Objective: To discuss a method to establish a three-dimensional model of healthy human knee joint, which can be used for further knee joint biomechanics analysis and simulation. Methods: CT scan and medical image three-dimensional reconstruction software (Mimics) were used to obtain the knee joint three-dimensional finite element model (FEM) according to reverse engineering theory. Results: FEM of knee joint with complete bone structure was established by Mimics. Conclusion: Three-dimensional FEM was established according to CT images exports as IGES file. The model can be used for knee joint biomechanics finite element analysis to provide references and proposals for the clinical diagnoses of knee joint illness, and the design of artificial knee joint prosthesis.
With the weight-bearing and motor function, knee joint is the most complex joint in human body. It is easily hurt or caught various diseases due to the mechanical environment and movement condition it is located. With the fastest-ageing society on earth, osteoarthritis and other diseases related will be a hot spot and it will affect people’s life standard. Reinforcing the research capacity has a magnificent meaning for improving elder people’s living quality. Current studies consider that the mechanism of osteoarthritis no matter caused by sports injuries or cartilage failure is the improper stress distribution in the joint [
Computer (CPU: Intel® Core™ i5-2430 2.40 GHz*2, RAM: 8.00 GB, GPU: GT-540M, OS: win7), CT images, Mimics medical image three-dimensional rebuilding software, Ansys 11.0 finite element analysis software. The CT images come from the database of visible human project of the US national library of medicine. 800 1 mm scanned healthy woman lower limbs CT images were downloaded as Dicom format. Mimics was programmed in 1992 and widely used in digital medical field. The initial propose was to apply CT scan images in rapid prototyping manufacturing. With the growing improvement, it is now widely used in Computer-Aided Mechanical Engineering, including medical three-dimensional modeling based on medical images, computer-aided design, finite element and hydromechanics analysis, rapid prototyping manufacturing, visual operation planning, anthropotomy measurement analysis, etc. Ansys is a powerful engineering stimulation software widely used in many fields including structural mechanics, multiphysics, fluid dynamics, explicit dynamics, electromagnetics, and hydrodynamics.
1) Input the data of the model: import the 800 Dicom CT images to Mimics. Original axial view, coronal plane and vertical plane from the scanned data was observed as
2) Rebuild the three-dimensional model: image thresholding segmentation was the first step of the modeling procedure and mask was obtained. Since it is the knee joint that need modeling, we selected the object region by “region growing” in the toolbar, shown as
3) Preliminary treatment of the finite element analysis: before the analysis, the model needed to be meshed to finite element grid model, this was obtained by FEA module in Mimics. The grid was optimized by remesh module. The finite element model (
4) Apply material properties to the model:
The parameters in
5) Loads and boundary conditions: approximately 40% of the body weight is applied to each knee when standing. In this paper, we consume the total weight is 60 Kg, so 235 N was applied on the mechanical axis of
Material | Young’s modulus (MPa) | Poisson’s radio (μ) |
---|---|---|
Femur | 12,000 | 0.3 |
Tibia | 6900 | 0.49 |
Patella | 12,000 | 0.3 |
the top femur. The boundary condition was set that tibia and femur were kept fixed in all direction. The model was solved by Ansys 11.0.
In this paper, we established the model of a healthy human knee joint, and conducted biomechanics analysis to it.
Von Mises stress was chosen to evaluate the stress index in this analysis. It is a combined stress defined according to the 4th strength theory reflecting the average stress level each dot inside the material, and one of the most objective indices in finite element analysis [
In this research, we built the knee joint model including distal femur, patella, and tibial plateau precisely based on the CT images of human lower limbs. This method can be used to establish knee joint model fast and accurately, and the file is suitable to directly transfer to finite element analysis software (Ansys) for biomechanics simulation.
However, the soft tissue of the knee joint (ligament, joint capsule, synovial fluid, etc.) was not obtained. This is due to the fact that CT image cannot provide the soft tissue outline as clear as the bone tissue [
Model with intact knee joint structure can be used in the further finite element analysis to simulate knee joint under certain conditions and the information obtained is beneficial to knee arthropathy diagnosis and knee prosthesis design [
traditional specimen test and clinical research cannot solve. Since 1960s, finite element method has widely applied in biomechanics analysis. It had successfully utilized in hip joint, knee joint, spine, shoulder, etc. [