Muscle:Zygomaticus Major

Zygomaticus major is a slender, superficial muscle of the mid-face that draws the angle of the mouth upward and laterally in smiling and laughing. Its trigger points (TrPs) refer pain in a distinctive arc from the cheek up along the side of the nose to the mid-forehead, and are among the most common unrecognised sources of apparent facial pain and headache. TrP tightness can measurably restrict jaw opening, and buccinator TrPs misdiagnosed as temporomandibular joint (TMJ) syndrome are a common parallel finding.

Anatomy

The zygomaticus major is a narrow, ribbon-like muscle of the cheek. It attaches:

• Above — to the malar surface of the zygomatic bone
• Below — to the angle of the mouth, where its fibres blend with those of the orbicularis oris

The muscle is also known by the older term zygomatic head of the quadratus labii superioris. Its parallel neighbour, the zygomaticus minor (zygomatic head of the levator labii superioris), assists the same action and may harbour satellite TrPs.

The fibres of the zygomaticus major, like all muscles of facial expression, lie within the superficial fascia. Histologically, facial muscles have fibre diameters approximately half those of limb muscles (32–40 μm versus 57–69 μm) and a disproportionately high percentage of type IIA fibres (48–68% versus 29% in limb muscles). Motor unit potentials are approximately half the duration and half the amplitude of limb muscles.

Innervation: Facial nerve (cranial nerve VII), buccal branch.

Primary action: Draws the angle of the mouth upward and laterally — the movement of smiling, laughing, or saying "Whee."

Functional unit: Assisted by zygomaticus minor. The orbicularis oris acts reciprocally with the zygomaticus major in speech and facial expression.

Referred Pain Pattern

TrPs in the zygomaticus major refer pain in a curving arc that begins at the cheek, travels along the lateral side of the nose, crosses the nasal bridge, and extends upward to the mid-forehead on the same side (Fig. 13.1B, Travell & Simons Vol. 1, 2nd ed.).

This referral pattern can produce apparent facial pain or forehead pain that has no local structural cause. Because the arc passes close to the nose and forehead, the pattern is readily mistaken for tension headache or sinus-related pain.

Activation and Perpetuating Factors

• Masticatory muscle dysfunction — severe myofascial dysfunction of the masticatory muscles causing trismus is the principal activating mechanism; the restricted opening places the zygomaticus major under sustained mechanical load
• Satellite activation — TrPs develop secondarily in the pain reference zone of the sternocleidomastoid (sternal division), which refers to the cheek; the zygomaticus major lies within this zone and may become a satellite focus
• Facial expression overload — sustained or exaggerated facial animation in tense individuals

Clinical Examination

Active Range of Motion

Movement	Normal	Finding with active TrPs
Interincisal opening	36–44 mm	May be reduced by 10–20 mm due to TrP tightness; can be improved by inactivating TrPs
Jaw deviation on opening	None	May deflect toward the side of masticatory TrP involvement

A quick bedside screen for jaw opening is that the patient should be able to fit two knuckles of the non-dominant hand between the upper and lower teeth. If this is not possible, measure interincisal distance in millimetres and document.

Trigger Point Examination

Positioning

The patient is positioned either supine or seated. The jaws are propped open as wide as is comfortable — adequate opening slackens the muscle and makes it accessible to palpation. Do not attempt to examine this muscle with the jaw closed.

Palpation Technique

Pincer palpation is the primary technique:

1. Place one digit (gloved) inside the cheek and one digit outside
2. The palpable taut band is appreciated chiefly by the outside finger as it rolls over the band running in the direction of the muscle fibres, from the zygomatic bone toward the angle of the mouth
3. Identify spot tenderness within the band — this is the TrP

Local twitch responses are not readily observed in the zygomaticus major, probably because it is difficult to place the muscle under sufficient stretch for this response to be elicited clearly.

Unilateral Palpebral Fissure Narrowing

Active TrPs in the zygomaticus major may contribute to a unilateral narrowing of the palpebral fissure on the affected side. This resembles the apparent ptosis seen with SCM sternal division TrPs and the ptosis of Horner's syndrome, but without any change in pupillary size. When upward gaze is tested, these patients tilt the head backward because they cannot raise the upper eyelid sufficiently to look up.

