What causes osteoarthritis?

People who have the bone disease osteoporosis are more likely than the general population to also have celiac disease, an intestinal disorder caused by intolerance to wheat flour (gluten). Celiac disease renders patients unable to absorb certain nutrients, including calcium and vitamin D -- both essential to bone health -- leading to osteoporosis. The good news? Researchers say that treating celiac disease with diet can help patients regain bone health.

The study involved 840 people, 266 patients with osteoporosis and 547 without. Nine of the patients with osteoporosis also had celiac disease, compared with only one of those without osteoporosis. Results suggested that 3 percent to 4 percent of people with osteoporosis have it because they have celiac disease. Source(s): http://www.mercola.com/2005/mar/19/osteo...

i would think mainly a deficiancy of vitamins, you can be prone to it if you suffer with allergies ie wheat gluten etc as you are missing out on the necesary vitamins, or vegetarian/vegan.
For me it is the result of a terrible bone break in 1994. The cartilage has been slowly disappearing. Now there are spots where I have none. For others it seems to be part of the aging process.
Primary osteoarthritis is mostly related to aging. With aging, the water content of the cartilage increases and the protein makeup of cartilage degenerates. Repetitive use of the joints over the years irritates and inflames the cartilage, causing joint pain and swelling. Eventually, cartilage begins to degenerate by flaking or forming tiny crevasses. In advanced cases, there is a total loss of the cartilage cushion between the bones of the joints. Loss of cartilage cushion causes friction between the bones, leading to pain and limitation of joint mobility. Inflammation of the cartilage can also stimulate new bone outgrowths (spurs) to form around the joints. Osteoarthritis occasionally can be found in multiple members of the same family, implying an heredity (genetic) basis for this condition.
http://www.medicinenet.com/osteoarthriti...