Biomechanical investigation of S2 alar‐iliac screw and S1 pedicle screw fixation in the treatment of Denis type II sacral fractures

Abstract Although S2 alar‐iliac screw technique has been widely used in spinal surgery, its applicability to pelvic fractures is largely unknown. This study aimed to evaluate the biomechanical stability of S2 alar‐iliac screw and S1 pedicle screw fixation in the treatment of Denis II sacral fractures. Twenty‐eight artificial pelvic fracture models were treated with unilateral lumbopelvic fixation, sacroiliac screw fixation, S2 alar‐iliac screw and S1 pedicle screw fixation, and S2 alar‐iliac screw and contralateral S1 pedicle screw fixation (Groups 1–4, respectively; N = 7 per group). Each model was cyclically tested under increasing axial compression. Optical motion‐tracking was used to assess relative displacement and gap angle, and the number of failure cycles. Relative displacement was significantly smaller in Group 3 than in Groups 1 ( p = 0.004) and 4 ( p < 0.001) but not significantly different between Groups 3 and 2 ( p = 0.290). The gap angle in Group 3 was significantly smaller than that in Group 1 ( p = 0.009) on the sagittal plane but significantly larger than that in Group 4 ( p = 0.006) on the horizontal plane. A number of failure cycles was significantly higher in Group 3 than in Groups 1 ( p = 0.002) and 4 ( p = 0.004) but not significantly different between Groups 3 and 2 ( p = 0.910). From a biomechanical perspective, S2 alar‐iliac screw and S1 pedicle screw fixation can provide good stability in the treatment of Denis II sacral fractures.