Biomechanical experiment method of novel magnesium controlled-release dynamic intramedullary nail

Abstract

The invention relates to a biomechanical experiment method of a novel magnesium controlled-release dynamic intramedullary nail, which comprises an intramedullary nail, a nail-withdrawing-preventing bolt, a material exchange hole and a gasket, the surface of the intramedullary nail is provided with an upper hole and a lower hole, the upper hole is the nail-withdrawing-preventing bolt, the lower hole is the material exchange hole, the gasket is embedded in the middle of the surface of the intramedullary nail, and the gasket is embedded in the middle of the surface of the intramedullary nail. A magnesium controlled release-dynamic compression coupling mechanism is provided for the first time, and a degradable material technology is combined with an orthopedic internal fixation dynamic idea; the magnesium alloy gasket structure is innovatively designed, automatic power compression of the intramedullary nail is achieved, and the intramedullary nail is powered without a secondary operation; innovative application of the magnesium alloy in large orthopedic implants is created, and the application field of degradable materials is expanded.

Description

Technical Field

[0001] This invention relates to the field of medical technology, specifically a novel biomechanical experimental method for magnesium-controlled release dynamic intramedullary nails. Background Technology

[0002] Femoral shaft fractures are a common traumatic disease in orthopedic clinics, accounting for approximately 6% of all fractures, and are frequently caused by high-energy trauma such as traffic accidents and falls. With the rapid development of the global transportation industry and the accelerating aging of the population, the incidence of femoral shaft fractures is showing an upward trend year by year. Intramedullary nailing, as the "gold standard" for treating femoral shaft fractures, has advantages such as minimal trauma, reliable fixation, and rapid healing, and has been widely used in clinical practice. However, traditional intramedullary nailing uses a static fixation method, which, while providing good initial stability, still has a high rate of nonunion in some complex fracture types. Literature reports that the nonunion rate of surgically treated femoral shaft fractures is 4.6-13.9%, with complex fracture types (such as type B and type C fractures) being an independent risk factor for postoperative nonunion. Nonunion not only causes long-term pain for patients but also requires multiple surgeries, resulting in high medical costs and placing a heavy burden on families and society.

[0003] Recent biomechanical studies on fracture healing have shown that moderate micromotion stimulation plays a crucial role in promoting callus formation and fracture healing. The "strain theory" proposed by Perren et al. indicates that a strain of 2-10% at the fracture ends is beneficial for callus formation, while excessive rigid fixation inhibits fracture healing. This theory laid the foundation for the concept of dynamic fixation. Traditional dynamic fixation is mainly achieved through intraoperative manipulation, such as dynamic screws, but this method is complex, timing is difficult, and its clinical application is limited.

[0004] Previously, some institutions have actively explored the field of dynamic fixation. Orthofix's intelligent intramedullary nail system uses shape memory alloy technology to achieve delayed compression; however, the technology is complex, and its operation is complex and technically demanding, which may affect its clinical application. While Smith & Nephew Endoscopy's absorbable screw technology has solved the problem of secondary surgery to some extent, the degradation time is difficult to control precisely, resulting in limited clinical effectiveness.

[0005] Based on the current state of research both domestically and internationally, the traditional static fixation mode of intramedullary nails can no longer meet the treatment needs of complex fractures. Developing new dynamic intramedullary nail systems is an important direction for the development of orthopedic internal fixation technology. However, existing dynamic fixation techniques generally suffer from problems such as complex operation, high cost, and uncertain results, and there is an urgent need to develop a simpler, more efficient, and controllable dynamic fixation system. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a novel biomechanical experimental method for magnesium-controlled release dynamic intramedullary nails. It proposes for the first time a "magnesium-controlled release-dynamic compression" coupling mechanism, combining biodegradable material technology with the concept of dynamic internal fixation in orthopedics. It innovatively designs a magnesium alloy gasket structure to achieve automated dynamic compression of the intramedullary nail, eliminating the need for a secondary surgery for intramedullary nail dynamization. It pioneers the innovative application of magnesium alloys in large orthopedic implants and expands the application field of biodegradable materials.

[0007] To achieve the above objectives, the present invention provides a novel biomechanical experimental method for a magnesium-controlled release dynamic intramedullary nail, comprising: an intramedullary nail, an anti-removal bolt, a mass exchange hole, and a gasket. The surface of the intramedullary nail has two holes, one at the top and one at the bottom. The upper hole is for the anti-removal bolt, and the lower hole is for the mass exchange hole. The gasket is embedded in the middle of the surface of the intramedullary nail. The anti-removal bolt serves to prevent the intramedullary nail from being pulled out, and the mass exchange hole is for facilitating the outflow of liquid after the magnesium metal degrades.

