The effect of follower load on the range of motion, facet joint force, and intradiscal pressure of the cervical spine: a finite element study

Follower loads are used to simulate physiological compressive loads on the human spine. These compressive loads represent the load-carrying capacity of the human cervical spine and play an important role in maintaining its stability. However, under different follower loads the biomechanical response of the cervical spine is unknown. Therefore, the aim of this study was to determine the effect of follower load on the biomechanics of the cervical spine. A three-dimensional nonlinear finite element (FE) model of the cervical spine (C3–C7) was developed and validated. Using this FE model, we evaluated the effect of different follower loads (0 N, 50 N, 100 N, and 150 N) on the range of motion (ROM), facet joint forces (FJFs), and intradiscal pressure (IDP) in the cervical spine. In addition, a moment of 1 Nm was applied in three anatomical planes (sagittal, coronal, and transverse planes) to simulate different postures. The results indicate that as follower load was increased, the ROM of the cervical spine in extension decreased (4.06°–0.95°), but increased in other postures (flexion 4.19°–6.04°, lateral bending 1.74–3.03°, axial rotation 2.64°–4.11°). Follower loads increased the FJF in all postures (0 N–52 N). In lateral bending (LB), FJFs were only generated in the ipsilateral facet joints. In axial rotation (AR), there was large asymmetry in the FJF, which increased as follower load increased. The IDP of each segment increased nonlinearly with increasing follower load in all postures (0.01 MPa–1.23 MPa). In summary, follower loads caused changes in motion and loading patterns in the cervical spine (C3–C7). Therefore, in common daily activities, we should pay attention to the muscle strength of the neck through exercise to adapt to the biomechanical changes in the cervical spine following an increase in follower load.