Human Posterior Cricoarytenoid Muscle Compartments: Anatomy and Mechanics

OBJECTIVE: To document the presence and functional significance of distinct anatomical compartments in the human posterior cricoarytenoid muscle (PCA). DESIGN: Anatomic study of human cadaver larynges. SUBJECTS: Seventeen fresh larynges, harvested at autopsy from 8 men and 9 women, with no history of laryngeal disease or surgery. INTERVENTIONS: Twenty-three PCA muscles from 12 human cadaver larynges were dissected. Computed tomographic scanning and rigid body mechanical analysis were used to compute 3-dimensional motion with simulated individual contraction of PCA compartments in 5 fresh larynges. RESULTS: Discrete medial and lateral bellies with different orientations of muscle fibers were found in every muscle. The 2 bellies insert on opposing aspects of the muscular process of the arytenoid. Very little linear translation was effected by either muscle. The axes of rotation attributable to the 2 bellies differed significantly, with the medial belly effecting rotation about a more vertical axis. The axis of rotation for the lateral muscle belly was nearer the anterior posterior axis than that of the medial belly. CONCLUSIONS: These data indicate that PCA muscle contraction results in arytenoid rotation about a variable oblique axis without significant lateral gliding. There are 2 bellies within the human PCA muscle with differing mechanical actions on the cricoarytenoid joint.