Three-dimensional reconstruction technology is the cornerstone of digital surgical technology, and it has a milestone significance as the beginning of digital technology. Three-dimensional reconstruction technology can not only provide intuitive, clear and specific three-dimensional tissue images, but also can be controlled by doctors in the digital software to make them move. Thus, doctors can observe the lesions and their adjacent relationship with the surrounding important anatomical structures from various angles, which are more intuitively. Surgeons can also judge the location and range of tumors so as to determine the safe boundary for tumor resection. It is obvious that the technology provide strong support to make accurate diagnosis and treatment [11].
Three dimensional reconstruction technology is also widely used in clinical practice. It is also one of the earliest digital technologies applied in our department. At present, patients with advanced head and neck malignant tumor who need surgical treatment in our department are treated with three-dimensional reconstruction routinely when important adjacent tissues or structures of head and neck are involved. In this study, all patients in DS group used 3D reconstruction technology before operation. With this technology, we can accurately reconstruct the three-dimensional structure of head and neck in computer software, and judge the location, range, invasion and destruction of bone tissue on the 3D reconstruction model. Intuitive three-dimensional images help the doctor to design the operation and implement accurate resection (Fig. 3-b). At the same time, it is helpful for surgeons to explain the operation plan to patients before operation and it promote the communication between doctors and patients. Our results also show that the combination of 3D reconstructed images and 3D printed models can effectively improve the postoperative satisfaction of patients.
CAD technology is based on imaging data, which in the digital software for virtual design of surgical process. In our clinical work, we found that in the traditional treatment mode, the resection range of head and neck tumor is usually roughly determined by the operator according to clinical examination and imaging examination, which lacks personalized surgical design. With the prevalence of vascularized free tissue flap repair and reconstruction, for example, when the tumor area is large and the maxilla and mandible are involved, the appearance of the patients is obviously effected. The restoration of occlusion relationship and the three-dimensional position of the grafts are usually determined by the experience of the operator. However, this "experience dependent" positioning method usually lacks sufficient accuracy and stability, resulting in inaccurate head and neck reconstruction and transplantation. If three-dimensional position of bone reconstruction is not ideal, it is difficult to obtain satisfactory occlusal relationship and masticatory function recovery, and can not achieve the precise reconstruction of personalized function and beauty.
And CAD technology enables doctors to use various digital software to carry out tumor resection and reconstruction in virtual model before operation. According to the nature and three-dimensional position of the tumor, the scope of resection was determined, and especially when bone reconstruction is involved, the position of osteotomy line is designed in the digital software for virtual osteotomy [12]. In particular, the mandible has a unique horseshoe-shaped structure. Mandibular tumors usually lead to destruction of the mandible bone, so it is difficult to restore the normal shape of the mandible [13]. In the cases of mandibular reconstruction we provided, we used CAD technology to simulate the whole mandible before operation, and restored the shape of mandible according to the data before mandible amputation by digital software. According to the range and location of the defect, the length and angle of each segment of bone graft were precisely designed to meet the needs of shape and function repair in three-dimensional position (Fig. 1a, b).
The core of CAM technology is 3D printing technology. In recent years, there are more and more auxiliary applications in head and neck surgery. This technique is one of the important ways to transform the preoperative design into the actual operation process. At the same time, we can design the osteotomy guide plate, shaping guide plate and other surgical guide plates simultaneously while making the virtual design scheme for patients with head and neck tumor involving the jaw bone, and manufacture the same proportion of real objects through 3D printing technology. In the process of mandible osteotomy, fibula cutting and shaping, the corresponding 3D printing guide plate is used to guide the operation, so as to transform the preoperative virtual design scheme into the actual operation. By this way, we can achieve the goal of precise resection and accurate reconstruction. In addition, according to the preoperative design, the reconstruction model of mandible after fibula or iliac reconstruction can be printed out, and personalized reconstruction titanium plate can be pre-bent to guide the accurate restoration of jaw shape and occlusion relationship (Fig. 1C and Fig. 3C), which reduces the dependence on subjective experience, simplifies the operation and reduces the difficulty of operation. Some studies [14] compared the coincidence degree between preoperative design and postoperative actual mandible, fibula osteotomy line and reconstruction titanium plate. It was considered that the maximum error of reconstruction came from the manual bending reconstruction titanium plate, which also proved the reliability of digital surgical technology applied to jaw defect reconstruction. CAD / CAM technology is used in most cases in this study. The results of this study also show that the pre-bent titanium plate can better shape and reduce the stress of titanium plate. It also reduce the risk of titanium plate displacement, deformation and exposure after surgery. Patients could obtain better facial appearance and reduce unnecessary broad scar. Other surgical related complications also decreased from the study results, although there was no statistically significant difference.
