Osteotomy guide

Abstract

The present invention provides an osteotomy guide, comprising: a frame, having a main rod, a first support rod and a second support rod, and forming a U-shaped structure; a positioning structure, arranged on the second support rod, suitable for positioning at the position of the fibula head; a first guide sleeve, arranged on the first support rod, having a first center guide hole, the center axis of the first center guide hole passes through the center position of the positioning structure; a positioning column, rotatably sleeved on the first guide sleeve, having a plurality of through holes; a second guide sleeve, detachably mounted inside one of the through holes, the second guide sleeve having a second center guide hole, the center axis of the first center guide hole being parallel to the center axis of the second center guide hole. The osteotomy guide of the present invention can use the first guide sleeve and the second guide sleeve to limit the insertion position and insertion direction of the Kirschner wire after determining the osteotomy position, without deflection, and complete high-quality osteotomy at one time, with high surgical efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of auxiliary tools for orthopedic osteotomy, and in particular to an osteotomy guide for auxiliary positioning of proximal high tibial osteotomy. Background Art

[0002] Patients with genu varum, especially young patients with genu varum due to proximal tibial dysplasia, need to undergo proximal tibial high osteotomy for simple medial knee pain. The treatment mechanism of proximal tibial high osteotomy is to transfer the weight-bearing line from the inflamed and worn medial compartment of the knee joint to the relatively normal lateral compartment through proximal tibial osteotomy, thereby achieving the purpose of relieving arthritis symptoms.

[0003] Specifically, the normal force line of the knee joint usually has more weight on the medial side and less weight on the lateral side. If there is a certain degree of varus deformity of the tibia, the pressure on the medial compartment cartilage will increase significantly and exceed the tolerance of the cartilage, thus triggering a vicious cycle of cartilage wear and inflammation, forming medial osteoarthritis. Before osteoarthritis develops to the lateral side, high proximal tibial osteotomy can correct the varus deformity of the tibia and appropriately transfer the force line of the lower limb to the normal lateral compartment, thereby significantly reducing the pressure in the medial compartment and restoring it to the normal range that the cartilage can withstand, thereby effectively preventing cartilage wear, relieving pain symptoms, and even allowing the worn cartilage and injured meniscus to self-repair.

[0004] Corrective surgery for high proximal tibial osteotomy requires open osteotomy on the medial side of the tibia to correct the varus angle of the proximal tibia, thereby correcting the weight-bearing line of the entire lower limb. Specifically, the measurement position is fixed from the medial side of the proximal tibia, and the osteotomy is performed in the direction of the fibular head. After that, the osteotomy area is distracted to correct the angle between the proximal tibial articular surface and the tibial force line. The traditional osteotomy method is generally blindly performed after fluoroscopy, that is, two pairs of parallel Kirschner wires are inserted, and then an oscillating saw is used to cut the osteotomy close to a pair of parallel Kirschner wires. This traditional method of inserting Kirschner wires is not assisted by tools and is prone to deflection. Fluorescence is required after insertion, and once deflection occurs, it must be corrected, resulting in low surgical efficiency. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the technical defects in the prior art that when performing proximal high tibial osteotomy orthopedic surgery, there are no special tools and the surgery is generally performed blindly after fluoroscopy, which is prone to deviation and needs to be corrected once it occurs, resulting in low surgical efficiency, thereby providing an osteotomy guide that can improve surgical efficiency.

[0006] To this end, the present invention provides an osteotomy guide, comprising:

[0007] The frame comprises a main rod, a first support rod fixedly connected to one end of the main rod, and a second support rod slidably mounted on the main rod, wherein the first support rod is parallel to the second support rod and forms a U-shaped structure together with the main rod;

[0008] A positioning structure, disposed on the second support rod, suitable for positioning at the fibular head;

[0009] A first guide sleeve, fixedly disposed on the first support rod, having a first central guide hole, wherein the central axis of the first central guide hole passes through the central position of the positioning structure;

[0010] A positioning column is rotatably sleeved on the first guide sleeve, and the positioning column is provided with a plurality of through holes;

[0011] The second guide sleeve is detachably mounted inside one of the through holes, and the second guide sleeve has a second central guide hole, and the central axis of the first central guide hole is parallel to the central axis of the second central guide hole.

