Knee effusion is a more technical term that many people don’t know what is going on, but when it comes to knee swelling, the general public is probably very familiar with it. In fact, many times it is the fluid in the knee joint that causes the swelling, which is academically known as knee effusion. There are many causes of knee effusion, and they are divided into the following categories: 1. The most common is simple synovitis, in which there is a certain amount of synovial fluid in the knee joint, which is renewed every day and absorbed every day to maintain a constant amount, but if the synovial membrane of the knee is hyperplastic, the ability to generate is greater than the ability to absorb, and over time, the synovial fluid inside will become more and more, which will cause knee effusion; 2. This is a more troublesome type of synovitis, that is, pigmented nodular synovitis, which is a more troublesome effusion, patients tend to repeatedly knee joint effusion, and swelling is very serious, if the doctor does a knee puncture to extract the fluid is bloody, need to be alert to this disease; 3, gouty arthritis, with the improvement of living standards, the diet structure has also changed, the diet is getting better and better, the consumption of meat is also more and more Gout patients are also becoming more and more common, perhaps in the impression that only the toes and other parts of the body can appear gout, but in fact, this is not the case, gout is uric acid salt crystals, which can be precipitated in various organs of the body, including the heart, gouty knee arthritis caused by fluid is not uncommon in outpatient clinics, including many young children; 4, infectious factors, more knee joint infections occur, including atopic infections, including Such as tuberculosis infection, as well as non-specific bacterial infection, bacteria multiply in the knee joint, the body will produce an inflammatory response, this will appear a large amount of fluid, the typical performance of redness, swelling, heat and pain, patients are often accompanied by fever symptoms, at this time need to be particularly vigilant, can be early to the regular hospital; if it is late, the infection progresses faster and longer, but also involves the joint cartilage and the bones within the joint, causing spondylitis.