Nickel-titanium memory alloy ship-shaped connector

Abstract

The invention relates to the technical field of medical apparatuses and instruments, and discloses a nickel-titanium memory alloy ship-shaped connector which comprises a connecting frame, two annular frames, a connecting rod and a connecting rod. An extension part is arranged on the ring frame, the extension part comprises two extension arms, and the two extension arms are both connected to the inner wall of the ring frame in a sliding mode; a reset part is further arranged on the ring frame and used for manually driving the two extension arms to retract into the ring frame. Through the arrangement of the extension parts, the two extension arms can automatically extend out and form an annular structure with the annular frame after the annular frame is in contact with a bone, so that the stability of fixing the bone is greatly improved, independent installation operation is not needed, the operation time is saved, and by utilizing the characteristics of nickel-titanium memory alloy, the operation efficiency is greatly improved. The annular frame and the extension arms above the annular frame can automatically hold the skeleton tightly after being heated, use of skeleton fixing pieces is reduced, and then damage to the skeleton is reduced.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, specifically to a nickel-titanium shape memory alloy boat-shaped bone setter. Background Technology

[0002] In orthopedic clinical treatment, the boat-shaped bone setter is a medical device used for fracture reduction and fixation. Existing boat-shaped bone setters usually consist of a support structure and auxiliary connecting components. The support structure often adopts an arc or boat-shaped design that conforms to the anatomical shape of human bones to adapt to the physiological curve of the fracture site and improve the fit between the support structure and the bone surface. The auxiliary connecting components include bone fixation components such as bone screws and bone plates, which are used to enhance the fixation stability between the support structure and the bone and provide a stable environment for bone healing.

[0003] However, the existing technology has the following problems: The existing boat-shaped bone fixation device has a near-semi-circular contact area with the bone. Therefore, the contact area between the fixation structure and the bone is limited, requiring medical staff to install additional bone fixation components to optimize the fixation effect. This results in a longer overall installation operation time and a more complicated procedure. Furthermore, the more bone fixation components used, the more damage to the bone, which can easily lead to sequelae. Summary of the Invention

[0004] The purpose of this invention is to provide a nickel-titanium shape memory alloy boat-shaped bone graft to solve the above-mentioned problems and overcome the defects of the prior art, as detailed below.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a nickel-titanium shape memory alloy boat-shaped bone setter, comprising: a connecting frame, on which two ring frames are mounted. The ring frames are semi-circular and hollow, and are made of nickel-titanium shape memory alloy. When heated, the ring frames generate an inward contraction elastic force. An extension portion is provided on each ring frame, comprising two extension arms. Both extension arms are slidably connected to the inner wall of the ring frame. When heated, the two extension arms extend from both ends of the ring frame and form a ring structure with the ring frame. A reset portion is also provided on the ring frame for manually driving the two extension arms to retract into the ring frame.

[0006] Preferably, the extension portion further includes a fixing seat, which is installed inside the ring frame. Two arc-shaped springs are connected to the fixing seat. The two arc-shaped springs are located inside the two extension arms respectively, and the ends of the two arc-shaped springs away from the fixing seat are connected to the inner walls of the two extension arms respectively.

[0007] Preferably, both the arc spring and the extension arm are made of nickel-titanium shape memory alloy. When the arc spring is heated, it can generate elastic force and drive the extension arm to extend outward from the ring frame. When the two extension arms are heated, they will generate elastic force that bends towards each other.

[0008] Preferably, the extension arm is provided with a locking mechanism, which includes a fixing block, a pin, and a cylindrical spring. The fixing block is installed on the inner wall of the extension arm, the pin is vertically slidably connected to the extension arm, and the cylindrical spring is connected between the inner wall of the pin and the fixing block.

[0009] Preferably, the ring frame has two limiting holes, and the pin can be inserted into the limiting holes after the extension arm is extended outward into place.

[0010] Preferably, the extension portion further includes a stabilizing mechanism, which includes a first protrusion and a second protrusion. The first protrusion and the second protrusion are respectively connected to the ends of the two extension arms away from the fixed base. The first protrusion is connected with a plurality of inserts, and the second protrusion is provided with a plurality of square slots. The plurality of inserts can be respectively embedded in the plurality of square slots when the two extension arms are extended outward into position.

