Design method of femoral neck minimally invasive fixing system

Abstract

The invention relates to a design method of a femoral neck minimally invasive fixing system. The design method comprises the steps that a femoral neck three-dimensional model containing a Pauwels III type fracture line is established based on CT scanning data, and bone material attributes are defined; importing an internal fixation system preliminary model containing a femoral neck power cross nail and a near-end hollow nail into the model, and setting the size and position parameters of the internal fixation system preliminary model; setting finite element analysis conditions for the model, and applying a load simulating a physiological state to calculate stress distribution, displacement and fatigue life; identifying a stress concentration area based on an analysis result, and adjusting design parameters according to the stress concentration area; and repeating the iteration steps of finite element analysis and parameter adjustment until the stress distribution is uniform and the maximum stress is lower than the yield strength of the material. Compared with the prior art, computer simulation is used for replacing a traditional physical test, the structure of the internal fixing system can be rapidly optimized, the research and development period is remarkably shortened, and the risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of medical device design technology, and in particular to a design method for a minimally invasive femoral neck fixation system. Background Technology

[0002] In the treatment of femoral neck fractures, especially for Pauwels type III high-angle fractures, traditional internal fixation systems such as compression plates, intramedullary nails, or Liss plates often suffer from instability due to insufficient matching with the patient's anatomical morphology, affecting the fracture healing process and easily leading to complications such as malunion, delayed healing, or knee stiffness.

[0003] In related technologies, Chinese invention patent application CN118121300A discloses a design method for anatomical plates for treating distal femoral fractures. This method customizes the plate by acquiring a three-dimensional model of the patient, simulating reduction, performing finite element analysis, and extracting lattice data. Although it improves anatomical matching to some extent, it still has significant drawbacks: First, this design method relies on iterative physical prototypes and lacks an efficient computer simulation optimization mechanism, resulting in a long development cycle and high costs. Second, finite element analysis is only used for preliminary verification and fails to achieve dynamic parameter adjustment and rapid iteration. It cannot accurately predict and improve the mechanical properties of the internal fixation system before manufacturing a physical prototype, thus making it difficult to ensure the stability and safety of the final design under complex loads.

[0004] These shortcomings are most notable in the low efficiency of designing and optimizing minimally invasive femoral neck fixation systems, failing to meet clinical demands for rapid, precise, and low-cost customization. Specifically, traditional methods, as described in CN118121300 A, require repeated physical testing, which not only prolongs development time but also increases risks. This is especially true for cases with complex biomechanical environments, such as Pauwels type III fractures, where the stress distribution and fatigue life of the fixation system are difficult to optimize in advance, easily leading to fixation failure.

[0005] Therefore, there is an urgent need in this field for a technical solution that can enable rapid iterative optimization of minimally invasive femoral neck fixation systems, accurately predict and improve their mechanical properties before manufacturing physical prototypes, so as to significantly shorten the research and development cycle, reduce development costs, and ensure that the final design has excellent stability and safety in the treatment of Pauwels type III fractures. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a design method for a minimally invasive femoral neck fixation system. By combining computer simulation and finite element analysis, the invention enables rapid iterative optimization of the minimally invasive femoral neck fixation system. It can accurately predict and improve the mechanical properties of the system before manufacturing a physical prototype, thereby significantly shortening the research and development cycle, reducing development costs, and ensuring that the final design has excellent stability and safety in the treatment of Pauwels type III fractures.

[0007] The objective of this invention can be achieved through the following technical solutions: This invention provides a design method for a minimally invasive femoral neck fixation system, comprising the following steps: S1. Based on CT scan data, establish a three-dimensional geometric model including the femoral neck and Pauwels type III fracture line, and define the material properties of the bone; S2. Import the preliminary design model of the internal fixation system into the three-dimensional geometric model established in S1. The internal fixation system includes a femoral neck dynamic cross screw and a proximal cannulated screw, and set the diameter, length, and screw hole position parameters of the femoral neck dynamic cross screw and the proximal cannulated screw. S3. Set finite element analysis conditions in the preliminary design model obtained in S2, including applying loads simulating physiological states to calculate stress distribution, displacement, fatigue life, and perform finite element analysis. S4. Based on the finite element analysis results obtained in S3, identify stress concentration areas and adjust the design parameters of the internal fixation system based on the analysis results, including moving the nail hole position to be perpendicular to the fracture line or changing the tilt angle of the nail. S5. Repeat the steps in S3 to set the finite element analysis conditions and in S4 to adjust the design parameters until the stress distribution is uniform and the maximum stress is lower than the material yield strength.

[0008] Furthermore, in S1, the specific process of establishing a three-dimensional geometric model containing the femoral neck and Pauwels type III fracture line based on CT scan data, and defining the material properties of the bone, includes: The femoral CT scan data was reconstructed into an initial three-dimensional model using medical image processing software. Then, the fracture line geometry was created on the initial three-dimensional model based on the high-angle characteristics of Pauwels type III fracture, and finally a three-dimensional geometric model containing the accurate fracture morphology was obtained. In this model, the skeletal components are assigned material properties including density and elastic modulus.

