Pectoralis minor (chest, shoulder, arm, hand pain):

Translation: "Pectoralis minor" means "the smaller muscle of the breast." It attaches to your third, fourth and fifth ribs (your fifth rib is just under the nipple of your breast), and goes diagonally upward toward your armpit to attach to a bony extension sticking out of the front of your shoulderblade at the upper outer edge. It lies under the pectoralis major; notice in the picture that the pectoralis major has to be pressed out of the way to work on it. Its jobs are to rotate your shoulderblade downward (clockwise seen from behind, counterclockwise seen from in front), and to hold your shoulderblade in place against pressure from your arm. Trigger points in this muscle can cause pain in your chest, your shoulder, your arm and your hand. Its a common source of pain, and frequently overlooked. See below.

Observations on Pectoralis Minor:

If you think about the basic physics of it, when your forearm moves downward, your upper arm wants to move upward. And the harder you push downward against resistance, the harder your upper arm wants to move upward. So in order for your hand and wrist and forearm to move downward and push against anything, something has to hold your upper arm in place.

And that something is the pectoralis minor. It originates on the third, fourth and fifth ribs, and inserts (attaches) on the coracoid process, which is a bony extension sticking out of the front of the shoulderblade at the upper, outer corner. When there is a downward force of the forearm against resistance, and therefore an upward force of the upper arm, the pectoralis minor pulls down on the outer corner of the shoulderblade, keeping the shoulder in place and giving the arm a solid brace to work from, or enabling the arm to push the whole body upward. Such movements include pushing oneself up out of a swimming pool, or even a chair, or away from a table, hammering a nail, climbing a tree or chinning on a bar -- any action that requires downward motion of the forearm.

Now, there are certainly other muscles attached to the coracoid process: the short head of the biceps and the coracobrachialis also insert there. But they are attached to the arm itself, and therefore can't help hold the shoulder down; they can only stabilize the arm in its socket (the glenohumeral joint) to keep the shoulder from becoming disjointed. So it's pectoralis minor that is the real workhorse in these situations, and hardly gets any credit, because almost nobody even knows it's there. That's why it has to notify us of its presence from time to time with pain: pain in the chest, in the shoulder, and all the way down the inside of the arm to the tips of the last three fingers. It can also cause pain or numbness by entrapping the brachial nerve (the main nerve to the arm), which runs directly under it near the top.

Have you ever had your arm go to sleep when it was raised over your head?
That's pectoralis minor pressing against your brachial nerve.

We do need to acknowledge a helper, though: while pectoralis minor pulls down on the outer corner of the shoulderblade, the rhomboids (rhomboid major and rhomboid minor) are pulling up on the inner edge, toward the spine. The rhomboids originate on the vertebrae in your upper back and lower neck (thoracic and cervical) area, and run diagonally down to the inner (medial) edge of the scapula (shoulderblade). So as the shoulderblade rotates clockwise as seen from behind, the rhomboids pull up on the inner edge and pectoralis minor pulls down on the outer corner. That's why pain in pectoralis minor is often accompanied by pain in the rhomboids.

Are there special jobs or activities that are likely to produce pectoralis minor pain? All of us use our arms so much that we are all at risk, but in particular we might think of any situation involving climbing, such as rappelling, phone and electric line repair, house painting and roofing, and any activity that requires a constant downward pressure -- whether a heavy or gentle pressure -- of the arms, such as operating a pneumatic hammer, playing the piano, or, yes, even keyboarding at a computer terminal. Note that the pain referral zones for pectoralis minor overlap those for carpal tunnel syndrome: think twice and get nerve conduction tests before agreeing to surgery.

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