Implant Shape and Modeling Approaches Effects on the Biomechanical Tibia-Bone Response

Finite element analysis (FEA) is commonly used to simulate the complex fractured bone fixed with plate and screws system which is often simplified through approximations. To ensure a biomechanical predictions quality, different numerical modeling approaches simulating the screw-bone contact are investigated to assess the impact of simplifying the screw design and the contact condition on screw stiffness fixation into the tibia bone: (i) self-tapping screw (TS), (ii) tie cylindrical screw (TCS) and (iii) frictional cylindrical screw (FCS). The pull-out and compression tests are conducted to evaluate the strength state, the stress and the strain generated in the bone around the screw. The highest stress, observed around the bone interface, is located in the cortical bone mainly in TS-model, that is beyond the yield stress compared to the TCS and FCS models. The simplification to a cylindrical screw underestimates the strength of the screw-bone fixation in FCS-model, however it is excessively overestimated at the tie interface cases. Under compression loading tests, the commonly used model of the cylindrical screw with tie (TCS) or frictional contact (FCS), underestimates the level of the stress and strain at the screw-bone interface, which affects the accuracy of the numerical response.