There are two identifiable types of Osteoarthritis, Primary Osteoarthritis and Secondary Osteoarthritis. Primary Osteoarthritis is related to but not specifically caused by the process of aging, since many people in their latter stages of life (past the age of retirement) do not show any signs of arthritis while other people who are much younger do; it is characterized by the inflammation of the tissue in the joint which causes pain and stiffness - although nowhere near the pain level of rheumatoid arthritis. Unfortunately the body's defense and response to Primary Osteoarthritis while the joint is slowly degenerating can be to create new bone outgrowth - which are actually worse due to spurs being formed - increasing the agitation and pain brought on by osteoarthritis.
Secondary Osteoarthritis is caused by other processes than Primary, and often only afflict a few joints (such as in the case of injury) - however the inflammation and agitation are usually the same as Primary for the afflicted joints. Causes of Secondary Osteoarthritis include genetic traits that deform joints and shapes of joints, or interfere with cartilage generation, hormone imbalances, direct injury to the joint (such as a fall that splits or ruins the cartilage), diabetes, surgery, being overweight or morbidly obese, and inflammatory diseases like Lyme and gout. In addition to this there is the unconfirmed and scientifically unproven theory about cracking joints by manually extending them (such as popping your fingers).
Osteoarthritis is the most common form of arthritis and it affects roughly four out of five people by the age of sixty five - whether or not they actually feel it. Osteoarthritis afflicts about thirty million people in the United States with painful symptoms that require a visit to the doctors office with most patients approaching the age for retirement. The causes of Osteoarthritis are usually hereditary (meaning if your mom had it, and your dad had it, and your grandparents had it - you will most likely have it too), in fact more than half are blamed on it being carried by members of the same family who pass it on to their progeny - however other causes may be as wide a range as allergies, infections, or fungi that might cause it, although analysis of these causes has not been confirmed as of the writing of this article - injuries to the joints and the destruction of a joint's synovial sac may also contribute to the acceleration of osteoarthritis.