Method for constructing uterus main ligament and sacral ligament positioning and pelvic floor finite element evolution model

Abstract

The invention discloses a uterus main ligament and sacral ligament positioning and pelvic floor finite element evolution model construction method, and belongs to the field of two-dimensional digital modeling and biomechanical research. According to the pelvic floor anatomy structure, the starting point and the ending point of the main ligament and the sacral ligament in the two-dimensional finite element model are determined, and a distributed nonlinear super-elastic spring set is provided for simulating the suspension mechanical property of the main ligament and the sacral ligament. An organ tissue proportional damage simulation method and a proportional damage expression are provided, and the mechanical property of the pelvic floor organ damage is simulated by multiplying a nonlinear material stress-strain curve of the pelvic floor organ tissue by a proportional damage factor. A concentrated load applying method and a concentrated force-displacement expression of initial form and position characteristics are provided, and initial reproductive fissure and uterus-vagina angles are simulated. The evolution model can visually display the trend of mechanical change and shape and position characteristic change in the process that the pelvic floor is evolved into severe prolapse from the initial stage of injury, and a basis is provided for reconstruction operation design of pelvic organ prolapse.

Description

Technical Field

[0001] The present invention belongs to the field of two-dimensional digital modeling and biomechanics research, and is mainly a method for positioning the main uterine ligaments and sacral ligaments and constructing a finite element evolution model of the pelvic floor. Specifically, it is a method for accurately positioning and mechanically simulating the complex three-dimensional main ligaments and sacral ligaments of the pelvic floor in a two-dimensional finite element model, while simulating the proportional damage and initial shape and position characteristics of organ tissues, to construct a finite element evolution model of the pelvic floor. Technical Background

[0002] Pelvic organ prolapse refers to a disease in which tissues and organs prolapse from the vaginal opening due to weakened support of the pelvic floor muscles and skeletal system. Pelvic organ prolapse can be divided into anterior vaginal wall prolapse, uterine prolapse and posterior vaginal wall prolapse according to the prolapse site, of which bladder prolapse accounts for 34.3% of prolapse cases, uterine prolapse accounts for 14.2%, and rectocele accounts for 18.6%. According to a survey of pelvic organ prolapse cases in rural women in China, the total prevalence of POP is 9.21%, and POP has become a high-incidence disease that troubles women. In the process of digital modeling and analysis of the pelvic floor, due to the complex multi-factor combined injury of the pelvic floor organs, changes in shape and position characteristics, and the important influence of the hyperelastic mechanical properties of ligament soft tissue, there is currently no effective positioning method and accurate mechanical simulation method for the main uterine ligament and sacral ligament. The lack of simulation methods for soft tissue injury mechanics and initial shape and position characteristics has led to slow progress in pelvic floor biomechanics research. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for positioning the cardinal ligaments and sacral ligaments of the uterus and constructing a finite element evolution model of the pelvic floor. The starting and ending positioning processes of the cardinal ligaments and sacral ligaments are simple, efficient, and require little manual processing, and the biomechanical effects of the cardinal ligaments and sacral ligaments in the two-dimensional pelvic floor system can be guaranteed; a proportional damage simulation method for pelvic floor organ tissues is adopted, which can avoid a large number of complicated in vivo / ex vivo material mechanics experiments on soft tissue injuries, thereby quickly and effectively analyzing the damage mechanical behavior of organ tissues with multi-factor damage; a concentrated force load application method is adopted, which can be independent of the magnetic resonance images of different clinical patients, and different initial shape and position feature settings of the pelvic floor can be conveniently and quickly realized, and applied to the construction of a two-dimensional evolution model of the pelvic floor and biomechanical analysis, providing effective assistance for the process simulation of the evolution of pelvic floor prolapse.

[0004] The technical solution adopted by the present invention is: a method for positioning the cardinal uterine ligament and the sacral ligament and constructing a finite element evolution model of the pelvic floor, and the specific steps are as follows:

[0005] Step 1: Based on the pelvic floor magnetic resonance imaging (MRI) of healthy women, a midsagittal two-dimensional image and a cross-sectional image set with clear organ contours are obtained, which are used as important materials for constructing a two-dimensional pelvic floor finite element model;

[0006] Step 2: Based on the midsagittal two-dimensional image selected in step 1, a two-dimensional pelvic floor finite element model without prolapse is established using finite element software, and the starting and ending points of the main ligament and the sacral ligament in the two-dimensional pelvic floor finite element model are determined according to the pelvic floor anatomical structure and the midsagittal two-dimensional image. According to the pelvic floor anatomical principles and the main ligament, combined with the cross-sectional image set, a distributed nonlinear hyperelastic spring group is used in the two-dimensional pelvic floor finite element model to perform equivalence on the main ligament and the sacral ligament.

