Shoulder glenoid positioner

Abstract

The utility model relates to a kind of shoulder joint glen positioning device, the shoulder joint glen positioning device includes: positioning main body, main sliding member and sliding pointer, the positioning main body is equipped with guide slot, the guide slot extends along the axial direction of the positioning main body, the main sliding member includes longitudinal rod and transverse rod, the longitudinal rod is cooperated in the guide slot and adjustable along the axial position of the positioning main body, the transverse rod is connected with the longitudinal rod and extends along the radial direction of the positioning main body, the sliding pointer is connected with the transverse rod, and adjustable along the position of the extension direction of the transverse rod.The shoulder joint glen positioning device of the utility model can satisfy the use demand of different patients, and positioning accuracy is higher, and surgical effect is better.

Description

Technical Field

[0001] This utility model relates to the field of medical device technology, specifically to a shoulder joint glenoid locator. Background Technology

[0002] With increased physical activity and frequent sports injuries, the incidence of shoulder joint diseases has risen significantly. In the field of shoulder joint prostheses, multiple custom-designed components are typically used to create anatomical or reverse prostheses to meet diverse clinical needs. These prostheses require highly accurate positioning within the glenoid cavity of the shoulder joint, and the precision of this step directly impacts the final surgical outcome. Among these, the glenoid locator plays a crucial role in the prosthesis placement process. However, in current techniques, the glenoid locator has a fixed size, making it difficult to adapt to individual patient anatomical differences, resulting in poor compatibility and inaccurate positioning, thus affecting surgical outcomes. Utility Model Content

[0003] This utility model aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, embodiments of this utility model propose a glenoid locator for shoulder joints, which can meet the needs of different patients, has high positioning accuracy, and results in good surgical outcomes.

[0005] The shoulder glenoid locator of this utility model includes: a positioning body, on which a guide groove is provided, the guide groove extending along the axial direction of the positioning body; a main sliding member, the main sliding member including a longitudinal rod and a transverse rod, the longitudinal rod fitting in the guide groove and being adjustable along the axial direction of the positioning body, the transverse rod being connected to the longitudinal rod and extending radially along the positioning body; and a sliding pointer, the sliding pointer being connected to the transverse rod and being adjustable along the extension direction of the transverse rod.

[0006] According to an embodiment of this utility model, the glenoid locator for shoulder joints features a longitudinal rod that engages within a guide groove and whose axial position along the positioning body is adjustable. The sliding pointer's position along the extension direction of the transverse rod is also adjustable. This allows the surgeon to transfer preoperative planning parameters to the glenoid locator, positioning the longitudinal rod and sliding pointer to their designated positions. Consequently, the glenoid prosthesis positioning can be completed without the need for other physical models or specialized tools. Furthermore, since both the height and width of the glenoid locator are adjustable, it can meet the needs of different patients, offering high positioning accuracy and improving surgical outcomes.

[0007] In some embodiments, the sliding pointer includes a sliding block and a pointer portion. The sliding block is slidably engaged with the transverse rod. The transverse rod has a first identifier arranged along its extension direction. The pointer portion is located on the side of the sliding block opposite to the longitudinal rod, and the pointer portion extends along the axial direction of the positioning body.

[0008] In some embodiments, the glenoid locator further includes a first ball-head plunger, which passes through the sliding block and elastically abuts against the transverse rod.

[0009] In some embodiments, the glenoid locator further includes a handle, which is sleeved on the end of the positioning body away from the sliding pointer. At least one of the handle and the positioning body is provided with a second ball plunger, which elastically abuts against the longitudinal rod.

[0010] In some embodiments, there is an installation gap between the handle and the positioning body, one end of the longitudinal rod opposite to the transverse rod is inserted into the installation gap, and the second ball plunger passes through the handle and extends into the installation gap, and elastically abuts against the longitudinal rod.

[0011] In some embodiments, the handle has a pressure plate portion that defines the installation gap between the pressure plate portion and the positioning body. The glenoid fossa positioner further includes a locking nut that is sleeved on the pressure plate portion and threadedly engaged with the pressure plate portion to press the pressure plate portion.

[0012] In some embodiments, the handle has a pressing portion that defines the installation gap between the pressing portion and the positioning body. The inner side of the pressing portion is provided with a first toothed surface, and the longitudinal rod is provided with a second toothed surface. The first toothed surface and the second ball plunger both cooperate with the second toothed surface.

