Establishment Of Three-dimensional Finite Element Model Of Hip Joint In Child And Preliminary Biomechanical Analysis

Background: finite element analysis is a boundary science that relates field such as applied mathematical, modern mechanics and computer science. It is mainly used to model and solve physics problems including engineering mechanics, heat, electromagnetism and so on. Finite element analysis has found wide applications gradually in search of body biomechanics since Brekelmans and Rybicki used it to study bone biomechanics in 1972, which has achieved notable results and made one of the most significant studying methods in bone biomechanics. Finite element analysis applied to hip study is mainly focus on evaluation of adult hip biomechanics, optimum design of artificial device and discussion of individual Plan in China and abroad, and there are little reports about establishment and stress analysis of child hip model based 3-D finite element analysis. Despite Chengxuan MA and A Liang.st had established child hip model based 2-D finite element analysis, there are not any reports about establishment and biomechanics analysis of normal child hip model including cartilage based 3-D finite element analysis.Obejective: (1)to establish normal child hip model including cartilage based 3-D finite element analysis. (2)to preliminarily study the characters of cartilage thickness distribution in child hip and the biological significance of that by measuring shape of the cartilage in the hip; (3)to imitate position of standing on one leg based on the model, check the model whether can be used for biomechanics research or not ,and study characters of stress distribution on the surface of normal child hip joint.Methods: gets a specimen of normal child, scans it thinly by 64-layer CT in order to get Dicom-formed computer image data, uses Mimics, a medical image processing software and Geomagic Studio Version 8.0, a reverse engineering and 3-D detecting software to establish hip 3-D entity physical model, and introduces model into ANSYS10.0 software to establish 3-D finite element analysis by modelling via entity, differentiating grid and setting up the attributes of the unit. Then imitates standing on one leg on the basis of the model, determines bounds condition and adds physiological loads. Preliminarily studies biomechanical characters of stress distribution in child hip standing on one leg.Results:1. We have established normal child hip model based 3-D finite element analysis successfully: the model including joint bone and complete cartilage in hip has a good morphological form which is similar to entity specimen highly. It is easy to get intuitional and entire impression of hip since the model can be rotated freely and observed from different angles.2. We have found out that cartilage in acetabulum and the head of femur have difference thickness by morphological measurement .the entirety tendency of the distribution is :the cartilage in the head of the femur is thicker in the center and thiner around ,but in acetabulum is thinner in the center and thicker around , existence of the labrum adds 36%volume of the acetabulum.3. We have found out by analysis of child hip standing on one leg based 3-D finite element analysis that :the stress of normal hip standing on one leg is concentrated in the uppermost part of the cartilage surface in the head of the femur, the vault region of the cartilage surface in acetabulum and the relative region of joint head. The stress is distributed by radial symmetry and decreased gradually outward, and the peak contact pressure was 1.25MPa,and the contact force is 437N,about 2.5 times of body-weight.Conclusion:1.It is practicable to establish 3-D finite element analysis model fast by CT scanning and image data from the software of Mimics, which exceedingly improve the speed and accuracy of establishing the model of finite element analysis.2.The model can represent systematic anatomy morphology of child hip, and it can be used for the study of biomechanics.