Methods for constructing a surgical model of internal fixation with plates for distal radius fractures

Abstract

This invention belongs to the field of medical devices, specifically relating to a method for constructing a surgical model for internal fixation with plates for distal radius fractures. The method includes the following steps: Step (1) establishing a geometric model of the radius; Step (2) establishing a geometric model of the internal fixation device; Step (3) assembling the overall geometric model; Step (4) establishing an overall finite element model. The model constructed by this invention can highly replicate the actual situation of internal fixation surgery with plates for distal radius fractures, providing a precise simulation platform for the study of surgical plans. Through finite element analysis, the mechanical properties of the surgical process and the postoperative bone healing stage can be comprehensively and accurately analyzed, providing a scientific and reliable basis for clinicians to select appropriate internal fixation materials and surgical plans, thus helping to improve the success rate of surgery and the patient's recovery.

Description

Technical Field

[0001] This invention belongs to the field of medical devices, specifically relating to a method for constructing a surgical model for internal fixation with plates for distal radius fractures. Background Technology

[0002] Traditional evaluation of the performance of implantable medical materials mainly relies on mechanical testing, which requires a lot of time and effort in actual testing. With the advancement and maturity of finite element analysis technology, the finite element method can effectively reduce the consumption of manpower and material resources caused by testing, while efficiently and accurately calculating the mechanical response characteristics of the research object.

[0003] Current research on treatment options for distal radius fractures using traditional methods struggles to comprehensively and accurately simulate the surgical process and the changes in mechanical properties during the postoperative bone healing stage, thus failing to provide detailed and reliable theoretical support for clinical surgery. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing a surgical model of distal radius fracture with plate internal fixation.

[0005] The technical solution for achieving the objective of this invention is: a method for constructing a surgical model for internal fixation with plates for distal radius fractures, comprising the following steps:

[0006] Step (1): Establish the geometric model of the radius;

[0007] Step (2): Establish the geometric model of the internal fixation device;

[0008] Step (3): Assemble the overall geometric model;

[0009] Step (4): Establish the overall finite element model.

[0010] Furthermore, step (1) includes the following steps:

[0011] Step (11): Import the arm CT scan data, select the radius region by setting the mask area of ​​cortical bone and cancellous bone, remove non-target bone structures, fill the cavity of the pixel area of ​​cortical bone and cancellous bone, and reverse model to generate the original radius geometric model.

[0012] Step (12): Repair the original radius geometric model generated in step (11).

[0013] Further, step (12) specifically involves removing non-manifold edges, self-intersecting edges, highly refractive edges, nail-like structures, and existing void channels from the radial surface to achieve preliminary smoothing of the radial model surface;

[0014] Construct the surface contour of the model and divide it into quadrilateral surface patches of similar area. Within the contour of the divided quadrilateral surface patches, transform each quadrilateral surface patch into a smaller quadrilateral grid, repair the grid pattern with deviation, and generate a smooth model.

[0015] Furthermore, step (2) includes establishing the geometric model of the locking plate and the geometric model of the screw.

[0016] Further, step (3) specifically involves: importing the cortical bone, cancellous bone and locking plate model, fixing the relative positions of the cortical bone and cancellous bone, making the bottom of the locking plate fit against the surface of the cortical bone, assembling screws at the screw holes, adjusting the relative positional relationship between the screws and the steel plate threads and holes, and completing the assembly of the overall geometric model.

[0017] Furthermore, step (4) specifically includes the following steps:

[0018] Step (41): Model discretization: Import the overall geometric model, cut out a fracture callus area of ​​(1±0.1)mm×(1±0.1)mm at a distance of 2±1cm from the distal articular surface of the radius, and perform finite element mesh discretization by combining tetrahedral mesh and hexahedral mesh, so that the mesh of the screw thread is aligned with the mesh of the contact area of ​​the radius and the plate, the cortical bone and cancellous bone are connected by common nodes, and the contact mesh is set for the other parts;

[0019] Step (42): Material parameters: Cancellous bone is equivalent to a continuous, uniform, isotropic single linear elastic material. The material properties of internal fixation material and radial callus at different healing stages are set, as well as the degradation rate of biodegradable material during the healing process.

