Humeral stress remodelling locations differ in Thoroughbred racehorses training and racing on dirt compared to synthetic racetrack surfaces.
BACKGROUND
Veterinarians have observed a putative change in the location of humeral stress remodelling in Thoroughbred racehorses with change from dirt to synthetic racetrack surfaces.


OBJECTIVE
To determine whether the location and severity of humeral stress remodelling differs between Thoroughbred racehorses exercising on dirt and synthetic racetrack surfaces, the potential significance of different locations of stress remodelling, and the potential usefulness of scintigraphy for prevention of complete humeral fracture.


METHODS
Scintigraphic images of humeri from 841 Thoroughbred racehorses at 3 racetracks during 2 years before and after conversion from dirt to synthetic surfaces were evaluated for location and severity of lesions. The effects of surface on lesion distributions were examined using Chi-square or Fisher's exact tests. Archived fractured humeri were examined to determine the location and severity of stress remodelling associated with complete fracture. Databases were queried to determine whether racehorses with scintigraphic lesions suffered humeral fracture and whether racehorses with a complete humeral fracture had had a scintigraphic examination.


RESULTS
Horses at synthetic racetracks had a greater proportion of distal humeral lesions, whereas horses at dirt racetracks had a greater proportion of caudoproximal lesions (P<0.001). Proximal lesions were more likely to be severe than distal lesions (P<0.001). Most complete fractures were associated with caudoproximal lesions, which were more often severe than distal lesions (P = 0.002). None of the horses with a scintigraphic lesion had a complete humeral fracture. None of the horses with a complete humeral fracture underwent scintigraphic examination.


CONCLUSIONS
Race surface affected humeral scintigraphic lesion location and hence the location of stress remodelling. Lesion severity was associated with lesion location. Complete humeral fracture was associated with caudoproximal stress remodelling and lack of scintigraphic examination.


CONCLUSIONS
Risk for complete humeral fracture may be lower on synthetic surfaces than on dirt surfaces, and, by inference, for horses examined using scintigraphy.
William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, USA.
A N
AN
Dimock
K D
KD
Hoffman
S M
SM
Puchalski
S M
SM
Stover
D000818:Animals; D016723:Bone Remodeling / Q000502:physiology*; D050723:Fractures, Bone / Q000473:pathology / Q000662:veterinary; D006736:Horses / Q000502:physiology*; D006811:Humerus / Q000502:physiology*; D011877:Radionuclide Imaging / Q000662:veterinary; D012189:Retrospective Studies; D012420:Running; D013177:Sports; D013312:Stress, Physiological; D013499:Surface Properties