A Degradable Magnesium-based Interface Screw with High Torque Resistance and Tendon-cutting Prevention

Abstract

The present invention provides a degradable magnesium-based interfacial screw with high torque resistance and prevention of tendon cutting and slippage, including a body provided with threads thereon. The body is penetrated with a hollow first channel and a second channel, and the length of the first channel accounts for 50-60% of the total length of the body. The present invention solves the problem of surgical operation difficulties and effectively improves the success rate of screw implantation by increasing the contact depth of the interfacial screw screwdriver and improving its anti-torque performance. Further, the thread support type design effectively prevents tendon slippage, and the distributed structure of thick and thin threads effectively avoids tendon cutting damage, effectively solving the clinical application problems of magnesium-based interfacial screws.

Description

Technical Field

[0001] The present invention relates to the field of medical devices, and particularly to a degradable magnesium-based interface screw with high torque and anti-tendon cutting and slipping properties. Background Art

[0002] Injury to the anterior cruciate ligament (ACL) will cause instability of the patient's knee joint, resulting in increased wear of the articular cartilage surface, and will greatly accelerate the occurrence of osteoarthritis. ACL reconstruction is an effective means to clinically restore the knee joint function of patients and avoid or delay the occurrence of osteoarthritis.

[0003] The main process of clinical ACL reconstruction is as follows: Take an autologous or allogeneic tendon graft, fold and braid it, wrap it with a gauze moistened with normal saline for later use. Flex the knee to 90°, use an arthroscopic shaver to remove the scar tissue, ACL stump and adipose tissue in the intercondylar fossa, and then use a plasma knife to mark the inner openings of the ACL tibial tunnel and femoral tunnel. Then, use an ACL tibial aiming device and a femoral aiming device for positioning, drill the tibial and femoral tunnel guide pins respectively, then use a drill bit similar in size to the tendon graft to expand the bone tunnel, place the tendon graft in the bone tunnel, and finally use an endobutton (loop plate) or a guide pin-guided interface screw to fix the tendon graft at the femoral and tibial ends.

[0004] In China, the number of ACL reconstructions per year exceeds 100,000, but the proportion of revisions due to unsatisfactory tendon-bone interface healing leading to reconstruction failure is still as high as 10%, which is related to the insufficient performance of the interface screws for fixing tendon grafts clinically. Traditional metal interface screws have too high an elastic modulus and are prone to the stress shielding effect, while degradable polymer screws will induce the appearance of aseptic inflammation due to the local accumulation of acidic small molecule compounds, resulting in bone tunnel expansion. Therefore, they all have an adverse impact on the healing of the tendon-bone interface.

[0005] Chinese Patent with application publication number CN 109537025 A discloses a metal composite material containing an anti-corrosion coating, a degradable magnesium alloy bone screw and its application. Its focus is on designing an anti-corrosion coating, and the structural design of the screw itself is unreasonable, with a high implantation failure rate and is not suitable for implantation in parts such as the anterior cruciate ligament. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and deficiencies of existing interfacial screws, and provide a degradable magnesium-based interfacial screw with high torque resistance and tendon cutting and slipping prevention, which can be applied to preclinical anterior cruciate ligament reconstruction. Its unique design can improve the screw's anti-torque performance and prevent tendon cutting injury and slipping. The hollow interfacial screw of the present invention has a support-type thread structure, where the depth of the first channel is large, which is beneficial to improving the screw torque. The thread support-type design can prevent tendon slipping, while the distributed structure of thick and thin threads can avoid tendon cutting injury, effectively solving the clinical application problems of magnesium-based interfacial screws.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] A degradable magnesium-based interfacial screw with high torque resistance and tendon cutting and slipping prevention, including a body, with threads provided on the body. The body sequentially penetrates through a hollow first channel and a second channel from top to bottom, and the length of the first channel accounts for 50-60% of the total length of the body.

[0009] Optionally, the length L1 of the first channel is 12-18 mm.

[0010] Optionally, the first channel can be in the shape of an internal hexagonal cylinder, internal hexagonal cylinder, straight line, cross, etc. By mechanically simulating the maximum torque that screws with different notches can withstand, the internal hexagonal notch screw is finally preferred.

[0011] Optionally, the second channel is cylindrical.

