Fluid accumulation in the knee area is actually an accumulation of fluid inside the knee joint, mainly caused by synovial inflammation of the synovial membrane of the knee joint, which produces inflammation products, including exudate, that may accumulate inside the knee joint. Since the joint is a closed cavity and cannot be drained, a more pronounced effusion will form locally. There are more inflammatory causes of knee joint effusion, as follows: 1. Aged degenerative knee arthritis, which can easily cause local effusion; 2. Excessive exercise or trauma, which can easily lead to local injury and cause knee joint effusion; 3. Immune rheumatic diseases can involve the synovial membrane and cause synovial joint effusion, such as rheumatoid arthritis, ankylosing spondylitis, lupus erythematosus, etc.; 4. If the knee joint has infection or tumor The effusion will be more obvious if it causes local inflammatory reaction. For effusion, on the one hand, the primary disease is treated, on the other hand, analgesic, antipyretic and anti-inflammatory drugs can be used, or local physiotherapy can be taken, and if necessary, aspiration can be performed.