A design method for a porous metal bone substitute for the cervical spine

Abstract

The present invention relates to a design method for a cervical vertebra porous metal bone substitute for elastic modulus adaptation by imitating stress distribution between cervical vertebrae interfaces, comprising the following steps: a first step, a cervical vertebrae model is reconstructed in three dimensions by performing CT scanning on a patient, force conditions are formulated according to the patient's weight, and stress distribution in a vertebra to be replaced is calculated by using finite element method; a second step, a three-periodic minimal surface unit is constructed; 3×3×3 three-periodic minimal surface units are stacked into a cubic module; machine learning is used to construct a relationship between the relative density of the units in the cubic module and the mechanical properties of the cubic module, so as to design a module with optimal strength under a given elastic modulus; a third step, finite element stress data S is meshed to obtain S2; a fourth step, a module corresponding to the elastic modulus E is filled into a meshed node, and then a Boolean operation of the intersection of an existing vertebral body shape and the meshed module is performed to obtain a cervical vertebra porous metal bone substitute.

Description

Technical Field

[0001] The invention relates to the technical field of medical devices, and in particular to a design method for a cervical porous metal bone substitute for adapting the elastic modulus by imitating the stress distribution between cervical vertebrae interfaces. Background Art

[0002] Anterior cervical vertebral subtotal resection is an important standard surgical procedure for the treatment of cervical spine diseases. This surgery directly removes the diseased cervical vertebral body and requires the transplantation of bone implants to reconstruct the anatomical structure of the cervical spine in order to achieve postoperative cervical spine stability and long-term bone integration, and restore physiological function as much as possible. The selection of ideal bone substitutes that are compatible with the cervical vertebral structure and biomechanical properties is of great significance, directly affecting the safety of the operation and the patient's postoperative quality of life, and is a pain point and difficult problem in clinical practice.

[0003] At present, the application of 3D printing to manufacture porous artificial vertebrae is one of the future development directions of cervical vertebrae bone substitutes. This method imitates the cancellous bone structure to build loose titanium alloy micropores, provides bone ingrowth space and bone integration induction effect, and has broad application prospects. However, the traditional 3D printed cervical vertebrae bone substitute design method still has some shortcomings. First, in order to meet the mechanical strength requirements of the implant site, the traditional 3D printed cervical vertebrae substitute has a large implant weight and elastic modulus redundancy, which may lead to postoperative implant settlement. Second, the traditional 3D printed cervical vertebrae bone substitute uses an internal porous structure with uniform pore morphology and arrangement rules. Its uniform elastic modulus and mechanical properties are difficult to adapt to the local mechanical environment of different areas of the cervical spine at the same time. Summary of the invention

[0004] The present invention aims to provide a design method for a porous metal bone substitute for the cervical vertebrae that imitates the stress distribution between the cervical vertebrae interfaces to adapt the elastic modulus. The technical problems to be solved include at least how to meet the mechanical strength requirements of the implant site for the bone substitute and reduce the elastic modulus and density as much as possible on a macro scale, while at the same time using a variable porous structure distribution to achieve an adaptive design of the local elastic modulus of the implant and the mechanical environment on a micro scale.

[0005] In order to achieve the above object, the present invention provides a design method for a cervical porous metal bone substitute for adapting the elastic modulus by imitating the stress distribution between cervical vertebrae interfaces, comprising the following steps:

[0006] The first step is to reconstruct the cervical spine model by performing a CT scan on the patient, formulate the force conditions according to the patient's weight, use finite element calculation to replace the stress distribution in the vertebral body, and obtain the stress data S (x, y, z, s) in the finite element mesh node, where x, y, z are three-dimensional coordinates and s is the node stress;

[0007] The second step is to construct a three-periodic minimal surface unit with a side length of a. 3×3×3 three-periodic minimal surface units are stacked into a cubic module with a side length of A=3a. Machine learning is used to construct the relationship between the relative density of the three-periodic minimal surface units in the cubic module and the mechanical properties of the cubic module, so as to design a module with optimal strength under a given elastic modulus.