[0012] Optionally, the body has an upper section, a middle section, and a lower section. The upper section accounts for 25-30% of the total length of the body, and the middle section accounts for 45-55% of the total length of the body.

[0013] Optionally, the diameter of the upper section is 8-12 mm, the diameter of the middle section is 6-12 mm, and the diameter of the lower section is 4-8 mm.

[0014] Optionally, the thread thickness of the upper section is 0.35 mm, the thread thickness of the middle section is 0.16-0.33 mm, and the thread thickness of the lower section is 0.19-1.4 mm.

[0015] Optionally, the pitch H of the upper section is 3 mm, the pitch H of the middle section is 2.8-2.82 mm, and the pitch H of the lower section 10 is 3-3.5 mm.

[0016] Optionally, the thread depth of the upper section is 1.45-2.25 mm, the thread depth of the middle section is 1.51-1.53 mm, and the thread depth of the lower section is 0.66-1.23 mm.

[0017] Optionally, the thread structure of the body is of a support type. The outer side of the thread sequentially includes a cutting surface, a first arc surface, and a second arc surface from top to bottom. The angle α formed by the cutting surface and the vertical surface is 50° - 56°, the central angle β corresponding to the first arc surface is 75° - 90°, and the central angle γ corresponding to the second arc surface is 75° - 90°.

[0018] Optionally, the diameter of the first channel is larger than that of the second channel. Due to the reduction of the diameter of the second channel, a clamping strip is formed at the connection between the second channel and the first channel. This clamping platform can limit the screwdriver, facilitating the screwdriver to smoothly implant the interface screw into parts such as the anterior cruciate ligament.

[0019] Optionally, the material of the degradable magnesium-based interface screw is degradable magnesium or magnesium alloy.

[0020] The present invention has the following beneficial effects:

[0021] By increasing the contact depth of the interface screw screwdriver, the present invention improves its anti-torque performance, solves the surgical operation problem, effectively improves the success rate of screw implantation. Further, the thread support type design effectively prevents tendon slippage, and the distributed structure of thick and thin threads effectively avoids tendon cutting damage, effectively solving the clinical application problem of magnesium-based interface screws. Description of the Drawings

[0022] Figure 1 It shows a cross-sectional view of the interface screw in the embodiment of the present invention.

[0023] Figure 2 It shows a schematic diagram of the channel of the interface screw in the embodiment of the present invention.

[0024] Figure 3 It shows a top view of the interface screw in the embodiment of the present invention.

[0025] Figure 4 It shows a bottom view of the interface screw in the embodiment of the present invention.

[0026] Figure 5 It shows a thread angle diagram of the interface screw in the embodiment of the present invention.

[0027] Figure 6 It shows a thread depth diagram of the interface screw in the embodiment of the present invention.

[0028] Figure 7 It shows a thread pitch diagram of the interface screw in the embodiment of the present invention.

[0029] Figure 8 It shows an upper thread thickness diagram of the interface screw in the embodiment of the present invention.

[0030] Figure 9It shows the middle thread thickness diagram of the interface screw in the embodiment of the present invention.

[0031] Figure 10 It shows the lower thread thickness diagram of the interface screw in the embodiment of the present invention.

[0032] Figure 11 It shows the schematic diagram of the thread structure of the interface screw in the embodiment of the present invention.

[0033] Figure 12 It shows the stress distribution diagram of the internal hexagon of the interface screw in the embodiment of the present invention (the depth of the internal hexagon in the left figure is 5 mm, and the depth of the internal hexagon in the right figure is 15 mm).

[0034] Figure 13 It shows the curve diagram of the relationship between the numerical torque and the rotation angle of two internal hexagon depths of the interface screw in the embodiment of the present invention.

[0035] Explanation of reference numerals: 1 - screw head, 2 - screw tail, 3 - thread, 31 - cutting surface, 32 - first arc surface, 33 - second arc surface, 4 - thread, 5 - first channel, 6 - second channel, 7 - screw wall, 8 - upper end, 9 - middle section, 10 - lower section, 11 - clamping platform. Detailed implementation manners

[0036] The following further illustrates the present invention in conjunction with the specification drawings and specific embodiments, but the embodiments do not impose any form of limitation on the present invention.

