There are four muscles which form the tendonous attachment of the rotator cuff within the shoulder allowing for fine motion as well as strength.  These are subscapularis, supraspinatus, infraspinatus and teres minor.  The supraspinatus is important in that it is predisposed to some type of degenerative changes secondary to its strategic placement on top of the shoulder. It is sometimes involved in impingement and pinching mechanics from the acromion (the top bone on your shoulder) as well as the humeral head (which compresses against the acromion during forward elevation of the arm as well as side elevation.)  The infraspinatus and teres minor cover the back portion of the humeral head and are used as external rotators (such as cocking your arm to throw a ball from back to front).   The subscapularis is the anterior portion which crosses over the front of the shoulder and is required for certain types of motion, including internal rotation of your shoulder (i.e., grabbing your wallet out of your back pocket or putting your bra on).  The frequencies of tears vary based on age.  Under the age 40, approximately 30% to 35% of people will have tears and other associated injuries to their shoulder joint from trauma.  The incidence or rotator cuff tears associated with trauma increases once you reach the age of 60 and can be as high as 80%.  Once a thorough clinical evaluation as well as appropriate radiographic (x-rays) and diagnostic tests (MRI or MR arthrogram) have been performed and a positive rotator cuff tear has been identified, there are several treatment options. These treatments could include conservative injections, physical therapy with strengthening, the use of pain medication and/or surgical intervention.  Surgical intervention for rotator cuff repair can either be performed arthroscopically (through small strategically placed portals in the shoulder no larger than the width of your fingernail,) or through a traditional open approach for direct visualization.  Standard arthroscopic surgical procedures and arthroscopic rotator cuff repairs are becoming commonplace and are performed as out patient procedures, depending on the extent of damage and repair required.  Often, associated procedures performed with rotator cuff repairs are subacromial decompression and distal clavicle excision (to remove excess bone and bone spurs which impinge on the damaged rotator cuff and its blood supply).  This, and other surgeries, are quite extensive and you should discuss all your treatment options with your physician.