Structural Design And Research Of Precise Adjustable Internal Fixation System

Accurate adjustable internal fixation system is a new type of internal fixation system developed independently by the Orthopaedic Engineering Research Center of Yan’an Hospital of Kunming City on the basis of bridged combined internal fixation system(OBS).Accurate adjustable bone handling surgery is faced with the following problems:(1)it is impossible to directly use the patient’s skeleton for physical compression experiments;(2)in the treatment of long bone mid-segment missing fractures that need bone handling,the distance of bone handling still needs to be measured by a ruler,which is not accurate and time-consuming.In this paper,the finite element method(FEM)is used to assist the precise bone handling operation.Based on the previous research results of the orthopaedic Engineering Research Center of Yan’an Hospital,in front of many formulation schemes,the six-screw scheme of a single-hole bridge block and a double-hole bridge block at both ends of the section is the best formulation scheme.In this paper,the simplest and most common absence of the middle femoral segment was selected to study the status of bipedal and unipedal postoperatively,and to observe whether the precise adjustable internal fixation system can meet the needs of use in all cross-sectional conditions.In this paper,the cross-sectional spacing is 0 cm(control group),2 cm,4 cm and 6 cm respectively.The number of screw varies with the cross-sectional spacing,which is 0(control group),1,2 and 2,respectively.The finite element simulation analysis of femur and the internal fixator system on it needs to first calculate:(1)the stress state of the skeleton;(2)the mechanical properties and shape and size of the selected volunteers.According to the theoretical calculation,the femoral head in contact with the hip joint was subjected to 300 N vertical force and 600 N vertical force when the volunteers were standing on both feet,and the femoral head in contact with the hip joint was subjected to 600 N vertical force in the same direction.The smoothed femur model is simulated by finite elementmethod.The gray value of CT scan image is divided into different material aggregates according to different material properties,and then the material properties are given.After the material properties of femur and internal fixation system are given,the stress surface and fixed surface are added,and the finite element results of 8 working conditions are obtained.The maximum stress of all the eight working conditions occurs in the internal fixing system,mostly in the side gear slot of the regulating module.When standing on two feet,the maximum stress is 152.07 MPa,106.28 MPa,171.03 MPa and 113.48 MPa respectively;when standing on one foot,the maximum stress is 297.57 MPa,229.70 MPa,272.12 MPa and 218.70 MPa respectively.When standing on both feet,the maximum stress on bone was 14.26 MPa,9.98 MPa,17.07 MPa and 10.12 MPa,respectively.When standing on one foot,the maximum stress on bone was 27.35 MPa,20.81 MPa,26.40 MPa and 22.22 MPa,respectively.All the data are less than the allowable stress of the material,so it is concluded that the precise adjustable internal fixation system can meet the needs of all working conditions.Considering that it is impossible to use real bones for mechanical experiments,a3-D printed femoral model is used for mechanical compression experiments.The femoral model with precise adjustable internal fixation system was simulated again before the experiment.The material properties of femur and bone filler were given according to the three-dimensional printing material PLA plastic.In compression experiments,strain gauges are used to measure the surface strain of the model to verify the authenticity of the finite element simulation.The experimental results show that the precise adjustable internal fixation system can meet the needs of use.The authenticity and validity of the model for femur and the model with precise adjustable internal fixation system were confirmed by the 3D printing model of femur.Through the finite element analysis technology,it provides reliable theoretical support for the safety and reliability of the precise adjustable internal fixation system,and also provides guidance for the follow-up treatment of more complex comminuted fracture cases.