[0037] Magnesium metal is biodegradable, its mechanical modulus is much lower than that of traditional metals (titanium, stainless steel and cobalt-chromium alloy) and slightly higher than that of cortical bone, and it also has good biocompatibility. Therefore, it is expected to be developed into an ideal type of orthopedic internal implant device. More importantly, the magnesium ions generated during the degradation process of magnesium have the effect of promoting bone formation and can effectively enhance the ingrowth of new bone at the tendon-bone interface. Therefore, it shows the potential to be used as a new type of interface screw in clinical ACL reconstruction.

[0038] The magnesium-based interface screw mentioned in the present invention is used to fix the tendon graft in the tibial or femoral channel.

[0039] Our research group has been long-term committed to the research and development of biodegradable magnesium-based interface screws. The results of our previous research show that magnesium-based interface screws have shown excellent biological effects in promoting bone formation at the tendon-bone interface and reducing bone loss around the bone tunnel, which provides a scientific basis for the clinical application of magnesium-based interface screws.

[0040] The mechanical strength of magnesium and its alloys is insufficient, resulting in the screw head of the interface screw being easily damaged during the surgical operation, which becomes one of the main obstacles to its clinical application. Based on this, the embodiment of the present invention solves the surgical operation problem by increasing the contact depth of the interface screw screwdriver and improving its anti-torque performance.

[0041] Since the mechanical modulus of the interface screw made of magnesium and its alloys is still much higher than that of the degradable polymer, there is a possibility of tendon cutting injury. In the embodiment of the present invention, a segmented thread structure is designed to reduce the cutting of the tendon graft.

[0042] Degradable magnesium and its alloys are widely regarded as a class of highly promising orthopedic implant devices because their mechanical modulus is close to that of human bone and they have an osteogenic effect. The development of magnesium-based interface screws can provide a treatment strategy for the poor healing of the bone-building interface after clinical ACL reconstruction.

[0043] At present, the mechanical strength of magnesium metal is still insufficient, and it is easy to fail during the surgical operation, resulting in the deformation and fragmentation of the screw head. At the same time, as a metal-based interface screw, the traditional thread design structure will cause cutting damage to the tendon graft.

[0044] The thread design structure of the interface screw in the embodiment of the present invention can greatly affect the fixation effect of the tendon graft. By constructing a supporting thread, the slipping of the tendon graft is prevented, and the risk of knee joint instability is reduced.

[0045] The materials of the existing interface screws include traditional metal materials (titanium or stainless steel) and polymers such as polylactic acid and polyetheretherketone (PEEK) materials. The Young's modulus of traditional metal materials is too high, which is likely to produce a stress shielding effect and is not conducive to the ingrowth of new bone around; at the same time, it will cause cutting damage to the tendon graft. The mechanical strength of polymer interface screws is low, and they are prone to operational failure, and the possible acidic degradation products may cause aseptic inflammation, which is not conducive to the healing of the bone-building interface. The embodiment of the present invention uses a degradable magnesium-based material with a moderate mechanical modulus, close to that of human bone, which can avoid the stress shielding effect and reduce the damage to the tendon graft. At the same time, the magnesium ions generated during the degradation process can promote the growth of bone tissue.

[0046] In order to solve the above problems and strengthen the fixation effect of the tendon graft, the structure of the degradable magnesium-based interface screw with high torque and anti-tendon cutting and slipping provided by the embodiment of the present invention is as follows:

[0047] As Figures 1-11 shown, a degradable magnesium-based interface screw with high torque and anti-tendon cutting and slipping includes a body 1, a thread 3 is provided on the body 1, and a hollow first channel 5 and a second channel 6 penetrate through the body 1 from top to bottom in sequence. The length of the first channel 5 accounts for 50-60% of the total length of the body 1, including but not limited to 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%. By increasing the conduction length of the first channel 5, high torque is achieved, and the anti-torque performance of the screw is significantly improved.

[0048] In some embodiments, the length of the body 1 is 24 to 35 mm, including but not limited to 24 mm, 25 mm, 26 mm, 27 mm, 28 mm, 29 mm, 30 mm, 31 mm, 32 mm, 33 mm, 34 mm, 35 mm. The thread 3 can guide the screw into the channel between the tibia and the femur and anchor it to the tendon graft. The area of the thread 3 gradually decreases from the head to the tail of the screw, where the head diameter is 8 to 12 mm and the tail diameter is 4 to 8 mm. The above structural design of the thread 3 can also prevent the tendon or graft from slipping during fixation and play a supporting role.

