Muscle:Digastric

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The digastric is a two-bellied suprahyoid muscle of the anterior neck whose trigger points (TrPs) are among the most clinically deceptive in the head and neck region. Each belly has its own distinct referred pain pattern and its own set of clinical consequences. The posterior belly refers pain to the upper sternocleidomastoid (SCM) region — a pattern so convincingly similar to SCM TrP pain that it is aptly called "pseudo-sternocleidomastoid pain." The anterior belly refers pain to the four lower incisor teeth, a pattern that leads to unnecessary dental treatment when the muscle is not examined.

The digastric is closely linked to the masticatory muscles through shared function and reflex relationships. It nearly always develops TrPs secondary to TrPs in the mandibular elevator muscles — particularly the masseter — rather than in isolation. The mutual satellite relationship with the SCM (either muscle can drive the other) makes systematic examination of both essential whenever either is involved.

This page covers the digastric muscle primarily. The broader group of anterior neck muscles — suprahyoid, infrahyoid, and deep anterior vertebral muscles — are summarised at the end with their key clinical features.

Anatomy

The digastric has two bellies joined by a common intermediate tendon that is anchored indirectly to the hyoid bone through a fibrous loop (the suprahyoid aponeurosis). The tendon can slide through this loop.

Posterior belly
Arises from the mastoid notch on the mastoid process of the temporal bone, deep to the attachments of the longissimus capitis, splenius capitis, and SCM. Passes anteriorly and inferiorly to the intermediate tendon.
Anterior belly
Arises from the inferior border of the mandible close to its symphysis. Passes posteriorly and inferiorly to the intermediate tendon.

The tendon common to both bellies perforates the stylohyoid muscle, which lies near the front half of the posterior belly.

Suprahyoid group (superior attachment to hyoid): stylohyoid, mylohyoid, geniohyoid. These work with the digastric to open the mouth and can refer pain to the tongue, laryngeal region, and anterior neck.

Infrahyoid group (inferior attachment to hyoid): sternohyoid, sternothyroid, thyrohyoid, omohyoid. Provide the essential depressive force on the hyoid bone required for the suprahyoid muscles to function normally.

Deep anterior vertebral muscles: longus colli, longus capitis, rectus capitis anterior, rectus capitis lateralis. Lie along the anterior surface of the vertebral column, directly deep to the posterior wall of the pharynx. TrPs in the longus colli and longus capitis cause difficulty swallowing and a lump-in-throat sensation and are a significant source of unresolved posterior neck pain.

Innervation

  • Anterior belly and mylohyoid — alveolar branch of the trigeminal nerve (CN V)
  • Posterior belly and stylohyoid — facial nerve (CN VII), exiting the skull through the stylomastoid foramen
  • Infrahyoid muscles (sternohyoid, sternothyroid, omohyoid) — ansa cervicalis (C₁–C₃)
  • Thyrohyoid — C₁ fibres
  • Longus capitis — C₁–C₃; longus colli — C₂–C₆ ventral rami

Referred Pain Patterns

Posterior Belly

TrPs in the posterior belly refer pain to the upper part of the sternocleidomastoid muscle, to the throat in front of the SCM and under the chin, and sometimes extending to the occiput. This occipital component may activate satellite TrPs in the occipital portion of the occipitofrontalis muscle. Pain from digastric TrPs may also extend to the ear.

This pattern is called "pseudo-sternocleidomastoid pain" because it is so convincingly similar to SCM TrP referral that it is commonly attributed to the SCM. The critical diagnostic clue: when the SCM is cleared of TrPs, the pain and soreness persist in the upper SCM region. The area remains diffusely and moderately tender to palpation but is free of taut bands and local twitch responses — indicating the source is the posterior digastric, not the SCM.

Anterior Belly

TrPs in the anterior belly refer pain to the four lower incisor teeth and the alveolar ridge below them, and may be referred to the tongue. The responsible TrP is located just under the tip of the chin and can be on either side of the midline. This is a bilateral, nearly midline pain pattern. Glossodynia (burning tongue) can be caused by TrPs in the anterior belly.

Referred pain summary — Digastric
Belly TrP location Essential referred zone Key clinical trap
Posterior belly Behind the angle of the mandible, between the mastoid process and the angle of the jaw Upper SCM region; throat in front of SCM; under the chin; occiput Mistaken for SCM TrP pain — persists after SCM is cleared. Check digastric whenever SCM TrP treatment gives incomplete relief.
Anterior belly Just under the tip of the chin, either side of the midline Four lower incisor teeth + alveolar ridge below; tongue Mistaken for dental pathology — unnecessary extractions and root canals. Check this muscle in any patient with unexplained lower incisor pain.

