Three-dimensional measurement accuracy of skull surface landmarks.

Craniometric measurements from a three-dimensional (3-D) digitizing system were compared with those from sliding and spreading calipers. The 3-D system consisted of a 3-Space Digitizer, Macintosh Plus computer, and Unigraphics CAD/CAM system. Twenty-nine standard measurements were made and repeated on two normal and three deformed skulls. The percentage of difference was calculated for original versus repeat measures and caliper versus 3-D measures. For objective anatomic structures and fiducial points, there was less than 2 mm (maximum) of difference between 1) the original digitizer versus repeat 3-D measures and 2) caliper versus 3-D measures. This represented 2% or less measurement incongruence. There were no significant differences for these comparisons (p greater than 0.1), and all regressions were highly significant (P less than 0.001), with r2 greater than 0.999. 3-D measurements were made more easily and quickly than were caliper measurements, with no loss in precision. It is concluded that 3-D measurements are equivalent in quality to caliper measurements for craniometric studies, but are easier to obtain.