Arthritis means inflammation of joints. Rheumatoid arthritis (RA) is a common form of arthritis. (There are various other causes of arthritis and RA is just one cause.) About 1 in 100 people develops RA at some stage in their life. It can happen to anyone. It is not an hereditary disease. It can develop at any age, but most commonly starts between the ages of 40 and 60. It is about three times more common in women than in men.

Understanding Joints
A joint is where two bones meet. Joints allow movement and flexibility of various parts of the body. The movement of the bones is caused by muscles which pull on tendons that are attached to bone. Cartilage covers the end of bones. Between the cartilage of two bones that form a joint there is a small amount of thick fluid called synovial fluid. This lubricates the joint, which allows smooth movement between the bones.
The synovium is the tissue that surrounds a joint. Synovial fluid is made by cells of the synovium. The outer part of the synovium is called the capsule. This is tough, gives the joint stability, and stops the bones from moving out of joint. Surrounding ligaments and muscles also help to give support and stability to joints.

What causes rheumatoid arthritis?
RA is thought to be an autoimmune disease. The immune system normally makes antibodies (small proteins) to attack bacteria, viruses, and other germs. In people with autoimmune diseases, the immune system makes antibodies against tissues of the body. It is not clear why this happens. Some people have a tendency to develop autoimmune diseases. In such people, something might trigger the immune system to attack the body’s own tissues. The trigger is not known.
In people with RA, antibodies are formed against the synovium (the tissue that surrounds each joint). This causes inflammation in and around affected joints. Over time, the inflammation can damage the joint, the cartilage, and parts of the bone near to the joint.Which joints are affected in rheumatoid arthritis?The most commonly affected joints are the small joints of the fingers, thumbs, wrists, feet, and ankles. However, any joint may be affected. The knees are quite commonly affected. Less commonly, the hips, shoulders, elbows, and neck are involved. It is often symmetrical. So, for example, if a joint is affected in a right arm, the same joint in the left arm is also often affected. In some people, just a few joints are affected. In others, many joints are involved.

What are the symptoms of rheumatoid arthritis?
Joint symptomsThe common main symptoms are pain and stiffness of affected joints. The stiffness is usually worse first thing in the morning, or after you have been resting. The inflammation causes swelling around the affected joints.Other symptomsThese are known as extra-articular symptoms of RA (meaning outside of the joints). A variety of symptoms may occur. The cause of some of these is not fully understood:Small painless lumps (nodules) develop in about 1 in 4 cases. These commonly occur on the skin over the elbows and forearms, but usually do no harm.Inflammation around tendons may occur. This is because the tissue which covers tendons is similar to the synovium around the joints.Anaemia and tiredness are common.A fever, feeling unwell, weight loss, and muscle aches and pains sometimes occur.In a few cases, inflammation develops in other parts of the body, such as the lungs, heart, blood vessels, or eyes. This is uncommon but, if it occurs, can cause various symptoms and problems which are sometimes serious.

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