Other Anterior Neck Muscles

  • Mylohyoid — refers pain to the tongue; may cause glossodynia
  • Stylohyoid — head and neck pain attributed to this muscle in combination with the posterior digastric
  • Longus capitis / longus colli — difficulty swallowing, lump in the throat, dry mouth, sore throat without infection, persistent tickle in the throat. A significant source of unresolved posterior neck pain through sustained fascial tension.
  • Omohyoid — taut band tension can act as a constricting band across the brachial plexus; easily mistaken for the upper trapezius or scalene muscle when tense

Activation and Perpetuating Factors

Digastric

  • Masseter TrPs — the most specifically identified activating factor; the masseter-digastric relationship is unusually dependent on reflex interaction because the digastric bellies are practically devoid of muscle spindles
  • SCM TrPs — SCM key TrPs can induce satellite TrPs in the digastric; conversely, inactivating digastric TrPs can inactivate satellite SCM TrPs (bidirectional satellite relationship)
  • Retrusive bruxism — mandibular retrusion strongly recruits the digastric; the digastric is always active during mandibular retrusion
  • Mouth-breathing — a sign of which is inward rather than outward flaring of the nostrils during inhalation; may result from nasal polyps, deviated septum, sinusitis, or recurrent allergic rhinitis
  • Eagle syndrome — an elongated styloid process can cause mechanical irritation activating TrPs in the posterior belly and medial pterygoid; the patient complains of jaw angle pain with possible dizziness and visual blurring
  • Flexion-extension injuries ("whiplash") — can activate TrPs in the suprahyoid, infrahyoid, and deep anterior vertebral muscles; forward-head posture perpetuates them

Deep Anterior Vertebral Muscles (Longus Colli / Longus Capitis)

Forward-head posture is the primary perpetuating factor. Flexion-extension injuries are a common activating event. These muscles may develop persistent TrP tightness that tightens the anterior cervical fasciae, overloading posterior muscles and contributing to unresolved posterior neck and back pain.

Clinical Examination

Symptoms

Posterior digastric TrPs: The primary complaint may not be pain — the patient may first complain of difficulty swallowing and a sensation of a lump in the throat, or that something is stuck and won't go down. Head rotation to the involved side is likely to elicit referred pain or aggravate the swallowing problem. The patient is likely to point to the SCM on the involved side. The digastric pain component may only become apparent after concurrent SCM TrPs have been inactivated.

Anterior digastric TrPs: Chief symptom is pain in the lower incisor teeth. The source is perplexing if only the teeth are considered.

Longus colli / longus capitis TrPs: Difficulty swallowing, lump in the throat, dry mouth, sore throat without infection, persistent tickle in the throat. Posterior neck pain that does not resolve with posterior cervical treatment may originate from these anterior muscles.

Hyoid Assessment

The hyoid bone influences movements of the mandible, swallowing, and speech. The examiner should assess the hyoid for free movement laterally in both directions and should palpate for muscle tension in suprahyoid and/or infrahyoid muscles when lateral movement is restricted.

Tension in either belly of the digastric can be assessed by finding abnormal resistance when trying to shift the hyoid bone from side to side.

Mandibular Deviation Sign

Sustained TrP tension of the posterior digastric and stylohyoid muscles can deviate the mandible to the side of the active muscle when the jaws separate. If deviation is due solely to posterior digastric TrPs, the mandible is pulled to the involved side as the jaws start to separate, but with further opening it returns to the midline. This self-correcting deviation distinguishes muscle-driven deviation from articular causes.

Swallowing Test

An indicator that posterior digastric TrPs are contributing to difficulty swallowing: improvement of the swallowing symptom when the patient clenches the teeth while swallowing. Clenching may reciprocally inhibit the digastric TrP activity responsible for the difficulty.

Anterior Digastric Test

Ask the patient to pull the corners of the mouth downward vigorously enough to tense the anterior neck muscles. When positive, this Anterior Digastric Test activates the toothache and confirms the likelihood of TrPs in the anterior belly of at least one digastric muscle as the source of the lower incisor pain.

Trigger Point Examination

Posterior Belly

The patient is supine with the head extended to enlarge the space for palpation between the neck and the angle of the mandible. Palpate by rubbing across (perpendicular to the direction of) the fibres behind the angle of the mandible, and by sliding the finger upward toward the ear lobe along the anterior border of the SCM while pressing inward against the underlying neck muscles.

