Humeral stress remodelling locations differ in Thoroughbred racehorses training and racing on dirt compared to synthetic racetrack surfaces.
Authors: Dimock A N, Hoffman K D, Puchalski S M, Stover S M
Journal: Equine veterinary journal
Summary
# Humeral stress remodelling in Thoroughbreds: Surface-dependent patterns with fracture implications The racetrack surface fundamentally alters how mechanical stress is distributed through the equine humerus, with potentially significant implications for fracture risk in racing Thoroughbreds. Dimock and colleagues examined scintigraphic images from 841 racehorses at three facilities during the two-year transition from dirt to synthetic surfaces, comparing lesion location and severity before and after the changeover, and cross-referencing findings with archived fractured humeri and racing injury databases. Horses on synthetic tracks developed significantly more distal humeral lesions, whilst those on dirt surfaces exhibited predominantly caudoproximal remodelling (P<0.001); notably, proximal lesions were more severe than distal ones, and nearly all complete humeral fractures were associated with caudoproximal stress changes. The critical finding was the apparent protective effect of scintigraphic detection: no horse with an identified scintigraphic lesion subsequently suffered complete fracture, whilst no horse with a catastrophic fracture had undergone prior imaging. For practitioners, these results suggest that systematic scintigraphic screening may identify at-risk individuals before catastrophic failure, particularly on dirt surfaces where the high-risk caudoproximal remodelling pattern predominates, enabling targeted training modifications or surface changes to prevent career-ending injuries.
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Practical Takeaways
- •Racing surface type influences where humeral stress injury develops in Thoroughbreds—synthetic surfaces shift injury patterns distally compared to dirt, potentially reducing fracture risk
- •Caudoproximal humeral lesions detected on scintigraphy are more likely to be severe and associated with complete fracture risk; distal lesions appear less critical
- •Scintigraphic screening may identify at-risk horses before catastrophic fracture occurs, as no screened horses with lesions suffered complete fractures in this study
Key Findings
- •Synthetic racetrack surfaces were associated with greater proportion of distal humeral lesions, while dirt surfaces showed greater proportion of caudoproximal lesions (P<0.001)
- •Proximal lesions were significantly more likely to be severe than distal lesions (P<0.001)
- •Most complete humeral fractures were associated with caudoproximal lesions, which were more often severe than distal lesions (P=0.002)
- •No horses with scintigraphic lesions sustained complete humeral fracture, and no horses with complete humeral fracture had undergone scintigraphic examination