In recent years, the diagnosis of synovitis of the knee has been increasing, and the term “synovitis” has gradually become more accepted by the public, but the concept is vague and the treatment is confusing. Therefore, it is necessary to clarify the understanding in this area. 1. What is synovium? Synovium is a thin soft tissue located on the inner surface of the joint, rich in blood vessels, which covers most of the structures in the joint, except for the articular cartilage and meniscus. The synovial membrane secretes various substances needed by the joint and also absorbs and metabolizes metabolic products from the joint. Under normal conditions, there is a balance between this secretion and absorption. In a normal joint, there is only a small amount of fluid, which is used to nourish and lubricate the joint. 2.What is synovitis of the knee joint? When various external stimuli, such as cold, trauma, bleeding, certain systemic diseases, such as infection, gout, immune system diseases, hormone level changes and other factors will stimulate the synovial membrane, secrete a large amount of fluid, so that its secretion and absorption in a state of imbalance, manifested as an increase in the fluid in the joint, the clinical manifestations of the knee joint swelling, and generally known as synovitis. 3.What are the causes of synovitis of the knee joint? There are actually many causes of knee joint effusion, and some people even classify them into 10 categories. But basically, they can be grouped into two aspects: medical and surgical. Internal aspects, such as rheumatism, rheumatoid, tuberculosis, syphilis, gout, and insect and dog bites, can be treated conservatively, but early rheumatoid can be treated by arthroscopic removal of synovial membrane to prevent contracture deformity of the knee joint. Surgical aspects, such as: osteoarthrosis, synovial crepitus syndrome, meniscal injury, patellar subluxation, ligament injury, etc. even short-term joint overactivity. 4, diagnosis and treatment of knee synovitis There are many causes of knee synovitis, so the treatment of it should not be too single. The first step should be to find out what causes synovitis and to treat the cause professionally. Synovitis caused by diseases such as gout, rheumatism and rheumatoid diseases cannot be completely cured, but through scientific and standardized treatment, it is possible to alleviate and stop the further development of the disease. For osteoarthrosis, synovial crepitus syndrome, meniscal injury, ligament injury, and some intractable synovitis that are difficult to diagnose, minimally invasive arthroscopic techniques can be applied to diagnose and treat the disease, and good results have been received clinically in this area. Only through targeted treatment can synovitis of the knee be truly treated.