Combined type medical degradable magnesium alloy suture anchor with round head structure

Abstract

The invention discloses a medical degradable magnesium alloy suture anchor with a combined round head structure. The medical degradable magnesium alloy suture anchor is mainly suitable for repairing ligament-bone dead center fracture. Comprising an independent rivet head with a hexagonal boss and a hollow threaded rivet body, the rivet head is of a circular truncated cone structure, the upper portion of the rivet head is connected with a hexagonal prism boss and a combined structure coaxially integrated with a hollow cylinder, and a suture hole and a suture groove are formed in the hexagonal prism boss and used for a suture to penetrate through. A certain distance is reserved between the tail end of the hexagonal prism boss and the tail end of the cylinder for insertion of a screwing-in device. On the basis of ensuring the fixing effect of the magnesium alloy anchor on tendon bone / ligament-bone, the risk of anchor failure is reduced. The built-in line hole is beneficial to reducing contact with body fluid, and the round head structure is beneficial to eliminating stress corrosion caused by stress concentration after implantation. The combined structure is beneficial for improving the stability of a mechanical structure after the degradable magnesium alloy anchor is implanted.

Description

Technical Field

[0001] The present invention belongs to the field of magnesium alloy medical devices, and in particular relates to a combined round-knot medical degradable magnesium alloy suture anchor, which is suitable for repairing ligament-bone insertion ruptures in sports medicine. Background Art

[0002] High-intensity exercise often leads to ligament and tendon damage, as well as rupture of ligament-bone attachments. Suture anchor implantation is a common clinical strategy for treating tendon and ligament tears or avulsions. Compared with other surgical methods, the main advantages of using suture anchors are secure fixation, minimal soft tissue damage, limited surgical dissection, and ease of operation. Furthermore, the angle of implantation can be adjusted, resulting in superior biomechanical properties, which is crucial for functional restoration of the joint.

[0003] Currently, in clinical practice and cutting-edge research, suture anchors are primarily categorized into three types based on material type: non-biodegradable materials, biodegradable polymer materials, and biodegradable metal materials. Non-biodegradable suture anchors, primarily stainless steel and titanium alloys, exhibit excellent mechanical properties and provide high initial fixation strength. However, they require secondary surgery for removal and are often associated with complications. Long-term implantation can lead to stress shielding, osteoporosis, and cartilage damage. Biodegradable polymer suture anchors eliminate the need for a secondary surgical removal procedure, significantly reducing surgical risk. However, their disadvantages include undesirable biological reactions, limited fixation duration, low fixation strength, and a high risk of foreign body reactions. Bioactive ceramic suture anchors can significantly improve repair stability and healing quality, but their complex manufacturing process and stringent production conditions contribute to their high cost. Biodegradable metals, primarily magnesium, zinc, iron, and their alloys, offer potential applications as suture anchors due to their biodegradability and superior fixation strength compared to biodegradable polymer anchors.

[0004] Magnesium alloy is a highly promising bone implant material. Its advantages are primarily reflected in its biodegradability, excellent mechanical properties, biocompatibility, and bioactivity. Compared to iron and zinc alloys, magnesium alloys possess an elastic modulus similar to bone, a moderate degradation rate, improved biocompatibility, and osteoinduction and osseointegration properties. Its osteoinductive potential has been fully demonstrated in various preclinical animal models.

[0005] However, there are still many problems in the application of magnesium alloy suture anchors. Since the current suture anchors still refer to the traditional non-degradable anchors in terms of structural design, a series of disadvantages caused by the traditional structure when used for degradable anchors are ignored. The magnesium alloy implants with the current structure are very easy to fail after being implanted in the body. The failure forms are mainly due to the stress concentration effect that causes the anchor head to degrade too quickly, resulting in the anchor being loose due to the loose fixation between the anchor and the bone, and the bone repair at the tail of the anchor accelerates the ion exchange between the magnesium matrix and the tissue, causing the pores connected to the suture to degrade too quickly, resulting in the destruction of the ligament-bone connection. Although alloying and surface modification methods can be used to improve the problem of too fast degradation rate of magnesium alloys, they cannot effectively solve the failure problem caused by premature degradation of key parts of the anchor. Therefore, the present invention designs a medical degradable magnesium alloy suture anchor with a combined round head structure. Summary of the Invention

[0006] The purpose of the present invention is to propose a combined round-head structured medical degradable magnesium alloy suture anchor, which has the advantages of good degradation performance and mechanical properties. It can maintain a complete mechanical structure in the early stage of tendon-bone or ligament-bone healing and can eliminate the stress concentration effect after implantation, effectively solving the failure problem caused by excessive degradation of the nail head and the suture hole after anchor implantation.

