Hip joint prosthesis structure optimization method based on female menopausal factors

Abstract

The invention discloses a hip joint prosthesis structure optimization method based on female menopausal factors. The method comprises the following steps: S1, geometric modeling of a hip joint prosthesis; s2, establishing a multi-stage female menopausal factor femur-prosthesis finite element model; and S3, optimizing the evaluation indexes and the structure of the hip joint prosthesis. According to the invention, the influence of staged change of female postmenopausal on stiffness change and life of the hip joint prosthesis is studied, and a method for optimizing the internal local pore parameter structure and the prosthesis stiffness of the hip joint prosthesis is provided for the hip joint prosthesis, so that a more accurate experimental result can be obtained, a stress shielding effect is avoided, and the reliability of the hip joint prosthesis is improved. The long-term stability, the safety and the service life of the prosthesis are improved.

Description

Technical Field

[0001] The present invention relates to the field of the design of lower limb implants, and specifically to an optimization method for the structure of a hip joint prosthesis based on the factor of female menopause. Background Art

[0002] At present, the most effective treatment method for hip joint diseases in medicine is hip joint replacement. The success rate of artificial hip joint surgery is 84.2%. Due to various complications and long-term loosening of the prosthesis, the number of revisions is also increasing continuously, and the revision rate even exceeds 20%. Most of the reasons for revision are prosthesis loosening, prosthesis fracture, infection after replacement, periprosthetic fracture, etc. The main reasons for these problems are that the structure and working conditions of the human hip joint are relatively complex, and the surgery lacks safety and accuracy in the case of insufficient biomechanical experiments. There are significant differences in hip joint morphology and biomechanical load between men and women. The femoral morphology of women is more slender, the neck-shaft angle is larger, and the bone density is lower. The osteoporosis of postmenopausal women is particularly obvious, and the bone density decreases with age, which increases the difficulty of prosthesis implantation and the problem of prosthesis stability after surgery.

[0003] Previous studies mainly focused on the fixed age of young individuals or conducted follow-up studies on male individuals, but did not consider the changes after continuously implanting hip joint prostheses in postmenopausal female patients. By analyzing the bone tissue characteristics of postmenopausal women and optimizing the structural design of hip joint prostheses, the long-term stability and durability of the prostheses can be improved, thereby reducing the surgical failure rate and reoperation rate. Therefore, paying attention to the skeletal characteristics of postmenopausal women is of great significance for improving the adaptability of prosthesis implantation. Summary of the Invention

[0004] The present invention aims to study the influence of the factor of female menopause on the stiffness and lifespan of hip joint prostheses, and proposes a method for the internal local pore parameter structure and prosthesis stiffness based on the change of the local stiffness of hip joint prostheses to optimize the structure of hip joint prostheses.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An optimization method for the structure of a hip joint prosthesis based on the factor of female menopause, characterized in that the specific implementation includes the following steps:

[0007] S1. Geometric modeling of the hip joint prosthesis;

[0008] S2. Establishment of a finite element model of the femoral implant for postmenopausal women in multiple stages;

[0009] S3. Evaluation index and structural optimization of the hip joint prosthesis.

[0010] In the step S1, the specific process of geometric modeling of the hip joint prosthesis further includes the following steps:

[0011] S101. Establishment of the femoral geometric model:

[0012] Perform threshold segmentation on the CT images of the femur to highlight the femoral part to be extracted, and then perform operations such as region growing and mask editing to edit the femoral region and remove other parts outside the femur, so as to extract a preliminary rough three-dimensional femoral model with spikes. Then, perform general smoothing operations on the established model to make the established femoral geometric model smoother and more accurate.

[0013] S102. Further optimization of the femoral geometric model:

[0014] In S101, a preliminary geometric model of the femur has been established and basic smoothing processing has been performed on the model; however, there are still defects such as spikes and holes on the femoral geometric model. Therefore, it is necessary to fill the holes and remove the spikes on the established femoral model, and then perform a polishing operation to make the model smoother; manually extract the contour line of the model, construct a grid with the contour line and perform surface fitting on it to obtain a femoral model available for final finite element modeling.

[0015] S103. Establishment of the geometric model of the hip joint prosthesis:

[0016] The average density of the femur of women aged 50 to 80 is about 780 kg / m 3 , and the relational expression between the average density density of the female femur and the main parameters of the hip joint prosthesis is:

[0017] density = -676 + 10.813sl + 12.34nl - 0.328α - 0.02569sl 2 + 0.0535sl*nl - 0.091nl*α (1)

[0018] Where: density is the average density of the female femur, sl is the length of the hip joint prosthesis, nl is the length of the neck of the hip joint prosthesis, α is the azimuth angle of the neck of the hip joint prosthesis; determine that the prosthesis length is 150 mm, the prosthesis neck length is 50 mm, and the azimuth angle is 124° from formula (1), and construct an initial geometric model of the hip joint prosthesis.

