  In articular cartilage the orientation of collagen fibres is not uniform,
varying mostly with the depth on the tissue. Besides, the biomechanical
response of each layer of the articular cartilage differs from the neighbouring
ones, evolving through thickness as a function of the distribution, density and
orientation of the collagen fibres. Based on a finite element implementation, a
new continuum formulation is proposed to describe the remodelling and
reorientation of the collagen fibres under arbitrary mechanical loads: the
cartilaginous tissue is modelled based on a hyperelastic formulation, being the
ground isotropic matrix described by a neo-Hookean law and the fibrillar
anisotropic part modelled by a new anisotropic formulation introduced for the
first time in the present work, in which both reorientation and remodelling are
taken into account. To characterize the orientation of fibres, a structure
tensor is defined to represent the expected distribution and orientation of
fibres around a reference direction. The isotropic and anisotropic constitutive
parameters were determined by the good validation of the numerical models with
the experimental data available from the literature. Considering the effect of
realistic collagen fibre reorientation in the cartilage tissue, the remodelling
algorithm associated with a distribution of fibres model showed accurate
results with few numerical calculations.
