In addition to the specific structure of the bony structure itself, the stability of the knee joint depends on the constraints of the anterior and posterior cruciate ligaments, the balance of the medial and lateral collateral ligaments, and the balance of the strength of the knee extension device, quadriceps and carpuscles. Except for the highly restrictive and hinged prostheses, which rely less on the stability of the knee joint itself, all other non-restrictive and partially restrictive prostheses have certain requirements on the stability of the knee joint itself. In particular, the balance and stabilization of the medial and lateral collateral ligaments are important for maintaining normal function of the artificial joint after knee arthroplasty. Therefore, preoperative examination of the knee joint stability structures and assessment of joint stability are important for selecting the prosthesis and determining the surgical plan. 1. Cruciate ligament: It is the most important and strongest ligament structure to maintain the stability of the knee joint. The anterior cruciate ligament is tense when the knee joint is fully extended and relaxed when the joint is flexed, and its function is to prevent posterior dislocation of the femur, forward dislocation of the tibia, and over-extension and over-rotation of the knee joint; ② the posterior cruciate ligament is gradually tense with the flexion of the knee joint to prevent forward dislocation of the femur, posterior dislocation of the tibia, and over-flexion of the knee joint. 2. Lateral collateral ligament: ① The medial collateral ligament is divided into superficial and deep layers, with the superficial layer consisting of parallel fibers in the front and oblique fibers in the back; the deep layer consists of the thickened portion of the medial knee capsule. When the knee is fully extended, the superficial layer of the medial collateral ligament is tense to maintain joint stability; when the knee is flexed, the superficial oblique fibers are relaxed while the parallel fibers are tense, thus maintaining joint stability; it also controls the external rotation of the tibia on the femur. The lateral collateral ligament is located in the posterior 1/3 of the lateral knee and is tense when the knee is fully extended, but tends to relax when the knee is flexed. The stability of the lateral structures is maintained by the lateral collateral ligament, the biceps femoris, and the skeletal tibial bundle. The quadriceps and rouge muscles are involved in the dynamic stability of the knee joint: ① The main function of the quadriceps is to extend the knee, and the internal femoral oblique muscle also has the function of preventing the skeleton from being semi-dislocated outward; ② The main function of the rouge muscle is to flex the knee, and it consists of the biceps, semicondylar and semimembranosus muscles. It is worth pointing out that the stability of the artificial joint after implantation relies more on the balance of the periarticular structures, especially the lateral collateral ligaments. Whether or not the posterior cruciate ligament is preserved, the anterior stability of a knee joint with anterior cruciate ligament deficiency is dependent on the stability of the knee extension device, especially the strength of the quadriceps muscle. At the same time, the loss of the cruciate ligament’s “snapping” mechanism results in a less stable proprioception than in a normal knee.