Bone screw and bone screw manufacturing method

Abstract

To provide a bone screw in which a slide part, a fastening part, or a contact surface of a different material or component does not slide or is not broken easily.SOLUTION: A bone screw includes: a shaft part; a screw part located in a spiral manner in an axial direction of the shaft part in an outer peripheral part of the shaft part; a first end part located at the end part in an insertion direction of the shaft part; a second end part positioned at the end part in an extraction direction of the shaft part; a head located to encompass the second end part; and a fixing part which is fitted to the head and can fix a rod part to the head. At least one arithmetic surface roughness Ra of the second end part, a slide part of the head slidable to the second end part, and the fixing part ranges from 0.4 μm to 1.7 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to bone screws and methods for manufacturing bone screws.

Background Art

[0002] Bone screws are used in fracture surgery and spinal surgery. For example, by connecting pedicle screws inserted into the pedicles with a rod or the like, the spine is stabilized.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Bone screws during surgery or during the period of use are required to have a certain durability. For example, it is preferable that a bone screw inserted into bone does not deform even when a certain force acts. In particular, for a bone screw provided with a sliding portion or a fastening portion, it is preferable that the sliding portion or the fastening portion does not easily slide even when a certain force acts during surgery or during the period of use. Further, for a bone screw composed of a plurality of materials or parts, it is preferable that the joint portion of different materials or parts does not easily slide or break even when a certain force acts during surgery or during the period of use.

Means for Solving the Problems

[0005] The bone screw of the present invention includes a shaft portion, a screw portion that is helically located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, a first end portion located at the end portion in the insertion direction of the shaft portion, a second end portion located at the end portion in the removal direction of the shaft portion, a head portion located so as to include the second end portion, and a fixing portion attached to the head portion and capable of fixing a rod portion to the head portion. At least one of the arithmetic surface roughness Ra of the second end portion, the sliding portion of the head portion slidable with respect to the second end portion, and the fixing portion is 0.4 μm to 1.7 μm.

Effects of the Invention

[0006] According to the present invention, it is possible to provide a bone screw in which a sliding portion, a fastening portion, or a contact surface of different materials or components does not easily slide or break.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0008] The inventors have found a surface roughness in a bone screw provided with a sliding portion such that the sliding portion or the fastening portion does not easily slide. Further, the inventors have found a surface roughness in a bone screw composed of a plurality of materials or components such that the contact surfaces of different materials or components do not easily slide or break.

[0009] According to the present embodiment, it is possible to provide a bone screw in which a sliding portion, a fastening portion, or a contact surface of different materials or components does not easily slide or break.

[0010] Regarding the present embodiment, a medical bone screw fixed to the spine will be described with reference to the drawings. The bone screw of the present embodiment is used for the treatment of spinal diseases (for example, spinal deformity, spinal fracture, spinal canal stenosis, spinal dislocation, spinal instability, etc.) in order to enhance the stability of the spine. Further, by inserting a plurality of bone screws into the pedicles of the spine and connecting the plurality of bone screws with a rod portion, the bone screw of the present embodiment is used for treating spinal diseases by appropriately supporting the spine or restricting the movement of the spine.

[0011] FIG. 1 is a front view of the bone screw of the present embodiment. FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1. FIG. 3 is a perspective view of the bone screw of the present embodiment. FIG. 4(a) is a top view of the bone screw of the present embodiment. FIG. 4(b) is a bottom view of the bone screw of the present embodiment.

[0012] As shown in FIGS. 1 to 4, the bone screw 100 includes a shaft portion 1 and a screw portion 4 that is spirally located in the axial direction of the shaft portion 1 on the outer peripheral portion of the shaft portion 1. Further, the bone screw 100 includes a first end portion 2 located at the end portion in the insertion direction of the shaft portion 1 and a second end portion 3 located at the end portion in the removal direction of the shaft portion 1. Further, the bone screw 100 includes a head portion 5 that is located so as to include the second end portion. In the present embodiment, the head portion 5 is slidable with respect to the second end portion 3, but may be integrally or fixedly formed with the second end portion 3. Further, the bone screw 100 includes a fixing portion (set screw) 6 that is a fastening portion. The fixing portion 6 is attached to the head portion 5 and can fix a rod portion (not shown) to the head portion 5. Further, the bone screw 100 includes a contact portion (pusher) 7 that contacts the second end portion 3.

