Bone fixation member

Abstract

To provide a bone fixing member having joint strength resistant to exercise load, preventing pain, and blood flow inhibition or the like to subcutaneous tissues, and not inhibiting regeneration of bones.SOLUTION: A bone fixing member 100 is composed of a plate 10 to be abutted on the surface of a bone, and screws 20, 21 for fixing the plate to the bone. A plurality of screw holes 30, 31 for penetrating a screw portion of the screw are provided in the plate, a screw groove 24 is provided in an inner periphery of the screw hole, a thread 25 fitted into the screw groove of the screw hole is provided in an outer periphery of the head of the screw, and the screw portion of the screw is inserted into the bone via the screw hole. A surface at a bone side of the plate is bent so as to be adapted to the shape of the bone, and in the periphery at a skin side of the screw hole and / or at a bone contact surface side on the bent portion, a thickness of the plate at an opposite side to a direction in which a central axis of the screw is inclined to a perpendicular of a surface at a bone side of the plate is gradually made thick from the part of the periphery.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a structure of a bone fixation device that assists in the treatment of a fracture by contacting a plate with the outside of the bone at the fractured portion and fixing it with screws. [Background technology]

[0002] Conventional bone fixation devices typically consist of a bone plate (hereinafter simply referred to as a plate) and screws. As disclosed in, for example, References 1 and 2, a plate is a long, narrow, flat plate made of titanium or a titanium alloy that is aligned along the longitudinal direction of the bone. Figure 1 shows the basic method of using a bone fixation device, in which a screw is inserted into the fracture site from the outside of the plate and the plate is fixed to the fracture site by the screw. The head of the screw and the screw hole in the plate are not threaded, and when the screw is tightened, the threaded portion of the screw first enters the bone on both sides of the fracture surface, tightly fixing the two together. Further tightening of the screw pulls the fracture surface toward the plate, bringing the bone into contact with the plate.

[0003] Anatomically, bones are composed of a central portion called "cancellous bone" surrounded by "cortical bone," which is further covered by a tough, fibrous "periosteum." The "periosteum" is composed of a "fibrous layer" and an "osteogenic layer." This "osteogenic layer" is rich in osteoblasts, blood vessels, and nerves, and has bone-forming properties. It plays an important role in the repair process after bone tissue damage, such as fractures. Adhesion of the bones on both sides of the fracture surface by screws is an important condition for fracture repair. However, at the same time, if the plate and bone are too closely attached, blood flow to the "periosteum" on the surface of the bone can be reduced, causing serious problems such as insufficient blood supply for bone regeneration.

[0004] Therefore, a system called a locking plate was developed to promote healing while ensuring blood flow to the periosteum (Patent Document 3). A locking plate (hereinafter simply referred to as a "plate") has a thread groove / thread on the outside of the screw head and the inside of the screw hole in the plate that fit together, making it possible to fasten and fix the bones of the fracture, and the screw and plate, separately, without having to adhere the plate to the bone. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2008-541970 [Patent Document 2] Special Publication No. 61-000103 [Patent Document 3] Japanese Patent Application Laid-Open No. 2018-171446 Summary of the Invention [Problem to be solved by the invention]

[0006] Locking plates reduce pressure on the periosteum, enabling fixation of the fracture surface without compromising the therapeutic effects of bone regeneration. However, when screws are fastened to bone using a curved plate to reduce the risk of nerve damage or to fit the joint, it may be necessary to insert the screw at an angle relative to the bone surface. However, in such cases, the following new problems arise:

[0007] Figure 2 shows an example of an inclined screw insertion angle. When multiple screws are inserted and fixed parallel to each other into a bone (not shown) while maintaining a consistent, thin locking plate (15) thickness, screws (20) near the center of the plate can be inserted nearly perpendicular to the plate, allowing most of the screw head threads (25) to fit into the plate hole thread grooves (24). In contrast, screws (21) located near the edge of the plate have an arc-shaped cross section on the inner periphery of the plate to fit the bone periphery. Therefore, an angle is formed between the center line of the screw (dashed line) and the perpendicular line (arrow) to the arc, resulting in a portion of the screw head threads (25) being exposed on the outer (skin side) or inner (bone-contacting side) of the plate, or both (areas surrounded by chain lines).

[0008] If the angle between the center line of the screw 21 and the perpendicular to the arc becomes larger, the number of engagements between the threads 25 and the thread grooves 24 will further decrease, resulting in a problem of reduced fixation force between the screw 21 and the plate 15. Furthermore, if the number of fastening threads between the plate 21 and the screw hole 15 is small, the screw direction will be unstable and it will be likely to be inserted at an angle, resulting in an improper fastening state (cross-threading). In Patent Document 3, in order to fasten the screw at an angle relative to the plate, a special inclined thread groove is provided in the smallest inner diameter portion of the screw hole, which is conically carved from above and below, but the problems of reduced fixation force between the screw and the plate and unstable fastening direction are not solved.

