3D printing technology, also known as rapid prototyping (RP), is a technology for manufacturing physical models by stacking and printing layer by layer; Simply put, it is based on the patient's CT or MRI and other imaging data, the data is processed through computer software to construct a three-dimensional model, and finally a 3D printer is used to print it[4, 5]. In recent years, with the development of computer science and the innovation of printing technology, the research of 3D printing technology in orthopedics, especially in bone defect repair and reconstruction has become the research hotspot and focus of clinical orthopedics doctors[6]. On this basis, bone tumor specialists combine their 3D printing, trauma orthopedic fracture treatment and tumor bone defect repair and reconstruction treatment concepts, and perform comprehensive and multi-angle evaluations based on three-dimensional images and printed physical models; Develop individualized and precise treatment plans, design surgical approaches, determine the length, arc, number and direction of screws, determine the amount of iliac bone removal, and perform reasonable segmentation and allocation; Improve the safety and accuracy of operation, reduce operation time, trauma and bleeding, and reduce the risk of operation[4]. 3D printing technology is a good combination of digital imaging data and biomaterials, and it is applied to the field of clinical orthopaedic treatment to provide a personalized and accurate surgical scheme for difficult and complex orthopedic diseases, especially for the repair and reconstruction of bone defects[7].
Irregular bone has a special and complex overall morphological structure, different shapes and great differences, and has a multifaceted structure; it is the starting and ending point of many important muscle tissues, surrounded by important nerves and blood vessels and other tissue structures. and most of the irregular bones are located in important functional areas, responsible for a large number of protection of important organs, movement and weight-bearing functions. Therefore, when irregular bone is injured or defective, its special anatomical structure increases the difficulty of treatment. Failure to restore its morphological structure will lead to the loss of some important functions and cause great damage to the spiritual life of patients[8]. Aneurysmal bone cyst is a benign bone tumor-like lesion with unknown etiology, which is highly invasive and destructive[9]. Its first discovery was reported by Jaffe and Lichtenstei et al [10] in 1942. The incidence of ABC accounts for about 1% of bone tumors, which are mainly concentrated in the long bones of extremities and spine, while irregular bones such as scapula are rare[9, 11]. Although ABC is a benign bone tumor, its biological behavior is often invasive and easy to relapse. Its invasive and recurrent characteristics often lead to more serious bone destruction, and severe cases can be associated with pathological fractures, which brings some difficulties to treatment[12]. The treatment of aneurysmal bone cysts that occur in irregular bones is more challenging, and the repair and reconstruction of bone defects are also more difficult[11].
The progress of 3D printing technology combined with the innovation of digital imaging equipment has greatly promoted the treatment of irregular bone and other parts of the tumor bone defect. 3D printing technology has outstanding advantages in repairing irregular bone tumor bone defects:(1) Develop a surgical plan: By using the computer, the location of the peripheral nerves and blood vessels of the focus can be observed in many directions and angles, so as to avoid accidental injury to the nerves and vessels during the operation and accurately measure the volume of the tumor and bone defect, which provides a basis for cleaning up the focus before operation;According to the printed model preformed steel plate, determine the length and Radian of the steel plate and the number and direction of screws, and customize the personalized and accurate operation plan[13, 14]. (2) Simulated operation: Simulate the operation according to the operation plan, constantly improve the operation plan, and determine the best incision position and internal fixation position and direction. So as to reduce the time of operation and the amount of bleeding, reduce the risk of operation and patients' medical expenses. (3) Reduce the risk of surgical operation: The preoperative chief surgeon can use the model to communicate and explain the whole operation process and its important nodes to the team, including anesthesiologists, instrument nurses and internal fixation suppliers, and to simulate the operation. to help the whole surgical team improve their surgical skills and efficiency before operation. During the operation, the model can be put on the operating table after disinfection, and the model can be referred to at any time during the operation, so as to reduce the peeling and injury of soft tissue, reduce the time of operation, reduce the time of intraoperative bleeding, reduce the time of anesthesia, the frequency of use of C-arm and the dosage of antibiotics during operation. to reduce the risk of surgery[14-16]. Stefan Tserovski et al[4] the use of 3D printing technology combined with printed models to assist in diagnosis and treatment in hip revision not only improves the accuracy of diagnosis, but also helps the team to determine the type and size of the prosthesis before operation. (4) Match the donor site ilium: Simulate and match the defect site with the iliac bone through the computer, and accurately select the scapular bone defect site with the same shape or volume as the donor site iliac bone extraction site, and mark the body surface before the operation for faster and more accurate extraction, reducing the operation time and reducing the operation trauma[17, 18]. (5) Improve the efficiency of doctor-patient communication: In the past, preoperative communication between doctors and patients was mostly based on the patients' own X-ray, CT and other imaging data. For patients and their families without medical knowledge, it is very difficult to fully understand the condition and surgery[5]. Through the computer three-dimensional simulation map and 3D printed solid model, the structure of the real lesion can be presented in front of the eyes, which can more intuitively show the characteristics of the lesion to the patients and their families, explain and explain the treatment plan. so that patients and their families have a clearer understanding of the disease, improve the efficiency of doctor-patient communication, improve the relationship between doctors and patients, but also help patients to cooperate with rehabilitation treatment in the later stage[14, 19].