[0019] S104. Assembly and establishment of the geometric models of the femur and the prosthesis:

[0020] Assemble the optimized femoral geometric model with the initial hip joint prosthesis model to obtain a basic geometric model of the postmenopausal female femur and the hip joint prosthesis, and apply this model to the subsequent construction of the femur-prosthesis with postmenopausal female factors.

[0021] In step S2, the establishment of the finite element model of the multi-stage femoral implant for postmenopausal women further includes the following specific steps:

[0022] S201. Perform mesh generation on the established geometric models of the postmenopausal femur and hip prosthesis. Among them, the overall hip prosthesis and the cortical bone and cancellous bone in the corresponding femur are all divided using tetrahedral elements with a size of 3 mm.

[0023] S202. Determination of material parameters:

[0024] The age of the established geometric models of the initial postmenopausal femur and hip prosthesis is 45 years. In the initial femur model, the density of the cortical bone is 1980 kg / m 3 , the Young's modulus is 15.2 GPa, the corresponding Poisson's ratio is 0.26, the ultimate stress is 105.6 MPa, and the ultimate strain is 2.68%. The density of the femoral cancellous bone is 828 kg / m 3 , the Young's modulus is 0.7581 GPa, the corresponding Poisson's ratio is 0.33, the ultimate stress is 10.63 MPa; the ultimate strain is 13.42%. The hip prosthesis uses titanium alloy Ti-6Al-4V, the selected pore structure is a tetrahedral unit cell, the initial porosity is 30%, and the corresponding elastic modulus is 110 GPa.

[0025] S203. Construction of loads:

[0026] During the process of adding loads, two main states are considered. One state is static standing force. Apply constraints to the head of the hip prosthesis and apply a force F vertically to the femur to simulate the standing state, and its magnitude is about 400 N. The other state is dynamic force. The force received is divided into three directions, namely F x , F y , F z , and the resultant force of them is applied as the total force F, and the dynamic rotation of a person during movement, that is, torques in different directions, are simulated and added, namely M x , M y , M z .

[0027] S204. Construction of the multi-stage postmenopausal femur-prosthesis:

[0028] In the process of constructing a multi-stage finite element model of the femur-prosthesis for female menopause factors, the main consideration is the change of the femur with age after menopause in women; it is mainly reflected in two aspects. The first aspect is that the change of the femur after menopause in women is a special physiological phenomenon, and the Young's modulus, ultimate stress, and ultimate strain in the material parameters of the femur will all change with time. The second aspect is that the area of the medullary cavity will change with time.

[0029] In the first aspect, the ultimate stress Y of the femoral cortical bone after menopause in women c The relationship with age x is:

[0030] Y c = 129.19 - 0.4219x (2)

[0031] Where: Y c Is the ultimate stress of the femoral cortical bone after menopause in women, and x is the age of the patient.

[0032] The ultimate strain y of the femoral cortical bone after menopause in women c The relationship with age x is:

[0033] y c = 2.1251 - 0.00936x (3)

[0034] Where: y c Is the ultimate strain of the femoral cortical bone after menopause in women, and x is the age of the patient.

[0035] The Young's modulus S of the femoral cortical bone after menopause in women c The relationship with age x is:

[0036] S c = 17707.252 - 58.583x (4)

[0037] Where: S c Is the change of the Young's modulus of the femoral cortical bone after menopause in women, and x is the age of the patient.

[0038] The ultimate stress Y of the femoral cancellous bone after menopause in women t The relationship with age x is:

[0039] Y t = 10.5921 - 0.1006x (5)

[0040] Where: Y t Is the ultimate stress of the femoral cancellous bone after menopause in women, and x is the age of the patient.

[0041] The Young's modulus S of the femoral cancellous bone after menopause in women t The relationship with age x is:

[0042] S t = 868.919 - 3.387x (6)

[0043] Where: S t is the change in Young's modulus of cancellous bone in the femur after menopause in women, and x is the age of the patient.

[0044] The above equations (2) to (6) are used to construct a multi-stage finite element model of the femur with female menopause factors.

[0045] In the second aspect, the change in the femoral medullary cavity area is mainly caused by the changes in three parameters, which are: the cross-sectional area of the femur CSA, the medullary cavity area MCA, and the cortical bone area CBA; among them, the calculation formula for the cross-sectional area of the femur CSA is:

[0046] CSA = π * R csa 2 (7)

[0047] Where: CSA is the cross-sectional area of the femur, R csa is the outer radius of the femur, and π is the pi.

[0048] The calculation formula for the medullary cavity area MCA is:

[0049] MCA = π * R mca 2 (8)

[0050] Where: MCA is the medullary cavity area, R mca is the inner radius of the femoral medullary cavity, and π is the pi.

[0051] The calculation formula for the cortical bone area CBA is:

[0052] CBA = CSA - MCA (9)

[0053] Where: CBA is the cortical bone area, CSA is the cross-sectional area of the femur, and MCA is the medullary cavity area.

