The Rotator Cuff Explained! - Thrive Now Physiotherapy

The Rotator Cuff Explained!

Have you ever injured your Rotator Cuff?  This in one of the more common shoulder injuries I encounter on a daily basis.   I often find that my patients do not understand what the rotator cuff is, nor what it does in the shoulder joint—but they do understand that it hurts!

To start with, the rotator cuff is not a thing;  it is basically a collection of four muscles that work together to keep the shoulder joint centered in the socket.   A fifth muscle, the long head of biceps, while not technically part of the rotator cuff, also plays a major role. Muscles attach to bones via a tendon;  the rotator cuff tendons all attach at the front shoulder on the upper arm bone called the humerus.

The four rotator muscles are:


As pictured below, this muscle sits right on top of the shoulder blade (also called the scapula). It’s job is to help lift the arm out to the side but also to work with the other muscles to provide stability. Notably, it is the most often of the 4 muscles to become torn. It also, is the most likely one to develop tendonitis.

The Rotator Cuff Explained


This muscle sits squarely on the back side of your shoulder blade and helps rotate the upper arm bone outwardly, a motion that we call external rotation. Notably, it is usually one of the weakest muscles in the rotator cuff.

The Rotator Cuff Explained

Teres Minor

This muscle acts along with the infraspinatus to help rotate the upper arm bone out to the side.

Rotator Cuff Injuries & Rehab


The subscapularis is in the direct opposite position of the infraspinatus, instead of sitting on the back of the shoulder blade, it sits squarely on the front surface of it. As a result, it  helps control the exact opposite movement, it helps rotate the upper arm bone inwards.

medically accurate muscle illustration of the subscapularis

And, as we mentioned the important:

Long Head of Biceps

As mentioned, the long head of biceps is not technically one of the rotator cuff muscles. However, if you trace the path of its tendon you will see that it actually attaches deep inside the shoulder joint to a piece of cartilage called the labrum. The long head of biceps helps flex the shoulder forwards and it is also frequently torn along with the labrum that it attaches to.

medically accurate muscle illustration of the biceps brachii long head


Their Combined Function

So, now you know what each muscle does individually but what do they do as a group? Well, due to the shallow cup in the shoulder joint, there is an enormous amount of mobility in every direction;  however, this same shallowness leads the shoulder to be very unstable (think of jiggling a tennis ball in a cupped hand).  The rotator cuff basically acts as a timing mechanism to keep the head of the humerus (the ball) centered in the shallow socket on the outside edge of the shoulder blade, especially when your shoulder is raised to shoulder height or above.   Individually, the muscles are quite small and weak, but when working together,  they provide stability to the shoulder joint, to keep the ball and socket in an ideal place.

If you have rotator cuff problems, it is a good idea to have your shoulder assessed and make sure you are doing the appropriate activities to ensure a fast recovery.  Not every shoulder condition will necessarily  involve the rotator cuff, nor will strengthening alone solve every problem.  The physiotherapists at South Cowichan Physiotherapy and Sports Rehabilitation can give you a proper assessment and ensure you are on the road to a speedy recovery!   Call the office today at 250-743-3833 for an assessment.

Written by:



Co-Owner of South Cowichan Physiotherapy

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