Muscle:Scalene

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Scalene muscles are a group of three (sometimes four) muscles of the lateral neck whose trigger points (TrPs) are among the most commonly overlooked sources of shoulder, upper back, and arm pain in clinical practice. Their referral patterns extend from the chest anteriorly to the medial scapular border posteriorly, and down the arm to the thumb and index finger. They are intimately associated with the thoracic outlet, and TrP tautness in the scalenus anterior and medius is the primary myofascial mechanism responsible for the majority of cases clinically labelled as thoracic outlet syndrome.

Contents

Anatomy

The three major scalene muscles all attach above to the transverse processes of the cervical vertebrae and below to the first or second rib.

Scalenus anterior attaches above to the anterior tubercles of C3–C6 transverse processes and below by a tendon to the scalene tubercle on the inner border of the first rib, anterior to the groove for the subclavian artery. It lies in front of (anterior to) the subclavian artery.

Scalenus medius is the largest of the three. It attaches above to the posterior tubercles of C2–C7 transverse processes (sometimes only C4–C5) and below to the cranial surface of the first rib, posterior to the groove for the subclavian artery. The brachial plexus emerges from the groove between the anterior and middle scalene muscles.

Scalenus posterior attaches above to the posterior tubercles of the lowest two or three cervical vertebrae and below to the lateral surface of the second rib (sometimes also the third). It passes posterior to the scalenus medius, deep to the upper trapezius and levator scapulae.

Scalenus minimus is the most variable of all. It is present on at least one side in roughly three-quarters of people studied. It extends above to the anterior tubercle of C7 (sometimes also C6) and below to the fascia supporting the pleural dome and the inner border of the first rib. It lies behind and deep to the scalenus anterior, and its attachment to and reinforcement of the pleural dome make it clinically significant in respiratory overload.

Innervation: All scalene muscles are innervated by motor branches of the anterior primary divisions of spinal nerves C2 through C7, according to the segmental level of muscular attachment.

Primary actions: Bilateral — assist neck flexion and are the primary auxiliary muscles of inhalation (elevating and stabilising the first and second ribs). Unilateral — lateral flexion of the cervical spine. The scalene muscles are poorly placed to influence rotation of the neck significantly.

Functional unit: The scalene muscles on one side are synergistic with each other and with the sternocleidomastoid for sidebending (lateral flexion) of the neck. During inhalation, they are synergistic with the diaphragm and intercostal muscles, assisted by both divisions of the sternocleidomastoid.

Referred Pain Patterns

TrPs in any of the three major scalene muscles can produce any part of the composite referred pain pattern. Scalene TrPs rarely refer pain to the head, but are commonly associated with TrPs in other muscles (particularly the sternocleidomastoid) that do.

The composite pain pattern has three components:

Anterior and lateral chest: Persistent aching pain is referred anteriorly in two finger-like projections over the pectoral region, down to approximately the nipple level. This pattern commonly arises from TrPs in the scalenus medius or posterior. On the left, this pattern may be mistaken for angina pectoris because it is likely to be associated with muscular activity.

Upper back: Pain is referred posteriorly over the upper half of the vertebral border of the scapula and the adjacent interscapular region. When a patient presents with posterior shoulder pain particularly along the scapular border, scalene TrPs are among the most likely myofascial sources.

Arm and hand: Pain extends down the front and back of the arm (over biceps and triceps), skips the elbow, and reappears on the radial side of the forearm, the thumb, and the index finger. This pattern is distinct from the ulnar distribution typical of brachial plexus lower trunk entrapment.

Scalenus minimus: TrPs in this variable muscle refer pain strongly to the thumb and cover the lateral aspect of the arm from the deltoid insertion to the elbow, skipping the elbow to cover the dorsum of the forearm, wrist, hand, and all five digits. The referred sensation is often described as "numbness" with or without demonstrable hypoaesthesia.