[0007] The technical solution adopted by the present invention to solve its technical problem is: A combined round-head medical biodegradable magnesium alloy suture anchor comprises an independent anchor head with a hexagonal boss and a hollow threaded nail body, wherein: the anchor head is a truncated cone structure, the large end of the anchor head is provided with a hexagonal boss, the threaded nail body is a cylindrical structure, the threaded nail body is provided with a hexagonal through hole that is compatible with the hexagonal boss, the outer walls of the anchor head and the threaded nail body are both provided with threads, and when the anchor head and the threaded nail body are coaxially combined, the threads of the anchor head and the threaded nail body form a complete and continuous thread segment, the axial length of the hexagonal boss is smaller than the axial length of the hexagonal through hole, and the diameter of the hexagonal boss is slightly smaller than the diameter of the large end of the anchor head.

[0008] Furthermore, the thread is a trapezoidal thread, the thread height of the thread on the threaded nail body is the same as the thread width, the thread shape of the thread on the anchor nail head is the same as the threaded nail body, the thread height gradually decreases from the large head end to the small head end, and the pitch on the threaded nail body and the anchor nail head is equal.

[0009] Furthermore, a pair of oppositely disposed side surfaces of the hexagonal boss are provided with thread holes, and two thread grooves extending from the middle to the tail are opened on these two side surfaces, and the thread grooves and the thread holes are connected for the thread to pass through.

[0010] Furthermore, the wire groove is a semicircular wire groove, and the diameter of the wire groove is the same as the diameter of the wire hole.

[0011] Furthermore, the magnesium alloy material is ZE21C magnesium alloy.

[0012] Furthermore, the small end of the anchor head is provided with a round head structure.

[0013] A screwdriver for use with the above-mentioned magnesium alloy anchor includes a rod and a head, wherein both the rod and the head are hexagonal prisms, the rod is a handheld end, and the head is an adapter end, which cooperates with the anchor, and the diameter of the rod is larger than that of the head.

[0014] Furthermore, the screw-in tool is provided with a through hole in the axial direction for the passage of suture.

[0015] Furthermore, the screw-in tool head is adapted to the hexagonal column-shaped through hole of the threaded nail body away from the anchor nail head end.

[0016] A modular, rounded-headed, biodegradable magnesium alloy suture anchor with a medical design. Based on the principle that sharp corners generate extremely high stress peaks (the stress concentration factor is inversely proportional to the radius of curvature), a rounded transition reduces local curvature and stress concentration. The rounded head structure is applied to the small end of the anchor head, eliminating stress concentration after implantation. The anchor surface is also threaded throughout, ensuring the anchor's mechanical properties while preventing rapid degradation of the anchor head under stress during the initial implantation phase, potentially compromising its mechanical integrity. The boss is shaped like a regular hexagonal prism, with a diameter slightly smaller than that of the large end of the anchor head. Thread holes are provided on two opposing sides of the central portion of the boss, with thread slots extending above the holes and connecting to the holes. This prevents wear on the suture thread during implantation. The upper portion of the anchor body is a hollow cylinder with a hexagonal through-hole inside that mates with the boss. The height of the cylinder is higher than the height of the boss, leaving space for the screwdriver to be inserted after mating. The outside of the anchor adopts a screw-in thread, and the thread reaches the round head structure, so that the anchor can minimize the damage to the bone during the implantation process and enhance the mechanical properties of the suture anchor.

