Osteoarthritis (OA) -- also known as degenerative arthritis -- is the loss of joint cartilage, usually caused by age-related wear and tear. OA can also be caused by a previous trauma to the joint, such as a sports injury. This form of arthritis is the most common, and it affects about one out of every 15 people in the United States alone [source: Shiel].
The cartilage on the ends of your bones is made up of protein and serves as a shock absorber for the joint. As the years go by, more and more water ends up in the cartilage, slowly breaking down the protein. Soon, pieces of cartilage peel away, leaving small notches. As you continue using the joint, the damage increases. Left unchecked, OA will wear away all of the cartilage, meaning the two bone ends in a joint will rub against each other.
In severe cases of OA, you and your orthopedic surgeon may decide to replace the entire damaged joint (most commonly the knee or the hip). Hip replacements have a faster recovery time and a better long-term success rate because the hip's ball-and-socket joint is relatively simple and stable in design. Surgeons are doing great things with knees these days as well, but it's a much trickier joint to duplicate artificially and the replacement itself usually needs to be replaced after 10 or 15 years.
Sometimes cartilage breakdown will stimulate the bone to produce bony outgrowths known as spurs. These alone don't cause problems, but if they make contact with other bones or nerves, you're going to know about it. Spurs can develop pretty much anywhere, from your fingers (making them look disfigured or gnarled) to your spine, knees or neck. Sometimes these spurs will break loose and get embedded in the synovium that lines the joint. They can also lodge between a joint's two bones, preventing movement. The floating spur may slip back out of the way, allowing movement again, but continue floating back in and out of the joint, causing you ongoing discomfort. If spurs are causing you trouble, they can usually be removed, depending on their location. If they aren't causing you discomfort or mobility issues, spurs can be left alone.
Next, we'll learn about another form of arthritis: rheumatoid arthritis.