[0009] Furthermore, in S1, the medical image processing software includes one of Mimics and 3D Slicer; The specific process of creating fracture line geometry based on the high-angle characteristics of Pauwels type III fracture on the initial 3D model includes: first, setting a reference plane with an angle greater than 50 degrees to the longitudinal axis of the femur in the 3D modeling software according to the typical angle range of Pauwels type III fracture; then using the reference plane as a cutting tool to perform Boolean operations on the initial 3D model to generate high-angle fracture line geometry in order to accurately simulate the mechanical environment of Pauwels type III fracture.

[0010] Further, in S2, the preliminary design model of the internal fixation system is imported into the three-dimensional geometric model established in S1. The internal fixation system includes a femoral neck dynamic cross screw and a proximal cannulated screw, and the diameter, length, and screw hole position parameters of the femoral neck dynamic cross screw and the proximal cannulated screw are set. The specific process includes: Based on the three-dimensional geometric model completed by S1, a three-dimensional model of the femoral neck dynamic cross nail and proximal hollow nail is constructed in the preprocessing module of computer-aided design software or finite element analysis software, and the internal fixation system model is imported into the three-dimensional geometric model of the femoral neck in a virtual assembly manner. In the software environment, the diameter and length of the femoral neck dynamic cross screw, the diameter and length of the proximal hollow screw, and the spatial position and angle parameters of the proximal hollow screw hole on the femoral neck dynamic cross screw are set by parametric driving method, so that the relative positional relationship between the internal fixation system model and the bone model meets the preset fixation requirements, so that the internal fixation element can effectively cross the fracture line and apply pressure to the fracture end.

[0011] Furthermore, in S3, finite element analysis conditions are set in the preliminary design model obtained in S2, including applying loads simulating physiological states to calculate stress distribution, displacement, and fatigue life, and performing finite element analysis. The specific process includes: Finite element mesh generation is performed on the assembly model completed in S2; Define the boundary conditions of the model to simulate the fixed state of the distal femur, and apply a vertical shear load to the femoral head surface to simulate the effect of walking. Submit the data to the finite element analysis solver for calculation to obtain the stress distribution cloud map, displacement field data, and fatigue life prediction results for the internal fixation system under physiological load.

[0012] Furthermore, the specific process of defining the boundary conditions of the model to simulate the fixed state of the distal femur and applying the vertical shear load generated during walking to the femoral head surface includes: In the finite element analysis software, the degrees of freedom of all nodes of the distal femoral model section are constrained to achieve fixed support. Then, a concentrated force or distributed pressure with a direction perpendicular to the femoral neck axis and a magnitude set according to human body weight and movement state is applied to a specified area on the femoral head surface to simulate the vertical shear load generated during the single-leg support phase of walking. The specific process of submitting the data to the finite element analysis solver to obtain stress distribution cloud map, displacement field data, and fatigue life prediction results for the entire model under physiological load includes: First, an implicit static solver is selected to calculate stress and strain. After the solution is completed, the software post-processing module generates and displays the stress distribution cloud map and displacement field data on the bone and internal fixation system. Finally, based on the stress results and the SN curve of the material, the fatigue analysis tool of the software is used to predict the life of the internal fixation system under constant amplitude and obtain the fatigue life cycle number.

[0013] Furthermore, in S4, based on the finite element analysis results obtained in S3, stress concentration areas are identified, and the design parameters of the internal fixation system are adjusted based on the analysis results. The specific process includes: Based on the stress distribution cloud map on the internal fixation system obtained by S3, stress concentration areas where the stress exceeds the preset safety threshold are identified, including key areas such as the area around the proximal hollow screw hole on the femoral neck dynamic cross screw. Based on the spatial relative position of the identified stress concentration area and the fracture line, the design parameters of the preliminary design model are adjusted in a computer-aided design environment. The adjustment includes moving the spatial position of the proximal hollow screw hole so that its axis is as perpendicular as possible to the Pauwels III fracture line, or changing the implantation tilt angle of the femoral neck dynamic cross screw to optimize its force path. The adjusted design parameters were updated in the 3D model of the internal fixation system.

[0014] Furthermore, based on the spatial relative position of the identified stress concentration areas and fracture lines, the design parameters of the preliminary design model are adjusted in a targeted manner within the computer-aided design environment. The specific process includes: In computer-aided design software, measurement tools are used to quantitatively analyze the spatial angle between the current proximal hollow screw hole axis and the Pauwels type III fracture line. Based on the aforementioned spatial angle, if it is necessary to move the pin hole position, the spatial coordinates of the pin hole center point are directly modified through the parametric drive function of the software, so that it moves along the shaft of the femoral neck dynamic cross nail, and the pin hole axis direction is adjusted simultaneously until it is confirmed in the three-dimensional view that the axis forms an angle greater than 80 degrees with the fracture line, so as to achieve the pin placement requirement perpendicular to the fracture line; if it is necessary to change the implantation tilt angle of the femoral neck dynamic cross nail, the angle parameters of its penetrating path in the femoral head and femoral neck are modified to make its main load-bearing axis more consistent with the physiological load direction.

