Changes in Pelvic Incidence, Pelvic Tilt, and Sacral Slope in Situations of Pelvic Rotation

STUDY DESIGN Digitally reconstructed radiograph-based study. OBJECTIVE Using a computer-based method to determine what degree of pelvic rotation is acceptable for measuring the pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). The effectiveness of a geometrical formula used to calculate the angle of pelvic rotation proposed in a previous article was assessed. SUMMARY OF BACKGROUND DATA It is unclear whether PI, PT, and SS are valid with pelvic rotation while acquiring a radiograph. MATERIALS AND METHODS Ten 3-dimensionally reconstructed models were established with software and placed in a neutral orientation to orient all of the bones in a standing position. Next, 140 digitally reconstructed radiographs were obtained by rotating the models around the longitudinal axis of each pelvis in the software from 0 to 30 degrees at 2.5-degree intervals. PI, PT, and SS were measured. The rotation angle was considered to be acceptable when the change in the measured angle (compared with the "correct" position) was