Idiopathic knee joint deformity correction method based on combination of growth curve prediction and absorbable material time gradient regulation

Abstract

The invention discloses an idiopathic knee joint deformity correction method based on combination of growth curve prediction and absorbable material time gradient regulation and control, and is applied to the technical field of biomedical materials. Comprising the following steps: acquiring lower limb bone length data of a normal child, and drawing a growth curve; constructing and fitting a lower limb bone length model by using the growth curve data, and constructing a mathematical model for correcting idiopathic knee varus and valgus; constructing a prediction model to calculate the time of implanting the child patient with idiopathic genu varum into the steel plate for fixation during the semi-epiphyseal fixation; the absorbable zinc-magnesium alloy internal fixation nail plate with different in-vivo absorption time gradients is developed; the zinc-magnesium alloy internal fixation nail plate with the corresponding absorption time is selected for correction according to the time required by different child patients to be implanted into the steel plate for fixation. After a child patient receives a semi-epiphyseal block operation to achieve the correction effect, the internal fixation steel plate can be automatically absorbed and broken, the operation of taking out internal fixation again is omitted, the operation risk and pain are reduced, and the treatment cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biomedical materials, and more particularly to a method for correcting idiopathic knee deformity based on growth curve prediction and time gradient regulation of absorbable materials. BACKGROUND

[0002] During the process of bone maturation in children, the axial growth of long bones is mainly realized by endochondral ossification of the epiphyseal plate. Some idiopathic factors interfere with the local epiphyseal plate ossification process, causing uneven limb growth, which is the most common factor leading to angular deformity of the knee joint in adolescents. For patients with growth potential of the epiphyseal plate, the clinician usually chooses hemiepiphysiodesis to treat angular deformity of the knee joint in children. Its principle is to limit the longitudinal growth of the epiphyseal plate at the site by internal fixation device, while the epiphyseal plate on the opposite side still maintains normal growth potential, and finally achieves the purpose of correcting angular deformity. Its essence is to locally regulate the speed of endochondral ossification of the epiphyseal plate by artificial means to improve uneven ossification of the epiphyseal plate. In recent years, hemiepiphysiodesis has become the preferred method for treating angular deformity of the knee joint in adolescents and children. However, the material of the nail plate used in hemiepiphysiodesis at the present stage is non-absorbable metal, and the most common material is titanium alloy. Such internal fixation needs to be removed after achieving the expected orthopedic purpose to prevent overcorrection from causing angular deformity in the opposite direction of the knee joint, and the child has to undergo general anesthesia surgery again to remove the nail plate. Therefore, how to provide a method for correcting idiopathic knee deformity based on growth curve prediction and time gradient regulation of absorbable materials is a problem that needs to be solved by those skilled in the art. SUMMARY

[0003] Therefore, the present application provides a method for correcting idiopathic knee deformity based on growth curve prediction and time gradient regulation of absorbable materials, establishes the growth curve of the tibia and femur of a group of children, constructs a prediction model to predict the complete correction time of the child, designs an absorbable internal fixation nail plate system with different degradation time gradients for children patients undergoing hemiepiphysiodesis, and combines the above-mentioned prediction model of the correction time. The clinician can choose an absorbable internal fixation plate with a specific degradation time, so that the internal fixation plate of the child receiving hemiepiphysiodesis can be absorbed and broken after achieving the correction effect, eliminating the need for surgery to remove the internal fixation again.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0005] A method for correcting idiopathic knee deformity based on growth curve prediction and time gradient regulation of absorbable materials, comprising the following steps:

[0006] S1, collecting normal children's lower limb bone length data, and drawing a lower limb bone length growth curve;

[0007] S2, constructing a lower limb bone length model fitting a child group by using growth curve data, and constructing a mathematical model for correcting idiopathic knee varus and valgus;

[0008] S3, constructing a prediction model to calculate the time required for implanting a steel plate for internal fixation for a child with idiopathic knee varus and valgus to undergo half epiphysis fixation;

[0009] S4, developing absorbable zinc-magnesium alloy internal fixation nail plates with different in-vivo absorption time gradients;

[0010] S5, selecting a corresponding absorbable zinc-magnesium alloy internal fixation nail plate for correction according to the time required for implanting a steel plate for internal fixation for the child.

[0011] Optionally, the data collected in S1 is lower limb femur and tibia length data of normal children of different ages, and a tibia and femur length growth curve based on a child group is established as a basis for calculating the longitudinal growth potential of the child's tibia and femur, and then predicting the time required for correction after half epiphysis arrest.

[0012] Optionally, the mathematical model for correcting knee varus and valgus in S2 is:

[0013]

[0014] In the formula, L is the length of continuous growth, δ is the knee varus and valgus deformity angle, and r is the epiphysis length.

