The inflammatory process in rheumatoid arthritis
A healthy joint contains bone, cartilage (a spongy pad at the end of bones acting as a shock absorber) and ligaments (tough sheets of fibrous tissues that ‘strap’ the two bones of the joint together) enclosed in a thin membrane known as synovium. This membrane secretes a liquid called synovial fluid, which lubricates the joint like oil in a car, helping it to move smoothly.
In rheumatoid arthritis, the immune response is mistakenly directed at the synovium. An inflammatory reaction is triggered and immune cells flood to the joint, causing it to become swollen, painful and stiff. The immune cells release inflammatory chemicals and enzymes that:
- irritate nerve endings, aggravating the pain
- cause the synovial membrane to thicken and swell into the joint space, making the joint stiff
- increase the production of synovial fluid, compounding the swelling and stretching the joint membrane, which causes further pain
- destroy cartilage, making the joint painful and difficult to move
- stimulate the production of inflammatory tissue that invades the joint space, limiting the movement of the joint
- eventually, destroy the bone itself
These effects also cause the muscles around the joint to become weak and loosen the ligaments connecting the bones, leading to progressive destruction, deformity and instability of the joint.
