The rotator cuff is a group of four muscles (supraspinatus, infraspinatus, teres minor, subscapularis) which rotate the humerus and hold the shoulder in place by keeping the humeral head in the proper position inside the glenoid socket. These muscles allow everyday repetitive motions like scratching behind your head or back, painting, waxing, using hand tools, reaching, and lifting overhead. They are used extensively in athletic activities like throwing a ball, serving a tennis ball and driving a golf ball. Thus, chronic wear and tear or a fall or collision can cause injury to the rotator cuff. It is not uncommon for a patient to have intermittent shoulder pain for several years which is not completely relieved by rest and anti-inflammatory medication. Symptoms may include pain in the front, side, back or deep inside the shoulder especially with overhead movements. Putting on a bra, shirt or coat may be painful. To properly diagnosis a rotator cuff injury a complete examination of the shoulder and neck must be done. Injury to the rotator cuff comes in the form of muscle strain and tendonitis. There are three grades of strains. Grade I is a mild tear in the moderate tear which hinders range of motion with mild to moderate pain. Grade II is a moderate tear with a significant loss of range of motion with moderate to severe pain. Grade III is a severe or complete tear of the muscle which severely limits muscle which allows complete or almost complete range of motion with little or no pain. Tendonitis is an inflammation and fraying of the tendon (area where the muscle attaches to the bone). found this on a website, dont know how to qoute it to the website though.