Bone fixation member, base member, and bone fixation system

Abstract

This bone fixation member is fixed to a reception hole of a base member at a discretionary inclination angle within a prescribed range, and includes: a rod part that is inserted into the reception hole; and a head part that is insertion fit into the reception hole. The outer peripheral surface of the head part includes a plurality of pressure bonding outer peripheral surface sections that can pressure bond with the inner peripheral surface of the reception hole. The plurality of pressure bonding outer peripheral surface sections are each coordinated with different positions in the direction of a virtual axis and with different pitches in the circumferential direction of said axis.

Description

Bone Fixation Member, Base Member, and Bone Fixation System

[0001] The present invention relates to a bone fixing system that allows a bone fixing member to be fixed at any inclination angle within a predetermined range relative to a base member.

[0002] In the field of biomedical engineering, internal fixation devices, or so-called implant applications, are known for use in fracture treatment. This type of treatment includes treatment of fractures of the distal ends of bones such as the tibia, femur, and radius. Appropriate treatment of a fracture requires returning each broken bone to its normal position and fixing it in the desired position using a bone plate as a base member and a bone screw with a head-shaped portion.

[0003] For example, when treating a fracture of the distal end of the radius, the head plate and stem plate of the bone plate are abutted against the distal end and stem of the radius so as to straddle the fracture line, and bone screws are embedded into the radius through the through holes in the bone plate, thereby fixing the bone fragments of the distal end to the stem, and the individual fractured bones are reduced to their normal positions and fixed.

[0004] Since bone shapes and fracture conditions vary widely, in order to appropriately fix the bone fracture site according to the fracture condition, it is desirable that the bone screw be able to be fixed at an appropriate inclination angle relative to the bone plate according to the individual condition. One such fixation technique is, for example, forming a special female thread in the bone plate. Specifically, a through hole for passing the bone screw is formed in the bone plate, and a female thread is formed on the inner surface of the through hole to threadably engage with the male thread provided on the head of the bone screw.

[0005] The inner peripheral surface of the through hole is formed with multiple axially extending grooves, and the female thread is divided in the circumferential direction. This allows the male thread of the head of the bone screw to engage with the female thread of the through hole in the bone plate even when the helices are misaligned, allowing the bone screw to be fixed at a predetermined inclination angle, i.e., polyaxially, to the bone plate (see, for example, Patent Documents 1 and 2).

[0006] Special Publication No. 2010-536427 Publication Patent No. 4999327 Publication

[0007] Because external forces such as muscle force act on the distal end of the radius, if the bone screw loosens or shifts after the bone plate is fixed with the bone screw installed at the fractured portion of the distal end of the radius, the bone fragment at the fractured portion is likely to fall toward the shaft of the radius, and if this falls in place, there is a risk that the fracture will not heal normally.

[0008] For example, as described in Patent Document 1, when the through-hole of the bone plate and the head of the bone screw are formed spherically and a screw is formed on each spherical surface, the bone screw is a multi-axial type and can be embedded in an appropriate position at a predetermined inclination angle. However, since the bonding strength between the screws on each spherical surface is relatively weak, there is a risk that the fixed state between the bone screw and the bone plate will be released if excessive force is applied to the bone.

[0009] Furthermore, as in Patent Documents 1 and 2, when the female threads in the through-hole of the bone plate are formed intermittently in the circumferential direction, the bone screw can be tilted, but the tilt angle is limited to the points where the screws can mesh with each other, making it difficult to fix at a point that deviates from the fixed tilt angle. In such cases, the fixation force at the fixed tilt angle of the bone screw is very weak, and the bone screw is prone to loosening.

[0010] The present invention was made in consideration of the above-mentioned problems through intensive research by the inventor, and aims to provide a bone fixation member and a bone fixation system using the bone fixation member, which can be reliably fixed and released at any inclination angle within a predetermined range relative to a base member with a simple structure and can be used repeatedly.

