Stabillity Assessment of Osseointegrated Transfemoral Bone-Implant Systems using Finite Element Modal Analysis

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  • The dynamic response of osseointegrated implant systems can be used to evaluate the condition of the bone-implant interface (BII) and implant stability. The primary objective of this work is to develop a simplified dynamic 1D finite element (FE) model of the OPL transfemoral amputation (TFA) bone- implant system. The model’s intended clinical use is to compare the collected acceleration response generated from impact with the percutaneous adapter to the model’s prediction and solve for the unknown BII stiffness. The model utilizes linear vibration theory and thus should accurately capture the natural frequencies and mode shapes of interest. A simply supported uniform beam was modelled using Euler-Bernoulli, Rayleigh, and Timoshenko FE beam formulations and compared with the analytical solution for validation. Additionally, a 3D ABAQUS® model was developed and it showed that Timoshenko’s formulation is the most appropriate model due to the significant shearing effects of the higher modes. Afterwards, a simply supported TFA implant system was modelled with the 1D FE code and compared to the 3D ABAQUS® model. The results indicated that the 1D FE model accurately predicted the natural frequencies of interest with a maximum difference of 3.08 %. The interface stiffness was then introduced as a series of springs distributed over the effective length of the stem. The stiffness’ magnitude was controlled by k which was the total stiffness normalized with respect to the volume of the stem’s effective length. The matching between the 1D and 3D models was based on manipulating the k to match the first mode frequency and comparing the results for the remaining modes. This yielded highly similar natural frequencies and mode shapes for a short stem (effective length=115 (mm)) with two extreme interface conditions. The same values of k found for the short stem were then used to perform modal analysis for a long stem (effective length=160 (mm)) and it yielded highly similar results between the 1D and 3D models which indicates that k is independent from the implant’s geometry. The numerical analysis performed in this investigation sets the groundwork for a series of additional in-vitro and in-vivo analysis of TFA systems and ultimately the development of a non-invasive vibration-based stability measurement system.

    Part of the Proceedings of the Canadian Society for Mechanical Engineering International Congress 2022.

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    Attribution-NonCommercial 4.0 International