Fig. 1

Measurement of radiological parameters. A, B Post-operative change of intervertebral disc height is calculated as (a’ + b’)/2 − (a + b)/2. Cervical lordosis is defined as the angle between the inferior endplate of C2 vertebra and the inferior endplate of C7 vertebra. Endplate angle of the cranial vertebra is the angle between the upper and lower endplates of the cranial vertebral body at index level. Shell angle is recorded as the angle between the superior and inferior endplate of the prosthesis. FSU angulation is the angle between the superior endplate of cranial vertebral body and the inferior endplate of the caudal vertebral body at the indicated segment. C Prosthesis-endplate depth ratio is calculated as (P₁/E₁ + P₂/E₂)/2. FSU, functional spinal unit