Anatomical steel plate for tibial plateau posterior lateral column fracture

Abstract

The invention discloses an anatomical steel plate for tibial plateau posterior lateral column fracture, and relates to the technical field of medical instruments, the anatomical steel plate comprises an upper part, a middle part and a lower part, is composed of a vertical plate, a transition plate and an upper arc plate, forms a good fitting structure, and ensures the stability of a fracture part; the upper arc plate is provided with a second screw placement hole and a third screw placement hole which are crossed, and a first screw placement hole, a second screw placement hole and a second screw placement hole which are parallel to each other, so that screw fixation in two directions and angles is provided, multi-directional support is achieved, and the fixing stability of a fracture area is improved; screws are arranged in two directions between the tibial femoral shaft and the tibial plateau posterior lateral column fracture bone block, so that the fixing effect of the bone block is enhanced, and displacement is prevented; and the embedding seat is arranged at the position of the screw placing hole, so that the screw is prevented from being deflected in the placing process, a good occlusal force is ensured, and the fixing effect and the stability of the placing direction are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of medical devices, and in particular to an anatomical steel plate for tibial plateau posterolateral column fractures. Background Art

[0002] Tibial plateau fracture is one of the common knee injuries in trauma. Because it is an intra-articular fracture, it has high requirements for treatment. The goal of treatment is to flatten the joint surface, maintain good joint stability, normal lower limb force line, restore the range of motion of the knee joint, and avoid secondary traumatic arthritis. Posterolateral tibial plateau fracture is a special intra-articular fracture, accounting for 7% of tibial plateau fractures and about 42% of lateral and bicondylar tibial plateau fractures. Its injury mechanism is mainly due to the axial stress or valgus stress of the knee joint in the flexion state. For example, when the knee joint is bent and landed during cycling or running and jumping, the posterolateral side of the tibial plateau is hit by the lateral femoral condyle, resulting in a posterolateral plateau fracture. There are many classification methods for tibial plateau fractures. The Schatzker classification is mainly based on knee X-rays. Later, Luo et al. established a three-column classification based on the CT scan results of the tibial plateau. The plateau fractures are divided into lateral column, medial column and posterior column according to the anatomical landmarks of the top view of the plateau. Among them, the posterolateral tibial plateau fracture belongs to the posterior column fracture. Among them, the posterolateral tibial plateau fracture belongs to the lateral column h zone fracture. Due to the deep position of the posterolateral part, the fracture fragment is hidden, which makes it difficult to expose the surgical field. In addition, the front is blocked by the fibular head and lateral collateral ligament, resulting in a small space for operation. The anterolateral part is close to the common peroneal nerve, and the posterior part is close to the popliteal artery and vein and tibial nerve, which further increases the incidence of intraoperative complications. The quality of fracture reduction and the stability of fixation are precisely the key to the patient's postoperative clinical prognosis, so it is necessary to explore a relatively suitable surgical approach. The exposure of tibial plateau fractures usually chooses an incision adjacent to the fracture site, but it is not applicable to the posterolateral platform. On the one hand, the vascular and nerve bundles behind the tibia increase the risk of dissection. On the other hand, the bifurcation of the anterior tibial artery, which is slightly far from the direct posterolateral approach, also greatly increases the risk of accidental injury during surgery.

