Knee joint effusion is not harmful, the main discomfort is pain, activity limitation, etc. Continuous effusion may increase the risk of arthritis aggravation. 1. Pain: When there is a lot of fluid in the knee joint, the pressure on the knee joint is greater, which may cause pain, congestion and swelling of the joint. 2. Restriction of activities: Knee joint effusion may cause restriction of normal knee joint activities, which may affect normal walking, running, jumping, squatting and other movements and activities. 3. Increased arthritis: If the knee joint effusion is large and not absorbed for a long time, the inflammatory mediators in the effusion will repeatedly stimulate the intra-articular environment, resulting in increased inflammatory response, which will easily lead to the progression of arthritis. Knee joint effusion may also cause some other adverse reactions, so the occurrence of knee effusion should go to the regular hospital in time, under the guidance of the doctor for treatment.