Finite element study on effect of follower load on intersegmental rotation, facet joint force and nucleus pressure of the cervical spine

Background: The follower load is used to simulate the physiological compressive load of human spine. These compressive loads can maintain cervical spine’s mechanics stability and play a significant role in improving load-carrying capacity of the cervical spine. However, under different follower loads the biomechanical response of the cervical spine is unknown. So the aim of this study is to investigate the effect of follower load on biomechanics of the cervical spine. Results: In this study, a three-dimensional nonlinear finite element (FE) model of the cervical spine (C3-C7) was built and validated. Using this FE model of the cervical spine, we evaluated the effect of different follower loads on intersegmental rotation, facet joint force, and nucleus pressure in the cervical spine. The results indicated that with the follower load increased, the intersegmental rotation of the cervical spine in extension decreased, but the intersegmental rotation in other postures increased. The follower load increased the facet joint forces in all postures. In lateral bending (LB), the facet joint forces were only generated in the ipsilateral facet joints. In axial rotation (AR), there was a large asymmetry in the facet joint forces, and this asymmetry worsened with the follower load increased. The nucleus pressure of each segment nonlinearly increased with the follower load increased in all postures. Conclusion: An comprehensive analysis in intersegmental rotation, facet joint force and nucleus pressure under different follower loads can provide us a deeper understanding of the follower load in the human spine.