I. Meniscus location structure The meniscus is between the femoral condyle and tibial plateau, one inside and one outside, crescent-shaped; it is composed of 70% water and 30% organic material, 75% of the organic material is collagen, mainly type I collagen, arranged in a circular and parallel pattern. The lateral meniscus is larger in size and shape than the medial meniscus, and its mobility is greater. In adults, the vascular zone of the meniscus ranges from 10% to 30% of the outer periphery of the meniscus. Therefore, the meniscus is generally divided into three zones: the red zone (hemodynamic zone, located in the synovial margin of the meniscus in the range of 1 to 3 mm), the red-white zone (supplied by the terminal branches of the capillaries in the red zone, located in the range of 3 to 5 mm medial to the red zone), and the white zone (non-hemodynamic zone, located in the medial part of the red-white zone). MRI diagnosis and grading of meniscal injury When meniscal injury is considered, MRI should be performed as early as possible to reduce the misdiagnosis rate of meniscus. At present, most scholars at home and abroad follow the Stoller 3 grade standard. Grade I signal is meniscal degeneration, and the pathology is focal early meniscal mucus-like degeneration. Grade II MRI shows a horizontally linear intra-meniscal signal elevation shadow that may extend to the edge of the meniscal capsule but does not reach the edge of the meniscal articular surface. Grade II is a continuation of the grade I lesion, and the pathology shows more extensive mucinous degeneration. Grade III is a high signal within the meniscus reaching the meniscal articular surface margin, which appears as a parallel, oblique, stellate or irregular shaped abnormal signal on MRI. III. Meniscal injury characteristics and surgical repair Based on the history, symptoms, signs and MRI examination of the knee injury, the diagnosis of meniscal injury can generally be made. Meniscal injury mostly has a history of knee trauma, accompanied by knee pain during walking; some patients have symptoms of interlocking, and there is often pressure pain at the joint line, and the pressure pain point will shift with knee extension and flexion activities; the McKinsey test is positive. The specificity and sensitivity of MRI is high, but there are still false positives and false negatives, so if the situation allows, arthroscopy can be used to determine the site, type and degree of meniscal injury in order to select the appropriate treatment. If the meniscus is damaged or torn, these functions will be weakened and the mechanical stability of the knee joint will change, often leading to an early onset of osteoarthritis. Therefore, meniscal injuries should be repaired whenever possible. The advantages of arthroscopic surgery for meniscal injuries are the small incision, light trauma, and early functional exercise after surgery, as well as the ability to explore all parts of the knee joint to see if there are compound injuries such as articular cartilage and ligament injuries, so that they can be treated together. Arthroscopic surgical treatment has replaced open surgery as the best means of treatment for meniscal injuries. 3.1 Partial meniscectomy With further clinical studies on meniscal function, it is particularly important to preserve the meniscus. After partial meniscectomy, even if only the peripheral portion of the meniscus is removed and the vast majority is intact, there is still a considerable impact on the meniscus load bearing, as the more meniscus is removed, the higher the maximum pressure exerted on the tibial plateau. Partial meniscectomy can still cause degeneration of the articular cartilage, and the uneven forces on the meniscus after partial meniscectomy can result in new tears in other areas of the meniscus in some patients, requiring re-treatment. Nevertheless, partial meniscectomy remains indispensable for the treatment of meniscal injuries. For meniscus tears that are not suitable for repair, partial meniscectomy may still be considered if the meniscus does not heal well after repair, for example, if the meniscus does not heal well after repair. The type of tear is also an important factor in whether a meniscal tear is suitable for repair. Usually, tears such as radial and horizontal tears are difficult to heal, and partial resection is a common clinical treatment method. 3.2 Suture repair Due to the complications caused by total meniscectomy and subtotal meniscectomy, such as knee instability and osteoarthritis, meniscal suture repair has been gradually used in clinical practice. Suture repair is effective for meniscal hemorrhagic zone injuries, but not for hemorrhagic zone (i.e., white zone) injuries. Arthroscopic meniscal suture repair can be divided into inside-out suture repair, outside-in suture repair, and complete intra-articular suture repair. The inside-out repair technique is relatively commonly used in clinical practice. There is no difference in rotational stability of the repaired meniscus compared to the healthy side. Therefore, arthroscopic meniscal repair has become the main method of treatment for meniscal injury as far as the clinical situation allows. Grade I meniscus injury basically does not require surgical treatment; grade II injury with clinical symptoms does not improve after conservative treatment, and arthroscopic exploration is feasible; grade III injury is feasible with partial or total meniscus resection and molding, and repair of capsular rim tear is feasible.