When two or more bones' ends come together, a joint is created. The body has several distinct kinds of joints. As an illustration, the knee is referred to as a "hinge" joint because it can bend and straighten like a hinged door. The hip and shoulder are "ball-and-socket" joints, where one bone's rounded end fits into the other bone's cup-shaped section. Parts of an arthritic or diseased joint are surgically removed and replaced with prosthetic devices made of metal, plastic, or ceramic during a total joint replacement. The prosthesis is made to mimic the motion of a healthy, normal joint. The two most popular joint replacement procedures are hip and knee replacements.
