Abstract
Simple SummaryEarly detection of racehorses at risk of stress fracture is key to reducing the number of horses with catastrophic fractures while racing. Bone changes are often visible in the limbs of Thoroughbred racehorses in work, particularly in the fetlock region. However, it is currently unknown whether some of these changes indicate an impending fracture or are a healthy adaptation to high-speed exercise. This study looks at imaging and gross changes in a specific area (parasagittal grooves (PSGs) of the cannon bone) and the utility of X-ray, computed tomography (CT) and magnetic resonance imaging (MRI) to detect the changes. All fetlock joints were assessed from twenty horses that died during racing or training, including horses with and without fetlock fracture. Overall, X-ray was poor for detecting PSG changes. Some PSG changes on CT and MRI were common in Thoroughbred racehorses and possibly represent normal bone adaptation when seen in clinical cases. However, certain CT and MRI findings were more prevalent in horses with a fracture, possibly indicating microdamage accumulation and increased risk of fracture. Bilateral advanced imaging is recommended in clinical cases of suspected fetlock pathology.(1) Background: Parasagittal groove (PSG) changes are often present on advanced imaging of racing Thoroughbred fetlocks and have been suggested to indicate increased fracture risk. Currently, there is limited evidence differentiating the imaging appearance of prodromal changes in horses at risk of fracture from horses with normal adaptive modelling in response to galloping. This study aims to investigate imaging and gross PSG findings in racing Thoroughbreds and the comparative utility of different imaging modalities to detect PSG changes. (2) Methods: Cadaver limbs were collected from twenty deceased racing/training Thoroughbreds. All fetlocks of each horse were examined with radiography, low-field magnetic resonance imaging (MRI), computed tomography (CT), contrast arthrography and gross pathology. (3) Results: Horses with fetlock fracture were more likely to have lateromedial PSG sclerosis asymmetry and/or lateral PSG lysis. PSG lysis was not readily detected using MRI. PSG subchondral bone defects were difficult to differentiate from cartilage defects on MRI and were not associated with fractures. The clinical relevance of PSG STIR hyperintensity remains unclear. Overall, radiography was poor for detecting PSG changes. (4) Conclusions: Some PSG changes in Thoroughbred racehorses are common; however, certain findings are more prevalent in horses with fractures, possibly indicating microdamage accumulation. Bilateral advanced imaging is recommended in racehorses with suspected fetlock pathology.
Highlights
The increasing use of advanced imaging modalities for the examination of the fetlock region in racing Thoroughbreds has enabled improved identification of pathologies in horses presenting for lameness localized to the fetlock region [1]
(4) Conclusions: Some parasagittal grooves (PSG) changes in Thoroughbred racehorses are common; certain findings are more prevalent in horses with fractures, possibly indicating microdamage accumulation
The findings were investigated on a horse, limb and a horse, limb and PSG level, both as singular observations and in specific combinations, PSG level, both as singular observations and in specific combinations, with the goal of with the goal of identifying any changes that may have a positive association with fetlock identifying any changes that may have a positive association with fetlock fracture
Summary
The increasing use of advanced imaging modalities for the examination of the fetlock region in racing Thoroughbreds has enabled improved identification of pathologies in horses presenting for lameness localized to the fetlock region [1]. Interpretation of the imaging findings is complicated, by the fact that certain changes likely represent a normal adaptive response of bones and can be considered within normal limits for an athlete in work. At the time of writing, there is no solid evidence differentiating the imaging appearance of some pathologies from normal stress-related modeling in response to galloping. This makes it difficult to determine which of the subclinical abnormalities identified with advanced imaging truly represent a legitimate cause for concern
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