Middle positioner

Abstract

The utility model belongs to the technical field of unicompartmental knee arthroplasty instruments, and particularly relates to a centrally-positioned positioner, which comprises an anchoring plate, a centrally-positioned positioning device and a positioning device, wherein the anchoring plate is used for being inserted into a tibiofemoral joint gap on the inner side of a knee joint; the movable plate is attached to the surface of the anchoring plate and slides in the axial direction until the movable plate is attached to the knee joint thighbone inner side condyle, a plurality of positioning holes are distributed in the movable plate in the axial direction at equal intervals, a T-shaped groove is formed in the middle of the upper surface of the movable plate in the axial direction, the two sides of the T-shaped groove extend towards the two sides of the anchoring plate respectively, and a guide rod fixedly connected with the movable plate is inserted into an opening of the T-shaped groove; sliding blocks are integrally installed on the two sides of the end, located in the T-shaped groove, of the guide rod correspondingly, and the two sliding blocks are matched with the parts, extending towards the two sides, of the T-shaped groove correspondingly. According to the utility model, the movable centrally-positioned positioner plays a role in positioning and measuring in the centrally-positioned positioning process of the thighbone inner condyle, so that the thighbone side prosthesis can be positioned in the center of the thighbone inner condyle and is vertical to the tibial plateau prosthesis.

Description

Technical Field

[0001] The utility model belongs to the technical field of unicompartmental knee replacement instruments, and in particular relates to a central positioner. Background Art

[0002] The Oxford Unicompartmental Knee System has been successfully used to treat medial knee osteoarthritis since 1982. If surgical treatment is performed in the early stages of the disease, it can slow the progression of arthritis in other compartments of the knee and provide long-term symptom relief. Its products have been continuously improved, with a 10-year survival rate of up to 90% and an average wear of 0.03mm per year.

[0003] The traditional unicompartmental knee system mainly includes the tibial component and the meniscus liner, as follows:

[0004] Tibial component: It is also made of cast cobalt-chromium-molybdenum alloy. After the affected limb is flexed to about 90°, a skin incision is made on the inside of the patella from the inside edge of the patella to 3 cm below the joint line. Then, a joint capsule incision of about 2 cm is made along the skin incision to expose the tibial tuberosity to the anterior medial edge of the tibial plateau. After removing osteophytes, the femoral gap measurer, tibial saw guide and G-clamp are used at the same time to accurately locate the osteotomy plane, and the first osteotomy is performed on the tibial plateau at the knee joint. After the treatment is completed, the tibial template is fixed with screws at this location.

[0005] Femoral component: It is made of cast cobalt-chromium-molybdenum alloy. The unique spherical design can increase the strength, wear resistance and biocompatibility of the prosthesis. It mainly includes headed nails and headless nails.

[0006] Meniscal liner: Made from direct-molded ultra-high molecular weight polyethylene, it is highly wear-resistant and can slide over the tibial template.

[0007] Unicompartmental knee replacement currently uses a curved metal plate to probe into the gap between the tibia and femur, and a height-adjustable measuring block is set on the head of the metal plate to measure the size of the gap in real time. However, after calibrating the size of the gap, it is impossible to provide guidance for the drilling position of the femoral condyle, so medical staff often make judgments based on experience, which is prone to errors. Therefore, we propose a central positioner that can calibrate the medial tibiofemoral joint gap of the knee joint and limit the drilling position of the medial femoral condyle. Utility Model Content

[0008] The utility model aims to provide a central positioner, which plays a positioning and measuring role in the central positioning process of the medial femoral condyle by using a movable central positioner, so that the femoral prosthesis can be located in the center of the medial femoral condyle, and the femoral prosthesis is perpendicular to the tibial plateau prosthesis.