[0009] The easiest way to solve the problem of a decrease in the fixation force between the screw 21 and the plate 15 is to increase the thickness of the plate 15. However, this is not a desirable solution because it increases the volume of the plate 15 and lifts soft tissues, including the skin, which increases the burden on the patient. It is necessary to increase the amount of engagement while keeping the increase in volume to a minimum, but this is not an easy task to achieve.

[0010] In some cases, the thickness of a portion of the plate corresponding to the screw head is increased to increase the number of thread engagements between the screw 21 and the plate 15 (Patent Document 3, column

[0021] ), but if this increase in thickness is large, it may locally push up the soft tissue on the skin side, which may cause pain or obstruct blood flow to the subcutaneous tissue.

[0011] Conversely, increasing the thickness of the threaded portion of the plate on the bone-contacting surface can cause the entire plate to float off the bone, potentially pushing up a wider area of ​​subcutaneous tissue than would be possible if the thickness were increased outward, potentially causing pain and blood flow obstruction to the subcutaneous tissue. Furthermore, the increased thickness on the bone-contacting surface increases the contact pressure on the periosteum, potentially impairing blood flow to the periosteum. Thus, each of these conventional solutions creates new problems, making it difficult to find a solution for fastening the plate at an angled screw.

[0012] The object of the present invention is to provide a bone fixation device including a bone plate that has fastening strength sufficient to withstand the expected exercise load on the patient after surgery, prevents pain and obstruction of blood flow to the subcutaneous tissue, does not obstruct blood flow to the periosteum, and does not inhibit bone regeneration. [Means for solving the problem]

[0013] The bone fixing member of the present invention has the following features. A bone fixation member comprising a plate to be brought into contact with the surface of the bone and a screw to fix the plate to the bone, The plate is provided with a plurality of screw holes through which the threaded portions of the screws pass, and thread grooves are provided on the inner periphery of the screw holes; The screw thread portion of the screw has a thread for being inserted into a bone and fixing the bone, and a screw thread is provided on the outer periphery of the head of the screw to fit into a screw groove on the inner periphery of the screw hole, the bone-facing surface of the plate includes a curved portion adapted to conform to the contours of the bone; The thickness of the plate on the side opposite to the direction in which the central axis of the screw is inclined relative to the perpendicular to the bone-side surface of the plate, around the skin side of the screw hole in the curved portion and / or around the bone-contacting surface side, is gradually increased from the surrounding area.

[0014] Furthermore, when the cross-sectional shape of the bone-side surface of the curved portion forms part of an arc and the angle between the central axis of the screw and the perpendicular to the arc is 30° or more, it is preferable to provide a thickened portion around part of the screw hole. Furthermore, it is preferable that the thickened region is 2 / 3 or less of the arc. Furthermore, it is preferable that the thickness of the thickened portion around the screw hole is equivalent to 0.5 to 3 threads in terms of screw pitch. [Effects of the Invention]

[0015] By using this structure, it is possible to provide a bone fixation member that has fastening strength that can withstand expected exercise loads, prevents pain and obstruction of blood flow to subcutaneous tissue, does not obstruct blood flow to the periosteum, and does not inhibit bone regeneration. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a method for fixing a fractured bone with a bone plate and screws. [Figure 2] FIG. 2 is a cross-sectional view of a prior art bone plate / screw. [Figure 3] Figure 3 is a cross-sectional view of a bone plate / screw according to the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing features of a bone plate / screw according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] 3 shows a transverse cross-sectional view of a bone fixation device 100 according to the present invention. A screw groove 24 and a thread 25 are formed on the outside of the head of the screw 20 and on the inside of the screw hole 30. When the screw 20 is passed through the screw hole 30 and tightened, the threaded portion 26 of the screw 20 is first inserted into the bone (not shown) on both sides of the fracture surface, and the two are tightly fixed together. Next, the plate 10 is brought close to the bone, and the thread 25 on the head of the screw 20 is engaged with the thread 24 of the screw hole to complete the fastening process. In this case, the pressure between the plate 10 and the bone can be adjusted by adjusting the tightening strength of the screw so that it does not become excessive.

[0018] The angle at which a screw is inserted into a bone is not always perpendicular to the bone surface. For example, when fastening a plate and screw in a region close to the joint, such as in the case of HTO (high tibial osteotomy), it may be necessary to tilt the angle of the screw's central axis relative to the bone surface. Because the outer shape of the bone tissue is thicker in areas close to the joint, the plate attached there often has a curved shape that follows the slope of the part where the diameter of the bone changes, and it may not be possible to insert the screw perpendicular to the inner surface of the plate near this slope.

