The shoulder joint is the most mobile in the human body. On the other hand, because of its mobility, it lacks the stability other joints possess. The rotator cuff is composed of four muscles: supraspinatus, infraspinatus, teres minor, and subscapularis. These four muscles, along with ligaments within the joint, help keep the humerus (the bone of your upper arm) center within the joint. When the humerus is lying center in the joint, this allows for optimal movement and force generation throughout the motion whether it’s an overhead lift or simply reaching for something at home or work.
The supraspinatus is the first rotator cuff muscle we will discuss. It gets its name as it lies above (supra-) the spine (-spinatus) of the scapula or shoulder blade. The supraspinatus is responsible for the first 15° of shoulder abduction and acts throughout the movement (shown below). The supraspinatus originates in the supraspinous fossa of the scapula and inserts on the greater tubercle of the humerus. The tendon of the supraspinatus runs beneath the coracoacromial ligament. If there is a tendinopathy (tendinitis or tendinosis) involving the supraspinatus, you may have trouble initiating overhead movements. In such a case, the deltoids must work harder to move the arm overhead.
The infraspinatus lies below the spine of the scapula and externally or laterally rotates the arm. Compared to the teres minor, which is also an external rotator, the infraspinatus is the main driver when the arm is not abducted. It originates in the infraspinous fossa of the scapula and inserts on the greater tubercle of the humerus. External rotation is crucial for overhead throwers and even activities of daily living like combing one’s hair, eating, and shaking hands.
The third rotator cuff muscle is the teres minor. The teres minor originates on the lateral border of the scapula and inserts on the greater tubercle with the supraspinatus and infraspinatus. As mentioned above, the teres minor externally rotates the arm when the arm is abducted to 90° (shown below). The teres minor must not be confused with the teres major which inserts on the lesser tubercle of the humerus and internally rotates, adducts, and extends the arm.
Finally, the subscapularis is the fourth and final rotator cuff muscle. It is primarily an internal or medial rotator of the arm and also assists in extension. The subscapularis is a fan-shaped muscle that originates in the subscapular fossa of the scapula and inserts on the lesser tubercle of the humerus. In addition, the subscapularis tendon runs beneath the short head of the biceps and coracobrachialis. Subscapularis injuries are common in overhead throwers like baseball pitchers.
Stability in the shoulder joint, moving pain-free throughout movements, and having confidence in one’s tissues to manage loads is important to anyone training or performing activities of daily living. As anyone who has had a shoulder pathology knows, pain-free movements with our arms are often taken for granted. In the age of medical imaging, shoulders are commonly subject to MRIs and x-rays. In a study by Tempelhof, Rupp, and Seil, they concluded that as age increases, rotator cuff tears in the absence of symptoms is common. What this means is that as age increases, normal damage to rotator cuff muscles without any pain or functional impairment is typical and does not warrant imaging or surgery as long as movement is pain-free and does not affect function. If you are experiencing some pain in your shoulders as you age, know this is totally normal and can be resolved non-surgically in most cases. Physical therapy intervention for rotator cuff injuries can help patients regain lost motion, make the shoulder more stable, decrease pain, and facilitate the return to activities that were once painful or required compensatory strategies.
Resources
Tempelhof S, Rupp S, Seil R. Age-related prevalence of rotator cuff tears in asymptomatic shoulders. Journal of Shoulder and Elbow Surgery. 1999;8(4):296-299. doi:10.1016/s1058-2746(99)90148-9.
Images
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*Rotator cuff images were taken using Essential Anatomy 5 on iOS*
Aaron Burger | Physical Therapy 
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