Special equipment and aids.
Joint surfaces are usually smooth, but with osteoarthritis they become roughened and thinner.
Joint movements then become painful, and joints can become inflamed. We are not sure why some people develop osteoarthritis, and other people don't. Some things will increase your risk of developing arthritis, being overweight a previous injury to a joint, eg. Osteoarthritis is very common, and most of us will develop arthritis in one or more of our joints as we grow older. It is very rare under the age of 40.