Objective To summarize the current research progress of second sacral alar-iliac (S2AI) screw technique for reconstruction of spinopelvic stability. Methods The recent original literature concerning development, clinical applications, anatomy, imageology, and biomechanics of S2AI screw technique in reconstruction of spinopelvic stability was reviewed and analyzed. Results As a common clinical strategy for the reconstruction of spinopelvic stability, S2AI screws achieve satisfactory effectiveness of lumbosacral fixation without complications which were found during the application of traditional iliac screws technique. S2AI screw technique is more difficult to place screws by hand because of its narrow screw trajectory. Although the S2AI screws trajectory pass through 3 layers of bone cortex, the biomechanical cadaveric study demonstrate that no statistical difference in stiffness was found between the traditional iliac and S2AI screw in a spinopelvic fixation model. Conclusion S2AI screw technique should be a safe and feasible method for reconstruction of spinopelvic stability in place of the traditional iliac screw technique.
ObjectiveTo explore the differences in the implantation safety and stability of a single the S1 alar-iliac screw (S1AIS) or S2AIS for sacroiliac joint fixation, providing reference for selecting appropriate internal fixation in clinical practice. MethodsPatients who underwent pelvic CT examination between January 2024 and December 2024 were selected. CT data from 80 patients with normal pelvic structure who met the selection criteria were included in a 1:1 male to female ratio. CT digital reconstruction technology was used to measure the transverse and longitudinal diameters of the S1AIS and S2AIS insertable ranges, as well as the length, width, and sacral side length of the screw trajectory. The pelvic CT data from 30 patients were randomly selected based on a 1:1 male to female ratio for three-dimensional (3D) printing of pelvic samples. The SAISs with a diameter of 6.5 mm and 8 mm were implanted at the optimal entry/exit points on the left and right sides, respectively, to observe the perforation of the screw trajectory. The pelvic CT data from 1 patient was randomly selected for 3D printing of 10 pelvic samples to simulate Tile C2 fracture. They were divided into S1AIS group and S2AIS group (n=5), with one S1AIS and one S2AIS fixation used for posterior sacroiliac joint separation, and the specimen stiffness and maximum load were measured by using an electric tension torsion dual axis universal mechanical tester. ResultsThe anatomical parameter measurement showed that there was no significant difference in the length and width of the screw trajectory between S1AIS and S2AIS (P>0.05), but the transverse and longitudinal diameters of the insertable ranges, as well as the sacral side length of the screw trajectory, were all greater than those of S2AIS, with significant differences (P<0.05). After simulating the implantation of S1AIS and S2AIS with a diameter of 6.5 mm in pelvic specimens, no screw penetration was observed. Both S1AIS and S2AIS with a diameter of 8.0 mm showed screw penetration, with S2AIS having a higher incidence of posterior lateral sacral cortical penetration (46.7%) than S1AIS (3.3%) (P<0.05). The biomechanical test showed that the stiffness and maximum load of S2AIS were significantly lower than those of S1AIS (P<0.05). ConclusionAs a method to fix the sacroiliac joint, a single S1AIS has a larger insertable range, a longer sacral side length of the screw trajectory, a lower incidence of posterior lateral cortical rupture of the sacrum, and a greater fixation strength than S2AIS. Therefore, the implantation safety and fixation stability of a single S1AIS are superior to S2AIS, and a diameter less than 8.0 mm screws should be selected as S2AIS for Chinese people.