I. Composition of the knee joint The largest and most complex joint in the human body consists of two joint surfaces, namely, the tibiofemoral joint surface and the patellofemoral joint surface, and the main movement of the knee joint can be simplified as a hinge joint movement. Anatomy of the knee joint 1, cartilage, including the distal femoral cartilage, proximal tibial cartilage and patellar cartilage. Articular hyaline cartilage provides a relatively smooth and low friction surface for joint movement. 3mm-7mm thick. Thickness 3mm-7mm, with compressibility and a certain degree of elasticity, can be regarded as a viscoelastic body, with load cushioning effect. 2.Meniscus Viscoelastic fibrous cartilage, wedge-shaped cross-section, attached to the tibial plateau around. Divided into medial and lateral, both sides of the meniscus is connected with ligaments, corresponding to the inclusion of the medial and lateral femoral condyles. The main function of the meniscus is to cushion, distribute loads, and provide better stability. The lateral meniscus is relatively small and has an almost circular shape. The lateral meniscus has a relatively large deformation during joint movement. The medial meniscus is relatively large and “C” shaped. When the knee joint is in motion, basically the medial side is the fulcrum, and the medial side of the tibial plateau together with the meniscus bear a greater load. Ligaments The anterior and posterior cruciate ligaments are the two ligaments connecting the femur and tibia inside the knee joint, and they are cross-shaped. The main function of the anterior and posterior cruciate ligaments is to stabilize the anterior-posterior and rotational motion of the tibio-femoral joint of the knee. The medial collateral ligament and lateral collateral ligament, also known as the tibial collateral ligament and fibular collateral ligament, are found on the medial and lateral sides of the knee joint respectively. The anterior and posterior cruciate ligament-four-link model, a simplified model, is used to simulate the interaction of the ACL and PCL during joint motion. Third, knee joint motion The main form of knee tibio-femoral joint activity is flexion and extension. Extension up to 180 degrees, generally not more than 10 degrees of hyperextension. Daily activities flexion up to 140 degrees. Rotational motion occurs when the knee flexes more than 30 degrees. Fourth, the knee joint biomechanics 1, the static mechanics of the knee joint standing position of the static force (feet on the ground) for the body weight of 0.43 times, while walking up to 3.02 times the body weight, when going up the stairs can reach 4.25 times. The line from the center of the femoral head to the center of the ankle joint is the line of force (mechanical axis) of the entire lower extremity, and this axis passes medially through the center of the knee joint. The centerline through the femoral and tibial stems is called the anatomical axis. The mechanical axis of the femur has a 4 to 6° valgus angle to the anatomic axis of the femur. The femoral-tibial joint line is inclined approximately 3° medially. The anatomical axis of the tibia is co-linear with the mechanical axis of the tibia. 2, tibiofemoral joint mechanics In the knee joint in motion, the relative displacement of the meniscus with the joint activity, the strain of the articular cartilage tissue, so that the inter-articular pressure changes tend to moderate. In normal knee motion, the stress on the medial side of the joint is 50% more than the lateral side. The rotational motion of the knee in the horizontal plane is centered on the medial condyle. 3, patellofemoral joint mechanics The patellofemoral joint is an important structure involved in knee extension and flexion movements. The patella transmits the tension of the quadriceps muscle and bears the tension of the patellar ligament, and its articular surface itself bears the stress and the stress on the articular surface during the knee flexion movement is the focus of the study of the biomechanics of the patellofemoral joint. Lateral tilt and lateral displacement of the patella are the main forms of abnormal patellofemoral alignment present.