[0013] In some embodiments, the glenoid locator further includes a handle, which is sleeved on the end of the positioning body opposite to the sliding pointer. The positioning body is provided with a positioning pin, which extends radially along the positioning body. The side wall of the handle is provided with a limiting groove, and the positioning pin slides into the limiting groove along the axial direction of the positioning body.

[0014] In some embodiments, the limiting groove opens toward the side opposite to the sliding pointer, and the glenoid locator further includes a sealing member, which is detachably mounted on the end of the handle opposite to the sliding pointer and stops at the opening of the limiting groove.

[0015] In some embodiments, the positioning body is provided with multiple sets of second identifiers, which are arranged sequentially along the axial direction of the positioning body. Each set of second identifiers includes multiple arithmetic digits, which increase sequentially in the direction away from the main sliding member. The longitudinal rod is provided with an alignment symbol, which corresponds to the second identifier. And / or, there are multiple guide slots, which are arranged at intervals along the circumference of the positioning body. There are multiple main sliding members and multiple sliding pointers, which are installed one-to-one on the guide slots and one-to-one on the transverse rods. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the shoulder glenoid locator according to an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the shoulder glenoid locator according to another perspective of an embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram showing the connection between the main sliding member and the sliding pointer of the shoulder joint locator according to an embodiment of this utility model.

[0019] Figure 4 yes Figure 3 A magnified view of A in the middle.

[0020] Figure 5 This is an exploded view of the shoulder glenoid locator (after removing the main sliding member and the sliding pointer) according to an embodiment of this utility model.

[0021] Figure 6 This is a partial schematic diagram of the positioning body of the shoulder joint glenoid locator according to an embodiment of the present invention.

[0022] Figure 7 This is an installation cross-sectional view of the positioning body, handle, and locking nut of the shoulder joint glenoid locator according to an embodiment of this utility model.

[0023] Figure 8 This is a partial cross-sectional view of the second ball-head plunger and the positioning body of the shoulder joint glenoid locator according to an embodiment of the present invention.

[0024] Figure label:

[0025] 1. Positioning body; 11. Guide groove; 12. Positioning pin; 13. Second identifier; 14. Center through hole;

[0026] 2. Main sliding member; 21. Longitudinal rod; 211. Second tooth surface; 212. Alignment symbol; 213. Recessed part; 22. Transverse rod; 221. First identifier;

[0027] 3. Sliding pointer; 31. Sliding block; 32. Pointer section;

[0028] 4. Handle; 41. Installation gap; 42. Tableting part; 421. First toothed surface; 43. Limiting groove;

[0029] 51. First ball-head plunger; 52. Second ball-head plunger; 53. Locking nut; 54. Sealing component. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] The following is a reference appendix. Figures 1 to 8 This invention describes a shoulder glenoid locator according to an embodiment of the present invention.

[0032] like Figures 1 to 5 As shown, the glenoid fossa positioner of this utility model embodiment includes: a positioning body 1, a main sliding member 2, and a sliding pointer 3. The positioning body 1 is provided with a guide groove 11, which extends along the axial direction of the positioning body 1. The main sliding member 2 includes a longitudinal rod 21 and a transverse rod 22. The longitudinal rod 21 is fitted in the guide groove 11 and its position is adjustable along the axial direction of the positioning body 1. The transverse rod 22 is connected to the longitudinal rod 21 and extends radially along the positioning body 1. The sliding pointer 3 is connected to the transverse rod 22 and its position is adjustable along the extension direction of the transverse rod 22.

[0033] According to the embodiment of the present invention, the glenoid locator of the shoulder joint has an adjustable longitudinal rod 21 that fits in the guide groove 11 and is axially adjustable along the positioning body 1, and an adjustable sliding pointer 3 along the extension direction of the transverse rod 22. Thus, the doctor can transfer the planning parameters to the glenoid locator according to the preoperative plan to position the longitudinal rod 21 and the sliding pointer 3 to the set position, thereby completing the prosthesis positioning of the glenoid without the need for other physical models or special tools.

[0034] Furthermore, since both the height and width of the glenoid locator are adjustable, it is understood that the longitudinal rod 21 is adjustable along the axial position of the positioning body 1, i.e., the height of the glenoid locator can be adjusted. The sliding pointer 3 is adjustable along the extension direction of the transverse rod 22, i.e., the width of the glenoid locator can be adjusted. Therefore, the glenoid locator of this embodiment can meet the needs of different patients, has high positioning accuracy, and is beneficial to improving surgical outcomes.

[0035] Specifically, there are multiple guide grooves 11, which are arranged at intervals along the circumference of the positioning body 1. There are multiple main sliding members 2 and multiple sliding pointers 3. The multiple main sliding members 2 are installed on the guide grooves 11 in a one-to-one correspondence, and the multiple sliding pointers 3 are installed on the horizontal rods 22 in a one-to-one correspondence.

