Integrated porous backbone prosthesis based on 3D printing technology

Abstract

The invention discloses an integrated porous backbone prosthesis based on a 3D printing technology. The invention provides an integrated porous diaphysis prosthesis which comprises the following steps: 1, designing the integrated porous diaphysis prosthesis by utilizing a modular design method; 2, the permeability and mechanical property of the contact area are tested, the structure of the contact area is more similar to that of the thighbone through fusion design, and the porous structure provides conditions for bone cell growth; 3, biomechanical analysis and comparison are carried out on the bone cement type diaphysis prosthesis and the integrated porous diaphysis prosthesis, and it is found that the porous diaphysis prosthesis can reduce the stress shielding effect and promote bone tissue growth. The porous diaphysis prosthesis designed by the invention is more compactly attached to the femur and more conforms to the anatomical shape of the human body, and the force line of the lower limbs of the human body is prevented from being changed due to the structure of the prosthesis. The integrated porous backbone prosthesis simulates the structure of a natural bone to a great extent, the comprehensive performance is excellent, and bone cell growth, nutrient substance transportation and mechanical property support are improved to a great extent.

Description

Technical Field

[0001] The present invention relates to the technical field of reconstruction after femoral tumor resection, and in particular to an integrated porous bone prosthesis based on 3D printing technology that can reduce stress shielding effect. Background Art

[0002] Limb-sparing therapy is currently the main method for treating primary malignant bone tumors. The diaphyseal prosthesis reconstruction method not only has the advantages of less side damage, no influence on bone healing, and no risk of tumor cell implantation, but also can help patients recover the activity of the affected limb early and reduce related complications such as joint stiffness caused by limb immobilization. At present, the most commonly used diaphyseal prosthesis in clinical practice is still the modular bone cement prosthesis, which has good immediate stability and provides guarantee for the short-term recovery of patients. However, with the increase of use time, due to the mismatch between the elastic modulus of the prosthesis and the femur, the stress shielding effect gradually becomes prominent, and aseptic loosening problems are prone to occur, leading to bone absorption, collapse and other problems. In recent years, with the development of 3D printing technology, 3D printed porous structures have gradually been applied to implants. The porous structure has an interconnected pore structure, which can provide conditions for the growth of bone cells. At the same time, the bone-prosthesis composite structure can provide good connection strength. At the same time, the design of the porous structure can reduce the elastic modulus of the prosthesis, thereby effectively reducing or eliminating the "stress shielding" effect. However, common porous structures, such as body-centered cubic unit (BCC), face-centered cubic unit (FCC), diamond structure, etc., have problems such as insufficient compressive strength and stress concentration in unit cells, which are difficult to solve. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] In view of the above deficiencies in the prior art, the technical problem to be solved by the present invention is: to provide an integrated porous backbone prosthesis based on 3D printing technology, which, under the premise of ensuring that the porous backbone prosthesis has sufficient yield strength, makes its elastic modulus match that of bone tissue as much as possible, reduces the stress shielding effect, and solves the problem of stress concentration in the porous structure.

[0005] (II) Technical solution

[0006] In order to realize the above-mentioned integrated porous backbone prosthesis based on 3D printing technology, the present invention provides the following technical solutions:

[0007] First, based on the patient's CT and MRI data, the femoral model of the patient was reconstructed using 3D modeling software, and the simulated surgical plan was determined according to the tumor location to obtain the bone defect data model. According to the location and length of the bone defect, the basic geometric shape of the diaphyseal prosthesis was determined. The prosthesis was divided into modules using a modular design method. The fusion structure was constructed using the TPMS fusion formula in the contact area according to the distribution of the femoral skin and cancellous bone. The load-bearing area structure was optimized using the topological optimization method in the load-bearing area, and the load-bearing area design was completed in combination with a porous structure. Finally, the prosthesis model was formed by combining the lateral steel plate. The contact area was simulated for permeability and quasi-static compression to verify the module performance. The prosthesis was assembled with the bone defect model, and biomechanical analysis was performed to observe the femoral stress and determine whether good bone ingrowth could be achieved.