[0054] For postmenopausal women, the cross-sectional area of the femur CSA increases by 0.58% every 5 years, the medullary cavity area MCA increases by 7.82% every 5 years, and the cortical bone area CBA decreases by 6.37% every 5 years. Combine equations (7) to (9) to construct a multi-stage geometric model of the femur with female menopause factors; adjust the corresponding material parameters according to the influence of the above age variable on the femoral parameters of postmenopausal women, and adjust the size parameters of the femoral model in stages of five years to obtain a multi-stage femur-prosthesis model with female menopause factors for subsequent analysis.

[0055] S205. Construction of the load:

[0056] After obtaining the multi-stage finite element model of the femoral-prosthesis for female menopause factors, the same external loads as those on the basic model are applied to the finite element model for finite element analysis, and the loads are exactly the same as those defined in S203.

[0057] In step S3, the evaluation index and the structural optimization of the hip prosthesis further include the following specific steps:

[0058] S301. Evaluation index

[0059] Evaluation index 1: The prosthesis is subject to repeated loads during human movement for a long time and is prone to fatigue failure and fracture. Therefore, it is crucial to evaluate the fatigue life of the prosthesis under normal physiological loads and try to improve its safety and service life: Where: HFI is the Hoffman failure index, σ s is the normal stress, τ f is the shear stress, C s is the compressive strength, T s is the tensile strength, S s is the shear strength. When the value of the Hoffman failure index HFI is greater than 1, it indicates that the prosthesis will fail under repeated loads.

[0060] Evaluation index 2: When designing the prosthesis, the stiffness of the prosthesis should match the stiffness of the femur. If the stiffness of the prosthesis is too large, it will cause the stress shielding effect, that is, the bone will degenerate due to insufficient stress for a long time. If the stiffness of the prosthesis is too low, it cannot effectively share the load, resulting in early wear, displacement or even fracture of the prosthesis. The reasonable range of prosthesis stiffness should be: Where: G is the prosthesis stiffness, E bone is the elastic modulus of the femur, d is the diameter of the femur cross-section, L is the length of the femur, and π is the pi.

[0061] S302. Structural optimization of the hip prosthesis:

[0062] When optimizing the structure of the hip prosthesis, if the obtained Hoffman failure index HFI is greater than 1 or the prosthesis stiffness condition is not satisfied, the prosthesis needs to be optimized.

[0063] C s Compressive strength, T s Tensile strength, S s Shear strength calculation formulas are:

[0064] C s = 32.3ρ 1.75 ; T s = 13.5ρ 1.73 ; S s = 22.3ρ 1.56 (10)

[0065] Among them: ρ is the femoral density.

[0066] The normal stress σ s The calculation formula is:

[0067]

[0068] Among them: σ s is the normal stress, F is the force applied in the axial direction, l is the lattice side length, M z is the absolute value of the moment magnitude in the axial direction, and s is the lattice cross-section.

[0069] The shear stress τ f The calculation formula is:

[0070]

[0071] Among them: τ f is the shear stress, F f is the shear force, l is the lattice side length, and s is the lattice cross-section.

[0072] The above equations (10), (11), (12) are used for the calculation of evaluation index 1, and the total stress σ is obtained from equations (11) and (12) as:

[0073]

[0074] Among them: σ is the total stress, F is the force applied in the axial direction, l is the lattice side length, M z is the absolute value of the moment magnitude in the axial direction, s is the lattice cross-section, F f is the shear force.

[0075] The calculation formula for the unit cell volume V is:

[0076]

[0077] Among them: V is the unit cell volume, l is the lattice side length, and k is the proportionality factor.

[0078] When the proportionality factor k = 1, the solid volume V of the unit cell is obtained solid as:

[0079]

[0080] Among them: V solid is the solid volume of the unit cell, and l is the lattice side length.

[0081] The expression for the relative density P is obtained as:

[0082]

[0083] Where: V is the unit cell volume, and V solid is the solid volume of the unit cell, and k is the proportionality factor.

[0084] According to the finite element analysis numerical values, the expression of the prosthesis stiffness G and the relative density P obtained by fitting with a third-order polynomial is:

[0085] G = (0.2679P 3 + 0.3886P 2 + 0.2316P + 0.4203)G solid (17)

[0086] Where: G is the prosthesis stiffness, P is the relative density, and G solid is the solid stiffness of the prosthesis.