[0015] Furthermore, in S5, the specific process of repeating the steps of setting finite element analysis conditions in S3 and adjusting design parameters in S4 until the stress distribution is uniform and the maximum stress is lower than the material yield strength includes: The updated 3D model of the internal fixation system after adjusting the design parameters in S4 is used as the input for a new round of iteration. The steps in S3 are repeated to set the finite element analysis conditions, apply loads simulating physiological states, and perform finite element analysis to obtain a new stress distribution cloud map and maximum stress value. The new stress distribution cloud map and maximum stress value obtained from the new round of finite element analysis are compared with the results of the previous round to determine whether the stress concentration phenomenon has improved, whether the stress distribution has become more uniform, and whether the maximum stress value in the model has been lower than the yield strength of the internal fixation system material. If the judgment result does not simultaneously meet the two conditions of uniform stress distribution and maximum stress being lower than the material yield strength, then step S4 is executed again, that is, stress concentration areas are identified based on the new finite element analysis results and the design parameters are further adjusted. Then, the analysis step S3 is repeated to form a design iteration cycle. If the judgment result confirms that the stress distribution is uniform and the maximum stress value is stably lower than the material yield strength, then the iteration loop is terminated, and the optimized three-dimensional model of the internal fixation system, which has been verified at this time, is finally output.

[0016] Furthermore, the femoral neck dynamic cross screw in the internal fixation system is a hollow screw, and the proximal part of the screw body of the femoral neck dynamic cross screw is provided with a screw hole for receiving the proximal hollow screw. During the software-simulated implantation process, the proximal hollow nail is inserted from the lateral femoral cortex, passes through the nail hole on the femoral neck dynamic cross nail, and the tip of the proximal hollow nail points towards the subchondral bone of the femoral head, forming a cross-fixation structure with the femoral neck dynamic cross nail in space to achieve stable support and compression for Pauwels type III fractures.

[0017] The core concept of this invention lies in achieving precise and efficient design of a minimally invasive femoral neck fixation system through a computer simulation-driven iterative optimization closed loop. This method first constructs a three-dimensional geometric model containing a high-angle fracture line (Pauwels III) based on patient CT data and defines its biomechanical properties. Then, it imports this model into a parameterized internal fixation system model for virtual assembly. Finite element analysis is used to simulate stress distribution, displacement, and fatigue life under physiological loads, dynamically evaluating mechanical performance. Based on the simulation results, stress concentration areas are identified, and key parameters such as pin hole position angles or implantation angles are adjusted to ensure the fixation structure is perpendicular to the fracture line, optimizing the force path. Finally, through multiple iterative cycles of analysis-evaluation-adjustment, the stress distribution is made uniform and the maximum stress is lower than the material's yield strength. This allows for precise prediction and optimization of mechanical properties before manufacturing a physical prototype, significantly improving design efficiency and fixation reliability.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes an innovative design method combining computer simulation and finite element analysis to achieve rapid iterative optimization of a minimally invasive femoral neck fixation system. It can accurately predict and improve the mechanical properties before manufacturing a physical prototype, significantly shortening the R&D cycle, reducing development costs, and ensuring excellent stability and safety in treating Pauwels type III fractures. Specifically, by establishing a high-precision three-dimensional geometric model and a parametric internal fixation system, the stress distribution, displacement, and fatigue life under physiological loads are dynamically simulated. This allows designers to promptly identify stress concentration areas and adjust pin hole positions or implantation angles accordingly, avoiding the repeated modifications required in traditional physical experiments. This closed-loop optimization process not only improves design efficiency several times over, reducing material waste and manpower input, but also significantly reduces the risk of fixation failure by ensuring uniform stress distribution and that the maximum stress is below the material's yield strength. Attached Figure Description

[0019] Figure 1 This is an overall flowchart of the design method of the minimally invasive femoral neck fixation system in this invention; Figure 2 This is a schematic diagram of the process S2 in this invention; Figure 3 This is a schematic diagram of the process S3 in this invention; Figure 4 This is a schematic diagram of the process S4 in this invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, circuit structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0021] Example 1 See Figure 1 This invention provides a design method for a minimally invasive femoral neck fixation system, comprising the following steps: S1. Based on CT scan data, establish a three-dimensional geometric model including the femoral neck and Pauwels type III fracture line, and define the material properties of the bone.

[0022] In specific implementation, S1 involves establishing a three-dimensional geometric model containing the femoral neck and Pauwels type III fracture line based on CT scan data, and defining the material properties of the bone. The specific process includes: The femoral CT scan data was reconstructed into an initial three-dimensional model using medical image processing software. Then, the fracture line geometry was created on the initial three-dimensional model based on the high-angle characteristics of Pauwels type III fracture, and finally a three-dimensional geometric model containing the accurate fracture morphology was obtained. In this model, the skeletal components are assigned material properties including density and elastic modulus.

