Three-dimensional biomechanics of simulated laryngeal abduction in horses

To investigate the influence of simulated contraction of the cricoarytenoideus dorsalis (CAD) muscle on the 3-D motion of the arytenoid cartilage.

5 larynges from equine cadavers.

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.

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.

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.