Muscle:Sternocleidomastoid

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Sternocleidomastoid (SCM) is a paired, superficial muscle of the anterior neck with two distinct divisions — the sternal and clavicular heads — each producing a characteristically different pattern of referred symptoms when trigger points (TrPs) are active. The SCM is one of the most clinically complex muscles in the body: its referral patterns are extensive, its autonomic contributions are significant, and its TrPs are among the most commonly overlooked sources of head, face, and ear pain.

Anatomy

The SCM arises from two heads:

  • Sternal division — originates from the anterior surface of the manubrium sterni; inserts into the mastoid process and lateral half of the superior nuchal line
  • Clavicular division — originates from the medial third of the clavicle; inserts into the mastoid process and occipital bone

Primary actions: Unilaterally — ipsilateral lateral flexion and contralateral rotation of the head. Bilaterally — flexion of the cervical spine and elevation of the sternum during forced inspiration.

Innervation: Spinal accessory nerve (CN XI) and ventral rami of C2–C3.

Referred Pain Patterns

Sternal Division

TrPs in the sternal division refer to:

  • Cheek, temple, supraorbital ridge, and occiput (ipsilateral)
  • Upper sternal region
  • Vertex of the skull

Associated autonomic phenomena:

  • Profuse ipsilateral tearing — often more alarming to the patient than the pain itself
  • Conjunctival redness
  • Rhinitis
  • Apparent ptosis via narrowing of the palpebral fissure on the TrP side (not true ptosis)
  • Visual disturbance when viewing strongly contrasted vertical lines (e.g. venetian blinds or window frames) — distinct from blurred or double vision
  • Dry tingling cough when TrPs are present near the sternal attachment — a "cough TrP"
  • Sore throat (pharyngeal pain on swallowing) with central sternal division TrPs

Postural effect: When sternal division TrPs are strongly activated, the head tilts toward the side of the TrPs because of pain on holding the head upright. The patient prefers to lie with a pillow supporting the head so the sore side of the face does not bear weight.

Clavicular Division

TrPs in the clavicular division produce one or more of three dominant presentations — any one may predominate:

  1. Frontal headache — ipsilateral, often mistaken for tension or sinus headache
  2. Postural dizziness and imbalance — see Dizziness and Disequilibrium below
  3. Dysmetria — disturbed weight perception; the same object may feel heavier when held on the unaffected side if no bilateral TrP is present

Note: In rare cases, hearing may be impaired on the same side as the active clavicular division TrPs.

Activation and Perpetuating Factors

  • Forward head posture — the single most important perpetuating factor; see Postural Assessment
  • Sleeping prone or with insufficient cervical support
  • Sustained head rotation (driving, screen positioning)
  • Whiplash and cervical trauma
  • Wearing bifocals (chin-up posture)
  • Carrying a heavy bag on one shoulder
  • Emotional tension and chronic stress
  • Parafunctional habits — clenching, bruxism, gum chewing, nail biting
  • Scoliosis or lower limb length discrepancy

Clinical Examination

Postural Assessment

Postural assessment of the head and neck is the essential starting point for any patient with head, neck, or facial pain. The protocol described here follows Chapter 5, Section C of Travell & Simons' Myofascial Pain and Dysfunction: The Trigger Point Manual.

Plumb Line Assessment

A plumb line dropped from the external auditory meatus should pass through the shoulder, hip, and end slightly anterior to the lateral malleolus. Viewed from the front, the head should be centred, the shoulders level, and the clavicles essentially parallel to the ground.

Anterior Head Position Measurement

This is the single most clinically useful postural parameter in a patient with head and neck pain.

With a real or imaginary plumb line, measure from the crest of the thoracic kyphosis to the depth of the cervical curve:

Measurement Clinical significance
6 cm Normal
< 6 cm Seen post-traumatically (loss of cervical lordosis)
> 6 cm Anterior head position

Consequences of anterior head position:

  • Posterior cervical, upper trapezius, suboccipital, and splenius capitis muscles contract and shorten to allow forward gaze with the neck in hyperextension
  • If neck hyperextension is not present, cervical lordosis is lost — the SCM works at a mechanical disadvantage and becomes overloaded, as does splenius cervicis
  • Increased strain on the C1 occipitoatlantal joint — increased risk of compression pathology
  • Anteriorly, the suprahyoid and infrahyoid muscles are in stretch, placing pressure on the mandible, hyoid, and tongue; this results in TMJ intra-articular pressure from reflexive mandibular contraction

Shoulder and Pelvic Level

Observe for shoulder asymmetry. With a standing patient and active SCM TrPs:

  • If lower limb length discrepancy is less than 6 mm — the shoulder opposite the short leg sags
  • If discrepancy is 1.2 cm or greater — the shoulder on the short leg side droops

Corrective Axial Extension Exercise

  1. Stand relaxed with thumbs pointing forward
  2. Rotate thumbs outward to point backwards while inhaling, tightening buttocks and squeezing shoulder blades together
  3. Maintain this position on the exhale
  4. Gently move the head back to bring the ears in line with the acromioclavicular joints (axial extension position) — do not move the nose up or down, and do not open the mouth
  5. Hold for six seconds with thumbs fully supinated pointing backwards

The resting position of the tongue should be at the roof of the mouth (the position articulated with the letter "N"), not touching the upper teeth, with the teeth slightly apart.

