The ADS commonly developed in a skeletally mature spine due to the degenerative change without preexisting spinal deformity . The progressive degenerative mainly occurs in the lumbar spine, which result in load-sharing changes that involve the entire spine, eventually lead to loss of lumbar lordosis and resultant sagittal plane malalignment. Multiple degenerative pathology which included the disc collapse, facet hypertrophy, capsule degeneration, and ligamentous hypertrophy, affecting the load-sharing of both the anterior and posterior columns, ultimately leading to degenerative curves. Two factors have been found in associated with the severity of the ADS which were the magnitude of the curvature and the vertebrae rotation. [6–8].
Previous studies have indicated that there was an obvious correlation between the vertebrae rotation and the clinical symptoms irrespective of the degree of scoliosis . Although the exact mechanism of the vertebrae rotation in ADS was yet to be defined, it was assumed that asymmetry degeneration of facet joint may play an important role. [10–12]. Due to the asymmetry in the orientation of facet joint, the facet position was abnormal and the distribution of mechanical loads and stress in the spine changed which may be a potential cause of spinal degeneration [13–15] and instability [16–20]. Faraj  described that the vertebrae rotation was a risk factor for curve progression. It also has been shown that the vertebrae rotation can lead to the pain which caused by the degenerative facet joint or the decreased foraminal width [22, 23]. Therefore, the vertebrae rotation was an important index for the severity of the ADS. In our study, there are positive correlation between the vertebrae rotation and Cobb angle, coronal horizontal displacement distance, which was accordance with the previous studies. So, we can use the γ to evaluate the severity of ADS in the clinical.
As we all know, the vertebrae rotation in the patients with AIS have a great effect on the position of aorta. Milbrandt  showed that the thoracic aorta shifted to the left side of the curves and was positioned more left laterally and posteriorly to the vertebral body in right thoracic curves in patients with AIS. On the contrary, it moved to the right and was positioned anterior to the vertebral body in left thoracic curves. Liljenqvist and Sevastik [25, 26] studied the relative position of the aorta in patients with AIS, and found that the lateral displacement is larger and the vertical displacement is shorter. Studies on the position of the aorta in patients with AIS showed that the position of the aorta changed at different vertebrae rotation [24, 27–28]. While the effect of vertebrae rotation on the position of aorta in patients with ADS remains unclear. In our series, a quantitative relation between vertebrae rotation and radiological parameters on X-ray was firstly established. On the one hand, the regression equation indicated that vertebrae rotation in segments with scoliosis could be influenced by Cobb angle and coronal movement, which was a key information in bridging parameters on X-ray and MRI. On the other hand, when there was a lack of MRI with money constraints or other cases, vertebrae rotation could still be predicted by cheaper X-ray and thus the direction of pedicle screws implanting could then be identified. However, it was somewhat different on risk factors between LS and RS group. May be there was asymmetric anatomy construction distributing besides lumbar spine such as vessel and tissue, as well as bilateral discrepancy of muscularity in left- or right-side advantage of the body[4, 13]; Or it was just because of a little sample in this study and larger sample and multi-center studies could be developed.
Due to the vertebrae rotation, the structure of the vertebrate is complex and blur, so the insertion of pedicle screw was difficulty and may injury the aorta at a higher risk. Besides the patients of ADS usually complicated with advanced age, so the vascular elasticity was reduced and commonly combined with atherosclerosis . Therefore, it is important to make a clear understanding of the effect of vertebrae rotation on the position of aorta in patients with ADS to guide the spine physician on intraoperative manipulation and reduce the vascular-related complications. In our study, the effect of vertebrae rotation on the position of aorta in patients with ADS is different from the patients with AIS. The reason are as follows. AIS commonly manifested a regularly and smooth curve with a larger Cobb angle. While the ADS are mainly caused by the degeneration of intervertebral discs, facets and paravertebral muscles. The curve is irregularly and the Cobb angle is usually less than 40°, and the vertebrae rotation is of a moderate size and is limited to the apical levels [30, 31]. Besides, the ADS are commonly elderly patients, the vascular elasticity was reduced and the tethering ability of connective tissues were weakened, which lessen the effect of the vertebrae rotation. So, the vertebrae rotation has no significant effect on the position of aorta in patients with ADS.
In the spine surgery, the vascular injury is a rare but well recognized complication. Once happened, it would be catastrophic [32, 33]. Liu studied that due to the vertebrate rotatory and aliment changed, the risk of aorta injury caused by the misplace of screw would be increased . Due to the vertebrae rotation, the misplaced screw will be at a high potential. During the process of screw insertion, we usually determine the angle according to the rotation of the vertebral body to make sure the accurate of the screw insertion. For the patients with ADS, the effect of the vertebrae rotation on the screw insertion have been studied a lot, and the effect of the vertebrae rotation on the position of the aorta was also important to avoid the aorta injury. In our study, the outcome indicated that the vertebrae rotation has no significant effect on the position of aorta in patients with ADS. So, the position of the aorta in patients with ADS were not changed with the vertebrate rotation. In other words, the aorta maintained a relatively normal positon in patients with ADS. Therefore, we can evaluate the angle of screw and the position of the aorta simultaneously according to the vertebrate rotation. Not only ensuring the safety of screw insertion, but also avoiding the injury of the aorta.
There are some limitations in this study. Firstly, patients usually take the supine position during MRI examinations, but the surgery is usually performed in prone position. Whether the position of the aorta changes from supine to prone position is not clear. Secondly, the vertebrae rotation mainly affect the coronal balance, the sagittal balance was not clearly, so the conclusion may not be applicable for all ADS cases. Besides, the number of the cases in our study is relatively small, so the larger cases of research should be future studied.