Fig. 1

Schematic diagrams of the parameters. Radiographic measurements of cervical sagittal parameters in this study: C0-C2 Cobb angle: angle between the McGregor line and the C2 lower end plate, C2–C7 Cobb angle: angle between the lower plate of C2 and the lower plate of C7, C2–7 sagittal vertical axis(C2–7 SVA): the distance from the posterior, superior corner of C7 to the plumbline from the centroid of C2, C7 Slope: the distance from the posterior, superior corner of C7 to the plumbline from the centroid of C2, T1 Slope: angle between a horizontal line and the superior endplate of T1, and Spino-cranial angle(SCA): the angle is defined between the C7 slope and the straight line joining the middle of the C7 end plate and the middle of the sella turcica