Therefore, 3D printing technology is applied to the repair and reconstruction of irregular bone tumor bone defects, and the specific three-dimensional physical model can be printed based on the imaging data before the operation to further understand the specific situation of the tumor and bone defect and the distribution of blood vessels around the disease. Choose the appropriate personalized internal fixation, choose the appropriate approach and reduction method, and formulate the best surgical plan; effectively reduce the injury of the muscles, blood vessels and nerves during the operation, reduce the difficulty of the operation, shorten the operation time, and reduce the bleeding during the operation. Improve the safety of the operation, and reduce the damage of the donor site and the waste of the transplanted bone, thereby reducing the incidence of postoperative complications[1, 14, 19].
We only use 3D printed prosthesis for simulated surgery and select suitable iliac bones for repair and reconstruction, instead of directly using 3D printed prosthesis for treatment, mainly for the following reasons: (1) The average age of the patients is relatively young and the oldest age is only 32 years old. Compared with taking the discomfort of the iliac bone, directly using 3D printing prosthesis for treatment, the patient's long-term fixation of the foreign body in the body rejects the psychological and mental burden more severe; (2) Although the 3D printed prosthesis is closer to the defect than the iliac bone in the early stage, and it is easier to fix the muscle and other tissue structures, the iliac bone can be more in line with the physiological structure of the human body after long-term plastic transformation, and the muscles are more firmly attached;(3) Rejection and periprosthetic fractures are inevitable difficulties of the prosthesis. if they are serious, they may need to be treated by a second operation, which aggravates the trauma and economic burden of the patients[20, 21]; (4) The use of 3D printed prosthesis for repair and reconstruction, long-term shoulder joint activities may loosen or even fall off the screws, resulting in insecure fixation of the joints, loosening of the prosthesis, and muscle wear; and complications such as chronic pain are not conducive to postoperative recovery training[22]. Baichuan Wang et al[23] used computer-assisted 3d printed hemipelvis prosthesis to treat 11 cases of malignant bone tumors around the acetabulum, and 2 cases showed dislocation of hip prosthesis after surgery. Liang H et al[24] used three-dimensional printed pelvic prosthesis to reconstruct after resection of pelvic tumor. Of the 35 patients, 7 had delayed wound healing and 2 had hip dislocation. On the contrary, there is no rejection after repair and reconstruction with autogenous iliac bone; after absorption and shaping, the grafted bone can be completely integrated with the scapular bone to achieve bony healing, and the iliac bone and the scapular bone have the same contact area, and the muscle attaches more firmly to the bone surface. At the same time, the complications or adverse reactions such as chronic pain, rejection and prosthesis loosening can be avoided to the maximum extent, and the quality of life of patients can be improved[25].
We hope that the reported cases and treatments can provide a reference option for the repair and reconstruction of tumor bone defects in irregular bone sites. At the same time, this study also has some limitations and shortcomings. First of all, the follow-up time of the patients is short, and there is no comparative study with other treatment methods. Secondly, due to the small sample size, no statistical analysis was carried out. Finally, there are still differences in Constant-Murley scores due to individual factors such as patients' sensitivity to pain and the degree of completion of rehabilitation training. We hope to increase the number of samples, control the range of bone graft, prolong the follow-up time, explore a more objective evaluation system, and carry out statistical analysis in the later work. In the future, we hope to explore and make more use of the advantages of 3D printing technology, and combined with clinical practice to use it in the treatment of more bone tumor-related diseases for the benefit of patients.