[0012] As a preferred solution, the positioning structure is a positioning bowl suitable for buckling at the position of the fibular head.

[0013] As a preferred solution, the main rod is a polygonal prism structure, and the second support rod can move along the axial direction of the main rod but cannot rotate around the circumference of the main rod.

[0014] As a preferred solution, the second guide sleeve comprises a second guide sleeve body and an annular flange arranged at one end of the second guide sleeve body, and the outer diameter of the second guide sleeve body is consistent with the inner diameter of the through hole.

[0015] As a preferred embodiment, the present invention further comprises a position determining member, one end of which is rotatably mounted on the positioning column, and the other end of which has a comparison end, wherein the central axis of the first center guide hole and the central axis of the second center guide hole determine an osteotomy reference surface, and the distance between the comparison end and the osteotomy reference surface is a set distance.

[0016] As a preferred solution, the comparison end is provided with an insertion plate, and the insertion plate is parallel to the osteotomy reference surface.

[0017] As a preferred solution, the insertion plate is provided with a plurality of insertion guide holes, and the central axes of the plurality of insertion guide holes are parallel and coplanar, and are parallel to the osteotomy reference surface.

[0018] As a preferred embodiment, the position determining member includes a base, one end of the base forms a U-shaped structure, two opposite sides of the U-shaped structure have mounting holes rotatably mounted on the positioning column, and the other end of the base is provided with an indicator rod, the indicator rod is bent along the position of the proximal end of the medial tibia, and the top end of the indicator rod is the reference end.

[0019] As a preferred solution, the first guide sleeve is located on the inner side of the U-shaped structure, and all the through holes are located on the outer side of the U-shaped structure.

[0020] As a preferred solution, the main rod is provided with a scale, and the 0 scale position of the scale is flush with the end of the first guide sleeve facing the positioning structure; the scale increases from the 0 scale position in a direction away from the first support rod.

[0021] The technical solution provided by the present invention has the following advantages:

[0022] 1. The osteotomy guide of the present invention comprises a frame, a positioning structure, a first guide sleeve, a positioning column and a second guide sleeve; the positioning structure installed on the frame is suitable for positioning at the position of the fibula head, the first guide sleeve installed on the frame has a first center guide hole, the center axis of which passes through the center position of the positioning structure, and is used to guide the insertion of the first Kirschner wire; the positioning column is rotatably mounted on the first guide sleeve, and the second guide sleeve is installed in the through hole of the positioning column, and has a second center guide hole, the center axis of the first center guide hole is parallel to the center axis of the second center guide hole, so as to determine the osteotomy reference surface, because the osteotomy is performed by an oscillating saw close to the edge of the Kirschner wire, the osteotomy reference surface and the actual osteotomy surface differ by a distance of about the radius of the Kirschner wire.

[0023] When performing open osteotomy, after determining the osteotomy position, the first guide sleeve of the osteotomy guide of the present invention is placed against the required osteotomy position so that the osteotomy position is tangent to the first center guide hole, the second support rod is slid so that the positioning structure is placed against the fibular head position, the second guide sleeve is inserted into the appropriate through-hole position of the positioning column, the direction of the positioning column is adjusted so that the plane determined by the center axis of the second center guide hole and the center axis of the first center guide hole is consistent with the posterior tilt angle of the tibial plateau, and then the second Kirschner wire is passed through the second center guide hole and nailed into the tibia at the determined position. After the two Kirschner wires are nailed in, the osteotomy guide is removed, and an oscillating saw is used to perform osteotomy close to the two Kirschner wires until the opposite side is reached. The unilateral cortex cannot be completely cut off, and a hinge is formed, so that the osteotomy can heal as soon as possible.

[0024] The osteotomy guide of the present invention can, after determining the osteotomy position, use the first guide sleeve and the second guide sleeve to limit the insertion position and direction of the Kirschner wire without deflection, and can complete high-quality osteotomy in one go, with high surgical efficiency. In addition, the first guide sleeve, the second guide sleeve and the positioning column cooperate with each other to ensure that the first Kirschner wire and the second Kirschner wire remain parallel after insertion, making it convenient for the oscillating saw to closely adhere to the first Kirschner wire and the second Kirschner wire for osteotomy.

