Ultrasound, computed tomography (CT), MRI, and nuclear scintigraphy are finding a place alongside radiography (X rays) when it comes to assessing a horse’s soundness prior to sale. However, with the 50 shades of gray these technologies present, which diagnostic images will be most revealing?
Well, that depends.
During her presentation at the 2019 American Association of Equine Practitioners Convention, held Dec. 7-11 in Denver, Colorado, Florida-based radiologist Natasha Werpy, DVM, Dipl. ACVR, said prepurchase diagnostic imaging in Western performance horses is becoming more complex. Horses across all Western disciplines commonly show wear and tear in their feet, hocks, stifles, and knees. However, each sport tends to manifest its own set of problems.
“Watching these horses work and understanding their athletic expectations is really important because there are very specific predilection sites for injury within the different disciplines,” she said.
Knowing what those trouble spots are and how best to view them guides Werpy in her prepurchase imaging recommendations. Other factors that dictate the images needed include the horse’s age, the vet’s examination findings, and the buyer’s previous experiences and aversion to risk.
As imaging technologies advance, practitioners have learned the limitations of relying on radiographs alone. X rays might not catch certain problems or might show anomalies that aren’t useful for determining clinical relevance—especially when the horse is sound. Is it a blemish? Will it impact resale? Or could it affect performance over time? That’s when additional imaging techniques could provide a clearer picture of what’s really going on below the surface.
“I provide all the options and explain why they’re important,” Werpy said. “These sets of radiographs are produced for this reason. This ultrasound is important for this reason. We put them in priority order and subtract, working backward from the budget. But I’m going to explain what we might miss when we remove things from the list,” she said.
For example, ultrasound will reveal more about overall stifle health than radiographs alone. Does the joint have evidence of chronic inflammation? Does it contain debris? Is the joint capsule thickened? Being able to evaluate soft tissue is especially relevant in this area.
“The stifle is extremely important in our Western performance horses (and it has) complicated anatomy,” said Werpy. “Multiple imaging modalities are always best when evaluating the stifle.”
Similarly, when imaging front feet, two skyline angles are almost always better than one: The standard view for assessing the navicular bone and a second to better visualize the most common site for flexor surface erosions. However, standing MRI examination might be a better option if the purchase price of the horse justifies the cost, said Werpy, particularly when the two feet don’t match on film.
“There are plenty of other things that this applies to,” she added.
“When I look at things that are clinically relevant, the two categories that are super-easy are the ones that probably won’t cause lameness and the ones that probably will,” Werpy said. “The gray zone is where you see multiple horses with this finding, and sometimes it’s limiting and sometimes it is not a problem. It’s hard to make decisions about those horses.”
It’s important to consider performance-limiting issues versus resale-limiting issues, she said. The findings are seldom black and white. So, as with other aspects of the prepurchase exam, the ultimate goal of imaging is to provide a clearer view of key areas so a buyer can decide whether this is the right horse for the job.