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Pectoralis
minor (chest, shoulder, arm, hand pain
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Pain Referral Zone
Pectoralis minor originates on the third, fourth and fifth ribs and inserts on
the coracoid process of the scapula. Its principal function is downward rotation
and stabilization of the scapula. Note that it is involved in any downward
movement or pressure of the arm. It is a common trouble spot for pain. Trigger
points in pectoralis minor typically refer pain to the chest, shoulder, arm and
hand. See below.
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.
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.
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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