A ue5-based orthopedic preoperative planning method

Abstract

The application discloses a kind of orthopedic preoperative planning methods based on UE5, belong to the field of graphics processing technology, this method includes the following steps: first, the static three-dimensional grid model of the patient's affected area is converted into dynamic grid model;Second, based on dynamic grid model, the wound area to be repaired is demarcated on the model surface by interactive operation, and the morphological characteristics of wound surface are simulated and simulated;Subsequently, the virtual resection operation is performed on the demarcated wound area, and the wound defect model is generated;Then, the shape, tension distribution and matching degree of the transplanted skin with the wound surface are simulated;In the simulation area, the transplanted skin model and the surrounding tissue can be virtually cut;Finally, the suture process of the transplanted skin and the wound surface is simulated.The application combines wound treatment, graft design and interactive cutting and suture simulation, provides visual, adjustable preoperative planning for orthopedic surgery, helps to improve the rationality and accuracy of surgical plan, and reduces the risk of surgery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graphics processing, and particularly relates to a preoperative planning method for plastic surgery based on UE5. BACKGROUND

[0002] In plastic surgery, preoperative planning is crucial to the success of the operation. Traditional preoperative planning often relies on the experience of doctors and two-dimensional images, which is difficult to intuitively show the operation effect and assess the operation risk. With the development of computer graphics technology, three-dimensional visualization and simulation technology are gradually increasing in the medical field, but the existing related technology still has deficiencies in dynamic editing, biomechanical simulation, interactive operation and other aspects, which cannot meet the high precision and high flexibility requirements of preoperative design for plastic surgery, especially in the details of two-point triangular surface processing, closed area searching, incision vertex separation and tension calculation. SUMMARY

[0003] The present application aims to overcome the problems in the prior art and provides a preoperative planning method for plastic surgery based on UE5. It should be noted that UE5 is a known prior art platform, and its basic functions such as graphics rendering, physical simulation and general interaction are common knowledge in the field. The innovation of the present application lies in the customization of the platform for medical scenarios.

[0004] UE5 is a real-time 3D development platform known in the art, which comes with the following features:

[0005] Graphics rendering: relying on Nanite, Lumen and other technologies, it realizes real-time light and shadow rendering and material display of three-dimensional models;

[0006] Physical simulation: through the Chaos physics system, it provides rigid body collision and basic flexible deformation modeling capabilities;

[0007] Interactive functions: support mouse, joystick and other peripheral inputs to realize virtual object clicking, dragging and other common interactive responses.

[0008] The above functions are existing technologies that can be directly obtained by those skilled in the art, but they are not adapted to the medical characteristics of preoperative planning for plastic surgery (such as surgical incisions and flap simulation), and cannot meet the needs of surgical planning

[0009] The present application does not simply reuse the existing functions of UE5, but makes deep innovations based on them. The specific differences are as follows:

[0010] 1. Modification of physical simulation function: develop a dynamic triangular surface splitting algorithm to meet the needs of surgical cutting and incision separation;

[0011] 2. Modification of soft body simulation function: through dynamic mesh model, real-time addition and deletion of vertex and reorganization of triangular surface, and addition of constraint to simulation vertex to realize functions such as drag stitching;

[0012] 3. Extension of graphic rendering function: realization of medical tissue simulation, mapping of mechanical calculation result to visual effect;

[0013] The purpose of the application is achieved by the following technical solutions:

[0014] The application provides a preoperative planning method for orthopedic surgery based on UE5, comprising the following steps:

