Knee meniscal injury refers to the destruction and interruption of the continuity and integrity of the meniscal tissue, which can be divided into traumatic and degenerative tears. The former is mostly seen in adolescents, mostly due to knee torsional trauma; the latter is mostly seen in middle-aged and elderly people, and most of them have no obvious history of violent trauma, so it is an injury that occurs on the basis of meniscal tissue degeneration, and sometimes it is difficult to change the pathological changes of knee osteoarthritis in combination. In China, injuries to the lateral discoid meniscus are more common. If the injury to the meniscus is a barrel stem tear or flap tear, it is likely to produce clinical symptoms of interlocking. Other types of injuries such as small longitudinal tears, radial transverse tears, and horizontal tears are less likely to induce symptoms of interlocking, but may induce pain due to pulling and irritation of the synovial membrane during knee movement. Injury to the meniscus, which is critical to joint stability, will lead to joint pain, instability and load transfer disorders, resulting in the premature onset of osteoarthritis. 1. History of knee torsional injury or no obvious history of trauma. 2, physical examination has clear signs: the affected knee has varying degrees of restriction, some patients have joint popping and interlocking symptoms, joint space pressure pain is obvious, a few patients in the joint space can be found in the protrusion (meniscal tear protrusion). Most patients may have quadriceps atrophy. 3.Special examination: knee hyperextension test, knee hyperextension test, rotation squeeze test, meniscus anterior angle squeeze test, Apley test, meniscus gravity test, rocking test, disc meniscus flick test, etc. (1) X-rays: The front and side views of the knee joint are important for differential diagnosis and can exclude osteochondral injury, intra-articular free bodies, bone tumors, etc. They are also important in deciding whether to operate, and arthroscopic surgery is generally not indicated in cases of severe osteoarthritis. (2) CT examination: the role in the diagnosis of meniscal tears is more limited, and the accuracy rate is lower, and has been replaced by MRI examination. Meniscal tears appear on CT as changes in morphology and density. One or more irregular linear hypodense areas appear at the site of the tear. (3) MRI: A meniscal tear is diagnosed when linear high signal appears within the meniscus reaching its free edge or joint surface. According to the degree of abnormal signal changes within the meniscus in relation to the pathological changes, the different degrees and morphological abnormalities of meniscal degeneration and tears on MRI images can be classified as tertiary signals. Usually tertiary signal changes are seen pathologically as fibrocartilage fractures, so a meniscal tear is diagnosed when tertiary signal is seen on a slice of the meniscus with morphologic irregularities. (5) Arthroscopy: Arthroscopy can be performed when meniscal injury is only highly suspected clinically and cannot be confirmed or excluded by physical examination and ancillary tests. In recent years, arthroscopy has evolved from being used solely for diagnosis to both diagnosis and treatment, and the diseased meniscus can be treated at the same time when performing arthroscopic exploration. Pathological classification: (1) Traumatic tears: small longitudinal tears or incomplete meniscal tears with stable edges; long longitudinal tears or barrel stem-like tears with unstable edges; transverse tears or flap-like tears. (2) Degenerative tears: horizontal laminar tears, compound tears, discoid meniscus, meniscal cysts. 6, differential diagnosis: meniscal injury as the most common cause of mechanical internal disorders of the knee, mainly with synovial folds, subpatellar fat pad embedded, joint free body, cartilage injury and patellofemoral instability, intra-articular lesions causing mechanical internal disorders (such as synovial chondroma, pigmented villous nodule-like synovitis, etc.) to distinguish.