[0015] Optionally, S3 is:

[0016] According to the lower limb bone length model, the femur length f(x) of a child with knee valgus caused by femur deformity is calculated, the length after reaching the orthopedic purpose is f(x)+2πrδ / 360, and the expression formula of the time t required for femur distal epiphysis arrest for knee varus and valgus is:

[0017] t=f -1 (f(x)+2πrδ / (360*0.7))-x

[0018] In the formula, δ is the knee varus and valgus deformity angle, r is the epiphysis length, and x is the age of the child.

[0019] Similarly, the expression formula of the time t required for tibial proximal arrest for knee varus and valgus caused by tibial deformity is:

[0020] t=f -1 (f(x)+2πrδ / (360*0.6))-x

[0021] Optionally, S4 develops absorbable zinc-magnesium alloy internal fixation nail plates with different in-vivo absorption time gradients by adjusting the magnesium content in the zinc-magnesium alloy, specifically:

[0022] Zinc-magnesium alloys with different magnesium contents are prepared and mechanical property tests are performed; an 8-shaped nail plate system is established and finite element analysis is performed to obtain optimal size parameters; an animal experiment is performed using an absorbable steel plate that is proportionally reduced in size, and alloy ratios and size data of nail plate systems with different degradation times for children are derived using the obtained data.

[0023] Optionally, the preparation of zinc-magnesium alloys with different magnesium contents and the mechanical property tests are specifically as follows: zinc-magnesium alloys with different magnesium contents are prepared using a stir-friction solid-phase alloying technique, and metallographic microscopy, scanning electron microscopy, and X-ray diffraction analysis are performed on the prepared materials to study the microstructure of the materials before and after heat treatment, and the mechanical properties of the materials are studied through microhardness testing, compression property testing, and tensile testing.

[0024] Optionally, the establishment of the 8-shaped nail plate system and the finite element analysis are specifically as follows: UG is used to establish the 8-shaped nail plate system, the model is imported into ANSYS Workbench 19.2 for finite element analysis, the analysis includes bending, torsion, and pulling out, the simulation results of screw stress concentration under different loads are obtained, then by changing the size parameters of the nail plate, models with different parameters are established to explore the influence of each parameter on the simulation experiment, and through orthogonal experiment, the coupling effect of multiple factors is analyzed to obtain the optimal size parameters of each nail plate model.

[0025] Optionally, the derivation of alloy ratios and size data of nail plate systems with different degradation times for children using the obtained data is specifically as follows: an animal experiment is performed using an absorbable steel plate that is proportionally reduced in size and has different alloy ratios, according to the data obtained from the animal experiment, the nail plate system is proportionally enlarged to the size of the 8-shaped plate currently used for children, and according to the degradation rules of nail plate systems with different zinc-magnesium ratios in animals, alloy ratios and size data of nail plate systems with degradation times of 3, 6, 9, 12, 15, 18, 21, and 24 months are designed, respectively, to guide the production of nail plate systems for children's metaphyseal arrest.

[0026] Optionally, S4 develops absorbable zinc-magnesium alloy internal fixation nail plates with different in-vivo absorption time gradients by adjusting the topological structure of the zinc-magnesium alloy internal fixation nail plate, specifically as follows:

[0027] The material parameters of the absorbable zinc-magnesium alloy internal fixation nail plate are determined by standardizing the mechanical property test, and an initial finite element model is established. In the finite element environment, the process of applying external force by the clinical disrupter at a specific position of the absorbable zinc-magnesium alloy internal fixation nail plate is simulated, the maximum force value and the loading direction that can be provided by the disrupter are set, the stress concentration area and the crack initiation position under the action force are analyzed, and whether the action force is sufficient to induce fracture at different degradation stages is evaluated; based on the initial structure, a multi-objective topology optimization is set: sufficient stiffness and strength are ensured in the early degradation stage to withstand the epiphyseal growth force; at the target degradation time point, stress concentration occurs in the key area and the disrupter is easy to trigger fracture;

[0028] The finite element model is re-established, and two-stage verification is performed: the epiphyseal growth force is applied in the early degradation stage to simulate, the maximum strain and stress value of the fixator are verified to be lower than the material yield limit, and early failure is ensured; the epiphyseal growth force and the disrupter external force are applied in the late degradation stage, respectively, to verify that the disrupter can trigger fracture within the preset force value range, and the fracture position is consistent with the design; the residual strength of the remaining structure after degradation is analyzed to ensure that the fixator will not form sharp residual fragments to damage the tissue after fracture; an absorbable steel plate with the same proportion is designed and manufactured for animal experiments, and the obtained data are used to derive alloy ratio and size data of the nail plate system with different degradation times for children.

