Application of rotating platform-type knee prosthesis The rotating platform-type knee prosthesis has been used in the clinic for nearly 20 years and has achieved good clinical results. Compared with the fixed platform prosthesis design, it has many advantages, which are favorable to reduce the long-term revision rate of the rotating platform-type knee prosthesis. I. Advantages of rotating movable platform prosthesis (a) Reduce the wear and tear of polyethylene liner: Possible mechanism: 1, increase the contact area of tibiofemoral joint: the spherical design above increases the form-fit and contact area with the femoral condyle, which increases the stability of the joint, reduces the stress at the prosthesis-bone interface, and improves the long-term survival rate of the prosthesis. 2, change the tibiofemoral joint multidirectional motion into unidirectional motion: the rotating platform type prosthesis can rotate freely between the polyethylene liner below and the tibial platform prosthesis. By increasing the rotating plane, the complex multidirectional motion of the knee joint can be decomposed into flexion-extension and axial rotational motion as two unidirectional motions, [1-2], which will reduce the shear stress and wear and tear. 3.Automatic adjustment of rotational osteotomy force line: The rotational activity generated by the movable platform is not only conducive to the automatic adjustment of the tibial side polyethylene liner and femoral prosthesis, as well as the patella Q-angle and patellar force line, to avoid accelerated regional wear and tear due to the incorrect force line, but also conducive to the adjustment of patellofemoral trajectory, so as to make it in the optimal position, to avoid patellar subluxation. The design features of rotating platform prosthesis (take LINK MK II as an example): (1) The patellar groove is longer, wider and smoother, which is closer to the anatomy of the normal patellar groove, and provides an optimized trajectory for the patella, so that the patella passes through the deeper condylar fossa smoothly, which increases the mobility of the knee joint, and prevents the patella from popping in the process of moving to the distal end; (2) There is a difference between right and left, and the lateral condyle of the prosthesis is higher than the (3) The tibial platform chassis is asymmetric in design, with dovetail groove design on the upper part, which is conducive to the flexible rotation of the movable platform and prevents the liner from dislocating; (4) The radius of curvature of coronal plane of the distal femoral prosthesis and rotating platform are 22.6mm and 23.7mm, respectively, and the curvature ratio of both of them is 1.05. The radius of curvature of sagittal plane of the distal femur and the PE movable platform are 36.1mm and 13.0mm, respectively. The sagittal radii of curvature for the distal femur and the polyethylene mobile platform were 36.1 mm and 137.1 mm, respectively, with a curvature ratio of 1.03. These curvature ratios indicate that the Gemini MKII Lateral Femoral Prosthesis with the polyethylene rotating mobile platform is a significantly better conforming prosthesis than the fixed platform prosthesis, providing all-around stabilization for the question of prostheses. Joint stability is maintained even when the posterior cruciate ligament cannot be preserved. (5) The prosthesis does not require an intercondylar osteotomy, thus avoiding the risk of femoral condylar fracture caused by intercondylar osteotomy and shortening the operative time, reducing bleeding and blood transfusion. Complications and prevention of rotating platform TKA Although rotating platform TKA has the above advantages, it is also prone to tibiofemoral dislocation, separation of the liner from the metal chassis, and spinning out of the movable liner, and most scholars have calculated that the rate of postoperative dislocation is about 1%. The following methods have been suggested to avoid these complications: (i) Prevention can be obtained by determining the ideal anatomic line of force and selecting the appropriate liner thickness. (ii) Improved gap balancing techniques: The surgical technique associated with TKA using a mobile platform prosthesis is the same as that of a fixed platform, up to the point of obtaining the same flexion-extension gap. For example, when the extension gap is 2mm less than the flexion gap, the osteotomy of the distal femur can be increased by 2mm. On the contrary, when the flexion gap is smaller than the extension gap, a small l-size lateral femoral prosthesis can be used to adapt to the flexion gap and ensure flexion-extension balance. It must be emphasized that gap balance is the key to prevent rotational mobility platform liner dislodgement. If the knee is deliberately kept lax in the flexion position to increase flexion mobility, flexion instability or liner dislodgement will occur, so this method should be avoided; instead, the implantation of rotational mobility meniscus should keep the ligament of the flexion position relatively tense. (iii) Balance of ligament tension in extension and flexion: Three conditions must be present for successful TKA surgery, namely, an ideal longitudinal line of force, a balance of ligament tension in extension and flexion, and a balance of the gap between extension and flexion. If TKA surgery can fulfill these 3 conditions, the surgical outcome will be significantly improved. Of these 3 conditions, the first is the satisfaction of the longitudinal axis line of force, then the gap balance between extension and flexion after tibiofemoral osteotomy, and finally the ligament tension balance between extension and flexion of the knee joint. When there is asymmetry between the medial and lateral osteotomy gaps, the soft tissues on the narrow side of the gap should be loosened first, and ligament loosening should not be used at once, but should be gradual in order to gradually obtain the balance of ligament tension. (d) The occurrence of late dislocation may also be related to the laxity of the flexion gap due to prosthesis wear; intraoperative PCL rupture may be caused, which is often related to unskilled surgical operation and preoperative flexion deformity is too large, and the PCL contracture is heavy, so we believe that patients with deformity, especially fixed deformity >30 degrees, should have posterior stabilized knee prosthesis replacement. (v) In addition to ligamentous laxity as a cause of prosthesis dislocation, Hasegawa et al [4] suggested that excessive weakness of the quadriceps muscle is also a common cause of rotational platform dislocation. Therefore, the quadriceps muscle should be evaluated and exercised with emphasis in the perioperative period. Precautions for rotating platform prosthesis replacement ①Keep the rectangular flexion and extension knee gap balanced and ensure that the flexion gap is slightly tighter on this basis. The difference between the flexion and extension gaps should be less than 2 mm, in order to prevent the pads from spinning out. ② The liner should be installed in place only under certain external force rather than easily sliding into the gap. After installation, the entire knee joint activity should be carefully checked, and if the liner does not become dislocated when the knee is fully flexed and externally rotated, it will not become dislocated after surgery. (iii) Ensure that the appropriate amount of fat pad is removed intraoperatively to avoid soft tissue impingement. There are more methods of femoral prosthesis positioning, Whiteside line and femoral epicondylar axis can better determine the external rotation angle of femoral prosthesis, and the posterior condylar axis and fixed external rotator with 3° external rotation to this line are mostly used to position the femoral prosthesis in the clinic; however, the above positioning methods can be difficult to position due to local anatomical changes caused by osteoarthritis. The posterior condylar angle more truly reflects the rotational state of the femoral condyle. If the articular surface of the posterior condyle has been damaged or dysplastic, and it is necessary to use the medial or lateral epicondylar axis to locate it, it is recommended to use the positioning method of the medial epicondylar tip (clinical axis), but it is appropriate to increase the positioning of the external rotational angle of the prosthesis by 2°~3° accordingly.