Bone screw

Abstract

Provided is a bone screw having sufficient strength, the bone screw (1) containing reinforcing fibers (100) and being provided with: a shaft part (2); a tip section (3) positioned at the end of the shaft section in the insertion direction; a head part (4) positioned at the end of the shaft part in the extraction direction; and a screw thread (5) positioned in a spiral shape in the axial direction of the shaft portion on the outer peripheral portion of the shaft portion. The reinforcing fibers are configured so as to be disposed at a position extending in the axial direction of the shaft portion in the shaft portion.

Description

Technical Field

[0001] The present invention relates to a bone screw capable of being fixed to a bone of an animal. Background Art

[0002] In order to fix bones of animals (particularly humans) in surgeries in the field of neurosurgery and the like, bone screws including a tip portion that is inserted into the bone have been developed (see Patent Document 1).

[0003] Conventionally, bone screws that are substantially entirely made of metal (stainless steel, etc.) or PEEK (registered trademark) have been proposed in order to maintain strength for bone fixation.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 5443398

[0007] However, bone screws that are almost entirely made of metal (stainless steel, etc.) cause artifacts when medical images are captured, and become obstacles when performing surgery while checking medical images. In addition, PEEK (registered trademark) may have insufficient strength. Summary of the invention

[0008] The bone screw of the present invention includes reinforcing fibers and comprises: a shaft; a front end portion, the front end portion being located at the end of the shaft portion in the insertion direction; a head portion, the head portion being located at the end of the shaft portion in the extraction direction; and a thread, the thread being located spirally on the outer periphery of the shaft portion along the axial direction of the shaft portion, the reinforcing fibers being arranged at a position extending along the axial direction of the shaft portion in the shaft portion.

[0009] Advantageous Effects: According to the present invention, a bone screw having sufficient strength can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 1 and 2 are a side view and a cross-sectional view of the bone screw according to this embodiment.

[0011] Figure 2 It is a cross-sectional view of the shaft and threads of the bone screw according to the present embodiment.

[0012] Figure 3 This is a diagram showing that the angle of the thread of the present embodiment increases toward the insertion direction, and the increasing range is between 60 degrees and 80 degrees.

[0013] Figure 4 (a) is a diagram showing the head of the bone screw according to the present embodiment. Figure 4 (b) is a cross-sectional view of the bone screw taken along line BB according to the present embodiment.

[0014] Figure 5 It is a perspective view of the bone screw according to this embodiment.

[0015] Figure 6 It is a perspective view of the bone screw according to this embodiment.

[0016] Figure 7 It is a cross-sectional view taken along line CC of the bone screw according to the present embodiment.

[0017] Figure 8 It is a diagram showing examples of the types of threads of the bone screw according to the present embodiment.

[0018] Fig. 9 It is a diagram showing another example of the type of thread of the bone screw according to the present embodiment.

[0019] Fig.10 This is a diagram showing the bone screw of this embodiment housed in a housing, fixed by a nut in the housing and connected by a rod.

[0020] Fig.11 This is a CT image (medical image) taken when the bone screw 1 is screwed into the bone of an animal.

[0021] Fig.12 This table is obtained by evaluating the artifacts of bone screws in medical images captured according to the tantalum content.

[0022] In the figure: 1, bone screw; 2, shaft; 3, front end; 4, head; 5, thread; 6, shell; 7, rod; 20, hole; 21, shaft recess; 22, cut-off portion; 40, recess; 41, head protrusion; 41-1, polygonal portion; 100, reinforcing fiber. DETAILED DESCRIPTION

[0023] The bone screw according to this embodiment will be described using the drawings. Figure 1 1 and 2 are a side view and a cross-sectional view of the bone screw according to this embodiment. Figure 2 It is a cross-sectional view of the shaft and threads of the bone screw according to the present embodiment.

