what are the different types of knee implants?
['Metal on plastic. This is the most common type of implant. ... ', 'Ceramic on plastic. ... ', 'Ceramic on ceramic. ... ', 'Metal on metal. ... ', 'To learn more about your options for knee replacement surgery, read the Harvard Medical School guide Total Knee Replacement.', 'Image: m-gucci/Getty Images.', 'Disclaimer:']