Initial pressure on active TrPs in the posterior belly elicits exquisite local tenderness; sustained pressure may reproduce the patient's more distant neck and head pain.

No effort is made to distinguish the posterior digastric from the stylohyoid muscle during either palpation or injection — they are treated as a unit.

Anterior Belly

The patient is supine with the head tilted back and the neck extended to stretch the muscle. Palpate the soft tissues just beneath the point of the chin on both sides of the midline. A tender nodule may be felt in the muscle belly at the point of central TrP tenderness.

Tenderness at the base of the greater horns of the hyoid bone is likely to represent attachment TrP tenderness due to enthesopathy rather than a central TrP.

Omohyoid Pitfall

If the inferior belly of the omohyoid has a tender TrP and taut band, it can be mistaken for the anterior scalene muscle. The omohyoid is more superficial, comes out from beneath the SCM, and crosses diagonally over the anterior scalene. When tense, the omohyoid stands out under the skin like a rope when the head is tilted to the contralateral side — it can be mistaken for the upper trapezius or a scalene muscle.

Longus Colli Palpation

TrPs in the longus colli can be palpated with difficulty by placing the examining finger along a lateral border of the trachea between the SCM and the thyroid cartilage, then slowly advancing it by separating the musculature from the adjacent trachea by gentle rocking and wiggling motions of the finger until the vertebral column is reached. TrPs in the longus capitis can be palpated behind the posterior pharyngeal wall through the open mouth.

Differential Diagnosis

Differential diagnosis — Digastric and anterior neck TrPs
Pain pattern Digastric / anterior neck TrPs Key mimics How to distinguish
Upper SCM region pain and tenderness Posterior digastric TrP — "pseudo-SCM pain." Persists after SCM is cleared. No taut band in SCM region. SCM TrPs (sternal or clavicular division) Inactivate SCM TrPs first. If SCM region tenderness persists without taut bands or LTR in SCM → posterior digastric is the source. Palpate posterior digastric behind angle of jaw.
Lower incisor tooth pain Anterior digastric TrP. Bilateral, nearly midline. Positive Anterior Digastric Test. Dental pathology (pulpitis, periapical abscess, cracked tooth syndrome) Dental examination negative. Anterior Digastric Test positive — pulling corners of mouth down activates the toothache. TrP palpable under the chin.
Tongue pain / burning Mylohyoid or anterior digastric TrP. Glossodynia. Glossitis, geographic tongue, neurological causes, burning mouth syndrome TrPs palpable in mylohyoid or anterior digastric with referred tongue pain on compression. Inactivating these TrPs resolves the glossodynia.
Difficulty swallowing + lump in throat Posterior digastric, longus colli, longus capitis. Improved by clenching while swallowing (posterior digastric sign). Pharyngeal pathology, GERD, oesophageal dysmotility, globus hystericus Clenching-while-swallowing test. Longus colli TrPs: onset after whiplash, forward-head posture, persisting posterior neck pain.
Jaw angle pain + dizziness + visual blurring Eagle syndrome — elongated styloid process activating posterior digastric and stylohyoid TrPs. Also associated SCM TrPs producing the dizziness. TMJ disorder, trigeminal neuralgia, carotid artery dissection Ossified/elongated styloid palpable intraorally. Calcification of stylohyoid ligament visible on imaging. Dizziness from SCM satellite TrPs.
Throat/neck cord standing out on head tilt Omohyoid TrP — the tense inferior belly stands out diagonally across the neck. Scalene TrP, upper trapezius TrP Omohyoid is more superficial, exits from under SCM, crosses diagonally over anterior scalene. Fibre direction is oblique, not vertical like scalene.
Unresolved posterior cervical pain Longus colli / longus capitis TrP tension tightening anterior fasciae and overloading posterior muscles. Cervical disc disease, posterior cervical TrPs not responding to treatment If posterior neck pain persists despite adequate posterior treatment, assess anterior structures. Longus colli TrPs activated by whiplash; perpetuated by forward-head posture.

Eagle Syndrome

Eagle syndrome is caused by an abnormally elongated styloid process or calcification of the stylohyoid ligament, producing mechanical irritation of the posterior belly of the digastric and medial pterygoid. Active TrPs in the posterior digastric and stylohyoid muscles can result in sustained hyoid elevation and jaw angle pain. The calcification is palpable from inside the mouth and may require surgical removal if TrP treatment provides only partial relief. The associated dizziness and visual blurring are likely caused by satellite TrPs in the adjacent SCM muscle. Pressure of the calcified process against the carotid artery during extreme head rotation may cause pain and dizziness.

