Rheumatoid Arthritis: 13 Things You Should Know

Most people with arthritis have osteoarthritis, which commonly occurs with age.

But there's another type called rheumatoid arthritis (RA), a serious autoimmune disease. The two are often confused -- which can be endlessly frustrating for those with RA.

"Everybody says that arthritis is one word," says Christopher Evans, DSc, Ph.D., the Maurice Mueller Professor of Orthopaedic Surgery at Harvard Medical School in Boston. "But the conditions are quite different."

Here are 13 ways to tell the two apart.