[0024] like Figure 1 As shown in (a) in the figure, the bone screw 1 of this embodiment includes reinforcing fibers and comprises: a shaft 2; a front end 3, the front end 3 is located at the end of the shaft 2 in the insertion direction; a head 4, the head 4 is located at the end of the shaft 2 in the removal direction; and a thread 5, the thread 5 is located spirally on the outer periphery of the shaft 2 along the axial direction of the shaft 2.

[0025] Figure 1 (b) in the Figure 1 The cross-sectional view of AA in (a). Figure 1As shown in FIG. 2( b ), the reinforcing fibers 100 are arranged at positions extending in the axial direction of the shaft portion 2 in the shaft portion 2 . Figure 1 (c) in the formula is Figure 1 The cross section of the thread 5 in (b) is enlarged to obtain FIG. Figure 1 As shown in (c) in FIG. 8 , the reinforcing fiber 100 is bent in the thread 5 .

[0026] Although not shown, the reinforcing fiber 100 is arranged at a position extending in the same direction as the spiral direction of the thread 5 in the thread 5. The reinforcing fiber 100 is arranged at a position extending along the spiral direction of the thread 5.

[0027] Although not shown, the reinforcing fiber 100 is spirally wound around at least one of the shaft portion 2 and the screw thread 5 in the axial direction.

[0028] When the bone screw is injection molded using the reinforcing fiber 100, a mixed composition formed by mixing the reinforcing fiber 100 (e.g., 1 mm carbon fiber) and a resin (e.g., vinyl ester) is injected into a mold of the bone screw 1 from the head side of the bone screw 1 to the insertion direction of the bone screw 1. In this case, when the mixed composition is composed, the reinforcing fiber 100 is mixed into the resin in a manner that the reinforcing fiber 100 is arranged in a prescribed direction. For example, the reinforcing fiber 100 is mixed into the resin in a manner that the reinforcing fiber 100 is arranged in the axial direction of the bone screw 1. Alternatively, the reinforcing fiber 100 is mixed into the resin in a manner that the reinforcing fiber 100 is arranged in a position extending at a prescribed angle relative to the axial direction of the bone screw 1. Alternatively, the reinforcing fiber 100 is mixed into the resin in a manner that the reinforcing fiber 100 is arranged in the spiral direction of the thread 5 of the bone screw 1. The resin includes at least one of a thermosetting resin and a thermoplastic resin. For example, the resin is selected from epoxy resins, phenol resins, and unsaturated polyester resins.

[0029] As described above, by injecting the mixed composition in which the reinforcing fiber 100 is mixed at a predetermined position into the mold of the bone screw 1, the reinforcing fiber 100 is arranged at a position extending in the axial direction of the shaft portion 2, or the reinforcing fiber 100 is bent in the thread 5, or is arranged at a position extending in the same direction as the spiral direction of the thread 5, or is arranged at a position spirally wound around the axial direction in at least one of the shaft portion 2 and the thread 5.

[0030] In the molded bone screw 1 , the reinforcing fibers 100 are appropriately arranged in a predetermined direction, thereby enhancing at least one of the compressive strength, tensile strength, shear strength, torsional strength, and hardness of the bone screw 1 .

[0031] Preferably, the reinforcing fiber 100 is at least one of carbon fiber, aramid fiber, and glass fiber, but is not limited thereto.

[0032] Figure 2 It is a cross-sectional view of the bone screw 1 obtained by injection-molding a mixed composition of reinforcing fiber 100 and resin into a mold of the bone screw 1. The angle of the thread 5 is 60 degrees or more and 80 degrees or less.

[0033] As a result of the inventor's intensive research, the inventor found the angle of the thread 5 for properly molding the thread 5 of the bone screw 1 by injection molding the mixed composition of the reinforcing fiber 100 and the resin into the mold of the bone screw 1. When the angle of the thread portion in the mold is too small, the mixed composition cannot be sufficiently injected into the thread portion, and the thread 5 cannot be properly molded. On the other hand, when the angle of the thread portion in the mold is too large, the fixing strength of the bone screw 1 to the bone becomes insufficient, and it is easy to detach from the bone.

