Joint replacement involves surgery to replace the ends of bones in a damaged joint. This surgery creates new joint surfaces. In shoulder replacement surgery, doctors replace the ends of the damaged upper arm bone (humerus) and usually the shoulder bone (scapula) or cap them with artificial surfaces lined with plastic or metal and plastic. Shoulder joint components may be held in place with cement. Or they may be made with material that allows new bone to grow into the joint component over time to hold it in place without cement.