[0003] In summary, the current approach to the posterolateral column fracture of the tibial plateau has the following technical problems: In order to solve the problem of exposure of the posterolateral tibial plateau, it is necessary to maximize the operating space, avoid the surrounding nerves and blood vessels, and ensure that the steel plate and the inserted screws can act on the posterolateral column bone of the tibial plateau. The existing operation methods include the posterior position approach of the popliteal fossa, which directly exposes the posterolateral cortex for fixation. However, the distal side of the approach is limited by the bifurcation of the anterior tibial artery, and the medial side is affected by the vascular and nerve bundles in the popliteal fossa, so the exposure range and extension space are very limited. The existing technology of the anterolateral approach has the problem that the steel plate cannot completely cover the entire posterolateral area, lacks fixation of the edge steel plate, and cannot maintain the stability of the posterolateral joint surface. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides an anatomical plate for fractures of the posterolateral column of the tibial plateau. The extended arc-shaped hook can not only protect the nerves and blood vessels at the posterior side of the tibial plateau, avoiding damage to the nerves and blood vessels caused by nail insertion with changed directions, but also support the bone mass at the posterolateral side. By inserting nails in two directions, the problem that the holes on the existing plate are perpendicular to the bone surface at the corresponding positions and cannot extend backward, which avoids the problem that the anterior side in the middle of the tibial plateau at the nail insertion position cannot fix the posterior bone mass, and the nail insertion in the direction towards the middle of the tibial plateau makes the overall fixation effect more stable on the basis of fixing the bone mass.

[0005] To achieve the above technical objectives and reach the above technical effects, the present invention is realized through the following technical solutions:

[0006] An anatomical plate for fractures of the posterolateral column of the tibial plateau, including an upper part, a middle part and a lower part. The lower part is a vertical plate in a rectangular shape. The upper side of the vertical plate is provided with a middle part, which is a transition plate. The transition plate is an arc-shaped structure inclined to the left. The upper side of the transition plate is provided with an upper part, which is an arc-shaped upper arc plate;

[0007] The upper arc plate is provided with a first nail insertion hole and a second nail insertion hole parallel to the connection line of both ends of the upper arc plate. The first nail insertion hole and the second nail insertion hole are located on the upper arc plate above the transition plate. A third nail insertion hole is provided near the second nail insertion hole at the middle position of the upper arc plate, and the direction of the third nail insertion hole is towards the position of the posterior intercondylar area of the human tibia.

[0008] Further, the vertical plate is an arc segment structure recessed backward; it fits with the shaft of the tibia.

[0009] Further, a number of nail insertion holes are provided on the vertical plate and the transition plate according to the surgical needs.

[0010] Further, the inclination direction of the transition plate is a structure inclined backward and outward during the implementation, and the transition plate is a structure bent backward in the vertical direction, forming a structure that fits with the transition section from the shaft to the lateral condyle.

[0011] Further, the arc of the upper arc plate includes two arcs. The first arc starts from the side of the lateral condyle close to the tibial tubercle, surrounds the lateral condyle and wraps the lateral condyle above the fibula; so that the upper arc plate passes through the channel beside the tibia above the fibula. The first arc terminates above the fibula. The second arc starts from above the fibula and extends backward to the posterior intercondylar area to wrap the lateral condyle. The curvature of the second arc is greater than that of the first arc, and the second arc terminates at a position close to the posterior intercondylar area; thus completing the wrapping and positioning of the bone mass of the fracture of the posterolateral column of the tibial plateau. When inserting screws into the second arc direction through the first nail insertion hole and the second nail insertion hole of the upper arc plate on the transition plate, the positional relationship between the inserted screws and the bone mass is ensured to be stable.

[0012] Furthermore, a screw placement groove is provided on the upper arc plate on the side of the third screw placement hole away from the second screw placement hole; it is adapted to cooperate with the inserted screw.

[0013] Furthermore, the third screw placement hole is longitudinally misaligned with the first screw placement hole and the second screw placement hole.

[0014] Furthermore, the direction of the third screw placement hole is such that the inserted screw enters perpendicularly to the bone surface, intersecting with the first screw placement hole and the second screw placement hole, so as to stably fix the fracture of the posterolateral column of the tibial plateau.

[0015] Furthermore, fitting seats are provided on the upper arc plate at the positions of the first screw placement hole, the second screw placement hole, and the third screw placement hole; during the insertion process of the inserted screw, since the inserted screw is not perpendicular to the surface of the upper arc plate, a wrapped fixing structure cannot be formed around the inserted screw during the insertion process, and finally deflection occurs between the upper arc plate and the inserted screw. By forming a threaded meshing connection relationship that can cooperate with the inserted screw through the fitting seat and the upper arc plate, the problem of deflection is avoided.