[0034] exist Figure 2 In (a) and (b), the angles of thread 5 are 120 degrees and 100 degrees respectively. Figure 2 As shown in (a) and (b), the mixed composition is sufficiently injected into the threaded portion, but the angle of the threaded portion is too large and is easily separated from the bone.

[0035] Figure 2 The angles of the threads 5 in (c) and (d) are 80 degrees and 60 degrees respectively. Figure 2 As shown in (c) and (d), the mixed composition is fully injected into the threaded portion, the angle of the threaded portion is not too large, and it is not easy to detach from the bone. Therefore, the angle of the thread 5 is preferably greater than 60 degrees and less than 80 degrees. Preferably, the angle of the thread 5 is greater than 60 degrees and less than 75 degrees. More preferably, the angle of the thread 5 is greater than 65 degrees and less than 70 degrees.

[0036] Figure 3 1 is a diagram showing that the angle of the thread 5 increases as it moves toward the insertion direction of the bone screw 1, and the increase range is between 60 degrees and 80 degrees. Figure 3As shown, the angles θ1 to θ3 of the thread 5 increase as they are directed toward the insertion direction of the bone screw 1 (θ1<θ2<θ3), and the range of increase is between 60 and 80 degrees. Preferably, the angle of the thread 5 increases as it is directed toward the insertion direction of the bone screw 1, and the range of increase is between 60 and 75 degrees. More preferably, the angle of the thread 5 increases as it is directed toward the insertion direction of the bone screw 1, and the range of increase is between 65 and 75 degrees. In addition, the angle of the thread 5 may gradually increase within the above range as it is directed toward the insertion direction of the bone screw 1, or it may increase intermittently, and the part of the thread 5 may gradually increase within the above range as it is directed toward the insertion direction of the bone screw 1. In addition, the heights h1 to h3 of the thread 5 may also be lower as they are directed toward the insertion direction of the bone screw 1. The heights h1 to h3 of the thread 5 may also change according to the angle of the thread 5.

[0037] Figure 4 (a) is a diagram showing the head 4 of the bone screw 1. Figure 4 (b) is a cross-sectional view of the bone screw 1 taken along line BB. Figure 4 As shown in (b) in the figure, the head 4 has a head convex portion 41 in the insertion direction, and the head convex portion 41 is engaged with the shaft recess 21 of the shaft portion 2. In addition, at least one of the compressive strength, tensile strength, shear strength, torsional strength, and hardness of the joint portion (head convex portion 41) between the head 4 and the shaft portion 2 is higher than that of the shaft portion 2. For example, the head convex portion 41 includes at least one of a metal (for example, titanium, stainless steel, iron, nickel, cobalt, and superhard alloy), a ceramic (for example, zirconium oxide), a cermet, and a reinforcing fiber of a different composition from the reinforcing fiber 100. Here, for the reinforcing fiber of a different composition from the reinforcing fiber 100, as long as at least one of the mixing ratio, length, shape, and configuration of the reinforcing fiber 100 is different, the same type of reinforcing fiber as the reinforcing fiber 100 can also be used. In addition, as long as the reinforcing fiber of a different composition from the reinforcing fiber 100 is mixed with other reinforcing fibers, the same type of reinforcing fiber as the reinforcing fiber 100 can also be used.

[0038] Furthermore, even without depending on the head protrusion 41 and the shaft recess 21 , the joint between the head 4 and the shaft 2 preferably has at least one of higher compressive strength, tensile strength, shear strength, torsional strength, and hardness than the shaft 2 .