[0008] (III) Beneficial effects

[0009] Compared with the prior art, the present invention provides an integrated porous backbone prosthesis based on 3D printing technology, which has the following beneficial effects: the present invention introduces the concept of modular design in the design process of the backbone prosthesis, divides the prosthesis into different design areas, and adopts a fusion TPMS structure that is more similar to the human bone structure in the contact area, which effectively reduces the stress shielding effect and improves the connection strength between the femur and the prosthesis. The load-bearing area adopts a topological optimization method to optimize the overall structure while ensuring the load-bearing strength. Compared with the traditional bone cement prosthesis, the present invention can effectively improve the equivalent strain of the contact surface between the femur and the prosthesis, which is conducive to stimulating bone integration of the femur, and provides a feasible solution for the clinical treatment of bone defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a topology optimization result diagram of an embodiment of the present invention;

[0011] Figure 2 1 is a structural diagram of the upper and lower contact regions of an embodiment of the present invention, (a) upper contact region, (b) lower contact region;

[0012] Figure 3 This is a geometric model diagram of an integrated porous bone prosthesis according to an embodiment of the present invention;

[0013] Figure 4 is a diagram showing the simulation results of the contact zone permeability performance of an embodiment of the present invention;

[0014] Figure 5 is a diagram of the mechanical properties simulation results of the contact area of ​​an embodiment of the present invention; DETAILED DESCRIPTION

[0015] The following is a detailed description of the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The present invention provides an integrated porous bone prosthesis based on 3D printing technology, comprising the following steps:

[0017] The femur CT data of a patient was selected and imported into Mimics 21.0 software for analysis to generate a 3D model. The model was saved in STL format and imported into Geomagic studio 12 for further processing such as filling holes and smoothing surfaces to construct a femur solid model. According to the patient's condition, the femur model was stretched and resected to obtain the patient's bone defect model. The resected part was saved as the main part of the stem prosthesis, and the lateral steel plate was used to form the initial stem prosthesis model.

[0018] According to the modular design concept, the initial model of the backbone prosthesis is modularly divided into four parts: the load-bearing area, the upper and lower contact areas, and the lateral steel plate. The load-bearing area is designed by topological optimization, and the prosthesis is assembled with the bone defect model. The lower end of the femur is set to be completely fixed, and the joint force and muscle force are applied to the femoral head and greater trochanter respectively. The load-bearing area is set as the design area, and other parts are non-design domains. Physiological loads and distal fixation constraints are added. The strain energy density is used as an indicator to evaluate the flexibility or stiffness of the backbone prosthesis, which is defined as the sum of its unit strain energy. Minimizing the strain energy density can achieve the maximum stiffness of the backbone prosthesis at a given optimized volume fraction, thereby increasing its stability and obtaining the final topological optimization results. Figure 1 The contact area adopts a fused porous structure design. The internal and external structure areas are determined according to the femoral CT data. Based on the properties of the femoral structure and various TPMS structures, the fusion method of the external Diamond structure and the internal Gyroid structure is selected to build a fusion area model. The implicit modeling method is used to design based on the implicit equation of the TPMS structure.

[0019] The implicit functions of the two TPMS structures are as follows:

[0020]

[0021] The fusion formula is as follows:

[0022]

[0023] The present application adjusts the unit cell size of each structure by adjusting the parameter "L", adjusts the geometry and porosity by adjusting the constant "C", adjusts the size and smoothness of the fusion area by adjusting the "a" value to reduce the stress concentration of the overall structure, and adjusts the fusion formula "b" value to change the inner diameter of the structure.

[0024] The overall model is constructed based on the implicit surface method, and the ideal structure is obtained by adjusting different parameters. The final contact area structure is shown in Figure 2 The lateral steel plate is made of 3mm thick titanium alloy steel plate according to the clinical surgical requirements. The lateral steel plate is completely fitted with the prosthesis body to simulate the anatomical shape of human bone tissue and prevent the force line of the human lower limb from changing due to the change of the shape of the bracket. Finally, a complete design model of the backbone prosthesis is obtained. Figure 3 .

[0025] In order to explore the performance of the fusion area, the permeability performance simulation analysis and quasi-static compression simulation of the fusion area were carried out. The Fluent module in the commercial software ANSYS 2021R1 was used to analyze the flow behavior of all models. The pressure at the inlet and outlet of the contact area was obtained through simulation analysis. Figure 4 The overall permeability is calculated by pressure difference. The permeability coefficient of human bone is 0.01~12.1×10 -9 m 2 , the permeability of the upper and lower contact areas is calculated to be within this range. The commercial software Workbench2021R1 is used for quasi-static compression simulation. The elastic modulus and yield strength of the model are obtained through simulation analysis. Compared with the mechanical parameters of the human femur, it is found that the elastic modulus of the module is similar to that of the femur, and the yield strength is higher than that of the femur. Through simulation analysis, it is found that the performance of the contact area can be well matched with the femur, providing conditions for cell growth.

