Scoliosis correction effect evaluation method based on finite element analysis

Abstract

The invention relates to the field of finite element analysis and orthopedic braces, in particular to a scoliosis correction effect evaluation method based on finite element analysis. Comprising the steps of constructing a point cloud model according to a CT image; the point cloud model is converted into a triangular mesh model, the triangular mesh model is repaired and optimized, and then the triangular mesh model is converted into an entity curved surface model; the entity curved surface models are combined and assembled; material parameters and boundary conditions of all the parts are set, spring units are added, grid division is carried out, finite element simulation calculation is carried out, and stress and deformation results of the spine are obtained. According to the method, the effect of treating scoliosis by the brace is visualized by establishing the three-dimensional model and performing simulation analysis, reference is provided for design and application of the brace, and support is also provided for a personalized treatment scheme of a patient.

Description

Technical Field

[0001] The invention relates to the fields of finite element analysis and orthopedic braces, and in particular to a method for evaluating the effect of scoliosis correction based on finite element analysis. Background Art

[0002] Scoliosis is a three-dimensional deformity of the spine in which the spine curves sideways and is accompanied by rotation. A normal spine should be straight when viewed from the front or back, but in patients with scoliosis, the spine presents an "S" or "C" shaped curve. The severity of scoliosis can be measured by the Cobb angle, with a larger angle indicating a more severe curve: mild scoliosis (10-20 degrees), moderate scoliosis (20-40 degrees), and severe scoliosis (greater than 40 degrees). The treatment of patients with different scoliosis severities is also different. For patients with mild scoliosis, especially after the growth period has stopped, if the curvature is small, regular observation and monitoring can be performed. For moderate scoliosis (20-40 degrees), in patients during growth, wearing a brace may be recommended to prevent the curvature from worsening. Severe scoliosis (greater than 40 degrees), or in cases where brace treatment is ineffective, surgery may be required.

[0003] Finite element analysis is a numerical computing technique used to solve boundary value problems of complex physical systems. It simulates and predicts the behavior of the entire system by decomposing a continuum or structure into many interconnected finite small units (finite elements) and approximating the physical quantities (such as displacement, stress, temperature, electric field, etc.) on these small units. Finite element analysis is widely used in engineering and scientific fields such as mechanical design, civil engineering, aerospace, and automotive industries to analyze and optimize designs to improve safety, reliability, and performance.

[0004] During the treatment process of using braces to correct scoliosis, the correction effect is uncertain. The goal of brace treatment is to gradually correct the abnormal curvature of the spine by applying external force, so as to control the progression of the disease and improve the appearance of the spine. However, the correction effect of braces on the spine is a complex three-dimensional dynamic process, which is affected by many factors, such as the patient's age, gender, spinal flexibility, bone development, and the type and severity of the curvature. Traditional evaluation methods mainly rely on regular imaging examinations, which have obvious limitations: (1) Long-term use of medical imaging examinations will cause irreversible negative effects on the body of patients, especially adolescent patients. (2) Imaging evaluation can only provide information on changes in the spine on one plane, and it is difficult to fully describe the three-dimensional morphological changes of the spine in three-dimensional space. Finite element analysis can help solve these problems. By establishing a personalized three-dimensional spine model and brace model, the force and stress distribution applied by the brace on the spine are simulated, and the deformation and morphological changes of the spine during the correction process are predicted. Summary of the invention

[0005] In order to overcome the problem that it is difficult to evaluate the effect of the brace in treating scoliosis, the present invention provides a method for evaluating the effect of scoliosis correction based on finite element analysis, which can not only provide feedback on the correction effect of the brace, but also help doctors optimize the brace design and treatment plan, and improve the accuracy and effectiveness of the correction.

[0006] In order to achieve the above object, the present invention provides a method for evaluating the effect of scoliosis correction based on finite element analysis, comprising the following steps:

[0007] Step 1: Import the previous CT images into medical image processing software, extract each cone of the patient's spine, sacrum, ribs, costal cartilage, sternum, intervertebral disc, and human body contour, and export the model.

