Fig. 2

Effects of the variations in the nucleus cross-sectional areas and relative positions on the RoMs. The annulus can be approximated as two differently sized quadrangular annuls on a specific plane. M1 and M2 are set as the applied forward and backward torques (i.e., flexion and extension in the central section of the disc sagittal plane), R1 and R2 are the distances between the anterior and posterior parts perpendicular to the torque axis centre and edges of the nucleus, respectively. Changes in R1 and R2 originating from different nucleus positions and cross-sectional areas will induce changes in the RoM under the same M1 and M2. Furthermore, this change will extend to different sections if the force on the two-dimensional planar structure is extended to three-dimensional space

A = Annulus; N = Nucleus