Fig. 5

a. Distribution of the security index in S1 and S2 from the sagittal view. Red represents the area where the screw is placed accurately, which is close to the optimal screw corridor. Green represents the area where the screw can be placed safely but not in the optimal corridor. b. The whole screw is located in the safe corridor in a postoperative sagittal sacral view. c. The registered 3D model of the pelvis is shown from a posterior pelvic view