We developed two reconstruction techniques using patient-specific 3D printing graft reconstruction guides: 1) MBT using the visualization model designed based on the realistic-shaped graft model that contains the main aortic body and its branching vessels, making it possible to manually position the branching grafts on the artificial aortic graft and 2) GBT using the marking guides, in which the branching vessels in the visualization model were replaced by slightly protruding marking points. The patient-specific 3D printed graft reconstruction guides may provide following benefits: 1) The marking time can be minimized by checking and marking the ideal position of the patient’s segmental arteries in complex anatomy such as extremely tortuous spine and aorta. 2) With the improved accuracy and reproducibility of the aortic graft reconstruction, the techniques can be utilized easily even for those in the learning curves. 3) Owing to the improved procedural efficiency, the techniques may contribute to reducing the level of fatigue of operating surgeons during lengthy and exhausting surgery, thus increasing focus on important procedures.
Crawford extent II or III thoracoabdominal aortic aneurysm repair entails replacing the thoracoabdominal aorta and revascularising the visceral branches and intercostal or lumbar arteries simultaneously; therefore, it is regarded as the most extensive and challenging operation with high risks of surgery-related mortality and serious complications. The traditional Crawford’s island technique—a single aortic patch containing all four openings of visceral branches anastomosed with graft by side-to-side fashion—was previously accepted as a standard technique because it reduced the procedural burden19. However, it is reportedly common for patch aneurysm to develop in the remnant aortic island, especially among those with connective tissue disorders such as Marfan syndrome20–24. Although there are limited published reports on employing the pre-sewn multi-branched aortic graft in open repair of thoracoabdominal aortic aneurysm, its use is now a desirable option to prevent such aneurysm formation as observed in the conventional island-type aortic repair22,24−26. In addition, in cases where the ostia of the aortic branching arteries are displaced far away from each other, the use of a multi-branched graft may be the only way to effectively remove the diseased aorta.
Furthermore, paraplegia is a devastating complication of thoracoabdominal aortic aneurysm repair, particularly in extent II and III, and preventing it is a primary focus. Segmental arteries between T8 and L2 have been considered to play an important role in spinal cord protection and majority of institutes routinely incorporate large intercostal arteries into the surgery to restore spinal cord perfusion13,27. However, those arteries are mostly reimplanted as a single patch through side-by-side anastomosis, even when pre-sewn thoracoabdominal aortic aneurysm graft is used, which also increases the risk of future patch aneurysm, particularly in Marfan patients. To reconstruct a thoracoabdominal aorta using multi-branched aortic graft personalized to reflect individual anatomical variation, we introduce the use of MBT of 3DP for the open surgical repair of thoracoabdominal aortic aneurysm with reasonable operative outcomes. Furthermore, recently, we incorporated the GBT into the MBT to complement it and improve the procedural efficiency and accuracy. The aim of this study is to quantitatively evaluate these techniques.
In addition to the complexity of this high-risk open repair, it is difficult to ensure that vital branch arteries are in the proper positions when constructing patient-specific grafts. To overcome these challenges, Park et al. developed the octopod technique, an eight-branched aortic graft for reconstruction based on the IBT14. However, because the graft was reconstructed by measuring the diagonal line, height ,and angle based on CT images under anaesthetic induction in the operating room, it is difficult to understand the individual characteristics of patients in detail within a limited time, which affects the accuracy. For example, the second patient, who had Crawford extent II thoracoabdominal aortic aneurysm with severe scoliosis, had an extremely tortuous main aorta, affecting the visceral and segmental arteries, unlike the general anatomical structure4. Because the shape of the graft to be replaced should be connected to the aorta along the tortuous spine, the graft marked using the conventional IBT, calculated by slice thickness and number, may differ from the actual visceral arteries and segmental arteries positions. However, the MBT and GBT using graft reconstruction guides consisting of visualization model and marking guide efficiently reduce the graft marking time and solve anatomical hurdles. Using the three techniques, 135 mimic grafts (15 patients, three observers, and three techniques) ranging from aortic arch to iliac artery were evaluated in experiments. The grafts are a very realistic mimic of standard cylindrical model grafts they were used to bypass the expensive graft cost. The DGM, conventional IBT, MBT, and GBT were evaluated and compared based on graft marking accuracy and time requirements.
The errors of the experiments can be divided into marking error with medical images, 3DP errors, and human errors10,28,29. The marking errors of the conventional IBT were affected by the subjective measurement in CT images. The direction of the segmental arteries was measured from the centre points of the aorta and the segmental arteries, with the horizontal line. However, for the aneurysm patients, it manifested as elliptical, rather than circular, in the axial view, and the errors could be attributable to the incorrectness of the centre point of the aorta and the subjectivity of the centre point of the aorta and blood vessel (Supplementary Fig. S1)28,29. The differences of MBT and GBT arose from 3DP technologies errors, including machine and 3D printed model and guide errors. The machine error is triggered by environmental factors, such as temperature, humidity, and vibration, and the materials, resolution, and usage duration of the 3D printers. The 3D printed model and guide errors depend on the size, shape, printing direction, and printing angle of the guides and post-processing, including support removal, ultraviolet polymerization, and surface smoothing10,28. In addition, autoclave and steam sterilization with high temperatures can deform or distort the graft reconstruction guide30. To minimize such problems, we opted for ethylene oxide gas sterilization at a relatively low temperature. The three techniques were prone to human errors; errors also occurred when defined landmarks—diagonal line, height, and angle—are measured using a digital calliper and digital angle ruler in the experiments with the three observers. Even if only two landmarks were selected among the diagonal line, height, and angle, the third could be derived; however, the landmarks were measured directly without using a mathematical formula considering measurement error.