[0013] A rod portion (not shown) for connecting a plurality of bone screws is disposed in the concave portion 11 (FIG. 1) of the head portion 5 so as to contact the contact portion 7, and the fixing portion (male screw) 6 is fastened to the female screw 13 (FIG. 2) of the head portion 5 to compress and fix the rod portion. When the fixing portion (male screw) 6 is fastened to the female screw 13 (FIG. 2) of the head portion 5, the contact portion 7 together with the rod portion presses down the second end portion 3, so that the second end portion 3 is pressed and fixed to the sliding portion 12 (FIG. 2) of the head portion 5.

[0014] The arithmetic surface roughness Ra of at least one of the second end portion 3, the sliding portion 12 of the head portion 5 that is slidable with respect to the second end portion 3, and the fixing portion (male screw) 6 is 0.4 μm to 1.7 μm. For example, the arithmetic surface roughness Ra of a part of the second end portion 3 that contacts the sliding portion 12 (FIG. 2) of the head portion 5 is 0.4 μm to 1.7 μm. Further, the arithmetic surface roughness Ra of a part of the sliding portion 12 (FIG. 2) of the head portion 5 that contacts the second end portion 3 is 0.4 μm to 1.7 μm. Further, the arithmetic surface roughness Ra of a part of the fixing portion 6 that contacts the head portion 5 when the fixing portion 6 is attached to the head portion 5 is 0.4 μm to 1.7 μm.

[0015] Note that the arithmetic surface roughness Ra of only any one of the second end portion 3 and the sliding portion 12 of the head portion 5 that is slidable with respect to the second end portion 3 may be 0.4 μm to 1.7 μm.

[0016] Further, the arithmetic surface roughness Ra of the contact portion 7 is 0.4 μm to 1.7 μm. For example, the arithmetic surface roughness Ra of a part of the contact portion 7 that contacts the second end portion 3 is 0.4 μm to 1.7 μm.

[0017] Further, as shown in FIG. 2, the shaft portion 1 includes a shaft core portion 8 including the second end portion 3 and a shaft screw portion 9 located on the outer peripheral portion of the shaft core portion 8 and including the screw portion 4. The shaft core portion 8 is provided with a through hole 10 for allowing a guide wire or the like to pass therethrough. The arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 0.4 μm to 1.7 μm.

[0018] The shaft core portion 8 (or the second end portion) includes at least one of stainless steel, titanium, iron, nickel, cobalt, and cemented carbide. The shaft screw portion 9 (or the screw portion 4) includes a reinforced plastic. The reinforced plastic is at least one of carbon fiber reinforced plastic, glass fiber reinforced plastic, carbon fiber reinforced plastic, boron fiber reinforced plastic, aramid fiber reinforced plastic, kevlar fiber reinforced plastic, dyneema fiber reinforced plastic, and zylon fiber reinforced plastic.

[0019] Next, a method for manufacturing a bone screw will be described. The method for manufacturing a bone screw according to the present embodiment includes a step of performing surface processing with an arithmetic surface roughness Ra of 0.4 μm to 1.7 μm on at least one surface of the second end portion 3, the sliding portion 12 of the head slidable with respect to the second end portion 3, and the fixing portion 6. The method for manufacturing a bone screw according to the present embodiment includes a step of performing surface processing with an arithmetic surface roughness Ra of 0.4 μm to 1.7 μm on the surface of the shaft core portion 8 in contact with the shaft screw portion 9. The method for manufacturing a bone screw according to the present embodiment includes a step of performing surface processing with an arithmetic surface roughness Ra of 0.4 μm to 1.7 μm on the surface of the contact portion 7.