[0087] From equations (16) and (17), the relationship between the prosthesis stiffness G and the proportionality factor k is obtained:

[0088] G = (0.3879(3k 2 - 4k + 2) 3 + 0.3886(3k 2 - 4k + 2) 2 - 0.2316(3k 2 - 4k + 2) + 0.4203)G solid (18)

[0089] When it is determined that the Hoffman failure index HFI > 1, to avoid prosthesis failure, the lattice length and cross-section are adjusted in the area to be optimized to replace the previous parameters. According to formulas (11) and (12), the lattice side length and cross-section are adjusted to adjust the normal stress or shear stress to achieve the purpose of adjusting the Hoffman failure index, enhancing the stability and safety of the prosthesis. When the prosthesis stiffness or When this occurs, to avoid the stress shielding phenomenon, according to formula (18), there is no need to change the lattice side length and cross-section, and only the proportionality factor of the regional lattice needs to be adjusted to adjust the prosthesis stiffness to the effective range. When both the prosthesis stiffness and the Hoffman failure index fail, then the regional lattice length and its cross-section need to be redesigned. Then, the finite element model of the prosthesis after one structural optimization is recalculated and the prosthesis stiffness and Hoffman failure index are re-analyzed. If the hip joint prosthesis still does not meet the evaluation conditions of Index 1 and Index 2, then it re-enters the optimization stage to continue the optimization.

[0090] The beneficial effects of the present invention are:

[0091] Previous studies on hip joint prostheses mainly focused on the design of the shape of hip joint prostheses, the material selection and performance of hip joint prostheses, the stress changes between bones and prostheses after prosthesis implantation, the surgical implantation techniques of hip joint prostheses, the influence of age factors on bone integration, etc. Previous studies mainly focused on the influence of age factors on hip joint prostheses during the postoperative recovery stage, such as the influence of aging on the combination of implants and bone tissue, the differences in the amount of new bone formation and bone union rate with age changes, etc., without considering the situation of long-term implantation of hip joint prostheses in this special group of postmenopausal women. The femur of women is more slender, the neck-shaft angle is larger, and the bone density is lower. Osteoporosis in postmenopausal women is particularly obvious, and the bone density decreases with age. With age, the particularity of the bones of postmenopausal women will also bring changes in the material and geometric parameters of the lower limb femur, and this special change will lead to changes in the stress state of hip joint prostheses and also cause a certain reduction in service life. Therefore, it is necessary to study the influence of female menopause factors on the service life, safety, stiffness change, and stress change of hip joint prostheses, and to propose corresponding improvement methods for this kind of influence.

[0092] The present invention simulates the changes in local stiffness and stress of hip joint prostheses during the age change process of a female patient after menopause by constructing a multi-stage femur-prosthesis model considering female menopause factors. For the hip joint prosthesis with Hoffman failure index HFI > 1 and prosthesis stiffness or a structural optimization method is proposed, which prolongs its service life, improves safety, improves prosthesis adaptability and stability, and avoids the situation of stress shielding. In addition, the optimization method proposed by this structural optimization method of hip joint prostheses considering female menopause factors can also be used for the local stiffness failure of hip joint prostheses caused by other factors.

[0093] Compared with the existing technology, the specific advantages of the present invention are shown in the following aspects:

[0094] 1. The existing technology has not studied the influence of female menopause factors on the stress and stiffness distribution of hip joint prostheses. This patent establishes a multi-stage femur-prosthesis model considering female menopause factors through the finite element method, obtains the key design parameters of hip joint prostheses through femur density, and studies the stiffness change and stress change of hip joint prostheses in the body of postmenopausal women at different age stages, filling the gap in the study of the influence of female menopause factors on the stiffness change and stress change of hip joint prostheses.

[0095] 2. In the process of researching hip joint prostheses, the stress conditions, ultimate strain conditions, Young's modulus conditions of female postmenopausal femurs at different stages, and the phased dimensional changes of the femurs were not incorporated into the process of designing the femur-hip prostheses. In the process of researching the stress changes of hip joint prostheses in this patent, the stress-strain functions corresponding to the cancellous bone and cortical bone of female postmenopausal femurs at different stages were used as reference standards to determine whether hip joint prostheses with different structures can meet the stress requirements of patients at different stages, thus improving the design of hip joint prostheses.

[0096] 3. When researching the stiffness of hip joints in the prior art, no detailed relationship between relative density and prosthesis stiffness was proposed. In this patent, by introducing a scale factor, the relationship between relative density and the scale factor and the relationship between relative density and prosthesis stiffness were established. Using relative density as an intermediate variable, the relationship between the scale factor and prosthesis stiffness was obtained, making the final operation adjustment result more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 Flow chart for researching the influence of female postmenopausal factors on hip joint prostheses;

[0098] Figure 2 Schematic diagram of the optimization process of the hip joint prosthesis entering the structural optimization;

[0099] Figure 3 Schematic diagram of the structure of the hip joint prosthesis;

[0100] Figure 4 Simplified schematic diagram of the femur cross-section;

[0101] Figure 5 Direction of the load applied to the femur in the static standing state;

[0102] Figure 6 Direction of the load applied to the femur in the motion state; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0103] As Figure 1 shown, the specific implementation of a method for optimizing the structure of a hip joint prosthesis based on female postmenopausal factors described in this embodiment includes the following steps:

[0104] S1. Geometric modeling of the hip joint prosthesis;

[0105] S2. Establishment of a finite element model of the femur-prosthesis with multi-stage female postmenopausal factors;

[0106] S3. Evaluation indexes and structural optimization of the hip joint prosthesis.