[0008] As a further improvement of the present invention, the gasket is made of biodegradable magnesium alloy, the thickness of the gasket is 1mm to 2mm, and the diameter of the gasket is the same as the diameter of the intramedullary nail.

[0009] The biomechanical experimental method for this novel magnesium-controlled release dynamic intramedullary nail is as follows: I. Overall Technical Route Design: This method adopts the technical route of "theoretical simulation-experimental verification-optimization and improvement". It systematically evaluates the biomechanical performance of the novel magnesium-controlled release dynamic intramedullary nail by combining finite element numerical simulation with physical and mechanical testing. II. Preliminary Work Foundation and Finite Element Model Optimization ① Summary of preliminary finite element analysis work: The preliminary finite element analysis of the novel magnesium-controlled release dynamic intramedullary nail was completed. A three-dimensional finite element model of the intramedullary nail-femur system containing magnesium alloy spacers was established, and the feasibility of the dynamic compression mechanism was preliminarily verified. ② Further optimization of the finite element model: Based on the previous work, this study will optimize and improve the finite element model in the following aspects; III. Design of Physical Mechanics Experiment Schemes ①Sawbones femoral model selection: The fourth-generation synthetic femoral model (model 3406) produced by Pacific Research Laboratories was used. ② Intramedullary nail preparation: Intramedullary nail preparation in the traditional control group and the experimental group; ③ Magnesium alloy gasket preparation process: Mg-3Zn-0.5Ca alloy ingots are prepared by vacuum induction melting process, with melting temperature of 720±10℃ and protective atmosphere of SF6+CO2 (volume ratio 1:99). ④ Fracture model establishment: A standardized transverse fracture model of the midshaft of the femur was used; ⑤ Intramedullary nail implantation procedure: Intramedullary nail implantation shall be performed in accordance with the standard clinical procedure; IV. Mechanical Property Testing Methods ① Static mechanical testing: Static mechanical testing was conducted using an Instron E10000 electronic universal testing machine. The testing environment temperature was 20±2℃, and the relative humidity was 45-75%. ② Dynamic fatigue testing: A fatigue testing scheme was designed and fatigue loading was carried out in accordance with the ISO 7206-4 standard; V. Monitoring of Magnesium Alloy Degradation Behavior ①In vitro degradation experiment design: Establish a standardized in vitro degradation experimental environment and monitor degradation indicators; ② Dynamic compressive force monitoring system: A dedicated dynamic compressive force monitoring device is designed to monitor the axial displacement and compressive force changes of the intramedullary nail in real time during the degradation of the magnesium alloy gasket; VI. Comparative Analysis and Verification Methods ① Comparison of finite element results with experimental data: Establish a systematic verification scheme to ensure the reliability of finite element analysis results; ②Statistical analysis methods: Rigorous statistical methods were used to process the experimental data; ③ Quality control measures: employing blind evaluation, standardized operation, equipment calibration, data verification, and traceability recording. VII. Verification of Expected Technical Indicators Mechanical performance indicators, dynamic compression effect, and safety indicators were verified separately, and the verification data were compiled and archived.

[0010] This method utilizes the controllable degradation properties of magnesium alloy to achieve dynamic compression of the intramedullary nail by placing a biodegradable magnesium alloy spacer at the bottom of the nail. This innovative design retains the advantages of traditional intramedullary nails while incorporating the concept of dynamic fixation, potentially providing a new solution for the prevention of femoral shaft fracture nonunion. Furthermore, through finite element analysis and physical and mechanical testing, the biomechanical properties of the novel magnesium-controlled-release dynamic intramedullary nail are systematically evaluated, verifying the effectiveness of its dynamic compression mechanism. A quantitative relationship between the degradation time of the magnesium alloy spacer and the change in compressive force is established, providing parameter basis for clinical application. The mechanical stability differences between the magnesium-controlled-release dynamic intramedullary nail and the traditional static intramedullary nail are compared and analyzed, confirming its safety and superiority in clinical application. This provides a scientific biomechanical basis for the industrialization and clinical trial application of the novel intramedullary nail.

