The use of computed tomography to define zygomatic complex position.

PURPOSE: The purpose of this study was to analyze the use of midline references and landmarks to assess the position of the zygomatic complex relative to the cranial base, and to test the reliability of these measurements in assessing facial symmetry.
METHODS: Direct skull measurements were compared with measurements made on computed tomography (CT) images. The effect of CT scanner error, technologist error, gantry angle error, error of skull inclination, and error due to the presence of titanium rigid fixation hardware were assessed. To test observer variation and the effect of each level of error, 4 blinded bilateral measurements were repeated 3 times by 5 observers on both dry skull and CT scans. A mixed effect analysis of variance model then assessed for effect of method of measurement (dry skull vs CT), observer, CT scanner, technologist, gantry angle, skull inclination, and rigid fixation.
RESULTS: A total of 2,040 measurements were made. Measurements for zygomatic complex posterior and anterior width and height were reliable and had an interobserver variations of 0.02 +/- 0.03 mm, 0.5 +/- 0.4 mm, and 0.37 +/- 0.3 mm, respectively. The difference between dry skull and CT assessment for the 3 reliable measurements was 1.2 +/- 0.3 mm, 0.44 +/- 0.4 mm, and 1.1 +/- 0.5 mm, respectively. The errors produced by the CT scanner, technologist, and rigid internal fixation hardware were not clinically significant. The measurements were not sensitive to gantry angle and skull inclination changes of 10 degrees or less. A fourth measurement assessing zygomatic complex projection was found not to be accurate or reliable.
CONCLUSIONS: These findings suggest that the 3 CT scan measurements describing the position of the zygomatic complex relative to the cranial base are clinically useful. Copyright 2001 American Association of Oral and Maxillofacial Surgeons.