Image-Free Navigation

Image-free navigation can be used without preoperative and intraoperative imaging information and allows intraoperative registration of the anterior superior iliac spine. The pubic symphysis was registered, and virtual anterior pelvic plane (APP) coordinates were set according to reference markers. After registration of the internal surface of the acetabulum, the inclination and anteversion angles of the cup with respect to the APP reference were displayed. The pelvic tilt must be determined on preoperative images to place the cup according to the supine functional pelvic plane. The accuracy of cup placement for image-free navigation is 1.8°–4.4° for the inclination angle and 2.0°–11.6° for the anteversion angle, and there are reports that the accuracy of the anteversion angle is poor.