[0009] The technical solution adopted by the utility model is as follows:

[0010] A mid-position positioner, comprising:

[0011] An anchor plate, the anchor plate is used to be inserted into the medial tibiofemoral joint space of the knee joint;

[0012] The movable plate is attached to the surface of the anchor plate and slides axially until it is attached to the medial femoral condyle of the knee joint. The upper surface of the movable plate is equidistantly distributed axially with a plurality of positioning holes. When drilling the femur, the movable plate is slid along the middle of the upper surface of the anchor plate, gradually approaching the medial femoral condyle, and after aligning with the midline of the femoral osteotomy area, a micro drill needle is passed through the designated positioning hole to punch a guide hole at the midline position of the femoral osteotomy area; two mounting holes are symmetrically punched at the upper and lower positions of the guide hole, and the double columns of the femoral condyle prosthesis are respectively embedded in the medial femoral condyle; in this way, the anchor plate and the movable plate form a movable central positioner, and the movable central positioner is used to play a positioning and measuring role in the processes of drilling holes in the tibial section and the medial femoral condyle, etc., to provide guidance for the opening of the femoral drilling guide, and to limit the drilling position of the medial femoral condyle, so that the femoral prosthesis can be located in the center of the medial femoral condyle, and the femoral prosthesis is perpendicular to the tibial platform prosthesis.

[0013] A T-shaped groove is axially opened in the middle of the upper surface of the movable plate, and both sides of the T-shaped groove extend toward both sides of the anchor plate respectively. A guide rod fixedly connected to the movable plate is inserted at the opening of the T-shaped groove. When punching, the movable plate drives the guide rod to move and slide along the opening of the T-shaped groove, which limits the movable plate and makes the movable plate move along the center line of the anchor plate.

[0014] Slide blocks are integrally installed on both sides of one end of the guide rod located inside the T-shaped slot, and the two slide blocks are respectively adapted to the parts of the T-shaped slot extending toward both sides.

[0015] The four edges of the anchor plate are all integrally mounted with hammer heads, and the four hammer heads respectively extend toward the middle of one side of the anchor plate where they are located.

[0016] A slope is integrally arranged on one side of the four hammer heads facing the middle of the anchor plate.

[0017] The four hammer heads have rounded corners on one side away from the middle of the anchor plate.

[0018] A step groove is also provided on the upper surface of the anchor plate, and the step groove extends from one end of the anchor plate to the middle of the anchor plate.

[0019] The upper edges of the four hammer heads away from the anchor plate are all integrally installed with slope protection, and the slope protection has an arc on one side facing the anchor plate.

[0020] The technical effects achieved by the utility model are:

[0021] The utility model discloses a central positioning device for drilling and aligning a femur: the knee joint is flexed to about 45 degrees, and an electric drill is used to drill a hole in the femoral marrow; then an intramedullary rod is inserted until the intramedullary rod touches the inner surface of the femur; the knee joint is flexed to 90 degrees, an anchor plate 1 is inserted, and a movable plate 2 is slid along the middle of the upper surface of the anchor plate, gradually approaching the medial condyle of the femur, and after aligning with the midline of the femoral osteotomy area, a micro drill needle is passed through a designated positioning hole 3 to drill a hole in the midline of the femoral osteotomy area. A plurality of guide holes are formed; two mounting holes are respectively formed at the upper and lower positions of the guide holes, and the double columns of the femoral condyle prosthesis are respectively embedded in the medial femoral condyle; in this way, a movable central positioner composed of an anchor plate and a movable plate plays a positioning and measuring role in the central positioning process of the medial femoral condyle, guides the opening of the femoral drilling guide, limits the drilling position of the medial femoral condyle, enables the femoral prosthesis to be located in the center of the medial femoral condyle, and the femoral prosthesis is perpendicular to the tibial plateau prosthesis.

[0022] The utility model provides a central positioner. When drilling holes, the movable plate drives the guide rod to move and slide along the opening of the T-shaped groove, which plays a limiting role on the movable plate and makes the movable plate move along the center line of the anchor plate.

