Influences of the location of vertebral “IAR” on cervical spine kinematics

Different spine models have placed the IAR at various locations in the spine; more commonly, the central region of the intervertebral disk, the middle region of the subjacent vertebra, and the central region of the vertebral body. A computer simulation model of the cervical spine (C2-T1) was developed to investigate sagittal plane kinematics for different placements of the vertebral axis of rotation. Stiffness of the motion segment units was modeled with rotational springs. The combined loading vector applied to the spine replicated the in vitro experimental test results generated in the authors´ laboratory. Equal stiffnesses of each vertebra were used. The difference in force magnitude amongst the different cases was less than 1% of the applied load. Although the changes in rotational magnitudes were small, the relative differences varied not only with the different models, but also amongst the different vertebral levels