Construction method of distal radius fracture steel plate internal fixation operation model

Abstract

The invention belongs to the field of medical instruments, and particularly relates to a construction method of a distal radius fracture steel plate internal fixation operation model. Comprising the following steps: (1) establishing a radius geometric model; (2) establishing a geometric model of the internal fixation device; (3) assembling the overall geometric model; and (4) establishing an integral finite element model. The model constructed by the invention can highly restore the actual condition of the distal radius fracture steel plate internal fixation operation, and provides an accurate simulation platform for the research of an operation scheme; through finite element analysis, the mechanical characteristics in the operation process and the postoperative bone healing stage can be comprehensively and accurately analyzed, a scientific and reliable basis is provided for clinicians to select proper internal fixation materials and operation schemes, and the operation success rate and the patient rehabilitation effect can be improved.

Description

Technical Field

[0001] The invention belongs to the field of medical devices, and in particular relates to a method for constructing a distal radius fracture steel plate internal fixation surgical model. Background Art

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

[0003] At present, for the treatment of distal radius fractures, traditional research methods are difficult to fully and accurately simulate the surgical process and the changes in mechanical properties during the postoperative bone healing stage, and cannot provide a detailed and reliable theoretical basis for clinical surgery. Summary of the invention

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

[0005] The technical solution to achieve the purpose of the present invention is: a method for constructing a distal radius fracture plate internal fixation surgical model, comprising the following steps:

[0006] Step (1): Establishing a radial geometry model;

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

[0008] Step (3): assembling 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, set the mask area of ​​the cortical bone and cancellous bone, select the radius area in a targeted manner, remove the non-target bone structure, fill the cavities in the cortical bone and cancellous bone pixel area, and generate the original radius geometry model by reverse modeling;

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

[0013] Furthermore, step (12) specifically includes: removing non-manifold edges, self-intersecting edges, highly refractive edges, spikes and existing void channels on the surface of the radius, so as to achieve preliminary smoothing of the surface of the radius model;

[0014] Construct the model surface contour line and divide it into quadrilateral surface patches with similar areas. Within the divided quadrilateral surface patch contour line, convert each quadrilateral surface patch into a smaller quadrilateral grid, repair the grid map with deviation, and generate a smooth model.

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

[0016] Furthermore, step (3) is specifically as follows: importing the cortical bone, cancellous bone and locking plate model, fixing the relative position of the cortical bone and the 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 between the screw and the steel plate thread and hole, 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±1 cm from the distal articular surface of the radius, and perform finite element mesh discretization by combining tetrahedral meshes and hexahedral meshes, so that the meshes of the contact areas between the screw thread and the radius and the steel plate are aligned, the cortical bone and the cancellous bone are connected at a common node, and the remaining parts are set to contact meshes;

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

[0020] Step (43): Contact setting: setting 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 related parts is binding contact. The radius and the locking plate are standard contact. The callus area and the two end bones are connected by a common node and no contact is set.

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

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

[0023] Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) The model constructed by the present invention can highly restore the actual situation of distal radius fracture plate internal fixation surgery, 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) The mesh convergence verification during the model construction process ensures the accuracy of the finite element model and improves the reliability of the analysis results. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The cortical bone mask area is extracted according to the brightness threshold of the present invention; (a) is the cortical bone mask, (b) is the cortical bone profile mask, and (c) is the cortical bone profile mask.

[0028] Figure 2 The cancellous bone mask area extracted according to the brightness threshold of the present invention; (a) cancellous bone mask, (b) cancellous bone profile mask, (c) cancellous bone profile mask.

[0029] Figure 3 The mask areas of the radial cortical bone and cancellous bone of the present invention are as follows: (a) radial cortical bone mask, (b) radial cancellous bone mask.

[0030] Figure 4 The area after the radial cortical bone and cancellous bone mask are filled according to the present invention; (a) radial cortical bone mask, (b) radial cancellous bone mask.

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

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

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

[0034] Figure 8 Schematic diagram of locking steel plate.

[0035] Fig. 9 The geometric model of the locking plate; (a) the geometric model of the top of the locking plate, (b) the geometric model of the bottom of the locking plate, (c) the threaded hole and Kirschner wire hole on the head of the locking plate, and (d) the threaded hole and Kirschner wire hole on the body of the locking plate.

[0036] Fig.10 It is the overall assembly model and the partial enlarged view.

