Swollen joints happen when there is fluid in the tissues around the joints. It can be very uncomfortable and can make it difficult to move the affected joints. In some cases, swelling may cause affected joints to increase in size or appear to be an odd shape. Joint pain and swelling can affect more than one joint at a time. The most common joints to be affected by pain and swelling are elbows, wrists, shoulders, the base of the spine, knuckles, hips, knees or ankles.