Fixing member for multi-axis bone fixation device, and multi-axis bone fixation device including the fixing member

Abstract

To provide an anchoring member which is reduced in a possible failure under load, and a polyaxial bone anchoring device.SOLUTION: The anchoring member for the polyaxial bone anchoring device includes: a bone anchoring section (2) having a first end, a second end, and an engagement structure provided on at least a portion thereof; a head (3) having an outer surface portion that defines a portion of a sphere (S); a central axis; and a neck between the first end of the bone anchoring section (2) and the head (3). The neck includes a first portion that is closer to the head (3), where in at least one plane including the central axis, the first portion of the neck is concave with a first curvature, the neck further including a second portion between the first portion and the bone anchoring section (2), where in the at least one plane, the second portion is concave with a second curvature that is smaller than the first curvature.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a fixing member for a multi-axis bone fixation device and a multi-axis bone fixation device including the fixing member, and more particularly to a device used for the treatment of spinal diseases or trauma surgery.

Background Art

[0002] Conventionally, multi-axis bone fixation devices used for the treatment of spinal diseases are known. For example, US5,443,467 discloses a multi-axis bone fixation device including a fixing element having a shaft for fixing to bone and a head portion having a spherical segment shape, and the fixing element is rotatably supported by a receiving portion for coupling the fixing element to a spinal rod.

[0003] The portion of the fixing element located between the head portion and the shaft can be a region where the fixing element may fail due to loading.

[0004] US2017 / 0245894A1 discloses a multi-axis bone fixation device including an anchor body and a fastening portion, and the fastening portion includes a head portion, a threaded shaft extending distally with respect to the head portion, and a neck portion located between the head portion and the threaded shaft. The head portion has an outer surface that is at least partially convex and defines a part of a sphere defining a first diameter. The neck portion defines a second diameter, and the fastener defines a ratio of the first diameter to the second diameter in the range between about 2:1 and about 3:1.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a fixing member and a multi-axis bone fixation device improved with respect to failures that may occur due to loads.

Means for Solving the Problems

[0007] The above object is solved by the fixing member according to claim 1 and is also solved by the multi-axis bone fixation device according to claim 13.

[0008] According to one aspect of the present disclosure, a fixing member for a multi-axis bone fixation device includes a first end portion, a second end portion, and a bone fixation section having a bone engagement structure provided on at least a part thereof, a head portion having an outer surface portion defining a part of a sphere, a central axis extending through the head portion and the centers of the first end portion and the second end portion of the bone fixation section, and a neck portion located between the first end portion of the bone fixation section and the head portion. The neck portion includes a first portion closer to the head portion than the bone fixation section. In at least one plane including the central axis, the first portion of the neck portion is a concave surface having a first curvature, the neck portion further includes a second portion between the first portion and the bone fixation section, and in the at least one plane, the second portion is a concave surface having a second curvature smaller than the first curvature. When viewed from one end side of the central axis, the first portion is joined to the second portion in the axial direction.

[0009] With this design, the transition portion between the cylindrical portion of the bone fixation section or the neck portion and the head portion moves axially toward the center of the head portion. As a result, the distribution of the load acting on the head portion and / or the neck portion is improved. As a result, the strength of the fixing member against breakage, specifically the fatigue strength, increases particularly in the region of the neck portion.

[0010] According to another aspect of the present disclosure, the multi-axis bone fixation device includes the bone fixation member and a receiving portion including a seat for receiving the head portion, and the bone fixation section can take a plurality of angular positions with respect to the receiving portion.

[0011] The maximum turning angle formed by the fixing member with respect to the receiving portion can be increased as compared with a bone fixing member having a substantially cylindrical neck portion.

[0012] Further features and advantages will become apparent from the description of the embodiments using the accompanying drawings.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 8

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Figure 12

DETAILED DESCRIPTION OF THE INVENTION

[0014] Referring to FIGS. 1 and 2, the multi-axis bone fixation device according to Embodiment 1 includes a shank 2 for fixing to a bone or vertebra, and a fixing member 1 including a head portion 3. Further, a receiving portion 4 for rotatably receiving the head portion 3 of the fixing member 1 is provided, and the receiving portion 4 is configured to couple the fixing member 1 to the stabilization rod 100. A pressure member 5 may be provided to apply pressure to the head portion 3 within the receiving portion 4 so as to fix the head portion 3 at a specific angular position with respect to the receiving portion 4. The locking member 6 can form a part of the bone fixation device for fixing the rod 100 within the receiving portion 4, for example, in the form of a set screw.