[0037] Fig.11 It is an overall discrete model. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0039] Based on the CT scan data of the radius of a healthy volunteer, the complete original geometric model of the cortical bone and cancellous bone of the radius was reconstructed using the Mimics software. After further smoothing using the Geomagic Studio software, it was assembled with the established locking plate and screws in the Solidworks software to form a plate internal fixation surgical geometric model for distal radius fractures. The model was cut into a 1mm area using the HyperMesh software to simulate the radial callus area. Considering the differences in degradation rates of different degradable materials, the finite element meshes of all structures in each healing period were manually divided, and the material parameters, contacts, and constraints were set, as well as the application of different working loads. The finite element calculation and result analysis were completed in the ANSYS software. The specific steps include the following:

[0040] 1. Establishment of radial geometry model

[0041] The density of the limb bone tissue is much higher than that of other soft tissues. Therefore, in the three-dimensional image model of the palm constructed by Mimics software, the radius is easy to identify due to its significant density contrast. In the image presentation, the radius shows a unique annular structural feature, which stems from the double-layer distribution of its internal structure - cortical bone and cancellous bone. The cortical bone, with its high density and compact microstructure, constitutes the outer protective layer of the radius; the cancellous bone, with its relatively low density and rich internal cavity structure, forms a reticular support system inside the radius: including trabeculae, bone marrow and tissue fluid.

[0042] 1.1. Mimics reverse modeling of the radial rough geometry model

[0043] Since the shape of the radius is not a regular curved surface structure, it is impossible to use accurate surface equations to represent the inner and outer surfaces of the radius. It is necessary to process and model the CT scan data of the radius through the Mimics reverse modeling software. First, a healthy volunteer's arm is layered scanned by a CT machine, and the obtained CT scan data is converted and stored as a DICOM format image file. The image file in this file format can be imported into the Mimics software for further reverse modeling of the radius model. The specific operations are as follows:

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

[0045] (2) It can be seen from the pixel display of the brightness threshold area image that since the CT scanned image data of the volunteer's arm contains not only the radius, but also the ulna, carpal bones, and metacarpal bones, it is necessary to select the radius area in a targeted manner and remove other non-target bone structures to ensure that only the radius is present and generate a new mask, such as Figure 3 As shown;

[0046] (3) Since 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 cortical bone and cancellous bone pixel areas in each frame image for subsequent geometric model reconstruction, such as Figure 4 As shown;

[0047] (4) Finally, the “Calculate 3D” function command is used to reverse model the original geometric model of cortical bone and cancellous bone, see Figure 5 , and then export it as an STL format file that can be processed by Geomagic Studio software.

[0048] 1.2. Geomagic Studio radial geometry model repair processing

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

[0050] (1) After importing the STL file, the "Mesh Doctor" command can automatically analyze and remove the non-manifold edges, self-intersecting edges, highly refractive edges, spikes and existing gap channels on the radial surface, achieving preliminary smoothing of the radial model surface. Figure 6 ;

[0051] (2) The initially smooth radius surface model does not have an internal structure at this time, but only a thin layer of surface features. It needs to use the "precise surface" command for subsequent processing. First, manually construct the contour line of the model surface, and construct quadrilateral surface patches of similar size on the model surface. Figure 7(a) and (b). Use the "Construct Grid" command to convert each quadrilateral surface patch into a smaller quadrilateral grid within the contour of the divided quadrilateral surface patch. Use the "Relax Grid" command to repair the grid image with deviations to better match the surface characteristics of the model. Figure 7 (c), 7(d);

[0052] (4) After repairing the grid, directly use the "Automatic Surfacing" command to generate smooth radial cortical bone and cancellous bone models, and output them as a model file in Step format. The optimization process of the radial surface mesh involves multiple iterations. Through the steps of precise surface reconstruction, surface patch construction, grid and automatic surfacing, the radial surface is finally fitted and smoothed. At this point, the physical reverse modeling of the precise geometric model of the radius is completed, and the obtained model has fully met the conditions required for finite element analysis.

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

[0054] When discussing the strategy for selecting plates for distal radius fracture plate internal fixation surgery, there are usually two options: ordinary compression plates and locking plates. The fixing principle of ordinary compression plates is to screw the screws into a structure designed with a slope lock for fixation. It follows the spherical slip theory and relies on the friction between the radius and the surface of the plate to achieve the compression effect of the plate on the radius. The fixation of the locking plate does not rely on the friction between the radius and the surface of the plate. Its stability is maintained by the interface between the locking screw with locking threads at different angles and the plate. The pull-out force of the locking screw is much higher than that of the ordinary screw, and it is the preferred choice for distal radius fracture plate internal fixation surgery. Therefore, the internal fixation structure of the present invention is mainly composed of a locking plate and a locking screw (including an ordinary screw without a thread on the head), and geometric modeling is performed according to the models of the locking plate and screw provided by Nanjing First Hospital.

