage (P < 0.05). Repair tissue of all defects was characterized by galactosamine-to-glucosamine ratio significantly (P < 0.05) higher than that of normal articular cartilage. These results at 16 weeks after grafting indicate that sternal cartilage may potentially constitute a suitable substitute for articular cartilage in large osteochondral defects of horses.

Free access
in American Journal of Veterinary Research


OBJECTIVE To evaluate the effects of exercise in an underwater treadmill (UWT) on forelimb biomechanics and articular histologic outcomes in horses with experimentally induced osteoarthritis of the middle carpal joint.

ANIMALS 16 horses.

PROCEDURES An osteochondral fragment was induced arthroscopically (day 0) in 1 middle carpal joint of each horse. Beginning on day 15, horses were assigned to exercise in a UWT or in the UWT without water (simulating controlled hand walking) at the same speed, frequency, and duration. Thoracic and pelvic limb ground reaction forces, thoracic limb kinematics, and electromyographic results for select thoracic limb muscles acting on the carpi were collected on days -7 (baseline), 14, 42, and 70. Weekly evaluations included clinical assessments of lameness, response to carpal joint flexion, and goniometric measurements of thoracic limb articulations. At study conclusion, articular cartilage and synovial membrane from the middle carpal joints was histologically examined.

RESULTS Exercise in a UWT significantly reduced synovial membrane inflammation and resulted in significant clinical improvements with regard to symmetric thoracic limb loading, uniform activation patterns of select thoracic limb muscles, and return to baseline values for carpal joint flexion, compared with results for horses with simulated hand walking.

CONCLUSIONS AND CLINICAL RELEVANCE Overall improvements in thoracic limb function, joint range of motion, and synovial membrane integrity indicated that exercise in a UWT was a potentially viable therapeutic option for the management of carpal joint osteoarthritis in horses.

Full access
in American Journal of Veterinary Research


Objectives—To determine concentrations of matrix metalloproteinase (MMP)-2 and -9 in synovial fluid; and mRNA expression of MMP-1, -13, and -3; interleukin[ IL]-1α and β; and tumor necrosis factor(TNF)-α in synovial membrane and articular cartilage from horses with naturally occurring joint disease.

Sample Population—Synovial fluid (n = 76), synovial membrane (59), and articular cartilage (45) from 5 clinically normal horses and 55 horses with joint disease categorized as traumatic (acute [AT] or chronic [CT]), osteochondritis dissecans (OCD), or septic (S).

Procedure—Synovial fluid gelatinase concentrations were analyzed, using zymography. Synovial membrane and articular cartilage mRNA expression for MMP-1, -3, and -13, IL-1α and β, TNF-α, type-II collagen, and aggrecan were analyzed, using quantitative reverse transcriptase-polymerase chain reaction.

Results—Synovial fluid pro-MMP-2 concentration was significantly higher in diseased joints than normal joints. Septic joints had significantly higher concentrations of pro and active MMP-9. Stromelysin-1 was expressed in ≥ 80% of synovial membrane and articular cartilage samples and was strongly influenced by age. Collagenases were rarely expressed, with MMP- 13 expressed only in diseased joints. Interleukin-1β expression was significantly higher in all OCD samples and was influenced by age. Tumor necrosis factor- α expression was significantly higher in cartilage from joints with AT and OCD. There was no correlation between MMP or cytokines and type-II collagen or aggrecan expression.

Conclusions and Clinical Relevance—Matrix metalloproteinase- 2 and -3 are abundant in naturally occurring joint disease and normal joints. Interleukin-1β and TNF-α may be important in the pathogenesis of OCD. Age affects MMP and IL-1β concentrations. (Am J Vet Res 2001;62:1467–1477)

Full access
in American Journal of Veterinary Research


Objective—To assess the net mechanical load on the distal end of the third metacarpal bone in horses during walking and trotting.

Animals—3 Quarter Horses and 1 Thoroughbred.

