Expansion device for centrum cancellous bone in vertebroplasty

Abstract

The utility model discloses an expanding device for a cancellous bone of a centrum in a vertebroplasty. The expanding device comprises an outer fixed pipe fitting, an inner movable rod piece and a foldable drill bit, the outer fixing pipe fitting is arranged in a working channel of a target vertebral body; a foldable drill bit is arranged at the front end of the inner movable rod piece, the foldable drill bit is inserted from the first end of the outer fixing pipe piece and can be positioned after moving along the outer fixing pipe piece, and after the foldable drill bit extends out of the second end of the outer fixing pipe piece, the flare angle of the end of the foldable drill bit is gradually increased along with reduction of the overlapping size of the foldable drill bit and the outer fixing pipe piece. The end part of the foldable drill bit is provided with a plurality of concave contact surfaces, and the concave contact surfaces are used for forming a cavity with a rough interface in the cone when the foldable drill bit is screwed in. The centrum cancellous bone expansion device can perform accurate centrum cancellous bone expansion, promote uniform dispersion of bone cement, increase the contact area of the bone cement and the cancellous bone, prevent displacement of the bone cement after an operation, simplify operation steps and shorten operation time.

Description

Technical Field

[0001] The utility model relates to an auxiliary puncture device for minimally invasive percutaneous vertebroplasty, in particular to an expansion device for vertebral cancellous bone in vertebroplasty, belonging to the technical field of medical devices. Background Art

[0002] Percutaneous vertebroplasty (PVP), also known as vertebral reinforcement or vertebral filling, refers to the percutaneous puncture from the posterior route under the guidance of imaging technology, inserting the needle along the pedicle, injecting specific substances (such as bone cement PMMA material) into the diseased vertebral body, and observing the dynamic distribution of the injected substance in the vertebral body through a monitor. Uniform diffusion of bone cement in the vertebral body during surgery is a prerequisite for obtaining satisfactory surgical results and preventing complications of bone cement displacement after surgery. Especially for special fracture patients such as Kummell (old vertebral fracture nonunion) disease, a liquid-containing cavity is often formed in the fractured vertebral body. How to improve the uniform diffusion of bone cement and increase the contact area between bone cement and cancellous bone is crucial to preventing bone cement displacement after surgery.

[0003] At present, the following two methods are mainly used in clinical practice to promote bone cement diffusion:

[0004] ① Before injecting bone cement, a vertebral drill is used to drill and create a channel to facilitate the placement of the bone cement push rod and the diffusion of bone cement. However, the channel created by the vertebral drill is narrow, and the diffusion space of bone cement is limited. The injection of bone cement may result in excessive pressure, which increases the risk of bone cement leakage.

[0005] ② Using an expandable balloon to expand and create a cavity (also known as minimally invasive percutaneous kyphoplasty (PKP)). Although it can reduce the pressure during bone cement injection, the presence of the cavity may result in a dense surface, which is not conducive to the uniform diffusion of bone cement into the cancellous bone. It also increases the stress between the bone cement and the vertebral bone interface, making it easy for bone cement to shift after surgery. In addition, before implanting the expandable balloon, it is still necessary to drill the vertebral body to create a channel before the additional surgical steps can be implemented, which will prolong the operation time and increase the number of fluoroscopy times. Summary of the invention

[0006] In order to overcome the above-mentioned deficiencies of the prior art, the utility model provides an auxiliary device for promoting the diffusion of bone cement during vertebroplasty, which can accurately expand the vertebral cancellous bone, promote uniform diffusion of bone cement, increase the contact area between bone cement and cancellous bone, prevent postoperative displacement of bone cement, simplify surgical steps, and shorten surgical time.

[0007] The technical solution adopted by the utility model to solve its technical problems is:

[0008] A device for expanding vertebral cancellous bone in vertebroplasty, comprising:

[0009] An external fixation tube, the external fixation tube being inserted into a working channel of a target vertebra;

[0010] An inner movable rod, wherein a foldable drill bit is provided at the front end of the inner movable rod, wherein the foldable drill bit is inserted from the first end of the outer fixed tube and can be positioned after being displaced along the outer fixed tube, and when the foldable drill bit extends from the second end of the outer fixed tube, the end opening angle of the foldable drill bit gradually increases as the overlapping dimension with the outer fixed tube decreases;

[0011] The end of the foldable drill bit has a plurality of concave contact surfaces, and the concave contact surfaces are used to form a cavity with a rough interface in the cone when the foldable drill bit is screwed in.