Treatment

Trigger Point Release

Cervical muscles frequently work in pairs and are involved bilaterally — treat bilaterally. Correct excessive forward-head posture and give home instructions.

Posterior digastric — spray and release: Apply vapocoolant (or icing) over the anterior and posterior bellies, the area under the chin, the upper SCM, the mastoid area, and to the occiput if involved. Then apply postisometric relaxation with the patient supine: the clinician's hand resists the patient's attempt to open the mouth (isometric contraction phase) while the thumb exerts minimal pressure on the hyoid bone on the side of TrP involvement. The patient opens the mouth gently and breathes in, holds momentarily, then breathes out slowly and relaxes fully. As tension releases under the light thumb pressure, the hyoid bone moves toward the contralateral side. Repeat to gain complete release.

Anterior digastric and suprahyoid group — spray and release: Have the patient extend the head and neck sufficiently to take up slack in the anterior neck muscles. Apply parallel spray sweeps downward over the anterior neck. Then release the suprahyoid group by anchoring the hyoid bone with thumb and index fingers of one hand and taking up soft-tissue slack upward toward the mandible with the other hand. For infrahyoid release, anchor the hyoid with one hand and apply caudal pressure across the sternoclavicular junctions with the other.

A contract-relax procedure for the infrahyoid group: have the patient press the tip of the tongue firmly against the roof of the mouth, hold, then relax.

Omohyoid: Stretch by tilting the head to the contralateral side and depressing the scapula while applying down-sweeps of spray over the muscle.

TrP pressure release is effective for both bellies of the digastric. For the anterior belly, Hong's technique uses stretching massage with one finger inside the mouth and one outside.

Trigger Point Injection

⚠ Safety Notice: Procedures described on this page involve structures in close proximity to major vessels or neurovascular bundles. This page is intended for qualified clinicians. Always identify relevant anatomy before proceeding. This site is not validated for clinical use — see the site disclaimer.

Injection is reserved for TrP sensitivity that persists after spray and release and TrP pressure release.

Posterior belly: With the patient supine, fix the muscle between two fingers with the index finger displacing the external jugular vein. The taut band is localised between the fingers for tactile guidance. A local twitch response is an important indicator of successful injection. Needle penetration may cause a flash of referred pain over the occipital region — warn the patient.

Anterior belly: Head and neck extended. Localise TrP spot tenderness in the taut subcutaneous muscle fibres between two fingers of the palpating hand for injection.

Suprahyoid / infrahyoid muscles: A shorter 1-inch, 27-gauge needle with careful attention to local anatomy.

Patient Education

  • Stop retrusive bruxism — mandibular retrusion strongly recruits the digastric and is a primary activating and perpetuating factor
  • Restore nasal breathing — mouth breathing predisposes to digastric TrP activation; investigate and treat underlying cause (polyps, deviated septum, sinusitis, rhinitis)
  • Correct forward-head posture — essential for resolving longus colli and longus capitis TrPs and preventing recurrence
  • Self-TrP pressure release — the patient must learn to press on the posterior digastric deep to the angle of the mandible, not on the SCM where the referred tenderness is felt
  • Postisometric self-release: sitting at a table, chin supported by one hand, other hand at the hyoid bone — replicate the clinician's technique at home
  • Jaw protrusion exercise: if the mandible deviates to one side during active opening, the patient rhythmically resists the deviation by pushing the mandible to the opposite side with the fingers while the jaws are less than half open — this stretches a tight posterior digastric belly
  • Malocclusion: correct when symptoms persist after masticatory TrPs have been inactivated

Satellite Trigger Points

The digastric is deeply embedded in the masticatory functional unit. Satellite relationships are bidirectional and clinically critical:

  • Muscle:Masseter — the primary key TrP activating the digastric; masseter TrPs have been specifically identified as a driver
  • Muscle:Sternocleidomastoid — mutual satellite relationship; either muscle can drive the other; treat both systematically
  • Muscle:Temporalis — posterior fibres and deep masseter on the contralateral side may develop TrPs when sustained posterior digastric tension deviates the mandible
  • Muscle:Occipitofrontalis — occipital satellite TrPs may develop from the occipital component of posterior digastric referral
  • Longus colli, suprahyoid, and infrahyoid muscles — commonly co-involved in Eagle syndrome and whiplash presentations

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 12.
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