Osteoarthritis may begin with inflammation of the joint. Joint cartilage begins to degrade, swells, and over time becomes softer and less elastic. Clefts appear on the surface of the cartilage, which continues to degrade until the underlying bone is exposed. Bone then rubs against bone inside the joint. The bone becomes increasingly vascularized (filled with blood vessels), thicker, and denser. Changes in the structure of the underlying bone often cause osteophytes (bone spurs) to form. Primary OA has no clear cause, although it is related to changes that occur with age. It`s sometimes called “wear-and-tear osteoarthritis.” Secondary OA results from a predisposing cause, usually trauma.