The Occupancy of the Components in the Cervical Spine and Their Changes with Extension and Flexion

Study Design Retrospective case series. Objectives The kinematics of the cervical spine has been investigated by many researchers. However, the occupancy of the disk bulges, spinal cord, ligamentum flavum, and the rest of the canal as well as the changes of these structures with motion have not yet been investigated. The goal of this study is to investigate these dynamic changes. Methods The kinetic magnetic resonance images of 248 patients (124 men and 124 women) were evaluated, and the occupancy of each structure for each cervical level at neutral, flexion, and extension were calculated. Results Whole canal anteroposterior (AP) diameters showed significant differences between neutral-extension and flexion-extension at the C4–C5 and C5–C6 levels (p < 0.05). The mean disk bulges showed significant differences between neutral-flexion and flexion-extension at the C4–C5, C5–C6, C6–C7, and C7–T1 levels (p < 0.01). The mean spinal canal AP diameter showed significant differences between flexion-extension and neutral-extension at the C3–C4, C4–C5, C5–C6, and C6–C7 levels (p < 0.05). There were significant differences between neutral-flexion at the C4–C5, C5–C6, and C6–C7 levels (p < 0.05). The mean thickness of the ligamentum flavum showed significant differences between flexion-extension at the C3–C4, C4–C5, C5–C6, and C6–C7 levels (p < 0.001). There were significant differences between neutral-extension at the C3–C4 and C5–C6 levels (p < 0.05). There were significant differences between neutral-flexion at the C5–C6 and C6–C7 levels (p < 0.05). The mean thickness of the spinal cord showed significant differences between neutral-flexion at the C2–C3 and C3–C4 levels (p < 0.05). There were significant differences between flexion-extension at the C3–C4 and C4–C5 levels (p < 0.01). The rest of the canal showed significant differences between neutral-extension and flexion-extension at the C3–C4, C4–C5, C5–C6, and C6–C7 levels (p < 0.005). There were significant differences between neutral-flexion at the C5–C6 and C6–C7 levels (p < 0.01). Conclusions The occupancy of each structure in the cervical spine for each level was revealed by this study. In addition, the dynamic changes in the cervical spine with flexion and extension were seen to have different characteristics for each level.