Objectives: Surgical manipulation of the vocal fold posture, such as medialization thyroplasty or arytenoid adduction, aims to restore physiologic pre-phonatory glottal shape. However, physiologic pre-phonatory glottal shape has not been comprehensively described. We investigated vocal fold medial surface shape across interactions of thyroarytenoid (TA), cricothyroid (CT), and lateral cricoarytenoid/interarytenoid (LCA/IA) muscles.
Methods: An in vivo canine hemilarynx model was used. Pre-phonatory posture of the vocal fold medial surface was captured using high-speed video over 64 combinations of graded intrinsic laryngeal muscle (ILMs) activations from threshold to maximal activation (4 TA x 4 CT x 4 LCA/IA levels). Medial surface shape was reconstructed using a 3D interpolation algorithm of tattooed medial surface landmarks.
Results: Combined activation of ILMs yielded a range of unique pre-phonatory postures. Both LCA and TA activation contributed to glottal adduction but with greater contribution from TA. The transition from a convergent to a rectangular glottal shape was primarily mediated by higher levels of TA muscle activation. At higher combined activation levels of the LCA and TA, the posterior glottis adducted to a greater degree than the anterior. CT activation resulted in slight abduction of the vocal fold and a slightly more convergent glottis.
Conclusions: A comprehensive quantitative analysis of in vivo vocal fold medial surface from activation of adductor ILMs revealed the dominant effect of TA on achieving a rectangular pre-phonatory posture with increased medial surface height. This study comprehensively captures laryngeal pre-phonatory posture and may guide surgical attempts to manipulate glottal posture and improve voice