The rotator cuff is a group of four muscles (supraspinatus,
infraspinatus, teres minor, and subscapularis) that attach on the
upper part of the humerus and help stabilize your shoulder as well as
provide strength. There’s also an important muscle outside your
rotator cuff called the deltoid that’s imperative for powering the
shoulder joint. This is the muscle that you can feel underneath your
skin on the outer part of your shoulder.
In a healthy shoulder joint, the bone’s surface, where the ball and
socket rub together, is covered with a smooth, tough protective tissue
called cartilage. Arthritis causes damage to this area of the bone’s
surface and cartilage. These damaged surfaces eventually become
painful as they rub together.
As you might expect, there are a number of reasons why you might be
feeling pain in your shoulder including arthritis, rotator cuff tear,
dislocation, and more.