Knee meniscal injuries are commonly caused by extension and flexion of the knee joint 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 concert with the internal and external femoral condyles, with the rotation occurring between the meniscus and the tibial plateau, with one side of the meniscus moving forward and the other side moving 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 rotated further, the meniscus will tear when the tension on the fibrocartilage or the fibrous tissue around its periphery exceeds its own endurance. There are three types of meniscal injuries: peri-meniscal inflammation, meniscal degeneration, and meniscal tears. Symptoms: 1. Knee swelling and pain: Most patients have a history of injury and gradual swelling of the knee joint after injury, some patients have no obvious history of trauma. Knee pain often occurs in a certain position during exercise, and the pain may disappear after a change in position. The pain is located in the joint space on both sides. 2, playing limp: lower limb weakness, occasionally accompanied by playing “limp” symptoms, joint pain when moving, especially when going up and down the stairs, the symptoms are heavier when going downstairs. 3, muscle atrophy: long duration of the disease, the quadriceps muscle will gradually atrophy. 4. Interlocking: When the femoral condyles protrude into the rupture of the meniscus during movement and cannot be released, the knee joint extension and flexion may suddenly become impaired, forming interlocking. After relaxing the muscles, changing the position, rotating and flexing autonomously or passively, the interlock can be released. Examination: swelling and pressure pain in the joint. Swelling of the joint, floating patella test (+), fixed and limited pressure pain along the joint space. MRI and knee arthroscopy can confirm the diagnosis. Treatment: 1. Conservative treatment with physiotherapy, medication and external fixation: Meniscal periarthritis and meniscal degeneration can be treated by external fixation with braces or casts, combined with medication and physiotherapy, and local closure if necessary. 2, arthroscopic surgery: for conservative treatment has no effect or confirmed meniscus tear, can use arthroscopic minimally invasive surgery treatment. The surgery is less invasive, safer and more effective. The surgical methods include: arthroscopic examination and cleaning, meniscus suture, meniscoplasty, meniscus subtotal excision, meniscus total excision, etc. If the knee joint is combined with cruciate ligament rupture, it is necessary to perform cruciate ligament reconstruction. Postoperative knee brace immobilization and limitation of knee hyperflexion is required for about 4 weeks (depending on the surgery)