Effect of high-speed exercise on subchondral bone in the metacarpo-/metatarsophalangeal joints of 2-year-old Thoroughbred racehorses in their first year of training.

Abstract

BACKGROUND: Stress-induced bone injury can lead to catastrophic injuries in Thoroughbred racehorses. Accumulation of high-speed exercise can increase the risk of subchondral bone injury. OBJECTIVES: To investigate the effect of high-speed exercise on the subchondral bone of the metacarpo-metatarsophalangeal (MCP/MTP) joints using standing cone-beam computed tomography (CBCT) in young racing Thoroughbreds. STUDY DESIGN: Observational cohort study. METHODS: Forty-one 2-year-old Thoroughbred racehorses during their first year of training were evaluated at 0, 6 and 12&#x2009;months. Horses were evaluated for lameness and effusion of the MCP/MTP joints, and then standing CBCT was performed of the MCP/MTP joints. Subchondral bone hyperdensity (sclerosis) was measured (mm) at defined locations in the distal aspect of the third metacarpal (MC3)/metatarsal (MT3) bone and proximal phalanx (P1). CBCT scans were evaluated for subchondral bone hypodensity (pathology) in MC3/MT3, P1 and proximal sesamoid bones. Racing and training records were obtained from a national online database and trainers. RESULTS: Subchondral bone sclerosis (coefficient&#x2009;=&#x2009;0.45; p&#x2009;<&#x2009;0.003; 95% confidence interval [CI] 0.16-0.74) and pathology (IRR&#x2009;=&#x2009;1.01; p&#x2009;<&#x2009;0.001; 95% CI 1.00-1.01) increased significantly with the number of high-speed furlongs accumulated. Lameness was not associated with sclerosis or pathology; however, joint effusion was associated with both sclerosis (IRR&#x2009;=&#x2009;1.01; p&#x2009;=&#x2009;0.02; 95% CI 1.00-1.02) and pathology lesion (IRR&#x2009;=&#x2009;1.14; p&#x2009;<&#x2009;0.01; 95% CI 1.04-1.25). MAIN LIMITATIONS: Limitations include attrition of horses over time and lack of control over training and husbandry. CONCLUSIONS: An increase in high-speed work was associated with both an increase in subchondral bone sclerosis and pathology.