Osteoarthritis involves damage first to a joint's cartilage, and eventually the bones themselves can be affected. This wearing down can be caused by one or more of the following:
Age. As people get older, the joints are more likely to have endured daily wear or several small injuries. Some research also suggests that one's cartilage becomes less able to repair itself as one ages.
Obesity. Carrying extra weight is especially likely to put strain on the knees. Obesity has also been linked to osteoarthritis in the hands, although experts aren't yet sure how obesity affects those joints.
Occupation. Some jobs involve repeated movements that can strain certain joints. For instance, jobs that require a lot of squatting have been linked to osteoarthritis in the knees.
Previous joint injury or abnormality. These can include sports-related injuries, such as tears to the meniscus. Or a person may be born with abnormal alignment of the knee or another joint.
Additional factors that put one at higher risk for getting osteoarthritis include being female and having calcium-containing crystals in one's joints (also known as pseudogout).
Experts also believe that certain genetic factors may make some people more likely to develop osteoarthritis.