[0020] In the step of performing surface treatment, a blasting process is carried out. For example, a blasting process using white alumina, zircon beads, etc. is carried out. Also, separable parts may be blasted in a separated state. For example, when the shaft part 1, the head part 5, the fixing part 6, and the abutting part 7 are separable, each may be blasted in a separated state. Also, in the process of manufacturing the bone screw, before different parts are attached, the parts may be blasted. For example, before the shaft screw part 9 is attached, the shaft core part 8 may be blasted. In this case, after the shaft core part 8 is blasted, the shaft screw part 9 may be injection-molded on the outer peripheral part of the shaft core part 8 with the shaft core part 8 as the axis.

[0021] Next, the performance of the bone screw of this embodiment will be described. As shown in FIG. 5, a bending / extension moment test was carried out with reference to ASTM F1798. With the rod part 50 arranged in the concave part 11 (FIG. 1) of the bone screw 100 and the fixing part 6 fastened to the head part 5 with a torque of 8 Nm to 12 Nm, the rod part 50 was fixed, and a load (N) was applied at a position 25 mm from the central axis of the rod part 50. Then, the test was terminated when the bone screw 100 was significantly deformed, the maximum load (N) up to the termination point was measured, and the maximum load (N) was taken as the bending strength. The second end part 3 of the bone screw 100 of this embodiment and the sliding part (including the abutting part 7) of the head part 5 slidable with respect to the second end part 3 mainly contain titanium.

[0022] FIG. 6 is a diagram showing the results of the bending / extension moment test of the bone screw of Comparative Example 1 and the bone screw of this embodiment. As shown in FIG. 6, in the case of the bone screw of Comparative Example 1 (the arithmetic surface roughness Ra of the sliding part of the head part 5 slidable with respect to the second end part 3 and the second end part 3 is 0.29 μm to 0.38 μm), the bending strength was 212.4 N.

[0023] In contrast, in Example 1 of the present embodiment (the arithmetic surface roughness Ra of the sliding portion of the second end portion 3 and the head 5 slidable with respect to the second end portion 3 is 0.44 μm to 0.64 μm), the bending strength was 616.2 N. Further, in Example 2 of the present embodiment (the arithmetic surface roughness Ra of the sliding portion of the second end portion 3 and the head 5 slidable with respect to the second end portion 3 is 1.11 μm to 1.22 μm), the bending strength was 387.7 N. Furthermore, in Example 3 of the present embodiment (the arithmetic surface roughness Ra of the sliding portion of the second end portion 3 and the head 5 slidable with respect to the second end portion 3 is 1.22 μm to 1.68 μm), the bending strength was 450.0 N.

[0024] As a result, when at least one of the arithmetic surface roughness Ra of the sliding portion 12 of the head slidable with respect to the second end portion 3 and the second end portion 3 is 0.4 μm to 1.7 μm, the bending strength becomes 380 N to 620 N, and sufficient bending strength could be obtained as compared with Comparative Example 1. Preferably, when at least one of the arithmetic surface roughness Ra of the sliding portion 12 of the head 5 slidable with respect to the second end portion 3 and the second end portion 3 is 1.2 μm to 1.7 μm, the bending strength becomes 450 N, and sufficient bending strength could be obtained as compared with Comparative Example 1. More preferably, when at least one of the arithmetic surface roughness Ra of the sliding portion 12 of the head 5 slidable with respect to the second end portion 3 and the second end portion 3 is 0.4 μm to 0.7 μm, the bending strength becomes 616.2 N, and sufficient bending strength could be obtained as compared with Comparative Example 1.

[0025] Note that loosening of the fixing portion 6 was observed in Comparative Example 1, but there was no loosening of the fixing portion 6 in Examples 1 to 3. As a result, when the arithmetic surface roughness Ra of the fixing portion 6 is 0.4 μm to 1.7 μm, sufficient fastening strength (fixing strength) could be obtained as compared with Comparative Example 1. Preferably, the arithmetic surface roughness Ra of the fixing portion 6 is 1.2 μm to 1.7 μm. More preferably, the arithmetic surface roughness Ra of the fixing portion 6 is 0.4 μm to 0.7 μm.