[0055] 2.1. Establishment of locking plate geometry model

[0056] The locking plate consists of three parts: the head of the plate that fits the distal part of the radius, the neck of the plate that fits the distal part of the radius fracture, and the body of the plate that fits the long bone segment of the radius. Based on the locking plate provided by Nanjing First Hospital, measurement tools such as vernier calipers and screw rulers were used for measurement.

[0057] The length of the head of the plate is about 10.0mm, the width is about 20.0mm, and it consists of two rows of locking threaded holes whose normal directions are not parallel to each other and three Kirschner wire holes. The inner diameter of the thread of the head locking screw hole is 2.6mm, the thread width is 0.2mm, and the pitch is 0.6mm. The angle of the neck of the plate is 23°, and the length is about 6mm. The length of the body of the plate is about 48mm, the width is about 8mm, and it contains three mutually parallel locking threaded holes, two common screw pressure holes, and two Kirschner wire holes. The inner diameter of the top of the locking screw hole in the body is about 4.4mm, the inner diameter of the bottom is about 3.65mm, the thread width is 0.2mm, the pitch is 0.6mm, the top width of the common screw pressure hole is about 5.88mm, the bottom width is about 4.0mm, the side is arc-shaped, and there is no internal thread. The overall thickness of the plate is about 2.5mm, and the diameter of the Kirschner wire hole is 1.6mm.

[0058] Since the C1 type distal radius fracture occurs at the neck of the plate, when inserting screws during clinical surgery, screws are inserted into all the screw holes on the plate head and the three screw holes on the plate body near the neck of the plate to fix the plate. Screws are not inserted into the common pressure hole and the locking screw hole far from the fracture site. The screws are also installed according to the surgical arrangement during modeling. When actually modeling, it is necessary to appropriately simplify the plate structure model first, and ignore the modeling of the internal threads of the threaded holes that have not been inserted with locking screws, because this part has no effect on the overall force, so as to improve the modeling speed and calculation efficiency of the finite element model. See the schematic diagram of the locking plate. Figure 8 .

[0059] The geometric modeling of the locking steel plate is completed in Solidworks software based on the actual measurement results, see Fig. 9 .

[0060] 2.2. Screw geometry model establishment

[0061] The locking screw at the head of the locking plate is relatively slender, while the locking screw at the body of the locking plate is relatively thick and short. The length of the ordinary screw at the body of the locking plate is similar to that of the locking screw, but the head of the ordinary screw has no thread divisions, and the body thread is thicker. Based on the actual screws provided by the hospital, the measurement is also performed using measuring tools such as vernier calipers and screw rulers.

[0062] The head length of the plate head locking screw is about 2.5mm, and the specific data of the head thread have been given in Chapter 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 about 2.5mm, and the specific data of the head thread have been given in Chapter 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 ordinary screw of the steel plate body is about 3.2mm, the body screw diameter is 2.4mm, the thread width is 0.4mm, and the pitch is 1.0mm.

[0063] Plate internal fixation surgery requires that the screws must penetrate both sides of the radius, exposing at least 1 screw pitch distance to ensure that the screws can exert a firm locking relationship on the radius. Therefore, the length of the locking screw on the plate head ranges from 16.0mm to 22.0mm, and the length of the locking screw on the plate body and ordinary screw is approximately 15.0mm.

[0064] The geometric modeling of locking screws and ordinary screws is completed in Solidworks software based on the actual measurement results.

[0065] 3. Assembly of the overall geometric model

[0066] Solidworks software comes with the function of making assemblies from parts. The assembly process is as follows:

[0067] (1) First, the cortical bone, cancellous bone and locking plate model are introduced. After the relative positions of the cortical bone and cancellous bone are fixed, the locking plate is moved so that the bottom of the plate fits the surface of the cortical bone as closely as possible, thereby fixing the relative positions of the three.

[0068] (2) After the position of the locking steel plate is determined, assemble the corresponding screws in the corresponding screw holes. Use the "matching command" to adjust the relative position relationship between the locking screw thread and the steel plate thread so that they are fully installed without interference. Adjust the relative position relationship between the ordinary screw head and the pressure hole surface without mutual interference to complete the assembly of the overall geometric model. See Fig.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 stored as an XT format file and imported into the HyperMesh software for finite element mesh discretization to convert the geometric model into a finite element model. Before mesh discretization, a fracture callus area with a length of 1 mm needs to be cut out of the radius at a position 2.5 cm away from the distal articular surface of the radius.