[0008] Step 2: Import the model processed in step 1 into the 3D scanning data processing and repair software. First, redraw the mesh of the model and subdivide the mesh so that the model can be processed more finely; then clean and repair the model, fill holes, remove features, delete nails, etc. to make the model surface smoother; finally, fit the model to the surface and export the model.

[0009] Step 3: First, create a spinal correction brace model that the patient needs to wear in the 3D modeling software. Then import the model processed in step 2 into the 3D modeling software, use the combination operation to distinguish the cancellous bone and cortical bone of the skeleton as well as the human skin and fat tissue in the model, then assemble all the processed models at the origin and export the model.

[0010] Step 4: Create a new static structure in the finite element analysis software, set the material parameters of cancellous bone, cortical bone, endplate, annulus fibrosus, anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, supraspinal ligament, interspinous ligament, intertransverse ligament, etc., import the model processed in step 3 into the finite element analysis software, and add material properties to the corresponding model. Then mesh the model, add the correction force of fixed support and brace to the model, and finally solve the model. View the equivalent stress and total deformation of the model, expressed in the form of cloud map.

[0011] Furthermore, the grid subdivision size in step 2 is 0.5mm-1mm.

[0012] Furthermore, the precise surface operations in step 2 include editing contour lines, constructing surface patches, constructing grids, fitting surfaces, etc. If intersections occur when constructing surface patches, the contour lines need to be re-edited; if intersections occur when constructing grids, the surface patches need to be repaired.

[0013] Furthermore, when performing mesh division in step 4, it should be ensured that the divided meshes exist in three layers or more on the model.

[0014] Furthermore, in step 4, each ligament is simulated using a spring unit.

[0015] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0016] (1) Finite element analysis can create an accurate three-dimensional spinal model based on the patient's individual data (such as CT or MRI images). Taking into account the individual differences of each patient, such as anatomical structure, bone density, and soft tissue characteristics, it can perform highly personalized correction effect evaluation and provide more accurate correction mechanical analysis results.

[0017] (2) Since finite element analysis performs simulation calculations based on the initial imaging data, it can reduce the number of times patients undergo repeated X-rays or other radiological imaging examinations during the entire treatment process, thereby reducing the risk of radiation exposure.

[0018] (3) Finite element analysis visualizes the effect of the brace's corrective force on the spine, helping doctors and engineers to more intuitively understand how the force exerted by the brace on the spine affects the correction effect. Through visual mechanical analysis, doctors can better judge whether the brace has applied sufficient corrective force to the target area, while avoiding unnecessary pressure or stress concentration on non-target areas, thereby improving the brace's correction efficiency and the patient's wearing comfort. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0020] Figure 1 Schematic diagram of the process of the correction effect evaluation method of the present invention;

[0021] Figure 2 is a schematic diagram of extracting CT images in an embodiment of the present invention;

[0022] Figure 3 is a schematic diagram of re-gridding in an embodiment of the present invention;

[0023] Figure 4 is a schematic diagram of a fitting surface in an embodiment of the present invention;

[0024] Figure 5 This is a schematic diagram of a 3D model constructed in an embodiment of the present invention;

[0025] Figure 6 It is a schematic diagram of adding a spring unit in an embodiment of the present invention;

[0026] Figure 7 The resultant stress distribution cloud diagram of the bone in the embodiment of the present invention;

[0027] Figure 8 The result deformation distribution cloud diagram of the skeleton in the embodiment of the present invention;

[0028] Fig. 9 It is a cloud diagram of the resulting deformation distribution of the spine in the embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the purpose, technical solution and advantages of the embodiment of the present invention, the technical solution in the embodiment of the present invention is now described in detail in conjunction with the accompanying drawings. It should be pointed out that the described embodiment is only a part of the present invention, not all. The present invention is further described in detail below in conjunction with the accompanying drawings:

[0030] like Figure 1 As shown, the present invention discloses a method for evaluating the effect of scoliosis correction based on finite element analysis, comprising:

[0031] S1: construct a point cloud model based on the CT image. In this embodiment, MimicsResearch software is used to construct the point cloud model.

