I. Indications for knee arthroscopy Arthroscopy can accomplish many surgeries that used to require incision. In addition to diagnostic examination, it can be used for the treatment of articular cartilage injury, synovectomy, free body removal, and cleanup surgery for osteoarthrosis. According to the difference of the main structure of each joint, the meniscus of the knee joint can be sutured, shaped, and resected under the mirror, and the cruciate ligament can be reconstructed. Knee arthroscopic surgery 1, acute injury to the knee joint after acute trauma to the knee joint can form a bloody joint at the same time can be combined with other structural injuries. Arthroscopic examination found that about 58.7~90% combined with intra-articular injury. Among them, anterior cruciate ligament rupture is the most common, accounting for 65.6~72%, followed by meniscus injury, cartilage and osteochondral fracture, posterior cruciate ligament injury. In children and adolescents, osteochondral fractures are more common than ACL ruptures. Arthroscopy is a valuable diagnostic method due to the lack of a reliable basis for physical examination and radiographic diagnosis. The diagnosis can be clarified and appropriate treatment can be carried out under the microscope at the same time. 2.Surgery for synovial lesions All kinds of synovial lesions requiring synovectomy can be carried out under arthroscope. Through suprapatellar internal and external, anterior internal and external, anterior external, posterior internal and posterior external approaches, the synovial layer of the whole joint capsule and most of the fibrous layer including the anterior, posterior and lateral joint capsules can be shaved under the microscope. In particular, the posterior approach can be used to remove the synovial membrane of the posterior joint capsule, which is difficult to accomplish by incision. Synovial crease syndrome can be removed arthroscopically if conservative treatment is ineffective, which is simple, less traumatic and has good postoperative effect. 3.Repair of cartilage injury IV degree cartilage injury can be taken under the microscope bone marrow stimulation techniques such as grinding and shaping, drilling, microfracture technology to promote healing. Autologous osteochondral transplantation is to take osteochondral plugs from non-weight-bearing area and transplant them to the defective area for repair. Autologous chondrocyte transplantation has achieved good clinical results. 4.Meniscus injury surgery: Early on, the incision meniscus total cut surgery is often used, and the postoperative recovery is slow, and the cartilage damage is secondary in the long term. Arthroscopic meniscus can be partially resected, retaining part of the meniscus, the use of total excision can also retain the edge of the meniscus, to maintain joint stability, protection of cartilage plays an important role. Nowadays, it is more often applied to preserve the complete meniscus suture repair techniques, including various microscopic meniscus suture and internal fixation techniques. In addition, meniscus transplantation techniques have gradually arisen and developed. Meniscus transplantation mainly uses cryopreserved allogeneic meniscus, arthroscopic suture fixation, and the current report has better results. 5.Repair and reconstruction of cruciate ligament injury The cruciate ligament of the knee joint is an important stabilizing structure of the knee joint, and the clinical research on repair and reconstruction of its injury has made significant progress. Research shows that cruciate ligament rupture secondary articular cartilage and meniscus and other major internal structure damage, with the passage of time, meniscus and cartilage damage rate increases, the degree of aggravation; cruciate ligament rupture to wait for the articular cartilage degeneration before reconstruction of the ligament, the role of its degeneration relief is not obvious. Cruciate ligament rupture leads to multidirectional instability of the knee joint and can affect the contralateral knee joint; reconstruction of the cruciate ligament at an early stage after injury can restore the stability of the knee joint as early as possible, and prevent, delay, and mitigate secondary intra-articular injuries. The application and selection of reconstructed ligament grafts are still based on autologous tendon transplantation; the fixation method of the ligament has been improved significantly, which makes the fixation more reliable, and the postoperative recovery is fast and the clinical effect is good. At present, the idea of “anatomical reconstruction” has been put forward, and double-bundle reconstruction of the cruciate ligament has been started. The reasons for ligament reconstruction failure and revision surgery have various influencing factors, among which the incorrect position of the bone channel related to the surgical technique is the main one. At the same time, the development and application of modern techniques and equipment have contributed to the improvement of clinical treatment of cruciate ligament injuries. For example, the IntraFix and TransFix fixation methods make the ligament graft fixation more solid, which is conducive to early recovery; the application of computerized navigation technology and cruciate ligament reconstruction makes the positioning of the bony channel more accurate; at the same time, the use of a variety of effective meniscus suture methods makes the treatment of meniscus injuries during cruciate ligament reconstruction surgery more rapid; coupled with the application of reasonable and effective early postoperative rehabilitation procedures, the overall improvement of the clinical treatment level of cruciate ligament injuries has been achieved. rehabilitation procedures, the overall clinical results of ligament reconstruction have been improved.