Topography of motor endplates in the human posterior cricoarytenoid muscle: Implications for selective reinnervation

Abstract The posterior cricoarytenoid muscle (PCA) is the only intrinsic laryngeal muscle that abducts the vocal fold and is therefore a key target for selective reinnervation in bilateral vocal fold paralysis. Because its distal nerve supply is anatomically variable, direct implantation strategies may benefit from precise knowledge of motor endplate topography. We characterized the spatial distribution of motor endplates in bilateral posterior cricoarytenoid muscles obtained from five human body donors ( n = 5; four men and one woman; median age 80 years, range 79–98), yielding a total of 10 muscles for descriptive anatomical analysis. One left PCA was affected by documented unilateral vocal fold paralysis and was analyzed separately. Motor endplates were labeled with tetramethylrhodamine‐conjugated α‐bungarotoxin, imaged by whole‐slide fluorescence scanning, and detected using a standardized QuPath workflow. In the nine muscles without known laryngeal pathology, motor endplates were heterogeneously distributed, with higher‐density regions frequently forming an arcuate band. The vertical compartment contained a median of 71.5% of all detected endplates (range 52.8–87.3%) and showed a median areal density of 3.57 endplates/mm 2 , compared with 2.43 endplates/mm 2 in the horizontal compartment. Muscle fibers bearing multiple motor endplates were also observed. The paralyzed PCA showed high motor endplate density across a broader portion of the muscle, with less clearly defined spatial zonation. These findings support the existence of preferential motor endplate zones in the human PCA, while highlighting substantial anatomical variability, particularly in the pathological specimen. This variability may have implications for the positioning of donor nerve implants during selective laryngeal reinnervation.