[0020] Step (43): Contact settings: Set the contact pairs between the radius and the locking plate, the radius and the screw, and the locking plate and the screw. The screw surface and the locking plate are the contact surfaces. The friction coefficient is set to 0.1. The contact type between the screw and the relevant components is the binding contact. The radius and the locking plate are the standard contact. The callus area and the bones at both ends are connected by a common node and no contact is set.

[0021] Step (44): Constraints and loading: Apply 6 degrees of freedom full constraints to the mesh within 2±1cm of the proximal radius, and apply uniformly distributed loads to the articular surface and palmar side of the distal radius;

[0022] Step (45): Mesh convergence verification: Select a mesh size of 1.5±0.1mm.

[0023] Compared with the prior art, the significant advantages of this invention are:

[0024] (1) The model constructed in this invention can highly restore the actual situation of plate fixation surgery for distal radius fracture, providing an accurate simulation platform for the study of surgical plans.

[0025] (2) Finite element analysis can comprehensively and accurately analyze the mechanical properties of the surgical process and the postoperative bone healing stage, providing a scientific and reliable basis for clinicians to select appropriate internal fixation materials and surgical plans, which helps to improve the success rate of surgery and the patient's rehabilitation effect.

[0026] (3) Mesh convergence verification during model building ensures the accuracy of the finite element model and improves the reliability of the analysis results. Attached Figure Description

[0027] Figure 1 The cortical bone mask region is extracted based on the brightness threshold according to the present invention; (a) is the cortical bone mask, (b) is the cortical bone cross-sectional mask, and (c) is the cortical bone cross-sectional mask.

[0028] Figure 2 The cancellous bone mask region extracted based on the brightness threshold of the present invention is shown in (a) cancellous bone mask, (b) cancellous bone cross-sectional mask, and (c) cancellous bone cross-sectional mask.

[0029] Figure 3 The areas of the radial cortical bone and cancellous bone masking in this invention are: (a) radial cortical bone masking, (b) radial cancellous bone masking.

[0030] Figure 4 The area after filling with the radial cortical bone and cancellous bone mask of the present invention; (a) radial cortical bone mask, (b) radial cancellous bone mask.

[0031] Figure 5 Original models of radial cortical and cancellous bone; (a) Original model of radial cortical bone, (b) Original model of radial cancellous bone.

[0032] Figure 6 The model shows the surface of the radial cortical bone and cancellous bone after initial smoothing; (a) is the surface model of the radial cortical bone, and (b) is the surface model of the radial cancellous bone.

[0033] Figure 7 Outlines and grids of the radial cortical and cancellous bone; (a) outline of the radial cortical bone, (b) outline of the radial cancellous bone, (c) grid of the radial cortical bone, (d) grid of the radial cancellous bone.

[0034] Figure 8 This is a schematic diagram for locking the steel plate.

[0035] Figure 9 To lock the geometric model of the steel plate; (a) lock the top geometric model of the steel plate, (b) lock the bottom geometric model of the steel plate, (c) lock the threaded holes and Kirschner pin holes at the head of the steel plate, and (d) lock the threaded holes and Kirschner pin holes on the body of the steel plate.

[0036] Figure 10 This includes the overall assembly model and enlarged views of certain parts.

[0037] Figure 11 It is a discrete model of the whole. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings.