[0012] As described above, an expansion device for vertebral cancellous bone in vertebroplasty, optionally, the external fixation tube includes an outer tube body, a first force-bearing portion is provided on the outer periphery of the first end of the outer tube body, the second end of the outer tube body is used to insert the working channel, the outer diameter of the outer tube body is adapted to the working channel and can rotate relatively and displace axially.

[0013] As described above, an expansion device for vertebral cancellous bone in vertebroplasty, optionally, the inner movable rod comprises a hollow inner core, the front end portion of the hollow inner core is used to fix the foldable drill bit, the rear end portion of the hollow inner core is provided with a second force-bearing portion, the outer wall of the rear end portion of the hollow inner core is provided with an external threaded portion, the inner wall of the first end portion of the outer tube body is provided with an internal threaded portion, the external threaded portion is spirally connected to the internal threaded portion, and when the external threaded portion begins to be screwed into the internal threaded portion, the front end portion of the hollow inner core begins to extend out of the second end portion of the outer tube body.

[0014] As described above, in the expansion device for vertebral cancellous bone in vertebroplasty, optionally, the external threaded portion is provided with a scale mark in the axial direction, and the scale mark is used to display the matching length of the external threaded portion and the internal threaded portion.

[0015] As described above, an expansion device for vertebral cancellous bone in vertebroplasty, optionally, the foldable drill bit includes a fixed block and a plurality of expansion plates and support rods of the same number, the fixed block is fixedly connected to the inner side of the front end portion of the hollow inner core, one end of each of the expansion plates is fixedly connected to the front end portion of the hollow inner core, the other end of each of the expansion plates is respectively fixedly connected to one end of each of the support rods, and the other end of each of the support rods is fixedly connected to the fixed block; the angle between the support rod and the front end portion of the hollow inner core constitutes the end angle, the end angle is constrained by the expansion plate to form a preset angle, and the preset angle can be reduced under the action of external force; the outer surface formed by the connection of the expansion plate and the support rod constitutes the concave contact surface.

[0016] As described above, in the expansion device for vertebral cancellous bone in vertebroplasty, optionally, one end of the expansion piece connected to the support rod is extended to form a reflective portion, and the reflective portion is perpendicular to the bone interface inside the cone.

[0017] As described above, in the expansion device for vertebral cancellous bone in vertebroplasty, optionally, the overall shape of the expansion piece is inwardly folded, and the inwardly folded corner is located between the support rod and the hollow inner core and faces the fixing block.

[0018] With the help of the above technical solution, the utility model of a vertebral cancellous bone expansion device used in vertebroplasty can achieve at least the following technical advantages:

[0019] The expansion device of the utility model is provided with an external fixing pipe and an internal movable rod of a combined structure, and a foldable drill bit directly acting on the cone is provided at the front end of the internal movable rod. By utilizing the assembly relationship of the three, the foldable drill bit can be moved toward or away from the cone, and the precise expansion of the vertebral cancellous bone is achieved with the help of the foldable drill bit. A plurality of concave contact surfaces are provided at the end of the foldable drill bit, and a cavity with a rough interface is formed in the cancellous bone by utilizing the concave contact surfaces, so that the cavity based on the rough interface can promote uniform diffusion of bone cement, and can increase the contact area between bone cement and cancellous bone, thereby preventing postoperative displacement of bone cement. In addition, when the expansion device of the utility model is used as a whole, the external fixing pipe is inserted into the working channel of the target vertebra, and there is no need to insert a vertebral drill in advance, which can simplify the surgical steps and shorten the surgical time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0021] Figure 1 This is a structural diagram of the first state of an expansion device according to an embodiment of the utility model.

[0022] Figure 2 This is a second state structural diagram of an expansion device according to an embodiment of the utility model.