[0023] The utility model provides a central positioner, wherein the step groove forms a height difference at two hammer heads, and the central positioner can be inserted into the inner tibiofemoral joint gap of the knee joint with different opening degrees, so that the central positioner can be used in two sizes and has more diverse functions.

[0024] The utility model provides a central positioner, in which two adjacent slope guards can drag the two sides of the medial femoral condyle in an arc shape at the hammer heads, so as to facilitate the centering of the T-shaped slot without manual alignment, and facilitate the rapid calibration of the position of the guide hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a front view of a central positioner of the utility model;

[0026] Figure 2 It is a side view of a central positioner of the utility model;

[0027] Figure 3 It is a side view of the movable plate of the utility model;

[0028] Figure 4 It is a front view of the anchor plate of the utility model;

[0029] Figure 5 It is a side view of the anchor plate of the utility model;

[0030] Figure 6 It is a top view of the anchor plate of the utility model.

[0031] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0032] 1. Anchor plate; 2. Movable plate; 3. Positioning hole; 4. T-slot; 5. Guide rod; 6. Slider; 7. Hammer head; 8. Slope; 9. Step groove; 10. Slope protection. DETAILED DESCRIPTION

[0033] In order to make the purpose and advantages of the utility model more clear, the utility model is specifically described in combination with the following embodiments. It should be understood that the following text is only used to describe one or several specific implementations of the utility model, and does not strictly limit the protection scope of the specific request of the utility model.

[0034] like Figure 1-6 As shown, a central positioning device is mainly used in unicompartmental knee replacement, including:

[0035] An anchor plate 1, the anchor plate 1 is used for inserting into the unicondylar space between the tibia and the femur in the knee joint;

[0036] The movable plate 2 is attached to the surface of the anchor plate 1 and slides axially until it is attached to the medial femoral condyle of the knee joint. A plurality of positioning holes 3 are evenly distributed along the axial direction on the movable plate 2;

[0037] Unicompartmental knee replacement is indicated for the treatment of medial knee osteoarthritis. The patient must have full-thickness cartilage loss on both sides of the medial compartment of the knee and bone-on-bone contact, which can be confirmed by imaging or arthroscopy. The specific steps for this surgery are as follows:

[0038] Step 1: Preoperative X-ray template measurement: Use the template to draw the contour of the medial femoral condyle on the X-ray film. Compared with the long axis of the femoral shaft, the extension line of the prosthesis center column should be flexed 10°; the outer surface of the prosthesis diagram should be located about 2 mm outside the X-ray image, which is the thickness of the articular cartilage; for an accurate prosthesis, the proximal part of the prosthesis should be located about 2 mm outside the proximal bone surface of the femoral condyle, so that the prosthesis surface can be flush with the retained proximal cartilage;

[0039] Step 2: Treatment of the patient's limbs: After the thigh tourniquet is inflated, place the draped affected limb on the thigh support, and allow the hip joint to flex about 30°, with the lower limb in a hanging position; the knee joint must be able to flex completely freely, and the position of the affected limb should be able to allow the knee joint to flex about 110°. The thigh support must not be placed in the popliteal fossa, as this will increase the risk of popliteal vascular injury;

[0040] The knee joint was flexed to 90°, and a skin incision was made on the medial side of the patella from the medial edge of the patella to 3 cm below the joint line. The joint capsule was incised through the skin incision. The upper end of the joint capsule incision should be extended 2 cm proximally to the medial vastus muscle.

[0041] Then the joint capsule incision is extended downward along the medial edge of the patella to the medial side of the patellar ligament. The lower part of the incision exposes the tibial tuberosity to the anterior medial edge of the tibial plateau. As much medial meniscus as possible is removed without releasing the medial collateral ligament.

