PREDICTING PERFORMANCE AFTER TENDON INJURY
An international research effort has yielded a new method for predicting whether a racehorse will be able to return to the track after a tendon injury or would be better off directed toward a new career.
Researchers at the Hong Kong Jockey Club and University of Nottingham and Oakham Veterinary Hospital in England reviewed the records of 469 horses diagnosed with injuries of the superficial digital flexor tendon. In addition to ultrasound images and medical records, the researchers collected competition information for the horses to determine if they raced after rehabilitation. For the purposes of the study, a successful return to racing was defined as completing five or more races after the injury.
The ultrasound images were analyzed based on a number of factors, including the size of lesions and the extent to which tendon fibers were disrupted. “The tendon is basically like a rope made up of lots of smaller stretchy elastic fibers,” explains Sarah Freeman, BVetMed, PhD, who worked with Rafael Alzola Domingo, BVMS, MSc GP Cert (EqP), on the study. When an injury occurs, she says, “this can cause some of the fibers to snap, usually in the center of the tendon, giving a black hole appearance in the middle of the tendon on the ultrasound scan.” This is referred to as a core lesion.
The researchers discovered that when core lesions (at the site of maximum damage) measured less than 50 percent of the total cross section of tendon, the horses had a 29 to 35 percent probability of returning to racing. If the lesion was greater than 50 percent of the cross section, however, the horse had only an 11 to 16 percent chance of a successful return.
“The problem is that damaged tendons and ligaments rarely heal back to their original strength, and this means there is a chance of reinjury either at that site or next to it,” says Freeman. “We have always known bigger lesions are worse but had not been able to quantify it with values until now.”
The researchers also found a relationship between fiber pattern and a return to racing. “The ultrasound image is taken with a scanner along the long axis of the leg,” says Freeman. “We should see the tendon fibers aligned to run up and down the leg. If they are disrupted, there is inflammation between them. Some may be ruptured or they may be stretched and out of normal alignment. The more the fiber pattern is disrupted, the more the fibers are damaged and, again, the bigger the scar tissue and damaged area.”
Overall, the fiber pattern of an injury was the best predictor of whether a horse would return to racing; if the disrupted pattern was seen on less than 75 percent of the total cross section, the horse had a 49 to 99 percent chance of successfully returning to the track. In contrast, the success rate dropped to 14 percent when the area of fiber disruption was more than 75 percent of the total cross section.
Freeman says defining success as five races is a