Medical screw

Abstract

To provide a medical screw capable of rapid and firm tightening fixation in bone fixation on craniotomy surgery or the like in a neurosurgery field.SOLUTION: A medical screw 10 used for bone fixation includes: a shank 12; and a head 11 disposed in a proximal end of the shank 12. The medical screw includes a plurality of threads 121A, 121B substantially symmetrical to a central axis O12 of the shank 12 at a cross section perpendicular to the central axis O12. A multiple-thread structure may be formed in the shank 12. The multiple-thread structure may be a two-thread structure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a medical screw for use in bone fixation. [Background technology]

[0002] In a surgical procedure, bones may be fixed to each other with a bone fixing plate, and the bone fixing plate is fixed with a medical screw.

[0003] For example, in craniotomy for treating brain tumors, cerebral thrombosis, etc., a part of the skull is cut, the cut part (bone flap) is removed, and the skull is opened. After treatment through this opening, the bone flap is returned to the opening and fixed with a bone fixing plate. At this time, medical screws are screwed into the screw holes of the bone fixing plate and tightened to fix it (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-8112 A Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, medical screws have a single thread structure. When a medical screw with this single thread structure is used to fix a bone fixation plate, the distance (lead) that the medical screw advances when it is turned once is short, so it takes time to tighten and fix the plate with the medical screw. Furthermore, if the number of threads is increased to increase the strength of the tightening fixation, it takes even more time. On the other hand, if the lead is increased to shorten the time required for tightening and fixing, the strength of the tightening fixation decreases.

[0006] As described above, when conventional medical screws are used for bone fixation, it takes time to tighten and fix the screws, and the screws lack strength. [Means for solving the problem]

[0007] In order to solve the problems described above, the medical screw of the present invention comprises a shank and a head located at the base end of the shank, and has a plurality of thread portions approximately symmetrically about the central axis in a cross section perpendicular to the central axis of the shank.

[0008] In addition, the medical screw according to the present invention may have a multiple thread structure formed on the shaft portion.

[0009] In the medical screw according to the present invention, the multiple start thread structure may be a double start thread structure. Effect of the Invention

[0010] According to the present invention, it is possible to provide a medical screw that can be quickly and firmly fastened and fixed. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows (a) a front view and (b) a top view of a medical screw according to a first embodiment of the present invention. [Diagram 2] FIG. 2 shows the configuration of the medical screw according to the first embodiment of the present invention, in which (a) is a schematic front view and (b) is a sectional view taken along the line IIB-IIB'. [Diagram 3] FIG. 3 shows the configuration of a conventional medical screw, with (a) being a schematic front view and (b) being a cross-sectional view taken along the line IIIB-IIIB'. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <First embodiment> A medical screw according to a first embodiment of the present invention will be described with reference to Figs. 1 to 3.

[0013] <Configuration of medical screw> A medical screw 10 according to this embodiment includes a head portion 11 and a shaft portion 12, as shown in FIG.

[0014] The head 11 is disposed at the base end of the shaft 12. The head 11 is circular when viewed from above, and has a cross-shaped fitting groove 111. The shape of the head 11 is not limited to this, and may be polygonal when viewed from above. The shape of the fitting groove 111 is not limited to this, and may be another shape.

[0015] The shaft portion 12 has a stepped shape in which the diameter decreases from the base end to the tip, and the tip is pointed.

[0016] A double-thread screw structure is formed on the surface of shaft portion 12. In detail, a double-thread screw structure is formed in a spiral shape on the surface of shaft portion 12, and is formed such that valley portion 122A of one screw structure is disposed in crest portion 121B of the other screw structure.

[0017] The axial distance (pitch) P between adjacent threads in the double thread structure may be 0.5 mm to 0.8 mm. A is twice the pitch P. Similarly, the interval S of the thread portion 121B of the other screw structure B The pitch is also twice as large as the pitch P. The interval between the threads of each screw structure may be 1.0 mm to 1.6 mm.

[0018] The thread diameter d1 in the double thread structure decreases from the base end to the tip end. The thread diameter d1 on the base end side may be 1.4 mm to 2.0 mm. The thread diameter d1 on the tip end side may be 0.1 mm to 0.6 mm.

[0019] The root diameter d2 decreases from the base end to the tip end. The root diameter d2 on the base end side may be shorter than the thread diameter and may be 1.0 mm to 1.6 mm. The root diameter d2 on the tip end side may be shorter than the thread diameter and may be 0.1 mm to 0.4 mm.

[0020] The length L of the medical screw 10 may be 3 mm to 6 mm.

[0021] The medical screw 10 is constructed from titanium or a titanium alloy.

[0022] In the medical screw 10, the tip of a driver bit or the like is engaged with the engagement groove 111 of the head 11 and rotated to screw in the medical screw 10. The medical screw 10 is a self-drilling screw in which the shank 12 is screwed into a bone such as the skull or a bone flap while tapping, and then tightened and fixed.

[0023] In this embodiment, an example in which a double-start thread structure is used has been shown, but a multiple-start thread structure may also be used.

[0024] <Effects> The effects of the medical screw 10 according to this embodiment will be described with reference to FIGS.

[0025] Fig. 2(a) shows a schematic diagram of the medical screw 10, and Fig. 2(b) and (c) show a cross-sectional view taken along lines IIB-IIB' and IIC-IIC', respectively. In the figures, the shaded area indicates the area of ​​one screw structure, and the shaded area indicates the area of ​​the other screw structure.

[0026] For comparison, FIG. 3(a) shows a schematic diagram of a conventional medical screw, and FIGS. 3(b) and (c) show cross-sectional views taken along lines IIIB-IIIB' and IIIC-IIIC', respectively.

