The Application of 3D Printing Technology in the Classication and Preoperative Planning of Complex Tibial Plateau Fractures

Background: Tibial plateau fracture is one of the common intra-articular fractures in clinic. And its accurate classication and treatment is a dicult problem for orthopedic surgeons. Our research aims to investigate the application value of 3D printing in the classication and preoperative planning of complex tibial plateau fractures. Methods: 28 cases of complex tibial plateau fractures diagnosed and treated in our hospital from January, 2017 to January, 2019.01 were analyzed. Preoperative spiral CT scan was performed and then DICOM data were input into the computer. We use Mimics to process data. And 3D printing technology was applied to print the 3D model of fracture (1:1). Combined with the 3D printed model, the tibial plateau fractures were subdivided into seven types according to the geometric plane of the tibial plateau. The surgical approach was determined on the 3D printed model. And then simulated operations such as accurate reduction of fracture and selection of plate placement were performed. Results: The reconstructed 3D model of tibial plateau fracture can accurately reect the direction of fracture components displacement and the degree of plateau collapse. Also, it can help with the preoperative reconstructive plan for the tibial plateau fracture. The intraoperative fracture details were basically the same as the 3D printed model. And The fracture surface of the tibial plateau of all 28 patients was well improved in terms of restoring the anatomical structure. Conclusion: 3D printing technology can be used to guide the classication and preoperative planning of complex tibial plateau fractures.


Background
Tibial plateau fracture is one of the common intra-articular fractures in clinic. And its accurate classi cation and treatment is a di cult problem for orthopedic surgeons [1]. At present, the commonly used clinical classi cation method of tibial plateau fracture was put forward by Schatzker et al. [2] in 1949, which is based on X-ray. It does not consider the displacement of fracture in sagittal position. So sometimes the classi cation can not effectively guide the formulation of treatment plan, especially in the case of posterior tibial plateau. In 2009, Professor Luo Congfeng [3] proposed a three-column classi cation method of tibial plateau fractures based on CT, which divides the tibial plateau into lateral column region, medial column region and posterior column region. However, this classi cation method can not directly re ect the degree of comminution and collapse of the articular surface of the fracture.
Also, this classi cation method can not guide the design of preoperative operation well. Complex tibial plateau fractures are often associated with two-column or three-column fractures. Good preoperative planning can greatly shorten the operation time and improve restoration effect. With the emergence of 3D printing digital medical technology, accurate and individualized treatment has become the trend of orthopaedic trauma surgery [4]. Difffferent literature reviews have revealed an increasing use of 3D-printed models in surgery [5], orthopedics [6] and orthopedic trauma [7], interventional radiology [8], surgical Page 4/16 teaching and assessment [9], etc. The reported advantages of 3DP-based approaches refer to the strong capabilities of customization based on patient imagistic data (computer tomography (CT), magnetic resonance imaging (MRI)), improved visualization of anatomy allowing better diagnosis evaluation, a decrease in operating time and radiologic exposure during surgery, improved intervention accuracy, and enhanced communication among physicians and with patients [5,7] 1. Methods 1.1 Inclusion and exclusion criteria for cases.
Inclusion criteria: cases of unilateral closed tibial plateau fracture treated by surgery in the department of orthopaedics of our hospital during 2017.01-2019.01. complex tibial plateau fractures with doublecolumn or three-column injuries. The time from injury to operation was less than 14 days.
Exclusion criteria: patients with chronic lesions of knee joint and knee joint dysfunction before injury. complicated with vascular and nerve injury on the affected side. those with serious underlying diseases or unable to cooperate with treatment.

