A prospective clinical magnetic resonance imaging study.
To explore the differences in the position of the aorta relative to the spine in patients with single right thoracic adolescent idiopathic scoliosis (RT-AIS) in 2 different body positions (supine and prone).
Pedicle screws are used widely in scoliosis surgery. With an increase in the incidence of vascular complications that result from misplaced pedicle screws, studies regarding the spatial relationship of the aorta and the vertebral body have also gradually increased and show that the aorta is positioned more posteriorly in patients with RT-AIS than in normal subjects. In these imaging studies, the patients received computed tomographic or magnetic resonance (MR) scans in the supine position. Recent studies of subjects without a spinal deformity found that the aorta moves from a posterolateral to an anteromedial position when the subject changes from a supine position to a prone position. However, no studies investigated aorta shifting with changing body position in patients with AIS.
Twenty-six patients with single RT-AIS were recruited into this study. Each patient received an axial MR scan from T5 through L3 in both the supine and prone positions. In the Cartesian coordinate system, the left pedicle-aorta (LtP-Ao) angle, LtP-Ao distance, and vertebral rotation angle were measured from T5 through L3 in the axial plane MR images. We also simulated misplacement of the pedicle screw with commonly used length and 20° direction error, and the potential risk of aorta impingement was defined as the virtual pedicle screw crossing the aorta. The paired sample t test was used to compare these parameters between the 2 body positions.
The mean LtP-Ao angle and mean LtP-Ao distance differed between the body positions at each level. At the T5–T10 levels, the patients in the prone position exhibited significantly smaller LtP-Ao angles (26.2° vs. 38.8°; P, 0.01) and distances (27.0 vs. 30.7 mm; P, 0.01) than those in the supine position. The vertebral rotation angle was larger in the prone position than in the supine position at periapical levels, although this difference did not reach statistical significance (P . 0.05). The percentage of potential risk of aorta impingement was significantly higher in the prone position than in the supine position at the T5–T10 levels (19.7% vs. 6.6%, respectively; P, 0.05).
The aorta shifts more anteromedially and more closely to the spine at the T5–T10 levels when patients with RT-AIS change from the supine to the prone position. Thus, in the prone position, the aorta is potentially at a higher risk for injury from anterior and lateral cortex penetration by the left pedicle screws. The spinal surgeon should be aware of these altered conditions to avoid injury to the aorta during pedicle screw insertion in patients with RT-AIS who are in the prone position.
This study found that the aorta moves from a posterolateral to an anteromedial position when patients with right thoracic adolescent idiopathic scoliosis change from a supine to prone position. In the prone position, the aorta is at higher risk for injury from anterior and lateral cortical perforation at the T5–T10 levels, particularly in cases with larger vertebral rotation.
*Department of Spine Surgery, the Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China
†Department of Spine Surgery, the First Affiliated Hospital of Guangxi Medical University, Nanning, China.
Address correspondence and reprint requests to Yong Qiu, MD, Department of Spine Surgery, the Affiliated Drum Tower Hospital of Nanjing University Medical School, Zhongshan Rd., No. 321, Nanjing 210008, China; E-mail: firstname.lastname@example.org
Acknowledgment date: October 12, 2011. First revision date: January 13, 2012. Second revision date: February 28, 2012. Acceptance date: March 6, 2012.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Natural Science Foundation of Jiangsu Province, China (BK2009001), grant funds were received to support this work.
No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.