Reference structures for assessment of frontal head posture

The aim of the study was to test (a) the validity of the supra-orbital line as a substitute for the interpupillary line, and (b) the reproducibility o f two different approaches of assessing cranio- and cervico-vertical relati onships on frontal cephalograms. The material consisted of natural head pos ition frontal cephalograms of 21 healthy Finnish students and 11 Danish you ng adults prepared according to a method described previously, modified in the Danish sample by addition of spectacles with a wire to indicate the int erpupillary line. The cephalograms were analysed manually twice by two inve stigators with an interval of one week. The following reference lines were selected: (1) orbital line (ORB): a tangent to the extreme cranial point on the supra-orbital margins; (2) cranial line (CR): the line drawn through c rista galli and anterior nasal spine; (3) cervical line (CER): a line drawn through the midpoints of atlas (half the distance between the most median points on the tubercle of the transverse ligament), and C4 (half the distan ce between the most concave points of the lateral masses); (4) the main cou rse of the upper cervical spine (SPINE): a subjective impression of the spi nal inclination; (5) the interpupillary line (IP); and (6) the true vertica l and horizontal lines (VER, HOR). The angles were measured to the nearest 0.5 degrees. Intra- and inter-examiner reproducibility was calculated. The supra-orbital line almost coincided with the interpupillary line as the mean inclination between the lines was only 0.5 degrees. Both intra- and i nter-examiner errors were less for ORE and CER than for CR and the line ind icating the main course of the upper cervical spine (SPINE). The intra-exam iner reproducibility s(i) for ORB/HOR and CR/VER was 0.4 and 0.8 degrees re spectively, and for CER/VER and SPINE/VER 0.8 degrees and 1.0 degrees. Base d on these results, the supra-orbital line and the cervical line (defined a s the mid-transversal line between the atlas and the fourth cervical verteb ra) are recommended as reference lines for assessing frontal head posture.