Table 1.

Parameter values, up to four significant digits, describing the nonlinear torque–angle characteristics of the IVD (Eq. (3): $T_{\text{spring}}^{\text{disc}}\left(\phi \right)=p_1·tanh\left(\frac{{\phi }^3}{p_2}\right)+p_3·\phi$) in the three anatomical planes, cf. Figs. 1 and 4

Direction of movement	p1	p2	p3
Flexion (rotation about x-axis)	10.67	0.005913	− 1.685
Extension (rotation about x-axis)	5.196	0.008417	24.50
lateral flexion (rotation about y-axis)	6.929	0.001482	19.76
Axial rotation (rotation about z-axis)	4.399	0.001141	42.38