Longitudinal monitoring of fetlock lesions in Thoroughbred racehorses using standing 18F-sodium fluoride positron emission tomography.

The study investigated the repeatability of equine positron emission tomography (PET) using 18F-sodium fluoride (18F-NaF) to track the progression of injury in the fetlock joints of racehorses. The study provides evidence for the repeatability of PET findings and emphasizes its utility in making lay-up duration decisions in Thoroughbreds.

Research Methods

• The study is a prospective, longitudinal clinical study, conducted on 25 thoroughbred racehorses exhibiting signs related to fetlock injuries, totaling 54 fetlocks.
• 18F-NaF PET scans were performed thrice for each horse with intervals of six weeks between the scans, starting at the beginning of a 12-week lay-off period from racing.
• Areas of increased radiopharmaceutical uptake (IRU) were identified and quantified using maximal standardized uptake values (SUVmax). This indicates areas of heightened metabolic activity usually associated with injury or disease.
• The IRUs were categorized by two skilled observers using a new grading method.
• Statistical analysis was used to compare the differences in IRUs and SUVmax over time.

Results

• There was a high degree of repeatability in PET findings, with about 88% of the IRUs identified in initial scans also detected at the 6-week follow-up scan.
• The researchers found the palmar/plantar condyles of the fetlocks to be the most common sites of IRU, followed by the proximal sesamoid bones.
• During the 12-week rest period, 65% of fetlocks showed improvements in their IRU grades.
• Fetlocks with higher initial IRU grades were observed to take a longer time to heal compared to those with lower grades.

Conclusions

• The study concluded that PET findings in the fetlocks of racehorses were repeatable.
• The use of SUV-based grading for IRU was deemed potentially useful for making decisions regarding the appropriate duration for rest from racing, to let injuries heal.
• PET could be employed to monitor fetlock areas in thoroughbred racehorses that are at risk for catastrophic breakdown injuries.