title: The use of computed tomography to define zygomatic complex position.
abstract: OBJECTIVE
  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.
authors.affiliation: Division of Oral and Maxillofacial Surgery, Cambridge, Stratford, & Woodstock General Hospitals, Ontario, Canada. ianfurst@mobile.rogers.com
authors.forename: I M
authors.initials: IM
authors.lastname: Furst
authors.forename: P
authors.initials: P
authors.lastname: Austin
authors.forename: M
authors.initials: M
authors.lastname: Pharoah
authors.forename: J
authors.initials: J
authors.lastname: Mahoney
mesh_terms: D002508:Cephalometry / Q000379:methods*; D003951:Diagnostic Errors; D005145:Face / Q000033:anatomy & histology*; D006801:Humans; D019248:Jaw Fixation Techniques / Q000295:instrumentation; D008437:Maxilla / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D015588:Observer Variation; D017063:Outcome Assessment, Health Care / Q000379:methods; D015203:Reproducibility of Results; D019291:Skull Base / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D013701:Temporal Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014025:Titanium; D015898:Tomography Scanners, X-Ray Computed; D014057:Tomography, X-Ray Computed; D015050:Zygoma / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*
chemical_list: D014025:Titanium