[0072] Generally speaking, in HyperMesh software, common mesh types include tetrahedral mesh and hexahedral mesh. A tetrahedral mesh is composed of four triangular facets, usually defined by 6 nodes, and has good geometric feature adaptability. A hexahedral mesh presents a regular cubic shape, surrounded by six rectangular facets, usually defined by 8 nodes, with a regular mesh shape and high computational accuracy. Given that the radius, plate, and screw do not have regular geometric shapes, it is necessary to combine tetrahedral mesh and hexahedral mesh to balance geometric adaptability and computational efficiency when performing finite element mesh discretization. Tetrahedral mesh is used in areas with complex geometric shapes, while hexahedral mesh is used as much as possible in regular areas and areas where stress results are of particular concern.

[0073] At the same time, when dividing the finite element mesh, align the mesh of the area where the screw thread contacts the radius and the steel plate to facilitate the subsequent contact setting. The mesh between the cortical bone and the cancellous bone adopts a common node connection method, and contact meshes are set between the remaining components to represent the contact behavior. The finite element discrete model is as follows:

[0074] Among them, the radial cortical bone has 142,457 units, the cancellous bone has 145,130 units, the callus has 107 units, the locking plate has 31,659 units, the plate head screw has 76,928 units, the plate body screw has 29,874 units, and the overall finite element discretization has 426,155 units. The unit type of the finite element mesh is the three-dimensional 8-node isoparametric block solid185 unit, each node contains 3 degrees of freedom, and the overall discretization model is shown in Fig.11 .

[0075] 4.2 Material parameters

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

[0077] The internal fixation materials used in the present invention include titanium alloy materials, magnesium alloy degradable materials and polylactic acid degradable materials. Titanium alloy materials do not degrade, and the degradation of degradable materials is characterized by a reduction in volume. The connection between the screw head and the steel plate is not affected during the degradation process, and the degradation is carried out according to the principle of self-threading to the screw rod, and from the screw rod in the cortical bone area to the screw rod in the cancellous bone area. The healing effect of radial callus is reflected by the change in the elastic modulus of the callus material, which is set according to relevant references. The material properties of all materials involved in the finite element calculation in this article are given in Tables 1, 2, and 3. In Table 1, the granulation to osteogenesis period of callus tissue corresponds to six periods immediately after surgery, 1 month after surgery, 3 months after surgery, 6 months after surgery, 9 months after surgery, and 12 months after surgery.

[0078] Table 1 Radius material properties

[0079]

[0080] Table 2 Internal fixation material properties

[0081]

[0082]

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

[0084] Table 3 Degradation rate of two degradable materials

[0085]

[0086] 4.3. Contact settings

[0087] The present invention relates to the setting of contact pairs including radius and locking plate, radius and screw, locking plate and screw. According to the definition rule of contact surface, for the contact pair involving screws, the screw surface should be defined as the contact surface, and the friction coefficient is set to 0.1; in the contact pair of radius and locking plate, the locking plate is the contact surface, and the friction coefficient is set to 0.1. The radius and screw, locking plate and screw are in close contact, the contact type is set to binding contact, and the contact type between the radius and the locking plate is set to standard contact. Although the two ends of the callus area are in contact with the cortical bone and cancellous bone, the connection between the callus and the two bones at the two ends during the healing process is fixed connection, and is connected in a common node manner without contact.

[0088] 4.4. Constraints and Loading When setting constraints, the proximal end of the radius is equivalent to the fixed end, and the grid within 2.5 cm of the proximal end of the radius is subject to full constraints of 6 degrees of freedom, that is, in the three orthogonal directions of X, Y, and Z, the rotational and translational degrees of freedom of the proximal end of the radius are strictly restricted, which serves as the boundary condition.

[0089] According to the characteristics of hand movement, this paper mainly studies the static mechanical analysis of axial compression, dorsal bending, and articular surface torsion after plate internal fixation for distal radius fracture, and does not involve dynamic processes. According to relevant literature on human biomechanics, the application of three typical working loads is as follows: (1) an axial load of 100N is applied to the distal radius articular surface; (2) a load of 50N is applied along the palmar side of the distal radius in the dorsal extension direction of the radius; (3) a clockwise torsional load of 1N·m is applied to the distal radius articular surface.