[0026] Further, from the results of the above flexion-extension moment test, when the arithmetic surface roughness Ra of the contact portion 7 (corresponding to a part of the sliding portion of the head 5 slidable with respect to the second end portion 3) that contacts the second end portion 3 is 0.4 μm to 1.7 μm, sufficient bending strength can be obtained as compared with Comparative Example 1. Preferably, the arithmetic surface roughness Ra of the contact portion 7 that contacts the second end portion 3 is 1.2 μm to 1.7 μm. More preferably, the arithmetic surface roughness Ra of the contact portion 7 that contacts the second end portion 3 is 0.4 μm to 0.7 μm.

[0027] Next, as shown in FIG. 7, a torsional test was performed. With the rod portion 50 disposed in the concave portion 11 (FIG. 1) of the bone screw 100 and the fixing portion 6 fastened to the head 5 with a torque of 8 Nm to 12 Nm, the rod portion 50 was fixed, and torque (Nm) was applied to the shaft screw portion 9 (or the screw portion 4). Then, the test was terminated when the bone screw 100 was significantly deformed, the maximum torque (Nm) up to the termination point was measured, and the maximum torque (Nm) was taken as the torsional strength. The shaft core portion 8 of the bone screw 100 of the present embodiment (or the portion of the shaft core portion 8 in contact with the shaft screw portion 9) mainly contains titanium, and the shaft screw portion 9 (or the portion of the shaft screw portion 9 in contact with the shaft core portion 8) mainly contains carbon fiber reinforced plastic.

[0028] FIG. 8 is a diagram showing the results of the torsional test of the bone screw of Comparative Example 2 and the bone screw of the present embodiment. As shown in FIG. 8, in the case of the bone screw of Comparative Example 2 (the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 0.29 μm to 0.38 μm), the average torsional strength was 4.6 Nm.

[0029] In contrast, in the case of Example 4 of the present embodiment (the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 0.44 μm to 0.64 μm), the average torsional strength was 8.628 Nm. Further, in the case of Example 5 of the present embodiment (the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 1.11 μm to 1.22 μm), the average torsional strength was 8.912 Nm. Furthermore, in the case of Example 6 of the present embodiment (the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 1.22 μm to 1.68 μm), the average torsional strength was 8.956 Nm.

[0030] As a result, when the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 0.4 μm or more, sufficient torsional strength can be obtained as compared with Comparative Example 2. Preferably, the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 0.4 μm to 1.7 μm. More preferably, the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 1.1 μm to 1.7 μm. Even more preferably, the arithmetic surface roughness Ra of the shaft core portion 8 in contact with the shaft screw portion 9 is 1.2 μm to 1.7 μm.

[0031] Considering both the bending / extension moment test (FIG. 6) and the torsional test (FIG. 8) of the bone screw of the above-described present embodiment, when the second end portion 3 of the bone screw and the shaft core portion 8 are integrally or fixedly formed, the second end portion 3 and the shaft core portion 8 can be surface-treated simultaneously to reduce the man-hour and improve the production efficiency. Therefore, it is preferable to match the arithmetic surface roughness Ra of the second end portion 3 and the shaft core portion 8 of the bone screw within an appropriate range.

[0032] Therefore, the arithmetic surface roughness Ra of the second end portion 3 and the shaft core portion 8 of the bone screw is preferably 0.4 μm to 0.7 μm or 1.2 μm to 1.7 μm. Further, the arithmetic surface roughness Ra of the second end portion 3 and the shaft core portion 8 of the bone screw is preferably 0.4 μm to 0.7 μm.

[0033] As a result, by simultaneously performing surface treatment on the second end portion 3 of the bone screw and the shaft core portion 8, the production efficiency can be increased, and sufficient bending strength and torsional strength can be obtained.

[0034] As described above, the embodiments according to the present invention have been described. However, the present invention is not limited to these, and can be changed and modified within the scope described in the claims.

[0035] For example, in the step of performing surface treatment, in addition to the blasting treatment, etching, laser treatment, mechanical processing (such as milling, needle processing, and sanding), polishing treatment (such as shot peening), thermal spraying, and electrochemical processing (such as anodizing) may be used.

