Abstract
Introduction
Lumbar spine osteotomy has been widely adopted to correct thoracolumbar kyphosis in ankylosing spondylitis (AS) patients; however, catastrophic aortic complications may occur during the insertion of pedicle screws or the performance of osteotomy. To prevent these iatrogenic complications, it is essential to have a clear understanding of the spatial relationship between the aorta and the spine. Previous study reported that the aorta is positioned more anteromedially relative to the spine in AS patients with thoracolumbar kyphosis when compared with normal subjects. However, patients in the aforementioned study were performed computed tomographic scans in the supine position, which was different from the prone position adopted in surgery. To the best of our knowledge, no report has been published to investigate the difference in the position of the aorta relative to the vertebrae between supine and prone positions in AS patients with fixed thoracolumbar kyphosis. The objective of this study is to explore the differences in the anatomic position of the aorta relative to the spine between supine and prone positions in AS patients with thoracolumbar kyphosis.
Patients and Methods
From March 2013 to June 2014, 20 AS patients (19 males, 1 female) with thoracolumbar kyphosis with a mean age of 30.9 years (range, 19–46 years) were recruited into this study. Each patient received an axial MRI scan from T9 to L3 in both the supine and prone positions. The left pedicle-aorta (LtP-Ao) angle and LtP-Ao distance were measured at each level. Radiographs were analyzed to measure the global kyphosis (GK), thoracic kyphosis (TK), lumbar lordosis (LL), and the apex of the kyphotic curve was also recorded. The paired sample t-test was used to compare these parameters between different positions.
Results
At T9 to L3 levels, no significant difference was noted in LtP-Ao distances (43.84 vs. 44.58 mm; p = 0.054) and LtP-Ao angles (0.67 vs. 0.03 degrees; p = 0.058) for AS patients between supine and prone positions. The correlation analysis also revealed no significant correlation between shifting of the LtP-Ao angle and GK, TK, and LL at T9 to L3 levels in the prone position.
Conclusion
There is no significant change of the relative position between aorta and spine at T9 to L3 levels when patients change from supine to prone position. The result of this study suggested that in advanced stage of AS, the chronic inflammation may result in the firm adhesion between the aorta and anterior longitudinal ligament. Moreover, due to the reduced mobility and limited range of motion, the aorta is more vulnerable to be injured when the misplacement of pedicle screws and the stretching of the aorta occurs during surgery. Therefore, surgeons must keep this condition in mind to avoid catastrophic aortic complications.