[0039] Based on CT scan data of the radius from a healthy volunteer, a complete original geometric model of the radial cortex and cancellous bone was reconstructed using Mimics software. After further smoothing using Geomagic Studio software, it was assembled with a pre-built locking plate and screws in Solidworks software to form a geometric model for plate fixation surgery of distal radius fractures. A 1mm area was cut from this model using HyperMesh software to simulate the radial callus region. Considering the differences in degradation rates of different biodegradable materials, finite element meshes were manually generated for all structures at each healing stage. Material parameters, contact and constraint settings, and the application of different load conditions were completed. Finite element calculations and result analysis were performed in ANSYS software. The specific steps include the following:

[0040] 1. Establishment of the geometric model of the radius

[0041] The density of limb skeletal tissues far exceeds that of other soft tissues. Therefore, in the 3D hand image model constructed using Mimics software, the radius is easily identifiable due to its significant density contrast. In the image presentation, the radius exhibits a unique ring-shaped structural feature, stemming from its dual-layered internal structure—cortical bone and cancellous bone. Cortical bone, with its high density and compact microstructure, forms the outer protective layer of the radius; while cancellous bone, with its relatively lower density and abundant internal cavities, forms the internal reticular support system of the radius, including trabeculae, bone marrow, and tissue fluid.

[0042] 1.1. Mimics Reverse Modeling of Radial Rough Geometry

[0043] Because the radius is not a regular curved surface, its inner and outer surfaces cannot be represented by precise surface equations. Therefore, the CT scan data of the radius needs to be processed and modeled using the Mimics reverse engineering software. First, a healthy volunteer's arm was scanned layer by layer using a CT scanner. The resulting CT scan data was converted and stored as a DICOM format image file. This image file format can then be imported into Mimics software for further reverse engineering of the radius model. The specific steps are as follows:

[0044] (1) After importing the CT image in DICOM format, select a brightness threshold range of 226 to 2311 for cortical bone and 140 to 1000 for cancellous bone. Divide the CT image into cortical bone mask area and cancellous bone mask area, such as... Figure 1 , Figure 2 As shown;

[0045] (2) As can be seen from the pixel display of the brightness threshold region image, since the volunteer arm image data scanned by the CT machine includes not only the radius, but also the ulna, carpal bones, and metacarpal bones, it is necessary to selectively target the radius region, remove other non-target bone structures, ensure that only the radius is present, and generate a new mask, such as... Figure 3 As shown;

[0046] (3) Because the pixels inside the cortical bone and cancellous bone on the mask are not completely continuous and there are cavities, it is necessary to fill the cavity areas in the pixel regions of the cortical bone and cancellous bone in each frame of the image so that the geometric model can be reconstructed later. Figure 4 As shown;

[0047] (4) Finally, use the "Calculate 3D" function command to reverse engineer and generate the original geometric models of cortical and cancellous bone. See Figure 5 Then export it as an STL format file that can be processed by Geomagic Studio software.

[0048] 1.2. Geomagic Studio Radial Geometric Model Repair Processing

[0049] The geometric model obtained in Mimics software is actually just a surface mesh model composed of many irregular facets. After importing the radius STL format file into Geomagic Studio software, the initial rough curved surface of the radius is repaired to give the cortical and cancellous bone a highly smooth surface feature. The specific operation is as follows:

[0050] (1) After importing the STL format file, the "Mesh Doctor" command can be used to automatically analyze and remove non-manifold edges, self-intersecting edges, highly refractive edges, nail-like structures, and existing void channels on the radial surface, achieving preliminary smoothing of the radial model surface. See Figure 6 ;

[0051] (2) The initially smooth radial surface model does not yet have an internal structure; it is merely a thin surface feature and requires further processing using the "Precise Surface" command. First, manually construct the contour lines of the model surface, then construct quadrilateral surface patches of similar size on the model surface, see... Figure 7As shown in (a) and 7(b), the "Construct Grille" command is used to transform each quadrilateral surface patch into a smaller quadrilateral grille within the defined quadrilateral surface patch outline. The "Relax Grille" command is then used to correct any deviations in the grille pattern to better match the surface features of the model. See [link to relevant documentation]. Figure 7 (c), 7(d);

[0052] (4) After repairing the grid, directly use the "Automatic Surface Forming" command to generate a smoothed model of the radial cortical and cancellous bone, and output it as a Step format model file. The optimization process of the radial surface mesh involves multiple iterations, including precise surface reconstruction, surface patch construction, grid formation, and automatic surface formation, ultimately achieving the fitting and smoothing of the radial surface. At this point, the solidification reverse modeling of the precise geometric model of the radius is complete, and the resulting model fully meets the requirements for finite element analysis.