[0011] This method is currently lacking in mature magnesium-controlled dynamic intramedullary nail products both domestically and internationally. This study will provide important theoretical support and experimental data for the development of this innovative technology, filling a technological gap in China. Through the dynamic compression mechanism, it is expected to significantly reduce the nonunion rate of femoral shaft fractures, improve patient treatment outcomes, and reduce the risk of secondary surgery. It can reduce the nonunion rate of femoral shaft fractures and save a significant amount of medical expenses in my country each year, thus having significant socio-economic value. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the traditional intramedullary nailing procedure; Figure 2 This is a schematic diagram of the structure of the present invention; Figure 3 yes Figure 2 Enlarged view of point A in the middle; Figure 4 It is a detailed technology roadmap; Figure 5 These are stress diagrams of traditional intramedullary nails, new intramedullary nails with magnesium (simulating the immediate postoperative period), and new intramedullary nails without magnesium sheet (simulating the stress state of the intramedullary nail after the magnesium sheet dissolves upon discharge). Figure 6 The images show the stress distribution at the fracture ends of traditional intramedullary nails, new intramedullary nails with magnesium (simulating the immediate postoperative period), and new intramedullary nails without magnesium sheets (simulating the stress state of the intramedullary nail after the magnesium sheet dissolves upon discharge). Figure 7 This is a flowchart of the manufacturing process for magnesium alloy gaskets; Figure 8 These are diagrams illustrating the standardized fracture model fabrication process. Figure 9 This is a schematic diagram of a static mechanics testing device; Figure 10 It is a fatigue test load-time history curve; Figure 11 It is a fatigue test load-time history curve; Figure 12 This is a schematic diagram of a dynamic compression force monitoring system; Figure 13 This is a flowchart of the comparison and analysis between finite element and experimental results; In the diagram: 1. Intramedullary nail, 2. Anti-removal screw, 3. Material exchange hole, 4. Gasket. Detailed Implementation

[0013] The following describes, with reference to the accompanying drawings, a novel biomechanical experimental method for a magnesium-controlled release dynamic intramedullary nail according to the present invention.

[0014] The theoretical basis for this method is that fracture healing is a complex biomechanical process influenced by multiple factors. According to Wolff's law and Perren's strain theory, bone tissue reconstruction and healing require appropriate mechanical stimulation. Excessive rigid fixation leads to a "stress shielding effect," resulting in a lack of necessary micromotion stimulation at the fracture ends, thereby delaying callus formation and the fracture healing process. Studies have shown that axial strain of 2-10% at the fracture ends is most conducive to promoting endogenous callus formation, while strain of less than 2% mainly promotes intramembranous ossification.

[0015] While traditional intramedullary nailing provides good initial stability, its static fixation mode cannot be dynamically adjusted according to callus formation during the healing process. Clinical observations have shown that 6-8 weeks postoperatively is a critical period for callus formation, during which appropriate axial compression can significantly promote fracture healing. However, traditional dynamic manipulation requires complex mechanical operations during or after surgery, which not only increases the difficulty of the operation but also presents the problem of inaccurate timing.

[0016] Magnesium and magnesium alloys, as novel biodegradable materials, provide an important theoretical basis for this study due to their degradation mechanism. The electrochemical corrosion of magnesium in physiological environments follows the following reaction equation: Mg + 2H₂O → Mg(OH)₂ + H₂↑ Mg(OH)2 + 2Cl⁻→ MgCl2 + 2OH⁻ This controllable degradation process provides an ideal driving mechanism for achieving intelligent dynamic compression of intramedullary nails. By regulating the composition and microstructure of magnesium alloys, their degradation rate can be precisely controlled to match the biological timeline of fracture healing.

[0017] From a biomechanical perspective, the design of the magnesium alloy spacer at the base of the intramedullary nail fully utilizes mechanical principles. Initially, the magnesium alloy spacer provides support and maintains the stability of the fracture ends; as the magnesium alloy gradually degrades, the spacer shrinks in volume, causing the intramedullary nail to undergo axial displacement and exert a continuous compressive force on the fracture ends. This "time-mechanical" coupling mechanism is precisely the theoretical innovation of this study.

