[Hyoid bone position and airway accompanied with influence of head posture]

The position of hyoid bone has been analyzed using roentgenogram. But, due to the great variability with the change of head posture, the position could not be determined correctly. In the present study, we investigated the influence of head posture to the position of hyoid bone. Subjects consisted of 32 Japanese males, those mean age was 25.8 years. Lateral cephalograms had been taken for each subjects at 5 different head posture. The findings were as follows. 1. Superimposed on SN plane, hyoid bone moved along the line of menton to 4th cervical vertebrae (C4) with the change of head posture. The hyoid bone moved in parallel with the line of 3rd cervical vertebrae (C3) to C4 (cervical plane). In spite of these movements, RH kept an uniform ratio. 2. The distances between sella turcica and hyoid bone and between C3 and hyoid bone, and the angle between menton, porion and hyoid bone, were at constant value. 3. Some measurements included the distance between hyoid bone and menton and the angle between nasion, sella turcica, hyoid bone showed very high correlation with the change of head posture. 4. EpPW1 (the width of airway) and the distance from C4 to hyoid bone showed almost the same change. It means the position of hyoid bone has a great influence on airway.