 Pretty much all of your rotator cuff tendons are about as thick as your little finger, maybe as wide as two fingers. And there's one in the front of the ball, there's one on the top of the ball, and there's two in the back. So they form a cuff of tendons around the ball. The rotator cuff helps to stabilize the shoulder by pulling it into the socket. When your arm's in real close, the ball doesn't really need to be held into the socket real tightly. But if you get your arm away from your body and you're picking something up, the ball actually has to become compressed into the socket.