Posted on 03 Mar 2012 22:22
The scalene muscles are three paired muscles of the neck, located in the front on either side of the throat, just lateral to the sternocleidomastoid. There is an anterior scalene (scalenus anterior), a medial scalene (scalenus medius), and a posterior scalene (scalenus posterior). They derive their name from the Greek word skalenos and the later Latin scalenus meaning "uneven", similar to the scalene triangle in mathematics, which has all sides of unequal length. These muscles not only have different lengths but also considerable variety in their attachments and fiber arrangements. As you will see from the descriptions below, these muscles are in a very crowded place and are related to many important structures such as nerves and arteries that run through the neck.
The scalenes run deep to the sternocleidomastoid. They all start at the cervical vertebra and run to the first to second ribs. The anterior scalene runs almost vertically and its upper part is concealed by the SCM and the lower part is concealed by the clavicle. Along its medial border runs the carotid artery. The internal jugular vein, the intermediate tendon of the omohyoid, the phrenic nerve; and the transverse cervical and scapular arteries all lie between the anterior scalene and the sternocleidomastoid (in front of scalene behind the SCM). Between the muscle and the clavicle runs the subclavian vein. The rear of the muscle, its posterior border, makes contact with the brachial plexus nerve roots, which run between it and the medial scalene.
Together with the first rib these muscles form a triangle known as the scalene triangle or interscalene triangle,1 through which the brachial plexus nerves and the subclavian artery pass. Also behind the anterior scalene are the pleura of the lungs and the superior intercostal artery.
Just behind the anterior scalene is the scalenus medius, referring to the "middle" muscle. This muscle forms part of the floor of the posterior triangle of the neck2. The front of the muscle runs close the the brachial plexus and the upper two thoracic nerve roots run through it. It makes contact with the levator scapulae in the rear, and the dorsal scapular nerve and transverse cervical artery pass between the two. The upper two roots of the long thoracic nerve go through the muscle. Only the anterior and medial scalene can be palpated.
The Scalene Muscle Group
The posterior scalene is much shorter than the other two, and only starts at the lower cervical vertebra, where it attaches via two three tendinous slips. Whereas the first two attach to the first rib, the medius attaches to the second rib. 1,2,3,4,5,6.7
Some texts refer to a fourth scalene muscle, the scalenus minor. This variant does not always occur on both sides of the neck, but may be present in up to one-third of people. This normal variation may have implications in thoracic outlet syndromes, as does the scalenus anterior, resulting in a syndrome known as Scalenus Anterior sydrome or Scalenus Anticus syndrome (another name for the anterior muscle). The brachial plexus and the subclavian artery, as mentioned above, pass between the anterior scalene and the middle scalene. When present, the minimus inserts between the scalenus anterior and medius, passing behind the subclavian artery while the scalene anterior passes over and in front of it.7,8
At the top of the lungs is the suprapleural membrane, which is a dense fascial layer also called Sibson's fascia. This fascia is attached to the inner border of the first rib and the costal cartilage. The pleura of the lungs attach to this fascia underneath. The fascia attaches to the transverse process of the C7 vertebra and when muscle fibers are found in it, it is called the pleuralis muscle, which is another name for the scalenus minimus. So this suprapleural membrane could be regarded as a flattened out tendon of the scalenus minimus, meaning that the scalenus minimus is attached to the pleura of the lungs, or the pleural dome and then beyond to the first rib, lying behind the anterior scalene and the groove of the subclavian artery. The scalenus muscle is a reinforcement of Sibson's fascia, which serves to stiffen the thoracic inlet and the neck structures above it so that they are not "puffed" up and down during forced respiration.8
The scalenes are clearly individual muscles but the all work together as a functional unit. They are usually considered accessory muscles of inspirations, as they work to elevate and fix the first and second ribs, while serving to fix them during quiet breathing, becoming guy-wires from the neck. It was thought that they were only active during labored or forceful breathing. However, measurement of their activity with concentric needles electrodes have demonstrated their activity even during quiet, normal breathing, even when the intake of breath is quite small. This has caused some researchers to drop the "accessory" label and consider them primary muscles of inspiration.
During normal diaphragmatic breathing, the ribs are elevated by the intercostal muscles and the scalenes. The orientation of the ribs causes them, when elevated, to expand the chest to the sides and front which increases the thoracic volume available for the lungs to expand into, although a most of this expansion is into the abdominal space which is made available by the contraction of the diaphragm downward. Their exact role in breathing is difficult to resolve.