[0019] 3, the inner curvature of the plate is arc-shaped, and the center line (dashed line) of screw 20 near the center of the arc (dotted line) is approximately parallel to the perpendicular to the arc, so most of the threads 25 on the screw head are fitted into and fastened with the thread grooves 24 on the inside of plate hole 30. In contrast, in the case of plate hole 31 located near the end of the arc of the plate, in order to fasten screw 21 parallel to screw 20 at the center, screw 21 needs to be fastened at an angle to the right with respect to the perpendicular to the arc (arrow).

[0020] As can be seen by comparing the plate of the present invention with the conventional locking plate 15 shown in Figure 2, the thickness of the plate 10 is increased at the end of the arc on the skin side (the side opposite the screw inclination direction) around the plate hole 31 corresponding to the screw 21. Furthermore, the plate is also increased in thickness at the center of the arc on the bone-contacting side of the plate hole 31 (the side opposite the screw inclination direction). Figure 4 shows an enlarged view of these thickened areas. The thickened areas 12 and 13 relative to the base plate 10 are indicated by diagonal lines. However, it is not necessary to thicken both sides as in the example shown in Figure 3; only the skin side or the bone-contacting side may be thickened depending on the plate's intended use, bone shape, etc. In either case, as mentioned above, it is necessary to gradually increase the thickness of the plate 10 to avoid forming protrusions that are harmful to the subcutaneous tissue or periosteum.

[0021] As shown in Figure 3, when the bottom surface of the plate forms part of a circular arc and the central axis of the screw 21 is inclined by 30° or more from the perpendicular direction of the circular arc, it is necessary to provide the thickened portion on the skin side or bone contact side around the screw hole 31. If the angle is less than 30° but 15° or more, it may be preferable to provide a thickened portion. However, if the angle is less than 15°, a sufficient amount of engagement of the threaded portion can often be ensured without providing a thickened portion.

[0022] The area where the thickened portion is provided is preferably 2 / 3 or less, more preferably 1 / 2 or less, and even more preferably 1 / 3 or less of the above-mentioned arc. The height of the periphery of the screw hole 31 in the thickened portion is equivalent to a screw pitch of 0.5 to 3, preferably 0.5 to 2, and more preferably 0.5 to 1. Furthermore, this height does not need to be the same on the bone-contacting surface side and the skin side. It has been confirmed that within this range and height, the volume of the implanted plate does not increase significantly, and pain and blood flow obstruction to the subcutaneous tissue do not occur. Thus, according to the present invention, a bone plate can be realized that has a fastening strength sufficient to withstand expected exercise loads, making it less likely for the screw to come off the plate (backout), and prevents pain and blood flow obstruction to the subcutaneous tissue, and does not obstruct blood flow to the periosteum and does not inhibit bone regeneration.

[0023] In the above examples, the case where the cross section of the plate is a part of a circular arc has been described, but the same can also be applied to cases where the plate is curved in other shapes or is flat. When fastening a screw in a screw hole of such a plate shape at an angle relative to the perpendicular to the inner surface of the plate, the thickness of the plate can be gradually increased from the periphery on the skin side or the bone-contacting side of the screw hole on the opposite side from the direction in which the central axis of the screw is inclined relative to the perpendicular to the inner surface of the plate.

[0024] Although the present invention has been described based on the above-mentioned embodiment, it is obvious to those skilled in the art that various changes and modifications can be made within the spirit of the present invention and the scope of the appended claims. For example, although the present invention has been described using the example of fixing a fractured bone, it goes without saying that the present invention can also be applied to fixing bones other than fractures. [Explanation of symbols]

[0025] 100 Bone fixation member 10, 15 plates 12, 13 Thick part 20, 21 screws 24 thread grooves 25, screw thread 26 Screw thread 30, 31 Plate Hall

Claims

1. A bone fixation member comprising a plate to be brought into contact with the surface of the bone and a screw to fix the plate to the bone, The plate is provided with a plurality of screw holes through which the threaded portions of the screws pass, and thread grooves are provided on the inner periphery of the screw holes; The screw thread portion of the screw has a thread for being inserted into a bone and fixing the bone, and a screw thread is provided on the outer periphery of the head of the screw to fit into a screw groove on the inner periphery of the screw hole, the bone-facing surface of the plate includes a curved portion adapted to conform to the contours of the bone; The thickness of the plate on the opposite side to the direction in which the central axis of the screw is inclined with respect to the perpendicular line of the bone-side surface of the plate, among the periphery on the skin side of the screw hole of the curved portion and the periphery on the bone-contacting surface side, is gradually increased from the periphery. A bone fixation member characterized by:

2. 2. The bone fixation member according to claim 1, wherein the cross-sectional shape of the bone-side surface of the curved portion forms a part of a circular arc, and when the angle between the central axis of the screw and a perpendicular to the circular arc is 15° or more, a thickened portion is provided around a part of the periphery of the screw hole, and when the angle is less than 15°, the thickened portion is not provided.

3. 3. The bone fixation member according to claim 1, wherein the thickness of the thickened portion along the inner circumference of the screw hole in contact with the inner circumference corresponds to a screw pitch of 0.5 to 3 threads.

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