[0107] In the step S1, the specific process of geometric modeling of the hip joint prosthesis further includes the following steps:

[0108] S101. Establishment of the femoral geometric model:

[0109] Perform threshold segmentation on the CT images of the femur to highlight the femoral part to be extracted. Then, perform operations such as region growing and mask editing to edit the femoral region and remove other parts outside the femur, thereby extracting a preliminary rough three-dimensional femoral model with nail-like objects. Subsequently, perform general smoothing operations on the established model to make the established femoral geometric model smoother and more accurate.

[0110] S102. Further optimization of the femoral geometric model:

[0111] In S101, a preliminary geometric model of the femur has been established and basic smoothing processing has been performed on the model. However, there are still defects such as nail-like objects and holes on the femoral geometric model. Therefore, it is necessary to fill the holes and remove the nail-like objects on the established femoral model, and then perform a polishing operation to make the model smoother; manually extract the contour line of the model, construct a grid based on the contour line and perform surface fitting to obtain the final femoral model available for finite element modeling.

[0112] S103. Establishment of the hip prosthesis geometric model:

[0113] The average density of the trabecular bone of women aged 50 to 80 is about 780 kg / m 3 , and the length of the prosthesis is determined to be 150 mm, the length of the prosthesis neck is 50 mm, and the azimuth angle is 124° according to Equation (1) to construct an initial hip prosthesis geometric model.

[0114] S104. Assembly and establishment of the femoral and prosthesis geometric models:

[0115] Assemble the optimized femoral geometric model and the initial hip prosthesis model to obtain a basic geometric model of the femoral-prosthesis of postmenopausal women, and apply this model to the subsequent construction of the femoral-prosthesis with postmenopausal factors of women in multiple stages.

[0116] In the step S2, the establishment of the finite element model of the femoral-prosthesis with postmenopausal factors of women in multiple stages further includes the following steps:

[0117] S201. Perform mesh division operations on the established geometric model of the femoral-prosthesis of postmenopausal women. Among them, the whole hip prosthesis and the cortical bone and cancellous bone in the corresponding femur are all divided using tetrahedral elements with a size of 3 mm;

[0118] S202. Determination of material parameters:

[0119] The geometric model of the initial female menopause femur and hip joint prosthesis was established for a 45-year-old woman. In the initial femur model, the density of cortical bone was 1980 kg / m 3 , the Young's modulus was 15.2 GPa, the corresponding Poisson's ratio was 0.26, the ultimate stress was 105.6 MPa, and the ultimate strain was 2.68%. The density of cancellous bone in the femur was 828 kg / m 3 , the Young's modulus was 0.7581 GPa, the corresponding Poisson's ratio was 0.33, the ultimate stress was 10.63 MPa, and the ultimate strain was 13.42%. The hip joint prosthesis used titanium alloy Ti-6Al-4V. The selected pore structure was a tetrahedral unit cell, and the initial porosity was 30%, corresponding to an elastic modulus of 110 GPa.

[0120] S203. Construction of the load:

[0121] During the process of adding the load, two major states were mainly considered. One state was static standing stress. Constraints were applied to the head of the hip joint prosthesis, and a force F was applied vertically to the femur to simulate the standing state, and its magnitude was approximately 400 N. The other state was dynamic stress. The force received was divided into three directions, namely F x 、F y 、F z , and the resultant force of them was applied as the total stress F. And the dynamic rotation of a person during movement was simulated, that is, torques in different directions, namely M x 、M y 、M z .

[0122] S204. Construction of the multi-stage female menopause factor femur-prosthesis:

[0123] In the process of constructing a multi-stage finite element model of the femur-prosthesis for female menopause factors, the main consideration is the change of the femur after menopause with age. It is mainly reflected in two aspects. The first aspect is that the femur change after menopause in women has special physiological phenomena, and the Young's modulus, ultimate stress, and ultimate strain in the material parameters of the femur will all change with time. The second aspect is that the area of the medullary cavity will change with time; the changes of the cortical bone parameters of the femur in postmenopausal women are simulated through formulas (2), (3), and (4), the changes of the cancellous bone parameters of the femur in postmenopausal women are simulated through formulas (5) and (6), and the stagewise dimensional changes of the femur in postmenopausal women are simulated through the changes of CSA, MCA, and CBA in formula (9). The cross-sectional area CSA of the femur in postmenopausal women increases by 0.58% every 5 years, the medullary cavity area MCA increases by 7.82% every 5 years, and the cortical bone area CBA decreases by 6.37% every 5 years. According to the influence of the above age variables on the femur parameters of postmenopausal women, the corresponding material parameters are adjusted, and the dimensional parameters of the femur model are adjusted in stages of five years to obtain a multi-stage finite element model of the femur-prosthesis for female menopause factors for subsequent analysis.