[0036] Understandably, multiple main sliding elements 2 can be individually adjusted along the axial direction of the positioning body 1, and multiple sliding pointers 3 can be individually adjusted along the radial direction of the positioning body 1. This allows the surgeon to adjust the main sliding elements 2 and sliding pointers 3 at different positions according to the patient's specific anatomical structure. By conducting detailed preoperative planning for the patient and transferring the numerical parameters from the preoperative planning software to the glenoid fossa locator, the surgeon can significantly improve the flexibility and efficiency of the surgical procedure. This allows the glenoid fossa locator to quickly adapt to the specific needs of different patients, thereby increasing the success rate of the surgery and reducing the risk of complications.

[0037] In the examples of this utility model, such as Figure 1 and Figure 2 As shown, there are five main sliding members 2, which are arranged at equal intervals along the circumference of the positioning body 1. There are also five sliding pointers 3, which are connected one-to-one with the five main sliding members 2.

[0038] like Figure 3 and Figure 4 As shown, taking a single sliding pointer 3 as an example, the sliding pointer 3 includes a sliding block 31 and a pointer part 32. The sliding block 31 is slidably engaged with the transverse rod 22. The transverse rod 22 is provided with a first identifier 221 arranged along its extension direction. The pointer part 32 is located on the side of the sliding block 31 opposite to the longitudinal rod 21, and the pointer part 32 extends along the axial direction of the positioning body 1. It can be understood that the first identifier 221 can provide a reference for the movement of the pointer part 32, thereby improving the accuracy of the sliding pointer 3 when moving. The pointer part 32 extends along the axial direction of the positioning body 1, that is, the pointer part 32 extends along the front end of the positioning body 1. The pointer part 32 can contact the patient's glenoid fossa, thereby improving the reliability of the glenoid fossa locator positioning.

[0039] Optionally, such as Figure 4 As shown, the glenoid fossa locator also includes a first ball-head plunger 51, which passes through the sliding block 31 and elastically abuts against the transverse rod 22. By elastically abutting the first ball-head plunger 51 against the transverse rod 22, the glenoid fossa locator of this embodiment of the invention provides damping force when the sliding pointer 3 moves relative to the transverse rod 22, thereby improving the accuracy of the sliding pointer 3's movement and preventing the sliding pointer 3 from wobbling relative to the transverse rod 22 after adjustment.

[0040] It should be noted that the first ball plunger 51 contains a ball and a spring. The spring presses the ball towards the ball, causing the ball to press against the wall of the transverse rod 22. When the force applied by the doctor to the sliding pointer 3 can overcome the elastic force of the first ball plunger 51, the sliding pointer 3 can slide relative to the transverse rod 22.

[0041] In one example, such as Figure 3 As shown, in order to facilitate the doctor's movement of the main sliding member 2, a recessed part 213 is provided on the longitudinal rod 21. The recessed part 213 has a groove structure so that the doctor can put his finger into the groove, thereby facilitating the doctor to slide the main sliding member 2.

[0042] Optionally, such as Figure 2 , Figure 5 and Figure 7 As shown, the glenoid fossa locator also includes a handle 4, which is sleeved on the end of the positioning body 1 opposite to the sliding pointer 3. At least one of the handle 4 and the positioning body 1 is provided with a second ball-head plunger 52, which elastically abuts against the longitudinal rod 21. It is understood that the handle 4, sleeved at the rear end of the positioning body 1, allows the doctor to hold the handle 4 for glenoid fossa positioning. Because the second ball-head plunger 52 elastically abuts against the longitudinal rod 21, the main sliding member 2 has a damping force when moving relative to the positioning body 1, thereby improving the accuracy of the main sliding member 2's movement and preventing axial wobbling of the main sliding member 2 relative to the positioning body 1 after adjustment.

[0043] It should be noted that the second ball plunger 52 contains a ball and a spring. The spring presses the ball towards the ball, causing the ball to press against the wall of the longitudinal rod 21. When the force applied by the doctor to the longitudinal rod 21 can overcome the elastic force of the second ball plunger 52, the longitudinal rod 21 can slide relative to the main body.

[0044] For example, the second ball plunger 52 is disposed on the positioning body 1. Or, for example, the second ball plunger 52 is disposed on the handle 4.

