Serratus Anterior…Part 11 of the grumbly muscle blog…

What is a serratus anterior and what does it do?

It’s known as the boxer’s muscle, not least because you can see it clearly defined on boxers with its classic serrated edge viable just below the arm pit, and because it helps protract the shoulder blade (brings the shoulder blade round) so you can punch, reach forward, or push away.

Additionally, it upwardly rotates the scapula (shoulder blade) with assistance from the trapezius (traps) muscle, so we need it when we do pretty much any arm and shoulder movements.

It also helps, again with help from the traps and rhomboids to posteriorly tilt the shoulder blade and outwardly rotate, and also helps to maintain something called the subacromial space, meaning it allows the bones in the shoulder joint to move and not impinge on one another. Reduction in the subacromial space can lead to tendon impingement and this is rather painful.

Finally, it ‘hugs’ he shoulder blade on to the rib cage and can lift the rib cage when we’re out of breath to help our breathing.

Its considered one of the main shoulder stabilizers, along with the traps, and rhomboids.

Anatomy

The muscle originates in a fan shape from ribs 1-8 and sometimes rib 9 as well.

It then inserts on the underside of the scapula.

It’s innervated by the long thoracic nerve which come from the nerve roots of C5-C7 in the neck.

What happens when it doesn’t work properly?

During an initial visual assessment sometimes you can see someone’s scapula ‘winging’, the medial boarder of the shoulder blade will just stick out awkwardly which is called pseudo-winging it’s a sign that the muscle is not functioning properly (see pictures). 

Other times you have to see it in action to spot it. All wall press is usually sufficient to spot dysfunction on this muscle.

When this muscle is weak, other muscles ‘take over’ which is why the scapula is left with an inwards tilt and internally rotated. Left unchecked, a little-known muscle called pectoralis minor makes the anterior tilt somewhat worse. Characteristically, you can see the bottom of the shoulder blade stick out prominently from the rib cage.

If this muscle is weak, it can also lead to altered function of the rotator cuff muscles which can lead to reduction of the sub acromial space and pain from sub acromial pain syndrome (SAPS); in short when you raise your arm, you experience pain and reduced range above 90-120 degrees.

It can refer pain down the inside of the arm and to the ring and little finger.  It can become very tender around the 5th-7th rib, can also refer pain between the shoulder blades and on the inside of the elbow which could make you think you have golfers’ elbow (medial epicondylitis).

What could lead to this happening?

Serratus anterior palsy can be commonly caused by damage to the long thoracic nerve during neck and shoulder surgeries. Other causes include strenuous work, physical trauma, infection, anaesthesia, Parsonage-Turner syndrome, Fascio-scapulo-humoral dystrophy (FSHMD) or idiopathic cause (the cause is unknown). Additionally, you can get neuropraxia of the nerve from stretch injuries or compression.

The muscle can also ‘avulse’ (be torn off) the scapula bone.

What can we do about it?

Strengthen the hell out of it, and the other shoulder stabilisers at the same time! Massage might ease pain around the ribs, but you can’t get to the underside of the shoulder blade and you can’t foam roll it. Strengthen, Strengthen, Strengthen!!

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