Absorbable interference screw

Abstract

This application relates to the field of medical device technology, and more particularly to an absorbable interference screw comprising a screw body and threads disposed on the screw body, wherein the threads comprise a high-profile thread and a low-profile thread, the high-profile and low-profile threads forming an integrated structure disposed on the surface of the screw body along its length. Compared to conventional absorbable interference screws with a single thread structure, the absorbable interference screw of this application improves axial pullout force by 20% to 35%, and reduces total bone loss during implantation and extraction by over 70%.

Description

Technical Field

[0001] The present application relates to the technical field of medical devices, and in particular to an absorbable interference screw. Background Art

[0002] In the medical device field, absorbable interference screws play a crucial role in tissue or implant fixation. With the advancement of medical technology and increasing patient demand for postoperative recovery, absorbable interference screws, owing to their advantage of eliminating the need for secondary surgical removal, have become an increasingly important option in clinical practice. However, existing absorbable interference screws still have numerous shortcomings in practical application.

[0003] From the perspective of fixation effect, the thread design of existing absorbable interference screws is relatively conventional (see Figure 1 ), the contact area between the thread and the tissue is limited. In practice, this doesn't generate sufficient friction to ensure stable fixation. For example, during the postoperative recovery phase of common fracture fixation surgery, poor screw fixation can lead to loosening and displacement of the implanted screws, preventing the fracture from healing as expected. In severe cases, reoperation may even be necessary, significantly impacting the patient's recovery and treatment outcomes.

[0004] In terms of mechanical performance, existing absorbable interference screws lack the same material properties as metal and PEEK-based ones. Furthermore, their limited thread profile and thread structure make them difficult to provide sufficient anchoring force to tissues or implants in all directions in the complex biomechanical environment of the human body. During normal patient activities, especially when subjected to significant tensile or shear forces, the screws' insufficient pullout resistance can lead to loosening of implants (such as ligaments), significantly compromising the long-term effectiveness of the surgery and failing to provide reliable support and fixation for the patient.

[0005] Furthermore, existing absorbable interference screws are poorly designed during screw insertion, causing significant damage to surrounding tissue. On one hand, during insertion, the screw threads can over-compress bone and soft tissue, leading to bone splitting and soft tissue tearing, which can affect normal tissue healing. On the other hand, the design's inability to accurately disperse stress can result in the generation of excessive bone debris, disrupting bone integrity and delaying bone healing, increasing pain and recovery time for patients.

[0006] In summary, the existing absorbable interference screws have obvious technical defects in terms of fixation effect, mechanical properties and impact on bone quality. It is urgent to develop a new type of absorbable interference screw to effectively solve the above problems and improve the clinical treatment effect and patient rehabilitation quality. Summary of the Invention

[0007] The purpose of this application is to provide an absorbable interface screw through a unique structural design to solve the problems raised in the above background technology, such as unstable fixation effect, unsatisfactory mechanical properties, easy bone splitting or excessive bone debris during implantation, etc., to provide more reliable protection for tissue repair and implant fixation.

[0008] To achieve the above objectives, this application adopts the following technical solutions:

[0009] An absorbable interface screw comprises a screw body and a thread arranged on the screw body, wherein the thread comprises a high-profile thread and a low-profile thread, and the high-profile thread and the low-profile thread form an integrated structure and are arranged on the surface of the screw body along the length direction of the screw body.

[0010] The unique, integrated high- and low-profile thread design allows the high-profile thread to quickly penetrate tissue during the initial implantation phase, providing strong grip to resist shear and tension forces, ensuring immediate stability during fixation. The low-profile thread increases the contact area and friction between the thread and tissue, distributing stress and preventing tissue damage or screw loosening caused by stress concentration. The synergistic effect of the high and low profiles significantly improves the screw's pullout resistance, ensuring stable fixation throughout the healing process and providing a solid foundation for tissue repair.

[0011] Furthermore, the thread structure design allows the screw to better adapt to tissues of varying densities and textures. For harder bone tissue, the high-profile thread can penetrate deeply to provide secure fixation. For softer tissue or more brittle bone, such as in osteoporosis patients, the low-profile thread increases friction and reduces tissue damage, thus expanding the screw's applicability.

