The rotator cuff is an anatomical term that is applied to define a group of four distinct muscles in the shoulder region that stabilize and strengthen the glenohumeral (shoulder) joint and allow rotational movements of the humerus. The rotator cuff is comprised of the following four muscles:

• Supraspinatus (Read more!)
• Infraspinatus (Read more!)
• Teres minor (Read more!)
• Subscapularis (Read more!)

These muscles are also commonly referred to as "SITS" muscles. Each capital letter in the mnemonic refers to the first letter of the muscle name. All these muscles arise from the scapula and insert into the humerus, forming a musculotendinous envelope around the shoulder joint.

Structure and functions of rotator cuff

The primary function of all rotator cuff muscles is to stabilize the glenohumeral joint by compressing the head of the humerus against the glenoid cavity of the scapula. The shoulder joint is a ball and socket type joint, meaning it allows one to perform a wide variety of movements. Therefore, it lacks bony stability and is considered an unstable joint. That is why it is stabilized collectively by non-contractile or static (i.e., joint capsule, labrum, ligaments) and contractile or dynamic (i.e., rotator cuff muscles, long head of the biceps brachii) tissues.

As mentioned previously, the rotator cuff is a musculotendinous structure. All four rotator cuff muscles originate from the landmarks of the scapula, and their tendons insert into the greater and lesser tubercles found on the proximal end of the humerus. The muscles of the rotator cuff transition into tendons as they come near their insertion sites. 

All rotator cuff muscles insert near to each other. They surround the shoulder joint and blend not only with each other but also with the joint capsule of the shoulder joint. This tissue union forms a musculotendinous collar that surrounds the joint anteriorly, posteriorly and superiorly. Hence, the name of the muscle group. Balanced strength and flexibility in these muscles are essential to maintain the functioning of the entire shoulder region. 

As the name of the muscle group also suggests, they not only stabilize the shoulder joint but also contribute to movements performed at the shoulder joint. These muscles mostly act as rotators, providing internal (medial) or external (lateral) rotation of the upper arm. Additionally, the supraspinatus is the only muscle of the group that does not act as a rotator. Instead, it activates during arm abduction.