Etiology Mostly caused by torsional external forces. When a leg is weight bearing and the lower leg is fixed in semi-flexion and external booth, the body and the femur are violently rotated internally and the medial meniscus is subjected to rotational pressure between the femoral condyle and the tibia, resulting in a meniscal tear. The greater the degree of knee flexion at the time of the sprain, the more posterior the tear site. The mechanism of injury to the lateral meniscus is the same, but the forces act in the opposite direction. If the torn meniscus slips partially between the joints, it causes mechanical impairment of joint movement and prevents joint extension and flexion, resulting in “interlocking”. In severe trauma cases, the meniscus, cruciate ligament and collateral ligament can be damaged at the same time. Meniscal injuries can occur at the anterior, posterior, middle or marginal part of the meniscus. The injury can be transverse, longitudinal, horizontal or irregular in shape, or even broken into intra-articular free bodies. Clinical presentation Most have a history of significant trauma. In the acute phase, there is significant pain, swelling, and fluid accumulation in the knee joint, and the joint flexion and extension activities are impaired. After the acute phase, the swelling and effusion may subside on their own, but there is still pain in the joint when moving, especially when going up and down stairs, going up and down slopes, squatting and standing, running and jumping, etc. In severe cases, there may be limp or dysfunction in flexion and extension, and some patients have interlocking phenomenon or popping when flexing and extending the knee. If the joint has obvious fluid (or blood), the fluid should be extracted under strict aseptic operation; if the joint has “interlocking”, the “interlocking” should be released by manipulation, and then the knee should be fixed with a tubular cast from the upper 1/3 of the thigh down to the ankle in The knee is then immobilized in a straight position for 4 weeks. The cast should be properly shaped so that the patient can walk with the cast on the floor. During the fixation period and after removal of the cast, the quadriceps should be actively exercised to prevent muscle atrophy. 2. Chronic phase If non-surgical treatment is ineffective, symptoms and signs are obvious, and the diagnosis is clear, the damaged meniscus should be removed surgically as early as possible to prevent traumatic arthritis. After surgery, the knee should be bandaged with pressure in the extended knee position, and the next day, the quadriceps should start to do resting contraction exercises, and 2-3 days later, the quadriceps should start to do straight leg raising exercises to prevent quadriceps atrophy, and two weeks later, the quadriceps should start to walk on the ground, and the normal function can be restored in 2-3 months after surgery. 3.Arthroscopic application Arthroscopy can be used for the treatment of meniscal injury. Meniscal edge tears can be repaired with sutures, and partial meniscal resection is usually performed to preserve the undamaged part. For those who suspect meniscus injury in early stage, emergency arthroscopy is feasible. Early treatment of meniscus injury can shorten the treatment course, improve the treatment effect and reduce the occurrence of injurious arthritis. It is less traumatic and quicker to recover through arthroscopic surgery.