| Background:Tibial plateau fracture is a kind of common injuries in traumatic orthopedic, with the growing increase of traffic accident injury, its incidence is also on the rise. Tibial plateau fracture is intra-articular fracture, which may cause the destruction of the articular surface of tibial plateau and affect the knee joint function. It is difficult to treat and easy to cause joint dysfunction. Posterior column fractures of tibial plateau is a special type, most of which are the result of the high-energy injuries, and are often part of the complex tibial plateau fractures, also it can appear alone. The mechanism of this injury is mainly because of the axial violence on the posterior tibial condyle when knee joint is flexing. When in severe trauma, it can also cause damages of cruciate ligament, meniscus and popliteal fossa vessels in different degrees.For a long time, the posterior column fracture of tibial plateau did not get enough attention and fully understanding. The fracture lines of posterior column fracture are usually located in coronal plane; however, the posteromedial condylar and posterolateral condylar are overlap in lateral X-ray images and cannot be accurately showed. It may cause missed diagnosis and interference treatment. The traditional classification systems like Schatzker classification and AO classification are not descript the posterior column fracture independently; blind area exists in guiding clinical treatment and diagnosis. In recent years, basic and clinical research of tibial plateau fractures developed new trends. Due to the standard and mature treatment of the medial and lateral column fractures, research focuses gradually transfer to the posterior column fracture. Although a variety of surgical approaches and fixation products are constantly being proposed, the risk of nerves and vessels injury in popliteal fossa is high because of the complex anatomical structures of the posterior knee joint and the difficulty in surgical exposure and fracture reduction, especially for those with simultaneous posteromedial and posterolateral column fractures. The conventional surgery approaches and internal fixation devices are difficult to meet the requirements of fracture reduction and fixation.Medical equipment, especially fracture fixation devices, is strict in the requirement of the mechanical properties. If the poor designed internal fixation plates are use, the stress concentration may be caused in the screw holes of the plate and consequently cause plate fracture. Meanwhile, the plates cannot be too hard, otherwise is may affect fracture healing by making a strong effect of stress shielding. By conducting finite element analysis, the structure of stress, strain and displacement distribution can be showed. It enables designers to understand the mechanical characteristics of the structure, find the weak points of the structural strength or stiffness, and in the end improve and optimize the design.In the aspect of internal fixation choice, many scholars conducted anatomical measurements and devices designing for posterior tibial plateau; however, due to the irregular anatomical structure and inaccurate description, no substantive progress has been made. Until now, there is no widely accepted and used dedicated anatomical plate for posterior tibial plateau. Surgeons have to use manual bended non-dedicated plates, such as plates for upper extremity and universal plates, to fix the fracture fragments of posterior tibial plateau. Non-exclusive plates cannot completely fit the fracture site; it is difficult to reach the requirements of solid fixation and may affect the quality of fracture fixation.By controlling the shape, structure, material properties and loading conditions of tissues, the finite element analysis method can simulate the mechanical environment of the body more accurately. For complex biomechanical analysis, it possesses high repeatability, easy control of experimental conditions and shorter experiment time, which provide a broad prospect for the development of orthopedic biomechanics.In summary, we will conduct this study by fine measurement of the anatomical structure of proximal tibial and design tibial plateau anatomic plates for Chinese people based on the original material of three-dimensional imaging data, verify its feasibility and practicality with the finite element analysis method, and finally expect to apply the plates clinically.Objectives:1. The three-dimensional morphological measurements of proximal posterior tibia were conducted to determine the distribution range and correlation of relevant anatomical parameters thus provide reference for the design of proximal posterior tibia plates and artificial knee prosthesis.2. New anatomical plates for proximal posterior tibia were designed and assessed its mechanic capability and feasibility of clinical application with three-dimensional finite element biomechanics analysis and control study.Methods:1. Imaging data acquisition and anatomical measurement60intact, healthy and dry tibial bone specimens (each30specimens in left and right groups) were conducted CT scans. The images were output in the form of DICOM and then inputted into Mimics14.1to reconstruct the tibial by digital three-dimensional reconstruction techniques. The anatomical sites were marked and the relevant anatomical parameters of proximal posterior tibia were measured.2. The design of anatomical platesThe plates, including anatomical plates for posterolateral, posteromedial column fracture and plates for posterior middle fracture, which can fit the geometric morphologic characteristics, were portrayed based on the anatomical measurement results in the SolidWorks software.3. The construction of fracture model and the assembly of finite element modelA healthy adult female volunteer was selected and the X-ray was applied to exclude lesions and mutation of lower extremities. Then the spiral CT scan, with the slice thickness of0.625mm, was conducted to get lower limbs tomography image data. The data was imported into Mimics14.1software