Bone microstructure in finite element modeling: the functional role of trabeculae in the femoral head of Sciurus vulgaris

Abstract

In arboreal habitats, animals encounter substrates of varying inclinations. Consequently, the external loads acting on the limb bones during arboreal locomotion are diverse in terms of magnitude and orientation. It is not well understood how limb bones are adapted to a broad range of loading directions and which functional role is adopted by the trabecular microstructure in particular. In this study, we conducted a finite element analysis of the proximal femur of the Eurasian red squirrel (Sciurus vulgaris) to assess the functional performance of the bone during horizontal (0° inclination) and uphill locomotion (30° and 60° inclination). To elucidate the functional significance of the femoral trabecular microstructure in particular, we compared a model using a realistic geometry that included trabecular bone with two models using hypothetical geometries, one being solid inside and the other being hollow inside (cortical bone only). We report that the von Mises stress in the proximal femur increases with increasing substrate inclination. The reason for that is the higher percentage of body mass acting on the hind limbs during uphill locomotion rather than architectural limitations of the microstructure. Furthermore, the model using a realistic geometry shows a high similarity in its functional performance to the hypothetical solid model by avoiding high peak loads in the cortex equally well. These findings highlight the exceptional ability of trabecular bone to maintain stability under external loading of varying directions while at the same time facilitating mineral exchange and bone (re)modeling.