There are many causes of joint effusion, such as joint trauma (soft tissue injury, etc.), arthritis (traumatic arthritis, osteoarthritis, etc.), intra-articular infection (intra-articular bacterial, tuberculosis infection, etc.), etc., and it is necessary to improve the examinations in order to clarify the cause of the disease. 1. Trauma: there is a clear history of trauma to the joints, which causes damage to the cartilage and synovium in the joints, intra-articular hemorrhage, which causes inflammation of the synovium, and increased secretion can cause joint effusion. 2. Arthritis: the most common types of arthritis are traumatic arthritis, osteoarthritis, rheumatoid arthritis, etc. Inflammation of the joints can lead to synovial membrane congestion, edema, oozing and other manifestations, and then increase secretion, resulting in joint effusion. 3. Joint infection: It is more common to have bacterial or tuberculosis infection in the joints, which can cause the exudate in the joints to increase, and then form joint effusion. It is often accompanied by redness, swelling, heat and pain in the joints. It is recommended that the patient go to the hospital, complete the auxiliary examination, in order to clarify the condition, and then the professional physician will give the appropriate treatment for the condition.