[0023] Meaning of reference numerals in the figure:

[0024] 1-external fixing pipe; 101-external pipe body; 1011-internal threaded part; 102-first force-bearing part;

[0025] 2-inner movable rod; 201-hollow inner core; 2011-external threaded portion; 2012-scale mark; 202-second force-bearing portion;

[0026] 3-foldable drill bit; 301-fixing block; 302-expansion sheet; 3021-reflection part; 303-support rod. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiment of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the utility model.

[0028] In related technologies, vertebral compression fractures caused by osteoporosis need to be treated by minimally invasive percutaneous vertebroplasty, and the process is roughly as follows:

[0029] 1. The patient is in prone position, local disinfection is performed, and local or general anesthesia is used depending on the situation;

[0030] 2. Select the puncture needle as needed. Generally, the pedicle approach is used. Puncture is performed under fluoroscopy. After the puncture is in place, the puncture needle core is removed.

[0031] 3. Use a special syringe to suck in the prepared bone cement (PMMA), load it into the spiral propulsion device, and assemble it firmly;

[0032] 4. Rotate the push rod of the spiral propulsion device and observe the state of the extruded bone cement. When it becomes toothpaste-like, quickly connect the syringe and the puncture needle firmly, perform the injection under fluoroscopy and observe the distribution of bone cement in the vertebral body;

[0033] 5. After the injection is completed, remove the spiral propulsion device, insert the puncture needle core, remove the puncture needle, bandage the local area, and the operation is completed.

[0034] In order to obtain satisfactory surgical results and prevent complications of postoperative bone cement displacement, it is necessary to ensure that the bone cement is evenly dispersed in the vertebral body during the operation. However, the above-mentioned bone cement dispersion through the spiral propulsion device requires the use of a vertebral drill to drill into a channel before injecting the bone cement to facilitate the insertion of the bone cement push rod. Since the channel made by the vertebral drill is narrow and the bone cement diffusion space is limited, the injection of bone cement may result in excessive pressure, which increases the risk of bone cement leakage.

[0035] In terms of promoting the diffusion of bone cement, vertebral compression fractures caused by osteoporosis can also be treated by percutaneous kyphoplasty. The main process is as follows:

[0036] 1. Under fluoroscopy, use a detachable needle holder to insert the puncture needle through the pedicle into the collapsed vertebral body. After confirmation, remove the needle holder, insert the working cannula along the needle core, and then remove the needle core to establish a working channel;

[0037] 2. Place the vertebral drill into the working cannula (a hollow vertebral drill can be used if a biopsy is required), observe under fluoroscopy, and remove the vertebral drill after reaching the required depth;

[0038] 3. Send the balloon into the collapsed vertebral body and confirm through fluoroscopy that the balloon should be completely extended out of the working cannula;

[0039] 4. Use a metered inflator to slowly inject contrast agent under fluoroscopy to expand the balloon, elevate the collapsed vertebral body and form a cavity, read the pressure value and volume, aspirate the contrast agent, shrink the balloon to a vacuum, and then slowly withdraw it;

[0040] 5. Under fluoroscopy, bone cement is injected into the vertebral body, and then the working sleeve is removed, and the operation is completed.

[0041] This method uses an expandable balloon to expand and create a cavity. Although it can reduce the pressure when injecting bone cement, the presence of the cavity may result in a dense surface, which is not conducive to the uniform diffusion of bone cement into the cancellous bone. It will also increase the stress between the bone cement and the vertebral bone interface, making it easy for bone cement to shift after surgery, and it cannot fundamentally solve the problem. In addition, before implanting the expandable balloon, it is still necessary to drill the vertebral body to create a channel before adding surgical steps, which has the disadvantages of prolonging the operation time and increasing the number of fluoroscopy.

[0042] In view of this, an embodiment of the utility model provides an expansion device for vertebral cancellous bone during vertebroplasty, which can not only perform precise vertebral cancellous bone expansion to form a honeycomb structure in the cancellous bone, promote uniform diffusion of bone cement, increase the contact area between bone cement and cancellous bone, and prevent postoperative bone cement displacement, but also simplify the surgical steps and shorten the operation time.