[0015] Additionally, as shown in FIG. 5, the receiving portion 4 has a first end portion 4a, i.e., the upper end, and an opposite second end portion 4b, i.e., the lower end, a symmetry axis M extending in a direction from the first end portion 4a to the second end portion 4b, and a coaxial bore 8. Adjacent to the first end portion 4a, a substantially U-shaped recess 9 is provided, and the recess 9 functions as a groove for receiving the rod 100. The recess 9 forms two free legs provided with a locking structure cooperating with the locking member 6, such as an internal thread 10.

[0016] Adjacent to or in proximity to the second end portion, a passage provided by the coaxial bore 8 The path narrows towards the second end portion 4b and forms an opening 11. The inner diameter of the opening 11 is sized to be able to guide the fixing member 1 provided with the shank 2 until the head portion 3 is seated on the seating portion 12 adjacent to the opening 11. The seating portion 12 for the head portion 3 can be designed as a spherical segment-shaped portion that coincides with the outer surface portion of the head portion 3.

[0017] Here, referring to FIGS. 3 and 4, the fixing member 1 has a central axis C that passes through the center of the head portion 3 and is coaxial with the major axis of the shank 2. The fixing member 1 is preferably an integral part. The shank 2 has a first end portion 21 facing the head portion 3 and a second end portion 22 on the opposite side. The second end portion 22 may be formed as a tip. At least a part of the outer surface of the shank 2 can be provided with a bone locking structure 20, for example, a bone screw. Thereby, the shank 2 forms the bone fixation section of the fixing member 1. The head portion 3 has a spherical outer surface portion 31 that defines a sphere S (see FIG. 4) having a diameter D 1 More specifically, in the embodiment, the head portion 3 has an axial length such that the diameter D of the sphere S 1 forms the widest width of the head portion 3. The cross-section of the sphere S in the plane P including the central axis C includes a circle (for example, see FIG. 6). The second end portion 2 of the shank of 2 On the opposite side, the head portion 3 is provided with a free end face 32. The free end face 32 may include a recess 3a for engaging a driver for driving the fixing element 1 into the bone. Also, the free end face 32 may be flat.

[0018] The neck portion 23 is formed between the head portion 3 and the first end portion 21 of the shank 2. The neck portion 23 includes a first portion 24 close to the head portion 3 and a second portion 25 close to the bone fixation section. The first portion 24 has an outer surface that is a concave surface having a first curvature. In the plane P, the surface of the first portion 24 of the neck portion 23 has a first radius of curvature R 1defines a circular portion having. The outer surface portions 31 of the neck portion 23 and the head portion 3 are preferably rotationally symmetric about the central axis C. Therefore, the first radius of curvature R in the first portion 24 1 is the same in all radial directions, whereby the first radius of curvature R 1 is the same in all planes including the central axis C. An edge 33 is formed at the portion where the first portion 24 of the neck portion 23 contacts the head portion 3. Due to the concave shape of the first portion 24, the width of the fixing member decreases from the head portion 3 towards the shank 2.

[0019] The second portion 25 of the neck portion 23 is a concave surface having a second curvature smaller than the first curvature. That is, the surface of the second portion 25 is curved less than the surface of the first portion 24. In the embodiment, in the plane P, the surface of the second portion 25 also defines a circular portion having a second radius of curvature R 2 . As shown in FIG. 4, the radius of curvature R 2 is larger than the radius of curvature R 1 . Due to rotational symmetry, the second radius of curvature R of the second portion 25 of the neck portion 23 2 is the same in all radial directions, whereby the second radius of curvature R2 is the same in the plane including the central axis C. As shown in the figure, the first portion 24 is continuously connected to the second portion 25.

[0020] The diameter D of the neck portion 23 in a plane orthogonal to the central axis C 2 is smaller than the first diameter D 1 at any axial position of either the first portion 24 or the second portion 25. More specifically, in the second portion 25, D 2 is such that the ratio of the first diameter (D 1 ) to the second diameter (D 2 ) is about 7:4. The ratio of the first diameter (D 2 ) to the second diameter (D 1 ) is preferably about 1 to less than 2. The axial length of the second portion 25 is larger than the axial length of the first portion 24. More specifically, the axial length of the second portion 25 is more than twice the axial length of the first portion 24.

