Why is the knee joint swollen and painful? Many people experience swelling and pain in the knee joint. After going to the hospital for intra-articular puncture treatment, they feel that the joint swelling disappears, but the swelling and pain return 2-3 days later. These conditions are usually caused by knee osteoarthritis and synovitis, which can cause temporary or long-term partial loss of labor and seriously affect the patient’s quality of life. There are many types of synovitis, including simple synovitis, choroidal nodular, rheumatoid, gouty, tuberculous, and traumatic synovitis. Some patients with simple or traumatic synovitis improve with conservative treatment, but other types of synovitis cannot be cured. For these patients who do not do well with conservative treatment, good results can be obtained with arthroscopic surgery to clean up the diseased synovial tissue. If these diseases are not treated aggressively, the diseased synovium continues to attack the cartilage, leading to joint destruction and loss of the best time for treatment. For patients with recurrent swelling and pain in the knee joint , this should be taken seriously.