Fig. 1
From: Digital anatomical study and clinical application of the ideal S2 alar-lliac screw trajectory
With the first sacral superior endplate plane, a three-dimensional coordinate system was established (A); a series of parallel cutting surfaces with a spacing of 3 mm was made in the coronal plane (B); the second sacral vertebra, sacroiliac joint, and iliac section outline were used as the target area (C); the maximum internal tangent circle was fitted to each section in the target area, and the center of the circle was marked (D)