What Exactly is the Rotator Cuff?

What Exactly is the rotator cuff? 

As a physical therapist, I've heard its name in many forms- Rotary cup, Roter cuff... you get the gist.  So, what exactly is the rotator cuff?  Let's start with a mini anatomy lesson.  In its simplest form, the rotator cuff is a group of four muscles that surround the front and back of your scapula (your shoulder blade).  The muscles are supraspinatus, infraspinatus, teres minor and subscapularis.  These muscles become tendons as they attach to a bone.  The uppermost of these muscles, the supraspinatus, has to travel through a small space, called the subacromial space on its way to its attachment on the humerus (the upper arm bone).  All 4 muscles come together to kind of wrap around the shoulder and form a cuff.   

This is important for many reasons- for one thing its attachments all around the humerus are important for just supporting the arm in the socket.  Just hanging or swinging your arm can be painful with a rotator cuff tear.  The rotator cuff also initiates the movement when elevating the arm, then other muscles kick in to assist in raising the arm afterwards.  Individually, these muscles can also internally or externally rotate the arm. 

Of course, trauma can cause an injury to the cuff- a fall, a yank, etc. Often, poor posture is the biggest culprit in strains and tendonitis.  These muscles originate behind your trunk and attach more around towards the front, so if your shoulders are very rounded and your posture is very slouched, those muscles will be overstretched.  When overstretched they become weaker and inefficient, which leads to breakdown and eventually pain.  It also causes more strain on support muscles which can lead to compensations (and eventually pain) elsewhere.