Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 7. Bone and articular cartilage response in the carpus.
OBJECTIVE
To describe features of the morphology of the carpus, quantify the thickness of hyaline and calcified cartilage, and to describe the morphology and density of subchondral bone in the third carpal bone (C3) of young Thoroughbred horses in early training.


METHODS
C3 of seven 2-year-old horses in training and seven untrained horses matched for age, sex and breed were assessed by gross appearance, computed tomography, fine-structure radiography, image analysis of high-resolution photographs, and histology.


RESULTS
Macroscopic lesions in cartilage were few and mild, and not significantly different between groups. High bone mineral density (BMD), in some cases typical of cortical bone, was confined to the dorsal load path, and was significantly higher in trained than in untrained horses (p<0.01). In the most dorsoproximal aspect of the radial articular facet, apparently outside the dorsal load path, the BMD in both trained and untrained horses was significantly less than in other regions of interest (ROIs). Adaptive increase in density was associated with thickening of the (junctions of) trabeculae oriented proximo-distally. Hyaline cartilage was thicker (p<0.001) in the concavity of the radial articular facet than dorsal or palmar to it, and was thicker in the trained than untrained group (p=0.007). No such differences were detected in the thickness of articular calcified cartilage (ACC).


CONCLUSIONS
The rapid response of bone in C3 to relatively small amounts of high-speed exercise was confirmed. A previously unreported increase in thickness of hyaline cartilage was evident, perhaps indicating that this tissue may be more responsive than hitherto thought, at least to particular types of exercise at particular times. These changes occurred with little evidence of abnormality, and thus appeared to be adaptive to the exercise regimen. The model developed should be used for further definition of the exercise stimulus required to produce adaptive, protective changes in sites susceptible to athletic injury.


CONCLUSIONS
The data will serve as reference for use in subsequent imaging studies in which sophisticated aids such as magnetic resonance imaging (MRI) may be used to predict carpal lesions.
Firth
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EC
Massey Equine, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. E.C.Firth@massey.ac.nz
Rogers
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CW
D000818:Animals; D015519:Bone Density / Q000502:physiology; D002348:Carpal Bones / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology; D005260:Female; D006736:Horses / Q000033:anatomy & histology / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012016:Reference Values; D014057:Tomography, X-Ray Computed / Q000662:veterinary