[0017] The material selected for the present invention is ZE21C brand magnesium alloy, which has the following main advantages: ZE21C magnesium alloy is a degradable magnesium alloy that overcomes problems such as cytotoxicity and excessively fast corrosion rate. After three extrusion molding, its material density is close to that of human bone density, and its elastic modulus is 45GPa, which is only about half of that of titanium alloy material, and it has a relatively lower stress shielding effect. In addition, the extruded magnesium alloy material has a high specific strength and excellent mechanical properties.

[0018] The application has the beneficial effects that the combined round head structure medical degradable magnesium alloy suture anchor has good mechanical properties and degradability, the fracture force and the anti-torsion performance of the combined anchor are improved, the combined structure has good protection effect on the anchor line hole, greatly slows down the degradation of the line hole, the round head structure eliminates the stress concentration effect after implantation, avoids the rapid degradation at the nail head, and reduces the risk of anchor failure after implantation. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of a combined round head structure medical degradable magnesium alloy suture anchor; Figure 2 is a schematic diagram of an anchor driver; Figure 3 is a schematic diagram of the assembly of the driver and the anchor; Figure 4 is an in vitro mechanical test on the suture anchor: a: pull-out force; b: fracture force; c: screw-in torque; Figure 5 is a schematic diagram of the morphology, degradation product distribution and composition of the suture anchor after immersion in hanks' solution for two weeks; Figure 6 is a schematic diagram of the in vitro morphology of the anchor after immersion in hanks' solution for two weeks after removing the degradation products; Figure 7 is a micro-CT cross-sectional view of the anchor immersed in hanks' solution for two weeks; Figure 8 is a finite element mechanical simulation of an in vivo implantation model; Figure 9 is a micro-CT reconstruction of the anchor after in vivo implantation; Figure 10 is the fracture force of the anchor after in vivo implantation (the red line is the initial pull-out force); In the figure: 1, threaded nail body, 2, anchor head, 3, round head structure, 4, hexagonal column boss, 5, line hole, 6, line slot, 7, thread, 8, stem, 9, head, 10, through hole, 11, hexagonal columnar through hole, 12, suture. DETAILED DESCRIPTION

[0020] The technical solutions of the application will be further specifically described below through specific embodiments.

[0021] EMBODIMENT: A combined round head structure medical degradable magnesium alloy suture anchor, such as Figure 1As shown, it includes an independent anchor head 2 with a regular hexagonal prism boss 4 and a hollow threaded nail body 1, wherein: the anchor head 2 is a truncated cone structure, and the large end of the anchor head 2 is provided with a regular hexagonal prism boss 4, the threaded nail body 1 is a cylindrical structure, and the interior of the threaded nail body 1 is provided with a hexagonal through hole 11 adapted to the regular hexagonal prism boss 4, and the outer walls of the threaded nail body 1 and the anchor head 2 are respectively provided with threads 71 ​​and threads 72, and when the anchor head 2 and the threaded nail body 1 are coaxially combined, the threads 72 of the anchor head 2 and the threads 71 ​​of the threaded nail body 1 form a complete and continuous thread segment, the axial length of the regular hexagonal prism boss 4 is smaller than the axial length of the regular hexagonal prism through hole 11, and the diameter of the regular hexagonal prism boss 4 is slightly smaller than the diameter of the large end of the anchor head 2.

[0022] Both the thread 71 and the thread 72 are trapezoidal threads. The thread height and thread width of the thread 71 on the threaded nail body are the same. The thread shape of the thread 72 on the anchor head 2 is the same as that of the threaded nail body 1. The height of the thread 72 gradually decreases from the large head end to the small head end, and the pitch on the threaded nail body 1 and the anchor head 2 are equal.

