Abstract: Objective To explore the clinical guiding significance of trailing edge of abdominal organs on the lateral lumbar X-ray in lateral puncture by spinal microendoscopy.Methods A total of 50 patients who had abdominal enchanced computed tomography (CT) examination in our hospital were included in the present study. We divided the spine from L1 to S1 into 16 axial levels, including the vertebral upper (the cranial endplates), middle and the under margin (caudal endplates). Then we respectively measured vertebral sagittal diameter (L) in every level, and established a coordinate axis (establishing Y axis by the extension of vertebral sagittal diameter and establishing X axis through the midpoint of the rear margin vertebral which was set to be point O). We set the cross point of the parallel line of X axis and the tangent line of post-renal fascia and parietal peritoneum's arc to be point D the projection of which was named D', then we measured the distance between point D' and point O which was called OD'. We set critical puncture point to be point C which is the cross point of the skin and the tangent line of the post-renal fascia and parietal peritoneum's arc through point O and the projection on axis Y of point C was named C'. Then we measured the distance between point C and point O and called OC'. The critical puncture angle (α) which is the crossing angle of the line OC and X axis was measured, and finally we calculated the ratio of OD' and L, and the ratio of OC' and L.Results All of the data show that the location of the projection of the lowest point of the post-renal fascia and parietal peritoneum and the location of the projection of the critical puncture point turns from the back side of the vertebral rear margin to ventral side from L1 to S1, and they are in the same location on the vertebral posterior margin at the middle level of L4. The critical puncture angle is also on declare from L1 to S1, and is about 0° at the middle level of L4. All of the data show that there is no statistical difference between each side of the body in the lowest point of the post-renal fascia and parietal peritoneum, critical puncture point and critical puncture angle.Conclusion This research defines the safe line and the definite range of the puncture point and puncture angle from L1 to S1 according to the projection of the lowest point of the post-renal fascia and parietal peritoneum. It provided an anatomical reference for avoiding intra-operative injury of post-renal fascia or abdominal organs.

Key words: postrenal fascia, microendoscopic, spiral CT