[0029] Optionally, S5 specifically comprises: collecting the age, gender, epiphyseal length, deformity position and deformity angle of the child, and introducing the data into a prediction model to obtain the time required for completing the semi-epiphyseal arrest; selecting an absorbable zinc-magnesium alloy steel plate with in-vivo degradation close to the time required for completing the semi-epiphyseal arrest, and performing the semi-epiphyseal arrest in the same way as using a traditional 8-shaped steel plate; the patient is regularly followed up after the operation, and CT examination is performed when the correction is completed after the operation to evaluate the integrity of the steel plate; if it is found that the steel plate has been broken in the weak area, and the correction is satisfactory, the treatment is ended; if the correction is satisfactory but the integrity of the steel plate still exists, a designed bone plate disrupter is used to pry the steel plate without incision under local anesthesia; the remaining residual steel plate continues to be harmlessly absorbed in the body, and the treatment is ended.

[0030] Compared with the prior art, the application provides a method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient regulation of absorbable material, which has the following beneficial effects: the method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient regulation of absorbable material is designed and developed, so that the internal fixation steel plate can be absorbed and broken after the child receives the epiphyseal arrest to achieve the correction effect, the surgery of removing the internal fixation is avoided, the minimally invasive epiphyseal arrest is more in line with the concept of minimally invasive surgery, effective reference information can be provided for clinicians to guide the determination of the timing of removing the internal fixation, the surgical risk and pain of the child due to the reoperation are reduced, the patient is avoided from reoperation and the economic burden caused by the reoperation, the social and economic benefits can be greatly improved, and the method mainly includes the following aspects: ① reducing the economic cost of reoperation, including the cost of surgery, the cost of rehabilitation, the cost of medical equipment, etc.; ② the psychological impact on the patient and the family; and ③ social cost, including the use of public medical resources, the expenditure of social insurance, etc. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute the embodiments of the application, and for those skilled in the art, other drawings can be obtained without creative labor based on the provided drawings.

[0032] Figure 1 The method for correcting idiopathic knee joint deformity of the application is shown in the flowchart;

[0033] Figure 2 The relationship between the subsequent growth length and the knee valgus correction angle is shown in the schematic diagram;

[0034] Figure 3 The preparation process of the absorbable zinc-magnesium alloy of the application is shown in the schematic diagram;

[0035] Figure 4 The female tibial length growth percentile curve in the embodiment of the application is shown in the graph;

[0036] Figure 5 The male tibial length growth percentile curve in the embodiment of the application is shown in the graph;

[0037] Figure 6 The female femoral length growth percentile curve in the embodiment of the application is shown in the graph;

[0038] Figure 7 The male femoral length growth percentile curve in the embodiment of the application is shown in the graph;

[0039] Figure 8 A schematic diagram of the zinc-magnesium alloy steel plate of the present application;

[0040] Figure 9 A fixed schematic diagram of the zinc-magnesium alloy steel plate of the present application;

[0041] Figure 10 A schematic diagram of the bone plate destroyer of the present application;

[0042] Figure 11 A schematic diagram of the process of inserting the bone plate destroyer into the zinc-magnesium alloy steel plate of the present application. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0044] The embodiments of the present application disclose a method for correcting idiopathic knee deformity based on growth curve prediction and time gradient control of absorbable materials, as shown in Figure 1 The method comprises the following steps:

[0045] S1, collecting normal children's lower limb bone length data, and drawing a lower limb bone length growth curve;

[0046] S2, using the growth curve data to construct a lower limb bone length model fitting a child group, and constructing a mathematical model for correcting idiopathic knee varus and valgus;

[0047] S3, constructing a prediction model to calculate the time required for a child with idiopathic knee varus and valgus to undergo half epiphysis fixation surgery;

[0048] S4, developing absorbable zinc-magnesium alloy internal fixation nails with different in-vivo absorption time gradients;

[0049] S5, selecting the corresponding absorbable zinc-magnesium alloy internal fixation nails for correction according to the time required for the child to undergo internal fixation of the implanted steel plate.

[0050] Further, the data collected in S1 is the lower limb femur and tibia length data of normal children of different ages, and the tibia and femur length growth curves based on a child group are established as the basis for calculating the longitudinal growth potential of the tibia and femur of children, and then the time required for correction after half epiphysis arrest surgery is predicted.

[0051] In the embodiment of the present application, the lower limb bone length and clinical diagnosis data of 2750 normal children are collected, and after inclusion and exclusion, 2019 children information are used for drawing the lower limb bone length growth curve, and the obtained curve is as shown in Figures 4-7 .