[0042] Surgeons who are still learning should enlarge the incision to allow for better exposure;

[0043] Step 3: Osteophyte removal: All osteophytes on the medial edge of the medial femoral condyle and the medial and lateral edges of the intercondylar notch must be removed. The surgical assistant flexes and extends the knee joint to move the incision up and down so that all osteophytes can be exposed in the field of vision. The osteophytes in front of the ACL insertion point on the tibial plateau and the osteophytes on the top of the intercondylar notch must be removed to correct the fixed flexion deformity. If there are large osteophytes around the patella, they should also be removed.

[0044] Use a 6mm narrow osteotome to remove the osteophytes from below the medial collateral ligament to the posterolateral edge of the medial femoral condyle. Only after the osteophytes are removed can there be enough space for inserting the saw blade into the intercondylar notch in the next step.

[0045] Step 4: Tibial plateau osteotomy: Place the knee joint in flexion and insert one end of the femoral condyle gauge according to the preoperative estimated model, with a starting thickness of 1 mm;

[0046] Remove all retractors, assess ligament tension, and adaptively select extra-small, small, medium, or large femoral condyle gauges to obtain appropriate ligament tension; if appropriate ligament tension is not obtained, use a different size of femoral condyle gauge until appropriate ligament tension is obtained; check the relationship between the front of the femoral condyle gauge and the approximate position of the cartilage surface of the patient before arthritis to determine the best model of the femoral component. The correct femoral condyle gauge should be inserted into the center of the medial compartment of the knee joint, and then the tibial saw guide should be inserted, and the long axis of the guide should be parallel to the long axis of the tibia;

[0047] By using the femoral condyle gauge, tibial saw guide and G-clip at the same time, the osteotomy plane can be accurately located; select the appropriate G-clip and connect it to the femoral gap gauge and tibial saw guide;

[0048] Then, a sagittal osteotomy of the tibia was performed using an oscillating saw and a rigid narrow saw blade;

[0049] Step 5: Femoral drilling and alignment: Flex the knee joint to about 45°, use a 4mm electric drill to drill the femoral intramedullary hole. This operation requires a 5mm opening cone. The femoral drilling position must be 1 cm in front of the anterior edge of the femur and close to the inner side of the inner wall of the femoral intercondylar fossa, and the drilling direction is toward the anterior superior iliac spine.

[0050] Then the intramedullary rod is inserted until it touches the inner surface of the femur;

[0051] Then, the knee joint is flexed to 90°, the anchor plate 1 is inserted, and the movable plate 2 is slid along the middle of the upper surface of the anchor plate, gradually approaching the medial femoral condyle, and after aligning with the midline of the femoral osteotomy area, a micro drill is passed through the designated positioning hole 3 to punch a number of guide holes at the midline position of the femoral osteotomy area; two mounting holes are respectively punched at the upper and lower positions of the guide holes, and the double columns of the femoral condyle prosthesis are respectively embedded in the medial femoral condyle; in this way, the movable center positioner composed of the anchor plate and the movable plate plays a positioning and measuring role in the process of center positioning of the medial femoral condyle, guides the opening of the femoral drilling guide, and limits the drilling position of the medial femoral condyle, so that the femoral prosthesis can be located in the center of the medial femoral condyle, and the femoral prosthesis is perpendicular to the tibial plateau prosthesis;

[0052] Simultaneously insert the femoral drill guide, assess the joint space thickness, insert the intramedullary rod connector onto the intramedullary rod, and insert its other end into the left / lateral hole of the femoral drill guide, ensuring that the guide is properly aligned;

[0053] Step 6: Femoral osteotomy: insert the posterior femoral osteotomy guide block into the drill hole and hammer it in to fix it;

[0054] Insert the retractor to protect the MCL, use a 12mm wide sagittal saw to resect the posterior articular surface of the femoral condyle, press down on the saw blade to slightly bend it to ensure that the saw blade is close to the lower surface of the posterior osteotomy guide block for osteotomy; operate carefully to avoid damaging the medial collateral ligament and anterior cruciate ligament; and remove the guide block with a hammer, making sure to remove it parallel to the femoral drill guide hole to avoid damaging these drill holes; remove the bone block;