Neurological symptoms from entrapment

In addition to referred pain, scalene TrPs can produce neurological symptoms through secondary entrapment of the lower trunk of the brachial plexus (C8–T1) as it exits the thorax by hooking over the first rib between the anterior and middle scalene muscles. This entrapment causes:

  • Ulnar pain, tingling, numbness, and dysaesthesia (chiefly 4th and 5th digits, ulnar side of hand and forearm)
  • Unexpected dropping of objects from the hand
  • Hand oedema, appearing diffusely distal to the wrist, particularly over the bases of the four fingers and dorsum of the hand — when present, this is characteristic; it is caused by entrapment of the subclavian vein and/or lymph duct as they pass across the first rib in front of the attachment of the scalenus anterior
  • Stiffness of the fingers, tightness of rings in the morning

TrP activity in the scalenus anterior alone can cause hand oedema through a separate mechanism: autonomic reflex suppression of peristaltic contractions of the lymph duct.

Activation and Perpetuating Factors

Scalene TrPs may be activated by:

  • Accidental trauma, including whiplash — 81% of whiplash patients with a pain complaint had at least one active scalene TrP
  • Pulling, lifting, or hauling (ropes, sailing, tug-of-war, horse handling)
  • Carrying awkwardly large objects
  • Playing certain musical instruments
  • Competitive swimming
  • Overuse of these respiratory muscles in paradoxical breathing
  • Hard paroxysms of coughing (allergy, pneumonia, bronchitis, asthma, emphysema)

Structural and postural perpetuating factors include:

  • Sleeping with the head low (head-end of bed slightly lower than foot-end, as when a thick rug is placed only under the foot of the bed) — this sustains shortening of the scalene muscles overnight
  • A tilted shoulder-girdle axis due to a lower limb-length inequality when standing
  • A small hemipelvis when seated
  • Loss of an upper limb or surgical removal of a heavy breast
  • Idiopathic scoliosis
  • An awkward leaning position assumed when seated to compensate for short upper arms that do not reach the armrests of most chairs, or to position the head to look at someone

Scalene TrPs are commonly activated secondary to TrPs in the sternocleidomastoid, with which they form a functional unit. Any systemic perpetuating factor (see Chapter 4) can also perpetuate scalene TrPs once activated.

Clinical Examination

Patients with scalene myofascial pain tend to move the arm and neck restlessly, as if trying to relieve a "sore" muscle. On examination:

  • Lateral neck sidebending to the opposite side is usually restricted by at least 30°
  • Neck rotation is painful only at the extreme range of motion to the same side, especially when the chin is then dipped down toward the shoulder (see Scalene-cramp Test below)
  • Scalene involvement itself causes no restriction of glenohumeral motion, and pain is not significantly increased by tests of shoulder movement — however, horizontal abduction at the shoulder may be limited by associated TrPs in the pectoral muscles

Cervical range of motion should be assessed with appropriate caution to avoid vertebral artery compromise. While the subject's neck is sidebent, the examiner should slowly and gently move the head and neck into varying degrees of rotation. This manoeuvre often brings out added pain or a "tight feeling" which, if the patient is then instructed to point to the troublesome area, the examiner can use as a starting point to palpate for TrPs.

Scalene-cramp Test

The patient rotates the head fully to the side of the pain and actively pulls the chin down into the hollow above the clavicle by flexing the head and neck. During the last part of this movement, the anterior and middle scalene muscles strongly contract while in the shortened position. This evokes a local cramp-like pain in the region of the TrP and may further activate the TrP, causing continuing moderate or severe referred pain.

Positive result: Local cramp pain at the TrP site, with or without referred pain at a distance.

This pain can be promptly relieved by application of spray and stretch to the activated TrP. If the patient was already in severe pain before attempting the test movement, the Scalene-relief Test should be tried first.

Scalene-relief Test

Referred pain from the scalenus anterior syndrome may be relieved by elevation of the arm and clavicle, because this manoeuvre removes pressure from structures traversing or attaching to the first rib (which can be elevated by TrP-shortened scalene muscles).

The patient places the painful forearm across the forehead while raising and pulling the shoulder forward to lift the clavicle off the underlying scalene muscles and plexus (Fig. 20.5C). This maximises the clearance beneath and behind the clavicle.

Positive result: Pain relief, ensuing immediately or within a few minutes.

This test is not affected by cervical radiculopathy, which helps distinguish scalene TrP pain from radicular pain.

Finger-flexion Test

This test must be performed with the metacarpophalangeal (MCP) joints actively held straight, in full extension. In this position, forceful contraction of the extensor digitorum is required, but the tightly closed fist does not.