Active Range of Motion

Cervical

  • Flexion: May be slightly restricted — lacking approximately one finger breadth between the chin and sternum with sufficiently painful TrPs
  • Rotation: May be reduced to approximately 10° toward the opposite side with active TrPs. The contracting SCM is reflexively inhibited by TrPs.

Mandibular Opening

Normal interincisal opening range is 36–44 mm, measured between the central incisor teeth. A practical bedside test is that the patient should be able to fit two knuckles of the non-dominant hand between the upper and lower teeth.

  • Opening > 60 mm is clinically significant TMJ hypermobility
  • Opening < 36 mm with deflection and hard end feel may indicate ankylosis or anteriorly displaced disc without reduction — refer to a specialist in TM disorders

Without measuring, observe the path of opening and closing for deflection and deviation from the midline:

  • The jaw will deviate (return to midline) with a disc displacement with reduction, or toward the side with elevator muscle TrPs
  • The jaw will deflect (not return to midline) toward the affected side with internal derangement, ankylosis, or restricted ROM

For the full TMJ screening examination protocol including joint palpation, noise assessment, and referral criteria, see Pain:TMJ_Screening_Examination.

SCM Trigger Point Examination

The TrP examination requires confirmation of:

  1. A taut band within the muscle
  2. Spot tenderness within that band
  3. Presence of referred pain
  4. Reproduction of the patient's familiar referred pain, or a local twitch response on snapping palpation

Positioning

The patient may be seated or supine. Slack the muscle by having the patient tilt the ear toward the shoulder on the symptomatic side, and if necessary turn the head away from the affected muscle.

Palpation Technique

  • Sternal division: Pincer palpation — encircle the muscle belly between thumb and forefinger. Snapping a taut band may cause a head jerk. Apply flat palpation at the origin (sternal attachment) and insertion (mastoid process).
  • Clavicular division: Flat palpation — the clavicular head lies deep and posterior to the sternal head; palpate from the medial clavicle upward toward the mastoid.
  • Platysma response: A prickling sensation in the face over the mandible is the characteristic response of TrPs in the overlying platysma muscle — distinguish this from SCM referral.

SCM Compression Test

Indicated when the patient reports sore throat or pharyngeal pain on swallowing, or a persistent dry tingling cough.

  1. Grasp the SCM firmly in a pincer grip
  2. Immobilise the tender region by steadily compressing the muscle belly
  3. Ask the patient to swallow

Positive result: The pharyngeal pain resolves with pincer grip compression, or even with superficial squeezing of the skin overlying the muscle. This confirms a sternal division TrP as the source of the referred throat pain.

Dizziness and Disequilibrium

Dizziness caused by clavicular division TrPs has a characteristic clinical profile that distinguishes it from vestibular pathology:

  • Romberg's sign is negative — the patient does not lose balance with eyes closed and feet together
  • Nystagmus is absent — presence of nystagmus indicates vestibular pathology, not myofascial origin
  • Straight-line walking test: Ask the patient to walk toward a fixed point across the room while fixing their gaze on it. In myofascial disequilibrium, the path veers toward the side of the active clavicular division TrP. This does not occur with true vestibular pathology.
  • Dizziness is postural — worsens on changing head load, hyperextension of the neck, lying without a pillow, rolling over in bed, or quick rotation of the head
  • Active TrPs add to car sickness and sea sickness; the patient may report nausea or anorexia

Hearing Restoration Manoeuvre

In some patients with clavicular division TrPs, reduced hearing on the affected side may temporarily resolve by:

  1. Rotating the head toward the affected side
  2. Tilting the chin downward

This relieves the reflex disturbance of the tensor tympani mediated by the TrP.

Weight Perception Test (Dysmetria)

When no bilateral TrP is present, the patient may report that the same object feels heavier when held on the unaffected side. This dysmetria is a characteristic feature of clavicular division TrP involvement.

Neurological Screen

This screen is indicated whenever the patient reports dizziness, spatial disorientation, or ear symptoms. The purpose is to exclude serious neurological pathology before attributing symptoms to SCM TrPs.

Romberg's Sign

Stand the patient with feet together and arms at sides. Observe with eyes open for 30 seconds, then eyes closed for 30 seconds.

  • Negative Romberg (normal sway with eyes closed) — consistent with SCM TrP dizziness
  • Positive Romberg (significant sway or stepping only with eyes closed) — indicates proprioceptive or posterior column deficit; excludes myofascial origin; refer to neurology

Nystagmus

Ask the patient to follow a finger to lateral gaze — hold each position for 30 seconds. Observe for rhythmic involuntary horizontal, vertical, or rotatory eye movement.

  • Absent nystagmus — consistent with SCM TrP dizziness
  • Present nystagmus — indicates vestibular pathology; see Pain:Ear_and_TMJ broad differential

Postural Blood Pressure

Take BP lying, then after 2 minutes sitting, then after 1 minute standing. A drop of ≥20 mmHg systolic or ≥10 mmHg diastolic on standing indicates orthostatic hypotension — consider adrenocortical insufficiency; refer to GP or endocrinology.