[0053] 2. Establishment of the geometric model of the internal fixation device

[0054] When discussing plate selection strategies for internal fixation surgery of distal radius fractures, two common options are considered: conventional compression plates and locking plates. Conventional compression plates fix the radius by screwing screws into a structure with a ramp-locking mechanism, following the spherical slip theory and relying on the friction between the radius and the plate surface to apply pressure. Locking plates, on the other hand, do not rely on friction between the radius and the plate surface. Their stability is maintained by the interface between locking screws with locking threads at different angles and the plate. Locking screws have significantly higher pull-out forces than conventional screws, making them the preferred choice for internal fixation surgery of distal radius fractures. Therefore, the internal fixation structure of this invention mainly consists of a locking plate and locking screws (including one conventional screw with an unthreaded head). Geometric modeling was performed based on the locking plate and screw models provided by Nanjing First Hospital.

[0055] 2.1. Establishment of the geometric model of the locking steel plate

[0056] The locking plate consists of three parts: the plate head that fits the distal radius, the plate neck that fits the fracture site of the distal radius, and the plate body that fits the long segment of the radius. Measurements were taken using calipers, screw gauges, and other measuring tools, based on a sample of the locking plate provided by Nanjing First Hospital.

[0057] The steel plate head is approximately 10.0 mm long and 20.0 mm wide, consisting of two rows of non-parallel locking threaded holes and three Kirschner wire holes. The inner diameter of the locking screw holes in the head is 2.6 mm, the thread width is 0.2 mm, and the pitch is 0.6 mm. The neck of the steel plate has an angle of 23° and a length of approximately 6 mm. The steel plate body is approximately 48 mm long and 8 mm wide, containing three parallel locking threaded holes, two standard screw clamping holes, and two Kirschner wire holes. The inner diameter of the locking screw holes in the body is approximately 4.4 mm at the top and 3.65 mm at the bottom, with a thread width of 0.2 mm and a pitch of 0.6 mm. The standard screw clamping holes have a top width of approximately 5.88 mm and a bottom width of approximately 4.0 mm, with curved sides and no internal threads. The overall thickness of the steel plate is approximately 2.5 mm, and the Kirschner wire hole diameter is 1.6 mm.

[0058] Because the C1 type distal radius fracture occurs at the neck of the plate, during clinical surgery, screws are inserted into all screw holes at the head of the plate and three screw holes near the neck of the plate body for fixation. One ordinary compression hole and one locking screw hole, located further from the fracture site, are left un-screwed. The screw placement is also based on the surgical arrangement during modeling. In actual modeling, the plate structure model needs to be appropriately simplified, ignoring the internal threads of the un-locking screwed holes, as this area has no impact on the overall stress distribution. This aims to improve the modeling speed and computational efficiency of the finite element model. A schematic diagram of the locking plate is shown below. Figure 8 .

[0059] In Solidworks software, a geometric model of the locking steel plate was completed based on the physical measurement results. (See...) Figure 9 .

[0060] 2.2. Establishment of the screw geometric model

[0061] The locking screws on the head of the locking plate are relatively thin and long, while those on the body of the locking plate are relatively thick and short. The length of the ordinary screws on the body of the locking plate is similar to that of the locking screws, but the ordinary screws have no threaded divisions on the head and the threads on the body are thicker. Based on the actual screws provided by the hospital, measurements were taken using measuring tools such as vernier calipers and screwdrivers.

