Laryngeal Model Provides Framework For Surgical Advances

To test novel techniques for managing laryngeal hemiplegia, more commonly referred to as "roaring," a research team from Cornell University has created a working model of the equine larynx.

Dysfunction of the left recurrent laryngeal nerve resulting in paralysis, either partial or complete, of the left arytenoid cartilage is a common cause of poor performance in athletic horses.

"The most effective treatment currently available for roaring is a prosthetic laryngoplasty with vocal cordectomy and ventriculectomy," explained study co-author Jon Cheetham, VetMB, PhD, Dipl. ACVS, from the department of Clinical Sciences at the Cornell's College of Veterinary Medicine.

These techniques are known as a "tie-back" surgery, which involves placing one or more sutures (stitches) to permanently abduct or "open" the abnormal arytenoid cartilage. In addition to the tie-back, the vocal cords and the ventricles can be removed to further dilate the airway to improve performance and reduce noise during exercise.

Unfortunately, the post-surgical recurrence of exercise intolerance and abnormal respiratory noise in Thoroughbred racehorses is high. According to Cheetham and colleagues, "The overall success rate of the various laryngoplasty techniques is modest at best, ranging from only 48-68%"

In an effort to improve this success rate, Cheetham and colleagues isolated and manipulated equine larynges to maximally abduct (retract) the paired arytenoid cartilages. Air flow assessment through these laryngeal models revealed that inspiratory air pressures in the model were equivalent to pressures that occur in horses exercising maximally.

"This model allows us to test various novel techniques for the management of roaring to improve the post-operative success rates in athletic horses," relayed Cheetham.

For example, Cheetham's research group used this model to study the effect of the injection of the bone cement polymethylmethacrylate into the cricoarytenoid joint of the larynx. Cheetham and colleagues hypothesized that this approach would abduct (dilate) the arytenoid cartilages.

"Our results demonstrate that injecting the bone cement into the cricoarytenoid joint fuses it and can help to hold the airway in an open position," relayed Cheetham. "This 'gluing' of the cricoarytenoid joint could prove to be a useful adjunct technique to minimize the loss of arytenoid abduction experienced post-operatively in horses undergoing laryngoplasty. Hopefully this will ultimately improve the success rate and post-surgical return to function."

The study, "In vitro model for testing novel implants for equine laryngoplasty," was published in the August 2008 edition of the journal Veterinary Surgery and the companion article, "Intra-articular stabilization of the equine cricoarytenoid joint," was published by the Equine Veterinary Journal in August 2008.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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