[0052] In the embodiment of the present application, based on the growth curve fitting model u=f(x), x is the age of the child, y is the femur or tibia length, and its inverse function is expressed as x=f -1 (y), in order to better fit the complex trend, the prediction model is a spline regression equation, and the function is a segmented polynomial. The equation is usually complex, and cannot be directly written as a linear regression equation. Therefore, a program is designed to calculate the prediction value instead of manually deriving it. Through the above fitting model, the approximate time required for the normal child to continuously grow a certain length of femur or tibia at a known age can be derived, which is used for the next step of prediction.

[0053] Further, the mathematical model for correcting the knee varus in S2 is specifically:

[0054]

[0055] In the formula, L is the continuous growth length, δ is the knee varus deformity angle, and r is the epiphysis length. The relationship between the subsequent growth length and the knee varus correction angle is as shown in Figure 2 .

[0056] If there is idiopathic knee varus deformity before the skeletal maturity period and it has a significant appearance effect, proximal tibial medial or distal femoral medial epiphysis arrest can be used. This operation achieves "self-correction" of deformity by retaining the continuous growth of the lateral epiphysis. After performing medial epiphysis arrest, the fitting model constructed by the growth curve can be used to predict the continuous growth of the lateral epiphysis. The lateral continuous growth is not a linear extension, but a circular arc growth trajectory with the epiphysis width as the radius. Accordingly, the mathematical relationship between the epiphysis length, the deformity angle and the continuous growth arc is established in the embodiment of the present application.

[0057] Further, S3 is specifically:

[0058] According to the lower limb bone length model, the femur or tibia length f(x) of the knee varus child is calculated. The femur or tibia length after reaching the orthopedic purpose is f(x)+2πrδ / 360. Then the time t required for the deformity to be approximately corrected after the child undergoes half epiphysis arrest is inferred, and the expression formula is:

[0059] t=f -1 (f(x)+2πrδ / (360))-x

[0060] In the formula, δ is the knee varus deformity angle, r is the epiphysis length, and x is the age.

[0061] Since both the proximal and distal femurs have epiphyseal growth plates, both contributing to the longitudinal length of the femur, and according to growth and development patterns, the distal femoral growth plate contributes approximately 70% of longitudinal femoral growth, while the proximal femoral growth plate contributes approximately 30%. Therefore, the time required for distal femoral block surgery to correct genu valgum in children needs to be adjusted. Similarly, according to growth and development patterns, the proximal tibial growth plate contributes approximately 60% of longitudinal tibial growth, while the distal tibial growth plate contributes approximately 40%. Therefore, the time required for proximal tibial block surgery to correct genu varum and valgum needs to be adjusted.

[0062] The corrected formula is as follows:

[0063] The formula for the time t required for distal femoral block surgery to correct genu varum or valgus caused by femoral abnormalities is as follows:

[0064] t = f -1 (f(x)+2πrδ / (360*0.7))-x

[0065] The formula for the time t required for proximal tibial block surgery to correct genu varum or valgus caused by tibial abnormalities is as follows:

[0066] t = f -1 (f(x)+2πrδ / (360*0.6))-x

[0067] In the formula, δ is the angle of genu varum / valgus deformity, r is the epiphyseal length, and x is age.

[0068] In this embodiment of the invention, assuming a child with genu valgum is currently aged x, the current angle of genu valgum deformity caused by the femur is δ, and the current length of the femoral epiphysis is r, the femoral length calculated according to the fitting model is f(x), and the length after achieving the corrective goal is f(x) + 2πrδ / 360, then the formula for estimating the approximate time t required for the deformity to be corrected after hemiepithelial arrest is as follows:

[0069] t = f -1 (f(x)+2πrδ / (360*0.7))-x.

[0070] Furthermore, S4 developed absorbable zinc-magnesium alloy internal fixation plates with different in vivo absorption time gradients by adjusting the magnesium content in the zinc-magnesium alloy. Specifically:

[0071] Zinc-magnesium alloys with different magnesium contents were prepared and their mechanical properties were tested. The preparation process of the zinc-magnesium alloys is as follows: Figure 3 As shown; an 8-shaped nail plate system was established and subjected to finite element analysis to obtain the optimal dimensional parameters; a scaled-down absorbable steel plate was designed and fabricated for animal experiments, and the obtained data were used to derive the alloy ratio and dimensional data of nail plate systems with different degradation times that can be used for children.