[0007] Step 3: In the finite element software, a simulation method and expression for proportional damage of organ tissues are proposed. The mechanical properties of the organs are reduced by multiplying the nonlinear material stress-strain curves corresponding to the various organ tissues of the pelvic floor by a given proportional damage factor, so as to simulate the damage of the mechanical properties of the pelvic floor organs.

[0008] Step 4: Based on the clinical statistical data and mechanical equivalent method of the initial shape and position characteristics of the pelvic floor, a concentrated load application method and concentrated force-displacement expression of the initial shape and position characteristics are proposed. The initial reproductive fissure and uterine-vaginal angle are simulated with concentrated force loads on the two-dimensional pelvic floor finite element model to analyze the shape and position characteristics change trend caused by the decrease in tissue mechanical properties of the pelvic floor. Combined with the proportional damage simulation method in step 3, a pelvic floor finite element evolution model is constructed.

[0009] Specifically, the positioning and parameter setting method of the present invention is applicable to the two-dimensional model positioning of different types of pelvic floor main ligaments and sacral ligaments, including a normal pelvic floor system without prolapse, an abnormal prolapsed pelvic floor system, a pelvic floor system at rest, and a pelvic floor system under VALSALVA action. This method can accurately position the main ligaments and sacral ligaments and maintain the accuracy of finite element analysis as much as possible. Similarly, the proportional damage simulation method and the initial shape and position feature construction method mentioned in the present invention are not limited to the hyperelastic material and pelvic floor two-dimensional model mentioned in the present invention.

[0010] Specifically, the specific steps of step 2 are:

[0011] 2.1) Use the medical imaging software Mimics to locate the starting point of the sacral ligament:

[0012] Starting point: Using the medical imaging software Mimics, in the cross-sectional image set, locate the 2nd to 3rd segment of the sacrum and coccyx from the bottom to the top on the sacrospinous ligament-coccygeal muscle complex on the pelvic side wall to determine the starting point of the sacral ligament. Due to individual physiological differences, the starting point of some patients may be located on the sacrum, piriformis muscle, sciatic foramen area or ischial spine. This starting point is used as the starting point of the sacral ligament.

[0013] End point: It is usually located at the uterine cervix or vagina. The specific end point position is determined by the MRI image of the specific patient. This point serves as the end point of the sacroiliac ligament.

[0014] 2.2) Use the medical imaging software Mimics to locate the starting point of the main uterine ligament:

[0015] Starting point: Using the medical imaging software Mimics, locate the sacroiliac joint at the top of the greater sciatic foramen on the ipsilateral pelvic side wall in the cross-sectional image set. This point is the starting point of the main uterine ligament.

[0016] End point: The cardinal ligament ends at the uterine cervix or the posterior side of the vagina. This insertion point serves as the end point of the cardinal ligament of the uterus.

[0017] 2.3) Based on the starting point and the end point determined in the above steps, in combination with the midsagittal two-dimensional image, a nearly parallel distributed nonlinear hyperelastic spring group is used in the two-dimensional pelvic floor finite element model to be equivalent to the main uterine ligament and the sacral ligament in the two-dimensional pelvic floor finite element model.

[0018] Specifically, the specific steps of step 3 are:

[0019] 3.1) Material samples were collected from various pelvic floor organs and tissues, and uniaxial tensile tests were performed on them.

[0020] 3.2) The nonlinear material stress-strain data of each healthy organ obtained by uniaxial tensile test were imported into finite element software to fit the nonlinear curves of Mooney-Rivlin, Ogden, Yeoh, and Neo-Hookean hyperelastic materials. Different hyperelastic material models were selected according to different organs.

