It was reported, "during final tightening tulip head became disengaged from screw shaft on a 7. 5 x 40 screw placed in the sacrum on a l4-s1 construct. Dr (b)(6) noted that there was a really good bite on the screw and that it was seated in a way that the rod did not sit in the bottom of the screw. The final tightening devices were placed onto the screw/blocker/rod to tighten and it did not feel right. Dr (b)(6) took the construct apart to check the screw and the tulip pulled right off. Dr (b)(6) did comment that his suspicion is that because of the strength of the screws purchase that it would not move upward so the joint, being the weakest part failed.