Patients often ask me, “Doctor, do I have synovitis in my knee joint?” What kind of disease is “synovitis”? Synovitis is a multifaceted disease that is characterized by synovial oozing, joint swelling and pain. It mainly occurs in the knee joint, which is the largest and most complex of all the joints in the body, and also has the largest synovial area. Most synovitis of the knee is complicated by various knee injuries, and synovitis can also occur with osteoarthritis, lupus erythematosus, psoriatic arthritis, gout, tuberculosis, rheumatic fever, and other diseases. In young patients, mild edema, pain, limitation of motion and limping of the knee joint begin to occur after injury when excessive exercise or joint sprain or trauma occurs. Synovial reactive effusion usually occurs 6 – 8 hours after injury, at which time the patient may suddenly notice thicker legs, swollen joints, inability to bend the knee joint, difficulty squatting with pain, and may have limited pressure painful spots around the joint. In chronic injury synovial, there may be no obvious history of trauma, but the main manifestations are knee tenderness and restricted movement, swelling that does not subside, and fear of squatting. It worsens with increased activity and decreases with rest. In the elderly, in the absence of obvious trauma, the majority of swollen joints have a definite cause: osteoarthritis or rheumatoid arthritis. Usually doctors perform a test called the “floating patella test”, which can easily distinguish between increased joint fluid and muscle swelling by pressing on the patella with the hand. If necessary, X-rays, ultrasound, etc. can be performed to help rule out other bone or joint diseases. For some patients with synovitis who do not have obvious signs and symptoms, MRI is an option. 1. Treatment is mainly based on limiting activities, eliminating swelling, and anti-inflammatory therapy. 2.Limit activities, first of all, let the joint get some rest, reduce the amount of activity, you can wear a brace. Avoid long-term strenuous exercise. 3.Anti-inflammatory treatment mainly includes oral antibiotics, aspirin, ibuprofen, etc. 4.Eliminate the swelling, which can be done by puncture, puncture to extract the fluid and blood accumulation, but this is only a temporary treatment to improve the symptoms. In severe cases, arthroscopic surgery may be required to remove the inflammatory tissue. Arthroscopic surgery is performed to clean out the hyperplastic synovial membrane and carefully clean the knee cavity to achieve the treatment goal and arthroscopic surgery is less invasive and quicker to recover.