[0021] 3.3) The proportional damage simulation method and proportional damage expression are used, and the proportional damage coefficient K is introduced. The data set of the stress-strain nonlinear curve of each organ is multiplied by the corresponding proportional damage coefficient K (0.05, 0.25, 0.5, 0.75, corresponding to organ damage degrees of 95%, 75%, 50%, and 25%, respectively) to simulate the damage degree of pelvic floor organ tissue. The smaller the proportional damage coefficient K, the lower the tensile stiffness of the material and the lower the material performance. Damage degree K * The relationship with the proportional damage coefficient K is:

[0022] K * =1-K,0<K<1 (1).

[0023] Specifically, the specific steps of step 4 are:

[0024] 4.1) In the two-dimensional pelvic floor finite element model, the concentrated load application method and concentrated force-displacement expression are used to apply a horizontal concentrated force load to the nodes at the bottom of the uterus, simulating the abnormal initial shape and position characteristics of the uterus-vaginal angle in an upright neutral uterus and a retroverted posterior uterus. Different concentrated force-angle expressions can be obtained for different two-dimensional pelvic floor finite element models by fitting curves. The expression obtained after fitting is:

[0025] θ=28.3+6139.1F v (2)

[0026] Where θ is the uterine-vaginal angle in degrees, F v is the concentrated force applied to the nodes at the fundus of the uterus, in Newtons.

[0027] 4.2) In the two-dimensional pelvic floor finite element model, the concentrated load application method and concentrated force-displacement expression are used to apply concentrated force loads to the nodes at the bottom of the vagina to simulate the expansion of the reproductive tract fissure of the physiological pelvic floor. Different concentrated force-displacement expressions can be obtained for different two-dimensional pelvic floor finite element models by fitting curves. The relationship between the reproductive fissure and the concentrated force can be fitted into an approximate linear relationship. The expression obtained after fitting is:

[0028] D GH =0.0189+3.96F u (3)

[0029] Where D GH is the width of the reproductive slit, in meters, F u It is the concentrated force applied to the bottom of the posterior wall of the vagina, measured in Newtons.

[0030] Specifically, the finite element software described is Ansys.

[0031] The beneficial effects of the present invention are:

[0032] (1) The present invention uses the healthy pelvic floor system of women with no history of pelvic organ prolapse as the research object, obtains its nuclear magnetic resonance image, and constructs a physiological pelvic floor without pelvic organ prolapse by using computer-aided design software and finite element analysis software, combined with uniaxial tensile data, statistical data, etc. By mechanically equivalently changing the initial shape and position characteristics of the pelvic floor and organ damage, a two-dimensional pelvic floor finite element evolution model with initial damage characteristics is obtained, which can simulate the evolution process from the initial damaged pelvic floor to the prolapsed pelvic floor under the action of multiple factors (such as abdominal pressure, anorectal pressure, and urine pressure). In this process, the influence of various factors on the degree of pelvic floor prolapse can be studied in detail, and the change law of pelvic floor prolapse can be obtained.

[0033] (2) The present invention provides a method for locating the starting points of the cardinal ligament and the sacral ligament. Combined with the magnetic resonance imaging, the cardinal ligament and the sacral ligament can be quickly located in the two-dimensional image of the midsagittal plane, providing an accurate starting point for the two-dimensional equivalence of the ligament, thereby ensuring that the ligament can play its important biomechanical role in the two-dimensional equivalence process.

[0034] (3) The present invention proposes a mechanical equivalent method for constructing the initial shape and position of the pelvic floor. Studies have shown that the initial shape and position characteristics will affect the stability of the pelvic floor system. By loading concentrated forces to change the initial shape and position characteristics of the pelvic floor finite element system, the effects of different physiological angles and different reproductive tract fissures on pelvic organ prolapse are studied. This means that a corresponding two-dimensional pelvic floor finite element model can be constructed for clinical cases to find personalized diagnosis and treatment plans, which is of great significance for reducing postoperative pain and improving treatment efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart for realizing the present invention;

[0036] Figure 2 It is the location of the origin and insertion of the cardinal uterine ligament and the sacral ligament on the MRI image;

[0037] Figure 3 It is a simple two-dimensional representation of the cardinal and sacroiliac ligaments of the uterus on MRI images;

[0038] Figure 4 It is a two-dimensional equivalent schematic diagram of the cardinal uterine ligament and the sacral ligament on the two-dimensional pelvic floor finite element model;

[0039] Figure 5 is the stress-strain curve of the levator ani muscle at different injury levels;

[0040] Figure 6 It is a two-dimensional finite element model of the physiological pelvic floor system and the changes in initial shape and position characteristics.

