Sometimes the rubbery outer layer of the articular cartilage that covers the ends of your bones deteriorates. The result is called osteoarthritis. Osteoarthritis affects the entire joint — causing cartilage loss, bone damage, formation of bone spurs, and soft tissue inflammation. Your cartilage loses its ability to absorb shocks and repair itself.

Since osteoarthritis results from wear-and-tear, it most often is seen in older people. In fact, half of the U.S. population aged 65 or older is likely to show evidence of osteoarthritis in at least one joint. There also is increasing evidence that genetics may play some role in this disease. In addition, osteoarthritis may be caused by certain diseases such as Paget's disease, by injury, or by sports- or work-related overuse of the shoulder.