[0045] Optionally, such as Figure 7 and Figure 8 As shown, there is an installation gap 41 between the handle 4 and the positioning body 1. The end of the longitudinal rod 21 facing away from the transverse rod 22 (i.e., the rear end of the longitudinal rod 21) is inserted into the installation gap 41. The second ball plunger 52 passes through the handle 4 and extends into the installation gap 41, elastically abutting against the longitudinal rod 21. It can be understood that the rear end of the longitudinal rod 21 is inserted into the installation gap 41 to initially position the longitudinal rod 21. Under the elastic abutment of the second ball plunger 52, the rear end of the longitudinal rod 21 can be fixed in the installation gap 41 between the handle 4 and the positioning body 1, thereby improving the stability of the connection between the longitudinal rod 21 and the positioning body 1.

[0046] Optionally, such as Figure 7 As shown, the handle 4 has a pressing part 42, which defines an installation gap 41 between the pressing part 42 and the positioning body 1. The glenoid fossa positioner also includes a locking nut 53, which is sleeved on the pressing part 42 and threadedly engaged with the pressing part 42 to press the pressing part 42. It can be understood that after the position of the main sliding member 2 of the glenoid fossa positioner is adjusted, in order to further limit the movement of the main sliding member 2 relative to the positioning body 1, the pressing part 42 can be pressed tightly by the locking nut 53, so that the rear end of the longitudinal rod 21 can be firmly fixed between the handle 4 and the positioning body 1, thereby improving the positioning accuracy of the glenoid fossa positioner.

[0047] For example, such as Figure 7 As shown, the inner side of the pressing part 42 is provided with a first toothed surface 421, and the longitudinal rod 21 is provided with a second toothed surface 211. The first toothed surface 421 and the second ball-head plunger 52 both cooperate with the second toothed surface 211, thereby increasing the frictional resistance between the longitudinal rod 21 and the pressing part 42 and the second ball-head plunger 52, making the use effect of the glenoid fossa positioner better and the positioning more accurate.

[0048] In some embodiments, such as Figure 2 and Figure 5 As shown, the glenoid fossa locator also includes a handle 4, which is sleeved on the end of the positioning body 1 opposite to the sliding pointer 3. The positioning body 1 has a positioning pin 12 extending radially. The side wall of the handle 4 has a limiting groove 43, into which the positioning pin 12 slides axially along the positioning body 1. It can be understood that, with the cooperation of the positioning pin 12 and the limiting groove 43, the positioning body 1 and the handle 4 can be circumferentially limited, meaning that the positioning body 1 and the handle 4 will not rotate relative to each other. This facilitates the surgeon's application of external force to the glenoid fossa locator, enabling convenient intraoperative manipulation.

[0049] Optionally, such as Figure 2 and Figure 5 As shown, the limiting groove 43 opens towards the side opposite to the sliding pointer 3. The glenoid fossa positioner also includes a sealing member 54, which is detachably mounted on the end of the handle 4 opposite to the sliding pointer 3 and stops at the opening of the limiting groove 43. It can be understood that the rear end opening of the limiting groove 43 allows the positioning pin 12 to slide into the limiting groove 43 simultaneously when the positioning body 1 passes through the handle 4 in a rear-to-front direction, thereby limiting the rotation of the positioning body 1 relative to the handle 4. Furthermore, the sealing member 54 can provide axial positioning for the positioning body 1, thereby improving the stability of the glenoid fossa positioner after assembly.

[0050] For example, the sealing element 54 and the rear end of the handle 4 can be threaded together to improve the ease of disassembly and assembly of the glenoid locator and ensure a reliable connection.

[0051] Specifically, such as Figure 6 As shown, the positioning body 1 is provided with multiple sets of second identifiers 13, which are arranged sequentially along the axial direction of the positioning body 1. Each set of second identifiers 13 includes multiple arithmetic progression numbers, which increase sequentially in the direction away from the main sliding member 2 (i.e., from front to back). Alignment symbols 212 are provided on the longitudinal rod 21, corresponding to the second identifiers 13. It can be understood that "arithmetic progression numbers" means that the difference between any two adjacent number symbols is a constant. There are multiple alignment symbols 212, each corresponding one-to-one with one of the sets of second identifiers 13. This allows doctors to more accurately position the main sliding member 2 using the alignment symbols 212 and the second identifiers 13.

[0052] The operation steps of the shoulder glenoid locator according to an embodiment of this utility model are as follows:

[0053] 1) Preoperative preparation: Based on the patient's CT or MRI image data, perform 3D simulation in advance on dedicated software to preset the optimal insertion point and angle of the main sliding component 2.