Procedures—Surface strains measured on the left third metacarpal bone of the Thorough-bred were used with a subject-specific model to calculate loading (axial compression, bending, and torsion) of the structure during walking and trotting. Forelimb kinematics and ground reaction forces measured in the 3 Quarter Horses were used with a musculoskeletal model of the distal portion of the forelimb to determine loading of the distal end of the third metacarpal bone.

Results—Both methods yielded consistent data regarding mechanical loading of the distal end of the third metacarpal bone. During walking and trotting, the distal end of the third metacarpal bone was loaded primarily in axial compression as a result of the sum of forces exerted on the metacarpal condyles by the proximal phalanx and proximal sesamoid bones.

Conclusions and Clinical Relevance—Results of strain gauge and kinematic analyses indicated that the major structures of the distal portion of the forelimb in horses acted to load the distal end of the third metacarpal bone in axial compression throughout the stance phase of the stride.

Full access
in American Journal of Veterinary Research


Objective—To evaluate use of infrared spectroscopy for diagnosis of traumatic arthritis in horses.

Animals—48 horses with traumatic arthritis and 5 clinically and radiographically normal horses.

Procedures—Synovial fluid samples were collected from 77 joints in 48 horses with traumatic arthritis. Paired samples (affected and control joints) from 29 horses and independent samples from an affected (n = 12) or control (7) joint from 19 horses were collected for model calibration. A second set of 20 normal validation samples was collected from 5 clinically and radiographically normal horses. Fourier transform infrared spectra of synovial fluids were acquired and manipulated, and data from affected joints were compared with controls to identify spectroscopic features that differed significantly between groups. A classification model that used linear discriminant analysis was developed. Performance of the model was determined by use of the 2 validation datasets.

Results—A classification model based on 3 infrared regions classified spectra from the calibration dataset with overall accuracy of 97% (sensitivity, 93%; specificity, 100%). The model, with cost-adjusted prior probabilities of 0.60:0.40, yielded overall accuracy of 89% (sensitivity, 83%; specificity, 100%) for the first validation sample dataset and 100% correct classification of the second set of independent normal control joints.

Conclusions and Clinical Relevance—The infrared spectroscopic patterns of fluid from joints with traumatic arthritis differed significantly from the corresponding patterns for controls. These alterations in absorption patterns may be used via an appropriate classification algorithm to differentiate the spectra of affected joints from those of controls.

Full access
in American Journal of Veterinary Research


OBJECTIVE To investigate potential associations between repository radiographic findings and subsequent performance of Quarter Horses competing in cutting events.

DESIGN Retrospective cohort study.

SAMPLE Repository radiographs (ie, radiographs obtained at the time of sale) for 343 client-owned horses.

PROCEDURES Repository radiographic findings were compared with objective measures of performance, including the likelihood of competing; the likelihood of earning money as a 3-year-old, as a 4-year-old, and as a 3- and 4-year-old combined; and the amount of money earned as a 3-year-old, as a 4-year-old, and as a 3- and 4-year-old combined.

RESULTS The presence of mild osteophytes involving the distal aspect of the tarsal joint was significantly associated with lower mean earnings as a 4-year-old. The presence of osteophytes on the dorsoproximal aspect of the middle phalanx of the hind limbs was significantly associated with an increased odds of earning money as a 4-year-old. Radiographic lesions of the medial femoral condyle of the stifle joint were not significantly associated with subsequent performance.

CONCLUSIONS AND CLINICAL RELEVANCE Most abnormalities identified on repository radiographs were not significantly associated with subsequent performance. The significant association between mild tarsal osteophytosis and earnings was unexpected. Results of the present study indicated the need for further investigation of the relationship between radiographic findings and performance outcome in Western performance horses.

Full access
in Journal of the American Veterinary Medical Association



To evaluate the effects of a gene transfer approach to IL-1β inhibition in an equine osteochondral chip fragment model of joint injury using a self-complementary adeno-associated virus with interleukin receptor antagonist transgene cassette (scAAVIL-1ra), as posttraumatic osteoarthritis in horses, similar to people, is a significant clinical problem.


16 horses were utilized for the study.


