 [ Symptoms ] what is osteoarthritis of the knee and how is it treated [ Disease ] arthritis of the knee is an inflammatory disorder of the knee joint that is often painful arthritis has many causes osteoarthritis oa is caused by degeneration of cartilage in the knee in its extreme form the menisci cartilage will be completely eroded and the femur will rub on the tibia bone on bone osteoarthritis causes a chronically painful knee that is often more painful with activity treatment is aimed at pain control with over the counter pain relievers anti inflammatory medications either over the counter or by your doctor is prescription are also quite helpful more severe oa can be treated with narcotic pain medicines or a knee joint replacement in which a synthetic joint replaces your knee joint