[0025] 2. The positioning structure of the osteotomy guide of the present invention is a positioning bowl, which is suitable for buckling at the position of the fibula head; the bowl-shaped structure is convenient for pressing and fixing, and is easy to operate.

[0026] 3. In the osteotomy guide of the present invention, the main rod is a polygonal column structure, and the second support rod can only move along the axial direction of the main rod but cannot rotate around the circumference of the main rod. Such an arrangement enables the positioning structure to only move back and forth in the direction of approaching or moving away from the first guide sleeve. During the movement, the positioning structure is always opposite to the first guide sleeve, thereby improving the adjustment efficiency.

[0027] 4. In the osteotomy guide of the present invention, the second guide sleeve comprises a second guide sleeve body and an annular flange. After the second guide sleeve is inserted into the through hole on the positioning column, it is pressed toward the positioning structure so as not to be completely immersed in the through hole, which is convenient for operation.

[0028] 5. The osteotomy guide of the present invention also includes a position determining member, one end of which is rotatably mounted on the positioning column, and the other end of which has a reference end. The central axis of the first center guide hole and the central axis of the second center guide hole determine an osteotomy reference surface (higher or lower than the actual osteotomy surface by the radius of one center guide hole), and then the distance between the reference end and the osteotomy reference surface is set to ensure that the actual osteotomy position is about 3.5 cm away from the medial tibial plateau, thereby meeting relevant surgical requirements (generally, on the side away from the fibula, the osteotomy position is required to be about 3.5 cm below the tibial plateau).

[0029] 6. The osteotomy guide of the present invention is provided with an insertion plate at the reference end, and the insertion plate is parallel to the osteotomy reference surface. Since during osteotomy, the osteotomy surface is required to have the same posterior inclination angle as the tibial plateau, after the insertion plate is provided parallel to the osteotomy reference surface, during the operation, the insertion plate is inserted into the tibial plateau position so that the insertion plate and the tibial plateau have the same posterior inclination angle. At this time, it can be ensured that the guidance of the Kirschner wire by the first guide sleeve and the second guide sleeve is the same as the above-mentioned posterior inclination angle, thereby ensuring that the bone plane cut close to the Kirschner wire is also the same as the above-mentioned inclination angle.

[0030] 7. The osteotomy guide of the present invention has a plurality of insertion guide holes on the insertion plate, and the central axes of the plurality of insertion guide holes are parallel and coplanar, and are parallel to the osteotomy reference plane; due to the influence of the joint capsule and ligaments at the medial tibial plateau position, the insertion of the insertion plate is relatively difficult. At this time, the insertion plate can be fixed by inserting at least two Kirschner wires at the insertion guide hole position, and the inclination angle of the insertion plate is made the same as the posterior inclination angle of the tibial plateau, thereby reducing the difficulty of inserting the insertion plate.

[0031] 8. The osteotomy guide of the present invention, the position determining part includes a base, one end of the base forms a U-shaped structure, and the two opposite sides of the U-shaped structure are rotatably mounted on the positioning column through a mounting hole; the other end of the base is provided with an indicator rod, the indicator rod is bent along the position of the proximal end of the medial tibia, and the top end is a comparison end; this structural design can adapt to the human bone structure from the tibial plateau to the proximal end of the tibia, facilitates comparison with the comparison end, and also facilitates the abutment of the first guide sleeve and the second guide sleeve at the positioning column position.

[0032] 9. In the osteotomy guide of the present invention, the first guide sleeve is located on the inner side of the U-shaped structure, and the through hole is located on the outer side of the U-shaped structure. The entire osteotomy guide has a compact structure, which is convenient for disassembly of the second guide sleeve, and the indicator rod is located in the center position, which is convenient for comparison of the comparison end.

[0033] 10. The osteotomy guide of the present invention has a scale on the main rod, and the 0 scale position is flush with the end of the first guide sleeve facing the positioning structure; when inserting the Kirschner wire, a Kirschner wire with a scale can be used. By observing the scale on the inserted Kirschner wire, the approximate position of the Kirschner wire can be known to avoid penetrating the tibia. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the prior art or the specific implementation manner of the present invention, the drawings used in the description of the prior art or the specific implementation manner are briefly introduced below.