[0016] Furthermore, a pressing plate is slidably connected in the screw placement groove, the pressing plate corresponds to the first screw placement hole and the second screw placement hole, and the moving direction of the pressing plate in the screw placement groove corresponds to the axial directions of the first screw placement hole and the second screw placement hole.

[0017] Furthermore, sliders are fixedly connected to both the upper and lower sides of the pressing plate, and grooves adapted to the sliders are formed on the upper arc plate at the position of the pressing plate.

[0018] Furthermore, a transmission wire is fixedly connected to the pressing plate, the transmission wire slides within the upper arc plate, the fitting seat is provided with a locking ring, the upper arc plate and the fitting seat are provided with slots adapted to the locking ring at the position of the locking ring, and a transmission wire is fixedly connected between the locking ring and the corresponding pressing plate; after the inserted screw is placed, the inserted screw abuts against the pressing plate, the pressing plate pulls the locking ring through the transmission wire, and the locking ring acts on the inserted screw, so that the inserted screw as a whole receives a radial force perpendicular to the axial direction of the insertion of the inserted screw, increasing the friction between the screw and the threads of the surrounding tissue, avoiding loosening of the inserted screw, and when the inserted screw loosens and rotates, it will also resist the locking ring to reset the locking ring, and the reset of the locking ring will make the pressing plate press tightly against the inserted screw, increasing the friction between the inserted screw and the threads of the surrounding tissue, thereby maintaining stability.

[0019] Furthermore, the distance between the upper and lower ends of the upper arc plate at the connection position with the transition plate gradually decreases towards the other end.

[0020] Furthermore, the distance between the upper and lower ends of the end of the upper arc plate away from the transition plate is 0.5 - 0.7 cm.

[0021] Further, the distance between the upper and lower sides of the upper arc plate gradually decreases, and the lower side is inclined upward;

[0022] By gradually decreasing the distance between the upper and lower sides, the upper arc plate can pass through the lateral edge of the tibial plateau on the upper side of the fibula.

[0023] Further, nail holes parallel to the third nail hole are provided below the first nail hole and the second nail hole.

[0024] Advantages of the present invention:

[0025] An anatomical steel plate for fractures of the posterolateral column of the tibial plateau is composed of a vertical plate, a transition plate and an upper arc plate, forming a good fitting structure to ensure the stability of the fracture site; the upper arc plate is provided with intersecting second nail holes and third nail holes, as well as parallel first nail holes, second nail holes and second nail holes, providing screw fixation in two directions and angles, achieving multi-directional support, increasing the fixation stability of the fracture area, and enabling screw insertion in two directions between the tibial femoral shaft and the fracture bone block of the posterolateral column of the tibial plateau, enhancing the fixation effect of the bone block and preventing displacement; a fitting seat is provided at the nail hole position to prevent the screw from deflecting during insertion, ensuring good biting force and the stability of the fixation effect and insertion direction; through the cooperation of the abutting plate and the slider, the abutting plate corresponding to the nail hole, and the cooperation of the locking ring and the transmission wire, the effect of the locking ring can be achieved, enhancing the friction between the screw and the bone tissue, reducing the risk of screw loosening, and further improving the fixation effect;

[0026] Through the above design, the anatomical steel plate for fractures of the posterolateral column of the tibial plateau of the present invention can effectively stabilize the fracture site of the posterolateral column of the tibial plateau, reduce postoperative complications, and promote healing.