[0023] The small end of the anchor head 2 is provided with a round head structure 3, and an arc transition is adopted at the end. The total height of the anchor head 2 and the round head structure 3 is 2 mm, the height of the anchor head 2 is 1.68 mm, the maximum diameter of the anchor head 2 is 2 mm, the minimum diameter is 1.29 mm, the diameter of the round head structure 3 is 1.29 mm, and the end diameter d formed by the arc transition is 0.51 mm. The big end of the anchor head 1 is connected to a regular hexagonal prism boss 4. The diameter of the circumscribed circle of the regular hexagonal prism boss 4 is 1.52mm, the side length is 0.76mm, and the height is 2.2mm. A wire hole 5 with a diameter of 0.5mm is opened on two opposite side surfaces of the regular hexagonal prism boss 1.2mm away from the top of the regular hexagonal prism boss. The wire hole 5 is a through hole, and two semicircular wire grooves 6 extending from the middle to the tail are opened on these two side surfaces. The semicircular wire grooves 6 are connected to the wire hole 5, and the diameter of the semicircular wire grooves 6 is 0.5mm. The threaded nail body 1 is a hollow cylinder with an outer diameter of 2mm and a height of 3.5mm. The circumscribed circle diameter of the internal regular hexagonal prism through hole is 1.6mm and the side length is 0.8mm. Thread 71 is a trapezoidal thread. Its height on the cylinder is the same as its width. The trapezoidal thread has an upper base width of 0.1 mm, a lower base width of 0.4 mm, a height of 0.3 mm, and a pitch of 0.8 mm. The thread shape of the anchor head 2 is the same as that of the screw body 1, with the thread height gradually decreasing from the large end to the small end. The pitch of the screw body 1 and the anchor head 2 are equal. The anchor is made of ZE21C magnesium alloy.

[0024] A screw-in device for the degradable magnesium alloy suture anchor with a combined round head structure, such as Figure 2As shown, the total length is 21.4 mm, consisting of a shaft 8 and a head 9. The shaft 8 has an axial length of 20 mm and a diameter of 2.31 mm, while the head 9 has an axial length of 1.4 mm and a circumscribed diameter of 1.52 mm. Both the shaft 8 and the head 9 are in the shape of a regular hexagonal prism, with the shaft 8 serving as the gripping end and the head 9 as the adapting end. The screw-in inserter has an axial through-hole 10 extending through both ends for passage of a suture 12.

[0025] The assembly and use method of the present invention is as follows: Figure 3 As shown, the suture 12 passes through the thread hole 5 of the anchor, and then both ends of the suture 12 pass through the through hole 10 of the screw-in tool, pass through the rod 8 of the screw-in tool, tighten the suture, and adapt the tail of the anchor to the adapter end of the screw-in tool.

[0026] When in use, it is first necessary to drill a hole in the bone to form a bone hole, then assemble the screw-in device and the suture anchor, align the tip of the anchor with the bone hole, and twist the rod 8 to drill the magnesium alloy suture anchor into the bone. During the rotation, the suture 12 is pressed on the rod 8. After the implantation is completed, the suture end is loosened, the implantation device is pulled out, the suture end is passed through the tendon or ligament, the tendon or ligament is tightened to the bone surface, and then a knot is tied and the excess thread is cut off.

[0027] The magnesium alloy suture anchor of the present application was subjected to in vivo and in vitro experimental studies, including mechanical testing, in vitro immersion testing, and animal experiments.

[0028] Mechanical testing: Pull-out and fracture force tests were performed on a ZQ990B mechanical tester. The pull-out force test process was as follows: (1) First, a guide hole was drilled on a 20 PCF polyurethane block and the assembled suture anchor was screwed in to a depth of 2 mm; (2) The polyurethane block was fixed with a clamp, and the suture was passed through the upper crossbeam and tied into a knot; (3) A tensile load was applied to the specimen, and the tensile rate was set to 5 mm / min. When the suture anchor was completely pulled out of the specimen block, the test was terminated and the load-displacement curve was saved. In the fracture force test, the assembled anchor was embedded and fixed with resin except for the suture part. The specific test process was similar to the pull-out force test steps, but the tensile rate was set to 50 mm / min. When the suture anchor or suture broke, the test was terminated and the load-displacement curve was saved. The screw-in torque test was performed using a PBSC-RP 30 performance tester. The test process is as follows: (1) Preparation of guide holes: First, use a bone drill or hole opener corresponding to the anchor specifications to pre-make a hole on the polyurethane block that meets the requirements of ASTM F1839 to provide precise positioning and guidance for the screwing of the suture anchor. (2) Setting parameters: Set the preload axial load to 1 N and the screwing speed to 3 r / min. (3) Assembly and insertion of the anchor: After the suture anchor is assembled, apply torque to screw the anchor into the polyurethane block to a certain depth. Apply axial load during the screwing process and record the torque curve. For detailed test results, see Figure 4 .