[0015] S1. Convert the static three-dimensional mesh model of the patient's affected area into a dynamic mesh model; so that the mesh model data can be dynamically edited at runtime. This step lays the foundation for subsequent interactive operation and simulation simulation. Through the characteristics of the dynamic mesh, various editing operations can be responded to in real time. S2. Based on the dynamic mesh model, the wound area to be repaired is marked on the model surface through interactive operation, and the morphological characteristics of the wound are simulated; the doctor can determine the area to be repaired according to the actual situation of the patient, and at the same time understand the basic form of the wound through simulation. S3. Perform virtual resection operation on the marked wound area to generate a wound defect model; this operation can simulate the resection process in surgery, providing accurate defect morphology reference for subsequent graft design. S4. Mark the graft skin area from the pre-set donor dynamic mesh, and simulate the morphology, tension distribution and matching degree of the graft skin with the wound through biomechanical simulation; through biomechanical simulation, the state of the graft skin in the body can be more realistically simulated, helping the doctor to evaluate the grafting effect. S5. In the simulation area, the graft skin model and the surrounding tissue are virtually cut, and drag operation is supported to realize secondary incision design, flexibly adjusting the incision position, angle and range; the system updates the dynamic mesh model in real time to reflect the effect after cutting and adjusting. S6. Simulate the suture process of the graft skin and the wound, and simulate the tissue morphology after suture through the deformation calculation of the dynamic mesh; through the simulation, the doctor can know the effect after suture in advance, and further evaluate the rationality of the surgical plan. S7. Based on the tissue morphology after simulation suture, triangular surface solving and reconstruction between two points are carried out, recursive search for vertices and triangular surfaces in the closed area is carried out, incision vertex separation is realized, and tension or tension is calculated according to the relationship between vertices and triangular surfaces. Triangular surface solving and reconstruction between two points can optimize the model structure, recursive search can help accurate positioning of the area, incision vertex separation can improve the cutting accuracy, and tension or tension calculation can more realistically simulate the stress state of the skin.

[0016] In some embodiments, the static three-dimensional mesh model of the patient's affected area is converted into a dynamic mesh model, comprising:

[0017] The repeated vertex optimization mesh structure is removed, and the calculation formula is: for a vertex in the vertex set and , if the absolute value of the position difference between the two vertices is less than a set threshold , that is

[0018] , it is determined that the vertex is repeated, and the vertex is merged, wherein represents the position of the vertex , and represents the position of the vertex ;

[0019] The normal of the mesh vertex is corrected, and the correction formula is

[0020] , wherein is the corrected normal, and is the normal of the adjacent triangular face. In this way, the accuracy of the model surface light rendering is improved, and the model is more consistent with the actual visual effect.

[0021] In some embodiments, the repeated vertex is determined and the merging processing includes:

[0022] Vertex list deduplication: in the vertex array of the mesh, the data of vertices i and j is found, the data includes the position information, the normal information and the vertex associated all triangular face information and the vertex information contained in the triangular face; the vertex with less triangular face information in or is deleted;

[0023] Triangular face association update: each triangular face data contains three vertex indexes, the vertex information of the triangular face associated with the deleted vertex or is replaced by the reserved vertex index, for example, the triangular face original vertex index is , wherein is the deleted vertex index, then vertex information in is replaced by , and the updated result is . It should be noted that if the vertex index of the triangular face associated with the deleted vertex contains the repeated vertex , the triangular face information is directly deleted without replacement processing;

[0024] It should be clear that the vertex list deduplication and triangle face association update of the present application is not simply processing UE5 model data, but deeply fuses particle information of flap simulation, adapts to tissue mechanics solving constraints in advance, converts regular grid optimization into a process serving orthopedic surgery simulation, which is different from the prior art.

[0025] In some embodiments, in the biomechanical simulation, the skin properties are simulated by creating particle masses and spring constraints, where the particle mass is calculated as

[0026] , where is the particle mass, is the total mass, is the number of particles; the stiffness of the spring constraint is set by the tensile stiffness and bending stiffness parameters to simulate the tensile and bending properties of the skin, and a damping coefficient is introduced to simulate the attenuation of skin motion, and the particle velocity update formula is

[0027] , where is the velocity value of the current frame, is the velocity value of the previous frame, is the motion attenuation value, is the interval time between the current frame and the previous frame, represents the acceleration; the skin tension distribution calculation uses the extended formula of Hooke's law:

[0028] , where is the tension, is the current length, is the original length, represents the tensile stiffness.