In the Bland-Altman analysis, the diagonal line, height, and angles in the conventional IBT at -45.96 to 33.83 mm, -46.70 to 33.34 mm, and − 39.05° to 13.05°, respectively, exhibited wider ranges of differences, compared to the MBT and GBT; the differences among the diagonal line and height tended to fall in the negative or positive region as the distance between the segmental artery and celiac artery increased, and the differences between the angles tended to be mostly distributed in the negative region from zero. Outliers tended to appear in the IBT as the distances from the celiac artery from the segmental arteries increased in the diagonal line and height, and occurred in patient with tortuous and swelling aneurysm aorta or scoliosis in the angle (Fig. 1a–c). In the MBT, the difference ranges for diagonal line, height, and angle were − 21.92 to 20.39 mm, -25.54 to 18.73 mm, and − 39.97° to 23.04°, respectively, and − 21.22 to 19.29 mm, -12.56 to 14.34 mm, and − 40.61° to 15.31°, respectively, in the GBT (Table 1). The diagonal line and height in the MBT and GBT were distributed in the region of the negative difference, as the measured distance was smaller, indicating a positive difference as the measured distance increased. The bias of the diagonal line and angles was greater in the GBT and the height was greater in the MBT (Fig. 1d-i). In the outliers of the MBT and GBT, the impact on the morphology of the aorta was greater than the distance of the segmental arteries. The MBT and GBT reduced the graft reconstruction time significantly, and the effect was proportional to the number of segmental arteries (Supplementary Fig. S2). For example, the graft reconstruction time for the first patient with the least number of segmental arteries was 10.5, 0.5, and 2.8 min with the conventional IBT, MBT, and GBT, respectively. For the fourteenth patient with 13 segmental arteries, graft reconstruction time was 36.5, 1.4, and 4.4 min with the IBT, MBT, and GBT, respectively. The average time requirement for the MBT and GBT reduced by 17.4 and 15.5 min, respectively, showing the effect reduced by more than six times compared to IBT. In addition, although, based on the marking time, the MBT was more efficient than the GBT, the GBT had superior accuracy. (Table 1).
The correlation coefficient (r14) for the diagonal line and height between the DGM and GBT was observed to be stronger than that of the IBT (r12) and MBT (r13), whereas a similar level of correlation was confirmed for the angles. Thus, it was implied that the GBT was the most similar to DGM (Table 2). In addition, the ICC was examined, to confirm the human error and the reproducibility of graft reconstruction among three observers in conventional IBT and new techniques. All the techniques showed high agreement, with 0.995 for the GBT and 0.986 for the IBT and MBT.
For the conventional IBT (without 3DP), and the MBT and GBT (with 3DP), questionnaires were administered to three surgeons with experience in the three techniques. The questionnaire had 26 questions classified into five categories: 1) level of contribution to understanding the anatomic structure, 2) usefulness for graft reconstruction, 3) satisfaction level for graft reconstruction, 4) benefits of 3DP technology to surgical outcomes, and 5) recommendability of 3DP for thoracoabdominal aorta surgery to other surgeons. For the contribution to understanding the anatomic structure, 58.3% of the answers indicated strong agreement, 25%, agreement, and 8.33%, neutral and disagreement for the MBT and GBT, whereas for the conventional IBT, 25% of the answers indicated neutral, 41.7%, disagreement, and 33.3%, strong disagreement. Under the usefulness for graft reconstruction, 88.9% of the answers indicated strong agreement and 11.11%, agreement, in the MBT and GBT, whereas 22.2% indicated disagreement and 77.8%, strong disagreement in the conventional IBT. Finally, for the MBT and GBT, satisfactoriness of graft reconstruction, surgical outcomes, and recommendability to other surgeons was 88.33%, 66.67%, and 16.67% of strong agreement, and 16.67%, 33.33%, and 83.33% of agreement, respectively, and, in the conventional IBT, 50% of disagreement and strong agreement were identified.
There are several limitations to this study. First, the procedures, from data acquisition to 3DP, lasted over a week, which made it difficult to apply the reconstruction techniques using patient-specific 3D printed graft reconstruction guides to open repair in patients with acute aortic rupture. Depending on the quality of the CT images, low-resolution images or slice thickness exceeding 3 mm made it difficult to identify the segmental arteries. In further studies, to reduce the graft reconstruction time, not only should the position of the segmental arteries on the graft be marked, functions, including the suturing and bonding process and the application for direct bioprinting process, should be developed.