[0062] The head length of the plate-head locking screw is approximately 2.5mm, and the specific data for the head thread is given in section 3.1.1. The body screw diameter is 2.0mm, the thread width is 0.2mm, and the pitch is 1.05mm. The head length of the plate-body locking screw is approximately 2.5mm, and the specific data for the head thread is given in section 3.1.1. The body screw diameter is 3.0mm, the thread width is 0.2mm, and the pitch is 1.05mm. The head length of the plate-body ordinary screw is approximately 3.2mm, the body screw diameter is 2.4mm, the thread width is 0.4mm, and the pitch is 1.0mm.

[0063] Internal fixation surgery with plates requires that the screws penetrate both sides of the radius, exposing at least one screw pitch to ensure that the screws can provide a firm locking relationship to the radius. Therefore, the length of the locking screws at the head of the plate varies from 16.0 mm to 22.0 mm, while the length of the locking screws and ordinary screws at the body of the plate is approximately 15.0 mm.

[0064] In Solidworks software, geometric models of locking screws and ordinary screws are completed based on physical measurement results.

[0065] 3. Assembly of the overall geometric model

[0066] Solidworks software has a built-in function to create assemblies from parts. The assembly process is as follows:

[0067] (1) First, import the model of cortical bone, cancellous bone and locking plate. After fixing the relative positions of cortical bone and cancellous bone, move the position of locking plate so that the bottom of the plate fits the surface of cortical bone as closely as possible, and fix the relative positions of the three.

[0068] (2) After determining the position of the locking steel plate, install the corresponding screws at the corresponding screw holes. Use the "Matching Command" to adjust the relative position of the locking screw threads and the steel plate threads to ensure they are fully installed without interference. Adjust the relative position of the ordinary screw heads and the pressure hole surfaces to ensure they do not interfere with each other. Complete the assembly of the overall geometric model. See [link to documentation]. Figure 10 .

[0069] 4. Establishment of the overall finite element model

[0070] 4.1 Model Discretization

[0071] After the overall geometric model is established, it is saved as an XT format file and imported into HyperMesh software for finite element mesh discretization, converting the geometric model into a finite element model. Before mesh discretization, a 1mm long fracture callus region needs to be cut from the radius at a position 2.5cm away from the distal articular surface.

[0072] Generally, in HyperMesh software, common mesh types fall into two main categories: tetrahedral meshes and hexahedral meshes. Tetrahedral meshes consist of four triangular facets, typically defined by six nodes, and offer good geometric adaptability. Hexahedral meshes exhibit a regular cubic shape, surrounded by six rectangular facets, and are typically defined by eight nodes. They have a regular shape and high computational accuracy. Given that the radius, plate, and screw do not possess regular geometric shapes, a combination of tetrahedral and hexahedral meshes is necessary for finite element mesh discretization to balance geometric adaptability and computational efficiency. Tetrahedral meshes are used in geometrically complex regions, while hexahedral meshes are preferred in regular regions and areas where stress results are of primary concern.

[0073] Simultaneously, during finite element mesh generation, the meshes in the areas where the screw threads contact the radius and plate are aligned to facilitate subsequent contact settings. The meshes between cortical bone and cancellous bone are connected using a shared-node method, while contact meshes are used between other components to represent contact behavior. The finite element discretization model is as follows:

[0074] The model consists of 142,457 elements for the radial cortical bone, 145,130 elements for the cancellous bone, 107 elements for the callus, 31,659 elements for the locking plate, 76,928 elements for the plate head screws, 29,874 elements for the plate body screws, and a total of 426,155 elements for the overall finite element discretization. The finite element mesh uses 3D 8-node isoparametric solid185 elements, with each node containing 3 degrees of freedom. The overall discretized model is shown below. Figure 11 .

[0075] 4.2 Material Parameters

[0076] In finite element simulation calculations, studies by G Cheun et al. have shown that the mechanical load-bearing capacity of cancellous bone has a very small impact on the finite element analysis results. Furthermore, this invention only analyzes the stress state of the radius without considering its internal flow characteristics. Therefore, without affecting the appearance structure, the entire cancellous bone region can be equivalent to a continuous, uniform, isotropic single linear elastic material.

