Modeling the dynamic behavior of implants used in total hip arthroplasty – MoDyBe

Total hip replacement (THR) is the most common orthopaedic surgery, with around 150,000 patients treated each year in France. Most THR surgeries are performed using the cementless press-fit technique, which consists of ensuring the primary stability of the implant during its insertion thanks to the pre-stressed state of the bone around the implant. The implants are inserted into bone tissue using impacts made with an orthopaedic hammer. The revision rate remains high, with dramatic consequences for the patient and the healthcare system. The stability of the implant is determinant for surgical success.
The ‘Modélisation et Simulation Multi Echelle’ laboratory (MSME, UMR CNRS) and the ‘Institut Mondor de Recherche Biomédicale’ (IMRB, UMR INSERM) of Henri Mondor Hospital have developed a prototype instrumented orthopaedic hammer that allows the measurement and analysis of the variation of the force as a function of time applied during an impact between the hammer and the ancillary. This technique allows to assess the primary stability of the femoral stem and acetabular cup during the surgery. However, this method is still immature because the multiscale and multiphysics dynamic behavior of the bone-implant interphase remains poorly understood. To go beyond empiricism and empirical techniques used by many surgeons, the approach is sorely lacking in mathematically rigorous methods to access the physical and geometric properties of the bone-implant interphase using a limited number of in vivo measurements.
The research hypotheses can be formulated by four fundamental questions: i) What are the appropriate biomechanical models to understand the multiscale and multiphysics dynamic behavior of the bone-implant system? ii) What are the appropriate high-performance computing methods to accurately solve the forward model of the bone-implant interaction subject to dynamic excitations? iii) Which robust inversion methods can be employed to retrieve the quantities of interest of the bone-implant interaction such as the bone-implant contact area? iv) How can preliminary clinical trials be performed to validate our forward and inverse models as well as the experimental set-up under development?
MoDyBe project aims to develop and validate mechanical models to study the dynamic behavior of the bone-implant interphase and robust numerical methods to improve the efficiency of impact measurement and analysis for implant primary stability assessment.
Four objectives are pursued. The first objective is to derive biomechanical models to understand the multiscale and multiphysics dynamic behavior of the bone-implant system based on the experimental configurations. The second objective will be to develop high-performance computing methods for the forward problem of the bone-implant interaction under dynamic excitations. The third objective will consist in developing robust model-based inversion methods to retrieve the quantities of interest corresponding to the bone-implant interaction such as stresses applied at the interface as well as the bone-implant contact area. In order to obtain real-time simulations useful to assist the surgeon in his assessment, surrogate models will be developed. The fourth objective will be to validate our approach in preliminary clinical trials, which will allow a comparison with the numerical results including the ones obtained by the inversion method.
MoDyBe will set up an original multiscale and multiphysics methodology, based on the coupling of: i) a preliminary clinical trial, ii) the development of multiscale and multiphysics models accounting for bone material properties and its environment, and iii) advanced simulation methods including model-based inversion approaches.
The success of MoDyBe, which associates the MSME lab, the IMRB and the INRIA project team Factas, will be secured by the consortium's complementary expertise in multiscale and multiphysics modeling, inverse problems and implant surgery.