[0011] The bone fixation member of the present invention is a bone fixation member that is fixed at any inclination angle within a predetermined range in a receiving hole of a base member, and has a rod portion that is inserted into the receiving hole and a head portion that is inserted and fitted into the receiving hole, and the outer surface of the head portion has a plurality of pressure-contact outer surface portions that can be pressed against the inner surface of the receiving hole, and the plurality of pressure-contact outer surface portions are each oriented at different positions in a virtual axial direction and at different phases in the circumferential direction of the axis.

[0012] In the bone fixation member of the present invention, the plurality of pressure-welding outer peripheral surface portions are arranged at equal intervals in the circumferential direction of the imaginary axis.

[0013] In the bone fixation member of the present invention, the plurality of pressure-welding outer peripheral surface portions are arranged at equal intervals in the axial direction of the virtual axis.

[0014] In the bone fixing member of the present invention, the plurality of press-contact outer peripheral surfaces are arranged on an imaginary spiral at positions moved in the axial and circumferential directions.

[0015] The bone fixing member of the present invention has a generally tack-like shape as a whole.

[0016] The bone fixing member of the present invention has a male thread portion on the rod portion, and has a generally rivet-like spiral shape as a whole.

[0017] The base member of the present invention is a base member that fixes a bone fixation member at any inclination angle within a predetermined range, and has a receiving hole for inserting the bone fixation member, and the receiving hole has an entrance side opening, an inner opening, and an exit side opening for inserting the bone fixation member, the exit side opening has a smaller diameter than the entrance side opening, and has a guide portion whose diameter decreases from the entrance side opening toward the inner opening, and the inner surface from the inner opening to the exit side opening has a curved surface, and the head of the bone fixation member can be inserted into the curved surface.

[0018] The base member of the present invention is configured such that the curved surface has a maximum inner diameter midway between the inner opening and the outlet opening relative to the inner diameter of the inner opening and the inner diameter of the outlet opening.

[0019] In the base member of the present invention, the curved surfaces are formed such that the curvature of the curved surface close to the inner opening and the curvature of the curved surface close to the outlet opening are different from each other.

[0020] The base member of the present invention has a cylindrical parallel surface between the curved surface and the outlet opening.

[0021] In the base member of the present invention, the receiving hole is rotationally symmetrical by 360 degrees about the central axis.

[0022] The bone fixing system of the present invention includes the base member having a receiving portion through which the bone fixing member is inserted, and the bone fixing member can be fixed at any inclination angle within a predetermined range relative to the base member.

[0023] According to the present invention, the bone fixing member can be reliably fixed to the base member at any tilt angle within a predetermined range and can be easily released with a simple structure, allowing repeated use.

[0024] FIG. 1 is a perspective view showing a bone fixing system according to a first embodiment. FIG. 1 shows (a) a plan view, (b) a side view, (c) a bottom view, and (d) a front view of a bone plate. FIG. 2 shows a cross-sectional view of the through-hole in the bone plate of FIG. 2. FIG. 1 shows (a) a perspective view, (b) a plan view, and (c) a side view of a bone screw. FIG. 1 shows (a) an enlarged plan view, (b) a side view seen in the α direction, (c) a side view seen in the β direction, and (d) a side view seen in the γ direction of the head of the bone screw. FIG. 2 shows (a) a state before insertion, (b) a state during insertion, and (c) an inserted state of the bone screw attached to the bone plate. FIG. 3 shows a state in which the bone screw is inclined with respect to the bone plate at the maximum inclination angle within a predetermined cone angle range. FIG. 4 is a schematic front view of the head and the through-hole, showing another example of the shape and arrangement of the press-fit outer peripheral surface portion. FIG. 5 is a plan view of a bone pin. FIG. 6 shows (a) a cross-sectional view (b) an enlarged cross-sectional view of part B of (a) showing another example of the through-hole.

