RESUMO
OBJECTIVE: To compare the stability of sacroiliac screws fixation for the treatment of bilateral vertical sacral fractures to provide reference for clinic application. METHODS: A finite element model of Tile C pelvic ring injury (bilateral type Denis II fracture of sacrum) was produced. The bilateral sacral fractures were fixed with sacroiliac screws in 4 types of models respectively: two bidirectional sacroiliac screws fixation in the S1 segment, two bidirectional sacroiliac screws fixation in the S2 segment, one sacroiliac screw fixation in the S1 segment and one sacroiliac screw fixation in the S2 segment, two bidirectional sacroiliac screws fixation in S1 and S2 segments respectively. By the ABAQUS 6.9.1 software, in the case of standing on both feet, 600 N vertical load was imitated to be imposed to the superior surface of the sacrum and downward translation and backward angle displacement of the middle part of the sacral superior surface and everted angle displacement of the top of iliac bones were extracted for analysis. The stability of sacroiliac screws fixation was compared according to the principle of the better stability the smaller displacement. RESULTS: The stability of 2 bidirectional sacroiliac screws fixation in S1 and S2 segments respectively was markedly superior to that of 2 bidirectional sacroiliac screws fixation in S1 or S2 segment and was also markedly superior to that of one sacroiliac screw fixation in S1 segment and one sacroiliac screw fixation in S2 segment. The vertical and everted stability (the downward translation: 0.531 mm; the everted angle displacement: 0.156° (left side), 0.163° (right side)) of sacroiliac screws fixation in two bidirectional sacroiliac screws fixation in the S2 segment was superior to that of two bidirectional sacroiliac screws fixation in the S1 segment (the downward translation: 0.673 mm; the everted angle displacement: 0.200° (left side), 0.232° (right side)). The rotational stability of two bidirectional sacroiliac screws fixation in the S1 segment (the backward angle displacement: 0.269°) was superior to that of two bidirectional sacroiliac screws fixation in the S2 segment (the backward angle displacement: 0.287°). Moreover, the rotational stability of one sacroiliac screw fixation in the S1 segment and one sacroiliac screw fixation in the S2 segment was inferior to that of two bidirectional sacroiliac screws fixation in the S1 segment or two bidirectional sacroiliac screws fixation in the S2 segment, and the vertical and everted stability of one sacroiliac screw fixation in the S1 segment and one sacroiliac screw fixation in the S2 segment was between that of two bidirectional sacroiliac screws fixation in the S1 segment and two bidirectional sacroiliac screws fixation in the S2 segment. CONCLUSIONS: Two bidirectional sacroiliac screws fixation in S1 and S2 segments respectively is recommended to be utilized for fixing bilateral sacral fractures of Tile C pelvic ring injury as far as possible. It is suggested to choose sacral segments in which sacroiliac screws fixed according to vertical, rotational and everted stability degree of sacral fractures.