[0055] Now that the posterior aspect of the knee joint has been well exposed, the residual medial meniscus is removed;

[0056] In the MCL area, a small piece of meniscus should be retained to avoid the tibial component from damaging the MCL, and the posterior horn of the meniscus must be completely removed;

[0057] Among them, the femoral osteotomy area can be ground several times and the bone chips can be thoroughly cleaned;

[0058] Step 7: Trial: At this point, the knee is flexed 100°, the tibial template is inserted, and a single-column femoral component trial is used to confirm the flexion-extension gap balance;

[0059] With the meniscal liner in place, move the knee through the full range of motion to confirm knee stability, liner fixation, and absence of impingement.

[0060] Step 8. Final preparation: Insert the appropriate size of tibial template. To ensure the selection of the appropriate size, the rear edge of the template should be aligned with the posterior tibial cortex when placing the tibial template. Passing the universal osteotomy hook through the posterior tibial cortex will help to complete this step. The tibial template should be aligned with the medial tibial cortex or slightly overhang. If the overhang exceeds 2mm, a smaller tibial component should be used. Laterally press the tibial plateau against the sagittal osteotomy surface and fix it with screws.

[0061] Step 9: Fix the prosthesis: first place a small amount of bone cement on the tibial osteotomy surface and smooth it to make a thin layer of bone cement covering the entire tibial osteotomy surface, insert the tibial template and press it down, first press the back and then the front, and squeeze out the excess bone cement in the front of the tibia;

[0062] Then squeeze the second portion of bone cement into the femoral hole and coat the concave surface of the meniscus pad with bone cement. Place the meniscus pad coated with bone cement on the medial condyle of the femur at a 45° angle to the long axis of the femur. Compact the meniscus pad with a beater. Use a Woodson bone cement spatula to scrape off excess bone cement at the edge. Flex the knee joint 45° and maintain this position. Insert a suitable depth gauge to pressurize the bone cement. Do not fully straighten or flex the knee joint, otherwise the prosthesis may shake and cause the prosthesis to loosen.

[0063] Step 10. End: Close the incision as usual.

[0064] Meanwhile, a double-column femoral prosthesis was used in the femoral section, the inner arc surface of which was filled with a porous titanium plasma spray and hydroxyapatite double coating, and the tibial template had a PPS and HA double coating on all bone / prosthesis contact surfaces.

[0065] Among them, patients have the following points to note:

[0066] 1) There must be intact anterior and posterior cruciate ligaments, and anterior cruciate ligament deficiency is a contraindication for unicompartmental knee replacement;

[0067] 2) If the lateral knee radiograph shows posterior bone loss or uncorrectable lateral subluxation on the valgus stress radiograph, this suggests an anterior cruciate ligament (ACL) injury, and if the integrity of the ACL is in doubt, it should be assessed during surgery using a hook hook.

[0068] 3) The lateral compartment of the knee joint should be intact, with intact meniscus and full-thickness articular cartilage;

[0069] 4) The varus deformity within the joint must be able to be passively corrected to the pre-disease state, but it must not exceed the normal range. This can be confirmed by taking a valgus stress radiograph of the knee joint;

[0070] 5) Passive correction of joint deformity after valgus stress is more important than the degree of internal deformity. It is rare to passively correct a varus deformity of more than 15° to a neutral position. Therefore, soft tissue release should never be performed. If the medial collateral ligament is shortened and the varus deformity cannot be passively corrected, it indicates that the severity of the arthritis has exceeded the stage that can be treated by unicompartmental knee replacement. Therefore, this situation is a contraindication for unicompartmental knee replacement.

[0071] 6) The knee flexion deformity should be less than 15°. If the flexion deformity is greater than 15°, the anterior cruciate ligament is usually ruptured.

