What is Arthritis - Arthritis Action

What is Arthritis

There are thought to be 10 million people with some form of arthritis in the UK. It is the most common cause of disability in the UK and can affect people of all ages, not just older people.

The word “arthritis” means ‘inflammation in the joints’. Inflammation is a difficult thing to imagine and describe, but it is part of the body’s normal healing process, just like the healing of a cut or a bruise. Inflammation can be thought of as being like a bruise with swelling on the inside of the joints, and this can cause pain and stiffness.

A normal joint is the connection between 2 bones. The ends of the bones are covered by a layer of cartilage which acts as a shock absorber to protect the bones form damage. A thin membrane called the synovial membrane lines the joint and produces a small amount of joint fluid called synovial fluid which helps to lubricate the joint. The joint capsule holds the joint together loosely. Strong ligaments (not shown) help to anchor the bones together firmly and  muscles on top and across the joint the joint (not shown) move the joint in different directions.

The most common type of arthritis is osteoarthritis. This is often wrongly called “wear and tear” or “degenerative” arthritis and is more common in older people.

In a joint with osteoarthritis, minor injury triggers the body’s healing process. This can cause the build-up of fluid inside the joint and the formation of new bone leading to swelling. Chemicals in the joint fluid can lead to thinning of the joint cartilage. Degeneration is a misleading word, as in osteoarthritis the body is attempting to repair itself and can often cause no pain at all.

One reason for the pain and stiffness of osteoarthritis is thought to be due to nerve endings in and around the joint becoming more sensitive. These nerve endings can sometimes become more sensitive and can then continue to cause pain, even when the original cause of pain has settled.

The next most common types of arthritis are rheumatoid arthritis, where the immune system attacks the joints, causing swelling, pain and stiffness, and gout which is caused by crystals of uric acid irritating the joints. Rheumatoid arthritis and gout are two examples of “inflammatory arthritis” but there are many other forms of inflammatory arthritis including psoriatic arthritis and spondyloarthropathy (including ankylosing spondylitis).

Find out more, on our new Self-Management Resource.

Self-Management Resource


What causes arthritis?

As there are so many different types of arthritis, there is no one cause, but the following factors may be important.

  • Genetics – arthritis can sometimes run in families, especially rheumatoid arthritis and osteoarthritis of the fingers
  • Gender – some types of arthritis are more common in women and some in men
  • Age – osteoarthritis is usually a problem in later life whereas other types of arthritis such as rheumatoid arthritis and spondyloarthropathy commonly start in younger adults
  • Injury – damage to a joint, for example a broken bone or a football injury can cause osteoarthritis later in life
  • Infections – certain viral and other infections can trigger some types of arthritis
  • Lifestyle – osteoarthritis, especially osteoarthritis of the knees and hips is more common and causes more pain in people who are overweight. Drinking alcohol can trigger an attack of gout. Smoking is more common in people who develop rheumatoid arthritis

Read more about different types of arthritis