  • Normal: The fingertips can firmly touch the volar pads of the MCP joints
  • Positive (single finger): One or more fingertips fail to flex completely — indicates TrP activity in the part of the extensor digitorum that controls that finger (or the extensor indicis for the index finger)
  • Positive (all four fingers): All fingertips fail to touch the MCP volar pads — indicates active TrPs in the scalene muscles themselves, which reflexly inhibit the long finger flexors

The test is positive for scalene TrPs because scalene TrP activity apparently reflexly inhibits simultaneous distal interphalangeal (DIP) flexion by inhibiting the corresponding finger flexors. The finding is reversed to normal immediately after stretch and spray of the involved scalene muscles.

Note: A positive test is not simply due to oedema, since this test of distal interphalangeal flexion is frequently restored to normal immediately after stretch and spray of the involved scalene muscles.

Trigger Point Examination

In the authors' experience, scalene muscles harbour active TrPs in the following order of frequency: anterior, middle, posterior, and minimus.

The most reliable diagnostic criteria are: identification of a taut band by palpation, the presence of spot tenderness, the presence of referred pain, and reproduction of the patient's symptomatic pain. The local twitch response (LTR) is moderately difficult to elicit manually in the anterior and middle scalene and very difficult in the posterior scalene; it is characteristically elicited when a needle encounters the TrP.

Scalenus Anterior

The scalenus anterior is found by palpating the muscle behind the posterior border of the clavicular division of the sternocleidomastoid. The posterior border of the sternocleidomastoid can be approximated by briefly occluding the external jugular vein with finger pressure just above the clavicle — this vein usually crosses the scalenus anterior muscle at about the level of its active TrPs.

The patient's head should be positioned to take up any slack in the muscle and then the muscle is palpated along its anterior and posterior borders. Its posterior border marks the groove between the anterior and middle scalene muscles, in which the brachial plexus bundle of nerve fibres lies. In this groove, behind the clavicle, the pulsating subclavian artery is nearly always palpable where it passes between these muscles to cross over the first rib.

Two fingers of one hand straddle the scalenus anterior and middle scalene muscles; the index finger approaches the groove between these two muscles at the level of an upper TrP in the scalenus medius.

The inferior belly of the omohyoid muscle, when it has a tender TrP and taut bands, can easily be mistaken for the anterior scalene. These muscles have different fibre directions; the omohyoid is more superficial, comes out from behind the sternocleidomastoid, and crosses diagonally over the anterior scalene.

Scalenus Medius

The scalenus medius is parallel to and on the posterior side of the groove that contains the brachial plexus bundle. It is larger than the scalenus anterior and lies anterior to the free border of the upper trapezius. It can be palpated against the posterior tubercles of the transverse processes of the vertebrae, to which its digitations are attached.

Scalenus Posterior

The scalenus posterior is difficult to reach. It lies more horizontal than, and dorsal to, the scalenus medius. It passes anterior to the levator scapulae, which must be pushed aside at the point where the levator scapulae emerges near the anterior free border of the upper trapezius. Finding TrP tenderness requires palpation posterior to the scalenus medius and to the depth of the first rib.

Scalenus Minimus

Scalenus minimus TrP activity is usually discovered only after inactivation of TrPs in the other scalene muscles. Its involvement is then recognised by residual tenderness deep to the mid-portion of the scalenus anterior.

Entrapment — Thoracic Outlet Syndrome

The thoracic outlet syndrome (TOS) is a collection of symptoms, not a well-defined diagnosis. Abnormal tension of scalene muscles — most commonly due to TrP tautness — is the primary myofascial mechanism responsible for the majority of patients clinically labelled as TOS.

Mechanism: TrP tautness in the scalenus anterior and scalenus medius elevates the first rib, reducing the space through which the brachial plexus and subclavian artery pass. Entrapment of the lower trunk of the brachial plexus (C8–T1) is the most common result, causing ulnar pain, tingling, numbness, and dysaesthesia. TrP activity in the scalenus anterior can additionally cause hand oedema through compression or reflex suppression of venous and lymphatic drainage.

