The discoid meniscus is a rare meniscal deformity with more lateral than medial menisci. According to the classification system of Watanabe et al, the lateral discoid meniscus is classified as complete, incomplete and Wrisberg type according to the degree of lateral tibial plateau coverage and whether the tibial attachment of the posterior meniscus is normal. Most patients are asymptomatic, sometimes trauma leads to knee pain, soreness, weakness, tenderness, typical symptoms of a crisp, high-pitched popping sound when the knee is extended at 20-30° position, and some patients may have a sudden kneeling sensation. The pain is located in the lateral knee joint space, and flexion and extension are accompanied by a popping sound and lateral swing of the lower leg. The lateral tibial plateau is irregular and flattened, the femoral epicondyle is less developed, the medial tibial intercondylar ridge is higher than the lateral one, the bone density is denser, and the tip of the fibular head is elevated. These are not specific presentations, but we encounter this tired joint radiograph in our work that can suggest whether we have discoid cartilage. MRI imaging features: In coronal view, abnormal thickening, widening, and enlargement of the meniscus can be visualized, with a width greater than 15 mm; in sagittal view, because the transverse diameter of the lateral meniscus is about 11-12 mm, if scanned in 5 mm layers, three or more consecutive layers of the meniscus are connected at the anterior and posterior angles to form a “bow tie”. The diagnosis can be made if the meniscus is scanned with a thickness of 5mm and the anterior and posterior angles of 3 or more consecutive layers are connected to form a “bow tie”. If the anterior and posterior angles of the meniscus are connected in two consecutive layers of 5mm thickness to form a “bow tie” of the same height, the diagnosis can also be made.