[0043] Figure 1This is a structural schematic diagram of a preferred embodiment of the utility model in the first use state, at which time the foldable drill bit 3 in the expansion device is completely located in the external fixing pipe 1, and the foldable drill bit 3 is in a folded non-working state; Figure 2 It is a structural schematic diagram of a preferred embodiment of the utility model in the second use state. At this time, the foldable drill bit 3 in the expansion device is partially located in the external fixed pipe 1, and a certain size of end opening angle can be obtained for docking the expansion cone.

[0044] Reference Figure 1 and Figure 2 The utility model provides an expansion device for vertebral cancellous bone in vertebroplasty, comprising:

[0045] The external fixation pipe 1 is inserted into the working channel of the target vertebra. The external fixation pipe 1 is used to carry the working channel formed by puncturing in advance during the operation, so that there is no need to insert a vertebral drill in advance, which simplifies the surgical process.

[0046] The inner movable rod 2 has a foldable drill bit 3 at its front end, which is inserted from the first end of the outer fixed pipe 1 and can be positioned after being displaced along the outer fixed pipe 1. When the foldable drill bit 3 extends from the second end of the outer fixed pipe 1, the end opening angle of the foldable drill bit 3 gradually increases as the overlap size with the outer fixed pipe 1 decreases. The matching depth between the inner movable rod 2 and the outer fixed pipe 1 is adjustable and controllable, so as to realize the rotation of the foldable drill bit 3 toward the cone, and the operation is simple and convenient.

[0047] The end of the foldable drill bit 3 has a plurality of concave contact surfaces, which are used to form a cavity with a rough interface in the cone when the foldable drill bit 3 is screwed in.

[0048] The end opening angle of the foldable drill bit 3 is adjustable and controllable. The end opening angle can be expanded to different angles in an "inverted umbrella shape" as the inner movable rod 2 rotates relative to the external fixed pipe 1, and different specifications of the end of the foldable drill bit 3 are obtained to adapt to fractured vertebrae with different compression degrees. After the expansion is completed, as the inner movable rod 2 rotates out, the foldable drill bit 3 can be folded and retracted into the external fixed pipe 1 for easy removal; the end of the foldable drill bit 3 of fixed specifications, with the help of multiple concave contact surfaces at this time, acts on the bone interface, and forms a rough interface cavity in the cone through rotation and progressive action. The rough interface cavity can be used to promote the diffusion of bone cement and increase the contact area between bone cement and cancellous bone.

[0049] Optionally, the external fixed pipe fitting 1 described in this embodiment includes an outer tube body 101, a first force-bearing portion 102 is provided on the outer periphery of the first end of the outer tube body 101, the second end of the outer tube body 101 is used to be inserted into the working channel, and the outer diameter of the outer tube body 101 is adapted to the working channel and can rotate relatively and displace axially.

[0050] In a specific implementation, the first force-bearing portion 102 is used to receive external force to drive the relative movement of the outer tube body 101. For example, by holding the first force-bearing portion 102 and applying force, the outer tube body 101 can be displaced along the axial direction of the working channel or can rotate around the axis of the working channel, which is used to meet the need of inserting the external fixing pipe 1 into the working channel to a certain depth, or to meet the need of the linkage foldable drill bit 3 to rotate relative to the cone and / or move in and out. The specific structure of the first force-bearing portion 102 is not limited, and can be as shown in the figure, as long as the above functional requirements are met.

[0051] Optionally, the inner movable rod 2 described in this embodiment includes a hollow inner core 201, the front end of the hollow inner core 201 is used to fix the foldable drill bit 3, the rear end of the hollow inner core 201 is provided with a second force-bearing portion 202, the outer wall of the rear end of the hollow inner core 201 is provided with an external threaded portion 2011, the inner wall of the first end of the outer tube body 101 is provided with an internal threaded portion 1011, the external threaded portion 2011 is spirally connected with the internal threaded portion 1011, and when the external threaded portion 2011 begins to be screwed into the internal threaded portion 1011, the front end of the hollow inner core 201 begins to extend out of the second end of the outer tube body 101.

[0052] The specific structure of the second force-bearing portion 202 can be as shown in the figure, or it can be set arbitrarily, subject to the following functions: the second force-bearing portion 202 is used to receive the external force to drive the relative movement of the hollow inner core 201. For example, by holding the second force-bearing portion 202 and applying force, the hollow inner core 201 can be axially displaced along the outer tube body 101. During the axial displacement, the end opening angle of the foldable drill bit 3 can be adjusted and fixed by changing the degree of spiral fit with the outer tube body 101.

