What is a rotator cuff made of?

It's a tendon: A tendon is what attaches a muscle to a bone. This is what allows the skeleton to move. The muscle generates a force that is transmitted to the bone, through a tendon. In the shoulder, the rotator cuff starts out as 4 muscles attached to the shoulder blade. As they move toward the shoulder joint, the muscle turns into tendon. This tendon is the rotator cuff and helps to move the shoulder joint.

4 muscles.: The rotator cuff is a small group of 4 muscles that originate on your shoulder blade, and connect on the upper part of your arm bone.