The MRI confirmed a penetrating tear in the supraspinatus muscle and a lesion of the infraspinatus muscle. (wjon.org)
The muscles which comprise the rotator cuff are the subscapularis muscles, which moves your arm in an inward turning motion, known as internal rotation; the supraspinatus muscles, responsible for elevating your arm and moving it away from your body; the infraspinatus muscle, responsible for moving your arm in an outward turning motion, known as external rotation and the teres minor which is also responsible for the external rotation movement of your arm. (fitnessandpower.com)
The supraspinatus muscle runs along the top of the shoulder blade and inserts at the top of the arm (humerus bone). (sportsinjuryclinic.net)