Transient Horner's syndrome in horses following cervical plexus local anesthesia.

OBJECTIVE: To report the development of transient Horner's syndrome in horses following local anesthesia of the cervical plexus. ANIMALS: A total of 37 horses. STUDY DESIGN: Observational retrospective short case series. METHODS: Medical records of cases undergoing ultrasound-guided cervical plexus anesthesia for standing prosthetic laryngoplasty at a single referral institution were evaluated (2019-2020). RESULTS: Five of 37 horses (14%) developed transient signs of Horner's syndrome postoperatively. Obvious clinical signs began 2 to 5 h following local anesthesia and persisted for two to 4 h. Profuse unilateral sweating of the head and upper neck was the most apparent clinical sign. CONCLUSION: Transient clinical signs of Horner's syndrome were seen following unilateral local anesthesia of the cervical plexus. Long-term adverse sequelae were not observed.

Ex vivo modeling of the airflow dynamics and two-and three-dimensional biomechanical effects of suture placements for prosthetic laryngoplasty in horses.

OBJECTIVE: To identify the degree of left arytenoid cartilage (LAC) abduction that allows laryngeal airflow similar to that in galloping horses, assess 2-D and 3-D biomechanical effects of prosthetic laryngoplasty on LAC movement and airflow, and determine the influence of suture position through the muscular process of the arytenoid cartilage (MPA) on these variables. SAMPLE: 7 equine cadaver larynges. PROCEDURES: With the right arytenoid cartilage maximally abducted and inspiratory airflow simulated by vacuum, laryngeal airflow and translaryngeal pressure and impedance were measured at 12 incremental LAC abduction forces (0% to 100% [maximum abduction]) applied through laryngoplasty sutures passed caudocranially or mediolaterally through the left MPA. Cross-sectional area of the rima glottis and left-to-right angle quotient were determined from photographs at each abduction force; CT images were obtained at alternate forces. Arytenoid and cricoid cartilage markers allowed calculation of LAC roll, pitch, and yaw through use of Euler angles on 3-D reconstructed CT images. RESULTS: Translaryngeal pressure and impedance decreased, and airflow increased rapidly at low abduction forces, then slowed until a plateau was reached at approximately 50% of maximum abduction force. The greatest LAC motion was rocking (pitch). Suture position through the left MPA did not significantly affect airflow data. Approximately 50% of maximum abduction force, corresponding to a left arytenoid angle of approximately 30° and left-to-right angle quotient of 0.79 to 0.84, allowed airflow of approximately 61 ± 6.5 L/s. CONCLUSIONS AND CLINICAL RELEVANCE: Ex vivo modeling results suggested little benefit to LAC abduction forces > 50%, which allowed airflow similar to that reported elsewhere for galloping horses.

Three-dimensional biomechanics of simulated laryngeal abduction in horses.

OBJECTIVE: To investigate the influence of simulated contraction of the cricoarytenoideus dorsalis (CAD) muscle on the 3-D motion of the arytenoid cartilage. SAMPLE POPULATION: 5 larynges from equine cadavers. PROCEDURES: Serial computed tomographic scans of each larynx were conducted at 7 incremental forces simulating contraction of medial, lateral, and combined bellies of the left CAD muscle. Three-dimensional reconstruction of radiopaque markers placed at anatomic landmarks on the left arytenoid and cricoid cartilages enabled quantification of marker displacement according to a Cartesian coordinate system. Rotation (roll, pitch, and yaw) of dorsal and ventral arytenoid planes was calculated relative to a plane formed by the coordinates of 3 markers on the cricoid cartilage by use of Euler angles. RESULTS: Displacement and rotational data showed that rocking motion occurs throughout arytenoid abduction and most of the rotational component is attributable to pitch; greater pitch was associated with action of the lateral belly. Roll of the ventral arytenoid plane was principally associated with action of the medial belly, which counteracted the tendency of the arytenoid cartilage to rotate medially into the rima glottidis lumen. The distance between markers on the arytenoid cartilage was not constant during contraction because of slight deformation of the corniculate process of the arytenoid cartilage, therefore indicating that the arytenoid cartilage is not a rigid body during abduction. CONCLUSIONS AND CLINICAL RELEVANCE: Arytenoid cartilage abduction was dependent on the rocking motion elicited by the lateral belly of the CAD muscle; therefore, laryngoplasty suture placement should mimic the action of the lateral, rather than the medial, muscle belly.