Muscles and Tendons of the Rotator Cuff

A muscle is a type of tissue that can contract to provide mobility and strength.  A tendon is a structure that connects the muscle to the bone.

In the shoulder, injury to the rotator cuff is usually within the tendon.  These tendons have a vulnerable blood supply, called a watershed, that can cause susceptibility to injury. 

Rotator cuff muscles can be damaged as well, especially in the setting of chronic rotator cuff tears when the muscles become atrophied (wasted away).  In these cases, the muscle permanently changes as a result of not being used properly.  Atrophy of the rotator cuff muscles usually means a tear in the tendon has been present for a long time and may not be repairable.

The supraspinatus muscle is the most commonly injured rotator cuff muscle and tendon.  The supraspinatus is located directly on top of the shoulder, and the most important muscle involved in lifting the arm away from your side.

Injuries to the supraspinatus tendon often seen on an MRI include tendonitis, partial tears, and full-thickness tears (complete tears) of the tendon.

The infraspinatus tendon is just behind the supraspinatus and determining the beginning of one tendon and the end of the other can be difficult, they essentially blend into each other.

The subscapularis is a tendon in the front of the shoulder. This tendon is less commonly injured but can cause some unique challenges when it is injured. The motion called internal rotation of the shoulder is dependent on the subscapularis. In addition, the subscapularis helps provide stability to the shoulder and helps maintain the normal position of the biceps tendon.

Tears of the subscapularis can be found in very large tears of the rotator cuff, and also in patients who have had recent surgery. Often shoulder surgery is performed by entering the front of the joint, by detaching the subscapularis tendon. Injuries during recovery can lead to tearing of the healing tendon. This is a complication seen after shoulder replacement or open labral repair surgery.

The teres minor is the last of the rotator cuff muscles and the least commonly injured. The teres minor is in the back of the shoulder and involved with the movement of external rotation of the joint. External rotation is the movement with your elbow held at your side, and your hand pushes outwards. Usually, your doctor will test this muscle with this maneuver.

Most patients who are researching the names of the muscles and tendons have read them in an MRI report or a surgical report of their procedure.  When doctors are talking with patients, they generally refer to these structures as the rotator cuff, but more precisely they represent four distinct muscles and tendons that together provide much of the strength and mobility of our shoulder joint.