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Abstract :
[en] Introduction: Biomechanical experiments of the hip joint often only consider the loading of the femoral head, neglecting the effects generated by the muscle forces, due to the complex nature of the loading case at the femur. This study aims to examine the significance of neglecting the influence of the muscles to the loading of the bone, while proposing a more realistic setup for experimental testing of pertrochanteric femoral fractures. From the finite element simulations, a factorial analysis is done to assess the significance of the contribution of each individual muscle to the overall sectional forces and moments at the critical region of the femur.
Methods: Firstly, the forces acting on the bone are defined through numerical simulations using a musculoskeletal model of the human body, capable of estimating muscle and joint forces based on motion capture data. A total of 18 muscle forces and the hip joint contact force are calculated for 7 scenarios of different body movements. These forces are then applied to a CT scan based finite element model of the femur, to simulate the stresses on the bone under real load. The assessment is done at a typical cross section of pertrochanteric fractures.
Results: The factorial analysis reveals that from all the muscle forces acting on the femur, the gluteus medius is the most dominant and is considered statistically significant to the reactions being generated at the fracture section. It was observed that when the muscles are disregarded, there is a slight increase of the sectional reaction forces, while the moments are significantly reduced. This shows that the muscle forces are in fact contributing to the torque generated at the section of the fracture. Based on these results, a simplified loading case with only two force actuators was elaborated, generating an equivalent stress state at the fracture section when compared to the complete loading with all the muscles forces included.
Discussion: It is possible to perform a very realistic stress state at the region of interest of the bone by statistically analyzing the significance of the muscle and joint forces.