[0039] For example, although not shown in the figure, the shaft portion 2 may include a shaft projection in the extraction direction, and the shaft projection may be fitted into the head recess of the head portion 4. Figure 4In the embodiment, there is a convex portion on the head portion 4 and a concave portion on the shaft portion 2. Conversely, there may be a convex portion on the shaft portion 2 and a concave portion on the head portion 4. In addition, although not shown in the figure, there is a core portion, the core portion includes at least one of a metal (for example, titanium, stainless steel, iron, nickel, cobalt, and superhard alloy), a ceramic (for example, zirconium oxide), a metal ceramic, and a reinforcing fiber with a composition different from that of the reinforcing fiber 100, and the core portion is engaged with the head concave portion of the head portion 4 and the shaft concave portion 21 of the shaft portion 2. In other words, there are concave portions on the head portion 4 and the shaft portion 2, and the concave portions are connected by the core portion. In addition to this, the joint between the head portion 4 and the shaft portion 2 may have at least one of compressive strength, tensile strength, shear strength, torsional strength, and hardness that is higher than that of the shaft portion 2. In this case, as Figure 4 As shown, the joint portion may have a boundary surface between the head 4 and the shaft 2 based on different materials, or may be the same component (for example, the same reinforcing fiber) without a clear boundary surface. For example, since at least one of the mixing ratio, length, shape, and configuration of the same material (for example, the same reinforcing fiber) is continuously different, there is no clear boundary surface, but at least one of the compressive strength, tensile strength, shear strength, torsional strength, and hardness between the head 4 and the shaft 2 is higher than that of the shaft 2.

[0040] Thus, at least one of compressive strength, tensile strength, shear strength, torsional strength, and hardness can be enhanced in the portion between the head 4 and the shaft 2 to which a load is applied, thereby preventing the bone screw 1 from breaking or deforming.

[0041] Figure 5 is a stereoscopic view of the bone screw 1 . Figure 6 yes Figure 5 Perspective view of the bone screw 1. Figure 7 yes Figure 5 Cross-sectional view of CC of bone screw 1.

[0042] like Figure 5 to Figure 7 As shown, the head portion 4 includes a head protrusion 41 in the insertion direction, and the head protrusion 41 is fitted into the shaft recess 21 of the shaft portion 2 .

[0043] In addition, if Figure 6 As shown, the head convex portion 41 has a polygonal portion 41-1 whose cross section is orthogonal to the axial direction. The cross section of the polygonal portion 41-1 orthogonal to the axial direction is approximately quadrilateral and is chamfered. Preferably, the polygonal portion 41-1 is approximately triangular or even approximately hexagonal. Since the cross section of the head convex portion 41 orthogonal to the axial direction is polygonal, when a torque is generated in the rotation direction of the bone screw 1, the head convex portion 41 can be prevented from sliding or detaching from the shaft recess 21 in the rotation direction.

[0044] like Figure 7As shown, the head convex portion 41 has a cutout portion 22. The cutout portion 22 may include a rotation surface in the rotation direction of the bone screw 1, or may be in a flange shape. Since the head convex portion 41 has the cutout portion 22, it is possible to prevent the head convex portion 41 from sliding or detaching from the shaft recess 21 in the axial direction. In addition, although not shown, the head convex portion 41 may also have a thread located in the spiral direction opposite to the thread 5.

[0045] Similarly, the shaft recess 21 may include at least one of a polygonal portion having a polygonal cross section perpendicular to the axial direction, a thread located in a spiral direction opposite to the thread 5 , and a cutout portion.

[0046] In addition, as described above, when the convex portion of the shaft portion 2 is engaged with the concave portion of the head portion 4, or when the core portion is engaged with the head concave portion of the head portion 4 and the shaft concave portion of the shaft portion 2, the convex portion of the shaft portion 2, the concave portion of the head portion 4, and the core portion may also have: a polygonal portion having a polygonal cross-section orthogonal to the axial direction or a thread located in a spiral direction opposite to the thread 5, and at least one of a cut-off portion.

[0047] Furthermore, the core portion may include reinforcing fibers arranged at least one of a position extending in the axial direction and a position spirally wound around the circumference in the axial direction.