[0018] To verify the above theory, this application conducted the following experiments: I. Overall Design of Technical Route Building upon previous finite element analysis work, this study employs a "theoretical simulation-experimental verification-optimization and improvement" approach. By combining finite element numerical simulation with physical and mechanical testing, it systematically evaluates the biomechanical properties of a novel magnesium-controlled release dynamic intramedullary nail. (Reference) Figure 4 (Specific technical route) II. Preliminary Work and Finite Element Model Optimization (1) Summary of preliminary finite element analysis work Our research team has previously completed preliminary finite element analysis of a novel magnesium-controlled dynamic intramedullary nail, establishing a three-dimensional finite element model of the intramedullary nail-femoral system including a magnesium alloy spacer, and preliminarily verifying the feasibility of the dynamic compression mechanism. The preliminary work mainly included: ① A three-dimensional geometric model of the femur reconstructed based on CT data of healthy adult male volunteers, with model accuracy reaching the sub-millimeter level; ② A comparative analysis model was established for three states: traditional intramedullary nail, intramedullary nail with magnesium sheet, and intramedullary nail without magnesium sheet; (Reference) Figure 5 Stress performance of traditional intramedullary nails, new intramedullary nails with magnesium (simulating immediate postoperative conditions), and new intramedullary nails without magnesium sheets (simulating the stress state of the intramedullary nail after the magnesium sheet dissolves upon discharge) are compared. The dissolution of the magnesium alloy spacer in the new intramedullary nail without magnesium sheets releases space, allowing the intramedullary nail to compress the fracture ends, thus providing dynamic stress and helping to prevent femoral shaft nonunion. The stress at the fracture cross-section of the new intramedullary nail without magnesium sheets is significantly higher than that of both traditional and new intramedullary nails with magnesium sheets. ③ Stress distribution analysis under static loading conditions was completed, verifying the effectiveness of the intramedullary nail compression mechanism after magnesium sheet dissolution; (Reference) Figure 6 Traditional intramedullary nail, new intramedullary nail - magnesium-containing (simulating immediate postoperative condition), new intramedullary nail - without magnesium sheet (simulating stress state of intramedullary nail after magnesium sheet dissolution upon discharge). Stress manifestations at fracture ends (new intramedullary nail - without magnesium sheet allows for observation of close contact between fracture ends compared to the former two). ④ The basic geometric parameters and material properties of the magnesium alloy gaskets were preliminarily determined.

[0019] Preliminary results show that the stress in the fracture section increased significantly after the magnesium sheet dissolved, and the fracture ends were effectively compressed, verifying the correctness of the design concept.

[0020] (2) Further optimization of the finite element model Based on previous work, this study will optimize and improve the finite element model in the following aspects: ① Geometric model refinement and optimization The geometry of the magnesium alloy gasket is modeled in detail, including microscopic features such as edge chamfering and surface roughness. Optimize the fit between the intramedullary nail and the medullary cavity, taking into account the gap and contact state during actual implantation. Establish a series of parametric models for magnesium alloy gaskets of different specifications (thickness 1.0mm, 1.5mm, 2.0mm); ② Dynamic modeling of material properties A dynamic model was established to illustrate the changes in magnesium alloy material properties over degradation time, including the time-varying characteristics of parameters such as elastic modulus and Poisson's ratio. Considering the effect of volume shrinkage on the contact state during the degradation of magnesium alloys, A degradation kinetic equation for magnesium alloys is introduced to achieve coupled analysis of material properties and time. ③ Boundary conditions and load optimization Based on actual clinical conditions, the loading method was optimized to include various working conditions such as standing on one leg, walking, and climbing stairs. Considering the role of muscle force, apply the gluteus medius contraction force in the greater trochanter region of the femur. Optimize constraints to more realistically simulate the constraint state of the distal femur.

[0021] III. Design of Physical Mechanics Experiment Schemes (1) Preparation of experimental materials ① The Sawbones femoral model was selected using the fourth-generation synthetic femoral model (model 3406) produced by Pacific Research Laboratories. This model has a similar geometry and mechanical properties to the human femur, with a cortical bone density of 1.64 g / cm³, a cancellous bone density of 0.27 g / cm³, and elastic moduli of 16.7 GPa and 0.155 GPa, respectively, which fully meet the requirements of ASTM F1839 standard.

[0022] ② Intramedullary nail preparation: Traditional control group: The commonly used femoral intramedullary nail (300mm in length and 12mm in diameter) was selected, and the material was Ti-6Al-4V titanium alloy; Experimental group: Based on the same specifications of intramedullary nail, a magnesium alloy spacer was added to the bottom. The spacer material was Mg-3Zn-0.5Ca alloy, with a diameter of 12mm and thicknesses of 1.0mm, 1.5mm, and 2.0mm.

