Joint Knowledge: The Rotator Cuff

The shoulder is a remarkable joint!  It performs the upper body’s most powerful functions and allows for an intricate and complex range of motion. The muscles around the shoulder have been responsible, in part, for the rapid advance of primate evolution.

 

They are even important in human-to-human communication, helping convey frustration…

 

joy…

 

…and confidence.

 

The muscles that surround the shoulder joint are known as the rotator cuff. They help the shoulder perform all of its complicated and powerful movements of rotation (hence the name).

 

While the rotator cuff is present in most vertebrates, it is most pronounced in the primates including us humans. Monkeys and orangutans spend much of their lives in trees and must engage in constant climbing and swinging motions, requiring that the arms go above the head.  While we don’t do those activities much, we do use our rotator cuffs to perform all sorts of movements: mundane ones like brushing hair and awe-inspiring ones like 120 mile-per-hour tennis serves.

 

The Bones and the Little Joints

To get to know the rotator cuff muscles, let’s review the bones of the shoulder joint.

Three bones meet at the shoulder: the clavicle (or collarbone), which coasts over the top of the joint; the scapula, (or shoulder blade) a flat triangular bone; and the humerus, or arm bone.

The shoulder is complex and is, technically, made up smaller joints.  In fact, the shoulder is often called the shoulder complex.

The head of the humerus and a part of the scapula called the glenoid cavity form the ball and socket joint known as the glenohumeral joint. This is what we usually think of as “the shoulder joint.”

Over the top of the ball and socket, an extension of the scapula called the acromion forms the roof of the shoulder joint.

Just before the clavicle ends near the outside of the shoulder, it meets the acromion. Thus, the area is called the acromioclavicular joint, also known as the AC joint.

 

The Muscles

When a muscle crosses over a joint, it can contract and allow one of the joint’s bones to move in whichever direction that the crossover tendon is oriented. Think of you and a friend holding playing tug-of-war: if you pull on the rope, your friend moves towards whichever way the rope is moving.

All of the “crossover” muscles of the shoulder start on the scapula and land on the head of the humerus.  They surround the head of the humerus and allow it to move in several directions.  The glenohumeral joint has four of these “crossover” muscles, and they make up the rotator cuff. Let’s learn about these four marvelous muscles.

 

Supraspinatus

The supraspinatus muscle coasts over the top of the spine of the scapula on the backside, and inserts on the top of

the head of the humerus. When it contracts, it allows the arm to move away from the body, a type of motion called abduction. This muscle allows for jumping jacks or airplane arms (along with the larger deltoid muscle).

 

Infraspinatus

The infraspinatus, as its name suggests, floats under the spine of the scapula on the backside, and inserts on the back of the humeral head. This muscle is responsible for external rotation the shoulder, an action that allows for making the hitchhiking sign or swinging a backhand stroke in tennis.

 

Subscapularis

Along the front side of the scapula, on the opposite side of the infraspinatus, is a muscle called the subscapularis. This muscle extends from the scapula to the front side of the humeral head, allowing it to internally rotate. The subscapularis is what gives a “thumbs down,” serves a tennis forehand, or pours a glass of water. Large and versatile, this muscle also keeps the head of the humerus in its socket when the arm is raised above the head, allowing a person to raise a hand to ask a question, to shoot a basketball or hang up clothes.

 

Teres Minor

Another long, narrow muscle called the teres minor is located just below the infraspinatus and behind the subscapularis. It ends on the side and back of the head of the humerus. Accordingly, the teres minor splits the role of its neighbor muscles, helping with external rotation of the shoulder and stabilizing the humeral head when the arm is raised.

 

The Rotator Cuff in Sport

Several sports make use of explosive and violent contractions of these four muscles, making them vulnerable to impact and shear injuries. The most well-known of these is a rotator cuff tear, occurring when the tendon of one of the four muscles is partially or totally ruptured. Minor rotator cuff injuries, like contusions and tendonitis, can heal either by themselves or with physical therapy. Major rotator cuff injuries like tears often require surgery.

 

Athletes most prone to rotator cuff tears include:

• Baseball players (especially pitchers)
• Football players (especially quarterbacks)
• Javelin throwers
• Shot putters
• Tennis players
• Rugby players
• Wrestlers
• Ultimate players
• Golfers
• Bowlers

 

Care for the “Cuff”

 Since the muscles of the rotator cuff are prone to be overtaxed, it is crucial to care for them before and after participating in events that are likely to utilize them extensively.   Baseball pictures and football quarterbacks spend much of their time between games on shoulder strengthening exercises, often isolating each muscle with targeted weight training. Ice and rest are also important, and compression sleeves for the shoulder girdle have become increasingly popular.

Whether for serious athletes, weekend warriors, or those just up for the occasional game of catch, the rotator cuff allows the body to carry out remarkable functions. Improved understanding of the structure and purpose of this group of muscles leads to better care of these muscles, allowing everyone to enjoy the benefits of this formidable aspect of anatomy.

References

Craik, J. D., Mallina, R., Ramasamy, V., & Little, N. J. (2014). Human evolution and tears of the rotator cuff. International Orthopaedics, 38(3), 547–552. https://doi.org/10.1007/s00264-013-2204-y

Chang LR, Anand P, Varacallo M. Anatomy, Shoulder and Upper Limb, Glenohumeral Joint. [Updated 2020 Mar 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537018/

Jeno SH, Schindler GS. Anatomy, Shoulder and Upper Limb, Arm Supraspinatus Muscle. [Updated 2020 Mar 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537202/

Williams JM, Obremskey W. Anatomy, Shoulder and Upper Limb, Infraspinatus Muscle. [Updated 2020 Mar 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513255/

Aguirre K, Kiel J. Anatomy, Shoulder and Upper Limb, Subscapularis Muscle. [Updated 2020 Mar 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513344/

Juneja P, Hubbard JB. Anatomy, Shoulder and Upper Limb, Arm Teres Minor Muscle. [Updated 2019 Feb 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513324/

Varacallo M, El Bitar Y, Mair SD. Rotator Cuff Tendonitis. [Updated 2020 Mar 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532270/