The actions of the scalene muscles as movers of the neck and head are variously reported. They stabilize the cervical spine against lateral movement. The most common moving action attributed to them unilaterally is contralateral rotation of the cervical spine (rotation of head to the opposite side of working muscle). They have also been reported to be ipsilateral rotators (rotation to same side as working muscle). Bilaterally they are reported to be flexors of the neck. Their action in this regard depends on whether the thorax is fixed or the neck is fixed.1,2,3,4,5,6.7
Whether they are always active during breathing or not, the scalenes may become overactive in quiet breathing in upper chest breathing patterns. Prolonged coughing can overuse these muscles as well, and they may be especially problematic to asthma sufferers. Pain can come from myofascial trigger points in the scalenes or from thoracic outlet entrapment syndromes associated with the muscles.7
Origins, Insertions, and Actions
Origins: The Anterior Scalene (front scalene) originates on the anterior tubercles of the transverse processes of the third or fourth to the sixth cervical vertebrae.
The Scalenus Medius (middle scalene) originates on the posterior tubercles of the transverse processes of the first or second to seventh cervical vertebrae.
The Scalenus Posterior (rear scalene) attaches by two or three tendons from the posterior tubercles of the transverse processes of the the fifth or sixth to the seventh cervical vertebra (the last two or three).
Insertions: The scalenus anterior inserts onto the scalene tubercle and cranial crest of the firt rib, in front of the subclavian groove. The middle scalene inserts onto the cranial surface of the first rib, between the scalene tubercle and the subclavian groove. The posterior scalene inserts onto the outer surface of the second rib.
Actions: As above, the scalenes function as fixers and elevators of the first and second ribs during inspiration. The anterior and medial scalenes elevate the first rib and the posterior scalene elevates the second rib.
It is generally accepted that, acting unilaterally, they flex the head to the same side and acting bilaterally the flex the head forward (cervical flexion). Their roles as rotators of the neck given differently by different texts. Some report that all three scalenes rotate the head to the same side and some report that they all rotate it to the opposite side. Some report different functions for each scalene. According to Buford, et al., a multiple single-subject study on anesthetized macaques and human cadaver follow up revealed all three muscles as contralateral rotators of the cervical spine (rotating the head to the opposite side).4 The scalenes also help to laterally stabilize the neck, which is especially suited to the scalenus posterior.7
Sources of Scalene Trouble and Trigger Points
As stated above, breathing habits can be a cause of the scalenes being overworked. Here is a list of possible causes of scalene trouble which can lead to trigger points in the muscles or the neurovascular entrapment syndrome:
- labored breathing and/or habitual upper chest breathing (paradoxical), or chronic coughing, possibly associated with:
- nervous hyperventilation
- playing wind instruments
- work habits and activities such as:
- working for long periods with arms in front and possible slouched forward (as at a desk)
- working long periods with arms overhead
- work the requires repeatedly raising and lowering the arms
- carrying heavy loads at the sides
- pulling or lifting (especially with arms as waist)
- pulling ropes as in sailing
- wearing a heavy backpack
- poor posture with head-forward, kyphotic slouching and other problems such as:
- one short leg when standing
- small hemipelvis when sitting
- idopathic scoliosis
- sleeping with the head and neck low
- trauma from a hard fall or auto accident, whiplash (also affects sternocleidomastoid)7
Strength Training and Scalene Strain
When you strain on a heavy lift, such as a barbell squat, you may find yourself holding your breath while tensing the muscles in your shoulder and chest area. This can strain the scalenes. Learn to take your breaths into the diaphragm (discussed more below) and don't tense your neck, or crane if forward when lifting. Although it is a good idea to keep the shoulders pinned back during most lifting exercises, do not exaggerate this and do not excessively puff the chest out and up.
Scalene Trigger Point Symptoms
The scalenes, as should be obvious from the preceding description, are quite complicated muscles and so they can have many different trigger points. They refer pain to such a wide area of the chest, shoulders, arms, hands, and upper back that the symptoms can be mistaken for many different things or be blamed on trigger points in different muscles, which may the a problem as well but not the ultimate source of the pain. Since the scalenes are hidden and rarely mentioned or even thought about they are easily overlooked for more prominent (and popular) muscles. They may be the most likely muscle to harbor trigger points resulting in upper extremity pain, but unfortunately may also be the hardest to locate and treat.
