Comparison of the operation safety and biomechanical stability of sacral alar-iliac vs. sacroiliac screws in the fixation of sacroiliac joint in simulated models of low bone density

•Sacral alar-iliac screws (SAISs), especially S2AIS have been used for sacroiliac joint and were superiority to traditional sacroiliac screws (SISs) in patients with low bone density. However, no comparative study has examined both the insertion safety and biomechanical stability of different sacroiliac fixation methods.•This study investigated the insertion safety and biomechanical stability of different sacroiliac fixation methods, including SIS, transsacral-transiliac screw (TSTIS), S1 alar-iliac screw (S1AIS) and S2AIS in the treatment of sacroiliac joint in patients with low bone density.•We have demonstrated that the stability of S1AIS and S2AIS is similar, both stronger than that of SIS and TSTIS, which have shorter lengths of the screw trajectory on the ilium side. However, the safety zone of S2AIS at the insertion point is smaller than that of S1AIS.•Considering both safety and stability, S1AIS is the preferred choice for fixation of sacroiliac joint in patients with low bone density. Sacral alar-iliac screws (SAISs) have been used for sacroiliac joint and are superiority to traditional sacroiliac screws (SISs) in patients with low bone density. The aim of this study was to investigate the operation safety and biomechanical stability of the SIS, transsacral-transiliac screw (TSTIS), S1AIS and S2AIS in the treatment of sacroiliac joint in simulated models of low bone density. CT data from 80 normal pelvic structures were employed to measure the anatomical parameters, including the safety zones of the S1AIS and S2AIS at the insertion point and the trajectory lengths of the SIS, TSTIS, S1AIS and S2AIS. Sixteen synthetic pelvises with simulated osteoporotic bone structure were used to simulate type C Tile lesions and divided into 4 groups with an anterior plate and posterior fixation using one of the following: 1) one SIS on each side, 2) one TSTIS fixing both sides, 3) one S1AIS on each side, or 4) one S2AIS on each side. The stiffness and maximum load of the specimens were analyzed using a biomechanical machine under vertical loading. The safety zone of S1AIS was larger than that of S2AIS (p