What is rheumatoid arthritis?
Rheumatoid arthritis is an autoimmune disease that causes inflammation in your joints. The main symptoms are joint pain and swelling. It’s the second most common form of arthritis in the UK. To understand how rheumatoid arthritis develops, it helps to understand how a normal joint works.
How does a normal joint work?
A joint is where two or more bones meet. Your joints let your bones move freely but within limits.
The ends of your bones are covered with cartilage, which has a very smooth, slippery surface. The cartilage allows the ends of your bones to move against each other almost without friction. The joint is surrounded by the synovium, which produces a small amount of synovial fluid that nourishes the cartilage and lubricates the joint. The synovium has a tough outer layer called the capsule that, together with the ligaments, holds your joint in place and stops the bones moving too much. Strong fibrous bands called tendons anchor the muscles to the bones.
What happens in a joint affected by rheumatoid arthritis?
Rheumatoid arthritis causes inflammation in the synovium. The result is very similar to inflammation that you may have seen if you’ve had an infected cut or wound – it goes red, swells, produces extra fluid and hurts. The redness is caused by the flow of blood increasing. As a result, the inflamed joint may feel warmer than usual. The inflammation is caused by a build-up of fluid and cells in the synovium. Your joint hurts for two reasons:
- Your nerve endings are irritated by the chemicals produced by the inflammation.
- The capsule is stretched by the swelling in your joint.
When the inflammation goes down, the capsule remains stretched and can’t hold your joint in its proper position. This can make your joint unstable, and it can move into unusual or deformed positions. Some damage is done to the joints every time they're inflamed, and the joint can be worn away after repeated flare-ups (periods where your joints become inflamed and painful).