There are four rotator cuff tendons in each shoulder that attach the rotator cuff muscles to the top of the arm bone (humerus) and help the shoulder move. Each tendon is about 1 centimeter thick and 2 or 3 centimeters wide.
A partial rotator cuff tear is one that only goes partway through the tendon, while a full tear goes completely across the tendon. Most rotator cuff tears develop because of aging and go unnoticed. However, younger patients occasionally suffer from partial rotator cuff tears due to injury, like in sports that require overhead motion.