[0023] In specific implementation, in S1, the medical image processing software includes one of Mimics and 3D Slicer; The specific process of creating fracture line geometry based on the high-angle characteristics of Pauwels type III fracture on the initial 3D model includes: first, setting a reference plane with an angle greater than 50 degrees to the longitudinal axis of the femur in the 3D modeling software according to the typical angle range of Pauwels type III fracture; then using the reference plane as a cutting tool to perform Boolean operations on the initial 3D model to generate high-angle fracture line geometry in order to accurately simulate the mechanical environment of Pauwels type III fracture.

[0024] Step S1 constructs a highly realistic femoral neck fracture simulation environment from a biomechanical perspective using digital modeling technology. The technological foundation is acquiring real femoral CT scan data and using medical image processing software such as Mimics or 3D Slicer to reconstruct accurate three-dimensional geometric models of the femur from two-dimensional tomographic images. In the 3D modeling software, based on the clinical characteristic of the high-angle fracture type, a reference plane with an angle greater than 50 degrees to the longitudinal axis of the femur is created. This plane is then used as a cutting tool to perform Boolean operations on the complete bone model, thereby generating a high-angle fracture line geometry that conforms to clinical reality. This process accurately replicates the morphological features of the fracture, providing an accurate geometric basis for subsequent mechanical analysis. To ensure that the digital model reflects real physical behavior, key material property parameters such as density and elastic modulus need to be assigned to the bone. These properties define the deformation response characteristics of the bone under stress. Through the integration of the above series of technical operations, a three-dimensional digital model that combines realistic anatomical morphology, specific pathological features, and accurate material parameters is finally obtained.

[0025] S2. Import the preliminary design model of the internal fixation system into the three-dimensional geometric model established in S1. The internal fixation system includes a femoral neck dynamic cross screw and a proximal cannulated screw. Set the diameter, length, and screw hole position parameters of the femoral neck dynamic cross screw and the proximal cannulated screw. See [link to relevant documentation]. Figure 2 .

[0026] In specific implementation, in S2, the preliminary design model of the internal fixation system is imported into the three-dimensional geometric model established in S1. The internal fixation system includes a femoral neck dynamic cross screw and a proximal cannulated screw, and the diameter, length, and screw hole position parameters of the femoral neck dynamic cross screw and the proximal cannulated screw are set. The specific process includes: Based on the three-dimensional geometric model completed by S1, a three-dimensional model of the femoral neck dynamic cross nail and proximal hollow nail is constructed in the preprocessing module of computer-aided design software or finite element analysis software, and the internal fixation system model is imported into the three-dimensional geometric model of the femoral neck in a virtual assembly manner. In the software environment, the diameter and length of the femoral neck dynamic cross screw, the diameter and length of the proximal hollow screw, and the spatial position and angle parameters of the proximal hollow screw hole on the femoral neck dynamic cross screw are set by parametric driving method, so that the relative positional relationship between the internal fixation system model and the bone model meets the preset fixation requirements, so that the internal fixation element can effectively cross the fracture line and apply pressure to the fracture end.

[0027] S2 utilizes parametric digital assembly technology to construct a virtual prototype of an internal fixation system that can be quantified, analyzed, and optimized based on an established digital fracture model. Its implementation is based on the three-dimensional geometric model of the femoral neck generated by S1, which includes a precise Pauwels type III fracture line. On this model, using the preprocessing modules of computer-aided design software or finite element analysis software, three-dimensional solid models of the femoral neck dynamic cross screw and proximal cannulated screw are created respectively. These two components are then precisely placed into the bone model through virtual assembly operations. The key to this process lies in using a parametric driving method to set and control the critical dimensional and positional parameters of the internal fixation system. These parameters specifically include the diameter and length of the femoral neck dynamic cross screw, the diameter and length of the proximal cannulated screw, and, most importantly, the spatial coordinates and axial direction angle of the proximal cannulated screw hole located on the femoral neck dynamic cross screw body. By adjusting these parameters, it can be ensured that the internal fixation system and the bone model form a relative positional relationship that meets the requirements of clinical fixation. The core standard is to ensure that the spatial structure formed by the femoral neck dynamic cross screw and the proximal hollow screw can effectively cross the simulated high-angle fracture line and apply the expected compressive stress to the fracture ends.

[0028] S3. Set finite element analysis conditions in the preliminary design model obtained in S2, including applying loads simulating physiological states to calculate stress distribution, displacement, and fatigue life, and then perform finite element analysis. See [link to relevant documentation]. Figure 3 .

[0029] In specific implementation, in S3, finite element analysis conditions are set in the preliminary design model obtained in S2, including applying loads simulating physiological states to calculate stress distribution, displacement, and fatigue life, and performing finite element analysis. The specific process includes: Finite element mesh generation is performed on the assembly model completed in S2; Define the boundary conditions of the model to simulate the fixed state of the distal femur, and apply a vertical shear load to the femoral head surface to simulate the effect of walking. Submit the data to the finite element analysis solver for calculation to obtain the stress distribution cloud map, displacement field data, and fatigue life prediction results for the internal fixation system under physiological load.

