Finite Element Study On The Effect Of Acetabular External Edge Defect On The Initial Stability Of Acetabular Prosthesis

objective: In total hip arthroplasty,acetabular external edge defect will affect the stability of acetabular cup.however,previous studies have obtained the coverage of acetabular cup based on clinical experience and follow-up results,and the results are not the same.At present,there is no literature reported on the critical value of acetabular defect affecting the initial stability of acetabular prosthesis.For this reason,this study will use the popular finite element technology to grade the defect of the lateral edge of the acetabulum and analyze the initial stability between the cementless acetabular prosthesis and the host bone during hip arthroplasty,to explore the critical conditions to ensure the initial stability of the cup.Methods: based on the CT data of the pelvis of a healthy adult man,the three-dimensional model of the pelvis was reconstructed by computer software to simulate the reconstruction of the acetabular side of clinical total hip arthroplasty.The acetabular prosthesis was implanted with uncement compression without screws.Different defects of the external edge of the acetabulum were designed to simulate the clinical defect of the external edge of the acetabulum.The maximum contact force vector F of the hip joint under the normal walking gait is applied to the rotation center O of the semi-head model along the direction of the contact force of the hip joint,and different defective models are mechanically loaded until the model is stable.The fretting displacement of the acetabular cup relative to the host bone is 40 ? m as the critical value.The acetabular cup coverage of different defect models(The surface area of the cup in contact with the host bone accounts for the percentage of the total surface area of the cup model),the bone defect rate of the edge of the acetabular cup(the percentage of the arc length that did not cover the edge of the acetabular cup to the perimeter of the edge)and the fretting displacement of the acetabular cup relative to the host bone were calculated.Results:The acetabular force in the normal model is mainly in the acetabular weight-bearing area,and the distribution is more uniform,while in the defect model,the force is mainly concentrated at the junction of the acetabular defect and the host bone,and the stress is concentrated and distributed in a band.When ? =-25 °,the maximum fretting displacement of the acetabular cup relative to the host bone is 39 ? m,the acetabular coverage rate is 67.1%,and the bone defect rate at the edge of the acetabular cup is 38.9%.If you continue to reduce the ? angle,when ? =-27 °,the bone defect rate at the edge of the cup is 40%,or continue to increase the defect at the edge of the cup,and the bone defect rate at the edge of the cup is 41.9%,the acetabular coverage is about 65%.The maximum fretting displacement of the acetabular cup relative to the host bone will exceed 40 ? m,affecting the stability of the acetabular cup after implantation.Conclusion: when patients with acetabular external edge defect undergo total hip arthroplasty,the cementless acetabular prosthesis is implanted by pressing.In the case of no screw fixation,the acetabular coverage should be kept more than 70%,and the maximum fretting displacement of the acetabular cup relative to the host bone can be kept within 40 ? M.It can ensure the stability of the acetabular cup in normal gait.