Background A single iliosacral screw placed into the S1\nvertebral body has been shown to be clinically unreliable\nfor certain type C pelvic ring injuries. Insertion of a second\nsupplemental iliosacral screw into the S1 or S2 vertebral\nbody has been widely used. However, clinical fixation\nfailures have been reported using this technique, and a\nsupplemental long iliosacral or transsacral screw has been\nused. The purpose of this study was to compare the\nbiomechanical effect of a supplemental S1 long iliosacral\nscrew versus a transsacral screw in an unstable type C\nvertically oriented sacral fracture model.\nMaterials and methods A type C pelvic ring injury was\ncreated in ten osteopenic/osteoporotic cadaver pelves by\nperforming vertical osteotomies through zone 2 of the\nsacrum and the ipsilateral pubic rami. The sacrum was\nreduced maintaining a 2-mm fracture gap to simulate a\nclosed-reduction model. All specimens were fixed using\none 7.0-mm iliosacral screw into the S1 body. A supplemental\nlong iliosacral screw was placed into the S1 body in\nfive specimens. A supplemental transsacral S1 screw was\nplaced in the other five. Each pelvis underwent 100,000\ncycles at 250 N, followed by loading to failure. Vertical\ndisplacements at 25,000, 50,000, 75,000, and 100,000 cycles\nand failure force were recorded.\nResults Vertical displacement increased significantly\n(p\\0.05) within each group with each increase in the\nnumber of cycles. However, there was no statistically\nsignificant difference between groups in displacement or\nload to failure.\nConclusions Although intuitively a transsacral screw may\nseem to be better than a long iliosacral screw in conveying\nadditional stability to an unstable sacral fracture fixation\nconstruct, we were not able to identify any biomechanical\nadvantage of one method over the other.\nLevel of evidence Does not applyââ?¬â?biomechanical study.
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