General information.
A total of 28 patients were included in this study, including 20 males and 8 females, with an average age of 49.5 ± 2.5 years old. According to the theoretical basis of three-column classi cation of tibial plateau, combined with 3D printing model classi cation, there were 9 cases of type fracture, 7 cases of type fracture, 4 cases of type fracture and 8 cases of type fracture. All cases were treated with internal xation. The time from injury to operation was 12 days, with an average of 6.5 ± 1.3 days. This study has been approved by the Ethics Committee of our hospital. All patients have signed the informed consent form for the operation.
1.3 Using 3D printing model to re ne the classi cation of plateau fractures from the geometric plane 3column 3-zone typing method 3D model printing: all the 28 cases underwent 64-slice spiral CT thin-slice scanning (0.6mm) before operation, and the DICOM data were input into the computer. The Mimics software was used to process the data. And the 3D printing technique was used to print the three-dimensional model of the fracture (1:1).
Based on the classi cation of the geometric plane of the platform (Fig. 1), the overlooking view of the tibial plateau shows that the O point is the midpoint of the tibial spine line. The A' point is the tibial tubercle. The B' point is the medial crest of the tibial plateau. And the C 'point is the anterior edge of the bular head. The tibial plateau is divided into three plane parts by OA', OB' and OC', which are de ned as A zone, B zone and C zone respectively. (Table 1) The CT data of patients with quasi-fracture were processed on a special computer platform. And then the tibial plateau fracture model was printed 1:1 (Fig. 2). The printing machine is the selective laser sintering equipment Farsoon401. The printing material is nylon powder material for laser sintering.
The fractures were re-classi ed by three-column classi cation according to the fracture imaging data and 3D visual model so as to achieve accurate classi cation according to the principle.
Evaluate the displacement direction of the bone fracture block. And through the direction, distribution and movement of the fracture block, we can accurately evaluate the displacement direction of the bone fracture block.
Evaluate the collapse site of the articular surface. And through the detailed analysis and observation of the articular surface, we can determine the actual collapse site of the articular surface.
Establish the surgical approach. Through the analysis of the fracture mass and articular surface of the complex tibial plateau fracture, the intraoperative approach can be established to create conditions for reducing trauma injury.
Determine the position and the number of steel plate implantation. Predicting the position and number of steel plate implantation and the pre-bending data of steel plate before operation can effectively reduce the operation time, trauma injury and the use of anesthetic drugs.
Simulate the operation. The reduction of the fracture block and the placement of the steel plate can be performed on the 3D model according to the operation plan, so as to improve the pro ciency of the operation.
1.5 Preoperative scheme design of complex tibial plateau fracture (type -VII).
Type : supine position, choice of surgical approach: anterolateral peroneal head approach to x the lateral column, and whether to x it according to the stability of the posterior column (Fig. 4).
Type : oating position, choice of surgical approach: the meniscus was repaired by the anterolateral approach, the lateral column was xed by the anterolateral approach, and the medial column and the posterior column were xed by the posteromedial approach. (Fig. 6) 1.6 Surgical methods and postoperative management.
All patients were treated with general anesthesia or combined block anesthesia. After successful anesthesia, the affected limb was bound with a tourniquet with a pressure of 50 KPA for 90 minutes.
Antibiotics were routinely used before operation. Combined with preoperative classi cation, the operation was performed according to the surgical approach, fracture reduction mode, plate preshaping, screw direction and length designed before operation. During the operation, the mode and amount of bone graft were determined according to the collapse of the articular surface. Explore the articular surface to repair meniscus and ligament injuries that need one-stage surgical repair as far as possible [10]. Intraoperative C-arm uoroscopy con rmed the degree of fracture reduction and articular surface elevation. After operation, the negative pressure drainage tube was routinely indwelled and removed within 48 hours. Prophylactic use of antibiotics was used within 48 hours after operation. The contraction exercise of quadriceps femoris was performed on the 3rd day after operation. The exion and extension function of knee joint began to exercise 1 week later and partial weight-bearing began to be carried out 6 weeks after operation. And after the fracture healing was con rmed by X-ray 3 months after operation, patients began to bear weight completely gradually.

Observation indicators.
1.7.1 The coincidence rate between the preoperative planning and the nal surgical plan.
Each case of complex platform fracture was designed according to the 3D printing model before operation. The speci c surgical approach and implant scheme were designed. The speci c operation plan was recorded. The consistency rate between the nal operation plan and the preoperative plan was obtained.
1.7.2 Knee joint function score.
The patients were followed up for 1 year. During the follow-up, the anterior and lateral lms of the knee joint were taken and the knee joint function was evaluated by HSS score [11]. HSS score>85 was excellent, 70-84 was good, 60-69 was fair, and score<59 was poor. The above data were analyzed by SPSS18.0 statistical software. χ 2 test was used for the comparison of counting data. T test was used for the comparison of measurement data. The difference was statistically signi cant (P<0.05).

