Finite Element Analysis Of Different Fixation Methods For Ganz Osteotomy Of Crowe ? DDH

Objective:(1)To reconstruct a three-dimensional finite element model of adult hip dysplasia and test the effectiveness.(2)To investigate the influence of different fixation methods on Ganz osteotomy in treatment of Crowe type I DDH by finite element analysis.Method:(1)The DICOM data was obtained from CT scans of DDH adults.Both the effectiveness test and reconstruction of finite element model for pelvis containing ligament and cartilage were performed by Mimics17.0,Geomagic Studio2014,Hypermesh2013,Abaqus,6.12.(2)Following the standard procedure of Ganz osteotomy,osteotomy was performed on the dysplasia of the right hip joint and screws and plates were established and assembled by different fixation methods.The four fixation methods in this study were including parallel group,ilium three-dimensional group,acetabular three-dimensional group,and screw combined with plate group.The parallel group was three parallel screws from the iliac crest to reach the acetabular bone.The ilium three-dimensional group was three screws that are not parallel to each other by the iliac crest into acetabular bone;the acetabulum three-dimensional group is similar with the ilium three-dimensional group,and the difference lies in the entry of a screw from the acetabulum in the acetabulum three-dimensional group.The screw combined with plate group was a screw combined with a pelvic reconstruction plate.(3)In Abaqus software,the mechanical loading conditions were set up.The loading position was the upper endplate of sacral vertebrae,and the direction was vertical downward.The different loads were 500 N,1000N,2000 N and 4000 N respectively.The load increased gradually to simulate the load increasing process of the acetabulum under different loading conditions,which did not consider the force acting on the hip muscles and the direction of the acetabulum force.The boundary condition of the finite element model was to limit the total fixation of the acetabulum on both sides of the pelvis(U1=U2=U3=UR1=UR2=UR3).The effects of different fixations by Ganz osteotomy on the stress and displacement of the pelvis under different load conditions were simulated.Result:(1)The DDH finite element model was successfully reconstructed and effectiveness test showed that the model could be used in the later biomechanics test.(2)Displacement of the pelvis is obviously in the displacement cloud chart.The acetabular three-dimensional group and the screw combined with plate group are superior to the other two groups in terms of stability.In order of the maximal stress and maximum displacement for pelvis with the same load,it goes: parallel group,ilium three-dimensional group,screw combined with plate group,acetabular three-dimensional group,which indicated that the acetabular three-dimensional fixation had less possibility of fixator surrounding fracture,and the pelvis was more stable.The acetabular three-dimensional group was also the best in the maximal stress and maximum displacement for internal fixation.It was reported that when the load of titanium alloy reaches about 600 Mpa,then the failure comes.The results showed that under the applied load at 4000 N both the parallel group and the ilium three-dimensional group reached or surpassed the breaking load.Conclusion:(1)The DDH finite element model successfully reconstructed and effectiveness test showed that the model could be used in the follow-up biomechanics test.(2)Initial study on the optimal fixation of Ganz osteotomy of Crowe type I hip dysplasia showed that different fixation methods can directly affect the Von Mises stress distribution of the internal fixators and pelvis after the Ganz osteotomy.Acetabular three-dimensional fixation is indeed an effective fixation method for dysplastic hip osteotomy.