[0029] In vivo finite element simulation: The rat tibia and the new suture anchor model were assembled in Solidworks 2018 software and then imported into Ansys 2021R1 software for finite element simulation. The elastic modulus of the tibia was set to 20 GPa and the Poisson's ratio was 0.3. The model was then meshed, and the contact condition between the tibia and the suture anchor was set to binding. A vertical downward tensile force of 10 N and a normal tensile force of 2 N were applied to the suture anchor head and the proximal tibial articular surface respectively to explore the stress distribution state of the suture anchor during in vivo service. The test results are detailed in [1]. Figure 8 .

[0030] In vitro immersion test: Suture anchors were immersed in Hanks' solution in vitro, with a solution volume to sample area ratio of 20 mL / cm 2. The assembled anchor was suspended in a centrifuge tube with non-degradable sutures and soaked in Hanks' solution. This was done to prevent the upper and lower parts of the anchor from failing and to ensure the integrity of the anchor structure during the experiment. The centrifuge tube was then placed in a constant temperature water bath at 37°C for immersion, and the Hanks' solution was replaced every 24 hours. The suture anchor samples were taken out after immersion for 1, 4, 7, and 14 days. The removed samples were rinsed with deionized water to remove impurities attached to the surface, and then dried in an oven. The corrosion morphology of the sample surface was then observed using a scanning electron microscope, and the composition of the degradation products was analyzed by EDS energy spectrum. The suture anchor after immersion and washing away the corrosion products was reconstructed using micro-computed tomography. The internal structural state of the anchor line hole was observed by reconstructing the cross section of the model. The suture anchor after washing away the corrosion products was weighed, and the degradation rate was calculated by weight loss. The results are detailed in [1]. Figures 5 to 7 .

[0031] Animal Experiments: Adult Sprague-Dawley rats were used as experimental animals to establish a patellar ligament injury model and investigate the degradation and ligament repair of the novel biodegradable magnesium alloy suture anchor. Twelve adult rats weighing 300 ± 10 g were selected and divided into four groups of three rats each.

[0032] In this application, an injury model was established using the right patellar ligament of SD rats. The patellar ligament was sharply separated from the proximal tibia, and then a magnesium alloy anchor was implanted in the proximal tibia. The patellar ligament was then sutured to the proximal tibia using the edge-to-edge suture method. The experimental animals were then subjected to imaging examinations and histological studies at specific intervals. The results are detailed in Figure 9 and Figure 10 .

[0033] Result analysis: Mechanical testing: In vitro mechanical testing of the combined structural anchor model ( Figure 4 ) and in vivo implantation mechanical simulation ( Figure 8 ), the test results show that the fracture force (213.34N) is significantly greater than the pull-out force (123.11N), and there is no risk of anchor fracture under normal initial fixation conditions; the anchor is easy to implant, and the minimal reduction in torque during removal indicates that the fixation after implantation is firm and stable; the round head structure effectively eliminates the stress concentration effect at the nail head after anchor implantation.

[0034] In vitro immersion study: Morphological characterization, three magnesium nail samples of the present invention were immersed in Hanks' solution at 37°C for 2 weeks ( Figure 5), the surface of which is mostly attached degradation products, while the wire hole has significantly reduced degradation products. EDS analysis shows that the outer surface is based on calcium phosphate degradation products, while the wire hole is magnesium oxide, without calcium phosphate deposition, indicating that the wire hole is still in the first stage of corrosion, i.e. magnesium oxidation, with slight degradation. After removing the corrosion products (Fig. 6b) Figure 6 ), the structure near the wire hole of the sample after 2 weeks of degradation is smooth and complete. Micro-CT scanning of the anchor after immersion (Fig. 7) Figure 7 ) shows that the structure of the wire hole part of the anchor remains intact. The degradation rate of the combined ZE21C suture anchor is 2.30 ± 0.27 mm / year after 1 day of immersion, which is slightly lower than that of the integrated ZE21C suture anchor. Due to the larger specific surface area of the combined anchor, the degradation rate tends to be consistent in the later stage. The above results show that the combined structure effectively protects the wire hole, greatly reducing the degradation rate of the wire hole part.

