Fig. 1

Measurement of cervical alignment and radiological parameters. a measurement of CL, SVA, and T1S. b Measurement of OPCL. c Measurement of radiological parameters on flexion lateral image and d on extension lateral image. CL C2–C7 cervical lordosis, SVA C2–C7 sagittal vertical axis, T1S T1 slope, OPCL lordosis of operated segments, UCL lordosis of upper adjacent segment, LCL lordosis of lower adjacent segment