3D printing technology is the common name of additive manufacturing, also known as Rapid proto-manufacturing (RP). Its various names reflect the characteristics of this manufacturing technology from different perspectives. Based on the principle of discrete pile-up, 3D model CAD data drives the direct manufacturing of parts. With the rapid development of 3D printing technology in recent years, many European and American countries have successively introduced policies and measures to promote the development of 3D printing industry. In China, the State Council also attaches great importance to the development of 3D printing technology. In the "863 Plan" and "Made in China 2025", it emphasizes to accelerate the development of additive manufacturing technology.

At present, medical applications of 3D printing can be divided into several categories: 3D bio-printing; Personalized planting and anatomical models; Auxiliary medical instruments, including artificial limbs, surgical guides, rehabilitation AIDS, etc.; Drug research. In the field of orthopedics, it is mainly used for preoperative solid model, surgical guide plate, implants, education and scientific research, etc., and has been successfully applied to patients in many medical institutions. 3D printing has been put into clinical application in many hospitals at home and abroad, such as The Oxford Performance Materials Company and the First Affiliated Hospital of Xi 'an Jiaotong University in China. Compared with the two-dimensional images based on X image, CT or MR scan, 3D printed preoperative model can reflect the patient's condition, which can help doctors to make preoperative diagnosis and planning more effectively. Meanwhile, through surgical simulation, it can shorten the operation time and reduce the operation risk. The application of 3D printing technology in the field of orthopedics depends on the accurate data of human anatomical structure derived from medical images, which has a very good application value. In this paper, the principle of 3D printing related to orthopedics, the application status of orthopedics in preoperative solid model, surgical guide plate, implants, clinical teaching and scientific research, as well as its challenges and shortcomings were reviewed. Finally, the future of 3D printing was prospected.   

The principle and key technology of 3D printing based on orthopedic application

3D printing based on orthopedic applications is mainly achieved through Reverse Engineering (RE) and rapid proto-typing (RP), the process of which is shown in Figure 1.


Figure 1. Flow chart of 3D printing based on orthopedic applications

1.1 Reverse engineering

Reverse engineering is a process of scanning and measuring existing physical objects with various digital devices, obtaining dense point cloud data, and then obtaining digital model and THREE-DIMENSIONAL entity modeling of physical objects through computer-aided design technology. At present, many related software have been developed in the field of medical application of reverse engineering, such as MIMICS, Geomagic, Imageware, etc., as well as CAD software commonly used in the mechanical field, such as UG,PROE, sold-Works -. Much of the software is based on miniature simulation software from Materialise, based in Belgium, which can patch and reconstruct the scanned data to refine the printed 3D model. Is based on medical CT, MRI image 3D reconstruction and rapid prototyping application of professional software, more mature, application functions are complete, has a good image editing function.

1.2 Rapid prototyping

Rapid prototyping technology, also known as 3D printing technology, or additive manufacturing technology, is an emerging manufacturing technology that began to emerge gradually in the late 1980s. Based on the principle of layer upon layer, 3D printing technology is processed and formed as a solid model. It is characterized by digitalization, networking, personalization and customization, and is considered as the core technology to promote the third industrial revolution. At present, it has been vigorously developed as a strategic emerging industry in various countries, showing a bright future in the field of orthopedics.

Additive manufacturing technologies based on orthopedic treatment mainly include stereoscopic photocuring molding technology (SLA), selective laser melting technology (SLM), melt deposition technology (FDM), layered solid manufacturing technology (LOM), etc. In the field of orthopedics,SA has higher precision and faster molding speed. Combined with 3D printing technology, orthopaedic surgery becomes relatively easy and has great promotion value.

2. Application status of 3D printing technology in various fields of orthopedics

2.1 Preoperative solid model

The application of 3D printing in preoperative solid model of orthopedics is mainly reflected in the printing of 3D model of lesion site, which can provide doctors with more detailed anatomical information than medical image data and realize the transformation from 2D to 3D. 3D printing technology and reverse engineering technology, patients can be accurately printed entity model, the lesion site for physicians in the preoperative diagnosis of the lesion site complex relationships, such as 3 d printing neural anatomy model reflects the relationship between the lesions and normal brain structure (as shown in figure 2), help doctors to distinguish the neurovascular structures, such as this is one of the traditional CT image is difficult to do. In this way, patients can be explained more vividly and intuitively, and preoperative planning and simulation are more convenient

The 3D printing technologies applied to model printing mainly include SLA,DLP,SSFDM and so on


Figure 2. 3D model 1 for surgical planning by a neurosurgeon at Walter Reed National Military Medical Center

The application of 3D printing in preoperative solid model of orthopedics is relatively mature, and there are many successful cases and research reports at home and abroad.

(1) Domestic researchers such as Du Hao, Ding Huanwen, Yu Naichun and Diki Rong used 3D printed models to simulate preoperative planning and diagnosis, and successfully completed the operation with obvious effects. In August 2014, Professor Liu Zhongjun of The Third Hospital of Beijing Medical University completed the world's first 3D printed artificial vertebral body replacement operation. The first implant operation of 3D-printed titanium alloy prosthesis with direct metal molding in the First Affiliated Hospital of Xi 'an Jiaotong University -- the operation was planned and the optimal surgical incision was determined by using THE 3D printing model, and finally the 3D printed titanium alloy rib implant operation was successfully performed.

(2) The team at the BIOMED Institute in Belgium has successfully implanted the first 3D-printed titanium mandible prosthesis. According to the literature search, foreign case studies by scholars include Liu YF,xuLw, Sanghera, Kuhl, etc. Among them, Liu YF et al. used CT scanning and reverse engineering to reconstruct and print the mandible defect model, developed treatment plans and preoperative simulation, and determined relevant size parameters, which provided guarantee for the success of the operation. Digital design combined with 3D printing According to the printed bone joint prototype, the device size inserted into the medullary cavity can be designed, and the parameters of internal fixator or personalized prosthesis can be determined, so as to improve the safety and accuracy of surgery, thus improving the surgical efficacy.

Surgeons use 3D printing to assist in the treatment of complex surgical cases, such as the spine and pelvis in children. 3D printing is of great significance in the design of surgical plans, selection of implant type or external fixator, intraoperative reference to the patient's anatomy, accuracy of the osteotomy, and communication with the patient.

2.2 Surgical guide plate

The surgical guide plate is a surgical auxiliary positioning tool. With the progress and gradual popularization of D printing technology, the application of surgical guide plate has become the best choice for basic orthopedic surgeons. The advantages of 3D printing surgical navigation template are as follows: first, it can simplify operation, has auxiliary positioning function, has strong flexibility, and improves the accuracy of surgery; Secondly, it can reduce the risk of operation and improve the safety of operation, such as reducing the degree of blood vessel and nerve injury, and avoiding wound infection and other complications. Thirdly, the time and frequency of surgical fluoroscopy are reduced to protect doctors and patients from radiation exposure.

3D-print-based orthopedic surgical guide plate applications mainly include bone tumor resection, osteoarthritis surgery, complex fracture surgery, plastic or corrective surgery, etc. Among them, the common surgical site of the guide plate has the pelvis, joint, spine, etc.

Research progress of 3D printing technology in the field of orthopedics

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