Research On Biomechanics Of Pelvis And Implant Structure Optimization Under Minimally Invasive Internal Fixation

In recent years,the cases of disability and death caused by accidental pelvic fractures are increasing.Traditional internal fixation has a large incision and a long recovery process.Therefore,there is an urgent need for the innovation of pelvic repair technology.Minimally invasive internal fixation is a pelvic surgery technique which has been paid more attention in recent years.It has the characteristics of small incision and less blood loss.Factors such as the shape of the implants,the number of screws,and the fixation position are directly related to the postoperative fixation effect and recovery of the patient.Numerical simulation methods are used to conduct biomechanical simulation and research on the implant structure and surgical fixation plan,and evaluate the internal fixation effects of different types of pelvic injury cases.Theoretical support is provided for doctors to choose different internal fixation schemes in the face of different patients.It has good theoretical value and clinical guiding significance for optimizing surgical plans and improving surgical effects.The main research work of this subject is as follows:（1）Research on the biomechanical principles of pelvic internal fixation and the digital reconstruction of pelvis.The anatomy of pelvis is analyzed.The pelvic mechanics model is established.Combining the classification of pelvic fracture,the selection principle of screw placement and number is summarized.Pelvic CT images are taken.In Mimics software,the threshold is determined by the CT value change curve in the figure.The bones are obtained through the threshold segmentation and region growth algorithm and ligaments and soft tissues are established through anatomy.Finally,the consistency between the reconstructed pelvic model and the original pelvic structure is verified by t-test.（2）Through the simulation analysis of human biomechanics,the optimization study of the FE model of the internal fixation pelvis is carried out.Firstly,the implant position based on the pelvic model is optimized.The least square method is used to determine the position of screw-rod system and according to the CT image of pelvis,the tilt of body posture is calculated and the implantation angle is corrected.Combined with the operable angle of the operation,the implantation angle of the plate-fixed screw is determined by the relationship between the implantation angle of the characteristic surface of the acetabulum and the implantable length.Secondly,the FE boundary conditions in different postures are optimized based on the principle of multibody dynamics.The force changes of the pelvis during standing and walking are analyzed in Anybody software,and the maximum pressure and steady pressure are taken as the ultimate pressure and static pressure of different postures.（3）Optimization and clinical effect verification of minimally invasive internal fixation schemes in typical cases of pelvic fractures.According to the internal fixation design principles determined by the pelvic mechanics transfer model and the Stanford stress-bone reconstruction model,the internal fixation scheme is optimized based on the Tile B2 and Tile B3 fractures,and screw-rod fixation with three screws,screw-rod fixation with four screws are designed respectively.A Tile B2 fracture model of the left pubic bone fracture is established,and the fixation effects of screw-rod fixations with two screws and three screws and plate-screw fixation under different postures are compared by FEM.A Tile B3 pelvic fracture model with pubic fracture on both sides is established,and the effects of screw-rod fixations with three screws and four screws and plate-screw fixation are further compared.The rationality of the optimized scheme is verified.With the support of the Department of Traumatology and Orthopedics,Shanghai First People’s Hospital,patients with Tile B2 and Tile B3 pelvic fractures were treated with three-nail and four-pin fixation through minimally invasive surgery.The effectiveness of the optimized plans is verified by the actual recovery effect of the patient’s pelvis.At the same time,it also proved the feasibility of pelvic biomechanics research by FEM to optimize implants for different fracture cases.