Osteoarthritis is a chronic disease causing deterioration of the joint cartilage (the softer parts of bones, which cushion their connections to each other) and the formation of new bone (bone spurs) at the margins of the joints. The actual  cause of osteoarthritis is unknown for most people, but metabolic, genetic, chemical, and mechanical factors play a role in its development. It is the most common form of arthritis, and it is associated with age. It may first appear without symptoms between 30 and 40 years of age and is present in almost everyone by the age of 70. Symptoms generally appear in those who are middle aged. Before the age of 55 it occurs equally in both sexes. However, after 55 the incidence is higher in women.