Total knee joint prostheses are classified in various ways according to different design features.

1. According to whether the posterior cruciate ligament is preserved

According to whether the posterior cruciate ligament is preserved, the primary artificial knee replacement prosthesis can be divided into posterior cruciate ligament replacement (Posterior Stabilized, PS) and posterior cruciate ligament retention (Cruiate Retention, CR). In recent years, the tibial plateau of these two types of prostheses have been designed with different degrees of conformity and width of the central column according to the stability of the joint, the function of the ligament and the concept of the surgeon, so as to improve the stability of the joint and improve the kinematic performance.

(1) Features of CR and PS prostheses:

The CR prosthesis preserves the posterior cruciate ligament of the knee joint and reduces the number of surgical steps; it avoids further resection of the femoral condyle and preserves the bone mass; theoretically, it can increase flexion stability, reduce paradoxical anterior displacement, and achieve backward rolling. Helps preserve proprioception.

The PS prosthesis uses a cam-column structure to replace the function of the posterior cross in the design, so that the femoral prosthesis can be rolled back during flexion activities. During the operation, the femoral intercondylar osteotomy is required. Due to the removal of the posterior cruciate ligament, the flexion gap is larger, the posterior maneuver is easy, and the ligament balance is simpler and more straightforward.

(2) Relative indications of CR and PS prostheses:

Most patients undergoing primary total knee arthroplasty can use either a CR prosthesis or a PS prosthesis, and the choice of prosthesis depends mainly on the patient's condition and physician's experience. However, CR prosthesis is more suitable for patients with relatively normal posterior cruciate ligament function, relatively mild joint hyperplasia, and less severe joint deformity. PS prostheses can be widely used in most primary total knee replacements, including patients with severe hyperplasia and deformity. In patients with severe osteoporosis or bone defects, intramedullary lengthening rods may be required, and collateral ligament dysfunction may be required. Use restrictive spacers.

2. Fixed platform and movable platform prosthesis

The artificial knee joint prosthesis can be divided into fixed platform and movable platform according to the connection method of polyethylene gasket and metal tibial tray. Fixed platform prosthesis is a polyethylene component fixed to the tibial plateau by a locking mechanism. The polyethylene component of the movable platform prosthesis can move on the tibial plateau. In addition to forming a movable joint with the femoral prosthesis, the polyethylene spacer also allows a certain degree of movement between the tibial plateau and the tibial plateau.

The fixed platform prosthesis gasket is locked on the metal bracket, which is firm and reliable, and is more widely used. The geometries of the fixation spacers may vary widely from manufacturer to manufacturer to match their unique femoral prosthesis and improve the desired kinematics. It can also be easily changed to a restrictive shim if required.