Knee effusion, indicating that there is inflammation or injury, mainly for the following reasons: 1, synovitis, often occurs after cold or cold, manifested as a sore and edematous knee joint, feeling colder knee joint, when the synovial membrane appears aseptic inflammation, it will lead to local edema and cause effusion. 2, knee meniscal injury or synovial crepitus syndrome, the patient has a history of trauma or chronic This is the most common cause of osteoarthritis of the knee, which is mainly related to degenerative changes, and as the activity increases with age, the wear and tear of the cartilage becomes more pronounced, and the worn out cartilage becomes an inflammatory factor. This is the most common cause of arthritis.