Table A1: Some material constant approximations based upon Kurutz [18], Schmidt et al. [24] and the references therein. Y denotes the (determining elements of the matrix of) Young modulus (elastic moduli) in MPa, and v the Poisson ratio.

The orthotropic model
The orthotropic model Y=3500, ν=0.25, Density1≈1908 kg/m3
Intervertebral disc2 Y≈252, ν≈0.47, Density3≈1120 kg/m3

1Built-in approximation, see main text. 2 Based upon Kurutz [18] p.219-223, elastic fiber approximation (Y = 500,ν= 0.45) and fluid-like solid for nucleus pulposus (Y = 4, ν = 0.50), mean value was used. 3Approximated as 60% water and 40% collagen, see main text.