[0053] The hollow design of the hollow inner core 201 with open ends can release the pressure in the fractured vertebra in time during operation, reducing the pain of the patient during the operation. Especially for patients with Kummell's disease, the effusion formed in the vertebral body can be sucked along the hollow tube to promote better fit between bone cement and cancellous bone.

[0054] Optionally, the external threaded portion 2011 described in this embodiment is provided with a scale mark 2012 in the axial direction, and the scale mark 2012 is used to display the matching length between the external threaded portion 2011 and the internal threaded portion 1011 .

[0055] The intuitive scale mark 2012 can help the operator clearly understand the change in the length of the spiral fit between the external fixation pipe 1 and the internal movable rod 2, and indirectly and quantitatively understand the change in the end angle of the foldable drill bit 3, so as to achieve the purpose of accurately grasping the effect of vertebral cancellous bone expansion.

[0056] Optionally, the foldable drill bit 3 described in this embodiment includes a fixed block 301 and a plurality of expansion pieces 302 and support rods 303 of the same number, the fixed block 301 is fixedly connected to the inner side of the front end of the hollow inner core 201, one end of each expansion piece 302 is fixedly connected to the front end of the hollow inner core 201, the other end of each expansion piece 302 is fixedly connected to one end of each support rod 303, and the other end of each support rod 303 is fixedly connected to the fixed block 301; the angle between the support rod 303 and the front end of the hollow inner core 201 constitutes the end angle, the end angle is constrained by the expansion piece 302 to form a preset angle, and the preset angle can be reduced under the drive of external force, and the outer surface formed by the expansion piece 302 and the support rod 303 constitutes a concave contact surface. The principle that the preset angle can be changed elastically here can be based on the toughness and elasticity of the material of the expansion piece 302 itself, or based on its structural design, such as the overall inward folded shape, or a combination of material and structural design, or other conventional settings that can be replaced by those skilled in the art to achieve this function.

[0057] It should be noted that, when the foldable drill bit 3 in this embodiment is not constrained by the outer tube body 101, a plurality of support rods 303, for example four, are connected to the fixed block 301 at one end and are connected to four expansion pieces 302 at the other ends. All expansion pieces 302 are also connected to the hollow inner core 201, preferably evenly distributed on the surrounding walls of the hollow inner core 201. The expansion pieces 302 pull the support rods 303 to form an "inverted umbrella shape" at the front end of the hollow inner core 201, and the support rods 303 have a maximum opening angle relative to the hollow inner core 201 in static state. In the foldable drill bit 3 in this embodiment, because the small end of the "inverted umbrella shape" is located in the outer tube body 101, the opening angle of the support rods 303 relative to the hollow inner core 201 will decrease as the depth of the support rods 303 in the outer tube body 101 increases until it reaches a fully folded state.

[0058] According to the above functional requirements, the expansion sheet 302 can be composed of four high-toughness sheets. The specific material and specifications of the high-toughness sheets can be determined according to the specific situation to meet the requirements of expansion and contraction and folding.

[0059] Optionally, one end of the expansion piece 302 connected to the support rod 303 is extended to form a folded portion 3021, and the folded portion 3021 is perpendicular to the bone interface inside the cone. The expansion piece 302 is provided with the folded portion 3021 at the working end of the foldable drill bit 3, which can be perpendicular to the bone interface during the screwing process, which is more convenient for the successful construction of a cavity with a "honeycomb" rough interface.

[0060] Optionally, the overall shape of the expansion piece 302 is inwardly folded, and the inwardly folded corner is located between the support rod 303 and the hollow inner core 201 and faces the fixed block 301. It can be understood that the inwardly folded expansion piece 302 is mainly used to construct an inwardly concave contact surface, and is also used to assist in achieving the reversible change of the end opening angle of the foldable drill bit 3, that is, to achieve the elastic folding and automatic expansion functions of the foldable drill bit 3.

