There’s a new way for veterinarians to assess injuries to the upper (proximal) portion of horses’ hind-limb suspensory ligaments, which are notoriously difficult to assess. Veterinarians recently assessed acoustic myography, or AMG, and determined it could be useful for evaluating function of this ligament, which could mean more straightforward diagnoses, treatment recommendations, and monitoring of these injuries as they heal.
Study author Kent Allen, DVM, Cert. ISELP, of Virginia Equine Imaging, in The Plains, explained that imaging advancements have made it easier to visualize proximal suspensory ligament (PSL) structure but evaluating its function (especially during healing) has remained difficult. He recently worked with a research team—including Jillian Costello Chavers, DVM, who now owns and operates Magnolia Sport Horse Equine Lameness and Imaging, in Ocala, Florida, and colleagues from the University of Copenhagen, in Denmark—to test the modality’s potential for use in horses, and he described the team’s results at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.
The suspensory ligament—like all ligaments, which connect bone to bone—facilitates energy storage for movement. A small amount of muscle fiber in the structure provides tension. Veterinarians and researchers had long theorized that AMG—which measures how muscle and ligament fibers move—could help in lameness evaluation. They couldn’t test whether it had practical use, however, until scientists developed an appropriate tool. In 2013, Adrian Harrison, DPhil (Cantab), IVH, finally developed an effective AMG unit (marketed as the CURO), which essentially allows veterinarians to “listen” to the horse’s tissues. The research team evaluated this unit in their study.
The researchers sought to use AMG to differentiate between healthy and injured hind-limb PSLs in a group of horses whose owners were getting second-opinion hind-limb lameness evaluations. They conducted lameness exams, confirmed or ruled out proximal PSL injury (such as desmitis, inflammation, and tissue damage), then applied AMG sensors, walking and trotting the horses over a firm rubber surface.
Blinded clinicians (who didn’t see the AMG results) and a blinded researcher in Denmark (who didn’t know the workup results) compared data from 85 horses: 48 had yet-untreated PSL injury; 18 had non-PSL injury (lameness that did not block to the PSL using diagnostic analgesia); 4 had PSL injury that had been treated (horses that recovered and successfully returned to work); and 15 were sound.
They determined that a normal AMG reading was greater than 5, a chronic or low-level injury was 2.5 to 4.5, and an acute injury was less than 2.5.
The researchers found that scores in horses with PSL injuries were significantly different from the three other groups, Allen said, “with the majority of horses with PSL injury scoring less than 5.”
He likened healthy and unhealthy PSLs to a guitar: “Strum a tuned guitar string, and it’ll dampen normally and produce a pleasant sound.” Untuned, it won’t, instead producing a different note. Same goes for the “tuned” and “untuned” ligaments.
Allen said AMG won’t replace lameness examinations, including diagnostic analgesia and imaging. Rather, the preliminary study adds another promising tool to the toolbox for practitioners to diagnose and monitor hind-limb PSL injuries.
“It’s a complementary technique,” he said. “But it provides a quick and objective view of PSL function. AMG has the potential to provide valuable information from the preventive medicine, diagnostic, and rehab standpoints.”