Objective: While it is generally understood that extrinsic muscle activation may change the larynx position and orientation, the effect on vocal fold configuration, particularly the medial surface shape, remains largely unknown. In this study, the effects of passive hyoid bone movement on the true and false vocal fold configurations were investigated in excised human larynges.
Method: For each larynx, a window was opened on one thyroid lamina to provide a medial view of the true and false vocal folds. The larynx was mounted vertically with the cricoid cartilage fixed. The hyoid bone position was systematically modified along both the vertical and anterior-posterior directions. The three-dimensional shape of the vocal fold medial surface and false folds were reconstructed at different hyoid positions.
Results: The upward movement of the hyoid bone increased both the lateral depth and vertical span of the ventricle and retracted the false vocal folds. The hyoid movement also led to an upward movement of the thyroid cartilage, which decreased the vocal fold length, particularly when the hyoid bone was moved upward and posteriorly. There was a trend of increasing vocal fold thickness and decreasing vocal fold approximation with the upward hyoid movement, although it is statistically not significant.
Conclusions: These results suggest that extralaryngeal manipulations may only have a limited effect on the vocal fold medial surface shape, which appears to be largely controlled by the intrinsic laryngeal muscles.