The Applied Research Of Finite Element Method In The Personalized Precision Orthopedics Surgery

OBS is a novel fixation system which can realizing individualized accurate orthopedics surgery designed by Orthopedics in Yan'an Hospital Affiliated to Kunming Medical University.However,in order to achieve accurate and personalized orthopedics surgery,there are two problems:(1)the bone is a material with high individual differences,and can not measure the size and the mechanical parameters of the patient's bone in vitro;(2)there is no basic research on the OBS scheme at present,and the doctor does not have the knowledge of engineering mechanics.It brings difficulties to formulating operation scheme of personalized precision orthopedics surgery.Therefore,in view of these problem,we applied the finite element method to assist in the precise personalized orthopedics surgery.In view of the fact that there is no basic research on the OBS scheme and the matching of OBS is quite free,in the face of a large number of combinations,the study of the best fit for patients under multiple factors is undoubtedly a needle in a haystack.So,we select the cases of a patients with oblique fracture of shaft of tibia,and only consider the condition of two feet standing evenly,in order to exclude the influence of other factors,to study the two factors that have the greatest impact on the mechanical properties of the OBS scheme:(1)the number of screws;(2)the distance between the fracture and the screw closest to it.In this paper,the number of screws is divided into 4 and 6,and the distance is divided into 5mm,10 mm and 15 mm,so as to find the best OBS scheme for patients.For the finite element analysis of bone and its fixtures,it is necessary to know:(1)the force of the bone;(2)the patient's personalized bone mechanical properties,shape and size.According to the classical biomechanical study and the weight of the selected cases,the force of the unilateral tibial joint surface under the uniform standing of the two feet was 500 N and the direction is vertical downward.Then according to modern biomechanical study,based on CT image,the bone model is rebuilt and meshed.Finally the meshing model is divided into 10 regions and the material parameters of element in different regions are assigned respectively according to the gray value of CT image and the empirical formula.With the above preparations,the deformation and stress state of the 6 different scheme are calculated by finite element method.Displacement of fractured ends in fourscrew styles group were 0.610 mm,0.782 mm,1.005 mm.Displacement of fractured ends in six-screw styles group were 0.520 mm,0.758 mm,0.948 mm.The maximum stress on bone in four-screw styles group were 312.89 MPa,296.63 MPa,421.61 MPa.The maximum stress on bone in six-screw styles group were 318.54 MPa,244.50 MPa,573.50 MPa.In consideration of displacement of fractured ends and the maximum stress on bone,the most reasonable scheme is using six-screw styles while the distance between the fractured ends and the screw closest to it is 10 mm.After calculating the results of finite element method,the validity of finite element results is verified by experimental method.Finally,the research assisted to complete the personalized precision orthopedics surgery and provided technical guidance for it.The research also provided the research direction and the most basic theoretical basis for future research on the use of more complex OBS scheme in the treatment of more complex fracture.