Sagittal plane kinematics of the adult hyoid bone

Abstract

The hyoid bone is a unique bone in the skeleton not articulated to any other bone. The hyoid muscles, which attach to the hyoid bone, may play a role in neck mechanics, but analysis of their function requires quantifying hyoid bone mechanics. The goal of this study was to obtain the detailed kinematics of the hyoid bone over a large range of flexion-extension motion using radiographs at 5 postures. The position of the hyoid bone in the sagittal plane was characterized with respect to head, jaw, and vertebral movements. Sex differences in hyoid kinematics were also investigated. We hypothesized that (1) the position of the hyoid bone in the sagittal plane is linearly correlated with motion of the head, jaw, and vertebrae, and (2) the hyoid position, size, and kinematics are sex-specific. We found that the hyoid bone X, Y, and angular position generally had strong linear correlations with the positions of the head, jaw, and the cervical vertebrae C1-C4. Hyoid X and angular position was also correlated to C5. Sex differences were found in some regressions of the hyoid bone with respect to C1-C5. The angular and linear measurements of the hyoid bone showed sex differences in absolute values, which were not evident after normalization by posture or neck size. Incorporating these results to neck models would enable accurate modeling of the hyoid muscles. This may have implications for analyzing the mechanics of the cervical spine, including loads on neck structures and implants.

Figure 1

Lateral X-rays of a subject at five postures (from maximum voluntary extension to maximum flexion).

Figure 2

A. Lateral radiograph at the neutral posture, showing bony landmarks where lead beads were placed on the skin. A1/A2: left or right infraorbital socket; B1/B2: left or right tragus; C1/C2: left or right angle of jaw; D: tip of chin; E: intersection of chin and neck; F: sternal notch. B. Lateral radiograph with other landmarks digitized. Occ: external occipital protuberance; S: center of sella; Nas: the most anterior point of the frontonasal suture; ExtAud: external auditory meatus; Bas: basion; Opi: opisthion; InfOrb: infraorbitale; PosNas: posterior nasal spine; Gon: angle of the mandible (gonion); H1: the most anterior and superior point on hyoid bone; H2: the most posterior point on hyoid greater horn; Retr: most inferior and posterior point on the mandibular symphysis; Prog: the point on the madibular symphysis farthest from condylion (prognathion).

Figure 3

The definition of the T1 coordinate system (‘X’ and ‘Y’) and the definitions of the local vertebral body coordinate systems (‘x1’ and ‘y1’ through ‘x7’ and ‘y7’).

Figure 4

A. Hyoid bone trajectories (for point H1 in Figure 2B) in the C3 coordinate system for five postures of each subject, fit with a second order polynomial function. B. Hyoid bone trajectories (H1 in Figure 2B) in the T1 coordinate system for five postures of each subject, fit with a second order polynomial function. C. Trajectories of chin tip, centroid of C3 vertebral body and hyoid bone (H1 in Figure 2B) in the T1 coordinate system for five postures of each subject, fit with a second order polynomial function.

Figure 5

Regressions between hyoid bone and head (definitions in Table 2), which have no sex difference. A. Regression of angle of hyoid bone with respect to angle of head. B. Regression of X (anterior) position of hyoid bone with respect to X position of orbit. C. Regression of Y (superior) position of hyoid bone with respect to Y position of orbit.

Figure 6

Regressions between hyoid bone and C3 (definitions in Table 2), which have a significant sex difference (p<0.05). A. Regression of angle of hyoid bone with respect to angle of C3. B. Regression of X (anterior) position of hyoid bone with respect to X position of C3. C. Regression of Y (superior) position of hyoid bone with respect to X position of C3.