[Numerical treatment of bone as anisotropic material]

A three-dimensional finite element model of the femur shaft taking account of its microscopic structure has been developed. In the first instance, the material properties of a homogenised material replacing the inhomogeneous structure of compact bone were determined with the aid of a two-dimensional finite element model containing information on the bone structure and the mechanical behaviour of osteons. The bone structure with its irregular hole pattern (Haversian canals of the osteons) was idealised by assuming the bone to be a homogeneous plate with the holes arranged in a hexagonal or square pattern. The regular structure considered allowed on to compute the stresses and deformations of a modelled characteristic segment under given boundary conditions and loads. With these values new material constants (Young's and shear moduli, Poisson's ratios) of the continuum substitute were calculated. These constants were the material properties of the three-dimensional finite element model of the femur shaft, which was then used for stress calculations under the load components of the one-legged stance.