Fig. 1

d Represents the location of psoas muscle at every disc levels. The axial plane of 3 intervertebral discs was divided into 6 zones according to the method by Moro et al. [17], and the front tangential lines of the left psoas muscle were evaluated. The area between the anterior and posterior edge of the intervertebral disc was divided into zones I, II, III, and IV. The area anterior to the anterior edge and the area posterior to the posterior edge of the intervertebral disc were defined as zone A and zone P respectively. e Represents the location of major artery at every disc levels and the left part the axial plane of 3 intervertebral discs was divided into 5 zones, and the right tangential lines of the major artery were measured. The area between the median line(passing through the center of the disc and the spinous process)and the left edge of the intervertebral disc was divided into zones a, b, and c. The area right to the median line and the area left to the left edge of the intervertebral disc were defined as zone R and zone L respectively