With the popularization of national fitness sports and the progress of population aging, the incidence of knee cartilage injury due to various reasons is increasing year by year, which seriously affects people’s work and life. Articular cartilage is hyaline cartilage, which plays a vital role in the function of the joint. Because cartilage lacks direct blood supply, lymphatic circulation and innervation, and has the physiological characteristics of low metabolism, it mainly relies on joint fluid for nutrition, and its ability to repair itself after injury is very limited, which makes treatment very difficult and can lead to osteoarthritis if it continues to develop. How to repair damaged articular cartilage, restore the integrity of the joint surface and prevent joint degeneration has become an urgent problem in orthopedics and sports medicine, and has become one of the most popular areas of research. Cartilage functions: reduce friction, absorb shock, conduct and distribute load, and maintain and carry contact stress. Articular cartilage provides a smooth support surface on which bone tissue can slide frictionlessly or rotate and move against each other. In addition, the surface of articular cartilage acts as a soft cushion of variable shape that distributes and reduces the high load stresses that result from physical activity. Articular cartilage is an extremely elastic substance that can withstand tens of millions of cycles of weight-bearing activities during its lifetime. Osteochondral injuries of the knee are very common, with trauma (sprains, falls, etc.) and degenerative changes (osteoarthritis) being the main causes of cartilage damage. In over 31,516 knee arthroscopies, 63% of patients (19,827) had articular cartilage injuries, with the medial femoral condyle and patellofemoral joint being the most frequent sites of injury. Diagnosis (1) Clinical manifestations Persistent dull pain in the joint, aggravated by activity, may be manifested by playing soft leg. Patients with femoral condylar cartilage injury will experience pain around the joint space when running and going down stairs, while patellofemoral cartilage injury will cause pain in the front of the knee joint when going up stairs, half squatting or standing up from a sitting position. Joint mobility is generally normal, but if swelling of the joint or the presence of free bodies is present, joint movement may be limited or interlocked. (2) Physical examination Knee inversion or flexion deformity, quadriceps atrophy; joint flexion and extension limitation, knee hyperflexion and hyperextension pain (+), patellar crush test (+), patellar grinding test (+), floating patella test (+), etc. (3) Imaging X-ray shows degenerative changes such as narrowing of joint space and osteophytes, and also the presence of joint free bodies, etc. MRI is effective in evaluating articular cartilage damage, and can detect cartilage damage and subchondral bone lesions, as well as concomitant injuries such as meniscal tears and cruciate ligament injuries. Treatment Conservative treatment Principle: Conservative treatment for at least 3-6 months with activity modification, weight reduction, muscle training, etc. Drugs: non-steroidal anti-inflammatory drugs, oral glucosamine sulfate, corticosteroids, hyaluronic acid joint cavity injection, etc. Surgical treatment Indications: Total articular cartilage loss (grade III-IV injury), or conservative treatment does not provide effective relief. Contraindications: rheumatic or other systemic arthritis, poor joint forces and advanced degenerative changes (joint stenosis over 50%). Methods: joint cleanup, microfracture, autologous osteochondral graft (mosaic graft), allogeneic osteochondral graft, autologous chondrocyte transplantation (ACI), joint replacement, etc.