[0025] Embodiments of the fixing mechanism of the present invention will be described below with reference to the drawings. The dimensions, materials, shapes, and relative arrangements of components described in the embodiments or shown in the drawings are merely illustrative and are not intended to limit the scope of the present invention. For example, expressions expressing a relative or unambiguous arrangement, such as "parallel," "orthogonal," "vertical," "center," "concentric," or "coaxial," not only strictly express such an arrangement, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," "uniform," and "equal density," not only express strict equality, but also express tolerances or differences or ratios to the extent that the same function is achieved. For example, expressions expressing shapes such as a triangular pyramid, cone, triangular prism, and cylinder not only express shapes such as a triangular pyramid, cone, triangular prism, and cylinder in the strict geometric sense, but also express shapes including concave and convex portions and chamfered portions to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "formed," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0026] First, the overall schematic structure of the present invention will be described below.

[0027] As shown in Figures 1 and 2, the base member, bone plate 1, is formed, for example, in a generally thin plate shape (or may be formed three-dimensionally) and is used to treat fractures of the distal end of the radius in the left hand. Bone plate 1 is formed from a single metal plate, forming a generally T-shape, with a head plate portion 1a that contacts the distal end of the radius and a stem plate portion 1b that contacts the shaft of the radius from the palmar side. Bone plate 1 is made of an appropriate material, such as pure titanium or a titanium alloy, whose elastic modulus is close to that of bone. The base member is not limited to a thin plate-like member like a bone plate, but may also be a long, block-like member, or any three-dimensional thin plate-like member conforming to the shape of the bone.

[0028] The bone plate 1 is formed with a plurality of through holes 10 that penetrate from one surface to the other and serve as receiving holes for receiving heads 2a of bone screws 2 (described later). Seven through holes 10a are formed in the head plate 1a along the distal end edge of the head plate 1a and arranged in two rows that are approximately parallel to each other, and one through hole 10b is formed in the trunk plate 1b along the longitudinal direction of the trunk plate 1b.

[0029] As shown in Figures 1 and 4, the bone screw 2 serving as a bone fixation member comprises a head 2a and a rod portion 2b. The bone screw 2 is made of an appropriate material, such as a ceramic alloy, whose hardness is equal to or harder than that of the bone plate 1. The head 2a of the bone screw 2 is formed with a hexagonal star-shaped hole 21 into which a driver is inserted on the side opposite the rod portion 2b, and a male thread portion 20 is formed on the surface of the rod portion 2b. Note that, as shown in Figure 9, a rivet-shaped bone pin having a smooth surface on the surface of the rod portion 2b without a male thread portion may also be used, as long as it can be implanted and fixed into the radius.

[0030] The bone plate 1 is fixed to the radius by first placing the bone plate 1 so that the tip edge of the head plate 1a of the bone plate 1 is aligned with the subchondral bone at the distal end of the radius and the stem plate 1b is aligned with the shaft of the radius, and then inserting the bone screw 2 into the through hole 10 at any inclination angle within a predetermined range, and inserting a driver into the hexagonal star-shaped hole 21 of the head 2 and rotating it to screw (embed) the bone screw 2 into the radius. Once the bone plate 1 is fixed to the radius, the bone screw 2 and bone plate 1 are fixed at any desired inclination angle within a predetermined cone angle range by a fixation structure described below.

[0031] Next, the detailed structures of the bone plate 1 and bone screw 2 will be described, focusing on the fixation structure.

[0032] 3, the through hole 10 of the bone plate 1 has an opening 11 serving as an inlet opening on one surface and an opening 13 serving as an outlet opening on the other surface. A tapered surface 12 is formed on the inner peripheral surface of the through hole 10 on the side of the opening 11, and a curved surface 14 is formed on the side of the opening 13. Both the opening 11 and the opening 13 can be formed as perfect circles, with the central axis O of the through hole 10 passing through the centers of both circles. In other words, the receiving hole 10 can be formed with 360-degree rotational symmetry about the central axis O.