[0061] The present invention provides an expansion device for vertebral cancellous bone in vertebroplasty, and the specific use process is as follows:

[0062] Step 1: After the target vertebral working channel of the surgical patient is inserted, the external fixation pipe 1 is inserted along the working channel. After confirming that the depth of the external fixation pipe 1 is appropriate under fluoroscopy, the external fixation pipe 1 is fixed to the working channel, the depth of the external fixation pipe 1 is kept unchanged, and the internal movable rod 2 is gradually screwed in;

[0063] Step 2: After confirming that the opening angle of the foldable drill bit 3 is appropriate as the inner movable rod 2 is screwed in, the external fixation pipe 1 is rotated in situ and gradually pushed forward so that the foldable drill bit 3 forms a cavity with a rough interface in the vertebral body;

[0064] Step 3: After confirming that the cavity size is appropriate through perspective, fix the foldable drill bit 3, slowly screw out the inner movable rod 2, retract the foldable drill bit 3 into the outer fixing pipe 1, and pull out the outer fixing pipe 1.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification and equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A device for expanding vertebral cancellous bone in vertebroplasty, characterized in that: include: An external fixation tube, the external fixation tube being inserted into a working channel of a target vertebra; An inner movable rod, wherein a foldable drill bit is provided at the front end of the inner movable rod, and the foldable drill bit is inserted from the first end of the outer fixed pipe member and can be positioned after being displaced along the outer fixed pipe member; when the foldable drill bit extends from the second end of the outer fixed pipe member, the end opening angle of the foldable drill bit gradually increases as the overlapping dimension with the outer fixed pipe member decreases; The end of the foldable drill bit has a plurality of concave contact surfaces, and the concave contact surfaces are used to form a cavity with a rough interface in the cone when the foldable drill bit is screwed in.

2. The device for expanding vertebral cancellous bone in vertebroplasty according to claim 1, characterized in that: The external fixing pipe comprises an outer tube body, a first force-bearing portion is arranged on the outer periphery of the first end of the outer tube body, the second end of the outer tube body is used for plugging into the working channel, the outer diameter of the outer tube body is adapted to the working channel and can rotate relatively and move axially.

3. The device for expanding vertebral cancellous bone in vertebroplasty according to claim 2, characterized in that: The inner movable rod comprises a hollow inner core, the front end portion of the hollow inner core is used for fixedly connecting the foldable drill bit, and the rear end portion of the hollow inner core is provided with a second force-bearing portion; the outer wall of the rear end portion of the hollow inner core is provided with an external threaded portion, and the inner wall of the first end portion of the outer tube body is provided with an internal threaded portion, and the external threaded portion is spirally connected to the internal threaded portion; when the external threaded portion begins to be screwed into the internal threaded portion, the front end portion of the hollow inner core begins to extend out of the second end portion of the outer tube body.

4. The device for expanding vertebral cancellous bone in vertebroplasty according to claim 3, characterized in that: The external threaded portion is provided with a scale mark in the axial direction, and the scale mark is used to display the matching length of the external threaded portion and the internal threaded portion.

5. A device for expanding vertebral cancellous bone in vertebroplasty according to claim 3 or 4, characterized in that: The foldable drill bit includes a fixed block and a plurality of expansion plates and support rods of the same number, wherein the fixed block is fixedly connected to the inner side of the front end portion of the hollow inner core, one end of each of the expansion plates is fixedly connected to the front end portion of the hollow inner core, the other end of each of the expansion plates is respectively fixedly connected to one end of each of the support rods, and the other end of each of the support rods is fixedly connected to the fixed block; the angle between the support rod and the front end portion of the hollow inner core constitutes the end angle, which is constrained by the expansion plate to form a preset angle and can be reduced by an external force; the outer surface formed by the connection between the expansion plate and the support rod constitutes the concave contact surface.

6. The device for expanding vertebral cancellous bone in vertebroplasty according to claim 5, characterized in that: One end of the expansion piece connected to the support rod is extended to form a folded portion, and the folded portion is perpendicular to the bone interface inside the cone.

7. The device for expanding vertebral cancellous bone in vertebroplasty according to claim 6, characterized in that: The overall shape of the expansion piece is an inward folding type, and the inward folding corner is located between the support rod and the hollow inner core and faces the fixing block.

Images