[0072] 7) Under anesthesia, the patient's knee joint must be able to flex to more than 110° so that the femoral condyle can be manipulated during surgery;

[0073] 8) The patient's age, weight or activity level is not a contraindication to surgery, and chondrocalcinosis is not a contraindication to unicompartmental knee replacement;

[0074] 9) Unicompartmental knee replacement is strictly contraindicated in patients with any type of inflammatory arthritis;

[0075] 10) After opening the knee and performing a direct examination, a final decision is made as to whether a unicompartmental knee replacement can be performed.

[0076] like Figure 2 and Figure 3 As shown, a T-shaped slot 4 is axially opened in the middle of the upper surface of the movable plate 2, and both sides of the T-shaped slot 4 extend toward both sides of the anchor plate 1 respectively. A guide rod 5 fixedly connected to the movable plate 2 is inserted at the opening of the T-shaped slot 4. When punching, the movable plate 2 drives the guide rod 5 to move and slide along the opening of the T-shaped slot 4, which limits the movable plate 2 and makes the movable plate 2 move along the center line of the anchor plate 1.

[0077] like Figure 2 and Figure 3 As shown, sliders 6 are integrally installed on both sides of the guide rod 5 at one end inside the T-shaped slot 4. The two sliders 6 are respectively adapted to the parts of the T-shaped slot 4 extending to both sides, so that the guide rod 5 fits with the T-shaped slot 4, which can horizontally straighten the guide rod 5 and reduce the degree of skewness.

[0078] like Figure 4 , Figure 5 and Figure 6 As shown, the four edges of the anchor plate 1 are all integrally mounted with hammer heads 7, and the four hammer heads 7 extend respectively toward the middle of one side of the anchor plate 1 where they are located, so that two hammer heads are formed at both ends of the anchor plate 1, which is convenient for medical personnel to hold tightly.

[0079] like Figure 4 , Figure 5 and Figure 6As shown, the four hammer heads 7 are integrally provided with a slope 8 on one side facing the middle of the anchor plate 1, so that the two hammer heads can better fit the curvature of the hand, making it easier for medical staff to hold them, and reducing the edges and corners of the central positioner to prevent cuts to the hands.

[0080] like Figure 4 , Figure 5 and Figure 6 As shown, the four hammer heads 7 have rounded corners on one side away from the middle of the anchor plate 1, which further reduces the edges and corners of the central positioner, thereby preventing not only the medical staff's hands from being cut, but also the tissue at the opening from being cut.

[0081] like Figure 4 , Figure 5 and Figure 6 As shown, a step groove 9 is also provided on the upper surface of the anchor plate 1. The step groove 9 extends from one end of the anchor plate 1 to the middle of the anchor plate 1. The step groove 9 forms a height difference at the two hammer heads, and can be inserted into the medial tibiofemoral joint gap of the knee joint with different degrees of opening. A central positioner can be used in two sizes, and the functions are more diverse.

[0082] like Figure 4 , Figure 5 and Figure 6 As shown, the upper edges of the four hammer heads 7 away from the anchor plate 1 are all integrally installed with slope protection 10, and the slope protection 10 has an arc on the side facing the anchor plate 1. Two adjacent slope protections 10 can drag the two sides of the medial femoral condyle in an arc shape at their respective hammer heads, making it convenient to center the T-slot 4 without manual alignment, and facilitating quick calibration of the position of the guide hole.

[0083] like Figure 1 and Figure 2 As shown, the anchor plate 1, the movable plate 2 and the positioning hole 3 are all polished, with a small surface roughness, which will not wear the femur and tibia. Similarly, the surfaces of the T-slot 4, the guide rod 5, the slider 6, the hammer head 7, the slope 8, the step groove 9 and the slope protection 10 should be free of sharp edges, burrs, attachments and other defects to ensure that the entire central positioner will not cause unnecessary damage to the surrounding tissues during use. In addition, the roughness of these surfaces should also be controlled within a certain range to further reduce irritation and friction.