[0030] In practice, the specific process of defining the boundary conditions of the model to simulate the fixed state of the distal femur and applying the vertical shear load generated during walking to the femoral head surface includes: In the finite element analysis software, the degrees of freedom of all nodes of the distal femoral model section are constrained to achieve fixed support. Then, a concentrated force or distributed pressure with a direction perpendicular to the femoral neck axis and a magnitude set according to human body weight and movement state is applied to a specified area on the femoral head surface to simulate the vertical shear load generated during the single-leg support phase of walking. The specific process of submitting the data to the finite element analysis solver to obtain stress distribution cloud map, displacement field data, and fatigue life prediction results for the entire model under physiological load includes: First, an implicit static solver is selected to calculate stress and strain. After the solution is completed, the software post-processing module generates and displays the stress distribution cloud map and displacement field data on the bone and internal fixation system. Finally, based on the stress results and the SN curve of the material, the fatigue analysis tool of the software is used to predict the life of the internal fixation system under constant amplitude and obtain the fatigue life cycle number.

[0031] S3 uses finite element analysis (FEM) to perform biomechanical simulation on the assembled digital model of the bone fixation system, thereby quantitatively evaluating the system's structural performance and durability. This process begins with finite element mesh generation of the assembled model of the bone and internal fixation devices completed in S2, discretizing the continuous geometric model into a large number of tiny elements with specific shapes. Next, boundary conditions are defined to simulate the physiological stress state of a human body when standing or walking. Specifically, in the finite element analysis software, the degrees of freedom of all nodes on the distal femur model section are fully constrained to simulate the actual situation of the distal femur being fixed in the body. Simultaneously, a force perpendicular to the femoral neck axis is applied to a specific area on the femoral head surface. The magnitude of this force is set according to the body weight and movement state, and its form can be a concentrated force or distributed pressure, simulating the main vertical shear load borne by the joint during the single-leg support phase of walking. After preprocessing, the model is submitted to the finite element analysis solver for calculation, typically using an implicit static solver to solve for the stress and deformation of the model under static loads. After the solution is obtained, the software's post-processing module can acquire and visualize the detailed mechanical response results of the entire model under simulated physiological loads, mainly including stress distribution cloud maps and displacement field data on the bone and internal fixation system. Finally, based on the calculated stress results and combined with the stress-life curve (SN curve) of the internal fixation system's metallic material, the software's fatigue analysis tools are used to predict the lifespan of the internal fixation system under constant amplitude loads, thereby obtaining the estimated number of fatigue life cycles.

[0032] S4. Based on the finite element analysis results obtained in S3, identify stress concentration areas and adjust the design parameters of the internal fixation system based on the analysis results, including moving the pin hole positions to be perpendicular to the fracture line or changing the pin tilt angle. See [link to relevant documentation]. Figure 4 .

[0033] In practice, in S4, based on the finite element analysis results obtained in S3, stress concentration areas are identified, and the design parameters of the internal fixation system are adjusted based on the analysis results. The specific process includes: Based on the stress distribution cloud map on the internal fixation system obtained by S3, stress concentration areas where the stress exceeds the preset safety threshold are identified, including key areas such as the area around the proximal hollow screw hole on the femoral neck dynamic cross screw. Based on the spatial relative position of the identified stress concentration area and the fracture line, the design parameters of the preliminary design model are adjusted in a computer-aided design environment. The adjustment includes moving the spatial position of the proximal hollow screw hole so that its axis is as perpendicular as possible to the Pauwels III fracture line, or changing the implantation tilt angle of the femoral neck dynamic cross screw to optimize its force path. The adjusted design parameters were updated in the 3D model of the internal fixation system.

[0034] In practice, based on the spatial relative position of the identified stress concentration areas and fracture lines, the design parameters of the preliminary design model are adjusted in a computer-aided design environment. The specific process includes: In computer-aided design software, measurement tools are used to quantitatively analyze the spatial angle between the current proximal hollow screw hole axis and the Pauwels type III fracture line. Based on the aforementioned spatial angle, if it is necessary to move the pin hole position, the spatial coordinates of the pin hole center point are directly modified through the parametric drive function of the software, so that it moves along the shaft of the femoral neck dynamic cross nail, and the pin hole axis direction is adjusted simultaneously until it is confirmed in the three-dimensional view that the axis forms an angle greater than 80 degrees with the fracture line, so as to achieve the pin placement requirement perpendicular to the fracture line; if it is necessary to change the implantation tilt angle of the femoral neck dynamic cross nail, the angle parameters of its penetrating path in the femoral head and femoral neck are modified to make its main load-bearing axis more consistent with the physiological load direction.

