Rotator Cuff muscles, are a collection of 4 muscles that move the shoulder in a circular motion, like when a pitcher in baseball throws the ball. All of these muscles attach to the shoulder blade, then move into the upper part of the arm, close to the shoulder joint. These muscles include, infraspinatus, supraspinatus, subscapularis and teres minor. Any one of these muscles can be affected during a rotator cuff injury. At the same time, more then one can also be affected.
In these types of injuries, it is from the muscle having a tear/strain or tendinitis. It is also treated in the same way as the other conditions, only positioning will be different to have better access to the muscle or muscles that need to be worked on.
Though this condition is an overuse injury, it most commonly happens to pitchers in baseball. Or any other task that causes you to do a lot of rotation with the shoulder.
If you would like to read more on how the condition can be treated, with massage therapy, you can view Strains and Tendinitis articles.