Safety Evaluation And Finite Element Analysis Of Sacroiliac Joint Screw Implantation Assisted By 3D Printing Technology

Objective1.To evaluate the safety of screw implantation of the sacroiliac joint assisted by3 D printing technology.2.Finite element analysis was used to seek a stable,safe and easy to operate screw placement method,so as to provide a basis for the clinical application of sacroiliac joint screw implantation technology.MethodsUsing 3 d printing,sacroiliac joint damage model is made by antisepsis corpse pelvis,row CT scan imaging data obtained,using mimics software modeling,on the basis of sacral iliac anatomical characteristics,design the sacroiliac joint screw individual navigation templates,and in the navigation template aided by simulation in different number of sacroiliac joint screw;Postoperative pelvic specimens were scanned by CT,and the bone was opened along the screw direction to observe the screw direction and the position of the screw in the bony structure to evaluate its accuracy and safety.Based on the three-dimensional finite element model of the whole pelvis constructed by the ABAQUS finite element analysis system,the three-dimensional finite element models of posterior ring dislocation of the pelvis and different number of sacroiliac joint screws were established.The nonlinear finite element method was chosen for analysis on the basis of post-loading,and the stress distribution characteristics associated with the pelvis and implant can be obtained from stress nephogram,which also involve stress and displacement.Results1.Forty-seven screws entered the sacrum through the sacroiliac joint and did not invade the sacrum and iliac bone cortex.Two screw paths entered the sacrum through the sacroiliac joint,and penetrated 1.6mm and 1.8mm of the sacrum cortex,respectively.One screw path was inserted into the sacrum through the sacroiliac joint and penetrated 3.5mm out of the sacrum cortex.According to the Smith classification,the penetration of screws was determined according to CT images: 47 screws of grade O,2 screws of grade 1,and 1 screw of grade 2.2.The axial force transmission directions of the three pelvis models listed are very close,all of which take the sacrum through the sacroiliac joint as the reference point,follow the bilateral iliac bones,and finally transfer to the top edges of the acetabulum on both sides.A 600 N force is applied to the upper endplate of the first sacral vertebra.The maximum displacement of the normal pelvis is 0.08093 mm,and the maximum stress in the pelvis is 9.386 MPa.The double segments cover the first sacral vertebra and the second sacral vertebra.When screws are used for fixation,there are precise requirements for maximum displacement of pelvis and maximum screw displacement,as well as the maximum stress of screws and pelvis,After applying a 600 N force to the superior endplate of the first sacral vertebra,the former being 0.1118 mm and 0.08816 mm respectively,and the latter being 14.53 MPa and 13.51 MPa respectively.Two screws and one screw were used in the fixation of the first sacral vertebra and the second sacral vertebra at both levels.After the force of 600 N was applied to the upper endplate of the first sacral vertebra,the maximum displacement of the pelvis was about 0.09782 mm,the maximum stress of the screw was 12.35 MPa,the maximum displacement of the screw was 0.08111 mm,and the maximum stress of the pelvis was 11.59 MPa.Conclusion1.The 3D-printed navigation template technology can not only significantly improve the safety and accuracy of screw placement of the sacroiliac joint,reduce the deviation of screw placement,but also effectively inhibit the complications such as nerve and vascular injury,and reduce the risk of surgery.In addition,it also has the advantages of low cost and simple process,so there is a bright prospect of clinical application.2.Compared with the normal pelvis,the stability of the two kinds of two-segment fixation methods showed no substantial change.The fatigue resistance of the screws in the two-segment fixation method with three screws was better than that with two screws.Therefore,three-screw fixation is the first choice,but if the double screw fixation of the first sacral vertebra is performed unconditionally,the best fixation method is to select one screw at both levels for fixation.