[0077] The internal fixation materials used in this invention include titanium alloy, magnesium alloy biodegradable material, and polylactic acid biodegradable material. Titanium alloy does not degrade, while the degradation of biodegradable materials is characterized by a decrease in volume. The degradation process does not affect the connection between the screw head and the plate, and degradation proceeds according to the principle of threading from the screw itself to the shank, and from the shank in the cortical bone region to the shank in the cancellous bone region. The healing effect of radial callus is reflected in the change in the elastic modulus of the callus material, which is set according to relevant references. All material properties involved in the finite element calculations in this paper are given in Tables 1, 2, and 3. In Table 1, the granulation to osteogenic stage of the callus tissue corresponds to six periods: immediately postoperatively, 1 month postoperatively, 3 months postoperatively, 6 months postoperatively, 9 months postoperatively, and 12 months postoperatively.

[0078] Table 1. Radial Bone Material Properties

[0079]

[0080] Table 2. Properties of Internal Fixation Materials

[0081]

[0082]

[0083] The degradation rates of the two biodegradable materials during the healing process are shown in Table 3:

[0084] Table 3. Degradation rates of two biodegradable materials

[0085]

[0086] 4.3. Contact Settings

[0087] This invention relates to the arrangement of contact pairs including radius and locking plate, radius and screw, and locking plate and screw. According to the definition rules of contact surfaces, for the contact pair involving screws, the screw surface should be defined as the contact surface, and the coefficient of friction is set to 0.1. In the contact pair between radius and locking plate, the locking plate is the contact surface, and the coefficient of friction is set to 0.1. The radius and screw, and the locking plate and screw are in close contact, with the contact type set to bonded contact. The contact type between radius and locking plate is set to standard contact. Although the two ends of the callus region are in contact with cortical bone and cancellous bone, the connection between the callus and the two ends of the bone during the healing process is fixed, using a shared node connection, and no contact is set.

[0088] 4.4. Constraints and Loading: When setting constraints, the proximal radius is considered a fixed end. Apply full constraints of 6 degrees of freedom to the mesh within a 2.5cm range of the proximal radius. That is, the rotational and translational degrees of freedom of the proximal radius are strictly limited in the three orthogonal directions of X, Y, and Z. This serves as the boundary condition.

[0089] Based on the characteristics of hand movements, this invention mainly studies the static mechanical analysis of axial compression, dorsal bending, and articular surface torsion after internal fixation with plates for distal radius fractures, without involving the dynamic process. According to relevant literature on human biomechanics, the application of three typical load conditions is as follows: (1) applying an axial load of 100N to the articular surface of the distal radius; (2) applying a load of 50N along the palmar side of the distal radius in the direction of radial dorsiflexion; (3) applying a clockwise torsional load of 1N·m to the articular surface of the distal radius.

[0090] In finite element method (FEM) calculations, applying a large load to a single node often leads to abnormal stress concentration in the vicinity of that node due to concentrated forces, resulting in inaccurate stress and displacement distributions and causing deviations in the final calculation results. Therefore, it is advisable to avoid applying loads to single nodes and instead apply uniformly distributed loads to the entire area. When HyperMesh is used in conjunction with ANSYS for simulation, the application of uniformly distributed loads is achieved using RBE3 elements. RBE3 elements are mainly used to distribute loads such as forces and torques. By using RBE3 elements, all nodes in the entire area can be captured, and then a concentrated force can be applied to the central node, allowing the load to be evenly distributed to every node on the plane. The selection of the central node can be automatically calculated and generated by the system or manually set. Typically, the central node is a slave node, and the surrounding nodes are master nodes. The displacement of the slave nodes is the weighted average of the displacement of the master nodes, thereby achieving effective force transfer. If the nodes on the solid element are used as slave nodes, the structural stiffness will be slightly increased; if the slave nodes are suspended, the structural stiffness will not be increased and the calculation results will be more accurate. Therefore, in this invention, the specific load setting is to select the nodes on the distal radius articular surface and the palmar region of the distal radius as master nodes, and set a point in the air as a slave node, and apply the load to the set slave node to apply a uniformly distributed load.