[0033] The tapered surface 12 has a truncated cone shape with the central axis O as its centerline, and is formed so that its diameter decreases from one opening 11 to the other opening 13. The curved surface 14 has a spherical zone shape along an imaginary partial sphere whose center is on the central axis O. An inner opening 15 is formed by the intersection of the tapered surface 12 and the curved surface 14. The inner opening 15 has a perfect circle shape, and the central axis O of the through hole 10 passes through the center of the circle. The diameter of the opening 13 at one end of the curved surface 14, which is continuous with the tapered surface 12, is smaller than the diameter of the inner opening 15 at the other end.

[0034] In the through hole 10, the diameters of the opening 11, the inner opening 15, and the opening 13 have the following relationship.

[0035] Diameter of opening 11>diameter of inner opening 15>diameter of opening 13. In the embodiment, the diameter is increased from the inner opening 15 to the opening 13 and then reduced.

[0036] As shown in Figure 4, the head 2a of the bone screw 2 is provided at one end of the rod portion 2b. The head 2a has a modified spherical trapezoidal shape similar to an imaginary partial sphere (spherical trapezoidal shape) with its center line aligned with the central axis P (imaginary axis) of the rod portion 2b extending in the longitudinal direction. The head 2a is formed by combining three approximately true spheres, each partially overlapping the other. The outer peripheral surface 22 is composed of three curved surfaces 22a, 22b, and 22c, and each of the curved surfaces 22a, 22b, and 22c has a pressure-contact outer peripheral surface portion 23 (23a, 23b, and 23c) (the area indicated by diagonal lines in the figure). The maximum outer dimension of the outer peripheral surface 22 of the head 2a is slightly smaller than the inner diameter of the curved surface 14 of the through-hole 10, allowing the head 2a, when accommodated within the curved surface 14, to freely rotate within the curved surface 14.

[0037] The plurality of pressure-contact outer peripheral surfaces 23 (23a, 23b, 23c in this embodiment) are arranged at different positions in the axial direction of the rod portion 2b and at different phases in the circumferential direction of the axis. The pressure-contact outer peripheral surfaces 23 engage with the curved surface 14 that forms the inner circumferential surface of the through hole 10, thereby fixing the bone screw 2 to the bone plate 1 at any inclination angle within a predetermined range.

[0038] The head portion 2 a is configured to have a shape and size that allows it to pass through the opening 11 and the inner opening 15 but does not allow it to pass through the opening 13 .

[0039] In this embodiment, how the multiple press-fit outer peripheral surface portions 23 (23a, 23b, 23c) are arranged on the outer peripheral surface 22 (22a, 22b, 22c) of the head 2a will be described with reference to Figures 5(a) to (d).

[0040] 5(a) is an enlarged plan view of the head 2a, which shows that the angle from near the circumferential center of one press-fitted outer peripheral surface portion 23 to near the circumferential center of an adjacent press-fitted outer peripheral surface portion 23 is 120°. In other words, the press-fitted outer peripheral surface portions 23 (23a, 23b, 23c) are arranged at three locations equally spaced apart at angles of 120° in the circumferential direction around the central axis P.

[0041] Figure 5(b) is a side view of the head as viewed from the tangential direction α near the circumferential center of the press-fit outer peripheral surface portion 23a in Figure 5(a), Figure 5(c) is a side view of the head as viewed from the tangential direction β near the circumferential center of the press-fit outer peripheral surface portion 23b located at a position shifted 120° clockwise from the press-fit outer peripheral surface portion 23a in Figure 5(a), and Figure 5(d) is a side view of the head as viewed from the tangential direction γ near the circumferential center of the press-fit outer peripheral surface portion 23c located at a position shifted 120° clockwise from the press-fit outer peripheral surface portion 23b in Figure 5(a).

