Study design: A prospective magnetic resonance imaging (MRI) study.
Objective: The aim of this study was to quantitatively analyze the potential risks of aorta injury from thoracic pedicle screw (TPS) misplacement in right thoracic adolescent idiopathic scoliosis (RT-AIS) patients who are in the prone position.
Summary of background data: The aorta injuries are rare during posterior spinal surgery, but they can result in catastrophic complications when they do occur. However, we are aware of no prior studies that have used MRI images obtained with patients in the prone position for the purpose of systematically evaluating the potential risks of aorta injury due to TPS misplacement.
Materials and methods: This prospective study included 38 RT-AIS patients who underwent MRI scans in the prone position. We evaluated on the MRI images the aorta position relative to the scoliotic spine, and simulated placement of a left TPS with a lateral deviation different from the medium trajectory using Surgimap Spine imaging software. The maximum error of lateral direction was set to 10, 20, or 30 degrees (3 scenarios), and the length of the TPS was set at 30, 35, or 40 mm (3 scenarios). Sensitivity analysis was performed by variable direction errors and TPS lengths. The potential risk of aorta impingement was defined as the virtual TPS crossing the aorta. The percentages of potential risk of aorta impingement were calculated at each level in 9 scenarios.
Results: In the RT-AIS patients, the aorta shifted gradually from the left side of the vertebrae at midthoracic levels to a more anterior position at the lower thoracic levels, and was close to the vertebral body at T5-T6 and far away from the left cortex of vertebrae at T12. In 9 scenarios, with the increment of the lengths or/and direction errors of the simulated TPS, the risks of aorta impingement were consistently elevated at all the levels. The simulated 40 mm TPS at T5, T6, and T11 posed a higher potential risk of aorta injury (66%-74%) with a 30-degree lateral direction error.
Conclusions: Prone positioning may increase the potential risk of aorta injury in RT-AIS patients, particularly at T5-T6 and T11 even if a left TPS just barely touches the anteriolateral or lateral cortex of the vertebrae. Laterally misplaced TPSs should be removed at these high aorta-at-risk levels.