[0072] Further, the zinc-magnesium alloy with different magnesium content is prepared and mechanical property test is carried out, specifically: the zinc-magnesium alloy with different magnesium content is prepared by using a stirring friction solid-phase alloying technology, the microstructure of the prepared material before and after heat treatment is analyzed by using a metallographic microscope, a scanning electron microscope and X-ray diffraction, and the mechanical property of the material is researched by using a microhardness test, a compression property test and a tensile test.

[0073] In the embodiment of the application, the magnesium content ranges from 0 to 10 wt%.

[0074] Zinc-magnesium alloy as a new type of degradable biomedical implant metal material has been widely studied in the field of modern biomedicine, especially in bone implantation. Zinc is an essential nutrient element in the human body, which can promote the formation of new hemoglobin, and at the same time promote the synthesis of various enzymes, and can enhance the regenerative ability of wound tissue. In addition, as the fourth most abundant metal ion in the human body, magnesium is an important nutrient substance that all living organisms need to possess, which exists in every type of cell and can be effectively regulated by the body's self-balancing mechanism. Compared with traditional medical metal materials, the zinc-magnesium alloy used in the embodiment has the following advantages: 1) controllable biodegradability, the degradation rate of zinc-magnesium alloy in the body is controllable, which means that it can provide the necessary support and mechanical properties for a certain period of time according to the treatment needs, and then gradually degrades and is absorbed by the human body. This controllable biodegradability makes zinc-magnesium alloy have a significant advantage in bone fixation which requires temporary support; 2) suitable mechanical properties, the mechanical properties of zinc-magnesium alloy can be optimized through alloying (adjusting the magnesium content) and adjusting the preparation process to meet the specific medical application requirements; 3) good biocompatibility, after the zinc-magnesium alloy is implanted into the human body, it can be accepted by the human body and will not cause serious rejection or inflammatory reactions; 4) unique antibacterial ability, the zinc ions released by the degradation of zinc-magnesium alloy can destroy the membrane structure of bacteria and kill bacteria, which can effectively reduce the risk of postoperative infection. Although zinc-magnesium alloy material as a new type of degradable implant material has many advantages, there are still some challenges. First, the half-epiphysis arrest procedure for knee varus and valgus orthopedics has a longer service life than general internal fixation for fracture fixation. Generally, fracture healing is completed in 1-2 months, while the half-epiphysis arrest internal fixation is removed in 6 months to 2 years, which requires a higher degradation rate of internal fixation. Second, different children require different epiphysis fixation times. To avoid excessive correction caused by slow degradation of the nail plate or insufficient correction caused by rapid degradation, the performance of zinc-magnesium alloy needs to be controlled, not only to prolong the degradation time of internal fixation, but also to achieve controllable degradation of internal fixation. Based on this, the embodiment proposes the above-mentioned new method of preparing zinc-magnesium alloy by friction stir solid phase alloying, which uses the thermal-mechanical field established by high-speed stirring and friction between the stirring head and the material to realize the rapid mixing and alloying of zinc and magnesium materials. Compared with the traditional casting method, on the one hand, the new method can form a homogenized structure with specific grain orientation, fine grains and dispersed distribution of second phase, so as to precisely control the mechanical properties and degradation rate of the material; on the other hand, the new method eliminates the high-cost and long-period alloy smelting link, thereby realizing low-cost, high-efficiency and customized material preparation to meet the treatment needs of children of different age groups and reduce treatment costs.In addition, according to the characteristics that magnesium degrades fast and zinc degrades slowly, the zinc-magnesium alloy with different magnesium contents can be prepared by adjusting the alloy content, and the strength and toughness and corrosion resistance of the material can be improved by the method of structure optimization, so that the zinc-magnesium alloy nail plate system has sufficient mechanical support and appropriate degradation behavior, and the absorbable zinc-magnesium alloy internal fixation nail plate with different in-vivo absorption time gradients for treating children's knee varus by half epiphyseal arrest can be prepared. Meanwhile, in order to facilitate postoperative follow-up observation of whether the steel plate is broken or not, a weak area is designed on the steel plate, so that if the absorbable steel plate is slowly absorbed and the strength decreases, the steel plate will first break at the weak area, and the CT three-dimensional reconstruction inspection can better judge whether the steel plate has been broken. Finally, in order to prevent the steel plate from being completely broken after correction, a prying mechanism is added to the weak area, and a special designed bone plate destroyer is used without cutting, so that when the strength of the steel plate decreases and approaches to break but has not been broken after being placed in the body for a period of time, the steel plate can be artificially controlled to be pried, so as to further prevent overcorrection.

[0075] Further, the establishment of the 8-shaped nail plate system and the finite element analysis are as follows: the 8-shaped nail plate system is established by using UG, the model is imported into ANSYS Workbench 19.2 for finite element analysis, the analysis contents include bending, torsion and pulling out, the simulation results of screw stress concentration under different loads are obtained, then the models with different parameters are established by changing the size parameters of the nail plate, the influence law of each parameter on the simulation experiment is explored, and the best size parameters of each nail plate model are obtained by orthogonal experiment.