[0042] 5(b) to 5(d) show a horizontal line h1 passing through approximately the axial center of the press-fit outer peripheral surface portion 23a, a horizontal line h2 passing through approximately the axial center of the press-fit outer peripheral surface portion 23b, and a horizontal line h3 passing through approximately the axial center of the press-fit outer peripheral surface portion 23c. As can be seen from this, the press-fit outer peripheral surface portions 23a, 23b, and 23c are arranged so that they are sequentially shifted by a fixed amount (a predetermined pitch) from the hexagonal star-shaped hole 21 side toward the rod portion 2b side (in the drawings, they gradually descend by a fixed amount from top to bottom).

[0043] As described above, when viewing the head 2a from the side of the hexagonal star-shaped hole 21, the multiple press-fit outer peripheral surfaces 23 are arranged, so to speak, on an imaginary spiral so that as they move clockwise from the press-fit outer peripheral surface 23a (the rotation direction indicates the direction in the plan view of Figure 5(a) and will be the same hereinafter unless otherwise specified), in 120° increments, toward the press-fit outer peripheral surface portions 23b, 23c, they arrive at positions that are moved at approximately equal axial intervals toward the rod 2b side.

[0044] The procedure for fixing the bone screw 2 to the bone plate 1 at any desired inclination angle within a predetermined cone angle range will now be described.

[0045] As shown in Figure 6(a), the bone screw 2 is inclined at a desired angle relative to the bone plate 1 and set on one opening 11 side of the bone plate 1, and the rod portion 2b of the bone screw 2 is inserted from one opening 11 into the through hole 10. At this time, the bone screw 2 is guided and inserted into the through hole 10 by the tapered surface 12 serving as a guide portion of the bone plate 1.

[0046] As shown in Figure 6(b) , when the rod portion 2b of the bone screw 2 is inserted into the through hole 10, the lower part of the head portion 2a begins to be inserted from one opening 11 of the through hole 10, following the rod portion 2b. Here, because the maximum outer diameter of the outer peripheral surface 22 of the bone screw 2 is larger than the inner opening 15 of the through hole 10, the inserted head portion 2a is caught on the inner opening 15. Here, when the bone screw 2 is pushed in the insertion direction while rotating clockwise (the rotation direction indicates the direction in the plan view of Figure 5(a) , and will be the same hereinafter unless otherwise specified), the head portion 2a is inserted into the curved surface 14.

[0047] As shown in Figure 6(c) , the head 2a of the bone screw 2 is inserted into the curved surface 14, and the head 2a is rotated within the curved surface 14 to set the bone screw 2 at a desired inclination angle relative to the bone plate 1. Furthermore, when the bone screw 2 is pushed in while rotating it clockwise so that the pressure-contact outer surface portion 23 of the outer surface 22 of the head 2a is pressure-contacted with the inner surface of the curved surface 14 of the through hole 10, a state is created in which the three pressure-contact outer surface portions 23a, 23b, 23c and the curved surface 14 are engaged with each other by a pressure force, and the bone screw 2 is fixed to the bone plate 1.

[0048] This allows the bone screw 2 to be fixed at a desired inclination angle relative to the bone plate 1.

[0049] As shown in FIG. 7, the maximum inclination angle at which the bone screw 2 can be inclined at any angle relative to the bone plate 1 within a predetermined cone angle range is, for example, 15° from the central axis O of the through hole 10, and the dimensions of each part of the through hole 10 are designed to allow such inclination.

[0050] If it is desired to change the fixed position of the bone screw 2 relative to the bone plate 1, the engagement between the press-fit outer peripheral surface 23 and the curved surface 14 can be released by rotating the bone screw 2 counterclockwise (the rotation direction indicates the direction in the plan view of Figure 5(a) and will be the same hereinafter unless otherwise specified).

[0051] As described above, according to the present invention, the head (bone screw) can be reliably fixed and released to the bone plate at any inclination angle within a predetermined range with a simple structure, and can be used repeatedly.

[0052] 8(a) to 8(f) show other examples of the shape and arrangement of the press-welded outer peripheral surface portion.