Industrial Applicability

[0036] The present invention is useful as a bone screw in which a sliding portion, a fastening portion, or a contact surface between different materials or components does not easily slide or break.

Explanation of Reference Numerals

[0037] 1 Shaft portion 2 First end portion 3 Second end portion 4 Thread portion 5 Head 6 Fixing portion 7 Contact portion 8 Shaft core portion 9 Shaft thread portion 10 Through hole 11 Recessed portion 12 Sliding portion 13 Female screw 100 Bone screw

Claims

1. a shaft portion, a threaded portion spirally located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, a first end portion located at an end portion of the shaft portion in the insertion direction, a second end portion located at an end portion of the shaft portion in the removal direction, a head portion positioned so as to include the second end portion, and a fixing portion attached to the head portion and capable of fixing a rod portion to the head portion, wherein at least one of the arithmetic surface roughness Ra of the second end portion, the sliding portion of the head portion slidable with respect to the second end portion, and the fixing portion is 0.4 μm to 1.7 μm. A bone screw characterized by this.

2. a shaft portion, a threaded portion spirally located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, a first end portion located at an end portion of the shaft portion in the insertion direction, a second end portion located at an end portion of the shaft portion in the removal direction, wherein the shaft portion includes a shaft core portion including the second end portion, and a shaft threaded portion located on the outer peripheral portion of the shaft core portion and including the threaded portion, wherein the arithmetic surface roughness Ra of the shaft core portion in contact with the shaft threaded portion is 0.4 μm to 1.7 μm. A bone screw characterized by this.

3. a shaft portion, a threaded portion spirally located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, a first end portion located at an end portion of the shaft portion in the insertion direction, a second end portion located at an end portion of the shaft portion in the removal direction, and a contact portion that contacts the second end portion, wherein the arithmetic surface roughness Ra of the contact portion is 0.4 μm to 1.7 μm. A bone screw characterized by this.

4. The bone screw according to any one of Claims 1 to 3, wherein the threaded portion contains a reinforcing plastic.

5. The bone screw according to Claim 4, wherein the reinforcing plastic is at least one of carbon fiber reinforced plastic, glass fiber reinforced plastic, carbon fiber reinforced plastic, boron fiber reinforced plastic, aramid fiber reinforced plastic, kevlon fiber reinforced plastic, dyneema fiber reinforced plastic, and zylon fiber reinforced plastic.

6. The bone screw according to any one of Claims 1 to 3, wherein the second end portion contains at least one of stainless steel, titanium, iron, nickel, cobalt, and cemented carbide.

7. a shaft portion, A screw portion that is helically located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, A first end portion located at an end portion of the shaft portion in the insertion direction, A second end portion located at an end portion of the shaft portion in the removal direction, A head portion positioned so as to include the second end portion, In a bone screw including a fixing portion that is attached to the head portion and can fix a rod portion to the head portion, A method for manufacturing a bone screw, comprising the step of performing surface processing with an arithmetic surface roughness Ra of 0.4 μm to 1.7 μm on at least one surface of the second end portion, the sliding portion of the head portion slidable with respect to the second end portion, and the fixing portion.

8. A shaft portion, A screw portion that is helically located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, A first end portion located at an end portion of the shaft portion in the insertion direction, A second end portion located at an end portion of the shaft portion in the removal direction, and The shaft portion is A shaft core portion including the second end portion, In a bone screw including a shaft screw portion located on the outer peripheral portion of the shaft core portion and including the screw portion, A method for manufacturing a bone screw, comprising the step of performing surface processing with an arithmetic surface roughness Ra of 0.4 μm to 1.7 μm on the surface of the shaft core portion in contact with the shaft screw portion.

9. A shaft portion, A screw portion that is helically located in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion, A first end portion located at an end portion of the shaft portion in the insertion direction, A second end portion located at an end portion of the shaft portion in the removal direction, In a bone screw including a contact portion that contacts the second end portion, A method for manufacturing a bone screw, comprising the step of performing surface processing with an arithmetic surface roughness Ra of 0.4 μm to 1.7 μm on the surface of the contact portion.

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