Possible causes of synovial cysts include trauma and chronic injury, rheumatoid arthritis, gouty arthritis and so on. 1. Trauma and chronic injury: synovial cysts are caused by excessive flexion and extension of joints and frequent heavy physical labor, which leads to synovial membrane injury and edema. 2. Rheumatoid arthritis: Inflammation caused by autoimmune, hereditary, cold and humid environments, synovial cysts caused by inflammation eroding articular cartilage and bone tissues and damaging joints. 3. Gouty arthritis: due to high blood uric acid, resulting in uric acid crystals deposited in the joint muscles and soft tissues of the formation of inflammation, thus causing synovial cysts. Clinical manifestations of joint redness, swelling, pain and other symptoms. Synovial cysts may also have other causes, it is recommended to go to the regular hospital in a timely manner to improve the relevant examination, to clarify the cause of the disease, under the guidance of the doctor to carry out targeted treatment or treatment.