The spine kyphosis deformity is mainly caused by congenial, tuberculosis, ankylosing spondylitis, fracture, etc. [1, 2, 12–17]. The lumbar osteotomies are appropriate surgical techniques to improve the global sagittal balance of the spine, increasing the lumbar lordosis and decreasing the pelvic (lower PT) and the femoral (lower femoral flexion) compensation. Vertebral column decancellation (VCD), a combination of the eggshell technique, Smith-Petersen osteotomy (SPO), PSO, and vertebral column resection (VCR), is highly appropriate for the majority of patients with severe rigid kyphosis [6–8, 18–20]. Regardless of the type of osteotomy surgery, the general principle is to lengthen the anterior column or/and shorten posterior column [3–5]. In order to achieve a high level of correction of deformity, lengthening the anterior column is of great importance, which may result in injury. The complication of aorta injury is rare in the procedure of spinal osteotomy for the correction of Pott’s thoracolumbar angular kyphotic deformity.
Numerous previous studies have explored the changes of aorta after undergoing PSO. Weatherley et al. [9] reported patients with severe kyphotic deformity who underwent SPO. The corrected kyphosis angle was 45°, and the length of the aorta was stretched by 2 cm. Chang et al. [10] applied osteotomy in the treatment of kyphosis, and it was demonstrated that the aorta was lengthened by 2.8 cm (1.7–3.5). Ji et al. [11] reported that in case of osteotomy after the treatment of kyphosis, the length of the aorta was increased by 2.2 cm and the diameter of the aorta was decreased by 0.41 cm. Bourghli et al. [12] adapted a new surgical method of osteotomy to treat the angular kyphosis caused by fracture, and it was found that after surgery, the length of the aorta was increased by 2.3 cm. The above-mentioned studies indicated that due to elongation of the anterior column, the aorta may be stretched and vulnerable to injuries, especially in the elderly patients with reduced elasticity of the aortic wall. Once that is stretched seriously, the incidence of aortic injury increases. Besides, there is a relationship between the extension of the length of the aorta and the decrease of diameter of aorta, which may influence the hemodynamic. Therefore, vascular complications are required to be highly considered by surgeons.
Several scholars presented methods for measuring the length of the aorta. Chang et al. [10] used an atherosclerotic plaque to measure the change of the length of the aorta. Since no obvious calcification was observed in many cases, it therefore was not appropriate for all patients. Ji et al. [11] and Bourghli et al. [12] measured the length of the aorta between the instrumented vertebrate, and reported the changes in aorta. Although the aorta was fixed with aortic hiatus and branch vessel, the position of the aorta shifted with the change of body, indicating that their method is inaccurate. Besides, for the patient with angular kyphosis, the pathway of aorta is irregular and tortuosus, therefore, it is difficult and inaccurate to measure the length of the aorta using the above-mentioned methods. Hence, in the present study, we adapted a new method for measuring the length of the aorta in patients with angular kyphosis.
Firstly, we fixed two points as anchors and the length of aorta was obtained by measuring the distance between the two points. The proximal one was the origin of the left subclavian artery, and the distal was the fork of the iliac artery. As a result, the effects of modified aorta position on outcomes could be eliminated. Additionally, it is essential to acquire 3D image to accurately measure the length of the aorta. The most common approach in clinic is angiography, requiring injection of radio-opaque contrast agents. As performing angiography was dangerous for our patients with severe kyphotic deformity, we refused carrying out that examination. Alternatively, we used MIMICS software to establish a 3D reconstruction model of the aorta. This accurate method could measure the length of the aorta by measuring the length of the aortic diameter, without application of angiography, which could reflect the changes in the length of aorta.
Compared with previous methods described in the literature, the proposed method possesses a number of advantages as follows: firstly, for patients with severe kyphotic deformity, especially for patients with Pott’s thoracolumbar angular kyphotic deformity, the aorta ran in different directions, and it was hence incorrect to measure each segment of the aorta by 2D images. However, we can determine the 3D reconstruction model of the aorta by using MIMICS software, resulting in a precise measurement. Secondly, patients with severe kyphotic deformity are commonly complicated by ischemia, therefore, angiography for such patients may be dangerous. With the help of MIMICS, the risk of ischemia is significantly reduced. In addition, the fixed two points can eliminate the effects of movement of the aorta caused by the correction of deformity.
Although the proposed method could be used in an invasive manner to measure the length of aorta, it still has some limitations. Firstly, the proposed method requires calibration of location of aorta for several times manually, demonstrating that the mentioned method is time- and energy-consuming. Furthermore, due to anatomical variations of patients with deformity, an experienced spine surgeon should measure its length to reduce the error.