[0012] The low-profile thread is a multi-thread thread, preferably a double-thread thread, comprising a first low-profile thread and a second low-profile thread, and the high-profile thread is located between the first low-profile thread and the second low-profile thread.

[0013] Low-profile threads use multi-threads, such as a double-thread structure. During the process of screwing the screw into the tissue, it can not only apply anchoring force from two directions, forming a stable triangular support with the high-profile thread, and enhancing the screw's anti-rotation and anti-pullout capabilities in all directions, but also greatly reduce the torque required for screw insertion, thereby reducing damage to the bone during the implantation process, reducing the risk of bone splitting, and effectively controlling bone loss, providing more reliable protection for the patient's postoperative recovery.

[0014] The high-profile thread can be a pointed thread, a flat-top thread with rounded corners, or a domed thread, with a pointed thread being preferred. The sharp profile of the high-profile thread allows for precise bone penetration during rapid tissue penetration, minimizing excessive compression and damage to surrounding bone. Flat-top and domed threads with rounded corners provide a certain level of grip while also making gentler contact with tissue, minimizing damage, making them suitable for applications where tissue damage is less critical.

[0015] The tooth profile of the low-profile thread is different from the tooth profile of the high-profile thread.

[0016] Preferably, one side corner of the low-profile thread is rounded.

[0017] Preferably, the first low-profile thread and the second low-profile thread in the low-profile thread are both asymmetric threads with relatively smooth side surfaces connected to the high-profile thread.

[0018] The asymmetric design of the low-profile thread and the rounded transition allow the screw to contact the bone more gently during the screwing process, avoiding bone splitting or excessive bone debris due to stress concentration, thereby protecting the integrity of the bone to the greatest extent.

[0019] Preferably, the first low-profile thread, the second low-profile thread, and the high-profile thread have a rounded transition at their junctions. This rounded transition not only reduces stress concentration points and improves the fatigue strength of the screw, but also optimizes the screw-tissue interface, promoting tissue growth and healing, and providing strong support for the long-term stability of the screw.

[0020] When the high-profile thread is a pointed apex thread, the apex angle α is ≤ 45°, preferably α ≤ 42°, and more preferably 38° ≤ α ≤ 40°. A smaller apex angle results in a sharper apex, further enhancing the thread's ability to quickly penetrate tissue and precisely penetrate bone. This facilitates easier bone entry during implantation, reduces damage to surrounding bone, and improves the screw's grip and fixation effectiveness.

[0021] The height difference between the high-profile thread and the low-profile thread is 0.1 mm to 0.6 mm. When the interface screw is used to fix soft tissue, the height difference between the high-profile thread and the low-profile thread is preferably 0.1 mm to 0.3 mm.

[0022] Furthermore, the screw body includes a screw head, a screw middle and a screw tail, and the thread heights of the first low-profile thread and the second low-profile thread arranged in the thread at the screw head and / or the screw middle are not equal.

[0023] Preferably, the first low-profile thread near the screw's tail has a lower thread height than the second low-profile thread near the screw's head. This structure allows the screw to function differently at different locations. The higher thread height at the head provides stronger initial fixation and gripping force, ensuring initial stability during implantation. The lower thread height at the tail reduces compression on surrounding tissue, minimizing bone damage and facilitating smooth screw insertion.

[0024] Compared with the prior art, this application has the following beneficial effects:

[0025] (1) The absorbable interface screw of the present application adopts a unique integrated high and low thread design, breaking the limitation of the single thread of traditional screws. The synergistic effect of the high and low threads significantly improves the axial pull-out force of the screw. Experimental tests have shown that the axial pull-out force of the absorbable interface screw of the present application is improved by 20% to 35% compared with that of traditional absorbable interface screws.

