High-intensity exercise induces structural, compositional and metabolic changes in cuboidal bones--findings from an equine athlete model.

Fatigue fracture of cuboidal bones occurs in the human foot as well as the equine carpus. The racehorse provides a naturally-occurring model to study the effects of high-intensity exercise on the morphology and metabolism of cuboidal bones. We studied both the mineral and the collagenous matrix of the third (C(3)) and radial (C(r)) carpal bones of raced and non-raced Thoroughbred (TB) horses. We hypothesised that racehorses would show increases in the mineral component of these bones and post-translational modifications of the collagenous matrix alongside changes in markers of collagen remodelling and bone formation. C(3) and C(r) carpal bones were retrieved from raced TB horses (n=14) and non-raced TB horses (n=11). Standardised proximal-distal sections were taken from each bone and these were sliced transversely to study the proximal-distal differences in bone metabolism from the subchondral plate through to trabecular bone. Histomorphometry and bone mineral density measurements were performed in parallel with biochemical analyses including total collagen, collagen synthesis and cross-links, matrix metalloproteinases-2 and 9 and their inhibitors, calcium and phosphate, and bone alkaline phosphatase. The results of this study show that, while there is a net increase in bone formation in the racehorses, there is additionally an increase in bone collagen synthesis and remodelling, particularly within the trabecular regions of the bone. The increase in bone density would lead to greater stiffness, particularly in the cortical bone, and failure of this 'stiffer' cortical bone may result from its lack of support from the rapidly remodelling and structurally weakened underlying trabecular bone.

Assessment of a bone biopsy technique for measuring tiludronate in horses: a preliminary study.

This study assessed the feasibility of measuring tiludronate in horses using a minimally invasive bone biopsy technique. Eight horses were treated with intravenous (IV) tiludronate [1 mg/kg bodyweight (BW)], either once (n = 4) or twice, 28 d apart (n = 4). The horses that were treated once were euthanized on days 1, 43, 57, or 92 and those that were treated twice, were euthanized on days 112, 154, 194, or 364. Bone samples were taken bilaterally from each horse at 4 sites: the third metacarpal bone (MCIII), the 13th rib (R13), the tuber coxae (TC), and the cuboid bone (CB). Test samples were taken with a 5-mm diameter dental drill, while larger reference samples were taken with an osteotome. The concentrations of tiludronate were measured by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The TC was the easiest site to sample, and no technical difficulties were encountered for extraction and measurement. Drill sampling at the MCIII was difficult. Moreover, both the extraction and measurement caused technical problems and results were unreliable in most cases (93%). Drill samples obtained from the R13 were very small and access to the CB required considerable dissection, which would not be feasible in vivo. Forty-six percent and 36% of the tiludronate measurements performed on the R13 and CB samples, respectively, were unreliable. The ratio of tiludronate concentrations ranged from 73% to 185% (median: 118%) in the TC, 65% to 208% (median: 81%) in the R13, and 26% to 110% (median: 57%) in the CB. In all but 1 horse, the highest concentrations of tiludronate were found in the TC. It was concluded that bone biopsies performed at the TC were adequate for measuring tiludronate in horses and should be considered in future for repeated measurements over time in living animals.