The feeling of heat in the knee, which returns to normal in a few seconds, may be caused by physiological factors such as fatigue and mental stress. If there is persistent heat in the knee accompanied by swelling and pain, it may be caused by pathological factors such as osteoarthritis, rheumatism and rheumatoid arthritis. 1. Physiological factors: due to factors such as walking for a long time, bearing weight or mental tension, it can lead to tension and spasm of muscles and nerves around the knee joint, causing transient fever in the knee, which is a normal physiological phenomenon, and does not need to be dealt with occasionally. 2. Osteoarthritis: Osteoarthritis of the knee is a disease based on degenerative pathological changes, mostly seen in the middle-aged and elderly people, when the knee joint fluid increases, inflammatory reaction can be manifested as redness, swelling, heat and pain in the knee joint, restricted activities and other symptoms. 3. Rheumatoid or rheumatoid arthritis: associated with group A beta-hemolytic streptococcus infection, cold and dampness are the main triggers, manifested as redness, swelling, heat and pain in the knee joints, which may be accompanied by generalized fever symptoms. The knee feels hot and returns to normal in a few seconds. If the fever in the knee joint persists without relief, it is recommended that the patient consults the hospital in time to clarify the cause of the disease and treat it in time so as not to delay the condition.