Generally speaking, one knee pain and one knee pain may be caused by trauma, osteoarthritis, rheumatoid arthritis and other reasons. 1. Trauma: If one knee is traumatized, resulting in meniscus strain, ligament damage, muscle strain or fracture, etc., knee pain will occur. 2. Osteoarthritis: It is a chronic joint disease characterized by degenerative changes in articular cartilage and secondary osteophytes, which may manifest as joint pain, morning stiffness and joint enlargement. 3. Rheumatoid arthritis: mostly acute fever and joint pain, usually this disease occurs in the humid environment and weather, if suffered from cold, knee pain will be aggravated. In addition, one knee pain and one pain can also be seen in other diseases, it is recommended that patients go to the hospital in time to avoid delay.