What is Arthritis?

Arthritis is not a single condition. There are well over 150 kinds of arthritis, all of which affect one or more joints in the body. Some of these forms of arthritis don't involve any inflammation.

Arthritis does not only affect older people: many children also have arthrithis.

The word arthritis comes from Greek: arth- = joint and -itis = inflammation. So, arthritis really means inflammation of the joint.

Perhaps it is more useful to think of arthritis meaning problems with the joint!

The anatomy of a joint

A joint is a meeting of two bones so that movement can occur.

Parts of a typical joint -

Cartilage: This is a strong, smooth material which forms a cushion at the end of each bone in a joint. It absorbs shock and prevents bone from rubbing against bone. If the cartilage is damaged or degenerates, osteoarthritis can occur.

Synovial Membrane: This membrane encloses the synovial sack, filled with a lubricating fluid which protects and lubricates the joint. Synovitis occurs when this membrance becomes inflamed, and is typical of rheumatoid arthritis. An infection can also cause inflammation in the synovial fluid. The deposit of crystals in the synovial fluid is a characteristic of gout.

Bursa: This is a small lubricating sac which is not actually part of the joint but which lubricates the movement of muscle over muscle and of muscle over bone. The bursa can become inflamed causing bursitis.

Muscle: The muscles move bones by contracting and expanding. In conditions such as polymyalgia rheumatica, the muscles become inflamed.

Tendon: The tendon is a fibrous cord that attaches muscle to bone. Tendinitis is inflammation of the tendon.

Ligament: The ligaments are short fibrous cords that attach bone to bone, making up the joint capsule. A problem called enthesopathy occurs when ligaments become inflamed, as in ankylosing spondylitis.