All horses had an osteochondral chip fragment induced arthroscopically in one middle carpal joint while the contralateral joint was sham operated. Eight horses received either scAAVIL-1ra or saline in the osteoarthritis joint. Horses were evaluated over 70 days clinically (lameness, imaging, and biomarker analysis) and euthanized at 70 days and evaluated grossly, with imaging and histopathology.


The following findings were statistically significant. Injection of scAAVIL-1ra resulted in high synovial fluid levels of IL-1ra (0.5 to 9 μg/mL) throughout the duration of the experiment (70 days). Over the duration, we observed scAAVIL-1ra to improve lameness (lameness score relative improvement of 1.2 on a scale of 0 to 5), cause suppression of prostaglandin E2 (a relative decline of 30 pg/mL), and result in histological improvement in articular cartilage (decreased chondrocyte loss and chondrone formation) and subchondral bone (less osteochondral splitting and osteochondral lesions). Within the synovial membrane of scAAVIL-1ra–treated joints, we also observed perivascular infiltration with CD3-positive WBCs, suggesting lymphocytic T-cell perivascular infiltration commonly observed with viral transduction.


These data provide support for further evaluation and optimization of scAAVIL-1ra gene therapy to treat equine osteoarthritis.

Restricted access
in Journal of the American Veterinary Medical Association


OBJECTIVE To determine effects of prosthetic laryngoplasty on return to racing, performance index, and career longevity in racing Quarter Horses with recurrent laryngeal neuropathy (RLN) and to evaluate performance variables for horses with RLN undergoing prosthetic laryngoplasty, compared with a control horse population.

DESIGN Multicenter, retrospective cohort study.

ANIMALS 162 racing Quarter Horses with RLN treated with prosthetic laryngoplasty (case horses) and 324 racing Quarter Horse without RLN (control horses).

PROCEDURES Medical and race records of case and control horses examined at 5 referral centers between January 2000 and December 2015 were reviewed retrospectively. Two control horses were matched with each case horse. Return to racing, earnings, number of racing starts, performance index, and career longevity were evaluated.

RESULTS The odds of returning to racing did not differ significantly between case and control horses but decreased with increasing age. Neither racing starts nor career longevity were affected by prosthetic laryngoplasty or by RLN grade. In fact, horses undergoing laryngoplasty for treatment of RLN and horses with the lowest RLN grade before surgery had higher performance indices after the surgery, compared with indices for control horses.

CONCLUSIONS AND CLINICAL RELEVANCE The faster speeds and shorter distances raced with Quarter Horses could alter how RLN impacts respiratory variables and performance in Quarter Horses, compared with other racehorse breeds. Further study is needed to understand the impacts of RLN and surgical treatments for RLN in racing Quarter Horses.

Full access
in Journal of the American Veterinary Medical Association


OBJECTIVE To investigate risk factors for the development of pasture- and endocrinopathy-associated laminitis (PEAL) in horses and ponies in North America.

DESIGN Case-control study.

ANIMALS 199 horses with incident cases of PEAL and 351 horses from 2 control populations (healthy horses [n = 198] and horses with lameness not caused by laminitis [153]) that were evaluated in North America between January 2012 and December 2015 by veterinarian members of the American Association of Equine Practitioners.

PROCEDURES North American members of the American Association of Equine Practitioners were contacted to participate in the study, and participating veterinarians provided historical data on incident cases of PEAL, each matched with a healthy control and a lameness control. Conditional logistic regression analysis was used to compare data on PEAL-affected horses with data on horses from each set of controls.

RESULTS Horses with an obese body condition (ie, body condition score ≥ 7), generalized or regional adiposity (alone or in combination), preexisting endocrinopathy, or recent (within 30 days) glucocorticoid administration had increased odds of developing PEAL, compared with horses that did not have these findings.

CONCLUSIONS AND CLINICAL RELEVANCE The present study identified several risk factors for PEAL that may assist not only in managing and preventing this form of laminitis, but also in guiding future research into its pathogenesis.

Full access
in Journal of the American Veterinary Medical Association