[Finite element analysis of different internal fixation methods in treatment of elderly osteoporotic DayⅠpelvic crescent fracture].

OBJECTIVE: To explore the internal fixation method that best conforms to the mechanical principles for treating Day type I pelvic crescent fracture with elderly osteoporosis. METHODS: Based on the pelvic CT data of an elderly female osteoporosis volunteer, and the obtained data were imported into Mimics 21.0 software for three-dimensional reconstruction of the elderly pelvis, which were transformed into a solid model by Geomagic Wrap software. After verifying its validity, it was imported into Solidwork software to establish Day type-Ⅰpelvic crescent fracture, and six models of internal fixation were constructed on the fracture model. They were one LC-Ⅱscrew (group LC-Ⅱ), two LC-Ⅱscrews (group 2LC-Ⅱ), two LC-Ⅱscrews combined with one iliac crest screw (ICS)(group 2LC-II+ICS), anterior plate (AP) combined with one LC-Ⅱscrew (group AP+LC-II), anterior plate combined with two LC-Ⅱscrews(group AP+2LC-Ⅱ), and anterior double plate fixation (group 2AP). Finally, six kinds of internal fixation models were introduced into ANSYS software to solve the problem. By setting the corresponding boundary conditions, 500 N vertical downward load was applied to the superior endplate of the S1 to simulate human standing. The overall displacement of the pelvis, the stress of internal fixation and the difference between the postoperative stress of the pelvis and the original pelvic stress under the six internal fixation models were observed, and the effect of fixation was evaluated. RESULTS: The finite element model established in this study was proved to be effective. The overall displacement of the pelvis of the six groups was similar, with the largest in group LC-Ⅱ(0.744 mm) and the smallest in group 2LC-Ⅱ+ICS(0.664 mm), and the internal plant stress was mainly distributed at the broken end of the fracture, with the largest in group AP+2LC-Ⅱ(135.59 MPa) and the smallest in group 2LC-Ⅱ+ICS (25.51 MPa). The difference between postoperative pelvic stress and original pelvic stress was as follows:group 2LC-Ⅱ+ICS(6.357 MPa)