[0021] A cylindrical portion 26, which is a third part, may be provided between the second part 25 and the shank 2. The second part 25 is continuously joined to the cylindrical portion 26. The axial length of the cylindrical portion 26, which is the third part, may be smaller than the axial length of the second part 25. The outer diameter D of the cylindrical portion 26, which is the third part 3 may be the same as the core diameter D of the shank 2, or may be slightly larger than the core diameter D. At the transition portion between the second part 25 and the cylindrical portion 26, D C may be the same as D C At the transition between the second part 25 and the cylindrical portion 26, D 3 is D 2 and may be the same as well.

[0022] The pressure member 5 will be described with reference to FIGS. 1 and 5. The pressure member 5 may be formed as an integral part. The pressure member 5 has a substantially cylindrical structure and an outer diameter that allows axial movement within the bore 8 of the receiving portion 4. The pressure member 5 includes a substantially spherical recess 51 on the side facing the head portion 3 when the pressure member 5 and the head portion 3 are assembled within the receiving portion 4. The substantially spherical recess 51 is adapted to the size of the head portion 3. On the opposite side facing away from the head portion 3, a substantially cylindrical recess 52 is formed, and the recess 52 is configured to receive the rod 100. In the present embodiment, when the rod 100 is inserted into the recess 52, the surface of the rod extends above the side wall of the recess 52. When the fixing member 1 is assembled to the receiving portion 4, the coaxial bore 53 formed in the pressure member 5 permits access to the recess 3a of the head portion 3 using a tool such as a driver.

[0023] The locking member 6 is constituted by a set screw that can be screwed between the legs of the receiving portion 4. The locking member 6 is configured to contact the rod 100 when the rod 100 is inserted into the receiving portion 4.

[0024] The fixing member 1, the receiving part 4, the pressure member 5, and the locking member 6, like the rod 100, can be made of a biocompatible material such as titanium or stainless steel, a biocompatible alloy such as a NiTi alloy such as nitinol, magnesium or a magnesium alloy, or a biocompatible plastic material such as polyetheretherketone (PEEK) or poly-L-lactic acid (PLEA). In addition, the parts can be made of the same material as each other or of different materials.

[0025] Subsequently, as shown in FIGS. 5 to 7, the multi-axis bone fixation device may be pre-assembled with the fixing member 1 inserted into the receiving part 4 from the first end 4a until the head part 3 is stabilized on the seat part 12. The pressure member 5 may be rotationally fixed within the receiving part 4 by, for example, crimping using a crimping bore 54 on the outer surface of the pressure member 5.

[0026] In use, at least two fixing members 1, together with the receiving part 4, are inserted into the bone or inserted close to the spine and connected via the rod 100. The receiving part 4 may be pivoted relative to the fixing member 1 to insert the rod 100 into the receiving part 4, thereby facilitating the insertion of the rod 100. As shown in FIGS. 5 and 6, the maximum pivot angle α is defined by the neck part 23 abutting against the edge part 11a of the opening part 11 of the receiving part 4. The sizes of the head part 3 and the neck part 23 relative to the seat part 12 in the receiving part 4 are such that the edge part 11a abuts against the second part 25 of the neck part having a small curved part. At the position of the maximum pivot angle α, it is preferable that the first part 24 of the neck part 23 is within the seat part 12 of the receiving part 4 on the side where the fixing member 1 pivots.

[0027] Referring to FIG. 8, a comparative example of the fixing member 101 is shown. In the comparative example, the neck portion 123 has no portion extending into the sphere S defined by the spherical segment-shaped head portion 103. Comparing the fixing member according to the embodiment shown in FIG. 7 with the example of the fixing member in FIG. 8, when the neck portion 23 extends into the sphere S as shown in FIG. 7, the maximum turning angle α increases. Further, the strength of the fixing member 1 according to the embodiment shown in FIG. 7 against the load increases. Finally, between the head portion 3 and the neck portion 23, the force is dispersed in an improved manner.