[0076] Further, the alloy ratio and size data of the nail plate system with different degradation times for children are derived from the obtained data, and the specific steps are as follows: design and manufacture the absorbable steel plates with different alloy ratios in the same proportion, and conduct animal experiments, according to the data obtained from the animal experiments, the nail plate system is enlarged to the size of the eight-shaped plate used by children at present, and according to the degradation law of the nail plate system with different zinc-magnesium ratios in the animal body, the alloy ratio and size data of the nail plate system with degradation of 3, 6, 9, 12, 15, 18, 21 and 24 months are designed respectively, so as to guide the production of nail plate system for children's half epiphyseal arrest.

[0077] Further, in addition to the zinc-magnesium alloy internal fixation nail plate with different in-vivo absorption time gradients by adjusting the magnesium content in the zinc-magnesium alloy, S4 can also develop the zinc-magnesium alloy internal fixation nail plate with different in-vivo absorption time gradients by adjusting the topological structure of the zinc-magnesium alloy internal fixation nail plate, and the specific steps are as follows:

[0078] The material parameters of the absorbable zinc-magnesium alloy internal fixation nail plate are determined by standardizing the mechanical property test, and an initial finite element model is established. In the finite element environment, the process of applying external force by a clinical disrupter (such as a lever and a torque wrench) at a specific position of the absorbable zinc-magnesium alloy internal fixation nail plate is simulated, the maximum force value and the loading direction (such as vertical prying or shearing and twisting) that can be provided by the disrupter are set, the stress concentration area and the crack initiation position under the action of force are analyzed, and whether the force is sufficient to induce fracture at different degradation stages is evaluated; based on the initial structure, a multi-objective topology optimization is set: sufficient stiffness and strength are ensured at the early degradation stage to withstand the epiphyseal growth force; at the target degradation time point, stress concentration occurs in the key area and the disrupter is easy to trigger fracture; in the optimization process, non-primary stress materials are removed, weight reduction holes or cavitated areas are introduced, and potential weak points for fracture control are provided.

[0079] The finite element model is re-established, and two-stage verification is performed: the epiphyseal growth force is applied at the early degradation stage (0-3 months) to simulate, verify that the maximum strain and stress value of the fixator is lower than the material yield limit, and ensure that there is no early failure; the epiphyseal growth force and the disrupter external force are applied at the late degradation stage (target time point, such as 6 months) to verify that the disrupter can trigger fracture within the preset force value range, and the fracture position is consistent with the design; the residual strength of the remaining structure after degradation is analyzed to ensure that the fixator will not form sharp residual fragments to damage the tissue after fracture; an absorbable steel plate with the same proportion is designed and manufactured for animal experiments, and the obtained data are used to derive alloy ratio and size data of the nail plate system with different degradation times for children.

[0080] In the embodiment of the present application, the material parameters of the absorbable zinc-magnesium alloy internal fixation nail plate are determined as follows: an absorbable zinc-magnesium alloy is selected, and standard mechanical property tests are performed at different degradation periods (3 months, 6 months, 9 months, etc.), including tensile test, three-point bending test and compression test; the elastic modulus, yield strength, ultimate tensile strength and elongation at break at each period are recorded; in particular, the minimum breaking force required to cause structure fracture at each period is determined, and a time-mechanical property decay curve is established; the data are used as input material parameters for subsequent finite element modeling, and are used to determine the fracture timing design target.

[0081] The initial finite element model is established as follows: based on the child bone image data (CT or MRI), a three-dimensional bone model of the half epiphysis region is established, and a geometric model of the initial internal fixator is designed on the surface according to the surgical fixation position; software such as Mimics, 3-matic and SolidWorks is used to construct an assembly model; the bone and the fixator are imported into a finite element analysis software (such as ANSYS or Abaqus), the contact relationship (screw connection, surface contact, etc.) is set, and appropriate mesh (local refinement of key connection areas) is divided.

[0082] In the embodiments of the present application, the connection of the absorbable zinc-magnesium alloy internal fixation nail plate is designed to be weakened. On the basis of the optimized results, the predetermined fracture position is geometrically weakened, for example: reducing the cross-sectional size of the connection part; opening an "H-shaped" slot, a V-shaped slot or a fillet notch to guide the crack path; controlling the depth and width of the slot so as to neither affect the early mechanical properties nor easily trigger the fracture in the degradation later period.

