Sep 2014 27

The rotator cuff

By: Dave Wheeler

Research by the Derbyshire Royal Infirmary in 2007 showed that painters & decorators, people using vibrating tools (such as workers on roads) and those working overhead all tended to have more problems with their rotator cuff muscles.

If you're into weight-training, a golfer, a swimmer or a climber, statistically you're also more likely to develop problems with your rotator cuff through over-use.

So what is the rotator cuff?

It's a collection 4 muscles that surround the shoulder joint:


The muscles of the rotator cuff

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The function of the rotator cuff group

Before looking at each of the 4 muscles in turn, let's look at the job of the rotator cuff as a group.

The shoulder joint has an amazing range of movement, allowing the arm to go backwards, forwards, sideways, up and down.

To allow this big range of movement, the bone of the upper arm bone (the humerus) ends in a ball that sits in a shallow socket at the edge of the shoulder blade (scapula).

This particular part of the shoulder is called the glenohumeral joint.


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Because the socket in which the humerus sits is so shallow, muscles and tendons have the job of keeping it in place whilst still allowing the range of movement of the arm that's needed.

The 4 muscles of the rotator cuff which sit around the shoulder joint (as a cuff!) work together to stabilise the shoulder during movement.


The 4 rotator cuff muscles

As well as working together to stabilise the shoulder, each of the individual rotator cuff muscles has it's own function in moving (or articulating) the arm.


1. Supraspinatus

The supraspinatus muscle lies across the top of the shoulder blade and attaches along the top and just down the side of the ball of the humerus:


The supraspinatus muscle of the rotator cuff

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If you look at the picture and imagine the supraspinatus muscle contracting, then you'll realise that it'll pull on the top of the arm causing it to start moving up to the side.

So the supraspinatus initiates movement of the arm upwards to the side (this is movement is called abduction).

It's only a little muscle, so it's not strong enough to pull the arm all the way up - all it does is get the movement started. Once the arm's moved about 15 degrees then the larger deltoid muscle on the side of the upper arm takes over to do the big work of abducting the arm further.

Look again at the picture above of the supraspinatus - can you see how it tunnels under a piece of bone at the top outer edge of the shoulder blade? This projection of bone is called the acromion. The gap between the acromion and the ball of the humerus is very narrow.

If in your work or your sport you do a lot of moving your arm out to your side (especially if it's with weights such as sideways lat raises with dumbells), then the supraspinatus muscle will grow. Sometimes it can grow so much that it starts to rub against the bone of the acromion, causing pain.

There's a fairly easy test that your remedial massage therapist or physiotherapist can do to check whether the supraspinatus is damaged in this way. If it is, then the answer is to minimise the activity that's causing the problem.

(Sometimes physiotherapists call the supraspinatus the rotator cuff - so if you've been told that you have a rotator cuff tear by a physio, chances are they mean the supraspinatus.)


2. Teres Minor

The teres minor muscle run diagonally upwards across the top of the gap between your shoulder blade and your humerus (the bone of the upper arm). It's also a small muscle.


The teres minor muscle of the rotator cuff

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It's function is to rotate the arm outwards.

To understand outward rotation, put both arms out  horizontally to the side, then bend your elbows and allow your lower arms to hang down - like a scarecrow! Now keeping your upper arm horizontal and your elbow  still, rotate your lower arm and hand upwards, so that it no longer faces down, but faces straight up. That's outward rotation of the shouler.

It's really common for swimmers who do butterfly or front crawl to overuse the teres minor during their stroke; climbers, too, get a lot of trouble from this little muscle. Golfers, too, use this muscle a lot on the backswing.


3. Infraspinatus

The infraspinatus is a large flat muscle that fills the lower scoop of the shoulder blade.


The infraspinatus muscle of the rotator cuff

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The function of the infraspinatus is exactly the same as the teres minor - it is responsible for outward rotation of the arm. In anatomical terms, we say that the infraspinatus and the teres minor are complete synergists.


4. Subcapularis

The subscapularis sits on the other side of the shoulder blade - facing forwards in towards the body.


The subscapularis of the rotator cuff

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Because teres minor and infraspinatus sit at the back of the shoulder blade and attach to the back of the humerus, they rotate the arm outwards.

On the other hand, the subscapularis sits on the inside of the shoulder blade, facing the front  and it attaches to the front of the upper arm bone, so it has the opposite function - in other words, inwards rotation.

Because the subscapularis does the opposite to the teres minor and infraspinatus, it's calle the antagonist of those two muscles.

Again, swimmer and climbers are the obvious people who use their subscapularis a lot.


Keeping the rotator cuff muscles in good shape

Remember, not only do the individual muscles of the rotator cuff rotate your arm inwards or outwards, or start the raising of your arm, they also work together as a group to stabilise the shoulder joint itself.

Your work, lifestyle or sport might mean that one of these muscles becomes proportionally bigger and stronger than the other. Sports massage techniques can help to relax and stretch out over-used muslces; it's work that requires your sports massage therapist to know their anatomy well and to understand how you're using your shoulder.

Your therapist should also be able to give you strengthening exercises to make sure that the rotator cuff stays balanced and work properly together.

As always, if you think I can help, give me a call.