[0026] In order to explore whether the one-piece porous bone prosthesis can effectively reduce the stress shielding effect and promote bone ingrowth, a biomechanical analysis of the prosthesis model was performed. Wolf's law is introduced: if the bone tissue is subjected to external pressure for a long time, the bone density will increase to adapt to the external pressure (bone ingrowth). Similarly, if the bone tissue does not receive the corresponding mechanical stimulation for a long time, bone absorption will occur and reduce bone density (bone absorption). The bone reconstruction rate in bone reconstruction theory is defined as the rate of change of bone density. The rate of change of bone density is expressed by the following formula,

[0027]

[0028] Among them, S is the bone strain, s is the dead zone width, S refis the strain of healthy bone under the same load. When the bone density change rate is greater than 0, bone growth will occur in the femur; when the bone density change rate is equal to 0, the bone density remains unchanged; when the bone density change rate is less than 0, bone resorption will occur in the femur. Through biomechanical analysis, the strain of bone cement stem prosthesis and one-piece porous stem prosthesis are compared, as shown in Table 1, which shows that the one-piece porous stem prosthesis can increase the strain of the femur to a certain extent, thereby promoting the growth of bone tissue and improving the long-term stability of the prosthesis.

[0029] Table 1 Femoral strain table under three conditions

[0030]

[0031] In summary, after modularizing the backbone prosthesis, the present invention combines the bone defect model for biomechanical analysis and evaluates the performance of the one-piece porous backbone prosthesis. Compared with the bone cement-type backbone prosthesis, the one-piece porous backbone prosthesis can effectively reduce the stress shielding effect. At the same time, the contact area is similar to the structure of the human femur, which can provide favorable conditions for cell growth. 3D printing technology creates conditions for the manufacture of porous backbone prostheses. At the same time, the one-piece backbone prosthesis is more matched with the patient's femoral structure, the surgical plan is simpler, and the lateral steel plate is completely in line with the prosthesis body, which is more in line with the anatomical shape of human bone tissue, preventing the force line of the human lower limbs from changing due to changes in the shape of the prosthesis. The elastic modulus of the porous backbone prosthesis obtained by 3D printing is close to that of cancellous bone, which effectively reduces the stress shielding effect. At the same time, the yield strength is higher than the yield strength of cortical bone, which ensures the strength of the porous backbone prosthesis and provides a feasible solution for clinical bone defect treatment.

Claims

1. The one-piece porous backbone prosthesis described in the present invention is divided into a load-bearing area, an upper contact area, a lower contact area and a lateral steel plate according to the modular design concept. The load-bearing area design adopts a topological optimization design method to obtain a geometric structure with optimal material distribution, and at the same time combines a porous structure to form a complete load-bearing area; the contact area adopts a fused porous structure, and according to the TPMS structural performance, the external Diamond structure and the internal Gyroid structure are selected. The implicit function of the TPMS structure is as follows: Diamond: Gyroid: The fusion formula is as follows:

2. The present invention performs finite element analysis on the fusion area, observes the inlet and outlet pressure difference of the permeability simulation results, calculates the permeability of the components, compares it with the permeability of the femur, and verifies that the contact area can provide conditions for the growth of bone cells. Observe the simulation results of mechanical properties to verify that the components can meet the mechanical properties of the prosthesis. The biomechanical simulation of the bone cement-type stem prosthesis and the one-piece porous stem prosthesis is compared. According to the bone reconstruction theory, it is verified that the one-piece porous stem prosthesis can increase the strain of the femur to a certain extent, thereby promoting the growth of bone tissue and improving the long-term stability of the prosthesis. The one-piece porous stem prosthesis has an elastic modulus similar to that of the femur, and at the same time has a higher yield strength, which can meet the implantation requirements, and the porous structure provides conditions for the growth of bone cells. The porous stem prosthesis obtained by 3D printing can effectively reduce the stress shielding effect, and the yield strength is higher than the yield strength of the cortical bone, which ensures the strength of the porous stem prosthesis and provides a feasible solution for the clinical treatment of bone defects.

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