The hyoid triangle

Abstract

The importance of the hyoid bone lies in its unique anatomic relationships. It has no bony articulations but provides attachment for muscles, ligaments, and fascia of the pharynx, mandible, and cranium. Previous investigations into the hyoid position have employed various analyses, most of which have related the hyoid bone to the cranium, the S-N plane being very popular. These studies also remarked on the great variability of the hyoid position on even slight movement of the head. It appears that the two may be intimately related. This article introduces an analysis of the hyoid bone position known as the hyoid triangle. The triangle is formed by joining the cephalometric points retrognathion (the most inferior, posterior point on the mandibular symphysis). hyoidale (the most superior, anterior point on the body of the hyoid bone), and C3 (the most anteroinferior point on the third cervical vertebra). The hyoid triangle relates the hyoid bone to the vertebrae and to the mandible. Since the mandibular symphysis is at a level more comparable to the axis of rotation of the head than is the cranium, the effect of head movement will be minimized and thus the hyoid position can be determined more correctly. The hyoid triangle was applied to a sample of fifty-four pretreatment orthodontic patients. The sample was confined to Class I malocclusions with no significant abnormalities in the vertical dimension. Standard values are given for the dimensions of the hyoid triangle which indicate that the hyoid bone is less variable in position than previous research has suggested. The anteroposterior position of the hyoid bone relative to the cervical vertebrae was very constant in this sample, with a mean of 31.76 mm. and standard deviation of 2.9. The anteroposterior of the upper bony airway (AA-PNS) was also constant, with a mean value of 32.91 mm. and a standard deviation of 3.66. The correlation coefficient between the two anteroposterior dimensions (AA-PNS and C3-H) was 0.98. This finding indicates that the hyoid bone represents the anterior bony boundary of the pharynx at a lower level than PNS. It was also noted that there is no sexual dimorphism in hyoid bone position.