3.1 The importance of correct classification of tibial plateau fractures and preoperative planning
The treatment of complex tibial plateau fractures has always been a difficult problem in orthopaedics [7]. It is often accompanied by ligament, meniscus injury and serious damage of nerve, blood vessel and soft tissue, which makes the treatment of fracture more difficult [8]. Patients often have varying degrees of dysfunction after operation, which seriously affects their ability to work. How to deal with complex tibial plateau fractures, reduce fracture complications, and make a good recovery of knee joint function is particularly important.
The correct classification and preoperative planning of tibial plateau fractures are very important for the selection of surgical approaches and fixation methods. CT scanning can scan the tibial plateau in axial, coronal and sagittal planes to show the full picture of the tibial plateau[13-15]. While 3D printing can have a more intuitive understanding of the whole tibial plateau and the details of the fracture, which makes various measurements more convenient. Thus, we can have a quantitative understanding of the degree of fracture collapse and splitting. Also, it can provide a better reference for surgical approach and internal fixation placement [9].
3.2 Development of classification methods for tibial plateau fractures
A good classification method of tibial plateau fracture not only needs to accurately reflect the degree of fracture injury, but also needs to guide clinical treatment. Hohl-Moore classification is a classification method based on X-ray, which divides tibial plateau fractures into 5 kinds of primary fractures and 5 kinds of fracture and dislocation. However, this method can not accurately reflect the degree of soft tissue injury during fracture, and it is difficult to guide clinical treatment. Schatzker classification increases the type of VI fracture with separation of metaphysis and diaphysis, which is widely used in clinic. However, it also has disadvantages. In practical clinical application, simple collapse fracture is rare and can not be effectively distinguished. The fracture of the posterior lateral column of tibial plateau is not distinguished, which is easy to cause missed diagnosis and affect the choice of surgical treatment. The content of AO classification is detailed, which is conducive to academic research and communication. However, the content is too complex to remember. Also, it can not accurately reflect the relationship between articular surface collapse and fracture severity. Thus, it is not competent to guide the choice of clinical treatment and prognosis [10]. On the basis of the above, Luo Congfeng et al suggested the classical three-column classification method based on three-dimensional CT and analyzed the shape and location of the fracture from a three-dimensional point of view for the first time. It is divided into internal, external and posterior three columns according to the division, which can accurately guide the surgical approach. But this classification did not put forward the concept of posteromedial and posterolateral tibial plateau fractures. Mao Yujiang et al put forward the theory of "four columns and four quadrants" on this basis. This classification distinguishes the morphological differences between posteromedial and posterolateral column fractures, and is of great significance for the guidance of clinical posterior column fractures [12].
With the emergence of 3D printing technology, we can better obtain the solid model of the fracture site before operation. Compared with the solid model, the surgeon has a deeper understanding of the local structure of the fracture. On the basis of accurate classification, it is of greater significance to guide clinical surgery[16-18].
3.3 Advantages of 3D printing technique in classification and preoperative planning of complex tibial plateau fractures
Compared with CT scanning, 3D printing provides more details about proximal tibial bone and fracture, even the internal details of fracture. 3D printing can intuitively classify and fix the fracture as a more detailed preoperative plan, guide the mode of operation, surgical approach and fixation, which can provide better preoperative guidance for clinical practice. And it can provide the possibility to better improve the classification of tibial plateau fracture. It has the following three advantages:
Psychological advantage: After the 3D model of complex tibial plateau fracture is printed, the operator can intuitively understand the fracture state and displacement. So that the surgeon can have more time and more intuitive to design the operation plan, so as to get twice the result with half the effort.
Operational advantages: According to the operation on the simulated 3D model before operation, the plates and screws can be implanted smoothly during the operation. For medial and lateral plateau fractures, we can often see the articular surface of the plateau, the reduction of the articular surface is not very difficult, but in complex plateau fractures involving posterior column fractures, it may not be easy to see the posterior articular surface during operation. Therefore, the preoperative surgical design, the pre-shaping of the steel plate and the direction and length of the screw are of great help to the operation. It greatly simplifies the difficulty of the operation, shortens the operation time and reduces the surgical trauma injury[19-20].
Communication advantages: before operation, we use 3D printed models to communicate with patients. So that patients have a better understanding of the severity of their own fractures, as well as a certain understanding of the surgical plan and the expected effect of treatment. In this way, it can also eliminate the patients' fear. And the compliance will be better.
In summary, 3D printing technology can be used to further refine the classification of complex tibial plateau fractures. The surgical approach and internal fixation plan are planned through the solid model, which is intuitive and accurate. And the preoperative planning scheme is feasible, which greatly simplifies the operation and reduces the surgical trauma injury. Also, it can be used as a routine item of preoperative preparation. In the future, under the guidance of 3D printing template, the optimized preoperative planning of tibial plateau fracture and accurate internal fixation operation will be better applied into clinic.