[0023] ③ Magnesium alloy gasket manufacturing process Mg-3Zn-0.5Ca alloy ingots were prepared using a vacuum induction melting process at a melting temperature of 720±10℃ under a protective atmosphere of SF6+CO2 (volume ratio 1:99). The alloy ingots underwent homogenization heat treatment (420℃×8h), followed by hot extrusion molding (extrusion ratio 12:1, extrusion temperature 350℃). Finally, gaskets of the required specifications were obtained through precision machining, with a surface roughness Ra≤1.6μm. (Reference) Figure 7 (Magnesium alloy gasket manufacturing process) (2) Establishment of fracture model A standardized transverse fracture model of the midshaft of the femur was used. Specific operational steps: ① Use a precision saw blade to create a transverse fracture line with a width of 0.5 mm in the middle of the femoral shaft; ② The fracture line is located 150mm below the lesser trochanter of the femur, ensuring it is within the fixation range of the middle segment of the intramedullary nail; ③ The fracture ends are ground down to ensure a smooth fracture surface, simulating a simple transverse fracture in clinical practice; ④ All fracture models were fabricated by the same operator to ensure consistency. (Reference) Figure 8 Standardized fracture model fabrication process) (3) Intramedullary nail implantation procedure Intramedullary nail implantation was performed according to standard clinical procedures. ① A specialized intramedullary nail implantation instrument is used, with an opening made at the tip of the greater trochanter of the femur; ② Using guidewire guidance, the medullary canal is reamed to a diameter of 13mm to ensure a good fit of the intramedullary nail; ③ When implanting the intramedullary nail, the experimental group needs to ensure that the magnesium alloy spacer is tightly attached to the bottom of the intramedullary nail; ④ Use distal interlocking screws for fixation, with a screw diameter of 5mm and double corrugated material for fixation; ⑤ Postoperative X-ray examination is performed to ensure that the intramedullary nail is correctly positioned and without significant deviation.

[0024] IV. Mechanical Property Testing Methods (1) Static mechanical test Static mechanical tests were conducted using an Instron E10000 electronic universal testing machine at an ambient temperature of 20±2℃ and a relative humidity of 45-75%.