[0041] Note: Figure 2 (a) The starting point of the cardinal uterine ligament and the end point of the cardinal uterine ligament-sacral ligament combination; Figure 2 (b) is the origin of the sacroiliac ligament; Figure 6 (a) Represents the physiological pelvic floor and two concentrated force loading positions that change the shape and position characteristics. Figure 6 (b) represents the situation in which the pelvic floor system simultaneously experiences enlargement of the genital fissure and changes in the uterine-vaginal angle. DETAILED DESCRIPTION

[0042] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1: Figure 1-6 As shown, a method for positioning the main uterine ligament and the sacral ligament and constructing a finite element evolution model of the pelvic floor, the steps are as follows:

[0044] Step 1: A healthy young female volunteer with no history of pelvic organ prolapse was selected and signed an informed consent form before the MRI examination. The subject was scanned using a 3T MRI scanner while lying on his back. MRI images were acquired continuously in the axial, coronal, and sagittal planes. The field of view was 20 cm × 20 cm, the inter-slice spacing was 1 mm, and the slice thickness was 4 mm. Based on this MRI image, a midsagittal two-dimensional image and a cross-sectional image set with clear organ contours were obtained, and a two-dimensional pelvic floor finite element model containing the main features of the pelvic floor, such as the uterus, vagina, bladder, urethra, rectum, and sacrum, was established in combination with the pelvic floor anatomy.

[0045] Step 2: Use Mimics to open the woman's MRI image and determine the origin and insertion points of the cardinal ligament and the sacral ligament on the cross-sectional image set based on organ characteristics and organ relationships ( Figure 2 ) and a simple two-dimensional representation of the cardinal and sacral ligaments ( Figure 3 ). Computer-aided design software and finite element software were used to establish a two-dimensional solid model and a two-dimensional finite element model without prolapse, and the starting and ending points of the main ligament and the sacral ligament in the two-dimensional finite element model of the pelvic floor were determined according to the anatomical structure of the pelvic floor. According to the mechanical equivalent method, the anatomical principles of the pelvic floor, and the tensile test parameters of the main ligament and the sacral ligament, combined with the two-dimensional image of the midsagittal plane, a distributed nonlinear hyperelastic spring group was used in the two-dimensional pelvic floor finite element model to perform the equivalence of the main ligament and the sacral ligament.

[0046] ( Figure 4 ).

[0047] The specific steps are:

[0048] 2.1) Locate the starting point of the sacral ligament: Using the medical imaging software Mimics, locate the sacral ligament on the 2nd to 3rd segment of the sacrum and coccyx from the bottom to the top on the sacrospinous ligament-coccygeal muscle complex on the pelvic side wall in the cross-sectional image set as the starting point range of the sacral ligament, and combine the cross-sectional and coronal MRI images on the same horizontal plane to determine the exact location of the starting point of the sacral ligament. Due to individual physiological differences, the starting point of some patients may be located in the sacrum, piriformis muscle, sciatic foramen area or ischial spine, which is the starting point of the sacral ligament distribution;

[0049] 2.2) Locate the end point of the sacroiliac ligament: Use the medical imaging software Mimics to locate the uterine cervix or upper vagina in the cross-sectional image set. The specific end point is determined by the sacroiliac ligament insertion mark in the MRI coronal, cross-sectional and midsagittal two-dimensional images of the specific patient. This point is used as the end point of the sacroiliac ligament.

[0050] 2.3) Locate the starting point of the cardinal ligament: Using the medical imaging software Mimics, locate the sacroiliac joint at the top of the greater sciatic foramen of the ipsilateral pelvic side wall in the cross-sectional image set as the starting point of the cardinal uterine ligament. Combine the cross-sectional and coronal MRI images on the same horizontal plane to determine the exact position of the cardinal uterine ligament. This point is the starting point of the cardinal uterine ligament.