[0011] Preferably, the reset part includes a reel, a rotating shaft, and two pull ropes. The rotating shaft is rotatably mounted inside the fixed base. The reel is connected to the outer wall of the rotating shaft. One end of each of the two pull ropes is connected to the reel, and the other end of each pull rope is connected to two extension arms respectively. Both pull ropes are wound on the reel. When the reel rotates, it can drive the two extension arms to retract and reset by winding up the two pull ropes.

[0012] Preferably, the rotating shaft passes through the ring frame and the connecting frame, and the end of the rotating shaft located outside the connecting frame is provided with an internal hexagonal nut.

[0013] Preferably, a first bone pad is connected to the extension arm, and two second bone pads are installed on the ring frame. Both the first and second bone pads are used to contact the periosteum, and multiple protrusions are provided on the first and second bone pads respectively.

[0014] The beneficial effects are: 1. This nickel-titanium shape memory alloy boat-shaped bone fixation device, through the setting of the extension section, allows the two extension arms to automatically extend after the ring frame comes into contact with the bone, forming a ring structure with the ring frame, which greatly increases the stability of bone fixation and eliminates the need for separate installation operations, saving surgical time. Utilizing the characteristics of nickel-titanium shape memory alloy, the ring frame and the extension arms above it can automatically hug the bone after heating, reducing the use of bone fixation components and thus reducing damage to the bone.

[0015] 2. This nickel-titanium shape memory alloy boat-shaped bone setter, through the setting of the reset part, allows medical staff to remove the ring frame by rotating the reel on the shaft to wind up the two pull ropes. During the winding process, the two pull ropes pull the two extension arms to slide along the inner wall of the ring frame into the ring frame, thereby realizing the retraction and reset of the extension arms. After the extension arms retract and reset, the two ring frames can be removed, making the operation relatively convenient.

[0016] 3. This nickel-titanium shape memory alloy boat-shaped bone setter, through the setting of the locking mechanism, ensures that after the two extension arms are extended into place, the pins on the extension arms are locked by inserting into the limiting holes, so that the two extension arms cannot move on the ring frame temporarily. This ensures that the bone setter can continuously and stably fix the fracture site during the fracture healing period, avoids the displacement of the fracture ends due to the movement of the extension arms, and ensures the fracture healing effect. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the connecting frame structure of the present invention; Figure 3 This is a schematic diagram of the extension structure of the present invention; Figure 4 This is a schematic diagram of the arc-shaped spring structure of the present invention; Figure 5 This is a schematic diagram of the locking mechanism structure of the present invention; Figure 6 This is a schematic diagram of the pin structure of the present invention; Figure 7 This is a schematic diagram of the stabilizing mechanism structure of the present invention; Figure 8 This is a schematic diagram of the reset part structure of the present invention; Figure 9 This is a schematic diagram of the rope structure of the present invention.

[0019] The annotations in the attached figures are explained as follows: 1. Connecting frame; 2. Ring frame; 3. Extension section; 31. Extension arm; 32. Fixing base; 33. Curved spring; 4. Locking mechanism; 41. Fixing block; 42. Pin; 43. Cylindrical spring; 44. Limiting hole; 5. Stabilizing mechanism; 51. First protrusion; 52. Second protrusion; 53. Insert; 54. Square groove; 6. Reset section; 61. Reel; 62. Pull rope; 63. Rotary shaft; 7. First bone pad; 8. Second bone pad. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Example

[0021] Please see Figure 1 - Figure 9 A nickel-titanium shape memory alloy boat-shaped bone setter includes: a connecting frame 1, on which two ring frames 2 are installed. The ring frames 2 are semi-circular and hollow. The ring frames 2 are made of nickel-titanium shape memory alloy. When heated, the ring frames 2 can generate an inward contraction elastic force. After the ring frames 2 are implanted into the human body, they absorb heat from the human body, thereby raising the temperature and triggering their shape memory function, causing the ring frames 2 to generate an inward contraction elastic force. The ring frames 2 can use the inward contraction elastic force to play a role in embracing and fixing the fracture site. The two ring frames 2 are used to stabilize and clamp the bones on both sides of the fracture crack, keeping the bones in an aligned state and preventing the fracture ends from shifting during the healing process, thus providing a stable state for fracture healing.