[0029] In some embodiments, in the virtual resection operation, it is determined whether a point is on the triangle plane by calculating the distance from the point to the triangle plane, and the formula is:

[0030] , where is a point on the plane, is the plane normal vector, is the value of the plane equation; then the distance from a point outside the plane to the plane is

[0031] When is less than a set threshold, it is determined that the point is on the plane; the edge smoothing degree calculation uses the weighted average formula: the new position of the edge vertex

[0032] , where is the smoothed new position, is the current edge point, is the adjacent vertex weight, assigned inversely proportional to the distance.

[0033] In some embodiments, in the virtual cutting operation, the intersection point of the line segment connecting the two cutting points and the normal vector of the triangle face they are on forms a plane with the point the end points of the triangle edges contained in the triangle face associated with the point is the intersection point of , the formula is:

[0034] , , , , , , where represents the vector formed by the cutting point , represents the vector formed by the end point of the triangle edge , is the dot product of the triangle edge vector and the cutting plane, is the ray parameter, indicating the step ratio in the direction from , when and , it means that the intersection point is on the triangle edge; a new vertex is created through the intersection point , the new triangle face is reorganized through and , and according to the triangle edge relationship, it is moved to the plane side, and then is taken as the new recursive solution until the triangle face to be solved contains the vertex , the resulting intersection point is added to the cutting vertex set.

[0035] In some embodiments, the simulation of the suture process between the transplanted skin and the wound surface includes:

[0036] In the simulation of the suture process, the suture simulation is achieved by applying multi-level constraints to the vertices:

[0037] Rigid constraint: position constraint is applied to the suture point pair , the constraint equation is

[0038] , where is the The corresponding position of each frame, For each frame The corresponding position, is the stitching accuracy threshold, which ensures the constraint satisfaction through the position correction algorithm;

[0039] Elastic constraint: a spring constraint is applied to the influence vertex around the stitching point, and the constraint strength decays with distance, and the elastic force is

[0040] , wherein is the elastic coefficient, is the current distance, is the initial distance, is the unit directional vector;

[0041] Area constraint: set a maximum displacement threshold for the vertices within the stitching area, and the constraint formula is

[0042] , wherein is the current position of the vertex, is the initial position, is the maximum allowed displacement;

[0043] Moving distance calculation:

[0044] , , wherein and are two points to be stitched, is a method for obtaining the distance between and point position, is the moving speed, is the distance that point needs to move, is the distance that point needs to move, The method makes the value of not less than 0 and not greater than , is the frame interval duration, is the moving weight of , is the current distance of and , and the position of the two points is gradually adjusted through the moving distance to simulate the stitching effect.

[0045] In some embodiments, the two-point triangular surface solving and reconstruction includes:

[0046] First, determine the shortest path between the two points, and the set of triangular surfaces on the path is the solving target, and the two points are​ 、 , three vertices of a triangular face 、 、 , if and are on two sides of a triangular face , and the line segment intersects the triangular face , then the triangular face is one of the triangular faces on the path, and in this way a sequence of triangular faces between two points is constructed, and when reconstructing, the coordinates of the new triangular face vertices are calculated as new vertices

[0047] , wherein , 、 、 are weight coefficients assigned according to the position of the triangular face in the path.

[0048] In some embodiments, the recursive search for vertices and triangular faces within the closed region comprises:

[0049] starting from an initial vertex , recursively traversing vertices adjacent to the current vertex , if satisfies the closed region boundary condition, it is added to the set of region vertices, and the triangular faces containing and the vertices already in the set are added to the set of region triangular faces.

