Pre-existing stress fractures in the bones of racehorses rarely causelameness and may not be detected by radiography, but they appearto be a significant cause of fatal injuries, according to researchers at the UC Davis School of Veterinary Medicine. Stress fractures are tiny fractures that only penetrate part of the bone and result from the accumulation of microscopic damage incurred during race training. "Horses with an unexplained lameness or performances lower than expected should be evaluated by scintigraphy bone scan to detect any incomplete stress fractures," recommends Dr. Susan Stover, a professor of anatomy who is investigating the phenomenon. The training of horses with stress fractures can be reduced until the stress fracture heals, at which time the bone has regained strength and the horse can return to normal training and racing with minimal risk for a catastrophic complete fracture, Stover says.