Proximal sesamoid bone microdamage is localized to articular subchondral regions in Thoroughbred racehorses, with similar fracture toughness between fracture and controls.
Authors: Luedke Lauren K, Ilevbare Phoebe, Noordwijk Kira J, Palomino Pablo M, McDonough Sean P, Palmer Scott E, Basran Parminder S, Donnelly Eve, Reesink Heidi L
Journal: Veterinary surgery : VS
Summary
# Proximal Sesamoid Bone Integrity in Racehorses: What Microdamage Tells Us Proximal sesamoid bone (PSB) fractures remain a significant cause of catastrophic injury in racing Thoroughbreds, yet the mechanisms underlying failure remain poorly understood. This case-control study compared 12 horses with PSB fractures to 12 unaffected controls, examining whether accumulation of microdamage or reduced bone toughness explained fracture susceptibility. Using advanced imaging techniques (lead uranyl acetate micro-CT staining and histological analysis), researchers mapped microdamage distribution throughout the bones and measured fracture toughness through mechanical testing of bone microbeams. The findings challenge existing assumptions about PSB failure: whilst microdamage was indeed detected in affected horses, it localised exclusively to articular subchondral regions and showed no significant difference between fractured limbs and unaffected contralateral or control bones. Fracture toughness values were remarkably similar across all groups (fracture-contralateral 1.31 MPa√m versus control 1.35 MPa√m), suggesting that compromised material properties do not predispose horses to catastrophic failure. The only meaningful difference identified was training history—horses sustaining fractures spent proportionally more time in rest weeks during their careers. These results fundamentally shift focus away from intrinsic bone weakness as a primary causative factor, implying instead that PSB fractures may result from extrinsic biomechanical stresses, training intensity mismanagement, or acute traumatic episodes rather than cumulative microdamage. For practitioners, this suggests that routine diagnostic screening for subclinical bone degradation may have limited prognostic value, whilst optimising training load distribution and recovery protocols warrants greater attention in frac
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Practical Takeaways
- •Catastrophic proximal sesamoid bone fracture in racehorses is not predictable by measuring bone fracture toughness or microdamage patterns in the flexor cortex
- •The presence of microdamage in the articular region alone does not appear to be a risk factor for fracture; other factors related to training schedules and rest periods may be more significant
- •Training management strategies focusing on rest week distribution may be more relevant than bone material properties when considering PSB fracture prevention
Key Findings
- •Microdamage in proximal sesamoid bones was localized to articular subchondral regions, detected via lead uranyl acetate staining and histology
- •No significant difference in microdamage presence between contralateral limbs of fractured horses and control horses
- •Fracture toughness values were similar between contralateral limbs of fractured horses (1.31 MPa√m) and controls (1.35 MPa√m)
- •Horses sustaining PSB fracture spent a greater percentage of their careers in rest weeks compared to controls