Synovitis is a multifaceted disease that develops mainly in the knee joint. The knee is the joint with the largest number of synovial membranes, the largest joint surface and the most complex structure of the human body. Because the synovial membrane of the knee is extensive and located in the shallow part of the limb surface, there are more opportunities for injury and infection. Synovitis of the knee is a group of syndromes caused by sprains and various intra-articular injuries. It can cause temporary or long-term partial loss of labor force, which is harmful to both patients and society. The clinical diagnosis of synovitis is now so numerous and easy that it has become so pervasive that it is often a vague catch-all term for joint swelling for which the cause cannot be simply determined, causing annoyance and fear to many patients and their families. In fact, synovitis is a specific manifestation of a variety of diseases in the synovial tissue. Synovitis is not a disease, but a common manifestation of many diseases, a group of syndromes. Figure out the cause before treating synovitis Some patients are blindly treated without proper diagnosis, often losing the best time for treatment. It is highly recommended that the specific type of synovitis must be clarified before treatment, as the treatment options are completely different for synovitis of different nature. A comprehensive look, smell, question and cut, combined with physical and chemical examinations, including testing of various indicators of joint fluid, imaging examinations, including MRI, and minimally invasive arthroscopic techniques to explore and diagnose, we will make scientific choices for you to prevent missed diagnoses and avoid delays. There are many causes that can produce synovial inflammation, which one do you belong to initially? Bacterial infections, such as bacterial arthritis, tuberculous synovitis; immune system diseases, such as rheumatoid arthritis, Rhett’s arthritis, dry syndrome; physical irritation, such as meniscal injury bleeding irritation, cold irritation; chemical irritation, the internal environment is too acidic, too alkaline, such as gout urate caused by intra-articular exudation; endocrine disorders, changes in hormone levels, such as female menstruation, pregnancy, postpartum and menopause synovitis; vi. cumulative stress, joint overexertion, excessive load, surgery, etc.; vii. joint instability, including joint instability caused by fresh or old ligament damage to the joint, synovitis formed by bony compression of the synovium, stimulation; viii. stimulation of foreign proteins, animal and insect bites, such as cats, dogs, mosquitoes, pineal insects, etc. ix. pigmented villous nodular synovitis, a thickening of the synovial membrane of the knee caused by chronic inflammatory stimulation or abnormal lipid metabolism, with elongated villous or nodular growths on the synovial surface. Its nature is somewhere between benign and malignant tumors. Ten, pediatric synovitis generally belongs to viral infectious synovitis, also known as transient synovitis. After figuring out the cause, it will help the treatment plan and can take a lot less detours.