[0050] In some embodiments, the cut vertex separation comprises:

[0051] The distance ratio of a vertex on the cut line to the two endpoints of the cut is calculated, assuming that the two endpoints of the cut are 、 , the distance of the vertex to is , and the distance to is , the distance ratio

[0052] When is within the range of , the vertex is marked as a cut separation vertex, and is assigned to different vertex subsets according to the value of ; the vertices on both sides of the cutting plane are classified, assuming that the distance of a vertex to the cutting plane is , when , it is a positive side vertex of the plane, and when ​The time is the plane negative side vertex, The distance threshold value is established, the triangular surface across the cutting plane is split to generate a new triangular surface set, and the new vertex offset after splitting is calculated as , wherein The cutting plane normal vector is The separation distance parameter is established, the bidirectional mapping relationship of the cutting edge vertex is established, and the mapping strength coefficient is

[0053] , wherein , The distance of the corresponding vertex to the cutting start point is The attenuation coefficient is

[0054] The tension or tension according to the relationship between the vertex and the triangular surface is calculated, including:

[0055] For the vertex and the triangular surface containing , the formula for calculating the tension is

[0056] , wherein The deformation variable of the triangular surface is The initial area of the triangular surface is The tension coefficient is The calculation of the tension

[0057] , wherein The ratio of the distance of the vertex to the edges of the triangular surface to the length of the edges of the triangular surface is

[0058] It should be further pointed out that the technical features of the above-mentioned embodiments can be combined or replaced with each other to form new technical solutions without conflict.

[0059] Compared with the prior art, the present application has the following advantages:

[0060] The present application realizes the simulation of the organization of physical properties through the conversion of static grid to dynamic grid, and provides a visual and adjustable preoperative planning tool for plastic surgery by combining with wound treatment, transplantation design and interactive cutting and suture simulation. The newly added two-point triangular surface solving and reconstruction, recursive search for vertices and triangular surfaces in the closed area, incision vertex separation and calculation of tension or tension according to the relationship between the vertex and the triangular surface, and related formulas further improve the accuracy and authenticity of the simulation, and can more comprehensively simulate various conditions in the operation. Doctors can make more accurate surgical design and effect evaluation before operation, which helps to improve the rationality and accuracy of the surgical plan and reduce the risk of operation. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 A UE5-based orthopedic preoperative planning method flow chart is shown for an embodiment of the present application;

[0062] Figure 2 An optimization of repeated vertexes when converting a static mesh to a dynamic mesh is shown in the schematic diagram for an embodiment of the present application;

[0063] Figure 3 A schematic diagram of forming a cutting path point set is shown for an embodiment of the present application;

[0064] Figure 4 A schematic diagram of reconstructing a triangular face is shown for an embodiment of the present application;

[0065] Figure 5 A schematic diagram of solving the intersection of a cutting path and a triangular edge is shown for an embodiment of the present application;

[0066] Figure 6 A schematic diagram of separating a cutting vertex is shown for an embodiment of the present application. DETAILED DESCRIPTION

[0067] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0068] It should be noted that the defects in the above prior art solutions are the result of the inventors' practice and careful study, therefore, the discovery process of the above problems and the solutions proposed by the embodiments of the present application to solve the above problems should be the contribution of the inventors to the present application, and should not be understood as technical content known to those skilled in the art.

[0069] In an exemplary embodiment, with reference to FIG. 1, a UE5-based orthopedic preoperative planning method includes the following steps.

[0070] S1. Static mesh to dynamic mesh: In UE5, a static three-dimensional mesh model is converted to a dynamic mesh model by related components and functions. As shown in FIG. 2, in the conversion process, in order to optimize the mesh structure, repeated vertexes need to be removed. The conversion of the static three-dimensional mesh model of the patient's affected area to a dynamic mesh model includes:

[0071] Removing repeated vertexes to optimize mesh structure, the calculation formula is: for a vertex in the vertex set and , if the absolute value of the difference between the positions of two vertices is less than a set threshold , i.e.