[0008] Step 3: Mesh the finite element stress data S to obtain S2: According to the side length A of the cubic module, set the integer nodes (X A,Y A,Z A ); where X, Y, Z are integers; S2=(X A,Y A,Z A, s2), where s2 is (X A,Y A,Z A) is the average value of stress s of all nodes in a cube with a center and a surrounding side length of A;

[0009] Step 4: Set the linear relationship between s2 and elastic modulus E: E=k s2, k are constants; then the module corresponding to the elastic modulus E is filled into the meshed node, and then the existing vertebral body shape and the meshed module are subjected to a Boolean operation of intersection to obtain the cervical porous metal bone substitute that imitates the stress distribution between the cervical vertebrae interfaces and adapts the elastic modulus.

[0010] Preferably, the mechanical properties of the cubic module include elastic modulus and yield strength.

[0011] Preferably, the value of k is between 1 and 200.

[0012] Preferably, the finite element calculation in the first step specifically includes:

[0013] L1.1. Reconstruct the entire vertebral geometry based on CT data scanning and perform finite element meshing;

[0014] L1.2. Add bending moment (2.5-5N·m) and compressive load (50-100N) force conditions according to the patient's age and weight;

[0015] L1.3. Select the diseased vertebra to analyze the stress state and derive the stress magnitude (xn,yn,zn,Pn) of each node n; xn,yn,zn are the spatial coordinates of node n, and Pn is the Mises stress (i.e., Mise stress) magnitude of node n;

[0016] Preferably, the relationship between the relative density of the units in the module and the mechanical properties of the module constructed by machine learning in the second step specifically includes:

[0017] L2.1. Using mathematical expressions Construct a spiral unit, where c is used to adjust the relative density of the spiral unit. According to the empirical formula, the relative density of the spiral unit = 0.27c, so the value range of c is 0-3.7; a filling unit is formed by splicing 3×3×3 spiral units;

[0018] L2.2. 3D print filling units with different densities and measure their elastic modulus. Use convolutional neural network machine learning to learn the corresponding relationship between the filling unit density matrix and the strength and elastic modulus.

[0019] L2.3. Obtain the filling unit structure with the highest strength under different elastic moduli.

[0020] Preferably, the fourth step of obtaining the cervical porous metal bone substitute that imitates the stress distribution between cervical vertebrae interfaces and adapts the elastic modulus specifically includes:

[0021] L3.1. Extract the geometric structure of the artificial vertebral body at the diseased vertebral body;

[0022] L3.2. Meshing based on finite element node stress: Integer mesh nodes (X A,Y A,Z A) is the geometric center, and the strength value S=average(Pn) is constructed by the average stress value of the finite element nodes contained in the cube with A as the side length;

[0023] L3.3. Perform a Boolean operation on the intersection of the square pore structure filled with spiral units of corresponding strength and the outer shape of the artificial cone to obtain the final model of the artificial cone.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The design method of the porous metal bone substitute for the cervical vertebrae of the present invention, which imitates the stress distribution between the cervical vertebrae interfaces and performs elastic modulus adaptation, obtains the vertebral stress distribution according to the finite element method, which is more in line with the actual stress state, matches the modulus by calculating the stress, and has the feasibility of fully reducing the stress concentration inside the vertebrae. At the same time, machine learning is used to construct the highest strength unit under modulus adaptation, and the prepared vertebrae have higher safety redundancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the specific implementation methods of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0027] Figure 1 It is a schematic diagram of machine learning constructing a spiral unit-based filling unit.

[0028] Figure 2 It is a schematic diagram of the construction of the artificial vertebral body shape.

[0029] Figure 3 is a schematic diagram of the final model of the artificial cone.

[0030] Figure 4 It is a schematic diagram of finite element node stress meshing processing. DETAILED DESCRIPTION

[0031] The present invention is described in more detail hereinafter to facilitate understanding of the present invention.

