Areas of Humerus Stress in Horses Differ with Track Surface (AAEP 2010)

How much impact does a racing surface have on the horse's body and which parts are stressed most during work? According to Abigail N. Dimock, DVM, MS, of the University of California, Davis, who in collaboration with Kurt Hoffman, DVM, and other colleagues completed a study on the subject recently, track surface has more of an impact on bone stress than initially thought.

During a presentation at the 2010 American Association of Equine Practitioners convention, held Dec. 4-8 in Balitmore, Md., Dimock spoke about the study in which the team examined nuclear scintigraphy images of 930 Thoroughbred racehorses in order to determine whether areas of humerus remodeling (the bone located between the shoulder and elbow joints) changed when dirt tracks in California were transitioned to synthetic surfaces. The horses raced at three California racetracks (Del Mar, Hollywood Park, and Santa Anita) and the images were collected from Sept. 1, 2005, to July 1, 2009; although she has no definite history on the horses, Dimock presumes that the horses were scanned after being presented for lameness. The synthetic track was represented by 541 horses and dirt tracks were represented by 389.

In the study a reader (who had no knowledge of which surface the horse raced on) evaluated the scintigraphy scans, rating the severity of humerus lesions as mild, moderate, or severe, and also noting the location of each lesion.

In total, 166 horses from both groups had lesions (characterized by abnormal uptake in the scintigraphy images) in the humerus. Of those, 57 had bilateral abnormal uptake (areas of stress in both humeri). The blind reader rated 138 of the lesions as mild, 62 as moderate, and 31 lesions as severe. Dimock noted that neither the rate of injury nor the severity of the lesions was significantly different between the two surfaces.

Dimock noted, however, that the location of the lesions on the humerus differed drastically between horses running on dirt and synthetic tracks. Dimock found that horses that ran on synthetic surfaces had a much higher likeleiood of developing a lesion in the distal (or lower) humerus, while the proximal (or upper) region was more common in horses that ran on dirt.

"The study confirmed that the lesion location changed with the change in track surface," Dimock said.

It is unclear why the location of lesions changed with the change in track surface, she added.

"Continued monitoring is necessary to determine whether this change is associated with a change in the configuration of stress remodeling in other bones or the incidence of catastrophic fractures," Dimock wrote.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.