[0022] Furthermore, the ring frame 2 is provided with an extension section 3, which includes two extension arms 31. Both extension arms 31 are slidably connected to the inner wall of the ring frame 2. When heated, the two extension arms 31 extend from both ends of the ring frame 2, forming a ring structure. The extension section 3 also includes a fixing seat 32, which is installed inside the ring frame 2. Two arc-shaped springs 33 are connected to the fixing seat 32, located inside the two extension arms 31. The ends of the two arc-shaped springs 33 furthest from the fixing seat 32 are connected to the inner walls of the two extension arms 31. Both the arc-shaped springs 33 and the extension arms 31 are made of nickel-titanium shape memory alloy. When heated, the arc-shaped springs 33 generate elastic force, causing the extension arms 31 to extend outwards from the ring frame 2. When heated, the two extension arms 31 generate an elastic force that bends towards each other. When the ring frame 2 is implanted into the human body, under the influence of body heat, the arc-shaped springs 33 first trigger the shape memory effect to generate elastic force, which directly acts on the... The inner wall of the extension arm 31 pushes the extension arm 31 to slide along the inner wall of the ring frame 2 and extend it to the outside of the ring frame 2. At this time, the two extension arms 31 extend outward from both ends of the semi-circular ring frame 2, eventually forming a nearly closed ring structure. Subsequently, the extension arm 31 itself will also generate an elastic force to hold the bone when heated. When the ring structure formed by the two extension arms 31 and the ring frame 2 can adaptively adjust the holding range according to the specific size of the fracture site, it can be used for bone fracture fixation within a certain size range. Through the setting of the extension part 3, the two extension arms 31 can automatically extend out after the ring frame 2 contacts the bone and form a ring structure with the ring frame 2, which greatly increases the stability of bone fixation and eliminates the need for separate installation, saving surgical time. By utilizing the characteristics of nickel-titanium shape memory alloy, the ring frame 2 and the extension arms 31 above it can automatically hold the bone after heating, reducing the use of bone fixation components and thus reducing damage to the bone.

[0023] In addition, a locking mechanism 4 is provided on the extension arm 31. The locking mechanism 4 includes a fixing block 41, a pin 42, and a cylindrical spring 43. The fixing block 41 is installed on the inner wall of the extension arm 31. The pin 42 is vertically slidably connected to the extension arm 31. The cylindrical spring 43 is connected between the inner wall of the pin 42 and the fixing block 41. Two limiting holes 44 are provided on the ring frame 2. The pin 42 can be inserted into the limiting holes 44 after the extension arm 31 is extended outward. The fixing block 41 provides a fixed support point for the cylindrical spring 43. The cylindrical spring 43 is pre-compressed so that the cylindrical spring 43 always exerts an upward thrust on the pin 42, so that one end of the pin 42 always abuts against the inner wall of the ring frame 2. When the extension arm 31 slides outward along the inner wall of the ring frame 2, the pin 42 will slide on the inner wall of the ring frame 2 with the movement of the extension arm 31. At this time, the cylindrical spring 43... 3 is still in a compressed state. When the extension arm 31 is extended into place, the pin 42 aligns with the limiting hole 44 on the ring frame 2. At this time, the elastic force of the cylindrical spring 43 is released, causing the cylindrical spring 43 to push the pin 42 to slide vertically and insert into the limiting hole 44. Through the cooperation of the pin 42 and the limiting hole 44, the extension arm 31 is fixed relative to the ring frame 2, thereby locking the position of the extension arm 31. Through the setting of the locking mechanism 4, after the two extension arms 31 are extended into place, the pin 42 on the extension arm 31 is limited and locked by inserting into the limiting hole 44, so that the two extension arms 31 cannot extend or retract on the ring frame 2 temporarily. This ensures that the bone setter can continuously and stably fix the fracture site during the fracture healing period, avoids displacement of the fracture ends due to the movement of the extension arm 31, and ensures the fracture healing effect.