[0027] Of course, it is not necessary for any product implementing the present invention to achieve all the above advantages simultaneously. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] In the drawings, the components represented by the reference numerals are as follows:

[0030] Figure 1 It is a schematic diagram of the overall structure of the anatomical steel plate for fractures of the posterolateral column of the tibial plateau according to the embodiment of the present invention;

[0031] Figure 2Front-side structural schematic diagram of the anatomical plate for posterolateral column fractures of the tibial plateau according to the embodiments of the present invention;

[0032] Figure 3 Right-side structural schematic diagram of the anatomical plate for posterolateral column fractures of the tibial plateau according to the embodiments of the present invention;

[0033] Figure 4 Left-side structural schematic diagram of the anatomical plate for posterolateral column fractures of the tibial plateau according to the embodiments of the present invention;

[0034] Figure 5 Upper-side structural schematic diagram of the anatomical plate for posterolateral column fractures of the tibial plateau according to the embodiments of the present invention;

[0035] Figure 6 Top-view structural schematic diagram of the upper arc plate according to the embodiments of the present invention;

[0036] Figure 7 Rear-side structural schematic diagram of the anatomical plate for posterolateral column fractures of the tibial plateau according to the embodiments of the present invention;

[0037] Figure 8 Structural schematic diagram of the upper arc plate, screw placement trajectory and tibial cross-section according to the embodiments of the present invention;

[0038] Figure 9 Structural schematic diagram of the vertical plate, transition plate and upper arc plate according to the embodiments of the present invention;

[0039] Figure 10 Structural schematic diagram of the vertical plate, transition plate, upper arc plate and fitting seat according to the embodiments of the present invention;

[0040] Figure 11 Structural schematic diagram of the transition plate, upper arc plate, fitting seat and abutment plate according to the embodiments of the present invention;

[0041] Figure 12 Structural schematic diagram of the upper arc plate and fitting seat according to the embodiments of the present invention;

[0042] Figure 13 Structural schematic diagram of the upper arc plate and abutment plate according to the embodiments of the present invention;

[0043] Figure 14 Structural schematic diagram of the abutment plate and locking ring according to the embodiments of the present invention;

[0044] Figure 15 Another structural schematic diagram of the anatomical plate for posterolateral column fractures of the tibial plateau according to the embodiments of the present invention;

[0045] Figure 16Schematic diagram of the upper arc plate, screw placement trajectory, and tibial cross-section of another structure of the anatomical plate for posterior lateral column fractures of the tibial plateau according to the embodiments of the present invention.

[0046] 1 - vertical plate, 101 - lower screw hole, 2 - transition plate, 3 - upper arc plate, 301 - first screw hole, 302 - second screw hole, 303 - third screw hole, 310 - screw placement groove, 320 - fitting seat, 330 - abutting plate, 331 - slider, 332 - transfer wire, 333 - locking ring. Detailed implementation mode

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0048] Embodiment 1

[0049] As Figure 1-14 shown

[0050] An anatomical plate for posterior lateral column fractures of the tibial plateau according to the present invention includes an upper part, a middle part, and a lower part. The lower part is a vertical rectangular vertical plate (1). The upper side of the vertical plate (1) is provided with a middle part, which is a transition plate (2). The transition plate (2) is an arc surface structure inclined to the left. The upper side of the transition plate (2) is provided with an upper part, which is an arc-shaped upper arc plate (3). Two first screw holes (301) and second screw holes (302) parallel to the connection line at both ends of the upper arc plate (3) are provided on the upper arc plate (3). The first screw hole (301) and the second screw hole (302) are located on the upper arc plate (3) above the transition plate (2). A third screw hole (303) is provided near the second screw hole (302) at the middle position of the upper arc plate (3). The direction of the third screw hole (303) points to the position of the posterior intercondylar area of the human tibia;

[0051] The vertical plate (1) is an arc segment structure recessed backward and fits with the shaft of the tibia;

[0052] A number of screw holes are provided on the vertical plate (1) and the transition plate (2) according to the surgical needs;

[0053] The inclined direction of the transition plate (2) is a structure inclined backward and outward during the implementation. The transition plate (2) is a structure bent backward in the vertical direction, forming a structure that fits with the transition section from the shaft to the lateral condyle;

