Conservative treatment is not recommended for a fourth-degree meniscus tear with effusion cyst with old damage. The meniscus of the knee is a fibrocartilaginous tissue, which has poor healing ability and is difficult to repair itself once torn. A tear in the meniscus leads to an inflammatory response within the joint, resulting in an inflammatory effusion that can form a cyst-like structure at the edge of the meniscus, which can lead to cartilage damage when the meniscus becomes compressed. Conservative treatment can be chosen for common meniscus injuries, while a fourth degree meniscus tear in the knee is more serious and conservative treatment is less effective, and the cystic effusion needs to be treated with surgery, which is the only way to fundamentally release the cystic effusion. If the knee meniscus tear fourth degree accompanied by effusion cyst with old damage, it is recommended to go to the hospital in time, under the guidance of the doctor for standardized treatment.