Trigger points in the scalenes can be a source of interscapular pain (pain between the shoulder blades) and medial scapular border pain. This may be blamed on the rhomboid muscles. They may also refer pain to the chest, which can be mistaken for angina. Shoulder pain from scalene TrP's may pass for bursitis or tendonitis. Arm pain may be assumed to be a muscle strain, or, pain to the arms or hands may be diagnosed as a cervical nerve root compression caused by a ruptured or degenerated disc. Also, neuruovascular compression of scalene associated thoracic outlet syndrome may cause ischemic pain mistaken for cervical nerve root origin, although the pain patterns are different.9
According to Travell and Simons, the anterior scalene is most often affected by trigger points, followed in order of reducing frequency by the middle and then the posterior scalene. The anterior and medius are often involved together and when the minimus is affected, so are all three others.
Moving the head and neck around, trying to relieve your sore neck, may be an indication of scalene myofascial problems. This may cause you to be unable to bend your neck all the way to the opposite side (of the problem muscles). Scalene TP's do not restrict neck rotation as levator scapulae trigger points can, but there may be pain on the same side when turning your head as far as you can, especially if you also dip your chin down to your chest while doing so. Doing this may activate the referred pain pattern of your scalene TP's.
However, if you are in constant pain from scalene trigger points, which is quite possible, you may not be able to tell the difference between pain caused by turning your head and the general pain you already have. Travell and Simons describe a test called the "Scalene-relief test" that may be helpful to verify that your pain is coming from scalene TP's.
Assuming that one of both of your arms are in pain from scalene trigger points, place the painful arm across the top of your forehead, so that the crook of your elbow is resting on the forehead. Lift your shoulder forward and up. This will lift the clavicle off the scalene muscles underneath, thus relieving some of the pressure on them if they are tight and tender. Hold the position for a few minutes to see if your pain abates.
The action of lifting the clavicle up using the scalene-relief test can also lift it off of the underlying brachial plexus, if the nerves are being compressed by the clavicle. Therefore, this test can not verify one-hundred percent whether your pain is from myofascial trigger point origin or neurogenic origin (because the brachial plexus is being compressed). Therefore, you can also try the "Finger-Flexion test" to help establish whether the pain is of a primarily myofascial origin.
The finger flexion test tests for both extensor digitorum trigger points and for scalene trigger points. To do this test properly you must flex your fingers without making a tight fist. This means that you will bend your fingers but not bend the first (proximal) joints of your fingers, as you would when making a fist. The proximal joints of your finger are called the metacarpophalangeal joints (MCP's). You must keep these joint absolutely straight (fully extended) when performing the test.
So, straighten your fingers and then try to touch the volar pads of your hand with the tips of your fingers. The volar pads are the little pads just under the first joint of each finger. This means you will be bending only the second and third joints of your fingers but not the first joint. If all your fingers are able to touch the pads, the test is normal, meaning it does not indicate any trigger points in the scalenes OR the extensor digitorum. If only one or more of your fingers fails to touch the pads, this may indicate TP's in the part of the extensor digitorum that attaches to that finger. For instance, if your index finger will not touch the pad, it could mean that the part of the extensor digitorum that attaches to the index finger harbors a TP.
However, if all of the fingers fail to touch, this could point to scalene trigger points, which can tend to set up satellite trigger points in the extensor digitorum. The TP's could be in any or all of the scalenes. Remember, if you actually make a fist, the test is invalid because there would be no problem flexing the MCP joint, even if you have trigger points in the scalenes or ED muscles.
Trigger points in the sternocleidomastoids, which is also a muscle of inspiration, usually occur after the scalenes have been affected for a while and sternocleidomastoid TP's are commonly associated with scalene TP's. Also, associated are TP's of the trapezius and splenius capitis muscles.
Scalene Referred Pain Patterns
Any of the scalene muscles may refer pain to any of the associated areas but some are more likely to send pain to certain areas than others. Pain in the chest is referred in two finger-like projections to the pectoral region down to about the level of the nipple. This pain is more likely to be caused by trigger points in the lower part of the scalenus medius or posterior.
Scalene Trigger Points and Referred Pain Patterns
Shoulder pain from scalene TP's is not deep in the joint, but superficial and more to the deltoid muscle. This pain extends down the front and back of the arm, skipping the elbow and occurring again in the radial forearm, thumb, and index finger. This pain pattern of the upper extremity is more likely to be caused by TP's in the upper part of the scalenus anterior and medius.