[0072] , then it is determined that the vertices are repeated, and a merging process is performed thereon, wherein represents the position of vertex , and represents the position of vertex ;

[0073] The normal of the grid vertex is corrected, and the correction formula is

[0074] , wherein is the corrected normal, and is the normal of the adjacent triangular face. In UE5 is an extremely small threshold constant, and is usually 0.0001 units, which depends on the scale during modeling, such as 0.0001 mm in a millimeter-level scene;

[0075] Vertex list deduplication: in the vertex array of the grid, the data of vertices i and j are found, which includes the position information, normal information and all triangular face information associated with the vertex, and the vertex information contained in the triangular face; the vertex with less triangular face information in or is deleted;

[0076] Triangular face association update: each triangular face data contains three vertex indexes, the vertex information of the triangular face associated with the deleted vertex or is replaced by the reserved vertex index, such as the triangular face , wherein the original vertex index is , and is the deleted vertex index, then is replaced by in the vertex information of , and the updated result is . It should be noted that if the vertex index of the triangular face associated with the deleted vertex contains the repeated vertex , then the triangular face information is directly deleted without replacement processing;

[0077] S2. Defining the wound area and simulation: as shown in FIGS. 3 and 4, the doctor performs operations on the dynamic grid model through the interactive device to form a set of path points , creates a new model vertex at the path point, and reconstructs the triangular face according to the adjacent vertex. If the adjacent vertices are not in the same triangular face, then the intersection point needs to be calculated through a triangular face intersection point solving algorithm, and is added to the set The new model structure is obtained. Based on the characteristics of the dynamic mesh model, the delineated area is displayed in real time in response to the operation.

[0078] S3. Virtual resection generates a defect model: according to the delineated wound area, a virtual resection operation is performed. In the virtual resection operation, it is judged whether a point is on a triangular plane by calculating the distance from the point to the triangular plane, and the range of resection is determined, and the formula is:

[0079] wherein is a point on the plane, is a plane normal vector, is the value of the plane equation; then a point outside the plane is the distance from the point to the plane.

[0080] When is less than the set threshold, it is determined that the point is on the plane; the edge smoothing degree calculation adopts a weighted average formula: the new position of the edge vertex

[0081] wherein is the new position after smoothing, is the current edge point position, is the weight of the adjacent vertex, which is assigned in inverse proportion to the distance.

[0082] As shown in FIG. 5 and FIG. 6, in the virtual cutting operation, the intersection point of the line connecting the two cutting points and the plane formed by the normal vector of the triangular face containing the point associated with the triangular face is calculated, and the intersection point of the end points of the triangular edges contained in the triangular face and the line connecting the two cutting points is calculated, and the formula is:

[0083] wherein represents a vector formed by the cutting point , represents a vector formed by the end point of the triangular edge , is the dot product of the triangular edge vector and the cutting plane, is a ray parameter, which represents the step ratio in the direction from , , when and ​​​​​​The time represents the intersection on the triangle side; through the intersection Create a new vertex , through and Recombine the new triangular surface, and move to the plane Two sides according to the relationship of the triangle side, and then As the new Recursive solution until the triangular surface contains the vertex The resulting intersection is added to the cutting vertex set. Make the cutting vertex and surface continuous.

[0084] S4. Transplant skin area demarcation and simulation: after demarcating the transplant skin area from the preset donor area dynamic grid, perform biomechanical simulation. In the simulation, the transplant skin area is divided into multiple particles, where the particle mass is calculated in the following manner

[0085] , wherein is the particle mass, is the total mass, is the number of particles; the stiffness of the spring constraint is set by the tensile stiffness and bending stiffness parameters to simulate the tensile and bending properties of the skin, and a damping coefficient is introduced to simulate the attenuation of skin movement, and the particle velocity update formula is

[0086] , wherein is the velocity value of the current frame, is the velocity value of the previous frame, is the motion attenuation value, is the interval time between the current frame and the previous frame, represents the acceleration; the skin tension distribution calculation adopts the extended formula of Hooke's law:

[0087] , wherein is the tension, is the current length, is the original length, represents the tensile stiffness. Thus, the simulation of the form and wound matching degree of the transplant skin is realized.