[0024] In addition, the extension part 3 also includes a stabilizing mechanism 5, which includes a first protrusion 51 and a second protrusion 52. The first protrusion 51 and the second protrusion 52 are respectively connected to the ends of the two extension arms 31 away from the fixed base 32. The first protrusion 51 is connected to a plurality of inserts 53, and the second protrusion 52 is provided with a plurality of square slots 54. The plurality of inserts 53 can be respectively embedded in the plurality of square slots 54 when the two extension arms 31 are extended outward into their positions. When the two extension arms 31 are about to be extended outward into their positions, the ends of the two extension arms 31 away from the fixed base 32 approach each other. At this time, the plurality of inserts 53 on the first protrusion 51 are respectively connected to the second protrusion 52. Multiple square slots 54 on 52 are precisely aligned. As the two extension arms 31 continue to move, multiple inserts 53 are respectively embedded in the square slots 54. The inserts 53 and the square slots 54 adopt a concave-convex mating structure. This structure can effectively limit the relative movement of the ends of the two extension arms 31 in the horizontal and vertical directions, so that the two extension arms 31 form a stable connection relationship through the first protrusion 51 and the second protrusion 52. Furthermore, after the two extension arms 31 are connected, they can also disperse the force, so that the entire ring structure has the ability to disperse local forces, avoid excessive local forces on the ring frame 2 or the extension arms 31, which could lead to deformation, and further improve the overall stability of the ring structure.

[0025] It is worth noting that the ring frame 2 is also equipped with a reset part 6, which is used to manually drive the two extension arms 31 to retract into the ring frame 2. The reset part 6 includes a reel 61, a rotating shaft 63, and two pull ropes 62. The rotating shaft 63 is rotatably mounted inside the fixed base 32. The reel 61 is connected to the outer wall of the rotating shaft 63. One end of each of the two pull ropes 62 is connected to the reel 61, and the other end of each pull rope is connected to the two extension arms 31 respectively. Both pull ropes 62 are wound on the reel 61. When the reel 61 rotates, it can drive the two extension arms 31 to retract and reset by winding the two pull ropes 62. The rotating shaft 63 passes through the ring frame 2 and the connecting frame 1. The end of the rotating shaft 63 located outside the connecting frame 1 is provided with an internal hexagonal nut. When the two extension arms 31 extend outward, the two extension arms 31 respectively pull out the two pull ropes 62. When the two pull ropes 62 are pulled out, they drive the reel 61. When the rotating shaft 63 rotates, and the ring frame 2 needs to be disassembled, the extension arm 31 needs to be retracted back into the ring frame 2. Medical staff first press the two pins 42 to disengage the pins 42 from the limiting hole 44, thereby losing the limiting locking function. At the same time, use an Allen wrench to insert into the Allen nut at the end of the rotating shaft 63 and manually rotate the rotating shaft 63. When the rotating shaft 63 rotates, it drives the reel 61 to rotate synchronously, so that the reel 61 winds up the two pull ropes 62 by rotating. The pull ropes 62 generate tension during the winding process. This tension overcomes the elastic force of the arc spring 33 and the bending force of the extension arm 31, so that the two pull ropes 62 pull the two extension arms 31 along the inner wall of the ring frame 2 and slide into the ring frame 2 during the winding process, thereby realizing the retraction and reset of the extension arm 31. After the extension arm 31 retracts and resets, the two ring frames 2 can be disassembled. The operation is relatively convenient.

[0026] It is worth noting that the extension arm 31 is connected to the first bone pad 7, and the ring frame 2 is equipped with two second bone pads 8. Both the first bone pad 7 and the second bone pad 8 are used to contact the periosteum. The first bone pad 7 and the second bone pad 8 are respectively provided with multiple protrusions. The first bone pad 7 and the second bone pad 8 are components that directly contact the bone periosteum. Their main function is to protect the periosteum tissue, reduce the pressure and damage to the periosteum, and improve the fixation stability. The multiple protrusions on the surface of the first bone pad 7 and the second bone pad 8 not only increase the friction between them and the periosteum, but also allow for the flow of body fluids by utilizing the gaps between the multiple protrusions, thus reducing the possibility of local effusion and inflammation.

