Lame Horse? Maybe It’s a Muscle Tear

Researchers at Oregon State University looked at 14 case studies involving lameness related to muscle tears. Here’s what they found.
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Lame Horse? Maybe It’s a Muscle Tear
An ultrasound of the upper portion of a horse’s right forearm at the time of initial injury showing a hematoma and muscle damage within the ulnaris lateralis muscle. | Courtesy Dr. Stacy Semevolos/Oregon State University
If you can’t figure out why your horse is lame, consider the possibility that he might have torn a muscle. According to researchers, muscle tears could provoke lameness that might otherwise go undiagnosed.

“We’ve seen quite a few cases of lameness where nerve blocks to the lower limb didn’t result in improvement,” said Stacy Semevolos, DVM, MS, Dipl. ACVS, ACVSMR-Equine, director of professional and graduate programs and professor of large animal surgery at Oregon State University’s (OSU) Carlson College of Veterinary Medicine, in Corvallis.

“Most causes of lameness in horses are related to the joint or the foot (which would be temporarily resolved by nerve blocks),” said Semevolos. “We weren’t looking for muscle tears, per se, but this is what we found.”

A muscle tear is very much what it sounds like—a rupture in the muscle fibers, she said. Horses can experience muscle tears as a result of trauma, like a bad fall or a trailer injury, or overuse—although that’s less common. “Most of the cases we saw had obvious trauma, and the owner knew what had happened,” she said

Seven Years of Case Study

In their study, Semevolos and her fellow researchers examined details from 14 cases of horses referred to OSU’s clinic over a seven-year period that had received diagnoses of both lameness and muscle tear. Four Quarter Horses, two Thoroughbreds, two Arabians, two Warmbloods, one Irish Draught, one Irish Sport Horse, one Morgan, and one Paint represented the breed variety affected by the condition. That included six mares, six geldings, and two stallions aged 8 months to 23 years.

Six of the 14 cases involved more than one muscle, and all but two of the horses had severe (4 out of a scale of 5) lameness, Semevolos said. They all had swelling at the site of the tear, which could be easily felt when touching the skin. Most (nine) were also clearly tender in that area, reacting to touch. All but three had a known injury; the others were found lame in their stalls (possibly with unknown injuries). In all cases, an ultrasound examination showed the classical tissue disruption and related fluid collection around the muscle tear.

“Some of the horses had visible signs of trauma, with open wounds and actual cuts into the skin or muscle,” she said, adding that one horse had even been hit by a car. “Others had injuries where they overstretch, splaying out their limbs.” Distinguishing these tears from muscle soreness or sprains related to fatigue and overwork is important, she said.

A 9-year-old pleasure riding horse with multiple muscle tears and grade 4 lameness had to be euthanized due to the severity of his injuries, Semevolos said. Veterinarians euthanized another horse two weeks after leaving the hospital due to supporting-limb laminitis.

Rest and Rehab: How To Heal Torn Muscles

The other 12 horses, however, survived following stall rest and very controlled exercise, which is critical for optimum healing, she added. “The scar that the muscle develops is a fibrous tissue that’s not very flexible, so it can create a lot of restrictions of movement if it’s not managed correctly,” she said.

As such, owners and their veterinarians need to be sure to establish a “good balance” of rest followed by gradual work—leaving the muscle enough time to heal to a minimum while ensuring it’s progressively exercised to train flexibility in that newly grown scar tissue.

“Having a vet rechecking him on a regular basis to see how he’s healing is important,” Semevolos said. With a good rehabilitation program, horses could recover from tears over a period of months rather than a year or more, she said.

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Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

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