What is a Rotator Cuff?

(Originally posted on bcotoronto.com on June 21st, 2012)

In sports and in life in general we always hear about “Rotator Cuff” injuries or someone tells us, “I can’t do that, I hurt my rotator cuff”. We know it has something to do with the shoulder and can be fairly limiting once it is injured but what exactly is a rotator cuff? Well, that is answered very simply. Our rotator cuff is a group of four muscles that run from our shoulder blade (scapula) to our arm (humerus) and hold it in place.

These muscles are called the Supraspinatus, the Infraspinatus, the Subscapularus, and Teres Minor. The Supraspinatus muscle runs on the top side of the scapula, from the edge closest to the spine and out to the top surface of the humerus. It is paired with the Infraspinatus muscle that runs just below it along a similar path and attached to the back surface of the humerus. The Subscapularis, as the name suggests, is on the opposite side of the scapula between the scapula and the rib cage. It travels from the edge closest to the spine and out to the front side of the humerus directly underneath our Pectoralis muscles (the “Pecs”). The Teres minor muscle is a little muscle that mimics the pathway of the Infraspinatus. It originates of the outer edge of the scapula (the back wall of the arm pit) and grabs onto the humerus directly below where the Infraspinatus does. As I said before, these muscles are responsible for keeping the head of the humerus on the surface of the scapula.

Anterior (Front) Rotator Cuff Muscles

Anterior (Front) Rotator Cuff Muscles

 

Posterior (Back) Rotator Cuff Muscles

Posterior (Back) Rotator Cuff Muscles

The surface of the scapula where the humerus meets it is shaped like a very shallow bowl or cup. The humerus has a swelling at the top (the “head”) that fit into this cup. The best way to think about the shoulder joint is the image of a cane hanging from a shelf. There is very little connection between the two surfaces, and the support is precarious. In a properly functioning and aligned shoulder joint, the weight of the arm is supported by the scapula and the very large muscle that support the scapula and the small muscles that make up the rotator cuff only have to provide a small amount of force to pull the humerus horizontally to secure it’s connection to the scapula. But this is not the case in the majority of people.

Anterior (Front) Shoulder Bony Anatomy

Anterior (Front) Shoulder Bony Anatomy

 

Posterior (Back) Shoulder Bony Anatomy

Posterior (Back) Shoulder Bony Anatomy

As we have talked about over the past two weeks, bad posture is extremely common in our society and the most common postural malpositioning is a slouched thoracic spine and shoulders that are rolled forward. So if we took our shelf and rolled it forward (angling it down), what would happen to the cane? It’s going to fall off the shelf. Now what do you think is stopping our arm from falling off the shelf of our scapula? The rotator cuff! This means that the rotator cuff has gone from giving the humerus a slight pull to keep it on the scapula to holding the weight of the entire arm and any load that we are carrying. These four muscles are under a huge amount of strain they are not made for.

This stress causes them to become spasmed, tight, and very commonly painful. Painful trigger points in these muscles can refer pain or tingling sensations all the way down to the fingers. When muscles get to be so tight and spasmed as this the blood flow through them is limited and they do not get the proper nutrition or lubrication they need. Any tissue without the proper nutrition will become weak and fragile over time. This is why rotator cuff injuries are so common in western culture. Unhealthy muscles lead to increased risk of injury to those muscles.

An injured rotator cuff can be quite limiting. It heals incredibly slowly because it continues to be under strain from poor posture and causes a lot of pain. When the muscle merely strained it is difficult to carry anything with substantial weight and even to lift your arm. So you can imagine what it would be like with a muscle that is actually torn.

So my recommendation, if you wish to be able to carry your own groceries or lift up your kids or grandkids, is to improve your posture and make sure to get enough shoulder exercise, and drink lots of water. This will help keep your rotator cuff muscles happy and healthy for a long time. If you do injure your rotator cuff, your healing will be much easier, faster, and in the end better if you see a professional. Pain killers and muscle relaxants will not cut it. Find a chiropractor, massage therapist, or physiotherapist near you and reap the benefits of healthy muscle and posture.

Thanks for reading,
Dr. Ben

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