Finite element analysis of S 2AI-S 1 in the treatment of Denis type II sacral fracture / 中华骨科杂志

ABSTRACT

Objective:Comparison of biomechanical stability of S 2-alar-iliac screw and S 1 pedicle screw fixation (S 2AI-S 1) with conventional sacroiliac screw in the treatment of Denis type II sacral fractures by finite element analysis. Methods:The lumbar spine and pelvis of a male volunteer with normal skeletal structure were scanned by CT, followed by three-dimensional reconstruction. The finite element model of right Denis type II sacral fracture and pubic symphysis injury was constructed using ANSYS 17.0 software. The anterior pelvic ring is fixed with a five-hole steel plate, and the posterior pelvic ring is fixed with four different internal fixation methods, namely, sacroiliac screw (S 1 segment half-thread hollow screw), S 2AI-S 1 and S 2AI screw and contralateral S 1 screw fixation (S 2AI-CS 1). By restraining the bilateral acetabular and applying 500 N vertical stress above the L 4 vertebral body, the maximum displacement, maximum von Mises stress and vertical stiffness of the three groups of internal fixation were compared. Results:In terms of the maximum displacement of the sacrum in the vertical and anteroposterior directions, the S 2AI-S 1 model was the smallest (1.40 mm, 1.40 mm, respectively), while the S 2AI-CS 1 model was the largest (1.60 mm, 1.56 mm, respectively); In terms of the maximum displacement of the sacrum in the horizontal direction, the S 2AI-S 1 model is the smallest (0.19 mm), while the SIS model is the largest (0.37 mm); In terms of the maximum von Mises stress of internal fixation, the stress of the sacroiliac screw model is the largest (216.02 MPa), while the stress of the S 2AI-S 1 model is the smallest (39.82 MPa); In terms of the maximum von Mises stress of the bone around the screw, the stress of the sacroiliac screw model (39.68 MPa) is the largest and that of the S 2AI-S 1 model is the smallest (31.56 MPa); In terms of the vertical displacement of the center point of the upper surface of the S 1 vertebral body, the sacroiliac screw, S 2AI-S 1 and S 2AI-CS 1 groups were 0.83 mm, 0.73 mm and 0.93 mm, respectively. Using the vertical displacement of the center point of the upper surface of the S 1 vertebral body to predict the vertical stiffness of the three groups of models, from large to small, are S 2AI-S 1, sacroiliac screw and S 2AI-CS 1. Conclusion:S 2AI-S 1 fixation has good biomechanical stability in three-dimensional finite element analysis. It can be used as a new type of internal fixation for the treatment of sacral fractures and is worthy of promotion.