[0035] Based on the mechanical performance defects revealed by finite element simulation, S4 performs targeted parametric structural optimization of the implant, essentially a precision design adjustment process based on simulation feedback. This process begins with a detailed interpretation and analysis of the stress distribution cloud map of the internal fixation system obtained in S3. The focus is on identifying areas where stress values ​​exceed the allowable stress threshold preset according to the material safety factor. These stress concentration areas typically indicate structural weak points or potential fatigue failure origins. Among these, the area around the proximal hollow screw hole on the femoral neck dynamic cross screw is the most common critical area due to its abrupt geometric change. After accurately locating the problem area, it is necessary to deeply analyze the relative positional relationship between this stress concentration area and the Pauwels type III fracture line in three-dimensional space, using this as the theoretical basis for design adjustments. Subsequently, in the computer-aided design software environment, its measurement tools are used to precisely and quantitatively measure the spatial angle between the axial direction of the proximal hollow screw hole and the fracture line plane in the current design state. Based on the measurement results, if it is determined that the pin hole position needs optimization, the parametric driving function of the software is used to directly modify the three-dimensional coordinates of the pin hole center point on the femoral neck dynamic cross nail rod, and simultaneously adjust its axial direction. The optimization goal is to make the angle between the pin hole axis and the fracture line in the three-dimensional view greater than 80 degrees, thereby geometrically achieving a fixation method that passes through the fracture line as perpendicularly as possible to enhance holding force and compression effect. If it is determined that the force path of the main nail needs optimization, the angle parameters of the virtual implantation channel of the femoral neck dynamic cross nail in the femoral head and femoral neck are modified to make its main load-bearing axis more consistent with the direction of physiological load generated during simulated walking, thereby improving the force flow transmission efficiency of the overall structure. Finally, all confirmed design parameter changes are updated in the three-dimensional model of the internal fixation system, generating a new design version that has undergone one iteration of optimization, preparing for the next finite element analysis verification. Through this targeted, data-driven modification, the mechanical performance of the entire fixation system is gradually improved.

[0036] S5. Repeat the steps in S3 to set the finite element analysis conditions and in S4 to adjust the design parameters until the stress distribution is uniform and the maximum stress is lower than the material yield strength.

[0037] In specific implementation, S5 involves repeating the steps of setting finite element analysis conditions in S3 and adjusting design parameters in S4 until the stress distribution is uniform and the maximum stress is lower than the material's yield strength. The specific process includes: The updated 3D model of the internal fixation system after adjusting the design parameters in S4 is used as the input for a new round of iteration. The steps in S3 are repeated to set the finite element analysis conditions, apply loads simulating physiological states, and perform finite element analysis to obtain a new stress distribution cloud map and maximum stress value. The new stress distribution cloud map and maximum stress value obtained from the new round of finite element analysis are compared with the results of the previous round to determine whether the stress concentration phenomenon has improved, whether the stress distribution has become more uniform, and whether the maximum stress value in the model has been lower than the yield strength of the internal fixation system material. If the judgment result does not simultaneously meet the two conditions of uniform stress distribution and maximum stress being lower than the material yield strength, then step S4 is executed again, that is, stress concentration areas are identified based on the new finite element analysis results and the design parameters are further adjusted. Then, the analysis step S3 is repeated to form a design iteration cycle. If the judgment result confirms that the stress distribution is uniform and the maximum stress value is stably lower than the material yield strength, then the iteration loop is terminated, and the optimized three-dimensional model of the internal fixation system, which has been verified at this time, is finally output.

[0038] In specific implementation, the femoral neck dynamic cross screw in the internal fixation system is a hollow screw, and the proximal part of the screw body of the femoral neck dynamic cross screw is provided with a screw hole for accommodating the proximal hollow screw. During the software-simulated implantation process, the proximal hollow nail is inserted from the lateral femoral cortex, passes through the nail hole on the femoral neck dynamic cross nail, and the tip of the proximal hollow nail points towards the subchondral bone of the femoral head, forming a cross-fixation structure with the femoral neck dynamic cross nail in space to achieve stable support and compression for Pauwels type III fractures.

[0039] S5 establishes a closed-loop iterative optimization process based on finite element simulation feedback, enabling the design parameters of the internal fixation system to be systematically adjusted until its mechanical performance fully meets clinical safety standards. This process begins with the updated 3D model of the internal fixation system, after the design parameters were adjusted in step S4, serving as the starting point for a new round of calculations and analyses. The complete finite element analysis process defined in S3 is then re-executed, including setting boundary conditions, applying vertical shear loads generated during simulated single-leg support during walking, and performing calculations to obtain a new stress distribution cloud map and maximum stress value reflecting the model's mechanical behavior under the latest design conditions. Subsequently, the key results obtained from this round of analysis—namely, the stress distribution and maximum stress value—are quantitatively compared and qualitatively evaluated with the results of the previous round or the initial design state. The focus is on determining whether the previously existing stress concentration phenomenon has been significantly improved, whether the stress distribution across the entire structure has become more uniform, and most importantly, whether the maximum stress value in the model has been reduced to a safe range below the yield strength of the internal fixation system's manufacturing material.

