The knee joint is composed of the lower femur, upper tibia and skeleton, and is the joint that carries a lot of weight and has a lot of movement in the whole body. Structurally, the knee has the largest area of articular cartilage and the most synovial membranes, as well as the anterior and posterior cruciate ligaments and the medial and lateral menisci; functionally, the knee is not only a flexion and extension joint, but also has some ball and socket joint characteristics due to the shape and activity of the menisci. Therefore, the knee joint is not only able to flex and extend. It also has a certain range of rotational motion. Due to this complex structure and multi-axis movements, the incidence of knee injuries and disorders is high, with meniscal tears accounting for more than 2/3 of cases. The meniscus has important functions such as absorbing shock, transmitting load, nourishing joint cartilage, lubricating and increasing joint contact area, and maintaining joint stability. Sports injuries and inflammatory diseases can cause meniscal damage. Severe damage to the meniscus will lead to early and progressive degeneration of the articular cartilage, eventually leading to osteoarthritis of the knee. The meniscus is a fibrous cartilage structure composed of collagen, proteoglycans, and glycoproteins in a complex three-dimensional meshwork that transmits load, absorbs shock, stabilizes the joint, and transmits proprioception. The main component is type I collagen, most of which is arranged in a ring shape to resist tension; a small portion is arranged radially in the meniscus tissue, which can increase the tensile strength and stiffness of the meniscus. Only the peripheral part of the meniscus has a blood supply, while the medial 2/3 of the meniscus usually lacks blood supply and is nourished by synovial fluid. The differences in the blood supply to the meniscus structure also lead to differences in the healing potential of the meniscus at different injury sites, so different approaches are often used to repair the meniscus in the blood-supplied and ischemic areas. Treatment of meniscal injury Conservative treatment: When acute meniscal injury is associated with intra-articular blood accumulation, muscle spasm affects physical examination, making clinical diagnosis more difficult, so arthroscopic examination of the knee should be actively performed to clarify whether there is concurrent injury to other tissues and structures to avoid misdiagnosis and missed diagnosis. If there are no significant pathologic changes, conservative treatment is indicated to protect the torn tissue, reduce pain and swelling, and restore muscle tone and joint range of motion. After the injury, braking and icing of the knee joint should be performed, followed by knee rehabilitation physiotherapy 3 days after the injury to gradually restore muscle strength as well as joint exercises and walking. If there are no signs and symptoms after 6 weeks of the injury, the patient can resume walking completely; if there are signs of meniscus damage, knee arthroscopy should be performed. Patients with extended acute meniscal injuries that have not been effectively treated, as well as patients with chronic injuries, should also undergo arthroscopic knee surgery if signs and symptoms of meniscal tears are present on clinical examination. Surgical treatment: Knee arthroscopy not only provides a clear diagnosis of meniscal injury and corrects clinical diagnostic errors, but also clarifies the extent and degree of rupture, which allows for further determination of the specific modality and scope of surgery, and allows for the management of other secondary or concomitant lesions in the knee joint. Knee arthroscopy can be performed as an emergency for early suspected meniscal injuries to shorten the course of treatment, improve the outcome, and reduce the occurrence of injurious arthritis. The indications for surgery for meniscal injury are summarized as follows: 1. history of persistent pain and interlocking; 2. physical examination confirms limited joint compression, decreased joint mobility and a positive special test for meniscal examination; 3. exclusion of other causes of pain. The specific treatment for meniscal injury can be divided into meniscal revision, partial meniscectomy, complete meniscectomy, meniscal repair, meniscal reconstruction, discoid meniscoplasty, allogeneic meniscal transplantation and meniscal tissue engineering reconstruction, etc. Rehabilitation: The rehabilitation program is divided into 4 stages. Phase I: The goal of rehabilitation is to reduce swelling, relieve pain and promote tissue healing. It includes wearing a brace, moving the patella, ankle pump exercise, muscle strength training, and cold compresses. Stage II: The rehabilitation goal is to protect the repair area and train the joint mobility. This includes brace setting: brace mobility is set at 0°-30° of extension/flexion, and gradually increase the flexion angle to >120° within the pain tolerance range; patella mobility: reach the normal range as much as possible; ankle pump exercise, knee compression exercise, skateboard exercise, straight leg raise exercise; plyometric training: strengthen the quadriceps, adductor, and N cord muscles; weight bearing: first weight bearing Toe pointing (25% of body weight), gradually increasing within the tolerance range. Phase III: The rehabilitation goal was to obtain full range of joint mobility; intensive plyometric training; brace angle of motion was set at 0°-135° extension/flexion, and the brace was removed at 2 weeks; seated knee flexion/extension training was increased to obtain full range of joint mobility without pain; progressive elastic band resistance training; power bike: 10-20 min per session twice a day; micro-squat training; swimming training; proprioceptive training. Phase IV: The goal of rehabilitation is to achieve motor function in muscle strength, joint mobility, and proprioception. Continuous elastic band resistance training; loaded straight leg raise exercise; power bike training (increased resistance); swimming training; proprioceptive training; jogging training. The concept of tissue engineering provides hope for regeneration of meniscal tissues that are difficult to repair after injury; for patients with severe injuries that require meniscectomy or after meniscectomy For patients with severe damage requiring meniscectomy or after meniscectomy, allogeneic meniscus transplantation can be performed to reconstruct meniscus function.