Neurological signs and symptoms in TOS chiefly follow the ulnar distribution (4th and 5th digits, ulnar side of hand and forearm, occasionally the medial antebrachial cutaneous nerve territory). Mild hypesthesia to light touch, pinprick, and temperature change in the little finger may be present.

Articular dysfunction: Elevation of the first rib is a commonly observed finding with scalene TrP involvement. Because of the first rib's location under the clavicle, it can be palpated most easily at the head of the rib, posteriorly, at its articulation with the first thoracic vertebral segment. Treatment of first rib fixation and elevation uses a contract-relax technique applied to the scalene muscles (see Trigger Point Release below).

Diagnostic tests: Provocative vascular manoeuvres (Adson, costoclavicular, hyperabduction) have proven disappointingly unreliable for diagnosing TOS and are considerably more reliable as indicators of neurological entrapment than vascular entrapment. Electrodiagnostic tests are unreliable except in more chronic and severe cases. The most clinically useful test is reproduction of the patient's symptoms by applying supraclavicular pressure over the scalene muscle.

Differential from structural TOS: Cervical ribs and deformed first ribs are relatively rare (completely articulated cervical ribs in 0.17% of 40,000 consecutive chest X-rays). When present, a cervical rib can intensify symptoms because all structures crossing over it are more sharply angulated than usual. Patients with documented cervical ribs have obtained relief from symptoms of thoracic outlet entrapment with inactivation of their scalene TrPs. Regardless of the presence or absence of congenital anomalies, inactivation of scalene TrPs should always be the first-line intervention before surgical approaches are considered.

Differential Diagnosis

Condition Distinguishing features
C5–C6 radiculopathy Can produce a pain complaint very similar to that of scalene TrPs; both may be present simultaneously since neuropathy encourages development of forearm TrPs that refer pain to the wrist region, and middle scalene TrPs may be causing entrapment; forearm TrPs induced by nerve compression persist following successful surgery to relieve radiculopathy unless inactivated
Carpal tunnel syndrome May occur as a concurrent entrapment with TOS, or scalene TrPs may cause symptoms mimicking CTS; loss of normal mobility of structures forming the carpal tunnel often makes a major contribution to the entrapment; oedema reflexly originating from scalene TrPs can be another important contributing factor
C4, C5, C6 articular dysfunction Anterior and/or middle scalene TrPs are commonly associated with C4, C5, and C6 articular dysfunctions
Angina pectoris Left-sided anterior chest pattern from scalenus medius or posterior TrPs is likely to be associated with muscular activity and mimics cardiac pain; distinguish by provocation with muscular activity rather than exertion, and by response to scalene TrP treatment
Infraspinatus TrPs Infraspinatus refers deep joint pain to the anterior shoulder, which is not characteristic of scalene TrP pattern; scalene pain extends down the arm
Phantom limb pain Inactivation of scalene TrPs has been reported as one treatment for phantom limb pain in upper-extremity amputees

Treatment

Trigger Point Release

Positioning

The patient is seated for treatment. Before beginning, the pelvic and shoulder-girdle axes must be level — a small hemipelvis should be corrected by an ischial lift under the tuberosity on the small side to straighten the spine and level the shoulders. This is important for relaxation of overloaded neck muscles. The patient should slide the hips forward slightly on the chair seat, lean back comfortably against the backrest, and slip the fingers under the thigh to anchor the pectoral girdle and rib cage on the side to be stretched.

Spray and Stretch

Stretch and spray of the scalene muscles should always be applied bilaterally to avoid activating latent TrPs that might cause reactive cramping on the untreated side. A greater range of neck motion, and therefore more complete and lasting relief, usually occurs if all parts of the composite referred pain pattern are included in the vapocoolant application.

Scalenus anterior: After a few initial sweeps of spray, the head and neck of the seated patient is tilted toward the contralateral side and slightly back, resting against the clinician's body. Vapocoolant or icing is applied along the lines of the scalenus anterior fibres and over the referred pain pattern of the chest and arm (including to the thumb and index finger). The clinician then turns the patient's face toward the side of the involved anterior scalene (to take up additional slack), and the spray is directed downward over the muscle and arm.

Scalenus medius: The patient's face is held in a neutral forward position during stretching.

Scalenus posterior: The patient's face is turned away from the involved muscle during stretching.

