Chronic knee pain has a host of causes and it is difficult to pinpoint the underlying cause of your pain without a physical exam, diagnostic tests, and a thorough medical history. To help diagnose your condition, it is important to ask you more questions. In what part of the knee do you feel pain? How long does the pain last? Are there any activities that cause the pain? Do you have any other symptoms? With limited information, however, I can propose a general condition that might contribute to your chronic, severe knee pain. Such possibility is joint effusion, also referred to as "water on the knee" and "fluid on the knee," that causes swollen joints. A swollen joint is a symptom of osteoarthritis
("wear-and-tear" arthritis), rheumatoid arthritis, and gout. If your knee is swollen, red, and warm to touch, I may be concerned about inflammation due to rheumatoid arthritis, a crystalline arthritis, such as gout, or joint infection. Blood tests are necessary to rule it out. Other possible causes of knee pain by injuries and trauma-related problems include ligament injury
and cartilage wear-out, such as chondromalacia patella which causes knee pain under the knee cap due to softening of the cartilage. These conditions may not show up on routine X-rays. X-rays only show bone-related problems and are useful to verify that there is no break or dislocation when there is a history of trauma. You may need a MRI
to detect abnormality of knee joint showing bones, muscles, ligaments. A MRI can detect if there is a tear in the ligament or cartilage and any fluid present in your joint. You need to see an orthopedist who can order these tests for you and establish a diagnosis.