[0040] If the evaluation results show that the two key conditions of uniform stress distribution and maximum stress below the yield strength are not simultaneously met, it means that the design still needs improvement. The process then re-enters step S4, where new or residual stress concentration areas are identified based on the latest finite element analysis results. Based on this, the relevant design parameters of the femoral neck dynamic cross screw or proximal cannulated screw are further adjusted, such as continuing to optimize the screw hole position or implantation angle. After adjustment, the process returns to step S3 for a new round of simulation verification, thus forming a continuous iterative cycle of design-simulation-evaluation-modification. This cycle continues until the finite element analysis results after a certain iteration finally confirm that the stress distribution of the model has reached a satisfactory uniform state, and the maximum stress value has stably remained below the material's yield strength. At this point, the iterative cycle terminates. The final output is a three-dimensional model of the optimized internal fixation system that has undergone multiple simulation verifications and meets mechanical performance standards.

[0041] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A design method for a minimally invasive femoral neck fixation system, characterized in that, Includes the following steps: S1. Based on CT scan data, establish a three-dimensional geometric model including the femoral neck and Pauwels type III fracture line, and define the material properties of the bone; S2. Import the preliminary design model of the internal fixation system into the three-dimensional geometric model established in S1. The internal fixation system includes a femoral neck dynamic cross screw and a proximal cannulated screw, and set the diameter, length, and screw hole position parameters of the femoral neck dynamic cross screw and the proximal cannulated screw. S3. Set finite element analysis conditions in the preliminary design model obtained in S2, including applying loads simulating physiological states to calculate stress distribution, displacement, fatigue life, and perform finite element analysis. S4. Based on the finite element analysis results obtained in S3, identify stress concentration areas and adjust the design parameters of the internal fixation system based on the analysis results, including moving the nail hole position to be perpendicular to the fracture line or changing the tilt angle of the nail. S5. Repeat the steps in S3 to set the finite element analysis conditions and in S4 to adjust the design parameters until the stress distribution is uniform and the maximum stress is lower than the material yield strength.

2. The design method of a minimally invasive femoral neck fixation system according to claim 1, characterized in that, In S1, the specific process of establishing a three-dimensional geometric model containing the femoral neck and Pauwels type III fracture line based on CT scan data and defining the material properties of the bone includes: The femoral CT scan data was reconstructed into an initial three-dimensional model using medical image processing software. Then, the fracture line geometry was created on the initial three-dimensional model based on the high-angle characteristics of Pauwels type III fracture, and finally a three-dimensional geometric model containing the accurate fracture morphology was obtained. In this model, the skeletal components are assigned material properties including density and elastic modulus.

3. The design method of a minimally invasive femoral neck fixation system according to claim 2, characterized in that, In S1, the medical image processing software includes one of Mimics and 3D Slicer; The specific process of creating fracture line geometry based on the high-angle features of Pauwels type III fractures on the initial 3D model includes: First, in the 3D modeling software, a reference plane with an angle greater than 50 degrees to the longitudinal axis of the femur is set according to the typical angle range of Pauwels type III fracture. Then, the reference plane is used as a cutting tool to perform Boolean operations on the initial 3D model to generate high-angle fracture line geometry in order to accurately simulate the mechanical environment of Pauwels type III fracture.

4. The design method of a minimally invasive femoral neck fixation system according to claim 1, characterized in that, In S2, the preliminary design model of the internal fixation system is imported into the three-dimensional geometric model established in S1. The internal fixation system includes a femoral neck dynamic cross screw and a proximal cannulated screw. The diameter, length, and screw hole position parameters of the femoral neck dynamic cross screw and the proximal cannulated screw are set. The specific process includes: Based on the three-dimensional geometric model completed by S1, a three-dimensional model of the femoral neck dynamic cross nail and proximal hollow nail is constructed in the preprocessing module of computer-aided design software or finite element analysis software, and the internal fixation system model is imported into the three-dimensional geometric model of the femoral neck in a virtual assembly manner. In the software environment, the diameter and length of the femoral neck dynamic cross screw, the diameter and length of the proximal hollow screw, and the spatial position and angle parameters of the proximal hollow screw hole on the femoral neck dynamic cross screw are set by parametric driving method, so that the relative positional relationship between the internal fixation system model and the bone model meets the preset fixation requirements, so that the internal fixation element can effectively cross the fracture line and apply pressure to the fracture end.

5. The design method of a minimally invasive femoral neck fixation system according to claim 1, characterized in that, In S3, finite element analysis conditions are set in the preliminary design model obtained in S2, including applying loads simulating physiological states to calculate stress distribution, displacement, and fatigue life, and performing finite element analysis. The specific process includes: Finite element mesh generation is performed on the assembly model completed in S2; Define the boundary conditions of the model to simulate the fixed state of the distal femur, and apply a vertical shear load to the femoral head surface to simulate the effect of walking. Submit the data to the finite element analysis solver for calculation to obtain the stress distribution cloud map, displacement field data, and fatigue life prediction results for the internal fixation system under physiological load.