[0051] 2.4) Locate the end point of the cardinal ligament: Use the medical imaging software Mimics to locate the cervix uteri or the posterior side of the upper vagina in the cross-sectional image. The sacral ligament of most patients will connect with the cardinal ligament of the uterus at the end point to form a sacral ligament-cardinal ligament combination. The specific end point position is determined by the insertion marks of the sacral ligament in the MRI coronal, cross-sectional and midsagittal two-dimensional images of the specific patient, and this point is used as the end point of the cardinal ligament of the uterus.

[0052] 2.5) According to the above starting point and mechanical projection synthesis principle, combined with the midsagittal plane two-dimensional image, the combine14 spring damping unit was used in the finite element software ANSYS to simulate the connection between the main uterine ligament and the sacral ligament in the two-dimensional pelvic floor finite element model.

[0053] Step 3: In the finite element software, the mechanical properties of the organs are reduced by multiplying the material stress-strain curves corresponding to the various tissues and organs of the pelvic floor by a given factor (percentage) to simulate the loss of mechanical properties of the organs caused by pelvic floor damage.

[0054] The specific steps are:

[0055] 3.1) Sample materials from various pelvic floor organs and perform uniaxial tensile tests on them to obtain force-displacement curves of the sampled materials from various pelvic floor organs.

[0056] 3.2) The stress-strain data of each healthy organ of the pelvic floor obtained through uniaxial tensile test were imported into the finite element software ANSYS and fitted into the nonlinear curves of Mooney-Rivlin, Ogden, Yeoh, and Neo-Hookean hyperelastic material models.

[0057] The strain energy function of the Mooney-Rivlin model is expressed as:

[0058]

[0059]

[0060] Where W Mooney-rivlin Corresponding to its strain energy function, D 1 , C 10 , C 01 is the Mooney-Rivlin hyperelastic material parameter, ν is the Poisson's ratio of the material, J MRis the incompressible parameter of the Mooney-Rivlin model material, I 1 ,I 2 is the invariant of the right Cauchy–Green deformation tensor.

[0061] The strain energy function of the Ogden model is expressed as:

[0062]

[0063] Where W Ogden is the strain energy function of the Ogden material model, N is the model order, and u i , α i is the Ogden hyperelastic material parameter, D ogden is an incompressible parameter, is the reduced principal elongation, and the relationship between the reduced principal elongation is expressed as follows:

[0064]

[0065] Where J is the ratio of the deformed volume to the undeformed volume of the material, λ 1 , 2 , 3 are the principal stretches in the three directions of the strain tensor.

[0066] The strain energy function of the Yeoh material model is expressed as:

[0067]

[0068] Where D Yeoh , C i0 is the corresponding material parameter, is the principal strain invariant in uniaxial tension, and its relationship is expressed as:

[0069]

[0070] Where λ is the principal expansion rate of the maximum hyperelastic material.

[0071] The strain energy expression of the Neo-Hookean material model is:

[0072]

[0073] Where u is the initial shear modulus, D 1 is the material incompressibility parameter, and I is the strain tensor invariant. If the material is assumed to be incompressible, then J = 1 and the second term is 0.

[0074] The appropriate material model is selected for different pelvic floor organs based on the above strain energy function, the uniaxial tensile results of the organs, the mechanical behaviors of different tissues and organs, and the deformation range described by different hyperelastic constitutive models.

[0075] 3.3) Multiply the stress-strain data set of each organ by the corresponding proportional damage coefficient K to simulate the degree of damage to the pelvic floor organs. The smaller the proportional damage coefficient K, the lower the tensile stiffness of the material and the lower the material performance. In this embodiment, the levator ani muscles are damaged by 95%, 75%, 50%, and 25% respectively, and the degree of damage K is * The relationship with the proportional damage coefficient K is:

[0076] K * =1-K,0<K<1 (1).

[0077] Figure 5 Taking the proportional injury of the levator ani muscle as an example, the stress-strain data of the levator ani muscle material were multiplied by 0.05, 0.25, 0.5, and 0.75 to obtain the stress-strain curves of the levator ani muscle with injury degrees of 95%, 75%, 50%, and 25%.