2.1
The coincidence rate between the preoperative planning and the nal surgical plan.
The classi cation of tibial plateau fracture combined with 3D printing is basically consistent with what was seen during the operation. The fracture type and articular surface collapse seen during the operation are basically the same as the model, which is of great help to the understanding and operation of the operation. In all 28 cases, the nal operation plan of 26 cases was consistent with the design before operation. And 2 cases of them are type VII fracture. Before operation, the lateral column was xed by anterolateral approach and the medial column and posterior column were xed by posteromedial approach. The bone mass of lateral column was reduced and xed by anterolateral approach. It was found that the stability of posterior column was good. The coincidence rate between the preoperative planning and the nal surgical plan was 92.8% (the nal plan was consistent with the preoperative planning and design of the number of cases / total number of cases * 100%). The postoperative CT results showed that the collapse of the articular surface of the platform was well reduced in all 28 patients.

Knee joint function score.
During the follow-up 6 months after operation, the excellent and good rate of knee joint function was 85.7%. And the excellent and good rate of knee joint function 12 months after operation was 89.3%. Only one patient had poor knee joint function at 6 months after operation. And his knee joint function was improved after functional rehabilitation exercise. (Table 2)  3. Discussion

The importance of correct classi cation of tibial plateau fractures and preoperative planning
The treatment of complex tibial plateau fractures has always been a di cult problem in orthopaedics [12]. 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 di cult [13]. 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 classi cation and preoperative planning of tibial plateau fractures are very important for the selection of surgical approaches and xation methods. CT scanning can scan the tibial plateau in axial, coronal and sagittal planes to show the full picture of the tibial plateau [18][19][20]. 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 xation placement [14].

Development of classi cation methods for tibial plateau fractures
A good classi cation method of tibial plateau fracture not only needs to accurately re ect the degree of fracture injury, but also needs to guide clinical treatment. Hohl-Moore classi cation is a classi cation 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 re ect the degree of soft tissue injury during fracture, and it is di cult to guide clinical treatment. Schatzker classi cation 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 classi cation is detailed, which is conducive to academic research and communication. However, the content is too complex to remember. Also, it can not accurately re ect the relationship between articular surface collapse and fracture severity. Thus, it is not competent to guide the choice of clinical treatment and prognosis [15]. On the basis of the above, Luo Congfeng et al suggested the classical three-column classi cation method based on three-dimensional CT and analyzed the shape and location of the fracture from a three-dimensional point of view for the rst time [3]. It is divided into internal, external and posterior three columns according to the division, which can accurately guide the surgical approach. But this classi cation 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 the basis of three columns. This classi cation distinguishes the morphological differences between posteromedial and posterolateral column fractures, and is of great signi cance for the guidance of clinical posterior column fractures [17].
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 classi cation, it is of greater signi cance to guide clinical surgery [21][22][23].

Advantages of 3D printing technique in classi cation 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 [6][7]. 3D printing can intuitively classify and x the fracture as a more detailed preoperative plan, guide the mode of operation, surgical approach and xation, which can provide better preoperative guidance for clinical practice [24]. And it can provide the possibility to better improve the classi cation 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 di cult, 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 preshaping of the steel plate and the direction and length of the screw are of great help to the operation. It greatly simpli es the di culty of the operation, shortens the operation time and reduces the surgical trauma injury [25][26].
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 re ne the classi cation of complex tibial plateau fractures. The surgical approach and internal xation plan are planned through the solid model, which is intuitive and accurate. And the preoperative planning scheme is feasible, which greatly simpli es 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 xation operation will be better applied into clinic.

Declarations
Ethics approval and consent to participate All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.

Consent for publish
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.  Type V tibial plateau fracture A: 3D printed model B: Approach C,D: X-rays after the operation Figure 5 Type VI tibial plateau fracture A: 3D printed model B: Approach C,D: X-rays after the operation Figure 6 Type VII tibial plateau fracture A: 3D printed model B: Approach C,D: X-rays after the operation