[0025] ① Axial compression test Test objective: To evaluate the axial load-bearing capacity and stiffness of the intramedullary nail fixation system. Loading method: An axial compressive load is applied to the femoral head, with a load range of 0-2100N. Loading speed: 3 mm / min, continuously loaded until the target load or specimen failure. Measurement parameters: load-displacement curve, axial stiffness, yield load, ultimate load. Number of specimens: 15 per group, average value for statistical analysis. ② Torsional strength test Test objective: To evaluate the torsional resistance of the intramedullary nail fixation system. Loading method: Fix the distal femur and apply a torsional moment to the femoral head. Torsional angular velocity: 0.5° / s, maximum torsional angle: 15°. Measurement parameters: Torque-torsion angle curve, torsional stiffness, maximum torque. Loading direction: Simulates the internal and external rotation movements of the human body during walking. ③ Four-point bending test Test objective: To evaluate the performance of the intramedullary nail fixation system under bending loads. Support spacing: 200mm for outer supports, 100mm for inner supports. Loading speed: 2mm / min, maximum displacement: 20mm Measurement parameters: bending load-displacement curve, bending stiffness, bending strength; (reference) Figure 9 Schematic diagram of static mechanical testing device. (A shows a local observation of the osteotomy area, and B shows a complete sample with the implant mounted on the mechanical testing machine.) (2) Dynamic fatigue test ① Fatigue loading scheme The fatigue testing scheme was designed in accordance with ISO 7206-4 standard: Loading waveform: Sine wave, frequency 2Hz Load range: 50-500N (simulating partial load walking) Number of loops: 10 6 The test piece or sample failed. Failure criteria: Stiffness decreases by 25% or significant fracture occurs; ② Fatigue performance evaluation indicators Fatigue life: The number of cycles required to reach the failure criterion. Stiffness decay: The change in stiffness under different cycles. Failure Mode: Observe and record the failure location and failure mode of the specimen. Crack propagation: Regularly check for fatigue cracks. (Reference) Figure 10 (Fatigue test load-time history curve) V. Monitoring of Magnesium Alloy Degradation Behavior (1) In vitro degradation experimental design ① Experimental environment setup: Establish a standardized in vitro degradation experimental environment, using a constant temperature incubator at 37±0.5℃. Degradation medium: 0.9% NaCl solution, pH=7.4±0.1 Solution volume: 200 ml / sample (ensure the ratio of solution volume to sample surface area is ≥20 ml / cm²). Solution replacement: Replace with fresh solution every 24 hours to avoid the accumulation of degradation products. ② Degradation monitoring indicators Mass loss rate: Weighed every 24 hours using an analytical balance (accuracy 0.1 mg). Volume change rate: Measured weekly using micro-CT scans. Hydrogen release: Collected and measured daily using the water displacement method. Surface morphology changes: observed by scanning electron microscopy, once a week. Degradation product analysis: ICP-MS was used to determine the concentrations of Mg²⁺, Zn²⁺, and Ca²⁺ ions; (Reference) Figure 11 (Fatigue test load-time history curve) (2) Dynamic compression force monitoring system A dedicated dynamic compressive force monitoring device was designed to monitor the axial displacement and compressive force changes of the intramedullary nail in real time during the degradation of the magnesium alloy gasket. ①Composition of monitoring device Fixation clamp: simulates the constraint state of an intramedullary nail in the femur; Axial load sensor: range 0-1000N, accuracy 0.1N. Displacement sensor: measuring range 0-10mm, accuracy 0.001mm; data acquisition system: 24-hour continuous acquisition, sampling frequency 1Hz. Environmental control system: constant temperature of 37℃, simulating the internal environment. ② Monitoring parameters and data processing Axial displacement: Record the axial movement of the intramedullary nail as the magnesium sheet degrades; Compression force change: Calculate the time-varying curve of the contact pressure at the fracture ends; Degradation rate: Calculate the volumetric degradation rate of the magnesium sheet based on the displacement change; Compression efficiency: Evaluate the magnitude of the compressive force generated per unit amount of magnesium sheet degradation. (Reference) Figure 12 (Schematic diagram of dynamic compression force monitoring system) VI. Comparative Analysis and Verification Methods (1) Comparison of finite element results and experimental data Establish a systematic verification scheme to ensure the reliability of finite element analysis results: ① Stress distribution verification Attach strain gauges to the corresponding locations on the Sawbones model, measure the actual strain distribution, compare the stress distribution calculated by the finite element method with the experimentally measured strain distribution, calculate the error range, and for areas with an error exceeding 15%, the model needs to be re-optimized. ②Verification of displacement changes The surface displacement field of the specimen was measured using three-dimensional digital image correlation (3D-DIC) technology. The displacement distribution calculated by finite element method was compared with the experimental measurement results, with a focus on verifying the relative displacement of the fracture ends and the axial displacement of the intramedullary nail. ③ Dynamic process verification The finite element method (FEM) simulation of the magnesium sheet degradation-compression process was compared with experimental monitoring results to verify the consistency of the time-displacement-force relationship curves and optimize the material degradation parameters in the finite element model. (Reference) Figure 13 (Finite element method and experimental result comparison and analysis process) (2) Statistical analysis methods Experimental data were processed using rigorous statistical methods. ① Sample size calculation Based on the preliminary experimental results, the required sample size was calculated using G*Power 3.1.9 software. The expected effect size d=0.8, the significance level α=0.05, and the power 1-β=0.8. The calculation showed that at least 12 samples were needed per group. Considering a 10% sample loss, 15 samples were determined per group.

[0026] ②Statistical analysis strategies Descriptive statistics: Calculate mean, standard deviation, maximum, and minimum values; Normality test: Shapiro-Wilk test, P>0.05 is considered normal distribution; Between-group comparisons: Independent samples t-test for normally distributed data, Mann-Whitney U test for non-normally distributed data; Within-group comparisons: Paired t-test or Wilcoxon signed-rank test; Correlation analysis: Pearson or Spearman correlation analysis; Regression analysis: Establish a mathematical model of magnesium alloy degradation time and compressive force. ③ Quality control measures Blinded evaluation: Blinded design is used for both experimental operators and data analysts; Standardized operation: Detailed standard operating procedures (SOPs) are developed; Equipment calibration: All testing equipment is calibrated monthly; Data verification: Key data is entered and verified independently by two people; Traceability: A complete experimental record and data traceability system is established.

