The following article describes the anatomy, function and pathologies of the rotator cuff.
Anatomy of the rotator cuff
In the Human body, the rotator cuff is a functional anatomical unit located in the upper extremity. It consists of the following muscles: supraspinatus muscle, infraspinatus muscle, teres minor muscle and subscapularis muscle.
These muscles all originate from the scapula and insert in the humerus. The subscapularis muscle, for example, is very important for the internal rotation of the humerus. It arises from the subscapular fossa and inserts on the lesser tubercle of the humerus. The teres minor muscle originates from the lateral scapula border and inserts on the greater tubercle of the humerus. The supraspinatus muscle has its origin in the supraspinatous fossa and inserts on the greater tubercle of the humerus – similar to the teres minor muscle. The fourth muscle of the rotator cuff is the infraspinatus muscle. It originates in the infraspinatous fossa of the shoulder blade and inserts on the greater tubercle as well.
Function of the rotator cuff
The main function of the rotator cuff is to stabilize and center the humeral head in the joint socket, the glenoid cavity. In addition, the muscles tighten the joint capsule preventing a pinch during shoulder movements. Certainly the rotator cuff – as the name suggests – plays a major role in the internal and external rotation of the upper arm in the shoulder joint. All the muscles mentioned above fulfill different functions.
The subscapularis muscle is a powerful internal rotator which also supports the upper arm during abduction and adduction. Conversely, the teres minor muscle’s function consists primarily of external rotation, partly retroversion and adduction as well. The supraspinatus muscle performs abduction of the shoulder, especially abduction over 60 degrees. Finally, the infraspinatus muscle is a strong external rotator and additionally assists in both abduction and adduction.
Pathologies of the rotator cuff
When looking at pathologies of the rotator cuff – as in all joints - one needs to differentiate between degenerative and traumatic lesions. Here are two examples:
An example of a degenerative disease of the rotator cuff is the subacromial impingement syndrome. There the supraspinatus muscle tendon gets impinged at the acromion. This process is commonly caused by a thickened tendon or an inflammation of the overlying bursa leading to an enlargement, thus compressing the subacromial space. Another possible cause for an impingement is a bony subacromial spur resulting in a narrowing of the nerve with pain. A positive Neer sign when elevating the shoulder above 120 degrees is characteristic in the impingement syndrome.
The rotator cuff tear is an example of a traumatic lesion of the rotator cuff where it comes to a rupture of one or more tendons up to the point of a complete tear of the rotator cuff muscles. Often those ruptures have been preceded by degenerative changes in the rotator cuff. The treatment can be either of conservative or surgical nature (e.g. transosseous fixation), depending on the severity of the rupture and the patient’s age.
Even though the rotator cuff consists only of four muscles, it plays an essential role in the stability and mobility of the most flexible joint in the human body: the shoulder.