Have you ever heard the term rotator cuff, but wondered what it is? Maybe you’ve had a rotator cuff injury but were never shown shoulder anatomy, and were left feeling confused. Well, we are here to break it down and make it simple. By understanding shoulder anatomy, you can better understand why your physiotherapist gives you those funky exercises, why your shoulder may be painful in certain places, or why particular movements may make your pain worse.
The rotator cuff is a common sight for shoulder injuries and pain but many patients struggle to understand its anatomy. The rotator cuff is made up of four muscle groups (sometimes 5 depending on who you ask) with the acronym S.I.T.S - referencing the first letter of each muscle - Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis. Some practitioners will also include the Long Head of the Biceps in this grouping as well.
Let’s dive a little deeper into each muscle group…
Supraspinatus Muscle: This is the most superior muscle of the rotator cuff, sitting on the top portion of the scapula (shoulder blade) in a gully called the supraspinatus fossa. The tendon runs through a narrow space in the shoulder complex and attaches to the humerus (arm bone). Because of this muscle's orientation, it commonly gets compressed or squashed due to poor shoulder posture or biomechanics.
Its main action is to lift the arm out to the side, or abduction, for the first 10-15 degrees. It also assists the deltoid in abduction between 15-90 degrees.
Infraspinatus Muscle: Sits on the back of the shoulder blade and attaches to the outer side of the head of the humerus.
Its main action is to rotate the shoulder outwards (external rotation) and helps with extending the arm back..
Teres Minor: This muscle sits very close to the infraspinatus on the back of the shoulder blade but is much smaller, and also attaches to the outside of the head of the humerus.
Similar to the infraspinatus, its main action is to externally rotate the shoulder and assist with extension of the arm.
Subscapularis: This is the largest and strongest muscle of the rotator cuff. It sits on the front of the shoulder blade, between the shoulder blade and the ribcage, and attaches to the front of the humerus.
Its main action is to rotate the shoulder inward (internal rotation)
Understanding the four main muscles of the rotator cuff, their orientation, and the actions they are responsible for can help you comprehend why certain positions or movements may cause pain.
The Role of the Rotator Cuff
The rotator cuff is responsible for creating stability of the shoulder while assisting with movement. The four muscle groups form a “cuff” around the shoulder to aid in its stability, hence the term rotator cuff. The anatomy of the shoulder joint is inherently unstable, with a large humeral head making contact with the shallow surface of the scapula. In practical terms, think of a golf ball sitting on a golf tee, this seems unstable right? A small force could cause instability to the golf ball or cause it to fall off altogether. This rings true for the shoulder as well. The rotator cuff keeps the “golf ball on the tee” increasing the stability of the joint.
The rotator cuff is also involved in almost every movement of the upper limb, providing the “fine-tuning” of the shoulder. When you throw a baseball the rotator cuff is working, when you carry your groceries the rotator cuff is working, when you type at your desk… guess what, the rotator cuff is working. A healthy rotator cuff means you can type for 8 hours during a workday pain-free, while also heading to a tennis match and producing big forceful swings with confidence. It’s important to have a balance of strength and flexibility in these muscle groups to maintain good function of the entire shoulder complex.
It is well documented that if the balance of strength and flexibility is unequal in the rotator cuff, this then leads to dysfunction, pain, and impaired capabilities.
Common Rotator Cuff Injuries
Rotator cuff injuries can occur at any age. In the younger population, we typically see rotator cuff injuries from a trauma (like a fall) or from overuse with overhead activities (i.e. volleyball, baseball, and swimming). In the older population, rotator cuff injuries are typically due to impingement, and muscle degeneration, which can lead to calcification and tears. Poor biomechanics of the shoulder, like having rounded shoulders at your desk, can prematurely affect the quality of the rotator cuff muscles and tendons due to constant pressure and friction, making it more likely to develop pain, inflammation and tears.
The most common rotator cuff injuries are:
Rotator Cuff Tendonitis (acute inflammation of the tendon)
Rotator Cuff Tendinopathy (chronic inflammation and disorganization of the tendon)
Rotator Cuff Tears (small or large tear(s) of the muscles or tendons)
Impingement Syndrome (biomechanical dysfunction of the shoulder complex resulting in abnormal wear and tear)
Common Symptoms of Rotator Cuff Injuries
The most common symptoms of a rotator cuff injury are:
Pain on the front or side of the shoulder, often radiating down the arm
Painful range of motion, most commonly above shoulder height or when lifting the arm through abduction, external and internal rotation.
Muscle Weakness, most commonly in abduction and external rotation.
Functional Impairments - unable to push or pull without pain, lift overhead, or hand behind the back
It is worth noting that not all rotator cuff injuries are marked with pain or loss of function. Some people may have a significant tear on a scan but no loss in function or reported pain.
With all of this additional information about the rotator cuff, we hope you have a better understanding of the anatomy of the shoulder. Understanding the “why” behind your rehabilitation or the causes of your pain can be a powerful tool in your recovery.
If you have more questions reach out to your local physiotherapist. If you live locally in Port Alberni, reach out to one of us at www.portalberniphysiotherapy.ca or call us at 250-723-5112.