Evaluating the structural properties of suprahyoid muscles and their potential for moving the hyoid

Abstract

Superior and anterior hyoid movements are important events in pharyngeal deglutition. This cross-sectional study uses a cadaver model to document the structural properties of the muscles underlying these movements in an effort to understand how their morphology influences function. Measurements to determine physiological cross-sectional areas (PCSAs) of swallowing muscles were taken from hemisected head and neck formalin-fixed cadaver specimens (n = 13). Coordinates of muscle attachment sites and PCSAs were used to calculate î and ĵ unit force vectors, where î and ĵ represent anterior-posterior and superior-inferior directions, respectively. The suprahyoid muscle subsamples were grouped for analysis as follows: digastric (DG), geniohyoid (GH), mylohyoid (MH), and stylohyoid (SH). The ANOVA with Tukey HSD post hoc analysis of unit force vectors showed the following results: GH (-0.44 ± 0.15 cm(2)) >MH (-0.02 ± 0.21 cm(2)), DG (-0.05 ± 0.11 cm(2)), SH (0.14 ± 0.04 cm(2)), with negative values representing the anterior direction (p < 0.01); and MH (0.91 ± 0.28 cm(2)) >DG (0.29 ± 0.14 cm(2)), SH (0.22 ± 0.08 cm(2)), GH (12 ± 0.08 cm(2)), with positive values representing the superior direction (p < 0.01). The morphology of the suprahyoid muscles suggests that based on structural properties, the geniohyoid has the most potential to displace the hyoid in the anterior direction and the mylohyoid has the most potential to displace the hyoid in the superior direction. These data in complement with physiological findings may provide greater insight into these movements for those developing novel treatments for dysphagia.

Figures

Fig. 1

Illustration of the superior and anterior movement of the hyoid bone as seen in fluoroscopy under normal conditions

Fig. 2

Illustrated suprahyoid muscles with attachment sites and innervation. The suprahyoid and thyrohyoid muscles are thought to open the upper esophageal sphincter (UES), in addition to other functions

Fig. 3

Two-dimensional coordinates of muscle attachment points: anterior = −x; superior = +y; hyoid = (0,0). Arrows represent a mean line of action for the indicated muscle sample (n = 13)

Fig. 4

Means and standard deviations of anterior-posterior PCSA force unit vectors (cm2), with anterior = −, posterior = +, and hyoid position = 0. An analysis of variance with Tukey HSD of the unit force vector in the anterior-posterior direction shows that the geniohyoid has the most potential structurally to effect the anterior displacement of the hyoid (p < 0.01)

Fig. 5

Means and standard deviations of superior-inferior PCSA force unit vectors (cm2), with superior = + and hyoid position = 0. An analysis of variance with Tukey HSD of the unit force vector in the superior-inferior direction shows that the mylohyoid has the most potential structurally to effect the superior displacement of the hyoid (p < 0.01)