[0048] like Figure 6 and Figure 7 As shown, the bone screw 1 has a hole 20, and the hole 20 can penetrate the inside of the bone screw 1 in the axial direction. Figure 6 and Figure 7 In the embodiment, the hole 20 penetrates the interior of the bone screw 1 from the recess 40 of the head 4 to the distal end 3 .

[0049] The hole portion 20 is surrounded by a material including at least one of metal (e.g., titanium, stainless steel, iron, nickel, cobalt, and superhard alloy), ceramic (e.g., zirconium oxide), cermet, and reinforcing fibers of a composition different from that of the reinforcing fibers 100. Here, the reinforcing fibers of a composition different from that of the reinforcing fibers 100 may be different in at least one of the mixing ratio, length, shape, and arrangement of the reinforcing fibers 100, and the same type of reinforcing fibers as the reinforcing fibers 100 may be used. In addition, the reinforcing fibers of a composition different from that of the reinforcing fibers 100 may be mixed with other reinforcing fibers, and the same type of reinforcing fibers as the reinforcing fibers 100 may be used.

[0050] When the hole 20 surrounded by at least one of a metal (e.g., titanium, stainless steel, iron, nickel, cobalt, and superhard alloy), a ceramic (e.g., zirconium oxide), a metal ceramic, and reinforcing fibers having a composition different from that of the reinforcing fibers 100 is captured with a higher brightness than the peripheral portion of the hole 20 in a medical image such as a CT image, the hole 20 functions as a guide for grasping the position and direction of the bone screw 1 in the medical image.

[0051] In addition, at least a portion of the hole portion 20 may be surrounded by a material comprising at least one of metal (e.g., titanium, stainless steel, iron, nickel, cobalt, and superhard alloy), ceramic (e.g., zirconia), metal ceramic, and reinforcing fibers having a composition different from that of the reinforcing fibers 100.

[0052] Figure 8 1 is a diagram showing an example of the type of thread 5 of the bone screw 1. Figure 8 In the bone screw 1 of (a), the side angle of the thread 5 on the insertion direction is larger than the side angle of the thread 5 on the extraction direction. Figure 8 In the bone screw 1 of (b), the shaft 2 becomes thinner toward the insertion direction, and the valley diameter of the thread 5 becomes thinner and smaller toward the insertion direction. Figure 8 In the bone screw 1 of (b), the outer diameter of the thread 5 is substantially constant. Figure 8 In the bone screw 1 of (b), the height of the thread 5 increases toward the insertion direction. Figure 8 In the bone screw 1 of (b), the axial length of the top of the thread 5 decreases toward the insertion direction.

[0053] With such a shape of the thread 5 , the bone screw 1 can be securely fixed to the bone and can be easily removed from the bone.

[0054] Fig. 9 FIG. 1 is a diagram showing another example of the type of the thread 5 of the bone screw 1 . Fig. 9 is a cross-sectional view of the thread 5 of the bone screw 1. Fig. 9 In the bone screw 1 of (a), the side angle α of the thread 5 in the insertion direction is larger than the side angle β of the thread 5 in the extraction direction. Fig. 9 In the bone screw 1 of (b), the heights H1, H2, and H3 of the threads 5 (threads 5-1, 5-2, and 5-3) increase as they go toward the insertion direction. Fig. 9 In the bone screw 1 of (b), the axial lengths L1, L2, and L3 of the top of the thread 5 (threads 5-1, 5-2, and 5-3) decrease as they go toward the insertion direction. In addition, the valley diameter of the thread 5 and the angle γ of the thread 5 are substantially constant. Fig. 9In the bone screw 1 of (c), the shaft 2 becomes thinner as it moves toward the insertion direction, and the valley diameter of the thread 5 (threads 5-4, 5-5, 5-6) becomes thinner and smaller as it moves toward the insertion direction. On the other hand, the outer diameter of the thread 5 and the angle γ of the thread 5 are approximately constant. The heights H4, H5, and H6 of the thread 5 (threads 5-4, 5-5, 5-6) become larger as it moves toward the insertion direction. Fig. 9 In the bone screw 1 of (c), the axial lengths L4, L5, and L6 of the tops of the threads 5 (threads 5-4, 5-5, and 5-6) decrease toward the insertion direction.

