The rotator cuffs are made up by four muscles, these are the supraspinatus, infraspinatus, teres minor and subscapularis. These muscles aid in keeping the upper arm and shoulder into the socket with stability. They also each allow specific movements at the shoulder joint. The group of four muscles all originate within the shoulder blade, but all insert into different portions of the upper arm bone.
Supraspinatus: This muscle originates at the supraspinous fossa; the muscle belly passes laterally over the acromion process and inserts into the greater tubercle of the humerus bone. This muscle allows the first 15 degree’s movement of abduction, after this the deltoid and trapezius muscles will then allow further motion.
Infraspinatus: The origin of the infraspinatus is the infraspinatus fossa, and the insertion is also the greater tubercle of the humerus. The motion created by this muscle is lateral rotation of the shoulder, moving the arm away from the centreline of the body.
Teres Minor: A small narrow muscle on the back of the shoulder blade which sits underneath the infraspinatus. The origin is the lateral boarder of the scapula. This muscle contributes to external rotation of the arm of the body.
Subscapularis: This rotator cuff is the strongest and largest out of the three listed above. This muscle originates at the subscapularis fossa and inserts into the lesser tubercle of the humerus. The subscapularis allows greater motion at the shoulder and mainly aids in allowing medial rotation of the arm.