Constitutive laws in nonlinear modelling of anulus fibrosus

Different hyperelastic and hypoelastic laws are studied for collagen fibres of anulus fibrosus. For the large strains finite element analyses performed, fibres are distributed in the mode1 as truss elements, at four different layers between the solid elements which discretize the disc ground material, that is modelled by adopting hyperelastic constitutive laws. The overall response of L3-LA human intervertebral segment is studied with regard to healthy and degenerated conditions, with reference to a compressive axial load. The degenerated condition is related to an alteration of the properties of disc material and with a reduction of fibres quantity