Fig. 1. The intervertebral space ratio was measured by dividing half of the sum of the anterior (A) and posterior (B) intervertebral disc heights by the upper vertebral body height (H). The lumbar lordosis (LL) angle was measured as the angle between the superior endplates of L1 and S1. The segmental lordosis (α) angle was measured as the angle created by a line drawn from the superior endplate of the upper vertebra and a line drawn from the inferior endplate of the lower vertebra of the operation segment.