[0027] VII. Verification of Expected Technical Indicators (1) Verification of mechanical performance indicators Axial stiffness: ≥800 N / mm (not less than 90% of that of traditional intramedullary nails) Torsional stiffness: ≥3.0 N·m / ° (meets clinical use requirements) Fatigue life: ≥10 6 This cycle (meets relevant FDA standards) Ultimate load: ≥3000N (meets the requirements for daily activity loads) (2) Verification of dynamic compression effect Compression force range: 50-150N (within the effective treatment window) Compression displacement: 1-3mm (meets the biological requirements for fracture healing) Degradation period: 6-8 weeks (matching the critical period for callus formation) Compression process stability: displacement rate change <20% / cycle. (3) Verification of safety indicators Maximum von Mises stress: < 60% of the material's yield strength Stress concentration factor: <3.0 (to avoid excessive local stress concentration) Hydrogen release rate: <0.1 ml / cm²·day (meets biosafety requirements) Toxicity of degradation products: assessed according to ISO 10993 biological evaluation.

[0028] In summary, based on the initial design, the size, shape, and composition ratio of the magnesium alloy gasket were optimized, and a quantitative relationship between the magnesium alloy degradation rate and geometric parameters was established. Using different magnesium alloy formulations (Mg-Zn-Ca and Mg-Sr-Ca systems), the optimal component ratio was determined through in vitro degradation experiments, controlling the degradation cycle to 6-8 weeks, matching the critical period of callus formation.

[0029] A three-dimensional finite element model of the complete intramedullary nail-femoral system, including a magnesium alloy spacer, was constructed to simulate the biomechanical state in three stages: immediately after surgery (with the magnesium spacer), during the healing period (partial dissolution of the magnesium spacer), and in the late healing period (complete dissolution of the magnesium spacer). The stress distribution, displacement changes, and contact pressure at different stages were analyzed to evaluate the mechanical characteristics of the dynamic compression process.

[0030] A standardized femoral shaft fracture fixation model was established using the fourth-generation Sawbones femoral model. A magnesium-controlled dynamic intramedullary nail group and a traditional static intramedullary nail control group were designed. The differences in mechanical stability between the two fixation methods were quantitatively assessed through axial compression, torsion, and fatigue cycle tests.

[0031] An in vitro degradation testing system simulating a physiological environment was established to monitor the mass loss, volume change, and axial displacement of the magnesium alloy spacer and intramedullary nail in real time. Degradation time-compression force curves were plotted to provide quantitative reference for clinical applications.

[0032] The biodegradable magnesium alloy gasket 4 achieves controlled degradation by adding alloying elements such as Ca and Sr to regulate the degradation rate and mechanical properties of magnesium alloy. It also establishes a dynamic finite element model of material properties changing over time, accurately simulates the evolution of mechanical state during the degradation process of magnesium alloy, and designs a physical testing device that can simulate the dissolution process of magnesium sheet to achieve continuous monitoring of degradation-compression. At the same time, it establishes a comprehensive evaluation index system for the dynamic fixation effect of intramedullary nails.

[0033] The intramedullary nail 1 developed using this experimental method forms a complete biomechanical evaluation system, verifying the effectiveness and safety of its dynamic compression mechanism, providing a scientific basis for the clinical transformation of the product, specifically achieving a controllable magnesium alloy degradation cycle of 6-8 weeks, dynamic compression force controlled within the range of 50-150N, and overall mechanical properties of the intramedullary nail not lower than existing product standards.

[0034] This experimental method can achieve the following degradation parameters for magnesium alloys: degradation cycle of 6-8 weeks, degradation rate of 0.5-1.0 mm / year, and hydrogen release of <0.1 ml / cm²·day; mechanical properties: axial stiffness ≥800 N / mm, torsional stiffness ≥3.0 N·m / °, and fatigue life ≥10. 6 Cycle; Dynamic compression effect: axial compression force 50-150N, compression displacement 1-3mm, compression process is stable and controllable; Safety indicators: maximum stress < 60% of material yield strength, stress distribution is uniform, and there is no obvious stress concentration phenomenon.

[0035] In summary, this invention is the first to propose an innovative concept combining magnesium alloy controlled-release technology with dynamic fixation of intramedullary nails, and the technical approach is original; it establishes a preliminary biomechanical evaluation system for magnesium controlled-release dynamic intramedullary nails, providing a reference for the future formation of industry standards and technical specifications; and it masters the precise control technology of magnesium alloy pad degradation behavior, achieving precise matching between degradation time and fracture healing process.

[0036] Market Value: my country sees over 150,000 femoral shaft fracture cases annually, with an intramedullary nail market size of approximately 3 billion yuan. Imported products account for over 70% of this market. This invention, with its advanced technology and controllable costs, possesses enormous market substitution potential. It is projected to capture 15-20% of the domestic market share within five years, with estimated annual sales of 500-800 million yuan after industrialization, creating over 500 jobs. The cost of a single product is 40% lower than imported counterparts, saving patients 30% on treatment costs. By reducing fracture nonunion rates, it can save the country over 1.5 billion yuan in medical expenses annually, reducing the number of families impoverished due to illness. Furthermore, it improves the treatment success rate for femoral shaft fracture patients, enhancing their quality of life, shortening rehabilitation time, and reducing the social burden. It also promotes the technological upgrading of my country's orthopedic implant industry and enhances its international competitiveness.