[0026] (2) The low-profile thread adopts a multi-thread structure design, which can significantly reduce the torque required for screw insertion, reduce the damage to the bone during the implantation process, and thus significantly reduce the risk of bone splitting and effectively control bone loss. Experimental testing has shown that the total bone loss during the implantation and removal of the absorbable interface screw of this application is reduced by more than 74% compared to traditional absorbable interface screws. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is a schematic diagram of the overall structure of an existing absorbable interference screw;

[0029] Figure 2 Schematic diagram of the overall structure of the interface screw of Example 1;

[0030] Figure 3 Schematic cross-sectional view of the interface screw of Example 1;

[0031] Figure 4 for Figure 2 Enlarged view of the interface screw A;

[0032] Figure 5 Schematic diagram of the overall structure of the interface screw of Example 2;

[0033] Figure 6Schematic cross-sectional view of the interface screw of Example 2;

[0034] Figure 7 Schematic diagram of the overall structure of the interface screw of Example 3;

[0035] Figure 8 This is a schematic cross-sectional view of the interface screw of Example 3.

[0036] Figure numerals: 1, screw body; 11, screw head; 12, screw middle; 13, screw tail; 2, thread; 21, high-profile thread; 22, low-profile thread; 221, first low-profile thread; 222, second low-profile thread. DETAILED DESCRIPTION

[0037] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0038] It should be noted that when a component is referred to as being "fixed on" or "provided on" or "set on" another component, it may be directly on the other component or there may be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may be a central component at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in the specification of this application are for illustrative purposes only and do not represent the only implementation method.

[0039] Furthermore, 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 the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0040] In this application, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it can mean that the first feature is directly in contact with the second feature, or the first feature and the second feature are indirectly in contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it can mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is higher in level than the second feature. When a first feature is "below," "below," or "below" a second feature, it can mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is lower in level than the second feature.

[0041] Unless otherwise defined, all technical and scientific terms used in the specification of this application have the same meaning as commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in the specification of this application includes any and all combinations of one or more of the relevant listed items.

[0042] Example 1

[0043] The screw material is selected as follows: by weight, it contains 10 parts of polylactic acid PLLA, 60 parts of PLGA (85:15), 5 parts of PEG-400, 25 parts of hydroxyapatite powder with an average particle size of 750 mm and 2 parts of maleic anhydride.

[0044] After the above materials were mixed uniformly, an absorbable interference screw (screw size: φ7×25) was prepared by injection molding. The injection temperature was set at 210°C, the injection pressure was 240 bar, the holding time was 40 seconds, and the mold temperature was 35°C.

[0045] like Figures 1 to 3As shown, the absorbable interference screw of this embodiment includes a screw body 1 and a thread 2 provided on the screw body 1, the screw body 1 includes a screw head 11, a screw middle part 12 and a screw tail 13, the thread 2 includes a high-profile thread 21 and a low-profile thread 22, the high-profile thread 21 and the low-profile thread 22 are integrated into a structure and are provided on the surface of the screw body 1 along the length direction of the screw body 1; the high-profile thread 21 is a pointed top thread with a tooth top angle α value of 45°, the low-profile thread 22 includes a first low-profile thread 221 and a second low-profile thread 222, and the low-profile threads 22 are all asymmetric Thread, the high-profile thread 21 is arranged between the first low-profile thread 221 and the second low-profile thread 222, and the high-profile thread 21 has a rounded transition with the first low-profile thread 221 and the second low-profile thread 222 respectively, and the other side corners of the first low-profile thread 221 and the second low-profile thread 222 have a rounded transition; the thread height of the first low-profile thread 221 near the screw tail 13 is lower than the thread height of the second low-profile thread 222 near the screw head 11, and the thread height difference between the high-profile thread 21 and the second low-profile thread 222 is 0.15~0.2mm.

[0046] Example 2

[0047] Compared with embodiment 1, the only difference is that the high-tooth profile thread 21 of embodiment 2 is a flat-top thread with a rounded corner, and the fillet radius is 0.3 mm. Figure 4~Figure 5 shown.

[0048] Example 3

[0049] Compared with Example 1, the only difference is that the other side corners of the first low-profile thread 221 and the second low-profile thread 222 of Example 3 are in a right-angle transition, as shown in FIG. Figure 6-7 shown.

[0050] Example 4

[0051] Compared with Example 1, the only difference is that the high-profile thread 21 of Example 4 is a pointed-top thread with a tooth top angle α value of 42°.

[0052] Example 5

[0053] Compared with Example 1, the only difference is that the high-profile thread 21 of Example 5 is a pointed-top thread with a tooth top angle α of 40°.

[0054] Example 6

[0055] Compared with Example 1, the only difference is that the high-profile thread 21 of Example 5 is a pointed-top thread with a tooth top angle α value of 38°.