[0055] With such a shape of the thread 5 , the bone screw 1 can be securely fixed to the bone and can be easily removed from the bone.

[0056] Fig.10 The figure shows that the bone screw 1 accommodated in the housing 6 is fixed in the housing 6 by a nut (not shown) and connected by a rod 7 .

[0057] like Fig.10 As shown in (a), the thread 5-7 of the bone screw 1 has Figure 8 The thread 5 in (b) has the same shape. Fig.10 As shown in (b) in FIG. 1 , the pitch of the thread 5 of the bone screw 1 increases toward the insertion direction.

[0058] With such a shape of the thread 5 , the bone screw 1 can be securely fixed to the bone and can be easily removed from the bone.

[0059] Fig.11 This is a CT image (medical image) taken when the bone screw 11 is screwed into the bone of an animal (pig). Fig.11 In the invention, the bone screw 1 includes a mixture in which 0 wt % or more and 30 wt % or less (0 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %) of tantalum is mixed into a composition including reinforcing fibers.

[0060] Fig.12 It is based on Fig.11 The table was obtained by evaluating the artifacts of the bone screw 1 in the CT image (medical image) taken by measuring the tantalum content.

[0061] like Fig.11 and 12 As shown in the figure, the higher the content of tantalum in the mixture, the stronger the artifact of the bone screw 1 in the CT image (medical image). When the content of tantalum in the mixture is 25 wt % and 30 wt %, the evaluation of the artifact is A -, is acceptable. It can be predicted that other metals (titanium, stainless steel, iron, nickel, cobalt, and superhard alloys, etc.) will also obtain the same results. Therefore, the bone screw 1 (at least one of the shaft 2, the front end 3, the head 4, and the thread 5) comprises: a mixture of metals (tantalum, titanium, stainless steel, iron, nickel, cobalt, and superhard alloys, etc.) exceeding 0 wt% and below 30 wt% (preferably 10 wt% to 20 wt%, more preferably 10 wt% to 15 wt%) mixed in a composition containing reinforcing fibers 100.

[0062] While artifacts are reduced, when the polygonal portion 1 (at least one of the shaft 2, the distal end 3, the head 4, and the thread 5) is captured with a higher brightness than the peripheral portion in the medical image, the polygonal portion 1 (at least one of the shaft 2, the distal end 3, the head 4, and the thread 5) acts as a guide for grasping the position and direction of the bone screw 1 in the medical image.

[0063] In addition, the tip portion 3 may include a material that is photographed with a higher brightness in the medical image than the reinforcing fiber 100. For example, the tip portion 3 includes at least one of metal (e.g., titanium, stainless steel, iron, nickel, cobalt, and superhard alloy), ceramic (e.g., zirconium oxide), cermet, and reinforcing fibers having a composition different from that of the reinforcing fiber 100. When such a tip portion 3 is photographed with a higher brightness than the peripheral portion of the tip portion 3 in a medical image such as a CT image, the tip portion 3 functions as a guide for grasping the position and direction of the bone screw 1 in the medical image.

[0064] As mentioned above, although the embodiment which concerns on this invention was demonstrated, this invention is not limited to this, and it can change and modify within the scope of the claims.

[0065] Industrial Applicability

[0066] The present invention is useful as a bone screw having sufficient strength.

Claims

1. A bone screw, characterized in that: The bone screw comprises reinforcing fibers and has: Shaft; a front end portion, the front end portion being located at an end portion of the shaft portion in an insertion direction; a head portion, the head portion being located at an end portion of the shaft portion in a pulling-out direction; and a thread, the thread being spirally located on the outer periphery of the shaft portion along the axial direction of the shaft portion, The reinforcing fibers are arranged at positions in the shaft portion extending in the axial direction of the shaft portion.