[0088] S5. Virtual cutting and secondary incision design: the doctor performs virtual cutting on the transplant skin model and the surrounding tissue. Through the dragging operation of the mouse or other interactive devices, the secondary incision design is realized, and the position, angle and range of the incision are flexibly adjusted, and the system updates the dynamic grid model in real time to reflect the effect after cutting and adjustment.

[0089] The simulation of the suture process of the simulated transplant skin and the wound includes:

[0090] In the simulated stitching process, stitching simulation is achieved by applying multi-level constraints to the vertices:

[0091] Rigid constraint: Apply positional constraints to the suture point pair, assuming the suture point pair is... The constraint equations are

[0092] ,in for At the corresponding position in each frame, For each frame The corresponding position To determine the stitching accuracy threshold, a position correction algorithm is used to ensure that the constraints are met.

[0093] Elastic constraint: A spring constraint is applied to the influence vertices around the stitching point. The constraint strength decreases with distance, and the elastic force is...

[0094] ,in The elastic coefficient, Current distance, The initial distance, It is a unit direction vector;

[0095] Region constraint: Set a maximum displacement threshold for vertices within the stitching region. Constraint formula

[0096] ,in The current position of the vertex. The initial position, This is the maximum allowable displacement;

[0097] Distance Calculation:

[0098] , , ,in and For the two points that need to be sutured, To obtain and Methods for determining the distance between points For movement speed, For point The distance to be moved For point The distance to be moved The method makes The value will not be less than 0 and will not be greater than 0. , The frame interval duration for The moving weights, for and current distance, the two points position is adjusted step by step by the moving distance to simulate the suture effect.

[0099] S6. Triangular surface solving and reconstruction between two points: the shortest path between two points is determined first, and the triangular surface set on the path is the solving target, assuming that the two points are , , and the three vertices of the triangular surface are , , . If and are on the two sides of the triangular surface , and the line segment intersects the triangular surface , then the triangular surface is one of the triangular surfaces on the path. In this way, the triangular surface sequence between the two points is constructed, and when reconstructing, the new triangular surface vertex coordinates are calculated as the new vertex

[0100] , wherein , , , are weight coefficients assigned according to the position of the triangular surface in the path.

[0101] S7. Recursive search for vertices and triangular surfaces in the closed region: taking the initial vertex as the starting point, recursively traverse the vertices adjacent to the current vertex . If satisfies the closed region boundary condition, it is added to the region vertex set, and the triangular surface containing and the vertices already in the set is added to the region triangular surface set.

[0102] S8. Cut vertex separation: calculate the distance ratio of the vertex on the cut line to the two endpoints of the cut, assuming that the two endpoints of the cut are , , the distance of the vertex to is , and the distance to is , the distance ratio

[0103] When is in the range of , the vertex is marked as a cut separation vertex and is assigned to different vertex subsets according to the value; classify the vertices on both sides of the cutting plane, assuming that the distance of the vertex to the cutting plane is ,when When is the positive or negative vertex of the plane, when At that time, it is the negative vertex of the plane. The distance threshold is used; the triangular facets crossing the cutting plane are split to generate a new set of triangular faces. The offset of the new vertices after splitting is calculated as follows: ,in For the cutting plane normal vector, The separation distance parameter is used; a two-way mapping relationship is established between the vertices of the cutting edge, and the mapping intensity coefficient is...