[0049] In one embodiment, the first channel 5 is in the shape of an internal hexagonal cylinder, that is to say, the cross-section of the first channel 5 is a regular hexagon, which is convenient for a screwdriver to be inserted into the first channel 5. The first channel 5 can also be a cross-shaped channel, and a cross-shaped screwdriver can be used to implant it into the transplantation site.

[0050] In one embodiment, the length L1 of the first channel 5 is 12 to 18 mm, including but not limited to 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm. By increasing the conduction length of the first channel 5, the anti-torque performance of the screw can be effectively improved.

[0051] In one embodiment, the second channel 6 is cylindrical. The shape of the second channel 6 is not limited and can also be other regular or irregular shapes as long as it can allow a guide pin to pass through.

[0052] Specifically, the body 1 is a hollow structure, as Figure 2 , Figure 3 , Figure 4 shown. The first channel 5 is an internal hexagon and contacts the screwdriver. High torque is achieved by increasing the conduction length of the internal hexagon. The finite element analysis software is used to simulate the change of the depth of the internal hexagon of the screw, and the change of its anti-torque performance is as Figure 12 . According to the statistical measurement data as Figure 13 , it is proved that high anti-torque performance of the screw can be achieved by increasing the conduction length of the internal hexagon, and the suitable length range of its internal hexagon is 12 to 18 mm. The inside of the body 1 is conducted by the first channel 5 and the second channel 6. The second channel 6 at the lower part can specifically be cylindrical. This design is to facilitate the use of a long guide pin to guide the interface screw into the fixed position in the drilling channels at the proximal end of the tibia and the distal end of the femur. At the same time, it is also to enable the long guide pin to penetrate the screw, prevent the screw from falling off the long guide pin during the import process, enable the screw to be imported along the channel direction, and prevent the screw from shifting. The length L2 of the second channel 6 is 12 to 17 mm, including but not limited to 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm.

[0053] The interface screw is designed to be hollow. In one embodiment, the first channel is hexagonal and the second channel is cylindrical, and their lengths each account for half of the screw length. The hexagonal shape contacts with the screwdriver, increasing the insertion depth of the screwdriver, which is beneficial to improving the anti-torque performance of the interface screw. The cylindrical second channel is used for guiding the needle to implant the interface screw.

[0054] In one embodiment, the body 1 has an upper section 8, a middle section 9, and a lower section 10. The upper section 8 accounts for 25 - 30% of the total length of the body 1, including but not limited to 25%, 26%, 27%, 28%, 29%, 30%. The middle section 9 accounts for 45 - 55% of the total length of the body 1, including but not limited to 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%. According to the different functions of the interface screw implanted in different parts of the bone tunnel, it can effectively reduce the failure rate of traditional metal screw implantation.

[0055] In one embodiment, the diameter of the upper section 8 is 8 - 12 mm, the diameter of the middle section 9 is 6 - 12 mm, and the diameter of the lower section 10 is 4 - 8 mm.

[0056] In one embodiment, as Figures 5-10 shown, the thickness of the thread 4 of the upper section 8 is 0.35 - 0.45 mm, the thickness d of the thread 4 of the middle section 9 is 0.16 - 0.33 mm, including but not limited to 0.16 mm, 0.18 mm, 0.2 mm, 0.2 mm, 0.22 mm, 0.24 mm, 0.25 mm, 0.26 mm, 0.28 mm, 0.3 mm, 0.31 mm, 0.32 mm, 0.33 mm. The thickness d of the thread 4 of the lower section 10 is 0.19 - 1.4 mm, including but not limited to 0.19 mm, 0.20 mm, 0.25 mm, 0.30 mm, 0.35 mm, 0.40 mm, 0.45 mm, 0.50 mm, 0.55 mm, 0.60 mm, 0.65 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm. It is preferably 0.5 - 1.4 mm, more preferably 1 - 1.4 mm. The thread thickness of the lower section is relatively thick. Since it is a continuous thread, the thread thickness will not suddenly increase, having a buffering effect.

[0057] In one embodiment, the pitch H of the upper section 8 is 3 to 3.8 mm, including but not limited to 3 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, the pitch H of the middle section 9 is 2.8 to 2.82 mm, including but not limited to 2.80 mm, 2.81 mm, 2.82 mm, and the pitch H of the lower section 10 is 3 to 3.5 mm, including but not limited to 3 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm.