[0037] Once this method matures, it can be gradually expanded to developing countries such as Southeast Asia and South America. At the same time, it can be extended to the treatment of fractures of other long bones such as the tibia and humerus, with broad market prospects. Relying on the well-established medical device industry chain in the Yangtze River Delta region, it has good industrialization conditions and a solid foundation for promotion.

[0038] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0040] In the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0041] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A novel biomechanical experimental method for magnesium-controlled release dynamic intramedullary nails, characterized in that, include: Intramedullary nail (1), anti-removal screw (2), material exchange hole (3), gasket (4). The surface of the intramedullary nail (1) has two holes, one above the other. The upper hole is for the anti-removal screw (2), and the lower hole is for the material exchange hole (3). The gasket (4) is embedded in the middle of the surface of the intramedullary nail (1).

2. The biomechanical experimental method for a novel magnesium-controlled release dynamic intramedullary nail according to claim 1, characterized in that, The gasket (4) is made of biodegradable magnesium alloy. The thickness of the gasket (4) is 1 mm to 2 mm, and the diameter of the gasket (4) is the same as that of the intramedullary nail (1).

3. The biomechanical experimental method for a novel magnesium-controlled release dynamic intramedullary nail according to claim 1, the experimental method steps are as follows: I. Overall Technical Route Design: This method adopts the technical route of "theoretical simulation-experimental verification-optimization and improvement". It systematically evaluates the biomechanical performance of the novel magnesium-controlled release dynamic intramedullary nail by combining finite element numerical simulation with physical and mechanical testing. II. Preliminary Work Foundation and Finite Element Model Optimization ① Summary of preliminary finite element analysis work: The preliminary finite element analysis of the novel magnesium-controlled release dynamic intramedullary nail was completed. A three-dimensional finite element model of the intramedullary nail-femur system containing magnesium alloy spacers was established, and the feasibility of the dynamic compression mechanism was preliminarily verified. ② Further optimization of the finite element model: Based on the previous work, this study will optimize and improve the finite element model in the following aspects; III. Design of Physical Mechanics Experiment Schemes ①Sawbones femoral model selection: The fourth-generation synthetic femoral model (model 3406) produced by Pacific Research Laboratories was used. ② Intramedullary nail preparation: Intramedullary nails of the traditional control group and the experimental group were prepared (1); ③ Magnesium alloy gasket (4) Preparation process: Mg-3Zn-0.5Ca alloy ingots are prepared by vacuum induction melting process, melting temperature is 720±10℃, and the protective atmosphere is SF6+CO2 (volume ratio 1:99). ④ Fracture model establishment: A standardized transverse fracture model of the midshaft of the femur was used; ⑤ Intramedullary nail implantation procedure: Intramedullary nail implantation shall be performed in accordance with the standard clinical procedure; IV. Mechanical Property Testing Methods ① Static mechanical testing: Static mechanical testing was conducted using an Instron E10000 electronic universal testing machine. The testing environment temperature was 20±2℃, and the relative humidity was 45-75%. ② Dynamic fatigue testing: A fatigue testing scheme was designed and fatigue loading was carried out in accordance with the ISO 7206-4 standard; V. Monitoring of Magnesium Alloy Degradation Behavior ①In vitro degradation experiment design: Establish a standardized in vitro degradation experimental environment and monitor degradation indicators; ② Dynamic compressive force monitoring system: A dedicated dynamic compressive force monitoring device is designed to monitor the axial displacement and compressive force changes of the intramedullary nail in real time during the degradation of the magnesium alloy gasket; VI. Comparative Analysis and Verification Methods ① Comparison of finite element results with experimental data: Establish a systematic verification scheme to ensure the reliability of finite element analysis results; ②Statistical analysis methods: Rigorous statistical methods were used to process the experimental data; ③ Quality control measures: employing blind evaluation, standardized operation, equipment calibration, data verification, and traceability recording. VII. Verification of Expected Technical Indicators Mechanical performance indicators, dynamic compression effect, and safety indicators were verified separately, and the verification data were compiled and archived.

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