[0104] ,in , This represents the distance from the corresponding vertex to the starting point of the cut. The attenuation coefficient;

[0105] The calculation of tension or tensile force based on the relationship between the vertex and the triangular face includes:

[0106] For vertex and contain The formula for calculating the tensile force on the triangular facet is:

[0107] ,in For the deformation variable of the triangular face, Let the initial area of ​​the triangle be... Tension coefficient; tension The calculation considers the distances between the vertex and each side of the triangle face based on the tension force; the formula is:

[0108] ,in It is the ratio of the distance from the vertex to each side of the triangle to the side length of the triangle.

[0109] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A UE5-based orthopedic preoperative planning method, characterized by, The method comprises the following steps: S1. converting a static three-dimensional grid model of a patient's affected area into a dynamic grid model; S2. based on the dynamic grid model, defining a wound area to be repaired on the model surface through interactive operation, and simulating the morphological characteristics of the wound; S3. performing a virtual resection operation on the defined wound area to generate a wound defect model; S4. defining a skin graft area from a pre-set donor dynamic grid, and simulating the morphology, tension distribution and matching degree of the skin graft with the wound through biomechanical simulation; S5. in the simulation area, performing virtual cutting on the skin graft model and surrounding tissue, and supporting drag operation to realize secondary incision design, and flexibly adjusting the incision position, angle and range; S6. simulating the suture process of the skin graft and the wound, and calculating the tissue morphology after suture through the deformation of the dynamic grid; S7. based on the simulated tissue morphology after suture, solving and reconstructing triangular faces between two points, recursively searching for vertices and triangular faces in the closed area, realizing separation of incision vertices, and calculating tension or tension according to the relationship between vertices and triangular faces; The conversion of the static three-dimensional grid model of the patient's affected area into the dynamic grid model comprises: Remove duplicate vertex to optimize mesh structure, the formula is: for vertex in vertex set and , if the absolute value of the position difference of two vertices is less than the set threshold , that is If the vertex is duplicated, it is merged, wherein represents the position of the vertex represents the position of the vertex ;​ The correction formula of the grid vertex normal is , wherein is the modified normal, is the normal of the adjacent triangle. The simulation of the suture process of the skin graft and the wound comprises: In the simulation of suture, multi-level constraints are applied to the vertices to realize suture simulation: Rigid constraint: impose a position constraint on the suture point pair, let the suture point pair be , and the constraint equation is , wherein is at a position corresponding to each frame, is each frame corresponding position, is a stitching accuracy threshold value, which ensures constraint satisfaction through a position correction algorithm; Elastic constraint: spring constraint is applied to the vertices around the suture point, the constraint strength decays with distance, and the elastic force is , wherein is the elastic coefficient, is the current distance, is the initial distance, is the unit directional vector; Regional constraint: set a maximum displacement threshold for the vertices in the suture area, and the constraint formula is , wherein is the current position of the vertex, is the initial position, is the maximum allowed displacement; The calculation of the moving distance comprises: , , , wherein and are two point positions that need to be sutured, is a method for obtaining and the distance between the point positions, is the moving speed, is the distance that the point needs to move, is the distance that the point needs to move, the method makes the value of not less than 0 and not greater than , is the frame interval duration, is the moving weight of , is the current distance of and , and the two point positions are gradually adjusted by the moving distance to simulate the suture effect; the triangular surface solving and reconstruction between the two points comprises: First, the shortest path between two points is determined, and the set of triangular faces on the path is the solution target. Let the two points be , , the three vertices of the triangular face be , , , if and are on the two sides of the triangular face respectively, and the line segment intersects the triangular face , then the triangular face is one of the triangular faces on the path. In this way, the triangular face sequence between the two points is constructed, and when reconstructing, the new triangular face vertex coordinates are calculated as the new vertex , wherein , , , are weight coefficients assigned according to the position of the triangle in the path; said recursive search for vertices and triangles within the closed region comprises: Starting from the initial vertex , recursively traverse the vertex adjacent to the current vertex , if the closed region boundary condition is met, add it to the region vertex set, and add the triangular face containing and the vertex already in the set to the region triangular face set; the cut vertex separation includes: The ratio of the distance from the vertex on the cut line to the two end points of the cut is set, with the two end points of the cut being , , the distance from the vertex to is , and the distance to is , the distance ratio , when in range, mark the vertex as a cut-off vertex and assign it to different vertex subsets according to value; classify the vertices on both sides of the cutting plane, let the distance of vertex to the cutting plane be , when , it is a positive-side vertex of the plane, when , it is a negative-side vertex of the plane, is the distance threshold; split the triangular faces across the cutting plane to generate a new triangular face set, and the offset of the new vertex after splitting is calculated as , where is the normal vector of the cutting plane, is the separation distance parameter; establish a bidirectional mapping relationship of the cutting edge vertices, and the mapping strength coefficient is , wherein , is the distance of the corresponding vertex to the cut start point, is the decay coefficient; The calculation of the tension or tension according to the relationship between the vertices and the triangular faces comprises: For the vertex and the triangular face containing the formula for the calculation of the pull force is , wherein is a deformation variable of the triangular face, is an initial area of the triangular face, is a tension coefficient; tension The calculation of the tension takes into account the distance of the vertex from the sides of the triangular face on the basis of the tension, the formula being , wherein is the ratio of the distance of the vertex to the sides of the triangle to the length of the sides of the triangle.