[0035] In vivo animal study: Micro-CT examination was performed on the right tibia of SD rats implanted with magnesium alloy anchors (Fig. 8) Figure 9 ). The shape of the extracted anchor shows that the magnesium alloy anchor still maintains mechanical structural stability after 12 weeks of implantation. The head of the anchor does not degrade rapidly after implantation, and the structure of the wire hole remains intact. The breaking force of the anchor after implantation (Fig. 9) Figure 10 ) shows that the breaking force of the wire hole of the anchor gradually decreases during the implantation period, but the decrease is relatively slow and the breaking force at 12W (146.41 ± 6.80N) is still greater than the initial pull-out force (123.11N). This indicates that the combined round head structure of the degradable magnesium alloy suture anchor effectively slows down the degradation of the head and wire hole, reducing the risk of anchor failure after implantation.

[0036] In summary, the combined round head structure of the degradable magnesium alloy suture anchor has good mechanical properties and can effectively reduce the degradation rate of the head and wire hole, allowing the anchor to play a reliable fixation role and reducing the risk of failure.

[0037] The above-described embodiments are only a preferred scheme of the present application and do not limit the present application in any form. Other variants and modifications can be made without exceeding the technical solutions described in the claims.

Claims

1. A medical biodegradable magnesium alloy suture anchor with a combined round head structure, characterized in that: It includes an independent anchor head with a hexagonal prism boss and a hollow threaded nail body, wherein: the anchor head is a truncated cone structure, the large end of the anchor head is provided with a hexagonal prism boss, the threaded nail body is a cylindrical structure, the interior of the threaded nail body is provided with a hexagonal prism-shaped through hole that is compatible with the hexagonal prism boss, the outer walls of the anchor head and the threaded nail body are respectively provided with threads, and when the anchor head and the threaded nail body are coaxially combined, the threads of the anchor head and the threads of the threaded nail body form a complete and continuous thread segment, the axial length of the hexagonal prism boss is smaller than the axial length of the hexagonal prism-shaped through hole, and the diameter of the hexagonal prism boss is slightly smaller than the diameter of the large end of the anchor head.

2. The combined round-head structured medical biodegradable magnesium alloy suture anchor according to claim 1, characterized in that: The thread is a trapezoidal thread, the thread height of the thread on the threaded nail body is the same as the thread width, the thread shape of the thread on the anchor nail head is the same as the threaded nail body, the thread height gradually decreases from the large head end to the small head end, and the pitch on the threaded nail body and the anchor nail head is equal.

3. The combined round-head structured medical biodegradable magnesium alloy suture anchor according to claim 1, characterized in that: A pair of oppositely disposed side surfaces of the hexagonal prism boss are provided with thread holes, and two thread grooves extending from the middle to the tail are opened on the two side surfaces. The thread grooves are connected with the thread holes for thread passing.

4. The combined round-head structured medical biodegradable magnesium alloy suture anchor according to claim 1, characterized in that: The wire trough is a semicircular wire trough, and the diameter of the wire trough is the same as the diameter of the wire hole.

5. The combined round-head structured medical biodegradable magnesium alloy suture anchor according to claim 1, characterized in that: The magnesium alloy material is ZE21C magnesium alloy.

6. The combined round-head structured medical biodegradable magnesium alloy suture anchor according to claim 1, characterized in that: The small end of the anchor head is provided with a round head structure.

7. A screwing tool for use with the magnesium alloy anchor according to any one of claims 1 to 6, characterized in that: It includes a rod and a head, wherein both the rod and the head are hexagonal prisms, the rod is the handheld end, and the head is the adapter end, which cooperates with the anchor nail, and the diameter of the rod is larger than that of the head.

8. The screw-in tool according to claim 7, characterized in that The screw-in tool is axially provided with a through hole for the suture to pass through.

9. The screw-in tool according to claim 7, characterized in that The screwing device head is matched with the hexagonal column-shaped through hole of the threaded nail body away from the anchor nail head end.

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