A longitudinal study of radiodensity and radiographic appearance of the proximal sesamoid bones in Thoroughbred racehorses.
Authors: Boros Koppány, Dyson Sue, Pollard Danica, Nagy Annamária
Journal: Equine veterinary journal
Summary
# Editorial Summary: Proximal Sesamoid Bone Changes in Racehorses Over two years, researchers tracked 40 Thoroughbred yearlings with repeat radiographic and CT examinations of their metacarpophalangeal joints at approximately six-monthly intervals, measuring bone density (Hounsfield Units) and documenting surface changes including new bone formation, concavity and irregularity of the abaxial margins. Proximal sesamoid bone radiodensity increased progressively from 1064 HU at baseline to 1194.5 HU by the mid-study point, correlating strongly with the number of race starts (p<0.001), bodyweight-to-height ratio (p<0.001), and showing lateralisation patterns (medial bones denser than lateral, p=0.01). Whilst abaxial margin concavities and surface irregularities appeared more frequently in younger horses and medial bones—potentially representing normal developmental adaptation rather than pathology—new bone formation associated with higher vascular channel grades occurred predominantly on lateral sesamoids. These findings suggest that progressive bone mineralisation reflects the adaptive response to training and racing loads, that certain marginal irregularities may be developmental rather than clinically significant, and that radiographic improvement remains possible, offering an important perspective for practitioners interpreting serial radiographs and counselling owners on age-related sesamoid changes in young racehorses.
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Practical Takeaways
- •Progressive increase in sesamoid bone density during a racehorse's career correlates with racing intensity; this appears to be an adaptive response to training load rather than necessarily pathological
- •Young horses with concavities and surface irregularities on their sesamoid bones may not require intervention if these are normal developmental features; focus on monitoring rather than treating incidental radiographic changes
- •Radiographic grading of sesamoid bones can improve over time, so baseline imaging early in a horse's career provides valuable comparison data for assessing true degenerative changes versus remodeling
Key Findings
- •Mean radiodensity of proximal sesamoid bones increased from 1064.0 HU at baseline to 1194.5 HU at 18 months, with highest values at T3 (18 months into study)
- •Increasing radiodensity was significantly associated with number of race starts (p<0.001) and bodyweight:height ratio (p<0.001), and was higher in medial versus lateral sesamoid bones (p=0.01)
- •Abaxial margin concavities and irregularities were more common in younger horses and may represent normal developmental features rather than pathology
- •Radiographic improvement of sesamoid bone grades is possible during the 2-year follow-up period despite ongoing racing activity