Computed tomographic angiography measurements

To quantify the relative position of the aorta and spine, a Cartesian coordinate system was built up on the axial CT scans of the vertebral bodies according to the methods of Takeshita et al [10]. And the following parameters were measured at each level from T4 to L5 in group NC and apex level in group TB: (1) Left pedicle-aorta (LtP-Ao) angle (α), subtended by the y-axis and a line connecting the origin and the center of the aorta. (2) LtP-Ao distance (d1), defined as the distance between the origin and the edge of the aortic wall. (3) the pedicular line–aorta distance (d2), defined as the distance from the edge of the aorta to the x-axis. (4) vertebra/rib-aorta distance (d3), defined as the minimum distance from the edge of the aorta to vertebra or rib. These parameters were measured by 2 observers blinded to the information of the subjects.

From the axial images of CTA scans, we selected the vertebral segments with the minimum value of the pedicular line-aorta distance in group NC and classified them into three kinds of degrees based on the relative positions of aorta to the vertebra/rib. In grade 1, the aorta was seen at the antero-middle position of the vertebral body or antero-lateral position of the first third of the vertebral body; in grade 2, the aorta moved posteriorly from the first third of the vertebral body to the costal head; in grade 3, the aorta was located laterally to the costal head, the costal neck and the costal tubercle (Fig. 2). We evaluated the CTA images of patients with Pott’s deformity and found that in some patients, the aorta moved positively and laterally and was located in vicinity of the rib (Fig. 2), which we defined as grade 4.

The average left pedicle-aorta angle, left pedicle-aorta distance, the pedicular line-aorta distance and the vertebra/rib-aorta distance from T4-L3 levels for patients in group TB (dark bars) and patients in group NC (T4-L4, light bars)