The knee joint is the largest and most complex joint in the human body and includes three bones: the femur (thigh bone), tibia (calf bone) and patella (knee bone), which play a vital role in daily life for walking, going up and down stairs, and standing up from a sitting position. If the joint surface of the knee joint is worn, defective or damaged for various reasons, resulting in joint space narrowing, walking pain and functional impairment, the quality of life will be seriously affected. Artificial knee arthroplasty is one of the most effective and reliable means of treating advanced knee osteoarthritis. However, for an elderly patient, artificial knee arthroplasty is not a non-invasive or minimally invasive procedure like the installation of dentures, but requires a high level of preoperative preparation, of which the correct prosthesis selection is a prerequisite to ensure a satisfactory surgical outcome. There are many types of knee prostheses commonly used in clinical practice, and as many as a dozen manufacturers, so how should you choose a prosthesis in clinical practice? The first step is to understand the composition and classification of these prostheses. Knee prosthesis consists of the following three parts: 1. Femoral prosthesis: surface replacement of the end of the femur. The femoral prosthesis consists of a metal alloy. 2. Patellar prosthesis: replaces the inner surface of the patella that rubs against the femur. The patellar prosthesis consists of plastic with a metal alloy backing plate. 3.Tibial prosthesis: It can be a single or two-piece design. The single design consists of plastic and the two-piece design consists of a metal buttress attached to the bone and a plastic piece. The plastic spacer provides a smooth surface over which the femur moves. The plastic spacer is usually attached to the tibial bracket. Knee prosthesis classification: 1, according to the part of the knee prosthesis used can be divided into unicondylar prosthesis (single spacer prosthesis), double spacer prosthesis excluding patellofemoral joint replacement and total joint prosthesis (triple spacer prosthesis). 2.The prosthesis can be divided into cemented prosthesis and non-cemented prosthesis according to the fixation method. 3, according to the degree of mechanical restriction provided in the design of the prosthesis can be divided into non-restrictive prosthesis, partially restrictive prosthesis, highly restrictive prosthesis and fully restrictive prosthesis (hinged prosthesis). The choice of knee prosthesis: 1, the choice of unicondylar prosthesis; unicondylar prosthesis belongs to the non-restrictive prosthesis. For simple lesions of the medial or lateral interval, unicondylar replacement is theoretically an option. Successful unicondylar replacement surgery can maximize the preservation of the joint’s tissue structure and motor function and leave room for secondary TKA surgery. Currently, unicondylar prosthesis replacement accounts for a small percentage of knee replacement surgery. 2. Choice of fixation method: For knee prosthesis, the better long-term follow-up results of cemented fixation type prosthesis make this type of prosthesis widely accepted. In knee replacement surgery, the role of bone cement is not only to fix the prosthesis, but also to strengthen the bearing strength of the bone bed, especially on the tibial side. 3, the choice of different degrees of restriction of the total knee prosthesis: the mechanical restriction of the knee prosthesis provides the mechanical stability of the prosthesis, but at the same time forms a contradiction with the mobility of the joint. In general, less restrictive prosthesis can obtain better joint motion function, while there are higher requirements for the integrity of the joint stability structure and operation techniques. More restrictive prostheses are designed to provide additional mechanical stability to the prosthetic joint, but as a result may result in more bone cutting and loss of some joint mobility, and may lead to mechanical loosening of the prosthesis-bone interface due to their restrictive nature. (1) Non-restrictive prosthesis: Non-restrictive total knee prostheses are represented by the preserved posterior cruciate ligament (CR) prosthesis. The preserved posterior cruciate ligament (PCL) maintains the posterior stability of the prosthesis after implantation, thus allowing greater joint mobility by allowing the tibial articular surface to tend toward a less restrictive design with greater curvature. The design of these prostheses takes more into account the mobility of the joint and allows for less mechanical constraints on the prosthesis itself. The stability after replacement is more dependent on the integrity of the ligamentous structures that maintain the stability of the knee joint and the balance of the soft tissues surrounding the knee joint. This type of prosthesis, which preserves the cruciate ligament, can be chosen for younger patients with good joint stability and can be expected to achieve greater joint mobility. Currently, most patients choose this type of prosthesis. (2) Partially restrictive prosthesis: The partially restrictive knee prosthesis is represented by the posterior stable (PS) or posterior cruciate replacement (CS) type, which refers to those prostheses that fall between non-restrictive and highly restrictive. It replaces the function of the PCL by means of a central projection of the tibial pad and a corresponding intercondylar groove of the femur. The advantage is that it has a wide range of indications and is undoubtedly the best choice in cases of PCL insufficiency or where the PCL cannot be preserved due to knee flexion contracture. The disadvantage is that it requires more bone cutting than the CR prosthesis and may result in reduced joint mobility due to impingement of the femoral condyle on the posterior edge of the tibial prosthesis during hyperflexion. (3) Highly restrictive knee prosthesis: These prostheses such as CCK, TC3, etc. are designed for knee instability using a taller tibial projection and a more matched femur to obtain lateral and posterior stability. They are mainly used for initial replacement cases with lateral collateral ligament insufficiency, with large bone defects or severe deformities, and for revision surgery after initial replacement failure with non-restrictive or partially restrictive prostheses. (4) Fully restrictive knee prostheses: Fully restrictive prostheses are represented by hinged knees, which are designed with a hinge to provide sufficient mechanical stability to be used in total knee revision after knee tumor resection and loss of knee stability. In fact, although there are many brands of these prostheses, they are similar in design and their efficacy depends not only on the choice of prosthesis but also on the surgeon’s precise design and skillful operation as well as on the correct postoperative rehabilitation measures. Therefore, when selecting a prosthesis in clinical practice, the patient, the prosthesis design and supporting tools, and the operator should be taken into account. As long as we consider the above three aspects for each case, it is generally not difficult to select the correct prosthesis for clinical purposes.