There are many causes of knee pain, but they do not usually cause swelling of the lower extremities, and some diseases that cause swelling of the lower extremities do not usually cause knee pain, so knee pain and leg swelling may occur in middle-aged and older patients and are two different disorders. There are many causes of knee pain. For younger patients, injuries to the meniscus and cruciate ligaments as well as free bodies in the knee joint, gout, and rheumatoid arthritis may cause knee pain, and osteoarthritis, patellofemoral arthritis, and chondromalacia patellae, which occur in older patients, may also cause knee pain. The main cause of lower extremity swelling is microcirculation and capillary blockage in the lower extremities, which is commonly caused by some diseases of poor venous return, such as deep vein thrombosis or venous valve insufficiency. In these cases, conservative treatment can be attempted, such as oral non-steroidal anti-inflammatory drugs, local hot towels, microwaves, baking lamps or hot water foot soaks, all of which can help relieve knee pain and leg swelling. If conservative treatment does not work, it is best to seek further consultation with an orthopedic surgeon to assist in the diagnosis.