Sudden joint pain: 1. It may be that the stability of the ligaments around the joint is poor, and sudden external force leading to valgus or inversion can cause damage to the collateral ligaments, thus producing pain. This occurs in patients with a clear history of trauma and is characterized by swelling, petechiae, and restricted joint movement in addition to pain. 2. Cartilage damage is also an important cause of joint pain. When moving the joint, if sudden excessive force is exerted, it may cause meniscal tearing, which in turn produces pain and is accompanied by a popping sound when moving the joint and restricted joint movement. 3. Synovitis in the joint produces a large amount of When synovitis produces a large amount of fluid, there will also be pain, manifested as pressure, swelling, and a frictional sound. 4. When suffering from autoimmune system diseases, such as lupus erythematosus and rheumatoid arthritis, pain will also invade the joints. Sudden pain in the joints, especially persistent pain, is best to go to the hospital for examination as soon as possible.