[0091] At this point, the overall finite element model is complete. Save the resulting model as a CDB format file, which can then be imported into ANSYS software for finite element calculation and analysis.

[0092] 4.5. Grid Convergence Verification

[0093] For mesh convergence verification, a compression condition was selected, and different mesh sizes were set. The number of elements and maximum stress of the overall finite element model of distal radius fracture internal fixation are shown in Table 4. As the mesh size decreases, the number of elements in the model increases accordingly, and the maximum stress tends to stabilize. Increasing the number of meshes leads to longer computation time. Considering both the accuracy of the calculation results and the time cost, this paper selects a mesh size of 1.5 mm, which is the same as the mesh convergence verification size results obtained by Berge et al.

[0094] Table 4. Mesh Convergence Analysis Table

[0095]

Claims

1. A method for constructing a distal radius fracture plate internal fixation surgery model, characterized in that, Comprising the following steps: Step (1): establishing a radius geometry model; step (1) comprises the following steps: Step (11): importing hand arm CT scan data, by setting the cortical bone and cancellous bone mask area, directional selection of radius area, remove non-target bone structure, fill the cavity of cortical bone and cancellous bone pixel area, reverse modeling to generate the original radius geometry model; Step (12): the original radius geometry model generated in step (11) is repaired; Step (2): establishing the internal fixation device geometry model; step (2) includes establishing the locking plate geometry model and establishing the screw geometry model; Step (3): assembling the overall geometry model; Step (4): establishing the overall finite element model; step (4) specifically comprises the following steps: Step (41): model discretization: import the overall geometry model, cut out a (1±0.1)mm×(1±0.1)mm fracture callus area at a distance of 2±1cm from the distal radius articular surface, combine tetrahedral mesh and hexahedral mesh for finite element mesh discretization, align the mesh of the screw thread contact area with the radius and the steel plate, and connect the nodes between the cortical bone and the cancellous bone, and set the contact mesh for the rest of the components; Step (42): material parameters: equivalent cancellous bone to continuous, uniform, isotropic single linear elastic material, set the material properties of internal fixation material and radius callus at different healing periods, and the degradation rate of degradable material during healing process; Step (43): contact setting: set the contact pairs of radius and locking plate, radius and screw, locking plate and screw, the screw surface and the locking plate are the contact surface, the friction coefficient is set to 0.1, the screw and the related components are in contact type, the radius and the locking plate are in standard contact, the callus area and the two end bones are connected by the node and no contact is set; Step (44): constraint and loading: apply 6 degree of freedom full constraint to the mesh within 2±1cm of the proximal radius, and apply uniform load to the distal articular surface and the palmar side of the radius; Step (45): mesh convergence verification: select the grid size as 1.5±0.1mm.

2. The method of claim 1, wherein, Step (12) is specifically: removing the non-manifold edges, self-intersecting edges, highly refractive edges, spikes and existing gap channels on the surface of the radius, and realizing the preliminary smoothing of the surface of the radius model; Constructing the model surface contour line, dividing it into quadrilateral curved surface pieces with similar areas, and converting each quadrilateral curved surface piece into smaller quadrilateral grids in the divided quadrilateral curved surface piece contour line to repair the deviated grid map; generate a smooth model.

3. The method of claim 2, wherein, Step (3) is specifically: importing the cortical bone, cancellous bone and locking plate model, fixing the relative position of the cortical bone and cancellous bone, making the bottom of the locking plate fit the surface of the cortical bone, assembling the screw at the screw hole, adjusting the relative position relationship of the screw thread and the hole of the screw and the steel plate, and completing the assembly of the overall geometry model.

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