If there is swelling in the knee joint, but no significant pain or discomfort, it is more likely that there is fluid in the knee joint. The cause may be a spontaneous rupture of a blood vessel, or it may be due to a meniscal injury or synovitis. It is necessary to go to the orthopedic department for an interview with the doctor, who will make a preliminary judgment with the physical examination. An MRI of the knee can be performed to determine whether there is significant fluid accumulation and whether there is significant meniscal damage. In case of obvious effusion in the knee joint and the cause is not clear, knee aspiration can be considered to extract the effusion from the knee joint, and routine and biochemical tests of the knee joint effusion can be done to help relieve the swelling of the knee joint. The other thing is to clarify the cause of the knee effusion, and then do follow-up treatment according to the cause to help cure it completely.