The American Academy of Orthopaedic Surgeons describes a rotator cuff tear as a tendon tear of the four rotator cuff muscles that stabilize the shoulder. These include the supraspinatus, infraspinatus, subscapularis and teres minor muscles.
The supraspinatus muscle runs from the supraspinatous fossa of the top of the shoulderblade to the very top of the upper arm, according to Gray's Anatomy. The distal supraspinatus tendon is the muscle's farthest attachment to this portion of the upper arm. The supraspinatus helps to raise the arm at the shoulder. According to the AAOS, a rotator cuff injury can be painful when lifting the arm out to the side.