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Every bone is connected to at least one other bone. The area of connection where two or more bones come together is called a joint. Those involved in total joint replacement are known as "freely moveable joints." Examples of freely moveable joints are the knee, hip, shoulder and elbow.
Anatomy of Freely Moveable Joints
Freely moveable joints are alike in certain ways. They have a capsule, a cavity and a layer of cartilage over the ends of the joining bones.
Capsule
The joint capsule is made of the body's strongest and toughest material--fibrous connective tissue--and is lined with a smooth, silky surface. It produces fluid that lubricates and nourishes the bones and cartilage of the joint.
Cartilage
The material covering the ends of the bones is called articular cartilage. It is a smooth, firm cushion that allows the bones to move against each other without friction.
Ligaments
The ligaments are made of the same material as the joint capsule. They are very strong, leathery bands of fibrous connective tissue that connect bone to bone, reinforce the capsule and keep the bone in place.
Muscles
Muscles are tissues that extend from bone to bone and provide the power for movement.
Prosthesis
A prosthesis is an artificial part that replaces or supplements a natural part of the body. The prosthesis used in total joint replacement is very similar to the joint parts it is replacing. It has two, or sometimes three, parts. Usually one part of the prosthesis is made of metal; the other part is made of plastic or ceramic material. The reason for this is that metal and these materials move against each other with little friction. The prosthesis may or may not be cemented in place. Your surgeon will decide which is better for you. | 
