The discoid meniscus, or discoid cartilage, is a deformity of the meniscus of the knee. The normal meniscus is half-moon shaped, while the discoid meniscus is disc-shaped, larger and thicker than the normal meniscus, and prone to tearing injuries. The majority of discoid meniscus is the lateral meniscus and the medial discoid meniscus is very rare. The incidence of discoid meniscus is highest in Asians, 5-8 times higher than in Europe and the United States. The percentage of patients with discoid meniscus who have both knees with discoid meniscus is about 20%. Most discoid meniscus is unstable and requires surgical treatment. Diagnosis The symptoms of discoid meniscus are related to the type of disc and the presence or absence of meniscal injury. Those with a stable disc meniscus may have no discomfort. In the case of an unstable disc meniscus, the patient may have a history of knee injury and may have other manifestations of meniscal injury, including knee pain, swelling, limited motion, and interlocking (stuck), in addition to a popping knee. Imaging of discoid meniscus injury: magnetic resonance imaging (MRI) is the best test to diagnose discoid meniscus injury. MRI shows that the anterior and posterior angles of the meniscus are connected at more than 3 consecutive levels, and the diagnosis of discoid meniscus can be made. Treatment After the diagnosis of symptomatic discoid meniscus is confirmed, arthroscopic minimally invasive surgery is required for treatment, which is less invasive and allows the patient to recover quickly after surgery. Arthroscopic discoid meniscoplasty and, if necessary, meniscus repair can be performed at the same time to achieve excellent results.