The Horse

NOV 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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64 November 2018 The Horse | analysis, says Thilo Pfau, PhD, senior lecturer in bioengineering at the RVC. While inferior to the quality of an IMU or OMC test in a clinic, the method could give veterinarians an early indication of the possible presence of subtle hind-limb lameness before referral, he says. A Human Touch Machines might be able to give us information about precise asymmetries, but many researchers argue that nothing can replace the analytical powers of the human brain for diagnosing lameness. "I'm not opposed to using objective measurement systems, but their use should not be at the expense of looking at the horse clinically," Dyson says. "I think one of the real problems is that some of the users of the system stopped looking at the horse, and they expected it to answer all their problems. Some people don't really recognize the limitations of what objective measurements can tell you." Objective measurements can't, for example, distinguish mild nonpain- ful asymmetry from mild painful asymmetry—which is true lameness, she says. They can't explain pain that's mak- ing a horse unwilling to canter one direc- tion but trot symmetrically in a straight line. They can't pick up other signs of pain related to subtle lameness, such as difficulties performing specific move- ments when ridden, conflict behavior, or alterations in facial expressions. They can't currently see when horses compen- sate for pain in ways other than up-down asymmetry, such as swinging a limb out or moving hind limbs on a separate track from the front limbs. "We have used a GPS to objectively evaluate leaning in on a circle, reflecting lameness, but this can- not be done with (IMUs)," says Dyson. "All these units measure is the asym- metry in the ability to land and push off a leg, so there's obviously an inherent limitation there," she continues. "When I evaluate horses, I always look at them ridden, and I'm looking at any differences in the way the horse performs globally in not only trot but also canter. Does it look happy? Is it accepting the contact properly? Does the rider have an equal feel in the hands? I use many other things to help tell me if there's residual pain." On the contrary, objective evaluations could lead to excessive—and needless— additional testing, including nerve blocks (which numb a limb area temporarily to see if the horse moves normally after, indicating that's where the pain is com- ing from), she adds. "If you find yourself driven by objective gait analysis, you might keep using nerve blocks everywhere for asymmetry that is just natural and not related to pain and lameness." They can also lead to inaccurate STEP BY STEP A History of Force Plates, OMCs, and IMUs Researchers first started using force plates on the ground in the mid-1970s to help clini- cians give lameness exams some objectivity. Horses would walk or trot over the plates, and machines would calculate the forces each foot applied at each moment. While the use of force plates continued into the 21st century, researchers recognized the need for something more practical, because the plates are bulky, heavy, and only measure one stride in one place at a time. Around the turn of the millennium they came up with a force-measuring treadmill and pressure sensors veterinarians could place directly on the horse's feet. But those tools still lacked practicality for gait analysis, says Filipe Serra Braganca, DVM, a PhD candidate in equine musculoskeletal biology in Utrecht University's Faculty of Veterinary Medicine Depart- ment of Equine Sciences, in the Netherlands. Optical motion capture (OMC) became popular in the early 2000s for objective gait analysis and is currently the gold standard for objective kinematic analysis of movement in horses. But it's complicated to set up, Braganca says. It requires 10 to 15 reflective markers, placed at strategic points on horses' bodies, and about 18 infrared cameras recording mo- tion capture data at 200 Hz. Inertial measurement units (IMUs) measure linear and angular motion, mainly using accelerometers and gyroscopes. The technology originated in the 1930s for use in aircraft. German scientists incorporated accelerometers into lameness exams in the 1990s. In the early 2000s scientists developed a "micro" IMU that could fit into modern technologi- cal equipment such as mobile phones. That catapulted IMU technology into a variety of branches, including equine medicine by the middle of the decade, with a 2004 study by a University of Missouri team appearing in The American Journal of Veterinary Research. By 2012 Thilo Pfau, PhD, senior lecturer in bioengineering at The Royal Veterinary College, in the U.K., was analyzing equine footstep readings and ataxia (incoordination) with an IMU attached to the horse's pelvis. Meanwhile, an American team led by Colorado State Univer- sity's Valerie Moorman, DVM, PhD, Dipl. ACVS-LA, was evaluating gait symmetry analysis with an IMU attached to horses' hooves. Since those first tests, veterinarians and researchers have used IMU increasingly in equine gait analysis, leading to more than 30 published studies in peer-reviewed journals in the past six years.—Christa Lesté-Lasserre, MA Objective systems measure asymmetry, specically, but not all asymmetries are lameness-related. Dr. Marie Rhodin's team, for instance, used sensors to determine that rider effect and circling can exacerbate or cancel out asymmetry. COURTESY EMMA PERSSON-SJODIN

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