In this episode, Taralyn McCarrel, DVM, DACVS (LA), joined us to discuss recurrent laryngeal neuropathy (roaring) in horses and a new surgical technique she is developing to address the condition.
This episode of Disease Du Jour is brought to you by Equithrive.
What Is Happening Anatomically in a Horse That Roars?
McCarrel explained that roarers experience inspiratory obstruction.
“The nerve has become dysfunctional that controls the muscles that control the arytenoid cartilages as well as some other muscles in the throat,” she explained. “They lose the ability to move that cartilage, both open and shut, but open is more of a problem. When they’re exercising, what happens is that negative pressure, so the sucking of the air through the airway, pulls the paralyzed tissue into and across the airway and blocks it off.”
With severe collapse of the arytenoid and complete paralysis, horses can have more than 50% of the airway obliterated, she said. They can’t inhale enough air, and they therefore cannot continue exercising.
Tie-Back Surgery
Historically, roaring has been addressed with the tie-back surgery, which involves placing and tightening one or two sutures along the path of the paralyzed cricoarytenoideus dorsalis muscle to mimic contraction.
“When we do that, the goal is to hold the cartilage in an open position at all times,” McCarrel explained.
She said the procedure has a relatively high complication rate—mainly, that the cartilage does not stay as open as the surgeon would like. Dysphagia is another potential but rare complication.
New Surgical Technique
McCarrel has been developing a new surgical technique to address recurrent laryngeal neuropathy.
“One day I just happened to be sitting at my desk, and I had a pamphlet on my desk for a screw that had been designed for reattaching cartilage flaps in people,” she said. “And I was looking through a CT of a horse’s head, and one of the things that caught my eye was how much thicker the cartilage is where the arytenoid and the cricoid meet.
”So with a tieback, you’re putting the suture through the back of the cricoid, which anatomically in horses is extremely highly variable in shape and thickness and a bunch of other features, and it is also fairly thin. And that’s why we have this concern of the suture cutting into that cartilage,” she continued. “And so I started to think, ‘Well, could I just put a screw across this joint and utilize the thicker cartilage at the front and stay away from the back altogether?'” She envisioned placing the screws through tiny stab incisions using CT guidance, which would be atraumatic for the soft tissues.
This technique is still in the development phase. McCarrel has already published a paper proving the screws physically fit across the horse’s larynx. In a follow-up study, which is not yet published, she placed the screws across isolated larynges and applied negative pressure in a wind tunnel to prove they would stay in place. More recently, her team finished CT scanning the larynges of 30 horses of various sizes and breeds and modeled them in a medical modeling software to analyze various aspects of their shape and size. Then, they created inserts to place into the airway to push the arytenoids out into position.
“We put them back into the original larynges to check that it in fact put them where we wanted them,” she said. “And the next step is to now put those models that we’ve made into another 30 larynges that were not a part of the initial modeling.”
Listen to the podcast episode to learn more about McCarrel’s new surgical technique.
About Dr. Taralyn McCarrel
Taralyn McCarrel, DVM, DACVS (LA), is an Associate Professor of Large Animal Surgery at the Ontario Veterinary College, Department of Clinical Studies. She grew up in Brampton, Ontario, and spent her formative years riding horses and working at a nearby hunter-jumper barn. She gave up riding for several years in favor of academic pursuits, graduating from OVC’s Doctor of Veterinary Medicine program in 2006. She subsequently completed an internship in large animal medicine and surgery before moving to Ithaca, New York, to pursue research in comparative orthopedics and regenerative medicine at Cornell University. She later left academia to complete an equine surgery residency at Rood & Riddle Equine Hospital in Lexington, Kentucky, and attained board certification in large animal surgery with the American College of Veterinary Surgeons in 2014.
In 2015, McCarrel joined the University of Florida College of Veterinary Medicine, supporting both the Large Animal Surgery Service and the Equine Lameness and Imaging Services. A passionate teacher, she developed the Equine Lameness and Imaging course and coordinated the Equine Surgery and Laboratory course. She also served as a consulting surgeon for the University of Florida Veterinary Hospital at the World Equestrian Center in Ocala, Florida, when they opened a new state-of-the-art equine hospital in 2022.
McCarrel’s research focuses on orthobiologics, lameness diagnosis, and upper airway surgery.
Related Reading
- Disease Du Jour: Upper Airway Disorders in Horses
- Multifactorial Considerations for Poor Performance in Western Sport Horses
- The Ethics of Airway Surgery in Equine Athletes
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