fibrotic myopathy in horses

When fibrous tissue forms over horses’ hind hamstring tendons, they can develop gait abnormalities. The treatment of choice over the past 30 years for this “fibrotic myopathy” has been slicing the tendon—a procedure known as a tenotomy. But having horses lying down under general anesthesia hasn’t been ideal for performing the surgery.

That’s why equine surgeons in Iowa recently investigated the benefits and effectiveness of performing tenotomy of the semitendinosus muscle (part of the hamstring group) in standing, sedated horses. They found that the results are encouraging—at least as good as they are in surgeries under general anesthesia. And they also allow better surgical access to the target tissues.

“The increased ease of tendon palpation compared to the horse under general anesthesia makes the procedure quicker and easier, leading to smaller incisions and decreased soft tissue dissection surrounding the tenotomy site,” said David G. Suarez-Fuentes, DVM, of the Iowa State University College of Veterinary Medicine, in Ames.

Suarez-Fuentes and colleagues compared medical records and follow-up for 20 horses undergoing semitendinosus muscle tenotomy for fibrotic myopathy. Veterinarians operated on eight horses using the standing procedure and the other 12 using the traditional general anesthesia technique.

They found that the standing surgery led to good outcomes, he said. Of the six performance horses operated on while standing, five returned to their preinjury level of sport. Six of the nine performance horses operated on under general anesthesia returned to their preinjury level.

Overall, six of the eight standing horses showed gait improvements after surgery, Suarez-Fuentes said, as did six of the 12 general anesthesia horses.

Furthermore, two of the 12 horses in the general anesthesia group developed the complication of incisional drainage, he said. None of the horses in the standing group did.

While the trend appears to be that standing surgery yields better results than general surgery does for this procedure, it’s too soon to make that conclusion, Suarez-Fuentes said. It would require larger numbers of study horses.

Still, it seems clear that standing surgery gives at least equivalent results, he said. Plus, it reduces the added expenses and risks of general anesthesia. It also tends to make the surgery easier—mainly because the tendon is easier to find when the horse is standing up putting weight on it.

“We believe that performing semitendinosus tenotomy under standing sedation offers the advantage of the increased ease of palpation and manipulation of the semitendinosus tendon during the procedure,” Suarez-Fuentes said.

“This ease of identification is due to the increased tension in the tendon via involuntary semitendinosus muscle contraction, which is engaged as part of the combined muscular effort to support the hind limb when the horse is standing in a natural position,” he continued. “This helps us to palpate the tendon and identify it in an easier way, which may reduce the extent of dissection required to isolate the tendon (this is surgeon-dependent), thus reducing the likelihood of incisional complications due to a smaller incision.”

The standing surgery does require some surgeon flexibility, however. As the horse is standing, the surgeon must access the tendon low on the ground instead of lifted onto a table. Still, that hasn’t presented problems for the Iowa team, Suarez-Fuentes said.

“For us, it has been easy to perform the procedure under standing sedation and local anesthesia,” he said. “Horses tolerate the procedure well, and we didn’t encounter any major difficulties.”

The study, “Tenotomy of the semitendinosus muscle under standing sedation versus general anesthesia: Outcomes in 20 horses with fibrotic myopathy,” was published in Veterinary Surgery.