Rotator Cuff Muscles - An In-Depth Guide

The rotator cuff muscles are a group of four skeletal muscles located in the shoulder. They are 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.

Rotator cuff anatomy is unlike anything else in the human body. Each of the muscles has a distinct job to do. At the same time they all work together to provide stability and strength to the shoulder.

The Supraspinitus muscle

The supraspinatus is a relatively small muscle. The Supraspinatus muscle is responsible for abducting (lifting) the arm at the shoulder. It is the major contributor to arm movement for the first 30 degrees; after that the Deltoid muscle takes over. The Supraspinatus muscle is the most often injured of the rotator cuff tendons.

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 Subscapularis muscle

The Subscapularis is a relatively large triangular shaped muscle. The Subscapularis musclefills 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 is responsible for two things. Firstly, it helps to rotate the arm internally rotation. Secondly, when the arm is raised, it draws the humerus forward and downward. It is one of the more powerful rotator cuff muscles acting on shoulder joint, preventing displacement of the head of the humerus.

The Infraspinatus muscle

The Infraspinatus muscle is a thick triangular muscle. The Infraspinatus muscle occupies the majority of the infraspinatous fossa. It attaches to the infraspinous fossa of the scapula and to the greater tubercle of the humerus.

The Infraspinatus muscle is an external rotator of the shoulder joint and an abductor 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 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 works with the Infraspinatus muscle to internally rotate the arm. Occasionally muscle fibres from both the Teres Minor and the Infraspinatus can become fused.

How does this knowledge help us?

We now know the cuff is a group of distinctly different muscles. It is because of these differences that we know adopting a range of rotator cuff exercises or rotator cuff stretches is so important. This is especially true if doing rehab for a tear, strengthening or recovering from rotator cuff surgery.