[0054] 2) Installation position: Insert each main sliding component 2 into the installation gap 41 between the positioning body 1 and the handle 4 according to the preset position, and adjust the main sliding component 2 and the sliding pointer 3 to a suitable height, angle and width.

[0055] 3) Fine-tuning and locking: Use the second ball plunger 52 to precisely adjust each main sliding member 2 until each alignment symbol 212 is aligned with the mark of the corresponding second identifier 13, and then use the locking nut 53 to fix the multiple main sliding members 2.

[0056] 4) After ensuring that all main sliding parts 2 are locked, guide the surgical tools or guide pins to be correctly positioned through the central through hole 14 of the positioning body 1 to ensure the correct placement and fixation of the prosthesis.

[0057] 5) During the operation, the position of the prosthesis is checked by X-ray or other imaging techniques. If necessary, the main sliding component 2 can be adjusted to optimize the position of the prosthesis.

[0058] The shoulder joint locator of this invention has a sophisticated structure and is easy to operate. It can significantly improve the accuracy and success rate of surgical procedures, avoid complications, and thus improve the patient's treatment outcome and quality of life.

[0059] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0060] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0061] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0062] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0063] In this utility model, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0064] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A glenoid locator for shoulder joints, characterized in that, include: A positioning body, wherein the positioning body is provided with a guide groove, the guide groove extending along the axial direction of the positioning body; The main sliding member includes a longitudinal rod and a transverse rod. The longitudinal rod is fitted in the guide groove and its axial position is adjustable along the positioning body. The transverse rod is connected to the longitudinal rod and extends radially along the positioning body. A sliding pointer is connected to the horizontal rod, and its position is adjustable along the extension direction of the horizontal rod.

2. The glenoid locator according to claim 1, characterized in that, The sliding pointer includes a sliding block and a pointer portion. The sliding block is slidably engaged with the transverse rod. The transverse rod is provided with a first identifier arranged along its extension direction. The pointer portion is located on the side of the sliding block opposite to the longitudinal rod, and the pointer portion extends along the axial direction of the positioning body.

3. The glenoid locator according to claim 2, characterized in that, The glenoid locator further includes a first ball-head plunger, which passes through the sliding block and elastically abuts against the transverse rod.

4. The glenoid locator according to claim 1, characterized in that, The glenoid locator also includes a handle, which is sleeved on the end of the positioning body away from the sliding pointer. At least one of the handle and the positioning body is provided with a second ball plunger, which elastically abuts against the longitudinal rod.

5. The glenoid locator according to claim 4, characterized in that, There is an installation gap between the handle and the positioning body. The end of the longitudinal rod opposite to the transverse rod is inserted into the installation gap. The second ball plunger passes through the handle and extends into the installation gap, and elastically abuts against the longitudinal rod.

6. The glenoid locator according to claim 5, characterized in that, The handle has a pressure plate portion, and the installation gap is defined between the pressure plate portion and the positioning body. The glenoid fossa positioner also includes a locking nut, which is sleeved on the pressure plate portion and threadedly engaged with the pressure plate portion to press the pressure plate portion.

7. The glenoid locator according to claim 5, characterized in that, The handle has a pressing part, and the pressing part and the positioning body define the installation gap. The inner side of the pressing part is provided with a first toothed surface, and the longitudinal rod is provided with a second toothed surface. The first toothed surface and the second ball plunger both cooperate with the second toothed surface.

8. The glenoid locator according to claim 1, characterized in that, The glenoid locator also includes a handle, which is sleeved on the end of the positioning body opposite to the sliding pointer. The positioning body is provided with a positioning pin, which extends radially along the positioning body. The side wall of the handle is provided with a limiting groove, and the positioning pin slides into the limiting groove along the axial direction of the positioning body.

9. The glenoid locator according to claim 8, characterized in that, The limiting groove opens toward the side opposite to the sliding pointer, and the glenoid fossa positioner also includes a sealing member, which is detachably installed on the end of the handle opposite to the sliding pointer and stops at the opening of the limiting groove.

10. The glenoid locator according to any one of claims 1-9, characterized in that, The positioning body is provided with multiple sets of second identifiers, which are arranged sequentially along the axial direction of the positioning body. Each set of second identifiers includes multiple arithmetic numbers, which increase sequentially in the direction away from the main sliding member. The longitudinal rod is provided with an alignment symbol, which corresponds to the second identifier. And / or, there are multiple guide slots, which are arranged at intervals along the circumference of the positioning body. There are multiple main sliding members and multiple sliding pointers, with each main sliding member being installed on a corresponding guide slot and each sliding pointer being installed on a corresponding transverse rod.

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