[0078] Step 4: Based on the clinical statistical data of the initial shape and position characteristics of the pelvic floor, the initial genital fissure and uterine-vaginal angle are simulated in the form of concentrated force load on the two-dimensional pelvic floor finite element model according to the statistical data and mechanical equivalent method, so as to simulate the shape and position characteristic change trend of the pelvic floor caused by the decline of tissue mechanical properties. Set F u 、F v They are the concentrated forces that change the width of the genital fissure and the angle of the vagina and uterus, and their directions and locations of action are as follows: Figure 6 (a).

[0079] The specific steps are:

[0080] 4.1) In the finite element software ANSYS, a horizontal concentrated force load is applied to the nodes at the uterine fundus of the finite element model to simulate the situation when the uterine-vaginal angle is in an abnormal position (the uterus is not approximately parallel to the horizontal). Different concentrated force-angle expressions can be obtained by fitting the curve. In this embodiment, the expression obtained by discrete point fitting is:

[0081] θ=28.3+6139.1F v (2)

[0082] Where θ is the uterine-vaginal angle in degrees, F v is the concentrated force applied to the nodes at the fundus of the uterus, in Newtons.

[0083] 4.2) In the finite element software ANSYS, a horizontal concentrated force load is applied to the vaginal bottom of the finite element model to simulate the genital fissure. In this implementation case, the approximate linear relationship between the genital fissure and the concentrated force can be obtained by discrete point fitting:

[0084] D GH =0.0189+3.96F u (3)

[0085] Where D GH is the width of the reproductive slit, in meters, F u It is the concentrated force applied to the bottom of the posterior wall of the vagina, measured in Newtons.

[0086] 4.3) Through the above two steps, a pelvic floor finite element model with preliminary changes in shape and position characteristics can be constructed based on the physiological pelvic floor two-dimensional finite element model, such as Figure 6 (b).

[0087] It should be noted that the method of the present invention is applicable to the positioning of the cardinal ligaments and sacral ligaments of the uterus of healthy women and the simulation of pelvic floor organ injuries in healthy women. The cardinal ligament and sacral ligament positioning, proportional injury simulation method and pelvic floor morphology construction mentioned in the present invention are not limited to the above-mentioned patients, organs and injury proportions, and can be applied to the magnetic resonance images of other patients to construct a two-dimensional finite element evolution model when applicable.

[0088] The above is a detailed description of the implementation of the present invention in conjunction with the accompanying drawings. The present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in the field without departing from the purpose of the present invention.

Claims

1. A method for positioning the cardinal uterine ligament and the sacral ligament and constructing a finite element evolution model of the pelvic floor, characterized in that: Here are the steps: Step 1: Based on the pelvic floor magnetic resonance imaging (MRI) of healthy women, a mid-sagittal two-dimensional image and a cross-sectional image set with clear organ contours are obtained; Step 2: Based on the midsagittal two-dimensional image selected in step 1, a two-dimensional pelvic floor finite element model without prolapse is established using finite element software, and the starting and ending points of the main ligament and the sacral ligament in the two-dimensional pelvic floor finite element model are determined according to the pelvic floor anatomical structure and the midsagittal two-dimensional image. Based on the pelvic floor anatomical principles and the main ligament, combined with the cross-sectional image set, a distributed nonlinear hyperelastic spring group is used in the two-dimensional pelvic floor finite element model to perform equivalence on the main ligament and the sacral ligament; Step 3: In the finite element software, a simulation method and expression for proportional damage of organ tissues are proposed. The mechanical properties of the organs are reduced by multiplying the nonlinear material stress-strain curves corresponding to the various organ tissues of the pelvic floor by a given proportional damage factor, so as to simulate the damage of the mechanical properties of the pelvic floor organs. Step 4: Based on the clinical statistical data and mechanical equivalent method of the initial shape and position characteristics of the pelvic floor, a concentrated load application method and concentrated force-displacement expression of the initial shape and position characteristics are proposed. The initial genital fissure and uterine-vaginal angle are simulated on the two-dimensional pelvic floor finite element model with concentrated force load to analyze the change trend of the shape and position characteristics of the pelvic floor caused by the decrease in the mechanical properties of the tissue. Combined with the proportional damage simulation method in step 3, a pelvic floor finite element evolution model is constructed.