2. A preoperative orthopaedic planning method based on UE5 according to claim 1, characterized in that, The determination of the repeated vertices comprises: Vertex list deduplication: in the vertex array of the mesh, find vertices and Data including position information, normal information and all triangle face information associated with the vertex and vertex information contained in these triangle faces; delete vertices or with less triangle face information; Triangular face association update: each triangular face data contains three vertex indexes, and the corresponding deleted vertex in the vertex information of the triangular face associated with the deleted vertex i or j is replaced with the reserved vertex index.

3. A preoperative orthopaedic planning method based on UE5 according to claim 1, characterized in that, In the biomechanical simulation, the skin characteristics are simulated by creating particle mass and spring constraint, wherein the particle mass calculation method is , wherein is the particle mass, is the total mass, is the number of particles; the stiffness of the spring constraint is set by the tensile and bending stiffness parameters, which are used to simulate the tensile and bending properties of the skin, introducing a damping coefficient to simulate the attenuation of the skin motion, the particle velocity update formula is , wherein is a velocity value of a current frame, is a velocity value of a previous frame, is a motion decay value, is an interval time between the current frame and the previous frame, denotes an acceleration; the skin tension distribution calculation employs a Hooke's law extended formula: wherein is the tension, is the current length, is the original length, denotes the tensile stiffness.

4. The UE5-based orthopedic preoperative planning method of claim 1, wherein, In the virtual resection operation, whether a point is on the triangular plane is judged by calculating the distance from the point to the triangular plane, and the formula is: where is a point on the plane, is a normal vector to the plane, is the value of the plane equation; then a point outside the plane has a distance When less than a set threshold, the decision point is on the plane; The calculation of the cutting edge smoothness adopts a weighted average formula: the new position of the edge vertex wherein is the smoothed new position, is the current edge point position, is the adjacent vertex weight, assigned inversely proportional to the distance.

5. The preoperative orthopaedic surgical planning method based on UE5 of claim 1, wherein, In the virtual cutting operation, the two cutting points are connected and the normal vector of the triangle face formed by the connection and the point is calculated The intersection point of the triangle edge , the formula is: , , , , , , wherein is the vector formed by the cut point , is the vector formed by the end point of the triangle edge , is the triangle edge vector , is the dot product of the cut plane and is the ray parameter, indicating the step proportion in the direction from , when and , the intersection point is on the triangle edge; a new vertex is created by the intersection point , , the new triangle face is reorganized by and , and moved to the side of the plane according to the triangle edge relationship, and then is taken as the new and recursively solved until the triangle face to be solved contains the vertex , the obtained intersection point is added to the cut vertex set.

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