[0124] S205. Construction of loads:

[0125] After obtaining the multi-stage finite element model of the femur-prosthesis for female menopause factors, the same external loads as those of the basic model are applied to the finite element model for finite element analysis, and the loads are exactly the same as those defined in S203.

[0126] In step S3, the evaluation index and the structural optimization of the hip prosthesis further include the following steps:

[0127] S301. Evaluation index

[0128] Evaluation index 1: The prosthesis is subjected to repeated loads during human movement for a long time and is prone to fatigue failure and fracture. Therefore, it is crucial to evaluate the fatigue life of the prosthesis under normal physiological loads and try to improve its safety and service life: Where: HFI is the Hoffman failure index, σ s is the normal stress, τ f is the shear stress, C s is the compressive strength, T s is the tensile strength, S s is the shear strength; when the value of the Hoffman failure index HFI is greater than 1, it indicates that the prosthesis will fail under repeated loads.

[0129] Evaluation index 2: When designing a prosthesis, the stiffness of the prosthesis should match the stiffness of the femur. Too high a stiffness of the prosthesis will lead to stress shielding effect, that is, the bone will degenerate due to insufficient stress for a long time; too low a stiffness of the prosthesis will not effectively share the load, resulting in early wear, displacement or even fracture of the prosthesis; the reasonable range of prosthesis stiffness should be: Where: G is the prosthesis stiffness, E is bone is the elastic modulus of the femur, d is the diameter of the femoral section, L is the length of the femur, and π is the circumference of the circumference.

[0130] S302. Structural optimization of hip prosthesis:

[0131] When optimizing the structure of the hip prosthesis, the maximum stiffness value and Hoffman failure index of the hip prosthesis are first obtained through finite element analysis. If the corresponding values are in a suitable range, no optimization is required. When HFI>1 is judged, in order to avoid prosthesis failure, the lattice length and cross section are adjusted in the area to be optimized to replace the previous parameters. According to formulas (11) and (12), the lattice side length and cross section are adjusted to adjust the normal stress or tangential stress to achieve the purpose of adjusting the Hoffman failure index and enhance the stability and safety of the prosthesis. When the prosthesis stiffness is or To avoid stress shielding, according to formula (18), there is no need to change the lattice side length and cross section, only the scale factor of the regional lattice needs to be adjusted to adjust the prosthesis stiffness to the effective range; when the stiffness and the Hoffman failure index fail at the same time, it is necessary to redesign the regional lattice length and its cross section; then the finite element model of the prosthesis that has undergone a structural optimization is recalculated and the prosthesis stiffness and Hoffman failure index are reanalyzed. If the hip prosthesis still does not meet the evaluation conditions of indicator 1 and indicator 2, it re-enters the optimization stage and continues to optimize.

[0132] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that the present invention may have various modifications and variations. Various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and purpose of the present invention, and the scope of the present invention is limited by the claims and their equivalents.

Claims

1. An optimization method for the hip joint prosthesis structure based on female menopause factors, characterized in that: The specific implementation of the method includes the following steps: S1. Geometric modeling of hip joint prosthesis; S2. Establishment of a multi-stage finite element model of the femur-prosthesis considering female menopause factors; S3. Evaluation indicators and structural optimization of the hip joint prosthesis.

