Finite Element Analysis Of Different Internal Fixation Methods In The Treatment Of Elderly Osteoporotic Day Type-Ⅰ Crescent Pelvic Fracture

Objective:To establish different internal fixation methods for the treatment of elderly osteoporotic Day type-Ⅰ pelvic crescent fracture model,and to carry out finite element analysis of each fixed model under the same conditions,and to compare the overall stability and internal fixation stress of each fixed model,so as to provide theoretical basis for clinical treatment of elderly osteoporotic Day type-Ⅰ pelvic crescent fracture.Methods: CT data of the pelvis of a female volunteer with elderly osteoporosis were imported into Mimics software for three-dimensional reconstruction of the pelvis in the elderly.Geomagic software was used to transform the data into a solid model.After verifying its effectiveness,it was imported into Solidwork software to establish a Day type-Ⅰ pelvic crescent fracture,and different internal fixation models were constructed on the fracture model.There were one retrograde LC-II screw(Model A),two retrograde LC-II screws(Model B),two retrograde LC-II screws combined with one iliac crest screw(Model C),anterior plate combined with one retrograde LC-II screw(Model D),anterior plate combined with two retrograde LC-II screws(Model E),and anterior double plate fixation(Model F).Finally,different internal fixation models were imported into ANSYS software for solution.By setting the corresponding boundary conditions,a 500 N vertical downward load was applied to the end plate on the sacral 1 cone to simulate the human body standing.Finite element analysis was performed on different internal fixation methods to evaluate the biomechanical properties of each group of models.Evaluation index :(1)Compare the maximum displacement and maximum vertical displacement of the pelvis under different internal fixation devices;(2)Compare the stress distribution of the whole pelvis under different internal fixation devices and the difference between the postoperative stress and the original pelvic stress.Results:All the six internal fixation methods could effectively restore the biomechanical stability of the pelvic ring.Six different internal fixation methods were used to treat osteoporotic Day type-Ⅰ pelvic crescent fractures in the elderly.The overall pelvic displacement of each finite element model was compared as follows : Model C(0.664mm)<Model B(0.679mm)< Model E(0.689mm)< Model F(0.69mm)< Model A(0.744mm)<Model D(0.748mm);the stress of each finite element model is mainly distributed in the anterior edge of the sacrum,the sacral wing,the sacroiliac joint and the arch edge of the ilium.In this study,the difference between the postoperative stress and the original pelvic stress of different internal fixation pelvis is:Model C(6.357Mpa)< Model B(6.871Mpa)<Model D(11.205Mpa)< Model A(20.46Mpa)< Model F(105.06Mpa)< Model E(111.24Mpa).The overall displacement and vertical displacement of the pelvis were the smallest and the stress shielding effect was the smallest when the model C was used to fix the osteoporotic Day type-Ⅰ pelvic crescent fracture in the elderly,indicating that the mechanical compatibility of model C was superior.The maximum stress of different internal fixation combination models was lower than the yield stress of bone and plate screws.The risk of internal fixation fracture was relatively low,and the internal fixation safety was good.Conclusion: 1.In the finite element analysis of six kinds of internal fixation models,the maximum displacement,maximum vertical displacement and stress difference of model C(two retrograde LC-II screws combined with one iliac crest screw fixation)were the smallest,indicating that two retrograde LC-II screws combined with one iliac crest screw fixation of senile osteoporotic Day type-Ⅰ pelvic crescent fracture has good biomechanical advantages.2.Model B(two retrograde LC-II screws)and model C are similar in the overall biomechanical stability of the pelvis,but the vertical stability of the pelvis is not as good as two retrograde LC-II screws combined with one iliac crest screw.Two retrograde LC-II screws can be selected to fix the vertical fracture line for those who have difficulty in nailing the iliac margin.3.The overall stability of the pelvis of model F(anterior double plate fixation)is similar to that of model B,and the vertical displacement is smaller than that of model B,which can also play a role in stabilizing the pelvic ring.If you can ’t master the method of minimally invasive screw placement and no screw placement conditions,you can choose the method of anterior double plate fixation to fix iliac fracture and sacroiliac joint respectively.