There are many reasons for knee pain, which is not necessarily a sign of cancer, and may be related to arthritis, rheumatic diseases, synovitis, etc. Of course, cancer needs to be ruled out as well. 1. Arthritis: mostly seen in middle-aged and old-aged people, knee arthritis can be manifested as knee pain, popping, swelling and other symptoms. 2. Rheumatic diseases: Rheumatic diseases can invade muscles, joints and bones, and joint pain is the main cause, knee pain may be rheumatoid arthritis. 3. Synovitis: the synovial membrane is the inner layer of the knee joint capsule, when the synovial membrane is inflamed, it will ooze and thicken, and the main manifestation is pain. 4. Cancer: such as bone tumor will appear bone pain symptoms, if the knee pain persists for a long time, to cause attention, need to be ruled out through the examination. It is recommended that knee pain should go to the hospital in time to improve the relevant examination, identify the cause and then targeted treatment.