Pain is sometimes referred to the back, over the upper half of the inner border of the scapula and the interscapular region, caused by TP's in the anterior scalene. The scalenus minimus is associated with a more rare referred pain pattern in the lateral part of the arm, from the top of the deltoid down to the elbow, but again skipping the elbow itself. The pain reappears in the back of the forearm (dorsal area), wrist, hand, and all five fingers, becoming very concentrated in the thumb. There may be occasional numbness in the thumb.7
Scalene Trigger Point Self-Treatment
The first thing you need to do to get rid of your scalene trigger points is to eliminate the underlying causes. Simons and Travell recommends to place an 8 or 9cm block under the legs at the head of your bed, so that the top of your body is elevated and gentle traction of the scalenes is created. This seems far-fetched to the author, as do their recommendations to place your pillow in a position that is "just so" so that the scalenes are not aggravated. Certainly a good pillow, one not too thick or too thin, is a great idea but the idea that you can stay in one perfect position on your pillow all night long seems more like wishful thinking than therapy.
However, they also recommend a moist heating pad to be used over the scalenes for about 10 to 15 minutes before going to sleep, which may certainly help to relax the muscles.
Use proper ergonomic desk habits when working at your desk. There are many good resources on the web. Avoid slouching forward when working and refer to any of the scalene aggravating factors above.
Paradoxical breathing is a big problem for the scalenes. Read the article Paradoxical and Diaphragmatic Breathing to learn how to correct this faulty breathing pattern. Trying to treat your scalenes with self-release without correcting your upper chest breathing patterns is likely to yield only frustration. If you have a medical condition that produces chronic coughing, seek appropriate medical care to control the coughing.7
There are also some passive stretches you can perform to help restore the scalenes to their normal length:
Side-Bending Scalene Stretch
It may be helpful to apply a hot pack or heating pad across the neck for 10 to 15 minutes before performing this stretch. Between stretches, use proper diaphragmatic breathing, taking deep, slow, breaths, to relax the neck.
- Lie supine (face up) in your bed or on the floor
- Lower and anchor the shoulder of the side to be stretched by placing that side's hand under your buttock
- Bring the opposite hand over your head so that your fingers make contact with the top of the ear.
- Gently pull the head and neck so that it tilts to the opposite side of the side you want to stretch, relaxing your neck muscles as you do so. Try to pull your ear down to your shoulder.
- Now, you will rotate your head, and the degree of rotation will determine which scalene is targeted.
- To target the posterior scalene, turn your face toward the arm that is pulling
- To target the anterior scalene, turn your face away from the pulling arm.
- To target the middle scalene, look straight up at the ceiling, or just slightly toward the pulling arm.
- Concentrate your efforts on the muscle that feels the tightest when you rotate your head to target that muscle
- Hold the stretch for around six slow seconds7
Scalene Trigger Point Self-Release
For more complete instructions see The Trigger Point Therapy Workbook
Anterior Scalene: To find the anterior scalene your must find the clavicular branch of the sternocleidomastoid. Once you locate it, you want to find the posterior border of it, which is the rear part of the muscle toward the side of the neck. Using the opposite hand, just above your collar bone (clavicle) grasp the sternocleidomastoid with your fingers and thumbs and with your fingers, pull the SCM toward the front of your neck so that your fingers are brought further to the front of the neck underneath the SCM, where you can palpate the anterior scalene. Feel around this area, from the top part of the SCM under your ear down to the collar bone, and even a bit down underneath the bone, until you encounter a trigger point, which will cause a very weird pain and may create the referred pain patterns. Massage the area by pushing your fingers across the muscle toward the side of the neck, the skin moving with the fingers.
Middle Scalene: For the sclenus medius, massage the side of the neck, just behind the area you treated for the anterior muscle, using the same type of stroke.
Posterior Scalene: The posterior scalene is very difficult to directly palpate. It lies in the area where the upper trapezius attaches to the collar bone and is hidden behind the levator scapulae. Push your fingers into this area under the front of the trapezius where it attaches to the clavicle adn exert downward pressure while pulling your finger toward your throat, running the stroke parallel to the collar bone.7,9
Scalenes and Thoracic Outlet Syndrome
For a general overview of thoracic outlet syndrome refer to the link above. As described, the anterior and middle scalenes, together with the first rib at the bottom, form a small triangular space through which the brachial plexus and the subclavian artery pass to the costoclavicular space. This triangle can be from 0.4 to 3.5cm in width. The suclavian artery passes over the first rib and through the fissure formed by the scalenes. If the scalenes become shortened and tight, the artery can be compressed by the rib. The brachial plexus has nerve roots from C5 to c8 and T13. Like the subclavian artery, these nerves have no bony protection and are stretched tightly between the neck and the shoulder. Neurovascular compression caused by narrowing of this area is known as anterior scalene syndrome, scalenus anticus syndrome, or Naffziger syndrome.