[0035] Figure 1 It is a schematic diagram of the overall structure of the osteotomy guide of the present invention.

[0036] Figure 2 yes Figure 1 Another stereoscopic view of .

[0037] Figure 3 yes Figure 1 Improved structural diagram of the position determining component.

[0038] Figure numerals: 1. frame; 10. main rod; 11. first support rod; 12. second support rod; 2. positioning structure; 31. first guide sleeve; 310. first center guide hole; 32. second guide sleeve; 320. second center guide hole; 321. second guide sleeve body; 322. annular flange; 4. positioning column; 41. through hole; 5. position determining member; 50. base; 51. comparison end; 52. insertion plate; 53. mounting hole; 54. indicator rod; 55. side; 56. insertion guide hole. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0040] Example

[0041] This embodiment provides an osteotomy guide, such as Figure 1-2 As shown, it includes: a frame 1, having a main rod 10, a first support rod 11 fixedly connected to one end of the main rod 10, and a second support rod 12 slidably mounted on the main rod 10, the first support rod 11 is parallel to the second support rod 12, and together with the main rod 10 forms a U-shaped structure; a positioning structure 2, arranged on the second support rod 12, suitable for positioning at the head of the fibula; a first guide sleeve 31, fixedly arranged on the first support rod 11, having a first central guide hole 310, the central axis of the first central guide hole 310 passes through the central position of the positioning structure 2; a positioning column 4, rotatably mounted on the first guide sleeve 31, and a plurality of through holes 41 are provided on the positioning column 4; a second guide sleeve 32, detachably mounted inside one of the through holes 41, the second guide sleeve 32 having a second central guide hole 320, the central axis of the first central guide hole 310 is parallel to the central axis of the second central guide hole 320.

[0042] The central axis of the first center guide hole 310 is parallel to the central axis of the second center guide hole 320, and the osteotomy reference surface can be determined. Since the osteotomy is performed by an oscillating saw close to the edge of the Kirschner wire, the osteotomy reference surface is approximately one kirschner wire radius away from the actual osteotomy surface.

[0043] When performing open osteotomy, after determining the osteotomy position, the first guide sleeve 31 of the osteotomy guide of this embodiment is placed against the required osteotomy position so that the osteotomy position is tangent to the first center guide hole 310, the second support rod 12 is slid so that the positioning structure 2 is placed against the fibular head position, the second guide sleeve 32 is inserted into the appropriate through hole 41 of the positioning column 4, the direction of the positioning column 4 is adjusted so that the plane determined by the center axis of the second center guide hole 320 and the center axis of the first center guide hole 310 is consistent with the posterior tilt angle of the tibial plateau, and then at the determined position, the second Kirschner wire is passed through the second center guide hole 320 and nailed into the tibia. After the two Kirschner wires are nailed in, the osteotomy guide is removed, and an oscillating saw is used to perform osteotomy close to the two Kirschner wires until the opposite side is reached. The unilateral cortex cannot be completely cut off, and a hinge is formed to allow the osteotomy to heal as soon as possible.

[0044] The osteotomy guide of this embodiment can, after determining the osteotomy position, use the first guide sleeve 31 and the second guide sleeve 32 to limit the insertion position and direction of the Kirschner wire without deviation, thus completing high-quality osteotomy in one go and achieving high surgical efficiency. In addition, the first guide sleeve 31, the second guide sleeve 32 and the positioning column 4 cooperate with each other to ensure that the first Kirschner wire and the second Kirschner wire remain parallel after insertion, making it convenient for the oscillating saw to closely adhere to the first Kirschner wire and the second Kirschner wire for osteotomy.

[0045] The positioning structure is a positioning bowl, which is suitable for buckling at the position of the fibular head; the bowl-shaped structure is convenient for pressing and fixing, and is easy to operate.

[0046] The main rod 10 is a polygonal prism structure, and the second support rod 12 can move along the axial direction of the main rod 10, but cannot rotate around the circumference of the main rod 10. Specifically in this embodiment, the main rod 10 is a quadrangular prism, and the second support rod 12 is slidably mounted on the main rod 10 through a sliding sleeve with a quadrangular inner cavity.

