Fig. 4

a: Lamina opening angle. The angle is measured on a CT axial view between the line parallel to the connection of the posterior walls of the bilateral transverse foramen and the tangent line of the inner edge of the lamina. b: Sagittal diameter of the spinal canal. The distance between the posterior edge of the vertebral body and the anterior edge of the lamina is measured on a lateral X-ray. c: Cervical curvature. The cervical curvature is evaluated on a lateral cervical X-ray by measuring the vertical distance (D value) between the line connecting the C2 vertebral body and the lower edge of the C7 vertebral body and the apex of the cervical curve. d: C2-C7 Cobb angle. On a lateral cervical X-ray, the extension lines of the inferior endplates of the C2 and C7 vertebral bodies are drawn, and the angle between these two lines is measured