to build a three-dimensional model of the lower limb bones, then the model was imported into Geomagic Studio10.0software for smooth handling and simulated medial column or posterior midline osteotomy. The finite element models of different fixation methods were generated in accordance with the requirements of the orthopedic surgical fixation.4. Finite element biomechanics analysisFinite element analysis is divided into three studies, the first study is comparative study of the posterolateral tibial plateau column fracture fixation with anatomic plates and "T" type plate, the second study is comparative study of the posteromedial tibial plateau column fracture fixation with anatomic plates and "T" type plate, the third study is comparative study of the posterior middle tibial plateau fracture fixation with anatomic plates and "T" type plate. The above finite element fracture models were imported into ANSYS14.5software, the material properties, boundary conditions and loading mode were set. Then the normal one-leg load of slow walking (750N) was simulated, the analysis were conducted at the peak maximum. The assessment criteria are the stress distributions of the tibia, fracture fragment and plates and displacement values of fracture fragment and plates.Results:1. The CT-based reconstructional three-dimensional model has a high fidelity and a strong stereoscopic impression and can free to rotate to any angle to observe and measure. It comprehensively displayed the complex geometry shape of proximal tibia. Measurement results are as follows:the posterior central height of tibial plateau (8.46±1.62) mm, the posteromedial height of tibial plateau (12.27±1.93) mm, the posteromedial slope length of tibial plateau (14.71±2.27) mm, the posteromedial plateau-slope angle (132.02±11.62) mm, the posteromedial slope-diaphysis angle (147.28±10.72) mm, the posterolateral height of tibial plateau (11.31±1.74) mm, the posterolateral slope length of tibial plateau (14.45±2.26) mm, the posterolateral plateau-slope angle (124.01±9.81) mm, the posterolateral slope-diaphysis angle (141.88±9.09) mm, all measured parameters showed no significant difference on both sides (P>0.05). The posterior central height, the posterolateral height and the posterolateral slope length of tibial plateau are correlated to the total length of tibia (P <0.01).2. A complete tibia three-dimensional model was built using Mimics, Geomagic Studio and ANSYS software. After the finite element verification were established, the posteromedial column fracture model and posterior middle fracture model were built separately and been assembled with anatomical plates or T-shaped plates to build complete fracture-plate3D models.3. The finite element analysis was divided into three groups (posterolateral column fracture, posteromedial column fracture and posterior middle fracture). The posteromedial column fracture study showed that the overall stress distribution throughout the tibial was uniform and no stress concentration appeared after both anatomical and T-shaped plate fixation. The stress distribution was more reasonable (the maximum stress of internal fixation were51.024MPa and88.726MPa respectively) and the replacement was smaller (the maximum displacement of the fracture fragments were3.7701mm and6.6905mm respectively, the maximum displacement of the internal fixation were2.0731mm and6.7007mm respectively) in anatomical plate than in T-shaped plate. The posterior middle fracture study showed that the stress distribution was more reasonable (the maximum stress of internal fixation were31.438MPa and70.04IMPa respectively) in anatomical plate than in T-shaped plate. The replacement of fracture fragment and internal fixation was similar in anatomical plate than in T-shaped plate (the maximum displacement of the fracture fragments were6.9950mm and7.0048mm respectively, the maximum displacement of the internal fixation were6.9065mm and6.4828mm respectively).Conclusions:1. Basic principles and methods of three-dimensional imaging technology and digital medicine were used in this study. The three-dimensional model of tibial has a high similarity geometric, can accurately reflect the local anatomical features of the bones, has an accurate and reliable anatomical measurement results and is reusable. The anatomical measurement results provide a basis for plate designing. The tibial plateau posterior column fracture three-dimensional finite element models that generated by simulation osteotomy and fixation assembly are similar to the entity. They meet the requirements of the experimental analysis, the finite element analysis results are clear, intuitive and easy to observe.2. Both the anatomical plate and the traditional T-shaped plate can achieve the purpose of effectively fixation of tibial plateau posterolateral and posteromedial column fracture. The stress distribution was more reasonable in anatomical plate fixation, the occurrence of fatigue fracture of plate and fracture redisplacement is lower. It is a better choice for clinical use.3. Both the anatomical plate and the traditional T-shaped plate can achieve the purpose of effectively fixation of tibial plateau posteromedial column fracture and the internal fixation replacement values are close in both plates. The anatomical plate has a lower stress value and a more reasonable stress distribution, which indicates a better mechanical capability and more suitable for clinical application.4.Finite element analysis method applied in this study has some deficiencies. Because of the application of simplified models, ignoring the tension around the knee muscles, ligaments and other soft tissues was ignored; addition, the tibia is assumed to be homogeneous and the same properties of materials, which is different from bone entity. The stress loading method is also different from the fact. Finite element analysis and traditional biomechanical experiences should be combined to complement advantages in order to make results more realistic and objective. |
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