As a disease, arthritis is more complicated and varied than most people imagine. It can come in different forms and affect people in different ways. But the common thread through most forms of arthritis? Inflammation and stiffness of the joints.
Swelling may occur for two key reasons. Either the lining of the joint, known as the synovium, swells (synovitis) or the synovial fluid increases in volume (an effusion). It is an active process: inflammatory cells (mainly white cells) and more blood enter the joint, while many inflammatory molecules, such as small proteins (peptides) are released into the soft tissues around the joint. The increased blood flow makes the joint swell and feel warm. The inflammatory materials cause joint fluid to collect in and around the joint, which adds to the swelling. The type of joint swelling can vary depending on the type of arthritis you have.
Inflamed joints can feel especially stiff first thing in the morning. How long it lasts is important: an hour or more is suggestive of inflammatory arthritis. Defining morning stiffness is hard, although people with arthritis describe it as an ache combined with difficulty moving. Stiffness following exercise is usually a feature of osteoarthritis; it is a sign that the joints are starting to fail. People also feel stiff when they rest, such as sitting down after a walk or relaxing in the evening. The joints are sometimes said to “gel,” a term reminiscent of how gelatin sets – a gradual process of firming up. Joint stiffness may occur with or without joint pain. Stiffness can affect any joint– the fingers and hands, wrists, elbows, knees, ankles, feet, shoulders, hips, and even the jaw.