[0028] Referring to FIGS. 9 to 11, the fixing member according to Embodiment 2 will be described. The fixing member 1' differs from the fixing member 1 according to Embodiment 1 in the shape and size of the head portion. Since the other configurations are the same or similar, they will not be repeatedly described here. The same parts are given the same reference numerals as in Embodiment 1. The head portion 3' of the fixing member 1' has a diameter D 1’ which is 1’ compared with the diameter D 2 of the neck portion 23, may be larger than the diameter D 1 of the fixing member 1 according to Embodiment 1. More specifically, the ratio of D 2 to D 1’ may be between about 1 and about 3. On the side opposite to the free end face 32, the head portion has an undercut portion 34 extending between the edge portion 33 and the first portion 24 of the neck portion 23. The undercut portion 34 is orthogonal to the central axis C and 、 e is recessed in a virtual plane passing through the outermost portion of the edge portion 33 and in the direction towards the free end face 32 is concave. The undercut portion 34 is preferably curved in the same manner as the first portion 24 of the neck portion 23. More specifically, in the embodiment, the surface of the undercut portion 34 defines a part of a circular segment in a plane P that follows from the second portion 24 to the edge portion 33. Thereby, the radius of curvature D 1 of the undercut portion 34 can be made the same as the radius of curvature of the first portion 24 of the neck portion 23. However, the undercut portion 34 may have other shapes, for example, a non-circular shape.

[0029] With this design, the strength of the fixing member can be further increased. As shown in FIG. 11, by increasing the diameter of the head portion 3', the maximum turning angle α can be further increased.

[0030] Referring to FIG. 12, the multi-axis bone fixation device according to the second embodiment is shown to include a bone plate 200 as a component for receiving the fixing member 1. The bone plate 200 has a first surface 201 (i.e., the bone contact surface) and a second surface 202 on the opposite side. At least one, preferably two or more through holes 203 extend from the second surface 202 through the plate to the first surface 201. A seat portion 204 for the head portion of the fixing element 1 is formed on the wall portion that limits the through hole 203. Since the seat portion 204 has a shape corresponding to the spherical surface portion outside the head portion 3, the fixing member 1 can turn within the seat portion 204 at the maximum turning angle α to one side as long as the bone plate and the fixing member 1 are not embedded in the body. The fixing member is, for example, the fixing member 1 according to the first embodiment. Note that the fixing member may be the fixing member 1' according to the second embodiment. During use, the fixing member can be inserted into the bone at a predetermined angle whose range is determined by the maximum turning angle of the multi-axis bone fixation device. The strength of the fixing member against the load is improved. If necessary, a lock cap (not shown) may be provided in the through hole 203 to prevent the fixing member from retreating.

[0031] Note that the multi-axis bone fixation device is not limited to the embodiments shown above. The fixing member can be used together with any receiving portion that provides a seat for the head. Such a receiving portion may be a top-loading type in which the fixing member is inserted from the upper part of the receiving portion, or a bottom-loading type in which the fixing member is inserted such that the head portion passes through the lower side of the opening. Also, any bone plate or other surgical implant combined with the fixing member according to the above-described embodiments forms the multi-axis bone fixation device according to the present invention. The seat portion may have other shapes or may be provided in an insertion member within the receiving portion. Many different multi-axis bone fixation devices can be considered.

[0032] Various modifications of the fixing member can also be considered. For example, the bone fixation section may have any bone fixation structure and shape applicable to the fixation of bones or vertebrae. The head portion may also be non-rotationally symmetric. For example, the head portion may have two opposing planar portions, whereby the spherical portion allows the fixing member to pivot within the receiving portion only within one plane. The symmetry of the neck portion may correspond to the symmetry of the head portion.

Claims

1. A fixing member for a polyaxial bone anchoring device, comprising: a bone fixation section (2) having a first end (21), a second end (22) and a bone engaging structure provided on at least a portion thereof; a head portion (3, 3') having an outer surface portion (31) defining a portion of a sphere (S); a central axis (C) extending through the center of each of the head portions (3, 3') and the first end and the second end of the bone fixation section; a neck portion (23) located between the first end (21) of the bone fixing section (2) and the head portion (3), the neck portion (23) including a first portion (24) closer to the head portion (3) than the bone fixing section (2), an edge portion (33) is formed at a portion where the first portion (24) of the neck portion (23) contacts the head portion (3), and in at least one plane (P) including the central axis (C), the first portion (24) of the neck portion (23) is a concave surface having a first curvature, the neck portion (23) further comprises a second portion (25) between the first portion (24) and the bone fixation section (2), the first portion (24) being continuously connected to the second portion (25); In said at least one plane (P), said second portion (25) is concave having a second curvature that is smaller than said first curvature; The second portion (25) has an axial length greater than the axial length of the first portion (24).