[0032] Specifically, the CT images were imported into Mimics Research software, and the images to be extracted were selected using the “threshold”, such as Figure 2 As shown in the figure, the cones of the spine, sacrum, ribs, costal cartilage, sternum, intervertebral discs, and some organ tissues in the CT are extracted in sequence and saved as .STL format files. These bones or tissues need to be extracted separately to ensure the accuracy of the model and avoid crossover.

[0033] S2: Convert the point cloud model into a triangular mesh model in the 3D scanning data processing and repair software, repair and optimize the model, and then convert it into a solid surface model.

[0034] In this embodiment, the 3D scanning data processing and repair software uses Geomagic Wrap software. Specifically, the .STL format model processed in step S1 is imported into Geomagic Wrap software, and the surface patches at the self-intersection of the model are first deleted, and the holes of the model are filled using "Fill All" to make the model a closed surface. Then the model is "re-meshed" and the target side lengths of the cones of the spine, sacrum, ribs, costal cartilage, sternum, intervertebral discs, and some organ tissues are set to 0.1mm-0.3mm, and the target side lengths of the body surface contours are set to 4mm-6mm. Figure 3As shown. Then select the rough and obvious protruding noise points on the model surface, and perform the "Remove Features" operation until the model is roughly smooth and flat, and delete the small and scattered surface patches at the edge of the model. Select the entire model, and perform the "Delete Spikes" operation on the model, with the smoothing level set to 50-70. Open the "Mesh Doctor" and check whether there are errors such as non-manifold edges, self-intersections, highly refractive edges, spikes, small components, small holes, etc. If so, use the "Auto Repair" function in the "Mesh Doctor" to repair them until no errors appear.

[0035] After processing the surface patch of the model, enter "Precise Surface" and draw the contour curve at the location where the surface curvature of the model changes significantly. Then construct the surface patch and then the grid. If an error message appears when constructing the surface patch or the grid, you need to adjust the contour curve until the grid is successfully constructed. Then perform the "Fit Surface" operation on the model to check whether the surface of the fitted model is smooth. Figure 4 As shown, export the .STP format file after confirmation.

[0036] At the same time, in this step, it is necessary to build a cancellous bone model of the skeleton and perform the "offset as a whole" operation on the skeleton model. The cones of each segment of the spine are offset inward by 0.5mm-1mm, the ribs are offset inward by 0.3mm-0.6mm, the sacrum is offset inward by 1mm-2mm, and the sternum is offset inward by 1mm-1.5mm. Repeat the S2 operation and finally export it to a .STP format file.

[0037] S3: Combine and assemble various solid surface models in 3D modeling software.

[0038] In the present embodiment, the three-dimensional modeling software adopts Solidworks software. Specifically, the .STP format model processed in step S2 is imported into Solidworks software, and first saved as .SLDPRT file format, so as to facilitate the subsequent processing of the model. First create an assembly file, import all the bone files, including the complete model and cancellous bone model of each segment of the cone of the spine, sacrum, ribs, costal cartilage, and sternum, and save them as .SLDPRT file format. In the part drawing file, use "combine" to delete the cancellous bone model from the complete model, and the remaining is the cortical bone model of the skeleton. Repeat the above operation with the human body contour model, and delete each bone and part of the soft tissue.

[0039] Since these models are extracted and constructed from the same medical image, you only need to align the origins of each model when assembling them. Recreate an assembly file, import cortical bone, cancellous bone, costal cartilage, intervertebral disc, organ tissue, human body contour and orthopedic brace, select the coordinate origin of each model, and "align" them. Figure 5 As shown, it is finally exported as a .X_T format file.

[0040] S4: Set the material parameters and boundary conditions of each part in the finite element analysis software, add spring units, divide the mesh, perform finite element simulation calculations, and obtain the stress and deformation results of the spine. In this embodiment, the finite element analysis software used is Ansys Workbench software.

