Patellofemoral effusion, also known as knee joint effusion, is a long-term accumulation of fluid that can lead to swelling, pain, limited flexion and extension movements in the knee joint, and can seriously lead to limping and interfere with the patient’s normal activities. Patellofemoral effusion, also known as knee joint effusion, is mostly caused by trauma, infection, degenerative joint changes, etc., resulting in increased collection of synovial fluid in the joint and swelling of the knee joint. The presence of knee joint effusion, if not treated in time to draw out the excess fluid, may result in the continued increase of fluid, causing knee pain and swelling, and limitation of knee flexion and extension activities. Long-term untreated joint cavity effusion may lead to limping, elevated skin temperature, swelling and even deformity of the knee joint, which may seriously affect the patient’s daily activities. If there is more fluid in the joint cavity, there will be a floating sensation of the patella when pressing on the patella. When there is a suspicion of knee joint effusion, it is recommended to seek early medical examination and treatment, so as to avoid long-term oozing of fluid causing damage to the cartilage in the knee joint.