2. The bone screw according to claim 1, characterized in that A portion having at least one of compressive strength, tensile strength, shear strength, torsional strength, and hardness higher than that of the shaft portion exists between the head portion and the shaft portion.

3. The bone screw according to claim 1 or 2, characterized in that: The head portion has a head convex portion in the insertion direction, The head protrusion is fitted into the shaft recess of the shaft portion.

4. The bone screw according to claim 3, characterized in that: At least one of the head protrusion and the shaft recess includes at least one of a polygonal portion having a polygonal cross section perpendicular to the axial direction, a thread located in a spiral direction opposite to the thread, and a cutout portion.

5. The bone screw according to claim 3, characterized in that: The head protrusion includes at least one of metal, ceramic, metal ceramic, and reinforcing fiber having a composition different from that of the reinforcing fiber.

6. The bone screw according to claim 1 or 2, characterized in that: The shaft portion has a shaft protrusion in the extraction direction, The shaft protrusion is fitted into the head recess of the head.

7. The bone screw according to claim 6, characterized in that: At least one of the shaft protrusion and the head recess includes at least one of a polygonal portion having a polygonal cross section perpendicular to the axial direction, a thread located in a spiral direction opposite to the thread, and a cutout portion.

8. The bone screw according to claim 1 or 2, characterized in that: The bone screw comprises a core portion, wherein the core portion comprises at least one of metal, ceramic, cermet, and reinforcing fiber having a composition different from that of the reinforcing fiber. The core portion is fitted into the head recess of the head portion and the shaft recess of the shaft portion.

9. The bone screw according to claim 8, characterized in that The core portion includes the reinforcing fibers, and the reinforcing fibers are arranged at least one of a position extending in the axial direction and a position spirally wound around the axial direction.

10. The bone screw according to claim 1 or 2, characterized in that: The bone screw includes a hole portion, and the hole portion can penetrate the interior of the bone screw in the axial direction. The hole portion is surrounded by a material including at least one of metal, ceramic, cermet, and reinforcing fibers having a composition different from that of the reinforcing fibers.

11. The bone screw according to claim 1 or 2, characterized in that: The front end portion includes a material that is captured with a higher brightness than the reinforcing fibers in a medical image.

12. The bone screw according to claim 1 or 2, characterized in that: The reinforcing fiber extends so as to be arranged at a position spirally wound around the axial direction in at least one of the shaft portion and the thread.

13. The bone screw according to claim 1 or 2, characterized in that: The reinforcing fibers are arranged in the thread at positions extending in the same direction as a helical direction of the thread.

14. The bone screw according to claim 1 or 2, characterized in that: The reinforcing fibers are bent in the threads.

15. The bone screw according to claim 1 or 2, characterized in that: The reinforcing fiber is at least one of carbon fiber, aramid fiber, and glass fiber.

16. The bone screw according to claim 1 or 2, characterized in that: At least one of the shaft portion, the front end portion, the head portion, and the thread includes a mixture in which more than 0 wt % and 30 wt % or less of a metal is mixed in a composition including the reinforcing fiber.

17. The bone screw according to claim 1 or 2, characterized in that: The angle of the thread is greater than or equal to 60 degrees and less than or equal to 80 degrees.

18. The bone screw according to claim 1 or 2, characterized in that: The angle of the thread increases toward the insertion direction, and the increase range is between 60 degrees and 80 degrees.

19. The bone screw according to claim 1 or 2, characterized in that: A flank angle of the thread on one side in the insertion direction is greater than a flank angle of the thread on one side in the extraction direction.

20. The bone screw according to claim 1 or 2, characterized in that: The height of the thread increases toward the insertion direction.

21. The bone screw according to claim 1 or 2, characterized in that: The axial length of the top of the thread decreases toward the insertion direction.

22. The bone screw according to claim 1 or 2, characterized in that: The pitch of the threads increases toward the insertion direction.

Images