In a more intense physical training exercise, such as football, basketball, and rugby, the athletes are in a state of high-speed movement, and the fracture is a common serious injury. When treatment, it is necessary to restore the displaced fracture to normal place or close to the original anatomical relationship, in order to restore the scaffolding effect of the bone. After the fracture is restored, it is easy to slip again due to instability. Therefore, it is fixed in a satisfactory position by different methods to gradually heal. Commonly used fixing methods are: small splint, plaster bandage, external fixing bracket, traction brake fixing, etc. These fixing methods are called external fixation. If it is fixed by a surgical plate, a steel needle, a nail, an intramedullary nail, a screw, etc. We called internal fixation.
Medical devices, especially fracture fixers, have very strict requirements on mechanical properties. For example, in the bone plate for internal fixation of the fracture, the steel nail mounting hole on the plate is likely to cause stress concentration, resulting in fracture of the bone plate. At the same time, the bone plate can’t be made too hard, otherwise it will have a strong stress shielding effect on the healing bone and affect bone healing. The emergence of the finite element method effectively solves the above problems. The finite element method is a numerical algorithm used to analyze structural stress and strain in mechanical engineering. Through the finite element calculation, the stress, strain and displacement distribution of the fixed structure can be displayed, so that the designer can understand the mechanical properties and find the weak points of the structural strength or stiffness, thereby improving and optimizing the design to meet the mechanical performance requirements of the medical device. However, the medical industry practitioners do not have the theoretical basis of finite element analysis. The large-scale general finite element analysis software has complex analysis procedures and many parameters to be set. It is difficult for these people who have weak foundations to master the analysis methods in a short period of time.
Simright is designed to make simulation simple and efficient. The launch of the Simulator software is a good solution to the above problem. Simulator is a cloud structure simulation analysis software based on finite element method, which can help designers and engineers to perform structural quick check analysis online through a web browser. The software is simple in operation and quick in calculation response, and provides a user-friendly navigation menu bar for users to quickly grasp.
Taking the stress analysis of bone plate for internal fixation of tibia fracture with the Simulator as an example, firstly obtained by CT scan to obtain the original bone data, and then the 3D reconstruction technique is used to obtain an accurate three-dimensional model of the tibia for finite element analysis. The three-dimensional model of the tibia is shown below.
Import the acquired geometric model and the bone plate model into the Simulator for pre-processing. The intelligent contact recognition function of the software automatically binds the bone plate screw to the tibia, which saves the beginners from complicated contact setting work. The powerful meshing engine automatically adapts to complex feature geometries, generates high-quality meshes, and easily performs pre-processing.
By restraining the displacement and applying load at both ends of the tibia, the stress state of the internal fixation plate after fracture and the stress distribution of the broken bone were simulated to determine whether the bone plate structure would affect bone healing. And By predicting the stress state of the bones and bone plates after surgery, the risk of the surgical plan is greatly reduced.
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The external fixation stent is also very demanding on mechanical properties. Clinical studies have shown that the biomechanical properties of external fixation frame are poor, but because of its convenient operation, it does not damage blood supply at fracture site, and is suitable for severe open injury and infection cases. It is a more effective treatment for fractures.
Taking the fracture external fixation frame commonly used in clinical practice as an example, the geometry of fracture model is simplified to a thick-walled cylinder. The gap between two fracture segments is 1 cm, and the distance between bone and frame is 4 cm. The connection of external fixation frame and fracture of segment is shown in the figure below.
The stress state of fracture model is simplified to compression, bending and torsional loads of upper fracture segment, and the root of lower fracture segment is fixed. The displacement cloud diagram of simplified model of bone and stress distribution of external fixation bracket are shown in the figure below.
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Simulator has a variety of load loading methods and boundary constraints, which can easily simulate the stress of fracture model and fixed bracket. At the same time, the material library provides common metal and non-metal materials, and even the weaker personnel can quickly complete the mechanical analysis of external fixed support.