Dear Doctor;I work in the office and sit most of the time. Now my knee hurts from behind. Is that a sign of arthritis? I only have time for exercise at the weekend, which I do, but it is not helping the pain. Kayondo, 26.Dear Kayondo, You are too young to have the problem of degenerative changes of knee coming in old age. But yet prolonged immobilisation of the joints tends to make them stiff. Problem can be with the joint as well as the surrounding muscles and supporting tissues. The pain could also be due to a muscular strain or ligament pull induced by vigorous exercise, some momentarily bad position like during playing football, etc, situations. If the pain is severe take some pain killing medicine, avoid exercise for now. After the pain is relieved, start exercises and increase gradually. Meanwhile, using a crepe bandage to support the knees while working would be helpful. For your daily work, avoid sitting for long hours. In between, whenever you find time, get up and move around even if for 10 minutes.