There are several types of synovitis in the knee. If it is simple synovitis, it is not very harmful, it can only make the patient feel swelling, pain, or difficulty walking, etc. It is not serious to the knee joint. In this case, only non-steroidal anti-inflammatory painkillers are needed, and if synovial fluid production is controlled, there is little problem. However, more specific synovitis, such as hyperpigmented nodular synovitis, requires early treatment. Because hyperpigmented nodular synovitis is not only a synovial hyperplasia, its synovial hyperplasia can slowly worsen and is equivalent to a benign tumor that can erode the cartilage surface of the joint and even the subchondral bone. Therefore, once it is clear that it is hyperpigmented nodular synovitis, it is important to visit the hospital early for arthroscopic clearance.