Fig. 1

Four regions of the lumbar spine, as divided by Lee et al.: zone 1, the far-upward zone, within 3 mm of the lower edge of the upper pedicle; zone 2, the near-upward zone, between the lower edge of the upper vertebral body and 3 mm from the lower edge of the upper pedicle; zone 3, the near-downward zone, between the upper edge of the lower vertebral body and the midpoint level of the lower pedicle; and zone 4, the far-downward zone, between the midpoint of the lower pedicle and the lower edge of the lower pedicle