[0047] Such an arrangement enables the positioning structure 2 to move back and forth only in the direction of approaching or moving away from the first guide sleeve 31 . During the movement, the positioning structure 2 is always opposite to the first guide sleeve 31 , thereby improving the adjustment efficiency.

[0048] The second guide sleeve 32 includes a second guide sleeve body 321 and an annular flange 322 disposed at one end of the second guide sleeve body 321. The outer diameter of the second guide sleeve body 321 is consistent with the inner diameter of the through hole 41. After the second guide sleeve 32 is inserted into the through hole 41 on the positioning column 4, it is pressed toward the positioning structure 2 so that it does not completely sink into the through hole 41, which is convenient for operation.

[0049] It also includes a position determining member 5, one end of which is rotatably mounted on the positioning column 4, and the other end has a reference end 51. The central axis of the first center guide hole 310 and the central axis of the second center guide hole 320 determine an osteotomy reference surface (higher or lower than the actual osteotomy surface by the radius of a center guide hole). The distance between the reference end 51 and the osteotomy reference surface is set to ensure that the actual osteotomy position is about 3.5 cm away from the tibial plateau; thereby meeting relevant surgical requirements (generally, on the side away from the fibula, the osteotomy position is required to be about 3.5 cm below the tibial plateau).

[0050] The reference end 51 is provided with an insertion plate 52, and the insertion plate 52 is parallel to the osteotomy reference surface. During osteotomy, the osteotomy surface is required to have the same inclination angle as the tibial plateau; after the insertion plate 52 is provided parallel to the osteotomy reference surface, during the operation, the insertion plate 52 is inserted into the tibial plateau position so that the insertion plate 52 and the tibial plateau have the same posterior inclination angle, and at this time, the first guide sleeve 31 and the second guide sleeve 32 can be ensured to guide the Kirschner wire at the same inclination angle as the above, thereby ensuring that the bone plane cut close to the Kirschner wire is also at the same inclination angle as the above.

[0051] As an improvement plan, refer to Figure 3 As shown, the insertion plate 52 is provided with a plurality of insertion guide holes 56, and the central axes of the plurality of insertion guide holes 56 are parallel and coplanar, and are parallel to the osteotomy reference surface. Due to the influence of the joint capsule and ligaments at the medial tibial plateau, the insertion of the insertion plate 52 is relatively difficult. At this time, the insertion plate 52 can be fixed by inserting at least two Kirschner wires at the position of the insertion guide holes 56, and the inclination angle of the insertion plate 52 is made the same as the inclination angle of the bone plateau, thereby reducing the difficulty of inserting the insertion plate 52.

[0052] The position determining member 5 includes a base 50, one end of which forms a U-shaped structure, and two opposite sides 55 of the U-shaped structure have mounting holes 53 that can be rotatably sleeved on the positioning column 4, and the other end of the base 50 is provided with an indicator rod 54, which is bent along the position of the proximal end of the medial tibia, and the top of the indicator rod 54 is the reference end 51. This structural design can adapt to the human skeletal structure from the tibial plateau to the proximal end of the tibia, facilitate comparison of the reference end, and also facilitate the abutment of the first guide sleeve 31 and the second guide sleeve 32 at the position of the positioning column 4.

[0053] The first guide sleeve 31 is located inside the U-shaped structure, and all the through holes 41 are located outside the U-shaped structure, so that the entire osteotomy guide is compact, the second guide sleeve 32 is easy to disassemble, and the indicator rod 54 is located in the center, which is convenient for comparison of the comparison end.

[0054] The main rod 10 is provided with a scale, and the 0 scale position of the scale is flush with the end of the first guide sleeve 31 facing the positioning structure 2; the scale increases from the 0 scale position toward the direction away from the first support rod 11. When nailing the Kirschner wire, a Kirschner wire with a scale can be used. By observing the scale on the inserted Kirschner wire, the approximate position of the Kirschner wire can be known to avoid penetrating the tibia. In addition, it can also be set that when the Kirschner wire is inserted into the first guide sleeve 31 or the second guide sleeve 32 until the tip is flush with the 0 scale, the position of the Kirschner wire at the other end of the first guide sleeve 31 or the second guide sleeve 32 that is just not inserted is the 0 scale, and then the scale value increases in the direction away from the first guide sleeve 31 or the second guide sleeve 32, so that when the Kirschner wire is nailed in, the insertion depth of the Kirschner wire can be more conveniently known.

