When people talk about arthritis, in the majority of cases they are referring to Osteoarthritis. Osteoarthritis is the most common form of arthritis and is the second most common cause of long-term disability in the US. X-rays taken of individuals over the age of 65 show that over 50% have evidence of arthritic changes in knees and almost 100% of individuals over 75 years old. In general osteoarthritis is an overuse condition and directly correlates with wear and tear on the joints involved. There are certain occupations that predispose individuals earlier onset Osteoarthritis, and weight is also a factor for and primarily affects weight being joints: lumbar spine, hips, knees and feet. There is also a slightly higher incidence of Osteoarthritis in women over 55 years old, and this tends to involve the hands and fingers.
Osteoarthritis is primarily a disease caused by damage to the joints cartilage. It can be thought of as the tread wearing out on a tire, once the cartilage (tread) has worn down, then it cannot be replaced.