Characteristics of Cervical Spine Motion in Different Types of Cervical Alignment Kinematic MRI Study

Study Design: Retrospective study. Objective: To evaluate how each type of sagittal cervical alignment affects the motion of the upper and subaxial cervical spine using kinematic magnetic resonance imaging. Summary of Background Data: The sagittal malalignment of the cervical spine from degeneration in the subaxial cervical spine reflects a disruption in the kinematic properties of the cervical spine and affects the motion of adjacent segments. Changes in the sagittal parameters and kinematics of the upper cervical spine and upper thoracic spine due to the kyphosis are unknown. Methods: Kinematic magnetic resonance imaging of the cervical spine in neutral position from 311 patients, including 90 lordotic, 90 straight, 90 global kyphotic, and 41 segmental kyphotic were analyzed. The lordotic angle at the upper and lower cervical spine, and T1 slope were measured in the neutral position and again in flexion and extension for dynamic analysis. Results: The number of levels with significant disk degeneration was higher in the global kyphosis group. In the global kyphosis group, neutral sagittal parameters showed some characteristics of compensation to the malalignment. Compared with the lordotic group, patients with global kyphosis demonstrated significantly higher lordotic angle of the upper cervical spine and more horizontal Ti slope. The dynamic evaluation showed greater range of motion of the entire cervical spine and subaxial cervical spine in younger patients. However, we still found greater range of motion of the occipito-atlanto-axial complex in global kyphosis, even when controlling for age and number of levels with significant disk degeneration. Conclusion: Sagittal malalignment of the cervical spine affects all parts of the cervical motion complex. The global kyphotic alignment of subaxial cervical spine affects the kinematic properties of the occipito-atlanto-axial complex and upper thoracic spine to compensate for the alteration of cervical alignment. These differences are not seen in straight and segmental kyphosis.