[0084] like Figure 2 and Figure 3 As shown, the spacing between the positioning holes 3 is 3 mm, leaving enough space and providing the optional positions of the positioning holes 3 more densely, so that there is enough space to drill the two mounting holes on the medial condyle of the femur.

[0085] The working principle of the utility model is as follows: when drilling and aligning the femur, the knee joint is flexed about 45 degrees, and a 4mm electric drill is used to drill a hole in the femoral marrow. This operation requires the use of a 5mm opening cone. The femoral drilling position must be 1 cm in front of the front edge of the femur and close to the inner side of the inner wall of the intercondylar fossa of the femur, and the drilling direction is toward the anterior superior iliac spine.

[0086] Then the intramedullary rod is inserted until it touches the inner surface of the femur;

[0087] Then, the knee joint is flexed to 90°, the anchor plate 1 is inserted, and the movable plate 2 is slid along the middle of the upper surface of the anchor plate, gradually approaching the medial femoral condyle, and after aligning with the midline of the femoral osteotomy area, a micro drill is passed through the designated positioning hole 3 to punch a number of guide holes at the midline position of the femoral osteotomy area; two mounting holes are respectively punched at the upper and lower positions of the guide holes, and the double columns of the femoral condyle prosthesis are respectively embedded in the medial femoral condyle; in this way, the movable center positioner composed of the anchor plate and the movable plate plays a positioning and measuring role in the process of center positioning of the medial femoral condyle, provides guidance for the opening of the femoral drilling guide, limits the drilling position of the medial femoral condyle, and improves the installation accuracy of the femoral prosthesis.

[0088] The above is only a preferred embodiment of the present invention. It should be noted that, for ordinary technicians in the technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A central positioner, characterized in that: include: An anchoring plate (1), the anchoring plate (1) is used for being inserted into the medial tibiofemoral joint space of the knee joint; The movable plate (2) is attached to the surface of the anchor plate (1) and slides axially until it is attached to the medial femoral condyle of the knee joint. The movable plate (2) is provided with a plurality of positioning holes (3) equidistantly distributed along the axial direction.

2. A central positioner according to claim 1, characterized in that: A T-shaped groove (4) is axially provided in the middle of the upper surface of the movable plate (2), and two sides of the T-shaped groove (4) extend toward two sides of the anchor plate (1) respectively. A guide rod (5) fixedly connected to the movable plate (2) is inserted at the opening of the T-shaped groove (4).

3. A central positioner according to claim 2, characterized in that: Slide blocks (6) are integrally installed on both sides of one end of the guide rod (5) located inside the T-shaped slot (4), and the two slide blocks (6) are respectively adapted to the parts of the T-shaped slot (4) extending toward both sides.

4. A central positioner according to claim 1, characterized in that: The four edges of the anchor plate (1) are all integrally mounted with hammer heads (7), and the four hammer heads (7) respectively extend toward the middle of one side of the anchor plate (1) where they are located.

5. A central positioner according to claim 4, characterized in that: A slope (8) is integrally provided on one side of the four hammer heads (7) facing the middle of the anchor plate (1).

6. A central positioner according to claim 4, characterized in that: The four hammer heads (7) have rounded corners on one side away from the middle of the anchor plate (1).

7. A central positioner according to claim 1, characterized in that: The upper surface of the anchor plate (1) is also provided with a step groove (9), and the step groove (9) extends from one end of the anchor plate (1) to the middle of the anchor plate (1).

8. A central positioner according to claim 4, characterized in that: The upper edges of the four hammer heads (7) away from the anchor plate (1) are all integrally installed with a slope protection (10), and the slope protection (10) has an arc on one side facing the anchor plate (1).

9. A central positioner according to claim 1, characterized in that: The spacing between the positioning holes (3) is 3 mm.

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