Finite element modelling to investigate risk factors of periprosthetic fractures on total hip replacements

• Applicants: Privatdozent Dr.-Ing. Daniel Klüß; Professorin Dr.-Ing. Manuela Sander
• Subject Area: Biomaterials
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 385973984

Periprosthetic fractures represent a severe challenge in endoprosthetics which often can only be treated with an implant revision or a complex osteosynthetic reconstruction. To get a better understanding of the emergence of periprosthetic fractures and to develop effective measures for prevention, influencing factors on periprosthetic fractures at the hip joint need to be identified and biomechanically analyzed. Previous research projects of bone fracture under engineering point of views focused on fracture risk analyses on the femur without implant. In these fracture risk analyses potential locations of crack initiation and crack patterns at certain load conditions were determined by finite element analyses and in some cases verified by experiments. The material parameters were primarily depending on the bone density. Moreover, for the different kinds of bone tissue elastic-ideal plastic material behavior was often only assumed as well as anisotropy and densification of the trabecular bone was neglected. Objective of the present research project is to describe periprosthetic femur fractures by validated FE-models. In a new approach four methods of material modelling are investigated for the numerical simulations. This requires the representation of the material by elastic-ideal plastic behavior, with material parameters depending on HU values for every node of the FE-model. Furthermore, the crushable foam model and the material model according to Hosseini et al. are examined to reproduce anisotropy and densification of the bone tissue.For validation, the cementless hip endoprostheses stems are implanted into human femur specimen and the load cases sideway fall onto the hip and stumbling are investigated. Before conducting the experiments, the density and geometry of the bones is determined by CT scans and transferred into FE-models. To not only determine potential locations of crack initiation, failure criteria are developed and implemented with the aim to reproduce crack or failure patterns realistically. To identify criteria for reproducing fracture of bone tissue, separate experimental investigations on human bone specimens with varying stress states are performed. Thereby a detailed analysis and evaluation of the influencing factors of periprosthetic fractures such as surgical technique, implant design and patient specific factors are allowed to identify and reduce fracture risks.

• DFG Programme: Research Grants