Arthritis is a general term for a group of more than 100 diseases. The word "arthritis" means "joint inflammation." Inflammation is one of the body's natural reactions to disease or injury, and includes swelling, pain, and stiffness. Inflammation that lasts for a very long time or recurs, as in arthritis, can lead to tissue damage.
A joint is where two or more bones come together, such as the hip or knee.
The bones of a joint are covered with a smooth, spongy material called cartilage, which cushions the bones and allows the joint to move without pain. The joint is lined by the synovium. The synovium's lining produces a slippery fluid -- called synovial fluid -- that nourishes the joint and helps limit friction within. External to it is a strong fibrous casing called the joint capsule. Strong bands of tissue, called ligaments, connect the bones and help keep the joint stable. Muscles and tendons also support the joints and enable you to move.
With arthritis, an area in or around a joint becomes inflamed, causing pain, stiffness and, sometimes, difficulty moving. Some types of arthritis also affect other parts of the body, such as the skin and internal organs.
Different types of arthritis have different symptoms and the symptoms vary in severity from person to person. Osteoarthritis does not generally cause any symptoms outside the joint. Symptoms of other types of arthritis may include fatigue, fever, a rash and the signs of joint inflammation, including:
The cause of most types of arthritis is unknown. It's likely that there are many different causes. Researchers are examining the role of genetics (heredity) and lifestyle behaviors in the development of arthritis.
Although the exact cause of arthritis may not be known, there are several risk factors for arthritis. A risk factor is a trait or behavior that increases a person's chance of developing a disease or predisposes a person to a certain condition. Risk factors for arthritis include:
Arthritis is very common. It has been estimated that as many as 70 million Americans -- or about one in three -- have some form of arthritis or joint pain. It is a major cause of lost work time and serious disability for many people. Osteoarthritis, the most common form, affects more than 20 million Americans. Arthritis affects people of all ages, but is more common in older adults.