2. 2. The fixing member according to claim 1, wherein the axial length of the second portion (25) is at least twice the axial length of the first portion (24).

3. In said at least one plane (P), said sphere (S) defines a circle, 3. A fixing member according to claim 1 or 2, wherein the second portion (25) of the neck (23) lies at least partially within the circle.

4. 4. A fixing member according to claim 3, wherein said first portion (24) of said neck (23) lies entirely within said circle.

5. 5. A fixing member according to any one of the preceding claims, wherein the neck portion (23) is rotationally symmetrical about the central axis (C).

6. The fixing member according to any one of the preceding claims, wherein the outer surface portion (31) of the head portion (3,3') is rotationally symmetrical about the central axis (C).

7. 7. A fixing member according to claim 1, wherein the first portion (24) and the second portion (25) of the neck portion (23) are continuously connected to each other when viewed in the plane (P) at one end side of the central axis (C).

8. The first curvature has a first radius of curvature (R １ ) The second curvature has the first radius of curvature (R １ ) greater than the second radius of curvature (R ２ The fixing member according to claim 1 , further comprising:

9. 9. The fixing member according to claim 1, wherein the edge portion (33) is formed between the first portion (24) of the neck portion (23) and the head portion (3, 3').

10. The fixing member according to any one of the preceding claims, wherein the edge (33) is rounded.

11. A fixation member as described in any one of claims 1 to 10, wherein on the opposite side to the second end (22) of the bone fixation section (2), the head portion (3') has a free end surface (32), and on the opposite side to the free end surface (32), the head portion (3') has an undercut portion (34) extending between the edge portion (33) and the first portion (24) of the neck portion (23), the undercut portion (34) being perpendicular to the central axis (C) and recessed in a direction toward the free end surface (32) of the head portion (3') from an imaginary plane passing through the outermost part of the edge portion (33).

12. The fixing member according to claim 11, wherein in said plane (P), said undercut portion (34) includes a third curvature.

13. The fixation member of claim 12 , wherein the radius of curvature of the third curve is the same as the radius of curvature of the first curve.

14. The fixation member according to any one of the preceding claims, wherein a cylindrical portion (26) is formed between the second portion (25) of the neck (23) and the bone fixation section (2).

15. 15. The fixing member according to claim 14, wherein the cylindrical portion (26) is continuously joined to the second portion (25) in a direction towards the head portion (3).

16. The sphere (S) coupled to the outer surface portion (31) of the head portion (3) has a first diameter (D １ ) The neck portion (23) has a second diameter (D ２ ) The first diameter (D １ ) and the second diameter (D ２ ) (the second diameter (D ２ ) to the first diameter (D １ 12. The fixation member according to claim 1, wherein the ratio of (a) to (b) is about 1 to less than 2.

17. The first diameter (D １ ) and the second diameter (D ２ ) (the first diameter (D １ ): the second diameter (D ２ 17. The fixation member of claim 16, wherein:) is about 7:

4.

18. A fixing member according to any one of claims 1 to 17, a receiving part (4; 200) including a seat (12, 204) for receiving said head part (3, 3'), A polyaxial bone anchoring device, wherein said bone anchoring section (2) can assume a number of angular positions relative to said receiving part (4).

19. the receiving portion (4) includes a rod receiving recess (9) for receiving a spinal rod (100), or Polyaxial bone anchoring device according to claim 18, wherein the receiving part is formed as a bone plate (200) with at least one hole (203) for receiving the head part (3).

20. the seat (12, 204) of the receiving part (4, 200) includes a spherical portion that matches a spherical portion (31) of the head part (3) in such a way as to support the head part (3); 20. A polyaxial bone anchoring device according to claim 18 or 19, wherein at least a part of the second portion (25) of the neck portion (23) is located within a sphere defined by the spherical portion of the seat portion (12, 204) when the anchoring member (1, 1') is at a maximum pivot angle relative to the receiving part.

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