Carotid Auscultation

Auscultate with the diaphragm of a stethoscope over the carotid bifurcation (anterior to SCM at the level of the thyroid cartilage) and higher, with the patient holding their breath briefly.

  • Bruit present → carotid stenosis or subclavian steal syndrome (check BP in both arms; >15 mmHg difference between arms suggests subclavian steal); refer to vascular surgery

Horner Syndrome Exclusion

SCM TrPs produce autonomic phenomena that can superficially resemble Horner syndrome. Confirm the following to exclude true Horner syndrome:

  • Pupils equal and normally reactive — no miosis (constricted pupil)
  • No enophthalmos (sunken eye) — apparent ptosis is from palpebral fissure narrowing only, not true ptosis
  • Ciliospinal reflex present — pinch the skin on the back of the neck; the ipsilateral pupil should dilate
  • Extraocular movements full — no paralysis of extraocular muscles; eye symptoms are not conversion hysteria

CN XI — Spinal Accessory Nerve

Myogenic torticollis due to SCM contracture can compress CN XI on its course to the trapezius, resulting in ipsilateral trapezius weakness.

Test by asking the patient to perform resisted shoulder shrug bilaterally simultaneously. Compare side to side. Unilateral weakness with SCM TrPs = CN XI entrapment neuropathy. This should resolve with release of the SCM contracture. If weakness persists after treatment, refer to neurology.

Spasmodic Torticollis Differentiation

If involuntary or dystonic head rotation is present, distinguish spasmodic torticollis from SCM TrP-driven head posture:

  • Apply gentle pressure against the jaw on the side toward which the head is rotated
  • Positive: Rotation is inhibited or reduced by jaw pressure (geste antagoniste) → spasmodic torticollis
  • Positive: Dystonic movement ceases completely during sleep → spasmodic torticollis
  • Both features together are pathognomonic — refer to neurology; botulinum toxin is first-line treatment

Differential Diagnosis

SCM TrPs can mimic or co-exist with:

  • Vascular and cervicogenic headache
  • Vestibular dysfunction (distinguish by Romberg, nystagmus, and straight-line walking test)
  • Trigeminal neuralgia (tic douloureux) — SCM referral can produce facial pain in V2/V3 distribution; distinguish by quality (lancinating vs aching) and trigger zones
  • Ménière's disease — distinguish by fluctuating unilateral hearing loss, episodic rotational vertigo, and nystagmus
  • Spasmodic torticollis — distinguish by geste antagoniste and sleep cessation
  • Lymphadenopathy — soreness along the SCM belly is commonly misattributed to lymph node tenderness

For full differential diagnosis including rare mimics, see Pain:Ear_and_TMJ.

Treatment

Trigger Point Release

  • Spray and stretch — vapocoolant spray applied in a superior-to-inferior direction over the muscle belly and referred pain zone, followed by passive stretch into contralateral rotation and lateral flexion
  • Ischemic compression — sustained pincer grip pressure on the taut band until release is felt
  • Dry needling — sternal and clavicular heads separately

Postural Correction

Correction of anterior head position is essential for long-term resolution. See Axial Extension Exercise above and Patient Education below.

Note on Satellite TrPs

Treating SCM TrPs often produces spontaneous improvement in satellite TrPs without direct treatment. Address SCM first before treating satellites.

Patient Education

Sleep Posture

  • Best: supine on a firm surface. Soft beds strain all muscles — a sheet of plywood placed lengthwise under the mattress above the box spring improves firmness.
  • Side sleepers: pillows under the head and neck only, not the shoulders
  • Stomach sleepers: tie a sheet around the waist with a knot on the stomach to prevent rolling; alternatively place a pillow under the chest to reduce head rotation. Patients with lumbar disc dysfunction instructed to sleep prone should use a chest pillow and a pad under the forehead to reduce neck rotation.
  • Patients with clavicular division TrP dizziness: learn to roll the head on the pillow rather than lifting it when turning over in bed at night

Tongue Rest Position

The tongue should rest at the roof of the mouth in the position articulated by the letter "N" — not touching the upper teeth — with the teeth slightly apart. This reduces TMJ intra-articular pressure and jaw muscle activity.

Workstation Setup

  • Monitor distance: fingertips should just reach the screen with the arm extended
  • Monitor height: top third of the screen at eye level
  • Chair height: thighs horizontal, feet flat on the floor — no compression under the thighs from dangling feet
  • Desk height: surface at the level of the half-flexed elbow at rest

Driving

Lumbar support is essential. A firmly rolled towel approximately 30 cm (12 inches) wide and 8–10 cm (3–4 inches) in diameter placed at belt height provides effective lumbar support and reduces the posterior chain muscle loading that perpetuates SCM TrPs.

Satellite Trigger Points

The following muscles may develop TrPs as satellites of SCM or in association with chronic SCM TrP activity:

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 7.
  • Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1. 2nd ed. Chapter 5, Section C.
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