[0032] The design method of the porous metal bone substitute for the cervical vertebrae for adapting the elastic modulus by imitating the stress distribution between the cervical vertebrae interfaces of the present invention comprises the following steps:

[0033] The first step is to reconstruct the cervical spine model by performing a CT scan on the patient, formulate the force conditions according to the patient's weight, use finite element calculation to replace the stress distribution in the vertebral body, and obtain the stress data S (x, y, z, s) in the finite element mesh node, where x, y, z are three-dimensional coordinates and s is the node stress;

[0034] The second step is to construct a three-periodic minimal surface unit with a side length of a; 3×3×3 units are stacked into a cubic module with a side length of A=3a; machine learning is used to construct the relationship between the relative density of the units in the module and the mechanical properties (elastic modulus and yield strength) of the module, so as to design the module with the optimal strength under a given elastic modulus;

[0035] Step 3: Mesh the finite element stress data S to obtain S2: According to the side length A of the cubic module, set the integer nodes (X A,Y A,Z A ); where X, Y, Z are integers; S2=(X A,Y A,Z A, s2), where s2 is (X A,Y A,Z A) is the average value of stress s of all nodes in a cube with a center and a surrounding side length of A;

[0036] Step 4: Set the linear relationship between s2 and elastic modulus E: E=k s2, k are constants; then the module corresponding to the elastic modulus E is filled into the meshed nodes, and then the existing vertebral body shape and the meshed module are intersected by a Boolean operation to obtain the cervical porous metal bone substitute that imitates the stress distribution between the cervical vertebrae interfaces and adapts the elastic modulus.

[0037] Preferably, the value of k is between 1 and 200.

[0038] In a specific embodiment, the finite element calculation in the first step specifically includes:

[0039] L1.1. Reconstruct the entire vertebral geometry based on CT data scanning and perform finite element meshing;

[0040] L1.2. Add bending moment (2.5-5N·m) and compressive load (50-100 N) stress conditions according to the patient's age and weight;

[0041] L1.3. Select the diseased vertebra to analyze the stress state and derive the stress magnitude (xn,yn,zn,Pn) of each node n; xn,yn,zn are the spatial coordinates of node n, and Pn is the Mises stress (i.e., Mise stress) magnitude of node n;

[0042] In a specific embodiment, Figure 1 As shown in the figure, the relationship between the relative density of the unit in the module constructed by machine learning in the second step and the mechanical properties of the module specifically includes:

[0043] L2.1. Using mathematical expressions Construct a spiral unit, where c is used to adjust the relative density of the spiral unit. According to the empirical formula, the relative density of the spiral unit = 0.27c, so the value range of c is 0-3.7; a filling unit is formed by splicing 3×3×3 spiral units;

[0044] L2.2. 3D print filling units with different densities and measure their elastic modulus. Use convolutional neural network machine learning to learn the corresponding relationship between the filling unit density matrix and the strength and elastic modulus.

[0045] L2.3. Obtain the filling unit structure with the highest strength under different elastic moduli.

[0046] In a specific embodiment, Figure 2 and Figure 3 As shown, the fourth step of obtaining the cervical porous metal bone substitute for elastic modulus adaptation by imitating the stress distribution between cervical vertebrae interfaces specifically includes:

[0047] L3.1. Extract the geometric structure of the artificial vertebral body at the diseased vertebral body;

[0048] L3.2. Mesh the finite element stress data S to obtain S2: According to the side length A of the cubic module, set the integer nodes (X A,Y A,Z A ); where X, Y, Z are integers; S2=(X A,Y A,Z A, s2), where S2 is (X A,Y A,Z A) is the average value of stress s of all nodes in a cube with a center and a surrounding side length of A; Figure 4 shown.

[0049] L3.3. Perform a Boolean operation on the intersection of the square pore structure filled with spiral units of corresponding strength and the outer shape of the artificial cone to obtain the final model of the artificial cone.

[0050] The above describes the preferred embodiments of the present invention, but it is not intended to limit the present invention. Those skilled in the art may make improvements and changes to the embodiments disclosed herein without departing from the scope and spirit of the present invention.