[0053] 8(a) to 8(f) are diagrams showing the head and through-hole viewed from the front, showing the outline of the head (solid line) and the maximum diameter portion of the curved surface (dashed line) 14M.

[0054] 8(a), the head 200a is formed such that the diameters of the three substantially perfect spheres constituting the head 200a are smaller than those of the first embodiment, thereby reducing the contact area with the curved surfaces of the press-contact outer peripheral surface portions 230a to 230c.

[0055] In the second modification shown in FIG. 8( b), the head 201 a is formed such that the diameters of the three nearly perfect spheres that make up the head 201 a are smaller than those of the first embodiment, and the arrangement of the pressed outer peripheral surface portions is not uniform in the circumferential direction around the central axis P.

[0056] In the third modification shown in FIG. 8(c), the head 202a is formed such that the diameters of the three approximately perfect spheres that make up the head 202a are smaller than those of the first embodiment, and one of the spheres is made larger (larger).

[0057] 8(d), the head 203a has a smaller diameter and four substantially perfect spheres than those of the first embodiment, resulting in four press-contact outer peripheral surface portions 233a to 233d.

[0058] In the fifth modification shown in FIG. 8( e), the head 204 a is different from the fourth modification in that the press-contact outer peripheral surface portions 234 a, 234 b, 234 c, and 234 d are arranged at four locations evenly spaced at 90° angles in the circumferential direction around the central axis P.

[0059] In the sixth modification shown in Figure 8(f), in addition to the three press-contact outer peripheral surface portions 235a, 235b, and 235c of the head 205a in the first embodiment, a fourth press-contact outer peripheral surface portion 235d is positioned at a location offset 120° clockwise from the press-contact outer peripheral surface portion 235c. That is, the circumferential positions of the press-contact outer peripheral surface portion 235a and the press-contact outer peripheral surface portion 235d are approximately the same when viewed from the axial direction of the bone screw. Furthermore, the axial pitch of the press-contact outer peripheral surface portions 235a to 235d is positioned narrower than the axial pitch of the press-contact outer peripheral surface portions 23a to 23c in the first embodiment.

[0060] The number of press-welded outer peripheral surface portions may be two, or five or more.

[0061] Other examples of through-hole shapes are shown in Figure 10. Figure 10(a) is a cross-sectional view, and Figure 10(b) is an enlarged cross-sectional view of a portion of Figure 10(a).

[0062] 10, a through hole 100 serving as a receiving hole in a bone plate 1A has an opening 110 serving as an entrance opening on one surface and an opening 130 serving as an exit opening on the other surface. A tapered surface 120, a curved surface 140, and a parallel surface 160 are formed in this order on the inner peripheral surface of the through hole 100 from the opening 110 toward the opening 130. Both the opening 110 and the opening 130 are circular, and the central axis O of the through hole 100 passes through the centers of both circles.

[0063] The tapered surface 120 has a truncated cone shape with the central axis O as its center line, and is formed so that its diameter decreases from one opening 110 to the other opening 130. The tapered surface 120 is formed at an angle of approximately 20° with respect to the central axis O.

[0064] The curved surface 140 has a first curved surface 140a close to the tapered surface 120 and a second curved surface 140b close to the opening 130. The first and second curved surfaces 140a, 140b have a shape formed by combining two spherical zones along an imaginary partial sphere having a center on the central axis O. The first curved surface 140a expands in diameter from the tapered surface 120 side toward the second curved surface 140b side, while the second curved surface 140b contracts in diameter from the first curved surface 140a side toward the parallel surface 160 side. The curvatures of the first curved surface 140a and the second curved surface 140b are independently set so as to conform to the outer peripheral shape of the head of the bone screw to be inserted. In this embodiment, the curvature of the first curved surface 140a is set to be larger than the curvature of the second curved surface 140b, but this is not limited to this. The first curved surface 140a is the area from the apex of the triangular mark J2 to the apex of the triangular mark J3 in FIG. 10, and the second curved surface 140b is the area from the apex of the triangular mark J3 to the apex of the triangular mark J4.

