The meniscus is 2 crescent-shaped fibrocartilages located on the medial and lateral articular surfaces of the tibial plateau. Its cross section is triangular in shape, thick on the outside and thin on the inside, and slightly concave on the top, so that the meniscus injury type 1. coincides with the femoral condyles and is flat on the bottom, where it meets the tibial plateau. Such a structure precisely allows the femoral condyles to form a deeper depression in the tibial plateau, thus increasing the stability of the spherical femoral condyles to the tibial plateau. The anterior and posterior ends of the meniscus attach to the middle non-articular surface of the tibial plateau, anterior and posterior to the intercondylar spine, respectively. This part can also be called the anterior and posterior corners of the meniscus. 2.The marginal part of meniscus is thick and closely connected with the joint capsule, while the central part is thin and free. The medial meniscus is “C” shaped, with the anterior horn attached to the anterior cruciate ligament attachment point, and the posterior horn attached between the intercondylar tibial bulge and the posterior cruciate ligament attachment point, with the middle of its outer edge closely connected to the medial ligament. The lateral meniscus is “O” shaped, with its anterior horn attached before the ACL attachment point and its posterior horn attached before the posterior horn of the medial meniscus, and its outer edge is not attached to the lateral collateral ligament. 3. The meniscus can move with the movement of the knee joint, moving forward when the knee is extended and backward when the knee is flexed. The meniscus is fibrocartilage, which has no blood supply, and its nutrition mainly comes from synovial fluid, only the side part connected with the joint capsule gets some blood supply from synovial membrane. The role of the meniscus: 1. Weight-bearing When not bearing weight, the tibia and femur are not in contact, and the meniscus pads between the two. When weight-bearing, about 70% of the weight-bearing area is on the meniscus, which greatly reduces the stress on the tibial plateau, thus protecting the cartilage and the whole body joint. If the meniscus is removed, the peak pressure on the tibial plateau can rise twofold and will cause cartilage degeneration. It can be inferred that in the case of transverse meniscal tears, the weight-bearing function of the meniscus is completely lost. This requires us to cut as little as possible when removing parts of the meniscus. 2. Maintain the coordination of knee movement The meniscus moves together with the tibia, the medial meniscus is less displaced than the lateral meniscus, and the meniscus can be deformed during knee flexion and extension to adapt to the anatomical shape of the knee joint. The coordination of knee joint geometry is maintained, thus maintaining the coordination of knee joint movement. 3, Maintenance of stability Meniscectomy does not cause anterior tibial displacement when the ACL is intact, whereas it causes greater anterior tibial displacement when the ACL is ruptured. 4. Absorption shock There are some such patients with knee pain whose arthroscopic examination pathology did not reveal any abnormality, while their symptoms were obvious, and later their meniscus was found to have poor absorption function after examination. 5, lubricating the joint The meniscus also has functions such as lubricating the joint, the meniscus can evenly coat the joint surface with joint fluid, so that the friction coefficient of the joint is greatly reduced Etiology: 1, meniscal injuries are mostly caused by torsional external forces, when a leg is weight bearing, the lower leg is fixed in semi-flexion, when the external booth, the body and the femur are violently rotated internally, the medial meniscus is between the femoral condyle and the tibia, and is subjected to rotational pressure, which causes the meniscus to tear. The greater the degree of knee flexion at the time of sprain, the more posterior the tear site is. The mechanism of lateral meniscus injury is the same. But the direction of the force is opposite, the ruptured meniscus, such as part of the slide into the joint between the mechanical barriers to joint activity, preventing joint extension and flexion activities, the formation of “interlocking”. 2, meniscus injury can occur in the anterior corner, posterior corner, middle or edge of the meniscus. The shape of the injury can be transverse, longitudinal, horizontal or irregular, or even broken into intra-articular free bodies. The classifications are: marginal tears, transverse tears, longitudinal tears, horizontal tears, and anterior and posterior corner tears. In severe trauma cases, the meniscus, cruciate ligament and collateral ligament can be damaged at the same time. 3. After meniscal injury, the knee joint has severe pain, cannot straighten itself, and the joint is swollen. The pressure pain at the knee joint gap is an important basis for meniscal injury. When the knee joint is flexed, the tibia is fixed and the femur is strongly externally rotated, it can cause injury to the anterior horn of the lateral meniscus or the posterior horn of the medial meniscus. Strong internal rotation of the femur in flexion (or external rotation of the lower leg) can easily cause injury to the posterior horn of the lateral meniscus or the anterior part of the medial meniscus. Long-term compression and wear can cause degeneration, which can easily lead to tears. Pathology Knee meniscal injuries are commonly caused by extension and flexion of the knee accompanied by internal and external rotation or internal and external rotation of the lower leg, resulting in contradictory movements of the meniscus. When the knee is in extension, the femoral condyles slide over the meniscus, pushing the meniscus forward in extension and backward in flexion; when the knee is rotated, the meniscus moves in unison with the femoral internal and external condyles, and its rotation occurs between the meniscus and the tibial plateau, with one side of the meniscus forward and the other side backward. When the knee joint is in semi-flexion and the lower leg is internally or externally rotated, the meniscus is squeezed and cannot move. If the meniscus is suddenly straightened or further rotated, the meniscus will tear when the tension on the fibrocartilage or the fibrous tissue around the perimeter of the meniscus exceeds its own endurance. 1, Such as when the knee joint is flexed, the tibia is fixed, and the femur is strongly externally rotated, it can cause injury to the anterior angle of the lateral meniscus or the posterior angle of the medial meniscus. 2, Strong internal rotation of the femur in flexion (or external rotation of the lower leg) can easily cause injury to the posterior horn of the lateral meniscus or the anterior part of the medial meniscus. Long-term extrusion and wear can cause degeneration, which can easily result in tears. Abnormal loosening of the meniscus, instability after joint ligament injury, or obesity and excessive weight are all factors that make the meniscus susceptible to injury. Diagnosis: Specialized physical examination + MR MRI is by far the imaging tool with the highest positive sensitivity and accuracy rate for diagnosing meniscal injury and cruciate ligament rupture, with an accuracy rate of 98%. MRI of meniscal tears shows a low signal meniscus with linear or complex shaped high signal bands across the surface of the meniscus.