Effusion:
This is essentially inflammation manifesting itself through the epidermis. It is warm to the touch, and the articulation may become slightly enlarged and delicate. This occurs because inflammation increases blood flow to the affected area, resulting in discoloration. The increased blood flow is matched by an equal discharge of blood through the veins, and the excess fluid remains in the tissue, causing it to swell.
Because inflamed tissues are filled with fluid, they stretch; this tissue elongation stimulates nerve terminals, which transmit the pain signal to the brain. Inflammation primarily causes pain for this reason, and this symptom is more prevalent in arthritis caused by systemic inflammation, such as rheumatoid arthritis.
