Modified transpedicular screw starting point for S1 vertebra. (A) Cutting line of osteotomy drawn on inferior L5 articular process. (B) Osteotomy site of S1 articular process margin. Posterio-lateral margin is divided into upper and bottom halves. The osteotomy is performed at the upper part of the bottom half of S1 superior articular process. (C) The starting point within the osteotomy site of the superior S1 facet (x). The screw is gaining the saddle-like support in the inferior pole (b). (a) Resected inferior L5 facet.