[0065] A connection portion 180 between the tapered surface 120 and the curved surface 140 is rounded to form a curved surface that curves inward in the radial direction, in the opposite direction to the curved surface 140. The portion of the rounded connection portion 180 that protrudes most toward the center of the through hole 100 forms an inner opening 150. The inner opening 150 is shaped like a perfect circle, and the central axis O of the through hole 100 passes through the center of the circle. The connection portion 180 is the region from the apex of the triangular mark J1 to the apex of the triangular mark J2 in FIG. 10 .

[0066] The parallel surface 160 has a cylindrical shape with the central axis O as its center line. The parallel surface 160 has an opening 130 at one end and an opening 130' having the same diameter as the opening 130 at the other end opposite the opening 130.

[0067] The portion of the bone plate 1A below the second curved surface 140b around the parallel surface 160 constitutes a reinforcing portion. Therefore, even if the press-contact outer peripheral surface of the head engages with the second curved surface 140b with a pressing force so that a bone screw (not shown) can be fixed to the bone plate 1A at any inclination angle within a predetermined range, the portion of the second curved surface 140b located particularly below (on the parallel surface 160 side) will not be deformed toward the parallel surface 160, and the press-contact between the press-contact outer peripheral surface and the second curved surface 140b will be maintained.

[0068] Here, the diameters of the opening 110, the opening 130, the opening 130' and the inner opening 150 in the through hole 100 have the following relationship.

[0069] Diameter of opening 110 > Diameter of inner opening 150 > Diameter of opening 130' = Diameter of opening 130. Furthermore, the diameter is configured to increase from the inner opening 150 to the axis-perpendicular cross-sectional opening 170 between the first curved surface 140a and the second curved surface 140b, and to decrease from the axis-perpendicular cross-sectional opening 170 to opening 130'.

[0070] The opening 110 and the inner opening 150 are formed so that the head of the bone screw can pass through, while the opening 130' is formed so that the head of the bone screw cannot pass through, so that the head of the bone screw is held between the inner opening 150 and the opening 130' of the through hole 100.

[0071] As described above, according to another example of the through-hole shape, the curved surface 140 on the inner periphery of the through-hole is divided into a first curved surface 140a and a second curved surface 140b, and the curvature of each curved surface 140 can be set independently to match the shape of the head to be inserted, thereby making it possible to securely fix the head.

[0072] In the above modification, the curved surface 140 is configured with two surfaces, the first curved surface 140a and the second curved surface 140b, but it is not limited to two surfaces and may be configured with three or more surfaces.

[0073] The components of the first embodiment and its modifications described above can be combined with each other as long as there are no contradictions, and various modifications can be made without departing from the spirit of the present invention. Furthermore, there are no limitations on the materials or shapes of the components of the fixing mechanism.

[0074] The materials for the components can be either metal or plastic. Metals include stainless steel (SUS), titanium, etc., as well as alloys containing these.

[0075] Plastics (synthetic resins) include bioabsorbable polymers such as trimethylene carbonate (TMC), polyglycolic acid (PGA), polylactic acid (PLA), and poly-L-lactic acid (PLLA) and poly-DL-lactic acid (PDLLA).

[0076] The shape of the members may be, for example, plate-shaped, column-shaped, block-shaped, or the like, and may be applied to members of the same type or different types.

[0077] For example, the positions of the press-welded outer peripheral surface portions in the axial direction of the central axis P (virtual axis) do not have to be uniform.

[0078] Furthermore, the pressure-welded outer peripheral surface portions do not have to be arranged spirally in the axial direction of the central axis (virtual axis).

[0079] Alternatively, the peripheral portion of the pressure-welding outer peripheral surface may be recessed so that the pressure-welding outer peripheral surface clearly protrudes from the peripheral portion.