[0056] Example 7

[0057] Compared with Example 1, the only difference is that the high-profile thread 21 of Example 5 is a pointed-top thread with a tooth top angle α value of 35°.

[0058] Comparative Example 1

[0059] Compared with Example 1, the only difference is that the thread structure of Comparative Example 1 is a traditional single thread structure, such as Figure 8 shown.

[0060] Comparative Example 2

[0061] Compared with Example 1, the only difference is that the high-profile threads 21 and the low-profile threads 22 of Example 2 are arranged at intervals rather than being an integrated structure.

[0062] Performance testing:

[0063] Axial pull-out force: Tested according to the method specified in YY / T1504, and the test data are recorded in Table 1.

[0064] Bone loss is measured as follows:

[0065] (1) Use an electronic balance to weigh the mass of the 20pcf simulated bone block with the bone marrow tunnel drilled (the inner diameter of the bone tunnel is 1mm smaller than the outer diameter of the screw), recorded as M0;

[0066] (2) Use a dedicated screw implantation tool to slowly screw the interference screw into the preset position of the medullary canal along the center line of the medullary canal, check the stability of the screw, and adjust or fix it as needed to ensure that the screw has sufficient holding force;

[0067] (3) Use a dedicated screw removal tool to align the screw head and remove the screw gently and slowly to avoid causing pressure or damage to the surrounding bone tissue;

[0068] (4) After the screw is unscrewed, clean the bone debris remaining in the bone marrow canal of the bone sample and put it back on the electronic balance to reweigh the mass of the bone sample, which is recorded as M1.

[0069] (5) The bone loss caused by screw insertion and removal was calculated using the formula: Bone loss = (M0 - M1) / M × 100%, where M is the mass of the absorbable interference screw. Five absorbable interference screws from each example and comparative example were tested five times in parallel using the above test method. The average value was taken and the test results are shown in Table 1.

[0070] Table 1

[0071]

[0072] After conversion, the amount of bone loss during the implantation and unscrewing process of the absorbable interface screw obtained by using the technical solution of the present application is significantly improved compared with the bone loss of the absorbable interface screw of comparative example 1 with conventional thread design in the prior art, as shown in Table 2.

[0073] Table 2

[0074]

[0075] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of patent protection for the present application shall be determined by the appended claims.

Claims

1. An absorbable interference screw, characterized in that: The invention comprises a screw body (1) and a thread (2) arranged on the screw body (1), wherein the thread (2) comprises a high-profile thread (21) and a low-profile thread (22), wherein the high-profile thread and the low-profile thread form an integrated structure and are arranged on the surface of the screw body (1) along the length direction of the screw body (1); the low-profile thread (22) is a double-thread thread, comprising a first low-profile thread (221) and a second low-profile thread (222), wherein the high-profile thread is located between the first low-profile thread (221) and the second low-profile thread (222); and the high-profile thread (21) is a pointed top thread, wherein the pointed top thread has a tooth profile angle α of ≤45°.

2. The absorbable interference screw according to claim 1, wherein: The tooth profile of the low-profile thread (22) is different from the tooth profile of the high-profile thread (21), and a corner on one side of the low-profile thread is rounded.

3. The absorbable interference screw according to claim 1, characterized in that: The first low-profile thread (221) and the second low-profile thread (222) are both asymmetric threads with relatively flat side surfaces connected to the high-profile thread, and the connection between the first low-profile thread (221) and the second low-profile thread (222) and the high-profile thread (21) is a rounded transition.

4. The absorbable interference screw according to claim 1, wherein: The height difference between the high-profile thread and the low-profile thread is 0.1 mm to 0.6 mm.

5. The absorbable interference screw according to claim 1, characterized in that: The screw body (1) comprises a screw head (11), a screw middle part (12) and a screw tail part (13), and the thread heights of the first low-profile thread (221) and the second low-profile thread (222) in the thread (2) arranged at the screw head (11) and / or the screw middle part (12) are unequal.

6. The absorbable interference screw according to claim 5, characterized in that: The thread height of the first low-profile thread (221) near the screw tail (13) is lower than the thread height of the second low-profile thread (222) near the screw head (11).

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