Veterinary Science - Theses
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ItemEquine forelimb asymmetries and factors influencing hoof shape( 2014)This thesis provided detailed descriptions of bilateral asymmetries in equine distal forelimbs and explored factors influencing hoof shape. Measurement techniques described included the development of a photogrammetric method. This allowed for quick and highly accurate measurements to be taken from a 3-D model of the hoof, which was created from photographs taken at various locations surrounding the hoof. This is the first study to successfully recreate a hoof model from photographs, to measure proximal hoof circumference (PHC) using photogrammetry, and to demonstrate the feasibility of using it during an exercise study. Cadaver limbs were used to describe bilateral forelimb asymmetries. That study found significant differences in third metacarpal (MC3) bone weight, second phalanx (P2) specific gravity, and third phalanx (P3) angle. PHC also shared a linear relationship with several bone measurements; MC3 width, MC3 length, P3 angle, MC3 weight, and P3 weight. This was the first study to report bilateral differences in equine bone weight and specific gravity and to identify a relationship between PHC and internal bone measurements. There were also significant bilateral differences in ratios measured directly from yearling radiographs. Specifically A/B and G/H, and A/B shared a relationship with one performance variable. Other studies have reported radiographic asymmetries, but few have focused on young horses and performance. Factors that could influence hoof shape included increased load. Two pilot studies found that there were no changes in PHC with an increase in body weight or with the additional weight of a rider. The third acknowledged bilateral differences in hoof shape and loading using a pressure mat. It is one of the first studies to identify a difference in loading under the forelimbs, which warrants further investigation. Two preliminary studies found that there were no changes in PHC or hoof angle following a training period of exercise in a circle or immediately after exercise on a treadmill. This is one of the first studies to use horses exercising on a lunge-line. Previous research has found a change in PHC and hoof angle during race training, but this study did not show a difference after moderate intensity exercise. The farrier study indicated that the hoof changed shape as a result of trimming and growth. The farrier performing the trim affected some variables and hoof angle was more symmetrical post-trimming. This study supported previous work and contributed details on the magnitude of change. In the final experiment reported, shod horses exhibited a larger decrease in PHC and a decrease in hoof angle. This indicated that the shoes may limit deformation of the hoof which is supported by previous work. It is the first study to recognize PHC changes in shod horses. This thesis contributed to a greater understanding of equine asymmetries, their development, and factors influencing hoof shape. It aids in the design of beneficial hoof care practices.
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ItemDetection of subchondral bone pathology in the fetlock joint of Thoroughbred racehorses( 2013)REASONS FOR PERFORMING STUDY: Two common subchondral bone injuries occur within the fetlock joint; palmar osteochondral disease and condylar fracture of the distal metacarpus. Both result in lameness, whereas condylar fracture can potentially be life threatening. Pre-existing pathology is commonly identified in horses with condylar fractures, detection of which prior to fracture would have both welfare and economic benefits for the racing industry. However the close spatial association of these two conditions complicates imaging of the distal metacarpus/metatarsus. AIMS: To describe patterns of radiopharmaceutical uptake in fetlock joints of Thoroughbred racehorses and to evaluate racing performance post-scintigraphy and to assess the potential of high-resolution peripheral quantitative computed tomography to predict condylar fracture in Thoroughbred racehorses by imaging the subchondral bone of the distal palmar metacarpus and the cortical bone of the mid diaphysis. HYPOTHESES: Increased radiopharmaceutical uptake (IRU) in the metacarpal (MC) and metatarsal (MT) condyles is more common than IRU in the parasagittal grooves and is associated with poorer post-diagnosis performance than controls. Horses with lateral condylar fracture would have greater bone volume fraction, greater localised subchondral bone thickness at the fracture site and that articular surface fissures would be more prominent in the contralateral limb than controls. METHODS: Scintigraphic evaluation of the fetlock region - A retrospective, case control study was performed using horses undergoing scintigraphy for the investigation of lameness or poor performance. Location of IRU within the fetlock region was identified and graded in Thoroughbred (TB) racehorses presenting for scintigraphic examination. Performance variables were determined from race records for horses with moderate/marked MC/MT condylar IRU (cases), all other horses undergoing scintigraphy (scintigraphy controls), and age/sex matched controls from the last race in which a case participated (controls). Statistical analysis included quantile regression, Fisher’s exact test, Kaplan-Meier survival curves, log-rank test and Cox regression. High resolution peripheral quantitative computed tomography as a predictor of condylar fracture - A prospective, cross-sectional, case control study was performed using limbs from all TB racehorses that died or were euthanased on Victorian metropolitan racetracks between June 2007 and June 2009 (n=37). Groups were assigned as follows: horses with MC fractures with a condylar component (cases, n=13); horses with no limb fracture (controls, n=8); horses with fracture in other bones or disruption of suspensory apparatus (other fatal musculoskeletal injuries, n=16). The palmar distal aspect was removed and a 5cm length of midshaft of MC created and stored in 70% ethanol. The palmar condyles of MC and midshaft examined with high resolution peripheral quantitative computed tomography (HR-pQCT) and morphometric parameters computed. Statistical analysis included logistic regression and Spearman’s correlations. RESULTS: Scintigraphic evaluation of the fetlock region - Metacarpal/MT condylar IRU was identified in 103/220 horses with only 3/220 having parasagittal IRU. Moderate/marked IRU was identified in the forelimb MC and hindlimb MT condylar regions in 62 and 48 horses respectively with palmaromedial and plantarolateral IRU most common. Forelimb cases had fewer starts (P<0.001), reduced earnings (P<0.001), fewer wins (P=0.03) and fewer overall places (P<0.001) than controls. Hindlimb cases had fewer starts (P=0.003) and reduced earnings (P=0.01) than controls. Cases were more likely to return to racing later than controls following a rest period (P=0.003). Cases were older than scintigraphy controls (P<0.001). High resolution peripheral quantitative computed tomography as a predictor of condylar fracture - No significant differences were identified in HR-pQCT variables of distal MC and midshafts between cases and controls. Epiphyseal BV/TV was greater in injured limbs of horses with any fatal limb injury compared to controls (OR 1.20, 95% CI 1.01-1.42, P=0.034). An epiphyseal BV/TV >0.74 resulted in a sensitivity of 82.8% and specificity of 62.5% in identifying horses with fatal limb injury. In horses without condylar fracture, increased subchondral bone thickness was associated with POD lesions in the adjacent condyle (rs=0.65, P<0.001). CONCLUSIONS: The identification of condylar fractures prior to catastrophic injury remains challenging. Condylar fractures are rarely identified using bone phase scintigraphy and this may be because lameness is not observed by owners and trainers prior to fracture. Even with high resolution imaging of the distal metacarpus, early condylar fracture detection is challenging although increased BV/TV of the distal metacarpus may be useful for determining horses at risk of any fatal breakdown injury. HR-pQCT of the third metacarpal bone midshaft appears to be of no value for predicting fatal injury. Racehorses with moderate/marked condylar IRU have a shortened racing career, are less successful than age/sex matched controls and are older than other racehorses presented for scintigraphy. POTENTIAL RELEVANCE: Effective screening for condylar fractures prior to catastrophic breakdown would require imaging of horses that are not showing clinical signs of lameness or poor performance. Applying advanced imaging to all horses at regular intervals is not only cost prohibitive but the current evidence suggests it is unlikely to be highly effective. POD appears to be performance limiting in Thoroughbred racehorses.