Figure 2.

Lateral radiogram demonstrating the x- and y-axes.

Notes: A coordinate system was established with the y-axis forming a straight line connecting the lower edges of the second (white triangle) and fourth cervical vertebrae (black triangle) and x-axis forming a straight line drawn perpendicular from the lower end of the fourth cervical vertebra. The white circle indicates the hyoid bone. The distances between the maximum anterior-superior hyoid elevation and the hyoid position at the onset of elevation were defined as anterior and superior movement along the x- and y-axes, respectively. The extent of hyoid movement was normalized by dividing by the length of a straight line connecting the lower ends of the second and fourth cervical vertebrae on the y-axis.