Claims

1. A design method for a cervical porous metal bone substitute that imitates the stress distribution between cervical vertebrae interfaces to adapt the elastic modulus, characterized in that: The design method of the cervical porous metal bone substitute for elastic modulus adaptation by imitating the stress distribution between cervical vertebrae interfaces comprises the following steps: The first step is to reconstruct the cervical spine model by performing a CT scan on the patient, formulate the force conditions according to the patient's weight, use finite element calculation to replace the stress distribution in the vertebral body, and obtain the stress data S (x, y, z, s) in the finite element mesh node, where x, y, z are three-dimensional coordinates and s is the node stress; The second step is to construct a three-periodic minimal surface unit with a side length of a. 3×3×3 three-periodic minimal surface units are stacked into a cubic module with a side length of A=3a. Machine learning is used to construct the relationship between the relative density of the three-periodic minimal surface units in the cubic module and the mechanical properties of the cubic module, so as to design a module with optimal strength under a given elastic modulus. Step 3: Mesh the finite element stress data S to obtain S2: According to the side length A of the cubic module, set the integer nodes (X A,Y A,Z A ); where X, Y, Z are integers; S2=(X A,Y A,Z A, s2), where s2 is (X A,Y A,Z A) is the average value of stress s of all nodes in a cube with a center and a surrounding side length of A; Step 4: Set the linear relationship between s2 and elastic modulus E: E=k s2, k are constants; then the module corresponding to the elastic modulus E is filled into the meshed node, and then the existing vertebral body shape and the meshed module are subjected to a Boolean operation of the intersection to obtain the cervical porous metal bone substitute that imitates the stress distribution between the cervical vertebrae interfaces and adapts the elastic modulus.

2. The method for designing a porous metal bone substitute for the cervical vertebrae according to claim 1, wherein the method is characterized in that: The mechanical properties of the cubic module include elastic modulus and yield strength.

3. The method for designing a porous metal bone substitute for the cervical vertebrae according to claim 1, wherein the method is characterized in that: The value of k is between 1 and 200.

4. The method for designing a porous metal bone substitute for the cervical vertebrae according to claim 1, wherein the method is characterized in that: The finite element calculation in the first step specifically includes: L1.

1. Reconstruct the entire vertebral geometry based on CT data scanning and perform finite element meshing; L1.

2. Add bending moment and compression load conditions according to the patient's age and weight; L1.

3. Select the diseased vertebra for stress state analysis and derive the stress magnitude (xn,yn,zn,Pn) of each node n; xn,yn,zn are the spatial coordinates of node n, and Pn is the Mises stress of node n.

5. The method for designing a porous metal bone substitute for the cervical vertebrae by imitating the stress distribution between the cervical vertebrae interfaces and adapting the elastic modulus according to claim 1, characterized in that: The relationship between the relative density of the units in the module and the mechanical properties of the module constructed by machine learning in the second step specifically includes: L2.

1. Using mathematical expressions Construct a spiral unit, where c is used to adjust the relative density of the spiral unit, and a filling unit is formed by splicing 3×3×3 spiral units; L2.

2. 3D print filling units with different densities and measure their elastic modulus. Use convolutional neural network machine learning to learn the corresponding relationship between the filling unit density matrix and the strength and elastic modulus. L2.

3. Obtain the filling unit structure with the highest strength under different elastic moduli.

6. The method for designing a porous metal bone substitute for the cervical vertebrae by imitating the stress distribution between cervical vertebrae interfaces and adapting the elastic modulus according to claim 1, characterized in that: The fourth step of obtaining the cervical porous metal bone substitute that imitates the stress distribution between cervical vertebrae interfaces and adapts the elastic modulus specifically includes: L3.

1. Extract the geometric structure of the artificial vertebral body at the diseased vertebral body; L3.

2. Meshing based on finite element node stress: construct the strength value S=average(Pn) by taking the average stress value of the finite element nodes contained in a cube with an integer mesh node (X*A, Y*A, Z*A) as the geometric center and A as the side length; L3.

3. Perform a Boolean operation on the intersection of the square pore structure filled with spiral units of corresponding strength and the outer shape of the artificial cone to obtain the final model of the artificial cone.

7. The method for designing a porous metal bone substitute for the cervical vertebrae according to claim 4, wherein the method is characterized in that: The compression load is 50N to 100N.

8. The method for designing a porous metal bone substitute for the cervical vertebrae according to claim 4, wherein the method is characterized in that: The bending moment is 2.5 N·m to 5 N·m.

9. The method for designing a porous metal bone substitute for the cervical vertebrae according to claim 5, wherein the method is characterized in that: The relative density of the helical unit is equal to 0.27c.

10. The method for designing a porous metal bone substitute for the cervical vertebrae by imitating the stress distribution between cervical vertebrae interfaces and adapting the elastic modulus according to claim 5, characterized in that: The value range of c is 0-3.7.

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