When a horse injures his superficial digital flexor tendon, knowing the prognosis for recovery can help determine which treatment steps to take. While there are general standards for estimating long-term outcome, a new study has determined a more scientific method for predicting a horse’s chance of successfully returning to a performance career.
A research team focused on ultrasound images of Thoroughbred racehorses with SDFT injuries at initial presentation. “These injuries occur at high-intensity gallop work,” says lead researcher Rafael Alzola, BVMS, MSc, GPCert, Cert AVP, MRCVS, equine surgery resident at England’s Nottingham Veterinary School and Oakham Veterinary Hospital. He was joined by colleagues from the University of Nottingham, biotech company Oxtex Ltd. and the head veterinarian at the Hong Kong Jockey Club.
“You could probably get nearly all the [injured] horses back to racing and through one race,” adds Dr. Alzola. “But it is whether or not they have a successful career following the injury.”
The researchers began by examining ultrasound images at initial presentation taken at the Hong Kong Jockey Club between 2003 and 2014. The study included 469 horses with only SDFT injuries in front limbs. “The fantastic opportunity here was that all the horses are kept, trained and raced on the same track and looked after by the same vet group,” says Dr. Alzola. This eliminated many variables (such as track surface) that could have affected outcome.
All the injuries were graded using an established ultrasound scoring system. Then, the researchers used a statistical model to compare the injuries at initial presentation with the horses’ racing careers following injury. (This post-recovery follow-up stage is a primary reason the study has been ongoing for seven years.) The model identified which ultrasonographic features of the SDFT injury at initial presentation were good predictors of the horses’ ability to successfully return to racing (defined as completing five or more races).
The team looked at horses exhibiting core-lesion injuries, where the tendon fibers snap, leaving what looks like a black hole in the ultrasound image. In this type of injury, the cross-sectional area was the best predictive factor. This area is what you see when the image is taken with the ultrasound scanner perpendicular to the leg. It’s measured in the SDFT zone showing the most damage.
When the size of the core lesion was less than half that of the cross-sectional area, the horse had a roughly 29 to 35 percent chance of successfully racing again. If the lesion was larger, those odds decreased to around 11 to 16 percent.
For horses without core lesions—exhibiting strain and inflammation of the tendon fibers—researchers determined that the longitudinal fiber pattern was the best predictive factor. This pattern is what shows up when the ultrasound scanner is held parallel to the leg. It shows disruption in the alignment of the tendon fibers and again was measured in the zone with the most damage.
In horses where the longitudinal fiber pattern represented less than 75 percent of the total SDFT fibers, they had anywhere from a 49 to 99 percent chance of successfully racing again. But when the affected area was larger, the probability dropped to just 14 percent.
“The really important message from our perspective is that if a horse has an injury which is likely to recur or fail when they race again, their welfare will be better if this is recognized [early] and plans are made for an alternative career or retirement,” says Dr. Alzola. “We don’t want to write them off, but we want an informed, evidence-based decision on what is best for them in the long term.”
The team believes this study will set the stage for future work that can help provide more science-based prognoses for injured horses in other disciplines.
This article was originally published in the July 2018 issue of Practical Horseman.