Department of Spine Surgery, the Affiliated Drum Tower Hospital of Nanjing University Medical School, Zhongshan Road No. 321, Nanjing, China.
Spine (Phila Pa 1976). 2012 Aug 1;37(17):E1054-61. doi: 10.1097/BRS.0b013e3182600a7d.
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). CONCLUSION.: 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.
一项前瞻性临床磁共振成像研究。
探讨单右侧胸青少年特发性脊柱侧凸（RT-AIS）患者在两种体位（仰卧位和俯卧位）下主动脉相对于脊柱的位置差异。
椎弓根螺钉广泛应用于脊柱侧凸手术中。随着因椎弓根螺钉位置不当而导致的血管并发症发生率的增加，关于主动脉与椎体之间空间关系的研究也逐渐增多，结果表明 RT-AIS 患者的主动脉位置比正常人群更靠后。在这些影像学研究中，患者在仰卧位接受计算机断层扫描或磁共振（MR）扫描。最近对无脊柱畸形的受试者的研究发现，当受试者从仰卧位变为俯卧位时，主动脉从侧后方向前内侧移动。然而，尚无研究探讨 AIS 患者在改变体位时主动脉的移位情况。
本研究纳入了 26 例单右侧胸 AIS 患者。每位患者均接受 T5 至 L3 水平的轴向 MR 扫描，扫描体位分别为仰卧位和俯卧位。在笛卡尔坐标系中，从 T5 至 L3 水平的轴位 MR 图像上测量左侧椎弓根-主动脉（LtP-Ao）角度、LtP-Ao 距离和椎体旋转角度。我们还模拟了常用长度和 20°方向误差的椎弓根螺钉的错位，并将主动脉撞击的潜在风险定义为虚拟椎弓根螺钉穿过主动脉。采用配对样本 t 检验比较两种体位之间的这些参数。
在每个水平上，两种体位之间 LtP-Ao 角度和 LtP-Ao 距离的均值均存在差异。在 T5-T10 水平，俯卧位患者的 LtP-Ao 角度（26.2°比 38.8°；P ，0.01）和 LtP-Ao 距离（27.0 毫米比 30.7 毫米；P ，0.01）明显小于仰卧位患者。在根尖水平，俯卧位患者的椎体旋转角度大于仰卧位患者，但差异无统计学意义（P ，0.05）。T5-T10 水平，俯卧位患者潜在主动脉撞击风险的百分比显著高于仰卧位患者（19.7%比 6.6%；P ，0.05）。
在 RT-AIS 患者从仰卧位变为俯卧位时，T5-T10 水平的主动脉更向前内侧移位，并更靠近脊柱。因此，在俯卧位时，左侧椎弓根螺钉从前侧和外侧皮质穿透可能会对主动脉造成更高的损伤风险。脊柱外科医生在对 RT-AIS 患者进行俯卧位椎弓根螺钉置入时，应注意这些改变的情况，以避免损伤主动脉。
