Significance of Nonlinearity Consideration in Finite Element Analysis for Preclinical Strength Assessment of Extramedullary Femur Plates

Abstract

Accurate finite element (FE)-based evaluations demand realistic modeling of the bone-implant construct. For this, considering nonlinearity in the FE model sometimes becomes essential. Human femora exhibit nonlinear mechanical behavior, which could be attributed to material, large deformation, and boundary conditions. The nonlinearity due to material is specified as material nonlinearity, while due to large deformation or boundary conditions is specified as geometric nonlinearity. The objective of this study is to comprehend the importance of incorporating nonlinearity into FE analyses of extramedullary plates used to treat proximal femoral fractures. Two extramedullary implants—one proximal femoral locking plate (PFLP) and another variable angle-dynamic hip screw (VA-DHS)—were fixated with a femur analog having a simulated intertrochanteric fracture. The constructs were analyzed dynamically for normal walking gait activity and sideways fall scenarios. The analyses were carried out by considering both geometric as well as comprehensive (geometric and material) nonlinearity, and the same were compared with the results from linear models. The results obtained from FE analyses of intact and implanted constructs were validated from in vitro experimental data and FE analysis data reported in previous studies. The investigation revealed that a comprehensive nonlinear analysis, considering both geometric and material factors, can minimize the error percentage to less than 5% while comparing with the data obtained from the experimental approach. The PFLP implant was found to impart higher stiffness (∼30%) as compared to the VA-DHS implant under both load cases of walking and sideways fall.