[0041] 1. Set material properties: Add material parameters of each part and set them to the corresponding model. Cortical bone, cancellous bone, intervertebral disc, costal cartilage, and skin are simulated using linear material models. The specific parameters are shown in Table 1. Organ tissues are simulated using the Mooney-Rivlin nonlinear material model. The specific parameters are shown in Table 2.

[0042] Table 1 Linear material parameters

[0043]

[0044] Table 2 Organ tissue material parameters

[0045]

[0046]

[0047] 2. Connection: Figure 6 As shown, springs are added at the connection, and spring units are used to simulate each ligament. The ligament stiffness is shown in Table 3. The Ogden 3rd order model is selected for the ligament material properties, and the material parameters are shown in Table 4.

[0048] Table 3 Ligament stiffness

[0049] Stiffness(N / mm) Anterior longitudinal ligament 8.84 Posterior longitudinal ligament 5.84 Ligamentum flavum 15.48 supraspinal ligament 10.85 Interspinous ligament 2.41 Intertransverse ligament 0.19

[0050] Table 4 Ligament material parameters

[0051]

[0052] For the rest of the model contacts, the "binding" type of contact is used.

[0053] 3. Draw the finite element mesh: Select "tetrahedron" as the mesh drawing method, and set the mesh transition to "slow", which can effectively avoid sudden changes in mesh density and improve the continuity of the mesh. When drawing the mesh, it is necessary to ensure that there are more than 3 layers of mesh on the model, which can improve the accuracy and reliability of the calculation results. Set the mesh unit size of the body surface contour to 7mm, the mesh unit size of the cancellous bone to 0.5mm, the mesh unit size of the cortical bone to 0.5mm, the mesh unit size of the intervertebral disc to 0.1mm, and the mesh unit size of the orthotic brace to 0.1mm.

[0054] 4. Add boundary conditions: Select the bottom surface of the model and add fixed supports; add a 50N corrective force on both sides of the brace.

[0055] 5. Solution: In the finite element solution process, the key formulas can be summarized into the following steps, among which the stiffness matrix is ​​derived from the set material parameters.

[0056] (1) Node displacement equation (equilibrium equation)

[0057] Ku=F

[0058] K: global stiffness matrix, u: node displacement vector, F: external force vector

[0059] (2) Element stiffness matrix calculation formula

[0060] For each finite element, the stiffness matrix K e It can be expressed as:

[0061]

[0062] V e : unit volume, B: strain-displacement matrix, D: material stiffness matrix

[0063] (3) Displacement-strain relationship

[0064] ε=Bu

[0065] ε is the strain vector, B is the strain-displacement matrix

[0066] (4) Stress-strain relationship (constitutive relationship)

[0067] σ=Dε

[0068] σ: stress vector, D: material stiffness matrix, ε is the strain vector

[0069] (5) The solution formula for equivalent stress is:

[0070]

[0071] σ x , σ y , σ z are the three principal stress components, τ xy , τ yz , τ zx is the shear stress component.

[0072] (6) The solution formula for the deformation is:

[0073]

[0074] U x , Uy , U z are the displacement components of the node in the x, y, and z directions respectively.

[0075] In finite element analysis, the solution area is first divided into finite element units, and local equilibrium equations are constructed for each unit and combined into an overall system. The solution algorithm is mainly an iterative method. Select the initial guess solution u0, which can usually be set to a zero vector or an empirical guess solution. In the next steps, this initial solution will be continuously updated and optimized, gradually converging to the true solution. Use direct or iterative solution methods to calculate the increment Δu and update the current solution. In this example, the iterative algorithm uses the Newton-Raphson method, and its iterative process is as follows:

[0076] K(u n )Δu=-F(u n )

