Finite Element Analysis Of Medial Buttress Plate Combined With Cannulated Compression Screws For Pauwels Type Ⅲ Femoral Neck Fractures In Young Adults

Objective: In this study,the biomechanical performance of five different internal fixation methods for fixation of Pauwels type Ⅲ femoral neck fractures(FNF)in young adults was compared and analyzed using finite element analysis,and the advantages and disadvantages of the different internal fixation methods were further evaluated comprehensively,with the aim of providing a reference for the clinical treatment of Pauwels type Ⅲ FNF in young adults.Methods: One healthy adult volunteer was selected,the volunteer’s femur was scanned using CT scanning equipment,and the acquired CT image data was imported into Materialise’s interactive medical image control system(Mimics)in digital imaging and communications in medicine(DICOM)format.The original femur 3D model was created by Mimics software and preliminary optimization of the original femur 3D model was performed and output in stereolithography(STL)file format.Then,the above model files were imported into the automated reverse engineering software Geomagic Wrap for optimization,and the 3D models of cancellous bone and cortical bone were constructed and exported in Exchange structure of 3D picture files(STEP)file format after the "fitted surface" process.Open the above STP format file in Solidworks software,build a solid model of Pauwels Ⅲ FNF with a Pauwels angle of 70 °,and build a three-dimensional model of cannulated compression screws(CCS),cortical bone screws,1/3 tubular plate(1/3 TP),etc.according to the specifications of internal fixation devices used in the experiment.The constructed internal fixation device model is then positioned against the femoral model to complete the placement.Five models of FNF fixation were established according to the different fixation methods:Model I: 3 CCS "inverted triangle" fixation;Model II: Based on Model I,1/3 TP was placed(no proximal screws,2 screws were placed distal to the fracture);Model Ⅲ: Based on Model II,1 screw was added distal to the fracture;model IV: Based on model II,proximal screws were placed,and the direction of placement was parallel to the fracture line;model V: Based on model II,proximal screws were placed,and the direction of placement was human axial direction.Finally,the above models were imported into ANSYS for analysis.Evaluation indexes:(1)Overall displacement distribution and overall displacement peak of the model;(2)Displacement distribution and displacement peak of the fracture end;(3)Von-Mises stress distribution and stress peak of the CCS;(4)Displacement distribution and displacement peak of the CCS;(5)Von-Mises stress distribution and stress peak of the plate screw system;(6)Displacement distribution and displacement peak of the plate screw system.Results: The overall displacement peaks of each model from largest to smallest are:model Ⅰ(1.8316 mm),model Ⅱ(1.8274 mm),model Ⅳ(1.8273 mm),model Ⅲ(1.8270 mm),model Ⅴ(1.8245 mm),suggesting that the overall stability: model Ⅰ < model Ⅱ < model Ⅳ <model Ⅲ < model Ⅴ;The peak size of fracture end displacement of each model were: model Ⅰ:1.3096 mm;model Ⅱ: 1.3083 mm;model Ⅲ: 1.3082 mm;model Ⅳ: 1.3082 mm;model Ⅴ:1.3080 mm,suggesting the ability to maintain the stability of the fracture end: model Ⅰ <model Ⅱ < model Ⅲ = model Ⅳ < model Ⅴ;The Von-Mises stress distribution of each model CCS are comparable,and the peak stresses are,in descending order: Model I: 42.143 MPa;Model II: 41.165 MPa;Model Ⅲ: 41.068 MPa;Model IV: 41.017 MPa;Model V: 40.192 MPa,suggesting that the risk of yield fracture of CCS: Model I > Model II > Model Ⅲ >Model Ⅳ>Model V;The peak CCS displacements of each model are: model Ⅰ: 1.7696 mm;model Ⅱ: 1.7655 mm;model Ⅲ: 1.7651 mm;model Ⅳ: 1.7654 mm;model Ⅴ: 1.7629 mm,suggesting that the instrument stability of CCS: model Ⅰ < model Ⅱ < model Ⅳ < model Ⅲ <model Ⅴ;Von-Mises stress peaks for the steel plate and screw system: model Ⅲ(40.271 MPa)< model II(40.577 MPa)< model IV(41.084 MPa)< model V(41.406 MPa),suggesting the risk of yield fracture of the steel plate screw system: model Ⅲ < model II < model IV <model V;The peak displacement of the steel plate and screw system in each model of the experiment Model II(1.2106 mm)< Model Ⅲ(1.2107 mm)< Model IV(1.3856 mm)<Model V(1.7117 mm),suggesting that the stability of the steel plate screw system apparatus:Model II > Model Ⅲ > Model IV > Model V.Conclusion: 1.The combination of medial buttress plate(MBP)and CCS is recommended to reduce the risk of CCS fracture,improve the overall stability of the fracture internal fixation system,and maintain the stability of the fracture end;2.The placement of proximal screws reduces the instrumentation stability of the nail plate system and increases the risk of yield fracture of the nail plate system.When proximal screws are placed axially in the human body,the proximal screws are more likely to fracture due to stress concentration,so the fixation methods of Model IV and Model V should not be recommended;3.The overall stability and CCS instrumentation stability of the model with three screws placed distally without proximal screws(model Ⅲ)were better than those of models II and IV,the ability to maintain the stability of the fracture ends was comparable to those of models II and IV,the risk of yield fracture of the nail plate system was less than those of models II and IV,and the instrumentation stability of the nail plate system was comparable to that of model II but better than that of model IV.Compared with model V,the risk of yield fracture of the nail plate system was lower in model Ⅲ.Therefore,the fixation method of CCS combined with MBP,no proximal screw placement,and three screws distal to the fracture are more appropriate for the treatment of Pauwels type Ⅲ FNF in young adults.