The degree of head rotation determines which of the three major scalene muscles is specifically placed on stretch. Stretch and spray is followed immediately with moist heat.

Gravity-assisted Postisometric Relaxation

The patient lies supine with the TrP-involved muscle uppermost. The patient looks upward and breathes in (contraction phase for scalenes in this position), holds the breath and position for about 6 seconds, then slowly breathes out and lets the head and neck sink back to the table (relaxation phase). This is repeated three times. This technique is gentle, effective, and readily adapted for self-stretch at home.

Trigger Point Pressure Release

Sustained pressure on identified taut bands, complemented by instructing the patient to do slow relaxed breathing, is another effective technique for inactivating scalene TrPs.

Elevated First Rib Release

If first rib elevation is present, it must be addressed for complete relief. The clinician applies pressure to an elevated first rib on the right side with the right thumb beneath the upper trapezius muscle over the head of the first rib. The release is combined with a contract-relax (postisometric relaxation) technique whereby the patient attempts right sidebending of the neck against light resistance provided by the examiner's left hand, followed by relaxation. Full release is accomplished through sidebending with fine tuning, utilising rotation to isolate the precise muscle fibres that are shortened. The patient facilitates release first by breathing in and looking upward to the right (which also contracts the right scalene muscles). During the relaxation phase, the patient looks down to the left and breathes out; the examiner takes up slack by bringing the patient's scalene muscles to the new length barrier, while maintaining gentle downward pressure on the head of the first rib. This procedure can be repeated 3 to 5 times. The area can be pre-sprayed with vapocoolant.

Parallel Muscle Release

To fully lengthen the scalene muscles, it is often necessary to release parallel muscles that are also tense due to TrPs and that restrict sidebending of the neck. Examples are the upper trapezius and both the clavicular and sternal divisions of the sternocleidomastoid. Less frequently, a tense omohyoid muscle stands out under the skin like a rope as it stretches over other neck structures and attaches to the scapula — if it harbours TrPs, it must be released, as it can prevent full stretch of the trapezius and scalene muscles.

Trigger Point Injection

For injection of the anterior and middle scalene muscles, the patient lies supine and turns the head slightly away from the side to be injected. It may help to elevate both the head and shoulder slightly on a pillow to slacken the sternocleidomastoid and trapezius. The vertical groove between the anterior and middle scalene muscles which locates the brachial plexus is identified by palpation. The needle is directed away from the nerves and upward toward either the anterior or middle scalene muscle. A 2.5-cm (1-in), 23- or 24-gauge needle may be used. After injection, pressure is maintained for haemostasis. All scalene injections are made at least 3.8 cm (1½ in) above the clavicle. Injection is followed by spray and stretch, moist heat, and active side-bending movements to full range on both sides, with the patient lying supine.

For the scalenus posterior, the patient lies sidelying with the involved muscle uppermost. Because of its submerged position, a 22-gauge, at least 3.8-cm (1½-in) needle is used, directed tangentially and posteriorly.

For the scalenus minimus, the needle is inserted at least 3.5 cm (1½–2 in) above the clavicle, directed straight in rather than angled downward toward the apex of the lung, through the scalenus anterior and toward a transverse process. Care must be taken not to inject below the TrP tenderness of this muscle.

Warning: The apex of the lung ordinarily extends about 2.5 cm (1 in) above the clavicle. All scalene injections are made at least 3.8 cm (1½ in) above the clavicle. The needle must never be directed downward toward the apex of the lung.

Corrective Actions

Correction of poor posture is of paramount importance for long-term relief. In most patients, multiple factors contribute to the activation and reactivation of scalene TrPs. Identification and correction of all major perpetuating factors, together with local treatment, is required for complete lasting relief. Patients should be instructed in: stretching, coordinated respiration, reduction of postural and activity strain, and maintenance of body warmth.

Patient Education

Coordinated Respiration

Paradoxical respiration is a common source of abuse and overload of the scalene muscles. It is frequently adopted following abdominal surgery and by people who constantly retract a protruding abdomen. People who breathe paradoxically often complain of being "always out of breath" or that they "run out of breath" when talking.

