Functional orthotropic bone adaptation of a full-scale 3D human femur under distinct physiological activities: A unified FE-based analysis

Numerous investigations demonstrated the orthotropic characteristics of the femur, either in the proximal part or by considering it two-dimensional (2D). Many studies that have investigated orthotropic bone adaptation of the entire three-dimensional (3D) femur under cyclic loading induced during different physiological activities. To accurately capture adaptive behavior, one crucial factor is the way we assign orthotropic material orientation. This study investigates adaptive orthotropic bone remodeling using an FE diffusion-based approach for a 3D full-scale human femur geometry under different physiological activities. The comparison with the isotropic model is also carried out to observe the variations in results. To accomplish this, an FE model of the full right femur was developed to simulate bone adaptation using orthotropic and isotropic constitutive modelling. A FE method based on diffusion equations was presented to evaluate the complex continuum field of orthotropic orientations. Bone density evolution was predicted using a diffusion-based continuum remodeling approach. Results unveil an anatomically consistent local field of orthotropic orientations in longitudinal, circumferential, and radial directions. In orthotropic models, the density distribution was found to be substantially higher throughout the posterior part of the femoral diaphysis. Bone resorption was observed in the condyle region, the latero-superior greater trochanter region, and the superior region of the femoral head. A notable difference for the isotropic models is that the entire femur exhibits a uniform remodeling response, particularly in the diaphyseal. Overall, the orthotropic bone adaptation provides more detailed anatomical information regarding region-specific adaptation.