Kinematics of the Subaxial Cervical Spine in Rotation In Vivo Three-Dimensional Analysis

Abstract

In Brief Study Design. Three-dimensional intervertebral motions of the subaxial cervical spine during head rotation were investigated in healthy volunteers using three-dimensional magnetic resonance imaging (MRI). Objectives. To document intervertebral coupled motions of the subaxial cervical spine during rotation. Summary of Background Data. In vivo three-dimensional kinematics of the subaxial cervical spine in rotation have not previously been well described, since they are too complicated to follow using conventional radiography or computed tomography techniques. Methods. Ten healthy volunteers underwent three-dimensional MRI of the cervical spine in 11 positions with 15° increments during head rotation using a 1.0-T imager. Relative motions of the subaxial cervical spine were calculated by automatically superimposing a segmented three-dimensional MRI of the vertebra in the neutral position over images of each position using volume registration. Three-dimensional motions of adjacent vertebrae were represented with 6 df (6 degrees of freedoms) by Euler angles and translations on the coordinate system defined by Panjabi, then visualized in animations using surface bone models. Results. Mean axial rotation of the subaxial cervical spine in maximum head rotation (69.5°) was 2.2° at C2–C3, 4.5° at C3–C4, 4.6° at C4–C5, 4.0° at C5–C6, 1.6° at C6–C7, and 1.5° at C7–T1. Coupled lateral bending with axial rotation was observed in the same direction as axial rotation at all levels (C2–C3, 3.6°; C3–C4, 5.4°; C4–C5, 5.0°; C5–C6, 5.3°; C6–C7, 4.9°; C7–T1, 1.2°). Coupled extension with axial rotation occurred in the middle cervical region (C2–C3, 1.4°; C3–C4, 2.3°; C4–C5, 1.5°), while in the lower cervical region, flexion was coupled with axial rotation (C5–C6, 0.9°; C6–C7, 2.4°; C7–T1, 3.0°). Conclusions. We investigated intervertebral motions of the subaxial cervical spine during head rotation using a three-dimensional imaging system, and obtained the first accurate depictions of in vivo coupled motion. These findings will be helpful as the basis for understanding abnormal conditions. This study investigated three-dimensional intervertebral motions of the subaxial cervical spine during head rotation using three-dimensional MRI and provides the first accurate elucidation of in vivo coupled motion.