Fig. 1
From: Role of O-C2 angle in the development of dysphagia in patients with halo-vest fixation
Representative lateral plain X-rays of the cervical spine. O-C2 angle is defined as the angle between McGregor’s line (the line connecting the posterior edge of the hard palate to the most caudal portion of the occipital curve) and the inferior endplate line of C2. C2-C6 angle is defined as the angle between the inferior endplate line of C2 and the inferior endplate line of C6. The narrowest anteroposterior distance of the oropharynx between the tips of the uvula and epiglottis (double white arrow) is used as the nPAS. PIA represents the angle between McGregor’s line and the line made by drawing connecting the center of the C1 anterior arch to the apex of the cervical sagittal curvature