The Effect Of Hyoid Movement On Vocal Fold And False Vocal Fold Configurations In Excised Human Larynges.

OBJECTIVES: While it is generally understood that extrinsic muscle activation may change larynx position and orientation, its effect on vocal fold configuration, particularly the medial surface shape, remains largely unknown. In this study, the effects of 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 vocal fold and false vocal fold. The larynx was mounted vertically with the cricoid cartilage fixed. The hyoid bone position was systematically modified along both the superior and anterior-posterior directions. The three-dimensional shape of the vocal fold medial surface and false vocal fold was reconstructed at different hyoid positions.

RESULTS: Upward hyoid movement lifted the false vocal fold, increasing both the vertical width and depth of the ventricle. Upward hyoid movement also decreased vocal fold length and tilted the vocal fold upward and backward (except for anterior-superior hyoid movement), and increased glottal width (except for posterior-superior hyoid movement). The effect of upward hyoid movement on vocal fold vertical thickness was insignificant and larynx-specific.

CONCLUSIONS: These results suggest that extralaryngeal manipulations have more consistent effects on vocal fold length and tilting than the shape of the vocal fold medial surface, which appears to be largely controlled by intrinsic laryngeal muscles.