2. An optimization method for the hip joint prosthesis structure based on female menopause factors, characterized in that: In the step S1, the following specific steps are further included: S101. Establishment of the femoral geometric model: Perform threshold segmentation on the CT images of the femur to highlight the femur part to be extracted, and then perform operations such as region growing and mask editing to edit the femur region and remove other parts outside the femur, so as to extract a preliminary rough three-dimensional model of the femur with spikes. Then perform general smoothing operations on the established model to make the established femoral geometric model smoother and more accurate; S102. Further optimization of the femoral geometric model: In S101, a preliminary geometric model of the femur has been established and basic smoothing processing has been performed on the model; however, there are still defects such as spikes and holes on the femoral geometric model. Therefore, it is necessary to fill the holes and remove the spikes on the established femoral model, and then perform a polishing operation to make the model smoother; manually extract the contour lines of the model, construct a grid with the contour lines and perform surface fitting to obtain the final femoral model available for finite element modeling; S103. Establishment of the hip joint prosthesis geometric model: The average density of the femur of women aged 50 to 80 is about 780 kg / m 3 , and the relationship between the average femur density density of women and the main parameters of hip joint prostheses is: density = -676 + 10.813sl + 12.34nl - 0.328α - 0.02569sl 2 + 0.0535sl*nl - 0.091nl*α (1) Where: density is the average density of the female femur, sl is the length of the hip joint prosthesis, nl is the length of the neck of the hip joint prosthesis, and α is the azimuth angle of the neck of the hip joint prosthesis; the prosthesis length is determined to be 150 mm, the prosthesis neck length is 50 mm, and the azimuth angle is 124° by Equation (1), and an initial hip joint prosthesis geometric model is constructed; S104. Assembly and establishment of the femoral and prosthesis geometric models: Assemble the optimized femoral geometric model with the initial hip joint prosthesis model to obtain the basic geometric model of the post-menopausal female femur and hip joint prosthesis, and apply this model to the subsequent construction of the multi-stage femur-prosthesis considering female menopause factors; 3. An optimization method for the hip prosthesis structure based on female menopause factors according to claim 1, characterized in that: In the step S2, the following specific steps are further included: S201. Perform mesh division on the established geometric model of the post-menopausal female femur and hip joint prosthesis. Among them, the whole hip joint prosthesis and the cortical bone and cancellous bone in the corresponding femur are all divided with tetrahedral elements with a size of 3 mm; S202. Determination of material parameters: The established geometric model of the initial female menopause femur and hip prosthesis is 45 years old. In the initial femur model, the density of cortical bone is 1980 kg / m 3 , the Young's modulus is 15.2 GPa, the corresponding Poisson's ratio is 0.26, the ultimate stress is 105.6 MPa, the ultimate strain is 2.68%, and the density of the cancellous bone of the femur is 828 kg / m 3 , the Young's modulus is 0.7581 GPa, the corresponding Poisson's ratio is 0.33, the ultimate stress is 10.63 MPa, and the ultimate strain is 13.42%. The hip prosthesis uses titanium alloy Ti-6Al-4V. The selected pore structure is a tetrahedral unit cell, and the initial porosity is 30%, corresponding to an elastic modulus of 110 GPa; S203. Construction of loads: During the process of adding load, two major states are mainly considered. One state is static standing under force, where constraints are imposed on the head of the hip joint prosthesis and a force F is applied vertically to the femur to simulate the standing state, with its magnitude being approximately 400 N. The other state is dynamic loading, where the applied force is divided into three directions, namely F x , F y , and F z . The resultant force of these forces is taken as the total applied force F, and the dynamic rotation of a person during movement, i.e., torques in different directions, are simulated, namely M x , M y , and M z . S204. Construction of the multi-stage femur-prosthesis considering female menopause factors: In the process of constructing the multi-stage finite element model of the femur-prosthesis considering female menopause factors, the main consideration is the change of the femur after female menopause with age; it is mainly reflected in two aspects. The first aspect is that the change of the femur after female menopause has special physiological phenomena, and the Young's modulus, ultimate stress and ultimate strain in the material parameters of the corresponding femur will change with time; the second aspect is that the area of the medullary cavity will change with time; In the first aspect, the relationship between the ultimate stress Y of the femoral cortical bone after menopause in women c changing with age x is: Y c = 129.19 - 0.4219x (2) Where: Y c is the ultimate stress of the femoral cortical bone after menopause in women, and x is the age of the patient; The ultimate strain y of the femoral cortical bone after menopause in women c The relational expression for the change with age x is: y c = 2.1251 - 0.00936x (3) where: y c is the ultimate strain of the femoral cortical bone after menopause in women, and x is the age of the patient; Young's modulus S of femoral cortical bone in postmenopausal women c The relationship with age x is as follows: S c = 17707.252 - 58.583x (4) Where: S c is the change in Young's modulus of the femoral cortical bone after menopause in women, and x is the age of the patient; Ultimate stress Y of cancellous bone in femur after menopause in women t The relational expression for its variation with age x is as follows: Y t = 10.5921 - 0.1006x (5) Where: Y t is the ultimate stress of cancellous bone in the femur after menopause in women, and x is the age of the patient; Young's modulus S of cancellous bone in the femur after menopause in women t The relationship with age x is as follows: S t = 868.919 - 3.387x (6) Where: S t is the change in Young's modulus of cancellous bone in the femur after menopause in women, and x is the age of the patient; The above formulas (2) to (6) are used to construct the multi-stage finite element model of the femur considering female menopause factors; In a second aspect, the change in the femoral medullary cavity area is mainly caused by the changes in three parameters, namely: the cross-sectional area of