A small amount of fluid in the knee joint is normal for older patients, but not normal for younger patients, as follows: First, normal: older patients will experience increased wear and tear on the knee joint with age, and the joint is prone to mild synovial inflammation, resulting in a small amount of joint fluid, but generally the joint is only mildly painful and does not have restricted joint activity, so no special treatment is needed. Second, abnormal phenomenon: A small amount of fluid in the joint of a young patient is usually caused by trauma or can be caused by cold. The patient will have joint pain, swelling and limited activity, and needs active treatment to get relief from the symptoms. Therefore, the presence of a small amount of fluid in the knee joint should be judged according to different ages, and if there is an abnormal disease, timely treatment is needed. The leg muscle strength training should also be strengthened in normal life to protect the joint function.