Padraig G. Kelly

Objective: To describe (1) diagnosis of dynamic collapse of the cricotracheal ligament in a group of horses and (2) treatment and outcome of affected horses.Study Design: Retrospective case series.Animals: Thoroughbred horses (n = 8).Methods: Of 600 over ground dynamic endoscopic examinations performed, 8 Thoroughbred horses had cricotracheal ligament collapse (CTLC); 5 were 2 years old and in early training and 2 were mature horses in full work. CTLC was diagnosed if circumferential collapse of the cricotracheal ligament was identified during exercise. Seven horses had repeat endoscopic examination. Two horses unresponsive to conservative management were treated surgically.Results: Multiple abnormalities of the upper portion of the respiratory tract were identified along with CTLC in all five 2‐year‐old horses and resolution of CTLC was observed after treatment for upper airway inflammation. No concurrent respiratory abnormality was identified in the 2 mature horses. Surgical reduction of the cricotracheal space and imbrication of the cricotracheal ligament of these 2 horses resulted in resolution of clinical signs of CTLC.Conclusions: CTLC is a rare cause of dynamic obstruction in Thoroughbred racehorses. Resolution may occur after adaptation to training and after inflammation of the respiratory tract is resolved, but for horses with persistent CTLC, surgical reduction of the cricotracheal space and imbrication of the cricotracheal ligament may result in resolution of clinical signs.

Summary: Reasons for performing the study: Endoscopic examination of T horoughbred ( TB ) yearlings is performed routinely to determine the suitability of horses for racing and to ensure that the conditions of sale are satisfied. However, previous research has demonstrated that resting endoscopic examination can be inaccurate in the diagnosis of functional pathology of the upper portion of the respiratory tract ( URT ). Objectives: To investigate the feasibility of performing dynamic overground endoscopy in a group of TB yearlings and to compare the results of resting and dynamic endoscopic examination of the URT . Study design: Prospective cohort study. Methods: Resting (pre‐ and post exercise) and exercising endoscopy was performed on 57 TB yearlings at a single training yard. Observed abnormalities were recorded and graded. The results of resting and dynamic examination were compared. Results: Dynamic overground endoscopy was well tolerated and was performed with few complications. Laryngeal asymmetry (29 cases) was the most common abnormality identified at rest, while intermittent dorsal displacement of the soft palate ( IDDSP ; 19 cases) was the most common at exercise. Significant variation in laryngeal function and variation in the occurrence of IDDSP was noted between examinations. Other potentially significant pathology that was not noted at rest but was present during exercise included collapse of the apex of the corniculate process, pharyngeal collapse and cricotracheal ligament collapse. The occurrence of IDDSP at exercise was significantly associated with epiglottic structure grade > 2 and a recent history of respiratory tract infection. Conclusions: Dynamic overground endoscopy is safe and potentially useful when assessing URT function in TB yearlings. Significant variations in the results of endoscopy at rest and during exercise were identified, which indicate that resting endoscopy may not be sufficient to predict the occurrence of pathology during exercise. Potential relevance: Dynamic overground endoscopic examination could be considered a suitable means of assessing URT function in TB yearlings and may provide additional pertinent information to that obtained during standard resting examination.