Fig. 4

Relationship of position between the most secure operating center point and the osseous anatomical landmarks at L5-S1. (E. The central point of the ipsilateral L5 pedicle; F. The intersection of the upper edge of the sacrum and the vertical line passing through the central point of the L5 pedicle; D. The intersection of the horizontal line of the point “O” and the line segment “EF”; P. The intersection of the upper edge of the sacrum and the vertical line passing through the point “O”; O. The most secure operating center point during the PETLIF procedures; a. The horizontal line of the superior margin of the sacrum.)