Level of vocal folds as projected on the exterior thyroid cartilage

This study aims to identify the level of the vocal folds as projected on the exterior thyroid cartilage.

Anatomic study of human cadaver larynges.

The study includes 83 fresh larynges harvested at autopsy from 62 male and 21 female cadavers. The larynges were excised and divided in the midline posteriorly. One needle was inserted at the level of anterior commissure from endolarynx, and the other was inserted at the thyroid ala just anterior to the vocal process along the superior surface of the right vocal cord. Measurements of vocal cord projections on the thyroid ala were done with a caliper.

The mean value of the ratio of the distances from the superior thyroid notch to anterior commissure and the midline height from thyroid notch to the inferior border of thyroid cartilage was found to be 0.41 in males and 0.38 in females. No statistical differences were observed between these two groups (P =.062). We found that the distance from the anterior commissure to the inferior thyroid border in midline "c" was longer than the distance from the posterior border of the vocal cord to the inferior border of the inferior tubercle of the thyroid ala "d" in 44 (71%) males and in 7 (33%) females. On the other hand, "d" was longer than "c" in 8 (12.9%) males and in 8 (38.1%) females. These two distances were equal in 10 (16.1%) males and in 6 (28.6%) females.

In this study, we found that the anterior commissure lies approximately at the juncture of the upper two fifths and lower three fifths of the midline height of thyroid cartilage in the majority of the larynges of the male and female cadavers. The position of the posterior border of the vocal cords was found to be at a lower level than anterior commissure in two thirds of males and in one third of females. This means that the vocal cords slope downward posteriorly in the majority of the larynges of the males. This may be one of the causes of failure of some type I thyroplasties.