[0080] 1 Bone plate 10 Through hole (receiving hole) 11 Opening (entrance side opening) 12 Tapered surface (guiding portion) 13 Opening (exit side opening) 14 Curved surface 15 Inner opening 2 Bone screw (bone fixing member) 2a Head 2b Rod portion 22 (22a to 22c) Outer circumferential surface 23 (23a to 23c, 230a to 230c, 231a to 231c, 232a to 232c, 233a to 233d, 234a to 234d, 235a to 235d) Pressure-welded outer circumferential surface portion 100 Through hole (receiving hole) 110 Opening (entrance side opening) 120 Tapered surface (guiding portion) 130 Opening (exit side opening) 130′ opening 140 Curved surface 140a First curved surface 140b Second curved surface 150 Inner opening 160 Parallel surface

Claims

1. A bone fixation member that is fixed at an arbitrary inclination angle within a predetermined range in a receiving hole of a base member, the bone fixation member having a rod portion inserted into the receiving hole and a head portion inserted and fitted into the receiving hole, an outer peripheral surface of the head portion having a plurality of pressure contact outer peripheral surface portions that can be in pressure contact with an inner peripheral surface of the receiving hole, and the plurality of pressure contact outer peripheral surface portions being arranged at different positions in the virtual axis direction and at different phases in the circumferential direction of the axis, respectively. The bone fixation member is characterized by this arrangement.

2. The bone fixation member according to claim 1, wherein the plurality of pressure contact outer peripheral surface portions are arranged at equal intervals in the circumferential direction of the virtual axis.

3. The bone fixation member according to claim 1, wherein the plurality of pressure contact outer peripheral surface portions are arranged at equal intervals in the axial direction of the virtual axis.

4. The bone fixation member according to claim 1, wherein the plurality of pressure contact outer peripheral surfaces are arranged on a virtual helix at positions moved in the axial direction and the circumferential direction.

5. The bone fixation member according to claim 1, wherein the bone fixation member is substantially nail-shaped as a whole.

6. The bone fixation member according to claim 1, wherein the rod portion of the bone fixation member has a male screw portion and the bone fixation member is substantially screw-shaped as a whole.

7. A base member for fixing a bone fixation member at an arbitrary inclination angle within a predetermined range, the base member having a receiving hole through which the bone fixation member is inserted, the receiving hole having an inlet side opening, an inner opening, and an outlet side opening through which the bone fixation member is inserted, the outlet side opening being set to a smaller diameter than the inlet side opening, the receiving hole having a guiding portion that tapers from the inlet side opening toward the inner opening portion, an inner peripheral surface extending from the inner opening to the outlet side opening having a curved surface, and the curved surface being configured to allow the head portion of the bone fixation member to be inserted and fitted. The base member is characterized by this configuration.

8. The base member according to claim 7, wherein the curved surface is configured such that an inner diameter in the middle between the inner opening and the outlet side opening is the largest with respect to an inner diameter of the inner opening and an inner diameter of the outlet side opening.

9. The base member according to claim 7, wherein the curved surface is formed with different curvatures for a curvature of the curved surface near the inner opening and a curvature of the curved surface near the outlet side opening, respectively.

10. The base member according to claim 7, having a cylindrical parallel surface between the curved surface and the outlet side opening.

11. The base member according to claim 7, wherein the receiving hole is rotationally symmetric 360 degrees with respect to a central axis.

12. The bone fixation system comprising the base member according to any one of claims 7 to 11, which has a receiving portion through which the bone fixation member according to claim 1 is inserted, wherein the bone fixation member can be fixed at an arbitrary inclination angle within a predetermined range with respect to the base member.

13. The bone fixation system comprising the base member according to claim 7, which has a receiving portion through which the bone fixation member according to any one of claims 1 to 6 is inserted, wherein the bone fixation member can be fixed at an arbitrary inclination angle within a predetermined range with respect to the base member.

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