[0058] In one embodiment, the depth h of the thread 4 on the outer side of the screw body is 1.45 to 2.25 mm, including but not limited to 1.45 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.25 mm, the depth h of the thread 4 of the middle section 9 is 1.51 to 1.53 mm, and the depth h of the thread 4 of the lower section 10 is 0.66 to 1.23 mm, including but not limited to 0.66 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.1 mm, 1.2 mm, 1.23 mm.

[0059] The thickness of the thread on the outer side of the screw body is designed in a segmented manner. The thickness of the thread at the screw tail is large and the depth of the thread is shallow, which is beneficial for anchoring and avoiding fragmentation; the thickness of the thread in the middle section is small and the depth is large, which is convenient for cutting the bone tunnel and fixing the tendon graft; the thread from the middle section to the screw head becomes blunt and the depth is large to increase the fixation of the tendon graft and avoid excessive cutting of the tendon graft.

[0060] The change in the depth of the thread on the outer side of the interference screw will be accompanied by a change in the thickness of the inner wall of the screw. When the depth of the thread cutting increases, the thickness of the inner wall of the screw will become thinner, resulting in a smaller bearing capacity and being prone to fracture. However, it increases the contact area with the tendon graft and better anchors. On the contrary, it will increase the bearing capacity of the inner wall thickness of the screw and is not easy to break, but the effect of fixing the tendon graft becomes worse. The appropriate adjustment of the thread depth and the screw wall thickness parameters is beneficial to improve the fixation strength of the tendon graft while ensuring the normal use of the screw.

[0061] In one embodiment, as Figure 11As shown, the thread structure of the body 1 is of the support type. The thread 3 is specifically a concave support type structure. The outer side of the thread 3 sequentially includes a cutting surface 31, a first arc surface 32, and a second arc surface 33 from top to bottom. The cutting surface 31 can specifically be a plane, a curved surface, etc., preferably a plane. The angle α formed by the cutting surface 31 and the vertical plane ranges from 50° to 56°, and can specifically be any value within the above range, including but not limited to 50°, 51°, 52°, 53°, 54°, 55°, 56°. The vertical height M of the cutting surface 31 is 0.5 - 0.62 mm, preferably 0.5 mm. The perpendicular distance from the cutting surface 31 to the center line of the body 1 gradually decreases. The central angle β corresponding to the first arc surface 32 ranges from 75° to 90°, and can specifically be any value within the above range, including but not limited to 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 85°, 86°, 88°, 90°. The radius R1 of the first arc surface 32 is 0.7 - 0.95 mm, including but not limited to 0.7 mm, 0.8 mm, 0.9 mm, 0.95 mm, preferably 0.7 mm. The central angle γ corresponding to the second arc surface 33 ranges from 75° to 90°, and can specifically be any value within the above range, including but not limited to 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 85°, 86°, 88°, 90°. The radius R2 of the second arc surface 33 is 1.08 - 1.45 mm, including but not limited to 1.08 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.45 mm, preferably 1.45 mm. The first arc surface 32 and the second arc surface 33 are preferably circular arcs to reduce damage to the tendon.

[0062] The screw thread structure is designed in a three - segment form. The overall thread shape is of the support type. The radius of the third - segment arc is the largest, which can play a supporting role. The design of the thread can, on the one hand, cut the tendon graft to make it have better internal fixation, and on the other hand, prevent the tendon graft from slipping during the fixation process, avoiding joint instability after surgery. Specifically, the outer thread of the interference screw is cut into a three - segment form, changing the cutting angle of the thread so that the depth of the thread teeth remains unchanged, and changing the influence of the thread cutting angle on the stress distribution of the screw imported into the bone tunnel. If the inclination angle α of the first - segment cutting surface is appropriately reduced, the second - segment arc is gentle, and the third - segment arc is gentle, the stress distribution around the thread is reduced, which can protect the screw from breaking, and the supporting effect is better, and it can prevent the tendon graft from slipping.

[0063] If the inclination angle α of the first - segment cutting surface is appropriately increased, the second - segment arc β is steep, and the third - segment arc γ is steep, the stress of the screw in the middle part becomes smaller, making it more convenient for the screw to penetrate into the bone tunnel.

