The complexity of the shoulder can be perceived as a blessing and a curse. Perfect synchrony of the many elements of the shoulder translates in superb joint performance. And at the same time, each of these elements can develop problems, hurt and become disabling. Amongst the muscles of the shoulder region, the pectoralis minor is one of these elements that will occasionally become the sole reason for pain and loss of function. Many are not aware of this relatively uncommon condition, the pectoralis minor syndrome; but for those few patients that suffer from it, a somewhat simple solution does exist.
Tell me more about this muscle…
The big muscle that covers the front of the upper chest wall is the pectoralis major, very well known by those who like to lift weights. The pectoralis minor is smaller and deeper than the pectoralis major. The muscle fibers of the pectoralis minor originate from the 3rd, 4th and 5th ribs. These fibers travel obliquely (up and out) to coalesce into a tendon that attaches to a prominence of the shoulder blade named coracoid. When the pectoralis minor contracts, it tilts the shoulder blade in space three-dimensionally: the shoulder blade becomes slightly more parallel to the floor, and it is pulled down and forward, so that when seen from the back, the lower part of the shoulder blade tips out. And what lies right behind the pectoralis minor?: the blood vessels and nerves in route to the arm. These blood vessels are called subclavian (sub – under, clavian – collarbone) or brachial (arm) artery and vein. The accompanying bundle of nerves is called brachial plexus.
Pectoralis minor syndrome: what is it?
The term “syndrome” is used in Medicine and Surgery to lump a group of abnormalities which consistently occur together. Since the pectoralis minor connects the shoulder blade to the chest, and at the same time is close to nerves and vessels, the term pectoralis minor syndrome implies (1) abnormal mechanics of the shoulder blade plus (2) abnormalities involving the adjacent nerves and vessels. Some individuals with pectoralis minor syndrome will have every abnormality (shoulder blade, nerves and vessels) whereas other will only complaint of a fraction of symptoms.
Why would the pectoralis minor start to abnormally move the shoulder blade or to compress on the nerves and vessels behind? Most agree on four main reasons: (1) the pectoralis minor was injured in an accident, and when it healed it became shorter, scarred and inelastic; (2) the pectoralis minor has become very large over time (typically in athletes, where the practice of sports has led to muscle hypertrophy [hyper – large, trophy – growth]); (3) the individual was born with an abnormal pectoralis minor; or (4) a separate condition has kept the shoulder blade forward and down, and over time the pectoralis minor has shortened to accommodate the new position of the shoulder blade.
Evaluation of patients with possible pectoralis minor syndrome.
Individuals suffering with pectoralis minor syndrome may complain of shoulder pain, muscle contractures around the shoulder blade, limited movement of the shoulder, abnormal rubbing of the shoulder blade with the ribs (also called scapulothoracic crepitus), coldness in the hand and arm, numbness and tingling also in the hand and arm, and weakness.
When for any reason the shoulder blade cannot be moved well relative to the chest wall, surgeons use the term scapular dyskinesis (scapula – shoulder blade, dys – poor, kinesis – motion). Many conditions can lead to scapular dyskinesis, and an abnormal pectoralis minor is one of them. Similarly, the blood vessels and nerves of the arm can get squeezed in multiple locations. Compression of both the vessels and the nerves at the neck, under the collarbone or behind the pectoralis minor is called thoracic outlet syndrome, (thoracic – chest, outlet – exit point). As such, an abnormal pectoralis minor can be one of the multiple reasons for thoracic outlet syndrome. The role of the surgeon is to identify the constellation of symptoms that result from pectoralis minor syndrome, and at the same time rule out alternative reasons for the same symptoms.
What does this all mean in terms of evaluation? Surgeons looking for pectoralis minor syndrome will use one of several tests. The shoulder and shoulder blade are carefully examined, and not uncommonly the surgeon will notice that the lower pole of the shoulder blade tips out in comparison to the opposite side. The distance between the tip of the coracoid (which can be felt through the skin) and the center of the chest may be different from side to side. Deep pressure just inwards to the tip of the coracoid (over the pectoralis minor location) will be painful and may lead to numbness and tingling, which can be even more severe when poking several times over the location of the pectoralis minor (this is called Tinel sign). If the surgeon pulls the shoulder of the patient backwards, pain, numbness, tingling and coldness may worsen, and sometimes even the pulse at the wrist becomes fainter.
What about testing?
One frustrating feature of the pectoralis minor syndrome is that oftentimes all possible tests for evaluation are negative. Test that are oftentimes considered include (1) an electromyogram with nerve conduction studies (EMG) to assess the nerves; (2) some type of image with contrast (dye) that delineates the blood vessels (angiogram on xrays, computed tomography, or magnetic resonance), in order to determine whether the blood vessels become narrow as they pass behind the pectoralis minor; and (3) magnetic resonance or ultrasound to assess the pectoralis minor and brachial plexus. The degree of compression by the pectoralis minor can change with the position of the arm (this is called dynamic compression), which is why these tests may be normal in the resting position. Of all tests mentioned, ultrasound provides the best ability to assess for dynamic compression. Also, the pectoralis minor may be injected with a local anesthetic or corticosteroids while the muscle is visualized with ultrasound as another diagnostic test.
Any alternatives to surgery?
Yes. Physical therapy seems to work well for the majority of individuals with pectoralis minor syndrome. The main exercise recommended is called unilateral corner stretch or horizontal abduction stretch. The idea is to have the patient slowly stretch the pectoralis minor over time to solve the problem. It is also recommended to improve the strength and coordination of other muscles around the scapula, in particular the trapezius, rhomboids and serratus anterior. As mentioned before, the pectoralis minor can also be injected with corticosteroids while the muscle is visualized with ultrasound, and such injection can occasionally improve pain and other symptoms substantially.
What if surgery is required?
For patients that continue to complain of debilitating pain and other symptoms despite trying the program we just described, it has been our experience (as well as the experience of others) that surgically releasing the tendon of the pectoralis minor from the coracoid will improve the symptoms of pectoralis minor syndrome. This procedure (pectoralis minor release) has been performed for years by vascular surgeon using classic open surgery.
Shoulder surgeons have developed minimally invasive techniques to operate on the shoulder region using an arthroscopic camera and other instruments through several small skin cuts. Our preferred technique for release of the pectoralis minor is performed arthroscopically (endoscopically), which allows identification and treatment of any other conditions possibly contributing to shoulder pain. When performed for the correct patient, arthroscopic pectoralis minor release may provide a fast and relatively easy recovery!