The compensatory relationship of upper and subaxial cervical motion in the presence of cervical spondylosis

Study Design: This study was an in vivo kinematic magnetic resonance imaging analysis of cervical spinal motion in human subjects. Objective: The objective of the study was to identify associations between disk degeneration in the subaxial cervical spine and upper cervical spinal motion in patients with general age-related cervical spondylosis. Summary of Background Data: The kinematic relationship between the occipital-atlantoaxial complex and subaxial cervical spine in patients with cervical spondylosis and decreased cervical motion is not well understood. Methods: A total of 446 symptomatic patients who had neck pain with and without neurogenic symptoms were included in this study. Kinematic magnetic resonance imaging was performed with dynamic motion of the cervical spine in upright, weight-bearing neutral, flexion, and extension positions. Intervertebral disk degeneration for each segment from C2-3 to C7- T1 and sagittal angular motion between flexion and extension for each segment from Oc-C1 to C7-T1 was evaluated. Depending on the amount of sagittal subaxial angular motion, the patients were classified into 3 groups by sagittal angular motion using cutoff points based on tertile (<36-degree group: 149 cases; 36-47-degree group: 148 cases; and >47-degree group: 149 cases). Results: A significant correlation was found between subaxial angular motion and intervertebral disk degeneration, indicating that the subaxial motion decreases according to the degree of disk degeneration. Mean angular motion of the occipital-atlantoaxial complex, especially of Oc-C1, was significantly higher in the <36-degree and 36-47-degree group than in the >47-degree group, whereas no significant difference was found at C1-C2. Conclusions: Our study demonstrates that decreased subaxial cervical spinal motion is associated with intervertebral disk degeneration in a symptomatic population. This decrease in mobility at the subaxial cervical spine is compensated for by an increase in angular mobility of the upper cervical spine at the occipital-atlantoaxial complex, especially at Oc-C1.