Graduate Thesis Or Dissertation
 

Musculoskeletal Injury Pathogenesis in Racehorses

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k930c392r

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  • Racehorses are elite athletes that undergo repetitive stresses from jogging, cantering, and galloping exercises, and there is significant evidence that the majority of racehorse musculoskeletal injuries are due to repetitive stress or overuse. Musculoskeletal injuries have negative consequences on the racing industry through the loss of use or death of racehorses, injury or death of jockeys, economic loss for trainers and owners, and poor public perception of the racing industry. Pre-existing pathology has been shown to be associated with catastrophic racehorse fractures. The overall objectives of this dissertation were to investigate lesions and regions within racehorses that are suspected or known to accumulate pre-existing pathology that can lead to fracture. Third carpal bone fracture is one of the most common racehorse fractures. Additionally, lumbar vertebral fractures and diaphyseal or metaphyseal third metacarpal bone (MC3) fractures frequently result in horse euthanasia and jockey injury. Third carpal bone (C3) osteochondral disease is believed to predispose racehorses to C3 fracture, and subchondral porosities have been documented with advanced osteoarthrosis. Thirty C3s were collected bilaterally from 10 racehorses with unilateral, complete fracture (6 Thoroughbred, 4 Quarter Horse; 2-5 years old) and unilaterally from 10 age/breed matched racehorses without C3 fracture. Subchondral densification, gross cartilage lesions, dorsal lucencies and fracture surface lesions were quantified using gross, radiographic, computed tomography (CT), and microCT evaluations. Bone volume fraction (BV/TV) was assessed in 2 volumes of interest (VOIs) from the radial (VOIr) and intermediate facets (VOIi). Fractured surfaces had gross evidence of pre-existing lesions. Contralateral and control cartilage scores were not different (p=0.11). Radiographic, but not CT, densification scores were higher in contralateral bones compared to controls (p=0.01 and 0.21 respectively). Dorsal lucencies were detected frequently in both cases and controls with CT and radiographs (p=0.17 and 1.0 respectively). BV/TV was lowest in the VOIr of fractured C3s (82.8±4.9%), followed by the VOIr of contralateral bones (88.8±9.3%), which were significantly lower than all other VOIs (96.2±4.6% to 98.4±2.7%). C3 fractures occur in association with focal subchondral porosity, and a similar process occurs within contralateral bones. Knowledge of specific lesions associated with fracture should aid in lesion detection and fracture prevention. Spinal pathology in the lumbosacral region is a source of poor performance in horses. Prior research found lumbosacral anatomical variations and physeal closure abnormalities in Quarter Horse racehorses investigated for lumbar vertebral fracture. Lumbosacral specimens were collected from 16 Quarter Horses humanely euthanized for reasons other than lumbosacral disease or fracture (aged 0 to 22-years-old; 15 non-racehorses and 1 racehorse). Specimens were assessed using computed tomographic, gross, and histological (H&E stained sections) examination. Six lumbar vertebrae were found in 15/16 (94%) cases, with dorsal spinous process divergence at L5-L6 in 3/16 (19%) cases. Regions of physeal inactivity were present in cases as young as 4 months of age, with L4-S1 physes inactive in all cases 2 years of age or older. Residual cartilage was present within physes until 5-8 years of age. Chondrocyte disorganization (7/12; 58%) and retention (11/12; 92%) with increased bone compaction adjacent retention and disorganization was frequently observed in cases with un-fused physes. Nucleus pulposus tissue was present in 75% of cases. Lumbosacral articular facet pathology was present in 11/16 (69%) cases. Articular subchondral linear lucency with associated sclerosis was present in 9/16 (56%) cases (aged 4 months to 22 years). Physeal disorganization with bone compaction occurred frequently, potentially indicating specific mechanisms for physeal senescence or indicating stress and pathology in these regions. This study provides further insight into the equine lumbosacral spine. The anatomical and histological findings should provide veterinarians with information to aid them in performing more accurate diagnostics and treatments, as well as aid in future interpretation of potentially pathologic findings in this region. Pre-existing lesions with diaphyseal MC3 fracture without condylar involvement were recently described, warranting further investigation. Thirteen MC3s, collected bilaterally from racehorses with unilateral, complete diaphyseal or metaphyseal fracture without condylar involvement (Thoroughbreds; 2-5 years old) and unilaterally from 13 age/breed/sex/limb matched racehorses without MC3 fracture, were studied. Dorsal cortical expansion and lucencies were examined using gross, radiographic, and computed tomographic evaluations. Intact bones underwent single axial compression to failure. Data was analyzed with t-tests, ANOVA, and Fisher’s exact tests, with p≤0.05 set for statistical significance. Contralateral case bones were more likely to contain a dorsal cortical lucency (p=0.047), but not dorsal cortical expansion (p=0.73), than controls. Dorsal cortical lucencies were most frequently located in the distal diaphysis. All bones with a distal diaphyseal lucency broke through that region, while bones with middle diaphyseal lucencies did not. Case contralateral bone maximum compressive load was not different from controls (p=0.48). However, case bones had significantly lower maximum compressive loads when they broke through a cortical lucency compared to when they did not (p=0.027). Dorsal cortical expansion appears to be protective until fracture occurs through a porous region. Distal dorsal cortical lucency and older animals were overrepresented in cases compared to the current literature, potentially allowing for identification of horses at higher risk for diaphyseal fracture. This research provides valuable information and insight into racehorse fractures and fracture etiology in the third carpal bone, lumbosacral spine, and third metacarpal bone. This dissertation provides evidence that detection prior to catastrophic breakdown, while feasible, is difficult. These studies provide important information into racehorse fracture etiology, and should improve injury detection and fracture prevention.
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  • Equine lumbosacral vertebral research was supported by an American Quarter Horse Foundation Young Investigators Grant.
  • Third carpal bone research was funded through an Oregon State University DCS Resident Research Grant.
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  • Pending Publication
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  • 2020-01-03 to 2022-03-09

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