Normal diaphragmatic breathing involves coordinated contraction of the diaphragm with expansion of the lower thorax and elevation of the rib cage, all of which increase lung volume. In paradoxical respiration, the chest expands (moves up and out) while the abdomen moves in, elevating the diaphragm and decreasing lung volume. A normal effort thus produces inadequate tidal volume, and the muscles of the upper chest — especially the scalene muscles — overwork to exchange sufficient air.

The patient must learn to synchronise diaphragmatic (abdominal) and chest breathing. The patient begins by exhaling fully and identifying their paradoxical pattern by placing one hand on the chest and one on the abdomen. Diaphragmatic respiration alone is most easily learned if the patient holds the chest fixed in the collapsed position, and concentrates on breathing by alternately contracting the diaphragm and abdominal muscles (allowing the abdomen to move out during inhalation and move in during exhalation) without expanding the upper chest or elevating the sternum. Once smooth diaphragmatic breathing is achieved, the patient then learns to coordinate costal and diaphragmatic respiration together during inhalation and exhalation. The patient should practice coordinated breathing at intervals throughout the day and on retiring.

Patients who breathe paradoxically must learn this coordination in the recumbent position first, then transfer it to the seated and upright posture. A rocking chair can help establish the rhythm naturally.

Sleep and Pillow

Sleeping with the head and neck low when the head-end of the bed is slightly lower than the foot-end causes sustained shortening of the scalene muscles overnight and should be corrected. Scalene TrPs frequently cannot be permanently relieved without elevation of the head end of the bed. The head of the patient's bed should be raised 8 to 9 cm (3–3½ in) by placing blocks or telephone books under the legs at the head-end to tilt the bed frame. Two pillows used to improve "sinus drainage" flex the neck and cause anterior scalene shortening that can aggravate these TrPs.

The patient should use only one soft comfortable pillow of the right thickness to maintain a normal cervical lordosis. When lying on the affected side, the pillow under the head should be thick enough and bunched up between the neck and shoulder to prevent tilting of the head that would cause sustained shortening of the involved scalene muscles.

A foam rubber pillow should be discarded — the jiggle of the head and neck on a springy pillow aggravates scalene TrPs.

When lying supine, the patient should pull the corners of the pillow forward between the shoulder and the cheek on each side. This ensures the shoulders rest on the bed and not on the pillow, and that the cervical spine is in line with the thoracic spine. It also encourages a shoulder-down position, which avoids shortening and cramping of the chest-elevator (scalene) and scapula-elevator (levator scapulae and upper trapezius) muscles.

When turning over in bed, the patient should roll the head without lifting it off the pillow.

Body Warmth

Chilling the body, especially when resting, reduces peripheral blood flow and can lead to increased skeletal muscle irritability. In bed, an electric blanket can be invaluable. A high-necked sweater or warm scarf should be worn in bed when the bedroom is drafty. Such neck protection is often helpful on aeroplane flights. The patient can apply a moist heating pad over the scalene TrPs on the front of the neck for 10–15 min before going to sleep at night.

Satellite Trigger Points

  • Pectoralis major and pectoralis minor — develop TrPs in regions corresponding to the scalene-referred pattern of anterior chest pain
  • Long head of the triceps brachii — TrPs correspond to the scalene pattern of posterior arm pain
  • Deltoid — TrPs correspond to the anterior arm pattern
  • Extensor carpi radialis, extensor digitorum, extensor carpi ulnaris, and brachioradialis — secondary satellite TrPs in the dorsal forearm (a less common site of scalene pain)
  • Sternocleidomastoid — likely to become involved if scalene TrPs have been active for a considerable period of time
  • Upper trapezius, splenius cervicis — active TrPs in the scalenus medius are likely to be found in association with TrPs in these muscles
  • Brachialis (lateral part) — when induced as a satellite of scalene TrPs, both the brachialis and scalene muscles refer pain to the thumb, making this digit especially painful

When the omohyoid muscle develops TrPs and becomes tense, it can act as a constricting band across the brachial plexus. Because the tense omohyoid stands out prominently when the head is tilted to the other side, it can be mistaken for the upper trapezius or a scalene muscle. When the omohyoid harbours TrPs, it can prevent full stretch of the trapezius and scalene muscles, and must also be released.

References

  • Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1: The Upper Half of Body. 2nd ed. Baltimore: Williams & Wilkins; 1999. Chapter 20.
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