Is the Risk of Aorta Injury or Impingement Higher During Correction Surgery in Patients with Severe and Rigid Scoliosis?

Objective

To evaluate the position of the aorta relative to the spine and the risk of aortic injury during correction surgery in patients with idiopathic severe and rigid scoliosis (main curve Cobb angle >90° and flexibility <30%).

Methods

Twenty-seven patients with severe right thoracic/thoracolumbar scoliosis were recruited. The entry point–aorta distance (EAD), the left pedicle–aorta angle (α), the left aorta angle (β), and the vertebral rotation angle (γ) were measured from 4 vertebrae above (A4) to 4 below (B4) the apical vertebra (Apex) to quantify the spatial relationship between aorta and spine. We simulated the pedicle screw misplacement with variable direction error, length, and diameter to analyze the potential risk of aortic injury.

Results

The aorta shifted laterally and posteriorly as it descended from A4 and moved back medially and anteriorly from Apex. The potential risk of aortic injury increased with the augment of direction error and/or length of the screw, but the tendency was not significant with the augment of diameter. The risk peaked at A4, A3, and B2, when the screw length was 40 mm and diameter was 5.0 mm, and the direction error was 30°, whereas the risk was lowest at the apical level 14.3% (0%–40.7%) in any scenarios.

Conclusions

In patients with severe and rigid scoliosis, the aorta shifted more laterally and posteriorly, and the injury risk was lower at the apical level, compared with moderate scoliosis. Most potential risks can be minimized by careful preoperative planning and the assistance of intraoperative navigation or robotics.

Introduction

Severe and rigid scoliosis is commonly defined as the main curve Cobb angle >90°, with flexibility <30%, which mostly presents with rapid deformity progression and poor cardiopulmonary function.1, 2, 3, 4, 5 Surgical options include preoperative and/or perioperative halo-gravity traction, anterior release and posterior instrumentation, and spinal osteotomies, such as vertebral column resection.6, 7, 8 Typically, the risk of surrounding tissue injury by misplaced pedicle screws should not be ignored, especially the aorta. Severe vertebral rotation as well as abnormal pedicle morphology make it hard to place pedicle screws exactly. Main curve rigidity requires more torsional force intraoperatively to move over, which could break out the screws. Some investigators have focused on the spatial relationship between aorta and spine in patients with scoliosis, and several cases of serious iatrogenic aortic injury caused by pedicle screw misplacement have been reported.^9,10 However, only patients with a moderate primary curve (40°–70°) were included in those studies.11, 12, 13, 14, 15, 16, 17 It remains unknown whether those conclusions are appropriate for patients with severe and rigid scoliosis.

Severe and rigid scoliosis is often combined with challenging anatomy or other deformities, such as deformed rib cages, dysplastic pedicles, intravertebral torsion, and deformed dural sac, which could impede the precision of pedicle cannulation and screw insertion.¹⁸ Severe rotational deformity in apical levels and an angled curve could make vessels and neural elements malpositioned and easily injured. Furthermore, the aorta lay at an angle preoperatively, which was elongated and strained when the spinal column lengthened during scoliosis correction, making the aortic wall more vulnerable.19, 20, 21 Some previous studies^22,23 have reported spontaneous aorta rupture from an acute angle because of severe kyphoscoliosis. Thus, the irregular position of the aorta, the complicated anatomy, and the great difficulty in correction surgery may synchronously impose increased risk on the aorta. This study evaluates the aorta position relative to the vertebra and estimates the aortic injury risk caused by pedicle screw misplacement through computed tomography (CT) scan images in patients with severe and rigid scoliosis.