6. The design method of a minimally invasive femoral neck fixation system according to claim 5, characterized in that, The specific process of defining the boundary conditions of the model to simulate the fixed state of the distal femur and applying the vertical shear load generated during walking to the femoral head surface includes: In the finite element analysis software, the degrees of freedom of all nodes of the distal femoral model section are constrained to achieve fixed support. Then, a concentrated force or distributed pressure with a direction perpendicular to the femoral neck axis and a magnitude set according to human body weight and movement state is applied to a specified area on the femoral head surface to simulate the vertical shear load generated during the single-leg support phase of walking. The specific process of submitting the data to the finite element analysis solver to obtain stress distribution cloud map, displacement field data, and fatigue life prediction results for the entire model under physiological load includes: First, an implicit static solver is selected to calculate stress and strain. After the solution is completed, the software post-processing module generates and displays the stress distribution cloud map and displacement field data on the bone and internal fixation system. Finally, based on the stress results and the SN curve of the material, the fatigue analysis tool of the software is used to predict the life of the internal fixation system under constant amplitude and obtain the fatigue life cycle number.

7. The design method of a minimally invasive femoral neck fixation system according to claim 6, characterized in that, In S4, based on the finite element analysis results obtained in S3, stress concentration areas are identified, and the design parameters of the internal fixation system are adjusted based on the analysis results. The specific process includes: Based on the stress distribution cloud map on the internal fixation system obtained by S3, stress concentration areas where the stress exceeds the preset safety threshold are identified, including key areas such as the area around the proximal hollow screw hole on the femoral neck dynamic cross screw. Based on the spatial relative position of the identified stress concentration area and the fracture line, the design parameters of the preliminary design model are adjusted in a computer-aided design environment. The adjustment includes moving the spatial position of the proximal hollow screw hole so that its axis is as perpendicular as possible to the Pauwels III fracture line, or changing the implantation tilt angle of the femoral neck dynamic cross screw to optimize its force path. The adjusted design parameters were updated in the 3D model of the internal fixation system.

8. The design method of a minimally invasive femoral neck fixation system according to claim 7, characterized in that, Based on the spatial relative position of the identified stress concentration areas and fracture lines, the design parameters of the preliminary design model are adjusted in a computer-aided design environment. The specific process includes: In computer-aided design software, measurement tools are used to quantitatively analyze the spatial angle between the current proximal hollow screw hole axis and the Pauwels type III fracture line. Based on the aforementioned spatial angle, if it is necessary to move the pin hole position, the spatial coordinates of the pin hole center point are directly modified through the parametric drive function of the software, so that it moves along the shaft of the femoral neck dynamic cross nail, and the pin hole axis direction is adjusted simultaneously until it is confirmed in the three-dimensional view that the axis forms an angle greater than 80 degrees with the fracture line, so as to achieve the pin placement requirement perpendicular to the fracture line; if it is necessary to change the implantation tilt angle of the femoral neck dynamic cross nail, the angle parameters of its penetrating path in the femoral head and femoral neck are modified to make its main load-bearing axis more consistent with the physiological load direction.

9. The design method of a minimally invasive femoral neck fixation system according to claim 1, characterized in that, In S5, the specific process of repeating the steps of setting finite element analysis conditions in S3 and adjusting design parameters in S4 until the stress distribution is uniform and the maximum stress is lower than the material yield strength includes: The updated 3D model of the internal fixation system after adjusting the design parameters in S4 is used as the input for a new round of iteration. The steps in S3 are executed again to set the finite element analysis conditions, apply loads simulating physiological states, and perform finite element analysis to obtain a new stress distribution cloud map and maximum stress value. The new stress distribution cloud map and maximum stress value obtained from the new round of finite element analysis are compared with the results of the previous round to determine whether the stress concentration phenomenon has improved, whether the stress distribution has become more uniform, and whether the maximum stress value in the model has been lower than the yield strength of the internal fixation system material. If the judgment result does not simultaneously meet the two conditions of uniform stress distribution and maximum stress being lower than the material yield strength, then step S4 is executed again, that is, stress concentration areas are identified based on the new finite element analysis results and the design parameters are further adjusted. Then, the analysis step S3 is repeated to form a design iteration cycle. If the judgment result confirms that the stress distribution is uniform and the maximum stress value is stably lower than the material yield strength, then the iteration loop is terminated, and the optimized three-dimensional model of the internal fixation system, which has been verified at this time, is finally output.

10. The design method of a minimally invasive femoral neck fixation system according to claim 1, characterized in that, The femoral neck dynamic cross screw in the internal fixation system is a hollow screw, and the proximal part of the screw body of the femoral neck dynamic cross screw is provided with a screw hole for receiving the proximal hollow screw. During the software-simulated implantation process, the proximal hollow nail is inserted from the lateral femoral cortex, passes through the nail hole on the femoral neck dynamic cross nail, and the tip of the proximal hollow nail points towards the subchondral bone of the femoral head, forming a cross-fixation structure with the femoral neck dynamic cross nail in space to achieve stable support and compression for Pauwels type III fractures.

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