In this section I aim to provide you with a detailed understanding of the rotator cuff muscles.

In a previous sections on rotator cuff anatomy I highlighted the role that the rotator cuff muscle has within the shoulder.

Not only are your cuff muscles involved in the movement of the arm but they are a key part in maintaining the stability of the whole shoulder joint.

Let us start by reviewing the very basics. The cuff muscles are a group of four skeletal muscles that are present in the shoulder.

The four muscles are individually the Subscapularis, the Infraspinitus, the Teres Minor and the Supraspinitus (SItS). They all connect the Scapula or shoulder blade to the head of the Humerus or upper arm bone.

As you will see however each of the cuff muscles has a different job to do. That is why adopting a suitable range of rotator cuff exercises or rotator cuff stretches is so important.

There is no one exercise for all the rotator cuff muscles. If you want to avoid the pain of having to undergo rotator cuff surgery in the future then this information is important to you.

The Infraspinatus muscle

The Infraspinatus muscle is a thick triangular muscle. The Infraspinatus muscle occupies the major part of what is known as the infraspinatous fossa as shown above. It attaches to the infraspinous fossa of the scapula and to the greater tubercle of the humerus.

The Infraspinatus muscle fibers converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder joint, is inserted into the middle impression on the greater tubercle of the humerus.

The Infraspinatus muscle is supplied by both the suprascapular and circumflex scapular arteries and is innervated by the suprascapular nerve.

The Infraspinatus muscle is an external rotator of the shoulder joint and adductor of the arm. The Infraspinatus and Teres minor rotate the head of the humerus outward (external rotation); they also assist in carrying the arm backward.

It is known that the infraspinatus muscle is the major external rotator of the shoulder in comparison with the teres minor.

The Subscapularis muscle

Subscapularis muscle seen from the front through the ribs

The Subscapularis is another large triangular shaped muscle. The Subscapularis muscle fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint.

The Subscapularis muscle fibers end in a tendon which is inserted into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint.

The Subscapularis muscle is supplied by the Subscapular artery and is innervated by the upper and lower subscapular nerves

The Subscapularis muscle has two major roles. Firstly it helps to rotate the head of the humerus medially, that is internal rotation and secondly when the arm is raised, it draws the humerus forward and downward.

It is one of the more powerful cuff muscles acting on shoulder joint, preventing displacement of the head of the humerus.

The Supraspinitus muscle

The supraspinatus is a relatively small muscle that has its origin in the supraspinous fossa superior to the spine of the scapula. The Supraspinatus muscle abducts the arm at the shoulder. The Supraspinatus muscle is the most often injured of all rotator cuff muscles.

The supraspinatus muscle arises from the supraspinous fossa which is a shallow depression in the scapular above its spine. The supraspinatus muscle tendon passes beneath the acromion. The tendon is inserted into the most superior facet of the greater tubercle of the humerus.

The supraspinatus muscle is innervated by the suprascapular nerve is also supplied by the subscapular artery.

The supraspinitus muscle abducts, or lifts, the arm and is the major contributor for the first 30 degrees or so. After this point the deltoid muscle pretty much takes control.

The Teres Minor muscle

The Teres Minor muscle originates from the dorsal surface of the axillary border of the scapula. It connects to the lowest of the three impressions on the greater tubercle of the humerus.

The Teres Minor muscle is innervated by the axillary nerve that also innervates the Deltoid muscle. The Teres Minor muscle is supplied by the posterior circumflex humeral artery and the circumflex scapular artery.

The Teres Minor muscle works with the Infraspinatus muscle to laterally rotate the arm. Occasionally muscle fibres from both can become fused.

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