[0083] After the design is completed, experimental verification is carried out. The internal fixator sample is made according to the optimized structure (3D printing forming, CNC machining or injection molding can be selected), and experimental verification is carried out:

[0084] In vitro mechanical experiment: static loading and fatigue loading test are carried out on a universal material testing machine to measure the actual force value required for the trigger fracture of the breaker.

[0085] Bionic loading test: the sample is fixed on a bionic bone model or an isolated animal bone, and the change of its mechanical properties and fracture characteristics in the simulation of motion load and degradation medium is verified.

[0086] The experimental data are compared with the finite element prediction results. If they are inconsistent, the topology optimization step is iteratively modified.

[0087] Further, S5 specifically comprises: collecting the information of the age, gender, epiphysis length, deformity position (femur or tibia) and deformity angle of the patient, and introducing the collected information into the programmed program for predicting the correction time to obtain the time required for completing the correction of the semi-epiphysis arrest; selecting an absorbable zinc-magnesium alloy plate with an in-vivo degradation time close to the above-mentioned time (the degradation time is slightly longer than the predicted time, because the early fracture will lead to insufficient correction, and if the steel plate has not been fractured at the time of completing the correction, the strength of the steel plate has been significantly reduced, and we can destroy the steel plate by using a simple prying device); performing semi-epiphysis arrest, and the surgical method is the same as that of using a traditional 8-shaped steel plate to perform semi-epiphysis arrest; the patient is regularly followed up after the surgery, and CT examination is performed to evaluate the integrity of the steel plate when the correction is completed after the surgery. If the steel plate is found to have been fractured in the weak area and the correction is satisfactory, the treatment is ended. If the correction is satisfactory but the integrity of the steel plate still exists, a designed bone plate breaker is used to pry the steel plate without incision under local anesthesia. The remaining residual steel plate continues to be harmlessly absorbed in the body, and the treatment is ended. (The design of the absorbable zinc-magnesium alloy steel plate and the design of the bone plate breaker are shown in Figures 8-11)plate is not fully absorbed according to the predetermined schedule, the prying mechanism is also important. We designed a slot on the plate, which is the weak zone of the plate to be broken after self-degradation, to observe whether the plate is broken in follow-up visits. At the same time, the slot on the plate can also be used to pry the plate: to prevent the plate from not breaking, we designed a prying device that can pierce the skin and insert into the slot of the plate to pry the plate, preventing overcorrection. The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0088] The above description of disclosed embodiments enables those skilled in the art to carry out or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for correcting idiopathic knee joint deformity based on a combination of growth curve prediction and time gradient control of absorbable materials, characterized in that, Includes the following steps: S1. Collect lower limb bone length data of normal children and plot the lower limb bone length growth curve; S2. Using growth curve data, construct a lower limb bone length model that fits the child population, and construct a mathematical model for the correction of idiopathic genu varum and valgus. S3. Construct a predictive model to estimate the time required for plate implantation in hemiechiropractic fixation for children with idiopathic genu varum and genu valgum. S4. Develop absorbable zinc-magnesium alloy internal fixation plates with different in vivo absorption time gradients; S5. Select the appropriate absorbable zinc-magnesium alloy internal fixation plate for correction based on the time required for the child to have internal fixation with a steel plate.

2. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 1, characterized in that, The data collected in S1 are the femoral and tibia length data of normal children of different ages. The growth curves of tibia and femur length based on the children population are established as the basis for estimating the longitudinal growth potential of the tibia and femur in children, and then predicting the time required for correction after hemiepithelial arrest surgery.

3. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 1, characterized in that, The mathematical model for genu varum / valgum correction in S2 is as follows: In the formula, L is the continuous growth length, δ is the genu varum / valgus deformity angle, and r is the epiphyseal length.

4. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 1, characterized in that, S3 specifically refers to: The femoral length f(x) of children with genu valgum caused by femoral deformity was calculated based on the lower limb bone length model. The length after achieving the corrective goal is f(x) + 2πrδ / 360. The formula for the time t required for distal femoral hemiepithelial arrest to correct genu valgum and genu valgum is as follows: t=f -1 (f(x)+2πrδ / (360*0.7))-x In the formula, δ is the angle of genu varum / valgus deformity, r is the epiphyseal length, and x is the child's age; Similarly, the formula for the time t required for proximal tibial block surgery to correct varus or valgus deformities due to tibial deformity is as follows: t=f -1 (f(x)+2πrδ / (360*0.6))-x。 5. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 1, characterized in that, S4 developed absorbable zinc-magnesium alloy internal fixation plates with different in vivo absorption time gradients by adjusting the magnesium content in the zinc-magnesium alloy. Specifically: Zinc-magnesium alloys with different magnesium contents were prepared and their mechanical properties were tested. A figure-eight nail plate system was established and subjected to finite element analysis to obtain the optimal dimensional parameters. A scaled-down absorbable steel plate was designed and fabricated for animal experiments. The obtained data were used to derive the alloy ratio and dimensional data of nail plate systems with different degradation times that can be used for children.

6. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 5, characterized in that, The preparation of zinc-magnesium alloys with different magnesium contents and the testing of their mechanical properties are as follows: zinc-magnesium alloys with different magnesium contents are prepared using friction stir solid-state alloying technology. The microstructure of the prepared materials before and after heat treatment is studied by metallographic microscopy, scanning electron microscopy and X-ray diffraction analysis. The mechanical properties of the materials are studied by microhardness test, compression test and tensile test.

7. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 5, characterized in that, The establishment of the figure-eight nail plate system and its finite element analysis are as follows: The figure-eight nail plate system is established using UG, and the model is imported into ANSYS Workbench 19.2 for finite element analysis. The analysis includes bending, torsion, and pull-out, and the simulation results of screw stress concentration under different loads are obtained. Then, by changing the nail plate size parameters, models with different parameters are established to explore the influence of each parameter on the simulation experiment. The coupling effect of multiple factors is analyzed through orthogonal experiments to obtain the optimal size parameters of each nail plate model.

8. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 5, characterized in that, Using the obtained data, the alloy ratios and size data of nail-plate systems with different degradation times suitable for children were derived as follows: Absorbable steel plates with different alloy ratios were designed and manufactured at a proportional scale for animal experiments. Based on the data obtained from the animal experiments, the nail-plate system was scaled up proportionally to the size of the figure-eight plates currently used in children. Based on the degradation patterns of nail-plate systems with different zinc-magnesium ratios in animals, alloy ratios and size data of nail-plate systems with degradation times of 3, 6, 9, 12, 15, 18, 21, and 24 months were designed to guide the production of nail-plate systems for hemiepithelial block surgery in children.

9. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 1, characterized in that, S4 developed absorbable zinc-magnesium alloy internal fixation plates with different in vivo absorption time gradients by adjusting the topology of the zinc-magnesium alloy internal fixation plates. Specifically: The material parameters of the absorbable zinc-magnesium alloy internal fixation plate were determined through standardized mechanical performance testing. An initial finite element model was established, and the process of applying external force to specific locations of the absorbable zinc-magnesium alloy internal fixation plate using a clinical destructor was simulated in the finite element environment. The maximum force value and loading direction that the destructor could provide were set, and the stress concentration areas and crack initiation locations under the applied force were analyzed. It was also evaluated whether the applied force was sufficient to induce fracture at different stages of degradation. Based on the initial structure, multi-objective topology optimization was set: to ensure sufficient stiffness and strength to withstand epiphyseal growth forces in the early stage of degradation; and to ensure stress concentration in key areas at the target degradation time point, making it easy for the destructor to trigger fracture. A new finite element model was established for two-stage verification: in the early stage of degradation, epiphyseal growth force was applied to simulate the maximum strain and stress values ​​of the fixator, verifying that they were below the material yield limit and ensuring no early failure; in the later stage of degradation, epiphyseal growth force and external force from the destructor were applied to verify that the destructor could trigger fracture within the preset force range and that the fracture location was consistent with the design. The residual strength of the remaining structure after degradation was analyzed to ensure that the fixation device would not form sharp fragments that would damage tissue after fracture. A scaled-down absorbable steel plate was designed and fabricated for animal experiments. The obtained data were used to derive alloy ratios and dimensional data for nail-plate systems with different degradation times that can be used for children.

10. The method for correcting idiopathic knee joint deformity based on growth curve prediction and time gradient control of absorbable materials according to claim 1, characterized in that, S5 specifically involves collecting the child's age, sex, epiphyseal length, deformity location, and deformity angle, and importing this information into the prediction model to obtain the time required for a hemiepithelial arrest procedure to complete the correction. Hemiephalic fusion surgery was performed using an absorbable zinc-magnesium alloy plate that degrades in the body within a timeframe close to the time required for correction completion. The surgical procedure was the same as for hemiephalic fusion surgery using a traditional figure-eight plate. Patients were followed up regularly after surgery. A CT scan was performed to assess the integrity of the plate when correction was complete. If the plate was found to have fractured in a weak area and the correction was satisfactory, the treatment was considered complete. If the correction was satisfactory but the plate integrity was still present, a pre-designed bone plate destroyer was used to pry the plate off without incision under local anesthesia. The remaining residual plate continued to be harmlessly absorbed in the body, and the treatment was considered complete.

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