Knee pain in a 45-year-old woman going up and down stairs may be caused by high activity level, acute injury, synovitis, osteoarthritis, rheumatoid arthritis and other factors. 1. Large activity: daily exercise is small, suddenly up and down the stairs more, resulting in knee pain, which can be relieved by resting. 2. Acute injury: the knee area suffered acute injury, such as sprains, external blows, etc., resulting in soft tissue or bone damage, when going up and down the stairs will cause stimulation of the damaged area, which will cause pain symptoms. 3. Synovitis: It may be related to trauma, infection, joint degeneration and other factors, which can lead to synovial membrane damage, causing knee pain when walking up and down the stairs, and in serious cases, there will be joint swelling and joint effusion. 4. Osteoarthritis: it may be related to chronic strain, degenerative joint disease, which can lead to aseptic inflammation of the knee joint, localized damage to the joint, and cause pain when going up and down the stairs. 5. Rheumatoid arthritis: may be related to heredity, infection and other factors, will lead to the symptoms of pain in the knee joint area, the pain will be aggravated when going up and down the stairs, accompanied by joint swelling, morning stiffness, and even lead to joint deformity. If the knee pain of a 45-year-old woman going up and down stairs cannot be relieved by resting, it is recommended to consult a doctor for examination to clarify the specific cause and timely treatment.