Osteoarthritis, also known as degenerative joint disease,
occurs when the cushiony cartilage between two bones becomes worn down, and
the bones begin to rub against each other in the joint (the
area where two bones come together). This often leads to pain, swelling, a
decrease in motion at the joint, stiffness, or the formation of bone
spurs (tiny growths of new bone). While osteoarthritis can occur at
almost any joint, osteoarthritis of the knee is the most common type. More
than 10 million Americans have osteoarthritis of the knee. Most people affected
are older than 45 years.