It must be pointed out that although CAD / CAM technology has many advantages, it still has some shortcomings and limitations in our clinical work. The existing CAD technology is mainly based on bone tissue structure, which can not accurately estimate and judge the influence of soft tissue. All kinds of surgical guides are designed based on bone structure. In the actual operation process, the influence of soft tissue can not be ignored. On the one hand, the existence of soft tissue affects the preoperative judgment of tumor range. Once it is found that the actual resection range needs to be changed during the operation, the surgical guide plate will not be used; on the other hand, it will affect the fitting degree of the surgical guide plate and bone tissue, which will affect the accuracy of the operation to a certain extent.
In order to accurately estimate and judge the influence of soft tissue and solve the above problems, VR, AR and MR techniques have been gradually used in head and neck surgery in recent years. These technologies can provide "perspective function", which is equivalent to wearing "perspective eye" for doctors. Earlier, our department took the lead in the application of VR technology in preoperative evaluation and simulation, and achieved certain results [15]. Recently, we increased the application of MR technology in the reconstruction surgery, adjusted the imaging model of the patient, used the navigation technology embedded matching positioning on the patient, and operated the operation through the panoramic stereo imaging in the AR glasses. Moreover, with the displacement of the patient's position during the operation, the image can still maintain accurate positioning to assist the implementation of the precise operation (Fig. 7b-d). After our exploration, we found that the main advantages of this kind of technology are: (1) the new imaging technology can form embedded three-dimensional images, which can display the complex soft tissue situation in front of clinicians more intuitively. (2) Do not need to rely on the doctor's subjective impression to avoid the surgical risk caused by visual loopholes. (3) Reflect the osteotomy angle and osteotomy line planned before surgery in the operation.
In addition to the above-mentioned digital surgical techniques commonly used in our department, with the development of science and technology and social economy, more and more emerging technologies are used for precise repair and personalized reconstruction of head and neck tumors. Surgical navigation technology is another effective way to transform virtual design into surgical practice. Compared with the surgical guide plate, the advantage of navigation technology is that it can carry out "real-time" verification and guidance in three-dimensional position. The preoperative design of the surgical scheme can not only be carried out accurately, but also be flexibly adjusted according to the actual situation [16]. Three dimensional measurement and evaluation technology can match the reconstructed jaw model with the ideal designed model before operation, and analyze the reconstruction error by chromatographic analysis. The difference of the coordinates and angles of the main landmarks before and after the operation was compared to evaluate the accuracy of the repair and reconstruction. This method provides a quantitative evaluation standard for the reconstruction effect, and can intuitively help the surgeon to find intraoperative problems in order to better advance and improvement [17]. The surgical robot has a "sensing system" and a "vision system", which can accurately locate the operation position according to the preoperative design. In recent years, it has been used in a variety of head and neck surgery, and achieved good therapeutic effect [18]. However, there are few reports on the reconstruction of jaw defects. In recent years, it has been reported that the model and animal experiment of robot assisted free fibula flap for mandibular defect repair [19]. The experimental results show that the repair accuracy of surgical robot is significantly better than that of traditional surgery, which confirms the application value and advantages of surgical robot in mandibular reconstruction surgery.
The application of these digital surgical technologies can not only ensure the safety of surgery, reduce the difficulty of surgery, improve the effect of repair and facilitate the postoperative function, but also shorten the process of surgery and the recovery time of patients to a certain extent. However, it must be pointed out that our research results show that due to the high equipment cost, material cost and labor cost of these technologies, although there are many advantages and can save the time cost of doctors and patients, it also significantly increases the cost of surgery and hospitalization for patients. Therefore, in the process of clinical application, we can not only consider the advantages of the technology itself, but also combine the patient's own situation and economic conditions to selectively use effective digital technology. After all, compared with conventional experience repair, most of the indicators in this study, especially in the repair effect and the incidence of complications, have shown certain advantages, but there is no significant statistical difference. Of course, the limited sample size and retrospective research methods limit the stability and reliability of the research results, so in order to obtain more specific, accurate and comprehensive evaluation results, we need to further carry out large sample randomized controlled trials to verify. It is safe to say that under the guidance of the concept of precision medicine, with the development of digital technology and the efforts of clinicians, the level of head and neck reconstruction is bound to be raised to a new height.