Consider Trotting Speed when Diagnosing Subtle Lameness

Most horse owners are familiar with a typical lameness exam: The veterinarian observes the horse trotting briskly in a straight line, watching for signs of uneven movement. But if the patient is harboring a mild lameness, that brisk trot could be masking clinical signs, according to British researchers, whose recent study results indicate that evaluating milder forms of lameness in a straight-line trot could be more accurate when the handler keeps the speed down.

“Our study suggests that in sound to mildly lame horses, movement asymmetry (as measured objectively with equipment) doesn’t actually change much, if at all, when the horse is trotting fast on the straight,” said Sandra Starke, PhD candidate, researcher in the Department of Veterinary Clinical Sciences at the Royal Veterinary College, in Hatfield, UK. “However, more horses were judged sound at faster speeds when they were evaluated subjectively (visual examination). So it is possible that the horses are just going too fast for the asymmetry to be seen."

Starke and her colleagues evaluated 10 horses—ranging from sound to mildly lame in either the front or hind legs—as they trotted at slow, normal (“preferred”), and fast speeds, in both straight lines and circles. The researchers asked six experienced equine clinicians to evaluate these horses for lameness. Meanwhile, the team fitted the horses with sensors for an objective evaluation of asymmetry.

On a straight line, the practitioners judged more horses to be sound at the fast trot than at the other speeds; by contrast, the greatest number of mild lameness detections occurred at the slow trot. Even so, objective measurements still showed asymmetry at the fast trot in horses that had been determined sound by the observers, Starke said.

The circle, though, is a different story, she said. While speed didn’t seem to affect visual assessments, the sensors showed much more asymmetry of all the horses at higher speeds.

“For many expert assessors, limb movement is important when examining lameness in a circle,” Starke said. “So the subjective assessment might in part be based on something we did not measure; hence, we might not be able to expect a correlation between subjective and objective assessment. But also, the faster pace and increasing asymmetry might offset each other visually.”

Sensor-based lameness detection systems are "fantastic" aids, especially for mild cases, Starke said. However, the main commercially available system can be cost-prohibitive for some clinicians. And buying a less expensive option might be counterproductive because it could lead to faulty diagnoses, she added. Proper sensor placement, reliable measurement validation, and accurate data interpretation are key elements in objective lameness detection, and Starke believes an objective system might not necessarily be a better option compared to visual testing: “Technology can be as misleading as subjective bias when used the wrong way. And … current systems will not inform you about things such as toe-dragging, muscle atrophy, or choppy gait, so the visual examination is still very important.”

Starke recommended horses be visually evaluated several times on a straight line at trot speeds ranging from slow to fast. “You might find that asymmetry/lameness all of a sudden becomes apparent to the eye,” she said. This is true for any time lameness is suspected, but also when doing a prepurchase exam. “Dodgy dealers can figure out a horse’s optimal trotting speed to mask subtle lameness,” she added.

As for the circle, however, more research is needed before recommendations on trotting speed can be made, said Starke. “Determining lameness on the circle, both subjectively and objectively, is a big building site and needs much more explanation and evidence,” she said. Her research in this field is ongoing.

The study, "The effect of trotting speed on the evaluation of subtle lameness in horses," will appear in an upcoming issue of the Veterinary Journal

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.