The rotator cuff is the name given to the group of four muscles that are largely responsible for the ability to rotate the arm. Three of the four rotator cuff muscles are deep to the deltoid and trapezius muscles and cannot be seen unless those muscles are first removed and one is on the anterior side of the scapula bone and cannot be seen from the surface.
On the anterior side of scapula bone is a single muscle, the subscapularis. It is triangular in shape and covers the entire bone. Its origin is along the fossa that makes up most of the “wing” of the scapula and it inserts on the lesser tubercle of the humerus bone. The subscapularis muscle is shown in Figure 9-1.
On the posterior side of the scapula bone are the other three muscles of the rotator cuff. All three insert on the greater tubercle of the humerus, allowing them, in combination with the subscapularis, to control rotation of the arm. The supraspinatus muscle is above the spine of the scapula. The infraspinatus muscle is below the spine of the scapula. The relatively thin teres minor muscle is the most inferior of the rotator cuff muscles. The three posteriorly-positioned muscles of the rotator cuff are shown in Figure 9-2.
The teres major muscle has its origin on the scapula, like the rotator cuff muscles, but is not involved in rotating the arm. It inserts lower on the humerus than the rotator cuff muscles and is involved in adducting the arm (bringing it closer to the midline of the body.)
Lab 9 Exercises 9.1
- Using the full-scale arm model, locate and identify all four muscles of the rotator cuff, as well as the deltoid muscle and the teres major muscle.
- The following are muscles of arm rotation and adduction. For each, give its origin(s) and insertion(s) and whether or not it is part of the rotator cuff.
|Muscle||Origin(s)||Insertion(s)||Part of rotator cuff?|