Magnetic Resonance Imaging-Based Cohesive Extended Finite Element Modeling of Atypical Femoral Fracture

Atypical femoral fracture (AFF) is a rare fracture associated with prolonged bisphosphonate (BP) treatment that occurs in the subtrochanter and midshaft of the femur. The association of AFF with BP treatment suggests alterations in femoral material properties with treatment. Femoral geometry has also been identified as a potential contributor to AFF. This study aims to demonstrate the novel integration of high-resolution magnetic resonance imaging (MRI) with cohesive extended finite element method (XFEM) to assess AFF. Using this approach, we quantified the independent contributions of femoral geometry and material property distribution to fracture resistance at the AFF site. MRI-based finite element models of female donor femurs incorporating homogeneous and specimen-specific heterogeneous material properties derived from MRI-based bone volume fraction (BVF) were evaluated. To assess the predictive capability of the models, experimental testing of the femur under stance loading was performed. Simulation results showed that when only geometrical properties of the femur were considered anterior bowing angle and neck shaft angle showed negative and positive correlations with fracture load, respectively. Fracture load increased with increasing specimen-specific means BVF. Simulation femoral stiffness and lateral strains where AFF occurs correlated significantly with experimental values. Our findings demonstrate that MRI-based cohesive XFEM can assess crack formation in AFF and highlight the need for considering both geometrical and material properties when assessing AFF risk. This study lays the foundation for MRI-based AFF assessment, which can be extended to MRI-specific measurements that cannot be quantified by other imaging modalities.