Applied anatomy of the structures around sacrum and its relevancies

Objective: To discuss the relationship between structures around sacrum and the complications of sacral screw. Methods: The adjacent structures about the sacra were investigated on 58 cadavers, as well as the first anterior sacral foramina and the sacral canal. The simulated operations were performed on 10 cadavers for observing the place of the sacral screw and the relation between the place and structures around the sacrum. Results: The sacral plexus consists of the lumbosacral nerve trunk passing in front of the ala of sacrum crosswise, and the first sacral nerve coming from the first anterior sacral foramina. A safe triangular zone, which is located in front of the sacrum, is made up of the lumbosacral sympathetic trunk, the lumbosacral nerve trunk and the first sacral nerve. The medial part of the zone is safe for no important structure in it; and the superior gluteal artery and vein are in the lateral part of the zone. The iliac artery and vein are the neighbors of the triangular zone. The first sacral nerve has a diameter of (11.0±2.8) mm (6.0～17.0mm); and the lumbosacral nerve trunk is (7.6±2.2) mm (3.0～12.0mm). The sacral screw is safe at 0°～10°inward to the sagittal plane, because its point is located in the medial part of the triangular zone. The cause of bleeding during operation may be the small vessels coming from the first posterior sacral foramina or the posteromedial rami of the fifth lumbar vessel passing through the lateral sulcus of the sacrum. The simulated operations showed the sacral screw was in the body of the sacrum and out of the sacral canal through the five-seven o'clock point. Conclusions: The tip of the sacral screw maybe injury the sacral nerve and the iliac vessels. The placement of sacral screw through the five-seven o'clock point on the articular facet of the superior articular process was a safe and easy method.