The scalene triangle and associated structures. Notice the pectoralis minor. See how the axillary (subclavian) artery and brachial plexus run under the pec minor where it attaches to the scapula? A tight pec minor can lead to another entrapment syndrome which can cause pressure on the vessel and nerves when the arm is completely abducted and externally rotated because the tight pec minor pulls on and stretches these structures. Also, pulling the shoulders back in an extreme "military" posture, can cause the vessel and nerves to be compressed by the clavicle as the scapular is retracted.7
When we evolved from a quadruped to an erect position, the nerves and artery became bent over the first rib under tension. Also, the change from a thorax that is wider front to back, to one that is wider side to side, placed the nerves and arteries under more tension.
Normally, there is enough room in the scalene triangle for the brachial plexus and the subclavian artery. But sometimes anatomical variations or changes in the structures may cause narrowing, thus making compression more likely. The insertion of the scalene anterior and medius may be close together on the first rib, making the space narrower. There may be fibrous bands between the two muscles which act like a sling which elevates the artery and the brachial plexus. The presence of a scalenus minimus in the area can add to the problem. Also, a cervical rib4, or an elongated C7 transverse process can re-orient the borders of the scalenes, predisposing on to compression in the scalene triangle. It is even reported that shortening of the muscles can chronically elevate the firt rib so that the rib itself compresses the structures.10,11
When you have poor posture, with a forward head and rounded shoulders (slouching) the structures in the scalene triangle are put under more tension and the scalenes themselves may undergo changes due to the chronic strain, which can include fibrotic changes adn adhesions, further adding to the tension and compression of the brachial plexus and subclavian artery. Extended overhead work, wearing a knapsack for long periods, and simply getting older, can all cause your shoulders to slump forward and round, which makes the nerves and vessels have to travel and even further distance. This may be a bigger problem for women, who have shoulders lower to the thorax than men. Carrying heavy things at your sides for long periods, while becoming exerted and breathing heavily, can cause the scalenes to work overtime and this can possibly compress the structures. Anything that causes the muscles to tighten and shorten, or to hypertrophy, together with predisposing factors, can lead to the compression syndrome, as well as any repetitive strain or sudden injury that causes the associated tissues, ligaments, and muscles to shorten or swell. With forward-head posture, the sternocleidomastoid and pectoralis muscles, in addition to the scalenes, are likely to become shortened. 10,12
Some of these things can also cause narrowing of the costoclavicular space, which is the space between the first rib and the clavicle, causing neurovascular compression there and similar complaints as with anterior scalene syndrome.
Another potential outcome of the first rib being pulled up by chronically shortened scalenes is double crush syndrome. Double crush is a theoretic condition in which compression of the brachial plexus in the scalene space by the first rib causes the nerves to be susceptible to further compression injury at distal sites such as the elbow and wrist. It is not clear as to whether this theory is true, but there does seem to be a high incidence of carpal tunnel syndrome and cubital tunnel syndrome (at the elbow) associated with thoracic outlet syndrome. The theory holds that the symptoms are the result of the cumulative effect of several minor compressions along the nerves path.10
Scalenus anterior syndrome produces symptoms similar but not identical to scalene trigger points. Brachial plexus compression causes pain on the ulnar side of the hand (the side where your pinkie finger is) as opposed to the radial side (where you thumb is), or to the medial part. Along with this pain can come tingling and numbness. There may be weakness in the arm and hand, especially with overhead work. Objects may be suddenly dropped from the hand. Pain may also occur in the cervical region. Arterial compression, which is much more rare, can result in hand pain and weakness, numbness and tingling in the fingers, cold and pale fingers, and chronic arm fatigue. Thoracic outlet syndrome caused by the scalene anterior syndrome is likely to be misdiagnosed as carpal tunnel syndrome.7,14
You may have noticed a few tests described above to help determine whether your pain was from scalene trigger points. There are also tests that professionals use to determine whether the pain is from neurovascular compression. These test will not be described here as, should you be experiencing the symptoms of thoracic outlet syndrome described above, you should consult a physician. This is not a time for do-it-yourself! And remember, while trigger points can sometimes be self-treated, there is no shame in seeking professional help for them as well. The scalenes are especially difficult to deal with and they are associated with many important and vulnerable nerves and vessels. Should you try to treat them, you do so at your own risk! This article is meant to provide you information to help you make informed medical choices, it is not meant to replace professional medical advice.
All images on this page used under license. Images by LifeART (and/or) MediClip image copyright 2010. Wolters Kluwer Health, Inc.- Lippincott Williams & Wilkins. All rights reserved. Images not for reuse.
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This page created 03 Mar 2012 22:22
Last updated 23 Oct 2015 17:59