Hyoid position correlates with respiratory events and pulmonary function in obstructive sleep apnea patients.

A detailed cephalometric analysis was performed studied in the 66 obstructive sleep apnea patients and in 11 control subjects. The hyoid bone was found to be caudally displaced in the apnea patients compared to the control group, with a highly significant greater distance from the anterior nasal spine to the hyoid (H-ANS) from the second cervical vertebrae to the hyoid (H-C2), and from the nasion to hyoid (H-N), with smaller C2-H-N and C2-H-ANS angles even after exclusion of the 26 most obese subjects (BMI>27.9). On multiple regression analysis, after adjustment for age and BMI, increased H-C2 distance predicted (a) more severe nocturnal and daytime hypoxia (F = 12.4 and F = 7.4, with p < 0.01) and (b) lower values of FVC and FEV1 (percentage predicted; F = 30.5 and F = 21.6, with p < 0.01). IE50, an index of sleep-related inspiratory airflow limitation, showed a negative correlation with H-Gn (F = 17.1, with p < 0.01). These indexes did not predict AHIO in our study. Discussion Skeletal craniofacial and soft tissue abnormalities of the upper airways have been frequently reported in patients with OSA.3,4,6-8 These abnormalities predispose patients to pharyngeal occlusion and are related to the severity of OSA.5,6 One of the most studied types of cephalometric data in OSA patients is the low position of the hyoid bone.3,6,9,10 The position of the hyoid bone is limited by vertebral development and should be at the C3-C4 level by three years of age, and at C4 by adulthood.4,9 However, there is an abnormally low hyoid position in OSA patients. Usually, in cephalometric measurements, the position of the hyoid bone is calculated with respect to the anterior nasal spine and the gnathion. Instead, we found a highly statistically significant increase in the distance between the hyoid bone and the second cervical vertebrae (H-C2), which is considered to be a less variable anatomical parameter than other cephalometric points. The increased H-C2 distance retained a statistically significant value role even after the exclusion of the most obese subjects. This suggests that a low hyoid position may be considered to be a marker of airflow limitation in OSA patients, which is not otherwise explained by age or BMI. Moreover, our results seem to confirm that palatal surgery alone may not be adequate for the treatment of OSA.