Arthritis literally means "joint inflammation."  There are actually more than one hundred forms of arthritis, but osteoarthritis (sometimes called degenerative joint disease or osteoarthrosis) is the most common.  Most often, it affects older people, though it can strike younger people as well.  It's usually caused by the normal wear and tear of time, though, especially in younger people, it can also be caused by injury or trauma to the joint. Other causes are obesity, repeatedly stressing a joint (usually because of a job or certain sports), and genetic defects. 

Osteoarthritis generally affects cartilage.  Cartilage is the hard but slippery tissue on the end of bones, where they meet to make a joint.  It allows the bones to move smoothly against each other. Osteoarthritis is the breakdown of this cartilage tissue.  With less cartilage, the bones are less protected, and when they move, they rub against each other.  This causes pain and swelling and makes the movement less smooth.  After a while, it can cause the joint's shape to change, make small deposits of bone (called osteophytes or bone spurs) grow on the edges of the joint, or make small bits of cartilage or bone break off and float in the joint, causing more pain.

The disease affects people in a variety of ways.  Usually, the joints at the ends of the fingers (closest to the nail), thumbs, neck, lower back, knees, and hips are most affected by it.  In some people, it progresses slowly, or causes mild discomfort that doesn't interfere with daily living.  In others, it progresses rapidly, or causes greater pain, stiffness, and disability, which can limit activities at work and home. These problems can, in turn, lead to depression, anxiety, and other psychological issues. 
 
Rheumatoid arthritis is the second most common form of arthritis. It usually strikes at a younger age than osteoarthritis. It's caused by the body's own immune system attacking the tissues of the joints, which creates pain, inflammation, swelling, and redness in joints. After a while, it can make the joint's shape change and cause joint damage; it can even make people feel tired, ill, and unusually feverish.

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Key Point 1: Arthritis is a huge problem in the U.S. It is expensive and many people suffer with it. In fact, osteoarthritis is the leading cause of disability in this country.