Racehorses resuming training after fetlock injury are at risk of injury recurrence. 18F-NaF PET (positron emission tomography) is a pertinent tool for monitoring these horses after they resume training. However, until recently, we did not know the optimal time for scanning these horses after returning to work.
PET for Racehorses
During the 2023 American Association of Equine Practitioners Convention, Mathieu Spriet, DVM, MS, Dipl. ACVR, ECVDI, ACVR-EDI, from the University of California, Davis, School of Veterinary Medicine, presented results of a study conducted with 12 Thoroughbred racehorses. The horses were previously diagnosed with a fetlock injury using PET and had a layup of at least 90 days before resuming training. After resuming training, those horses underwent additional PET at 1, 2, 4, and 6 months.
“We looked for increased radiopharmaceutical uptake on the scans, the performance of these horses, and clinical information provided by attending veterinarians,” said Spriet. “Successful racing was defined as finishing in the top three.”
Five of the horses had primary palmar condylar injuries (not fractures), five had primary sesamoid injuries, and two had both condylar and sesamoid injuries.
Rate of Reinjury
Only six horses reached the conclusion of the six-month study without evidence of PET abnormalities, meaning reinjury occurred in 50% of the horses. No new lesions were identified in any of these horses. Lesion recurrence was appreciated at two months in one horse, four months in three horses, and six months in two horses.
Spriet said one case, in particular, “originally had severe increased radiopharmaceutical uptake and was laid up for nine months. After all uptake had resolved, the horse went back into training. Within one month, though, massive and nonspecific uptake was appreciated in the proximal P1. This reflected bone remodeling after the prolonged layup. This remodeling improved by two months after resuming training, but recurrence of the original lesion, although not as bad, was appreciated.”
For the six horses that resumed training, five raced successfully with no lesion recurrence, while one failed due to recurrence of the same lesion.
“The fetlock seems to have either a weakness of the condyles or the sesamoids, but whether this is due to conformation or an underlying developmental or genetic component is unclear,” Spriet noted.
Timing of PET Scans
This study’s results revealed most reinjuries occur four to six months after resuming training. And as demonstrated in the case described, PET scans performed early in training after the layup are low yield. They only show the expected remodeling of P1.
“Instead, peak training is the ideal time for PET scanning,” advised Spriet.
“A clean PET scan at peak training is a good indication that the horse is ready to race successfully, while the presence of abnormal PET findings at this stage are indicative of likely performance issues,” he explained. “For this reason, PET can be helpful as a training management tool to decide on the timing to resume racing or identify early recurrence of injury, allowing for training modification.”
PET has become more than a simple diagnostic tool only used when lameness is present, Spriet added.
“More and more trainers have started using PET for follow-up and training management,” he relayed.
