Fig. 2.

a–c The schematic shows the determination of the best-fit sagittal line segment and its midpoint of the sacral endplate. a The calculation of the mid-sagittal plane used an Iterative Closest Points algorithm based on the anterior pelvic plane. b Approximately 5000–8000 surface points (black) on the sacral endplate were automatically extracted to fit a sagittal line segment. For a better view of the sacrum, part of the left iliac bone was removed. c The midpoint (green) of the sagittal line segment was calculated by the software. For a better view of the sagittal line segment, the left part of the pelvis was removed