[0054] The radian of the upper arc plate (3) includes two arcs. The first arc starts from the side of the lateral condyle close to the tibial tubercle, surrounds the lateral condyle and wraps the lateral condyle on the upper side of the fibula; so that the upper arc plate (3) passes through the channel beside the tibia on the upper side of the fibula, and the first arc terminates on the upper side of the fibula. The second arc starts from the upper side of the fibula and extends backward to the intercondylar area to wrap the lateral condyle. The curvature of the second arc is greater than that of the first arc, and the second arc terminates at a position close to the posterior intercondylar area; thus completing the wrapping and positioning of the fracture fragment of the posterolateral column of the tibial plateau. When screws are inserted into the second arc direction through the first screw hole (301) and the second screw hole (302) of the upper arc plate (3) on the transition plate (2), the positional relationship between the inserted screws and the fracture fragment is ensured to be stable;

[0055] A screw placement groove (310) is provided on the upper arc plate (3) on the side away from the second screw hole (302) of the third screw hole (303); it is matched with the inserted screw;

[0056] The third screw hole (303) is longitudinally misaligned with the first screw hole (301) and the second screw hole (302);

[0057] The direction of the third screw hole (303) is such that the inserted screw enters perpendicular to the bone surface, forming an intersection with the first screw hole (301) and the second screw hole (302), so that the fixation of the fracture of the posterolateral column of the tibial plateau is stable;

[0058] The upper arc plate (3) is provided with a fitting seat (320) at the positions of the first screw hole (301), the second screw hole (302), and the third screw hole (303); during the process of inserting the screw, since the inserted screw is not perpendicular to the surface of the upper arc plate (3), a fixed structure that can wrap around the inserted screw cannot be formed around the upper arc plate (3) during the insertion process, and finally deflection occurs between the upper arc plate (3) and the inserted screw. By forming a threaded meshing connection relationship that can cooperate with the inserted screw through the fitting seat (320) and the upper arc plate (3), the problem of deflection is avoided;

[0059] A pressing plate (330) is slidably connected in the screw placement groove (310). The pressing plate (330) corresponds to the first screw hole (301) and the second screw hole (302), and the moving direction of the pressing plate (330) in the screw placement groove (310) corresponds to the axial directions of the first screw hole (301) and the second screw hole (302);

[0060] Sliders (331) are fixedly connected to the upper and lower sides of the pressing plate (330), and the upper arc plate (3) is provided with grooves at the position of the pressing plate (330) that cooperate with the sliders (331);

[0061] A transfer wire (332) is fixedly connected to the backing plate (330). The transfer wire (332) slides within the upper arc plate (3). The fitting seat (320) is provided with a locking ring (333). The upper arc plate (3) and the fitting seat (320) are provided with slots at the position of the locking ring (333) that cooperate with the locking ring (333). A transfer wire (332) is fixedly connected between the locking ring (333) and the corresponding backing plate (330). After the screw is inserted, the inserted screw abuts against the backing plate (330). The backing plate (330) pulls the locking ring (333) through the transfer wire (332). The locking ring (333) acts on the inserted screw, causing the entire inserted screw to be subjected to a radial force perpendicular to the axial direction of insertion of the inserted screw, increasing the friction between the screw and the threads of the surrounding tissue, preventing the inserted screw from loosening. When the inserted screw loosens and rotates, it will also resist the locking ring (333) to reset the locking ring (333), and the reset of the locking ring (333) will cause the backing plate (330) to press tightly against the inserted screw, increasing the friction between the inserted screw and the threads of the surrounding tissue, thereby maintaining stability.

[0062] Embodiment 2

[0063] As Figure 1-16 shown

[0064] The distance between the upper and lower ends of the upper arc plate (3) at the connection position with the transition plate (2) gradually decreases towards the other end.

[0065] The distance between the upper and lower ends of the upper arc plate (3) away from the transition plate (2) is 0.5 - 0.7 cm.

[0066] The distance between the upper and lower sides of the upper arc plate (3) gradually decreases and is formed by the lower side tilting upwards.

[0067] By gradually decreasing the distance between the upper and lower sides, the upper arc plate (3) can pass through the lateral edge of the tibial plateau on the upper side of the fibula.

