Anatomical localization of the motor entry point in the thyroarytenoid muscle.

INTRODUCTION: The aim of this study was to localize the motor entry point (MEP) of the thyroarytenoid muscle. METHODS: Eight cadaver larynges were dissected. A virtual plane was used to represent the MEP in a coordinate (X/Y/Z) system. The inferior border of the thyroid cartilage was linked to the center of the anterior arc of the cricoid cartilage (the Y-axis). The X-axis was set perpendicular to the Y-axis; the Z-axis passed through the posterior border of the thyroid lamina from the height of the insertion point. RESULTS: The mean X, Y, and Z coordinates were 6.2 mm, 9.1 mm, and 11.0 mm, respectively. The calculated angles of the lateral and superior deflections were 29.4° and 35.8°, respectively. The calculated insertion depth, that is, the distance from the insertion point to the MEP, was 15.6 mm. CONCLUSIONS: These results may help to improve the accuracy of needle insertion during diagnostic laryngeal electromyography or laryngeal electromyography-guided injections.