[0055] The method of using the osteotomy guide in this embodiment is as follows:

[0056] First, determine the osteotomy position, place the insertion plate 52 of the osteotomy guide of this embodiment to a position flush with the tibial plateau, and then use two Kirschner wires to pass through the insertion guide hole 56 to fix the insertion plate 52, and make the inclination angle of the insertion plate 52 the same as the posterior inclination angle of the tibial plateau;

[0057] Place the first guide sleeve 31 against the tibia, slide the second support rod 12, place the positioning structure 2 against the fibula head, insert the second guide sleeve 32 into the appropriate through hole 41 of the positioning column 4, pass the second Kirschner wire through the second center guide hole 320 of the second guide sleeve 32 and then nail it into the tibia. After the two Kirschner wires are nailed in, remove the osteotomy guide and use an oscillating saw to perform osteotomy close to the two Kirschner wires until the opposite side is reached.

[0058] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. An osteotomy guide, characterized in that: include: A frame (1) comprises a main rod (10), a first support rod (11) fixedly connected to one end of the main rod (10), and a second support rod (12) slidably mounted on the main rod (10), wherein the first support rod (11) is parallel to the second support rod (12) and forms a U-shaped structure together with the main rod (10); A positioning structure (2), arranged on the second support rod (12), suitable for positioning at the position of the fibular head; A first guide sleeve (31) is fixedly arranged on the first support rod (11) and has a first central guide hole (310), wherein the central axis of the first central guide hole (310) passes through the central position of the positioning structure (2); A positioning column (4) is rotatably sleeved on the first guide sleeve (31), and a plurality of through holes (41) are provided on the positioning column (4); a second guide sleeve (32) detachably mounted inside one of the through holes (41), the second guide sleeve (32) having a second central guide hole (320), the central axis of the first central guide hole (310) being parallel to the central axis of the second central guide hole (320); A position determining member (5), one end of which is rotatably mounted on the positioning column (4), and the other end of which has a reference end (51), the central axis of the first central guide hole (310) and the central axis of the second central guide hole (320) determine an osteotomy reference surface, and the distance between the reference end (51) and the osteotomy reference surface is a set distance; the reference end (51) is provided with an insertion plate (52), and the insertion plate (52) is parallel to the osteotomy reference surface; the insertion plate (52) is provided with a plurality of insertion guide holes (56 ), the central axes of a plurality of the insertion guide holes (56) are parallel and coplanar, and are parallel to the osteotomy reference surface; the position determining member (5) comprises a base (50), one end of the base (50) forms a U-shaped structure, two opposite side surfaces (55) of the U-shaped structure have mounting holes (53) rotatably sleeved on the positioning column (4), the other end of the base (50) is provided with an indicator rod (54), the indicator rod (54) is bent along the position of the proximal end of the medial tibia, and the top end of the indicator rod (54) is the reference end (51); The main rod (10) is provided with a scale, wherein the 0 scale position of the scale is flush with the end of the first guide sleeve (31) facing the positioning structure (2); and the scale increases from the 0 scale position in a direction away from the first support rod (11).

2. The osteotomy guide according to claim 1, characterized in that: The positioning structure (2) is a positioning bowl, which is suitable for buckling at the position of the fibular head.

3. The osteotomy guide according to claim 1, characterized in that: The main rod (10) is a polygonal prism structure, and the second support rod (12) can move along the axial direction of the main rod (10), but cannot rotate around the circumference of the main rod (10).

4. The osteotomy guide according to claim 1, characterized in that: The second guide sleeve (32) comprises a second guide sleeve body (321) and an annular flange (322) arranged at one end of the second guide sleeve body (321); the outer diameter of the second guide sleeve body (321) is consistent with the inner diameter of the through hole (41).

5. The osteotomy guide according to claim 1, characterized in that: The first guide sleeve (31) is located on the inner side of the U-shaped structure, and all the through holes (41) are located on the outer side of the U-shaped structure.

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