The most common form of arthritis, osteoarthritis, can affect any joint in the body, but most often afflicts the knees, hips, and fingers. Most people will develop osteoarthritis from the normal wear and tear on the joints through the years.
Joints contain cartilage, a rubbery material that cushions the ends of bones and facilitates movement. Over time, or if the joint has been injured, the cartilage wears away and the bones of the joint start rubbing together.
As bones rub together, bone spurs may form and the joint becomes stiff after long periods of activity or inactivity.