the femur CSA, the medullary cavity area MCA, and the cortical bone area CBA; among them, the calculation formula for the cross-sectional area of the femur CSA is: CSA = π * R csa 2 (7) Where: CSA is the cross-sectional area of the femur, R csa is the outer radius of the femur, and π is the pi; The calculation formula for the medullary cavity area MCA is: MCA = *R mca 2 (8) Where: MCA is the medullary cavity area, R mca is the inner radius of the femoral medullary cavity, and π is the pi; The calculation formula for the cortical bone area CBA is: CBA = CSA - MCA (9) Where: CBA is the cortical bone area, CSA is the cross-sectional area of the femur, and MCA is the medullary cavity area; For postmenopausal women, the cross-sectional area of the femur CSA increases by 0.58% every 5 years, the medullary cavity area MCA increases by 7.82% every 5 years, and the cortical bone area CBA decreases by 6.37% every 5 years. Combining equations (7) to (9), a multi-stage female menopause factor femoral geometric model is constructed; according to the influence of the above age variable on the femoral parameters of postmenopausal women, the corresponding material parameters are adjusted, and the size parameters of the femoral model are adjusted in stages of five years to obtain a multi-stage female menopause factor femur-prosthesis model for subsequent analysis; S205. Construction of the load: After obtaining the multi-stage female menopause factor femur-prosthesis finite element model, the same external load as the basic model is applied to the finite element model for finite element analysis, and the load is exactly the same as the load defined in S203; 4. A method for optimizing the structure of a hip joint prosthesis based on female menopause factors according to claim 1, characterized in that: In the step S3, the following specific steps are further included: S301. Evaluation index Evaluation Index 1: The prosthesis is subject to repeated loads during human movement for a long time and is prone to fatigue failure leading to fracture. Therefore, it is crucial to evaluate the fatigue life of the prosthesis under normal physiological loads and find ways to improve its safety and service life: Where: HFI is the Hoffman failure index, σ s is the normal stress, τ f is the shear stress, C s is the compressive strength, T s is the tensile strength, S s is the shear strength; when the value of the Hoffman failure index HFI is greater than 1, it indicates that the prosthesis will fail under repeated loads; Evaluation Index 2: When designing the prosthesis, the stiffness of the prosthesis should match that of the femur. Excessive stiffness of the prosthesis will lead to the stress shielding effect, that is, the bone degenerates due to insufficient stress over a long period of time; if the stiffness of the prosthesis is too low, it cannot effectively share the load, resulting in early wear, displacement or even fracture of the prosthesis; the reasonable range of prosthesis stiffness should be: Where: G is the stiffness of the prosthesis, E bone is the elastic modulus of the femur, d is the diameter of the femur cross-section, L is the length of the femur, and π is the pi; S302. Structural optimization of the hip joint prosthesis: When optimizing the structure of the hip joint prosthesis, if the obtained Hofmann failure index HFI is greater than 1 or the prosthesis stiffness condition is not satisfied, the prosthesis needs to be optimized; C s Compressive strength, T s Tensile strength, S s The shear strength calculation formula is: C s = 32.3ρ 1.75 ; T s = 13.5ρ 1.73 ; S s = 22.3ρ 1.56 (10) Where: ρ is the femoral density; Normal stress σ s The calculation formula is as follows: Where: σ s is the normal stress, F is the force applied in the axial direction, l is the lattice side length, M z is the absolute value of the magnitude of the torque in the axial direction, and s is the lattice cross-section; Tangential stress τ f The calculation formula is as follows: Where: τ f is the tangential stress, F f is the shear force, l is the lattice side length, and s is the lattice cross-section; The above equations (10), (11), and (12) are used for the calculation of evaluation index 1, and the total stress σ is obtained from equations (11) and (12) as: Where: σ is the total stress, F is the force applied in the axial direction, l is the lattice side length, M z is the absolute value of the moment magnitude in the axial direction, s is the lattice cross-section, F f is the shear force; The calculation formula for the unit cell volume V is: Where: V is the unit cell volume, l is the lattice side length, and k is the proportionality factor; When the scaling factor k = 1, the unit cell solid volume V is obtained solid as follows: Where: V solid is the volume of the unit cell entity, and l is the lattice edge length; The expression for the relative density P is obtained as: Where: V is the unit cell volume, V solid is the unit cell solid volume, and k is the scaling factor; According to the finite element analysis numerical values, the expression of the prosthesis stiffness G and the relative density P is obtained by fitting with a third-order polynomial as: G = (0.2679P 3 + 0.3886P 2 + 0.2316P + 0.4203)G solid (17) Where: G is the prosthesis stiffness, P is the relative density, and G solid is the prosthesis solid stiffness; The relationship between the prosthesis stiffness G and the proportionality factor k is obtained from equations (16) and (17): G = (0.3879(3k 2 - 4k + 2) 3 + 0.3886(3k 2 - 4k + 2) 2 - 0.2316(3k 2 - 4k + 2)+ 0.4203)G solid (18) When it is determined that the Hoffman failure index HFI > 1, to avoid prosthesis failure, adjust the lattice length and cross-section in the area to be optimized to replace the previous parameters. According to formulas (11) and (12), adjust the lattice side length and cross-section to adjust the normal stress or shear stress to achieve the purpose of adjusting the Hoffman failure index, enhancing the stability and safety of the prosthesis; when the prosthesis stiffness or When this is the case, to avoid the stress shielding phenomenon, according to formula (18), there is no need to change the lattice side length and cross-section. Only adjust the scale factor of the regional lattice to adjust the prosthesis stiffness to the effective range; when both the prosthesis stiffness and the Hoffman failure index fail, it is necessary to redesign the regional lattice length and its cross-section; then recalculate the finite element model of the prosthesis after one structural optimization and re-analyze the prosthesis stiffness and the Hoffman failure index. If the hip joint prosthesis still does not meet the evaluation conditions of Index 1 and Index 2, re-enter the optimization stage to continue the optimization.

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