[0027] Using the above structure, the working principle of this case is as follows: after the ring frame 2 is implanted into the human body, it absorbs heat from the body, thereby raising the temperature and triggering its shape memory function, causing the ring frame 2 to generate an inward contraction elastic force. The ring frame 2 uses the inward contraction elastic force to play a role in embracing and fixing the fracture site. The two ring frames 2 are used to stabilize and clamp the bones on both sides of the fracture crack, keeping the bones in an aligned state. When the ring frame 2 is implanted into the human body, under the action of the body heat, the arc spring 33 first triggers the shape memory effect to generate elastic force. This elastic force acts directly on the inner wall of the extension arm 31, thereby pushing the extension arm 31 to slide along the inner wall of the ring frame 2 and extend outward from the ring frame 2. At this time, the two extension arms 31 extend outward from both ends of the semi-circular ring frame 2 at the same time, finally forming a nearly closed ring structure. Subsequently, the extension arm 31 itself will also generate an elastic force to hold the bones when it is heated. When the ring structure composed of the two extension arms 31 and the ring frame 2 can adaptively adjust the embracing range according to the specific size of the fracture site, it can be applied to the fixation of bone fractures within a certain size range.

[0028] The fixing block 41 provides a fixed support point for the cylindrical spring 43. The cylindrical spring 43 is pre-compressed, so that it always exerts an upward thrust on the pin 42, keeping one end of the pin 42 against the inner wall of the ring frame 2. When the extension arm 31 slides outward along the inner wall of the ring frame 2, the pin 42 slides on the inner wall of the ring frame 2 as the extension arm 31 moves. At this time, the cylindrical spring 43 is still in a compressed state. When the extension arm 31 extends to its position, the pin 42 aligns with the limiting hole 44 on the ring frame 2. At this time, the elastic force of the cylindrical spring 43 is released, causing the cylindrical spring 43 to push the pin 42 to slide vertically and insert into the limiting hole 44. In section 4, the extension arm 31 is fixed relative to the ring frame 2 by the cooperation of the pin 42 and the limiting hole 44, thereby locking the position of the extension arm 31. When the two extension arms 31 are about to extend outward into place, the ends of the two extension arms 31 away from the fixed seat 32 approach each other. At this time, the multiple inserts 53 on the first protrusion 51 are precisely aligned with the multiple square grooves 54 on the second protrusion 52. As the two extension arms 31 continue to move, the multiple inserts 53 are embedded in the square grooves 54 respectively. The inserts 53 and the square grooves 54 adopt a concave-convex fit structure. This structure can effectively limit the relative movement of the ends of the two extension arms 31 in the horizontal and vertical directions.

[0029] As the two extension arms 31 extend outward, two pull ropes 62 are pulled out from each extension arm 31. The pull ropes 62, when pulled out, drive the reel 61 and the rotating shaft 63 to rotate. When it is necessary to disassemble the ring frame 2, the extension arms 31 must first be retracted back into the ring frame 2. Medical personnel first press the two pins 42 to disengage the pins 42 from the limiting holes 44, thus losing their limiting locking function. At the same time, an Allen wrench is inserted into the Allen nut at the end of the rotating shaft 63, and the rotating shaft 63 is manually rotated. When 63 rotates, it synchronously drives the reel 61 to rotate, so that the reel 61 winds up the two pull ropes 62 by rotating. The pull ropes 62 generate tension during the winding process. This tension overcomes the elastic force of the arc spring 33 and the bending force of the extension arm 31, so that the two pull ropes 62 pull the two extension arms 31 to slide along the inner wall of the ring frame 2 into the ring frame 2 during the winding process, thereby realizing the retraction and reset of the extension arms 31. After the extension arms 31 retract and reset, the two ring frames 2 can be disassembled, which is relatively convenient.