[0068] Below the first screw hole (301) and the second screw hole (302), there are screw holes parallel to the third screw hole (303).

[0069] In summary, an anatomical plate for posterolateral column fractures of the tibial plateau according to the present invention is composed of a vertical plate (1), a transition plate (2) and an upper arc plate (3), forming a good fitting structure to ensure the stability of the fracture site; the upper arc plate (3) is provided with intersecting second screw holes (302) and third screw holes (303), as well as parallel first screw holes (301), second screw holes (302) and second screw holes (302), providing screw fixation in two directions and angles, achieving multi-directional support, increasing the fixation stability of the fracture area, and enabling screw insertion in two directions between the tibial femoral shaft and the fracture fragment of the posterolateral column of the tibial plateau, enhancing the fixation effect of the fracture fragment and preventing displacement; a fitting seat (320) is provided at the position of the screw hole to prevent the screw from deflecting during insertion, ensuring good bite force, and guaranteeing the stability of the fixation effect and the insertion direction; through the cooperation of the abutting plate (330) and the slider (331), the abutting plate (330) corresponding to the screw hole, and the cooperation of the locking ring (333) and the transmission wire (332), the effect of the locking ring (333) can be achieved, enhancing the friction between the screw and the bone tissue, reducing the risk of screw loosening, and further improving the fixation effect; through the above design, an anatomical plate for posterolateral column fractures of the tibial plateau according to the present invention can effectively stabilize the fracture site of the posterolateral column of the tibial plateau, reduce postoperative complications, and promote healing.

[0070] In the description of this specification, the descriptions referring to terms such as "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0071] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the relevant technical fields can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. An anatomical steel plate for posterior lateral column fracture of tibial plateau, characterized in that: It includes an upper part, a middle part and a lower part, the lower part is a vertical rectangular vertical plate, the upper part of the vertical plate is provided with a middle part, the middle part is a transition plate, the transition plate is a curved surface structure inclined to the left, the upper part of the transition plate is provided with an upper part, and the upper part is an arc-shaped upper arc plate; The upper arc plate is provided with two first nail holes and a second nail hole which are parallel to the line connecting the two ends of the upper arc plate. The first nail hole and the second nail hole are located on the upper arc plate on the upper side of the transition plate. A third nail hole is provided in the middle of the upper arc plate near the second nail hole.

2. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 1, characterized in that: The vertical plate is an arc segment structure that is recessed backwards.

3. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 2, characterized in that: The vertical plate and the transition plate are provided with a plurality of nail holes according to surgical needs.

4. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 3, characterized in that: The transition plate is inclined toward the rear and outside in the distance implementation, and the transition plate is bent toward the rear in the vertical direction.

5. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 4, characterized in that: The upper arc plate is provided with a nail placement groove on a side of the third nail placement hole away from the second nail placement hole.

6. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 5, characterized in that: The third nail placement hole is staggered with the first nail placement hole and the second nail placement hole in the longitudinal direction.

7. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 6, characterized in that: The upper arc plate is provided with engaging seats at the positions of the first nail placement hole, the second nail placement hole and the third nail placement hole.

8. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 7, characterized in that: A butt plate is slidably connected in the nail placement groove, and the butt plate corresponds to the first nail placement hole and the second nail placement hole. The butt plate axially corresponds to the first nail placement hole and the second nail placement hole in the moving direction of the nail placement groove.

9. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 8, characterized in that: The upper and lower sides of the abutment plate are fixedly connected with sliding blocks, and the upper arc plate is provided with a groove matched with the sliding block at the abutment plate position.

10. The anatomical steel plate for tibial plateau posterolateral column fracture according to claim 9, characterized in that: A transfer wire is fixedly connected to the abutment plate, and the transfer wire slides in the upper arc plate. The engaging seat is provided with a locking ring. The upper arc plate and the engaging seat are provided with grooves matching the locking ring at the locking ring position. A transfer wire is fixedly connected between the locking ring and the corresponding abutment plate.

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