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EKİCİ, BÜLENT

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    The effects of static, dynamic and fatigue behavior on three-dimensional shape optimization of hip prosthesis by finite element method
    (ELSEVIER SCI LTD, 2007) EKİCİ, BÜLENT; Kayabasi, Oguz; Ekici, Bulent
    The finite element method, one of the most advanced simulation techniques in solid mechanics, is used for orthopedic biomechanics. It is used as a tool for the design and analysis of total joint replacement and other orthopedic devices. The design of hip joint prostheses is a complex process that requires close co-operation between engineers and surgeons. To design highly durable prostheses one has to take into account the natural processes occurring in the bone. One of the most important factors in the implant design is to reduce stress on the femur and the bone-cement. The purpose of this study is to investigate the behavior of newly designed implants under body weight load during stumbling by parametric modeling. Two different implant materials have been selected to study appropriate material and fatigue life resistant. In the parametric design, the prosthesis functional requirement is that the locking of stem to the femur head using cement should be strong enough to preclude unlocking during the life time of a patient and to prevent sliding of the implant into the bone-cement. In the finite element analysis, physical interactions among joints are simulated by contact algorithms. The femur-bone-cement interface and the bone-cement-implant interface surface to surface contact algorithms of ANSYS were used for implicit static analysis. Three stem-cement interface conditions are considered: completely bonded, debonded with coefficient of friction 0, and debonded with coefficient of friction 0.2. In the analysis, a viscoelastic material model is utilized for bone-cement. Numerical shape optimization is applied to the prosthesis. The results of finite element simulations are compared with Charnley's implant results and appropriate material for the implant is proposed. The best stem shapes fulfilling the desired functional requirements are chosen for the design. These findings can form a base for further research such as the optimum design of bone-implant hip prosthesis. (C) 2006 Published by Elsevier Ltd.
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    Probabilistic design of a newly designed cemented hip prosthesis using finite element method
    (ELSEVIER SCI LTD, 2008) EKİCİ, BÜLENT; Kayabasi, Oguz; Ekici, Bulent
    The finite element method is an important tool used in the design of orthopedic prosthesis. One of the important orthopedic applications is hip prosthesis replacement. This operation is so complex that it requires close co-operation between engineers and surgeons. They have to work together in order to produce durable and reliable hip joint prosthesis. The reason for this is that the nature of bone strongly affects the design. In reality, uncertainties exist in the system and environment that may make the application of a deterministic design decision unreliable. That is, the values of the variables that are acting on the system cannot be predicted with certainty. For instance, probabilistic approach was applied to the model after deterministic design results. Thus, using probabilistic approach reliability of newly design cemented hip prosthesis was quantified. The new design is modeled parametrically to investigate the effects of different geometrical parameters on the relative displacement. These parameters are then optimized. Using the results of this investigation, the probability of failure was investigated for both the initial and shape-optimized prosthesis designs using several simple performance functions describing fatigue theory (Goodman, Gerber, Soderberg), static and dynamic failure of the cement-pros thesis interface. The optimum geometry and material properties are then compared with Charnley's implant results. 0 2007 Elsevier Ltd. All rights reserved.