[0027] Conventional medical screws have a single thread structure, as shown in FIG. 3(a), and the lead is equal to the pitch.

[0028] On the other hand, the medical screw 10 according to the present embodiment has a multiple start thread structure, as shown in Fig. 2(a), and the lead is equal to the pitch multiplied by the number of starts. For example, in the case of a double start thread structure, the lead is twice the pitch, i.e., twice the lead of a single start thread structure.

[0029] In this way, according to the medical screw 10 of this embodiment, the lead can be set large, so that the screw can be quickly screwed into the bone.

[0030] Furthermore, a conventional medical screw with a single thread structure has only one thread portion T1 on the IIIB-IIIB' cross section as shown in Figure 3(b), and only one thread portion T2 on the IIIC-IIIC' cross section as shown in Figure 3(c).

[0031] In this way, the medical screw having a single thread structure has a central axis O of the shaft portion 22. 22 As a result, when screwing in a medical screw, it is difficult to apply a uniform force to the bone in a plane perpendicular to the axial direction, which makes it difficult to screw in stably because the screw is prone to wobbling during rotation.

[0032] On the other hand, in the medical screw 10 according to the present embodiment, as shown in FIG. 2(b), in the IIB-IIB′ cross section, the central axis O 12 Two threads T are approximately symmetrically arranged A1 , T B1 In addition, as shown in FIG. 2(c), in the IIC-IIC′ cross section, the central axis O 12 Two threads T are approximately symmetrically arranged A2 , T B2 has.

[0033] In this way, the medical screw 10 having a double thread structure has a central axis O of the shaft portion 12. 12 In a plane perpendicular to the central axis O 12 As a result, when the medical screw 10 is screwed in, force is applied evenly to the bone in a plane perpendicular to the axial direction, allowing for stable screwing without any deviation in rotation.

[0034] Here, for example, a medical screw with a triple-thread structure has three threads that are approximately symmetrical about the central axis on a plane perpendicular to the central axis of the shaft. Thus, a medical screw with a multiple-thread structure has threads that are approximately symmetrical about the central axis on a vertical plane, the number of threads being equal to the number of threads. This allows the force to be applied more uniformly to the bone on a plane perpendicular to the axial direction when the medical screw is screwed in, so there is no wobble in the rotation and it can be screwed in more stably.

[0035] As an example, in the case of a medical screw with one rotation, in a single thread structure, the screw is tightened by only one thread. In a screw that is tightened by only one thread, even if a deep groove is formed to increase the tightening strength, the screw structure (thread portion) may be damaged when tightened too hard.

[0036] On the other hand, with a multiple thread structure, the fastener is fastened using multiple threads, allowing for stable fastening.

[0037] For example, assuming a thread structure with a lead of 1.6 mm and one turn, pitch = lead / number of threads, so the pitch of a single-start thread structure is 1.6 mm. In this case, the number of tightening threads is lead / pitch, which is 1. On the other hand, the pitch of a double-start thread structure is 0.8 mm, and the number of tightening threads is 2.

[0038] In this way, when the angle of the thread is the same in a one-turn screw structure, the pitch of a multiple-start screw structure (for example, a two-start screw structure) is smaller than that of a single-start screw structure, so the groove can be formed shallower (the thread height can be reduced), and the diameter of the shaft can be reduced. This allows the thread diameter of the medical screw to be set to 1.4 mm to 2.0 mm.

[0039] In addition, a multiple start thread structure has more threads than a single start thread structure, which allows for a more stable tightening end when the screw is tightened.

[0040] Therefore, the multiple thread structure makes it possible to form a stable thread structure having many threads with a groove depth that allows the thread to be effectively fastened and fixed to a thin shank.

[0041] However, with a multiple-start thread structure, the lead is greater than with a single-start thread structure of the same pitch, and the angle of inclination of the thread crest (lead angle) is greater, so the greater the number of threads, the weaker the fastening force and the more likely it is to loosen.

[0042] In addition, in manufacturing a multi-thread structure, the greater the number of threads, the more difficult it is to cut the structure. For example, in the case of a four-thread structure, a process equivalent to the process of cutting four independent thread structures is required. In other words, in the four independent thread portions, the spacing between adjacent thread portions must be uniform and they must be cut to an equal depth.

[0043] Therefore, for medical screws, a two-start thread structure with fewer threads is preferable compared to multiple-start thread structures.

[0044] The medical screw according to the present embodiment can be quickly and firmly tightened and fixed to bone.

[0045] In the embodiment of the present invention, the structure, dimensions, materials, etc. of each component of the medical screw are shown as examples, but the present invention is not limited to these. Anything that can exert the function and effect of the medical screw may be used. [Industrial Applicability]

[0046] The present invention relates to a medical screw, which can be used as a medical device for bone fixation in craniotomy and other operations in the field of brain surgery. [Explanation of symbols]

[0047] 10 Medical Screws 11 Head 111 Engagement groove 12 Shaft 121A Thread part of one screw structure 121B Thread portion of the other screw structure 122A Root of one thread structure 122B The root of the other thread structure

Claims

1. A shaft portion, a head portion disposed at a base end of the shaft portion; Equipped with A medical screw having a plurality of threads arranged approximately symmetrically about a central axis of the shaft portion in a cross section perpendicular to the central axis of the shaft portion.

2. The medical screw according to claim 1 , wherein the shank portion has a multiple start thread structure.

3. The medical screw according to claim 2 , wherein the multiple start thread structure is a double start thread structure.

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