With standard, or anatomic, shoulder replacement surgery, a metal ball replaces the round ball of your arm bone, and a plastic socket replaces your shoulder socket. But in a reverse shoulder replacement, the positions of the ball and socket are reversed. The surgeon places a plastic cup attached to a stem on the top of your arm bone. In the socket part of your shoulder, the surgeon places a stem with screws going into your shoulder blade.
Reversing the parts allows different muscles to move your shoulder joint. Your deltoid muscles, which form the rounded curve of your shoulder, will move your shoulders once you have recovered, instead of your rotator cuff muscles.