Fig. 1
a The distance between point a and point b is the anterior height of the intervertebral space (D1). The distance between point c and point d is the posterior height of the intervertebral space (D2). IVH = (D1 + D2)/2. Point e is the peak of the inferior margin of the superior vertebral pedicle, and point f is the lowest point of the inferior margin of the superior vertebral pedicle. The distance between point e and point f is termed as the IFH. The area inside the region bounded by the yellow line is the IFA. b Point g is the midpoint of the anterior margin of the thecal sac. Point h is the midpoint of the posterior margin of the thecal sac. The distance between point g and point h is termed as the APD. The area inside the region bounded by the yellow line is the CSA