[0077] u n+1 =u n +Δu

[0078] After each update, check whether the convergence condition is met. If the convergence condition is met, the iteration process ends and the final solution is obtained; otherwise, continue to iterate. Repeat the above process until the convergence condition is met. After each iteration, the solution can be observed to be gradually improved, and finally a solution with high approximation accuracy is obtained. After the calculation is completed, the cloud map of equivalent stress and total deformation is output, such as Figure 7-Figure 9 As shown. The stress diagram shows the stress distribution caused by the pressure applied by the brace. The maximum equivalent stress is 33.056MPa, which is concentrated in the ribs and the upper area of ​​the spine (the red part in the figure). This stress distribution shows the compression of the spine and ribs by the brace during the correction process. The larger stress area may be where the correction force is more concentrated, indicating that the bones in these areas are subjected to greater forces. The deformation diagram shows the overall deformation of the spine and ribs. The maximum deformation value is 7.5377 mm, which is concentrated in the upper part of the spine and the rib area (the red part in the figure). The larger deformation is concentrated in the most severe scoliosis area. It can be seen from the two figures that the brace imposes a large deformation and stress on the upper area of ​​the spine (especially the area with severe scoliosis), indicating that this area has been effectively corrected. The deformation and stress in the lower area are small, indicating that the correction in this area is relatively stable.

[0079] The above content shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the specific embodiments described. The descriptions in these embodiments and the specification are only preferred examples of the present invention and are not intended to limit the scope of the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention, and these changes and improvements all fall within the scope of the protection claimed by the present invention. The scope of protection of the present invention shall be defined by the attached claims and their equivalents.

Claims

1. A method for evaluating the effect of scoliosis correction based on finite element analysis, characterized in that: The following steps are involved: Step 1: Construct a point cloud model based on CT images in medical image processing software; Step 2: Save the point cloud model as a triangular mesh model in the 3D scanning data processing and repair software, repair and optimize the triangular mesh model, and then convert the optimized triangular mesh model into a solid surface model through solidification; Step 3: Combine and assemble the solid surface models in the 3D modeling software to form a human body model; Step 4: Set the material parameters and boundary conditions of the human tissue in the human body model in the finite element analysis software, add spring units, and divide the mesh to establish a finite element model. Then perform finite element simulation calculations to obtain the equivalent stress and deformation results of the spine.

2. A method for evaluating the effect of scoliosis correction based on finite element analysis as claimed in claim 1, characterized in that: The model repair and optimization processing methods in step 2 include editing contour lines, constructing surface patches, constructing grids, and fitting surfaces.

3. The method for evaluating the effect of scoliosis correction based on finite element analysis as claimed in claim 1, characterized in that: In the step 3, when assembling the models, each model is assembled using the origin.

4. The method for evaluating the effect of scoliosis correction based on finite element analysis according to claim 1, characterized in that: In step 4, all bones in the human body model are simulated using linear material models, organ tissues are simulated using nonlinear elastic materials, and ligament tissues are simulated using spring units.

5. The method for evaluating the effect of scoliosis correction based on finite element analysis as claimed in claim 1, characterized in that: In step 4, the cortical bone and the cancellous bone in the human body model are connected by binding.

6. The method for evaluating the effect of scoliosis correction based on finite element analysis according to claim 1, characterized in that: When meshing the finite element model in step 4, it is necessary to ensure that each model is divided into at least 3 layers of meshes, and the mesh subdivision size is approximately 0.5mm-1mm.

7. The method for evaluating the effect of scoliosis correction based on finite element analysis according to claim 1, characterized in that: The calculation result obtained in step 4 is presented in the form of a cloud diagram.

8. The method for evaluating the effect of scoliosis correction based on finite element analysis as claimed in claim 4, characterized in that: When using linear materials to model bones and nonlinear elastic materials to simulate organ tissues, you only need to set the corresponding material properties on the model.

9. The method for evaluating the effect of scoliosis correction based on finite element analysis as claimed in claim 4, characterized in that: When using spring elements to simulate ligament tissue, you need to select the location where the spring element is applied, set the stiffness of the ligament, and finally add the material properties of the ligament.

10. The method for evaluating the effect of scoliosis correction based on finite element analysis according to claim 1, characterized in that: The solution is obtained by using the finite element algorithm.

Images