Understanding the Rotator Cuff   The rotator cuff is a group of four small muscles and their tendons in your shoulder that work together to keep the shoulder stable and allow it to move smoothly. These muscles act as the "support team" for the shoulder joint, helping to lift and rotate the arm in various directions. Each muscle attaches from the shoulder blade to the top of the arm bone, forming a "cuff" around the joint.   Role in Everyday Activities The rotator cuff is esse