[0064] In one embodiment, the tail of the body 1 is conical. This design enables the screw to be inserted into a smaller bone channel and is beneficial for anchoring. The penetration area (tail conical area) of the body 1 has a customized thread pitch and thread diameter. The thread pitch ranges from 2.8 mm to 4 mm, the thickness of the thread teeth gradually increases, the thread diameter ranges from 6 mm to 8 mm, the thread pitch gradually increases, and the diameter gradually decreases. The tail of the screw is designed to be conical, which is beneficial for screw anchoring and screwing in.

[0065] In one embodiment, the diameter of the first channel 5 is larger than that of the second channel 6, which facilitates the corresponding insertion of the screwdriver and the guide pin into the two channels. Since the diameter of the second channel 6 is reduced, a clamping platform 11 is formed at the connection between the first channel 5 and the second channel 6. The bottom of the internal hexagonal working section on the screwdriver abuts against the clamping platform 11, enabling the screwdriver to smoothly implant the interference screw into the tissue. The guide pin penetrates into the second channel 6 to play a guiding role.

[0066] The material used for the magnesium-based interference screw can be high-purity magnesium or a binary or multi-element magnesium alloy containing alloying elements such as Zn, Ca, Sr, and Si. It can exert the biological effects of magnesium ions, induce the migration and osteogenic differentiation of stem cells, and promote the ingrowth of new bone at the tendon-bone interface.

[0067] The interference screw of the embodiment of the present invention can also change the torque required for screwing in the screw and the effect of fixing the tendon graft by adjusting the screw pitch parameter.

[0068] The present invention can meet the operation requirements of preclinical anterior cruciate ligament reconstruction surgery, avoid the failure of the screw head due to breakage, effectively prevent tendon slip and cutting, and can stably fix the tendon graft.

[0069] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A degradable magnesium-based interface screw with high torque and anti-tendon cutting and slipping characteristics, characterized in that It includes a body (1) provided with a thread (3) thereon. The body (1) is successively penetrated from top to bottom by a hollow first channel (5) and a second channel (6). The length of the first channel (5) accounts for 50-60% of the total length of the body (1); the length L1 of the first channel (5) is 12-18 mm; the first channel (5) is in the shape of an internal hexagonal column, and the second channel (6) is in the shape of a cylinder; the body (1) has an upper section (8), a middle section (9), and a lower section (10). The upper section (8) accounts for 25-30% of the total length of the body (1), and the middle section (9) accounts for 45-55% of the total length of the body (1); the diameter of the upper section (8) is 8-12 mm, the diameter of the middle section (9) is 6-12 mm, and the diameter of the lower section (10) is 4-8 mm; the thickness of the outer thread of the screw body is designed in a segmented manner. The thickness of the thread at the screw tail is large and the depth of the thread is shallow, which is conducive to anchoring and avoiding fragmentation; the thickness of the thread in the middle section is small and the depth is large, which is convenient for cutting the bone tunnel and fixing the tendon graft; the thread from the middle section to the screw head becomes blunt and the depth is large to increase the fixation of the tendon graft and avoid excessive cutting of the tendon graft; the thickness of the thread (4) in the upper section (8) is 0.35 mm, the thickness of the thread (4) in the middle section (9) is 0.16-0.33 mm, and the thickness of the thread (4) in the lower section (10) is 1.4 mm; the pitch H of the upper section (8) is 3 mm, the pitch H of the middle section (9) is 2.8-2.82 mm, and the pitch H of the lower section (10) is 3-3.5 mm; the depth of the thread (4) in the upper section (8) is 1.45 mm, the depth of the thread (4) in the middle section (9) is 1.51-1.53 mm, and the depth of the thread (4) in the lower section (10) is 0.66 mm; the outer side of the thread (3) successively includes a cutting surface (31), a first arc surface (32), and a second arc surface (33) from top to bottom. The angle α formed by the cutting surface (31) and the vertical plane is 50°-56°, the central angle β corresponding to the first arc surface (32) is 75°-90°, and the central angle γ corresponding to the second arc surface (33) is 75°-90°; the cutting surface (31) is a plane; the diameter of the first channel (5) is larger than the diameter of the second channel (6). The material of the degradable magnesium-based interference screw is degradable magnesium or magnesium alloy.

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