Mr. Liu, a middle-aged man, had a knee injury a year ago, and at that time, there was no big problem with the X-ray and no heavy pain. But then, Mr. Liu’s right knee had intermittent pain, which would improve after rest, and his right knee would suddenly get “stuck” when going up and down stairs, accompanied by pain. The doctor confirmed through examination that Mr. Liu’s right knee had an old meniscus injury. The meniscus is a half-moon shaped cartilage pad in the knee joint, one on the inside and one on the outside, which mainly plays a role in cushioning pressure, reducing intra-articular friction and stabilizing the joint. Because the meniscus is a fibrous cartilage tissue, it does not show up on ordinary X-rays and CT films, and can only be examined by magnetic resonance imaging (MRI) to show the injury and lesion. The meniscus only has blood flow around 1/3 of it, so it may heal itself in younger patients with fresh injuries, but in other cases it is almost impossible to heal. Meniscal injuries are the most common form of knee disease and can be caused by trauma or as a result of aging. Patients often present with joint pain, swelling, and immobility after injury. Although the swelling and pain slowly disappear with medication, the patient’s joint may move with a “clicking” sound, accompanied by pain and weakness in the leg. When the above symptoms occur, it means that the meniscus may be damaged, and the patient should go to the hospital for timely treatment.