[0030] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A nickel-titanium shape memory alloy boat-shaped bone setter, characterized in that, include: Connecting frame (1), on which two ring frames (2) are installed. The ring frames (2) are semi-circular and hollow. The ring frames (2) are made of nickel-titanium shape memory alloy. The ring frames (2) can generate an inward contraction elastic force when heated. The ring frame (2) is provided with an extension part (3), the extension part (3) includes two extension arms (31), both extension arms (31) are slidably connected to the inner wall of the ring frame (2), and the two extension arms (31) can extend from both ends of the ring frame (2) respectively after being heated, and form a ring structure with the ring frame (2); The ring frame (2) is also provided with a reset part (6) for manually driving the two extension arms (31) to retract into the ring frame (2).

2. The nickel-titanium shape memory alloy boat-shaped bone graft according to claim 1, characterized in that: The extension part (3) also includes a fixing seat (32), which is installed inside the ring frame (2). Two arc springs (33) are connected to the fixing seat (32). The two arc springs (33) are located inside the two extension arms (31) respectively. The ends of the two arc springs (33) away from the fixing seat (32) are connected to the inner walls of the two extension arms (31) respectively.

3. The nickel-titanium shape memory alloy boat-shaped bone graft according to claim 2, characterized in that: The arc spring (33) and the extension arm (31) are both made of nickel-titanium shape memory alloy. When the arc spring (33) is heated, it can generate elastic force and drive the extension arm (31) to extend outward of the ring frame (2). When the two extension arms (31) are heated, they will generate elastic force that bends towards each other.

4. The nickel-titanium shape memory alloy boat-shaped bone setter according to claim 3, characterized in that: The extension arm (31) is provided with a locking mechanism (4), which includes a fixing block (41), a pin (42) and a cylindrical spring (43). The fixing block (41) is installed on the inner wall of the extension arm (31), the pin (42) is vertically slidably connected to the extension arm (31), and the cylindrical spring (43) is connected between the inner wall of the pin (42) and the fixing block (41).

5. The nickel-titanium shape memory alloy boat-shaped bone setter according to claim 4, characterized in that: Two limiting holes (44) are provided on the ring frame (2), and the pin (42) can be inserted into the limiting holes (44) after the extension arm (31) is extended outward into place.

6. The nickel-titanium shape memory alloy boat-shaped bone graft according to claim 3, characterized in that: The extension part (3) also includes a stabilizing mechanism (5), which includes a first protrusion (51) and a second protrusion (52). The first protrusion (51) and the second protrusion (52) are respectively connected to the ends of the two extension arms (31) away from the fixed base (32). The first protrusion (51) is connected with a plurality of inserts (53), and the second protrusion (52) is provided with a plurality of square slots (54). The plurality of inserts (53) can be embedded in the plurality of square slots (54) respectively when the two extension arms (31) are extended outward into place.

7. The nickel-titanium shape memory alloy boat-shaped bone setter according to claim 1, characterized in that: The reset part (6) includes a reel (61), a rotating shaft (63) and two pull ropes (62). The rotating shaft (63) is rotatably mounted inside the fixed base (32). The reel (61) is connected to the outer wall of the rotating shaft (63). One end of each of the two pull ropes (62) is connected to the reel (61), and the other end of each of the two pull ropes (62) is connected to the two extension arms (31) respectively. Both pull ropes (62) are wound on the reel (61). When the reel (61) rotates, it can drive the two extension arms (31) to retract and reset by winding up the two pull ropes (62).

8. The nickel-titanium shape memory alloy boat-shaped bone setter according to claim 7, characterized in that: The rotating shaft (63) passes through the ring frame (2) and the connecting frame (1), and the end of the rotating shaft (63) located outside the connecting frame (1) is provided with an internal hexagonal nut.

9. A nickel-titanium shape memory alloy boat-shaped bone setter according to claim 3, characterized in that: The extension arm (31) is connected to a first bone pad (7), and the ring frame (2) is equipped with two second bone pads (8). Both the first bone pad (7) and the second bone pad (8) are used to contact the periosteum. The first bone pad (7) and the second bone pad (8) are respectively provided with multiple protrusions.

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