[0090] In finite element calculations, if a large load is applied to a single node, it will often cause abnormal stress concentration in the vicinity of the node due to the concentrated force, which will lead to inaccurate stress and displacement distribution, causing deviations in the final calculation results. Therefore, it is necessary to avoid applying loads to a single node, but to apply uniform loads to the area. When HyperMesh is combined with ANSYS for simulation, the application process of uniform loads needs to be implemented with the help of RBE3 units. RBE3 units are mainly used to distribute loads such as force and torque. Through RBE3 units, all nodes in the entire area can be captured, and then concentrated forces are applied to the central node. The load can be evenly distributed to each node on the plane. The selection of the central node can be automatically calculated and generated by the system, or it can be set and selected by yourself. Usually, the central node is a slave node, the surrounding nodes are master nodes, and the displacement of the slave node is the weighted average of the master node, so as to achieve effective force transmission. If the nodes on the solid unit are used as slave nodes, the structural stiffness will be slightly increased; if the slave nodes are suspended in the air, the structural stiffness will not be increased, and the calculation results will be more accurate. Therefore, the specific setting of the load in the present invention is to select the nodes on the distal radius articular surface and the distal radius palmar area as the main nodes, and set a point in the air as a slave node, and apply the load to the set slave nodes to apply a uniformly distributed load.

[0091] At this point, the overall finite element model is established. The obtained model is saved as a CDB format file and can be imported into ANSYS software for finite element calculation and analysis.

[0092] 4.5. Verification of mesh convergence

[0093] When verifying the mesh convergence, the compression condition was selected and different mesh sizes were set. The number of units and the maximum stress of the overall finite element model of the distal radius fracture internal fixation are shown in Table 4. As the mesh size decreases, the corresponding number of units in the model increases, and the maximum stress tends to be stable. The increase in the number of meshes will lead to longer calculation time. Considering 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 result of Berge et al.

[0094] Table 4 Mesh convergence analysis table

[0095]

Claims

1. A method for constructing a distal radius fracture plate internal fixation surgical model, characterized in that: The steps include: Step (1): Establishing a radial geometry model; Step (2): establishing a geometric model of the internal fixation device; Step (3): assembling the overall geometric model; Step (4): Establish the overall finite element model.

2. The method according to claim 1, characterized in that Step (1) comprises the following steps: Step (11): import the arm CT scan data, set the mask area of ​​the cortical bone and cancellous bone, select the radius area in a targeted manner, remove the non-target bone structure, fill the cavities in the cortical bone and cancellous bone pixel area, and generate the original radius geometry model by reverse modeling; Step (12): Repair the original radial geometry model generated in step (11).

3. The method according to claim 2, characterized in that Step (12) specifically includes: removing non-manifold edges, self-intersecting edges, highly refractive edges, spikes and existing void channels on the surface of the radius, so as to achieve preliminary smoothing of the surface of the radius model; Construct the model surface contour line and divide it into quadrilateral surface patches with similar areas. Within the divided quadrilateral surface patch contour line, convert each quadrilateral surface patch into a smaller quadrilateral grid, repair the grid map with deviation, and generate a smooth model.

4. The method according to claim 3, characterized in that Step (2) includes establishing a locking plate geometric model and establishing a screw geometric model.

5. The method according to claim 4, characterized in that Step (3) is specifically as follows: 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 between the screw and the plate thread and hole, and completing the assembly of the overall geometric model.

6. The method according to claim 5, characterized in that Step (4) specifically includes the following steps: 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±1 cm from the distal articular surface of the radius, and perform finite element mesh discretization by combining tetrahedral meshes and hexahedral meshes, so that the meshes of the contact areas between the screw thread and the radius and the steel plate are aligned, the cortical bone and the cancellous bone are connected at a common node, and the remaining parts are set to contact meshes; Step (42): Material parameters: The cancellous bone is equivalent to a continuous, uniform, isotropic single linear elastic material, and the material properties of the internal fixation material and the radial bone callus at different healing periods, as well as the degradation rate of the degradable material during the healing process are set; Step (43): Contact setting: setting 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 related parts is binding contact. The radius and the locking plate are standard contact. The callus area and the two end bones are connected by a common node and no contact is set. Step (44): Constraint and loading: Apply full constraints of 6 degrees of freedom to the grid within 2±1 cm of the proximal radius, and apply uniform loads to the distal articular surface and palmar side of the radius; Step (45): Verify mesh convergence: Select a mesh size of 1.5 ± 0.1 mm.

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