2. A method for positioning the cardinal uterine ligament and the sacral ligament and constructing a finite element evolution model of the pelvic floor according to claim 1, characterized in that: The specific steps of step 2 are: 2.1) Use the medical imaging software Mimics to locate the starting point of the sacral ligament distribution: Starting point: Using the medical imaging software Mimics, in the cross-sectional image set, locate the 2nd to 3rd segment of the sacrum and coccyx from the bottom to the top on the sacrospinous ligament-coccygeal muscle complex on the pelvic side wall to determine the starting point of the sacral ligament. Due to individual physiological differences, the starting point of some patients is located on the sacrum, piriformis muscle, sciatic foramen area or ischial spine. This starting point is used as the starting point of the sacral ligament distribution; End point: generally located in the cervix or vaginal apex area. The specific end point location is determined by the MRI image of the specific patient. This area serves as the end point of the sacroiliac ligament distribution. 2.2) Using the medical imaging software Mimics, locate the starting point of the distribution of the main uterine ligaments: Starting point: Using the medical imaging software Mimics, locate the sacroiliac joint at the top of the greater sciatic foramen on the ipsilateral pelvic side wall in the cross-sectional image. This point is the starting point of the main uterine ligament. End point: The cardinal ligament ends at the uterine cervix or the posterior side of the vagina. This insertion point is the end point of the cardinal ligament of the uterus. 2.3) Based on the starting point and the end point determined in the above steps, in combination with the midsagittal two-dimensional image, a nearly parallel distributed nonlinear hyperelastic spring group is used in the two-dimensional pelvic floor finite element model to be equivalent to the main uterine ligament and the sacral ligament in the two-dimensional pelvic floor finite element model.

3. A method for positioning the cardinal uterine ligament and the sacral ligament and constructing a finite element evolution model of the pelvic floor according to claim 1, characterized in that: The specific steps of step 3 are: 3.1) Sampling materials from various pelvic floor organ tissues and conducting uniaxial tensile tests on them; 3.2) The nonlinear material stress-strain data of each healthy organ obtained by uniaxial tensile test were imported into finite element software to fit the nonlinear curves of Mooney-Rivlin, Ogden, Yeoh, and Neo-Hookean hyperelastic materials, and different hyperelastic material models were selected according to different organs; 3.3) The proportional damage simulation method and proportional damage expression are used to introduce the proportional damage coefficient K. The data set of the stress-strain nonlinear curve of each organ is multiplied by the corresponding proportional damage coefficient K to simulate the damage degree of the pelvic floor organ tissue. The smaller the proportional damage coefficient K, the lower the tensile stiffness of the material, the lower the material performance, and the higher the damage degree K. * The relationship with the proportional damage coefficient K is: K * =1-K,0<K<1 (1)。 4. The method for positioning the cardinal uterine ligament and the sacral ligament and constructing a finite element evolution model of the pelvic floor according to claim 1, characterized in that: The specific steps of step 4 are: 4.1) In the two-dimensional pelvic floor finite element model, the concentrated load application method and concentrated force-displacement expression are used to apply a horizontal concentrated force load to the nodes at the bottom of the uterus, simulating the abnormal initial shape and position characteristics of the uterus-vaginal angle in an upright median uterus and a retroverted posterior uterus. Different concentrated force-angle expressions are obtained for different two-dimensional pelvic floor finite element models by fitting curves. The expression obtained after fitting is: θ=28.3+6139.1F v (2) Where θ is the uterine-vaginal angle in degrees, F v is the concentrated force applied to the nodes of the uterine fundus, in Newtons; 4.2) In the two-dimensional pelvic floor finite element model, the concentrated load application method and concentrated force-displacement expression are used to apply concentrated force loads to the nodes at the bottom of the vagina to simulate the expansion of the reproductive tract fissure of the physiological pelvic floor. Different concentrated force-displacement expressions are obtained by fitting curves for different two-dimensional pelvic floor finite element models. The relationship between the reproductive fissure and the concentrated force is fitted to an approximate linear relationship, and the expression is: <h2 style=";text-align:left;direction:ltr">D<h2 style=";text-align:left;direction:ltr"> GH <h2 style=";text-align:left;direction:ltr"> =0.0089+3.96F<h2 style=";text-align:left;direction:ltr"> u <h2 style=";text-align:left;direction:ltr"> (3) Where D GH is the width of the reproductive slit, in meters, F u It is the concentrated force applied to the bottom of the posterior wall of the vagina, measured in Newtons.

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