FE Modelling Of Two Femur Fixation Implants

Sammanfattning: In the pool of women over the age of 50, the likeliness of an atypical fracture increase drastically, partly due to osteoporosis. With a pre-existing implant in the femur bone, inserted due to a prior atypical fracture, treating a later femoral neck fracture is complex and risky. Currently, a fractured femoral diaphysis is treated using an intermedullary nail which is fixed to the femur bone either through the femoral neck (Recon locking method)or through the lesser trochanter (Antegrade locking method). In a study conducted by Bögl et.al. JBJS102.17 (2020), pp. 1486-1494, it is found that the fixation of the intermedullary nail through the femoral neck reduces the risk of future femoral neck fractures. The study also states that more than 50% of the patients with atypical femoral fractures related to bisphosphonate treatment for osteoporosis (within the study sub population) were treated with the Antegrade locking implant. There does not exist much literature that reasons as to how one locking method is showing lesser risk of re-operation as compared to the other. The purpose of this study is to look into the effects these two implants have on the femur bone using the Finite Element Analysis (FEA). The study presented is aimed at comparing the results of the finite element analysis for the Recon implant model (Recon model) and Antegrade implant model (Antegrade model). The femur model without the implants (native bone model) is used to verify material behavior, while the other two are used for the comparison to study the stress-strain distribution, primarily in the neck region. This is a patient specific study, hence the femur bone model is generated using patient Computed Tomography (CT) scans. The bone model was assigned a heterogeneous isotropic material property derived from patient CT data. The finite element (FE) model of the bone was meshed using Hypermesh. The peak loading condition including the muscle forces were applied on the native bone model along with the Recon and the Antegrademodel. While the loading conditions during normal walking cycle were only applied to theRecon and the Antegrade model to compare the impacts of the two implant types. Both loading conditions were simulated by fixing the distal condyle region of the bone. The analysis results show that the Antegrade implant experiences much higher stresses and strains in the neck region as compared to Recon implant. Also, the presence of the intermedullary nail through the femur diaphysis helps to distribute the stresses and strains in the anterior distal diaphysis region of the bone. For the case of no implants, the model showed strains and stresses in the lateral distal region of femoral diaphysis.