why is rotator cuff shallow
The rotator cuff keeps the upper arm bone in the shoulder socket and lets you raise and twist your arm. The shoulder is a ball-and-socket joint. The ball at the top of the upper arm bone fits into the socket of the shoulder blade. This socket is shallow, which lets you move your arm in a wide range of motion. But it also means that the muscles and tendons of the rotator cuff have to work hard to hold the bones in place.