Horner syndrome exclusion:

• Pupils equal and reactive — no miosis
• No enophthalmos
• Apparent lid drooping is due to palpebral fissure narrowing, not true ptosis

Jaw Opening Restriction Assessment

Trigger-point tightness of the zygomaticus major muscle may cause restriction of normal jaw opening by 10 or 20 mm. This is identified by:

1. Measuring interincisal opening baseline
2. Inactivating TrPs in the zygomaticus major by pressure release or injection
3. Re-measuring jaw opening — improvement confirms the TrPs were contributing to the restriction

This restriction must be distinguished from TMJ articular pathology and masticatory muscle contracture (see Ear and TMJ diagnostic algorithm).

Differential Diagnosis

Pain from zygomaticus major TrPs is readily attributed to:

• Tension headache — the forehead component of the referral pattern is mistaken for tension-type headache without recognition of the facial muscle source
• Sinusitis — the arc along the nose and across the mid-forehead overlaps with the pain distribution of maxillary and frontal sinusitis; the absence of nasal symptoms, tenderness on direct sinus palpation, or fever helps distinguish TrP origin
• Trigeminal neuralgia — distinguished by the lancinating, electric-shock quality of trigeminal pain versus the dull aching arc of TrP referral; trigeminal neuralgia also has well-defined trigger zones (lip, cheek, tooth) producing paroxysmal rather than sustained pain
• TMJ syndrome — jaw-opening restriction from zygomaticus major TrP tightness can be misattributed to articular TMJ pathology; see TMJ Screening Examination

For full facial pain differential, see Face and Jaw diagnostic algorithm (coming soon).

Treatment

Trigger Point Release

Spray and Stretch

With the patient supine or seated, and jaws propped open:

1. Using a gloved hand, pull the corner of the mouth downward and forward, away from the zygomatic bone, to lengthen the muscle fibres
2. While the operator maintains tension on the muscle fibres, the patient exhales
3. Apply vapocoolant spray upward over the muscle and then over the distribution of the referred pain (along the lateral nose and up to the forehead)
4. Cover the patient's eye and nose during spray application to protect these areas
5. If the patient has asthma or another respiratory condition, substitute ice stroking for spray

Caution: It is difficult to obtain adequate stretch of this long, slack muscle, and spray and stretch may be ineffective as a stand-alone treatment.

Trigger Point Pressure Release

Zygomaticus TrPs can be effectively inactivated by sustained trigger point pressure release, combined with stroking massage of the nodule and taut band. This is often more reliable than spray and stretch given the difficulty of achieving adequate muscle lengthening.

Trigger Point Injection

Injection is usually more effective than stretch and spray for this muscle.

1. Position the patient supine or seated, jaws comfortably propped open
2. Grasp the TrP in a pincer hold between thumb and forefinger (one digit inside the cheek, one outside), as during examination
3. Inject the taut band at its most tender point under tactile guidance
4. Needle: 16 mm (5/8 inch), 25- or 26-gauge, with 0.5% procaine in isotonic saline

Warn the patient that ecchymosis can develop in the injected area.

Corrective Actions

The most important corrective priority is elimination of the key TrPs responsible for satellite activation:

• Sternocleidomastoid — sternal division TrPs refer to the cheek; resolving these reduces the satellite burden in the zygomaticus major
• Masseter, temporalis, medial pterygoid, lateral pterygoid — masticatory muscles driving trismus activate zygomaticus major TrPs by mechanical overload; address these first
• Upper trapezius — commonly co-active in forward head posture presentations

Address any perpetuating factors including jaw parafunctions (bruxism, clenching, nail biting, gum chewing) and ill-fitting dental appliances.

Satellite Trigger Points

Muscles that may develop TrPs as satellites of zygomaticus major involvement, or that co-activate as part of the same clinical syndrome:

• Zygomaticus minor — parallel muscle with overlapping function and location
• Orbicularis oculi — lies in the pain reference zone; may develop satellite TrPs producing the "jumpy print" visual symptom and apparent palpebral ptosis
• Platysma — overlies the SCM; secondary activation common in SCM–scalene syndrome
• Buccinator — frequently co-involved; refers pain locally to the cheek and as a subzygomatic ache in the jaw; commonly misdiagnosed as TMJ syndrome

Related Pages

• Face and Jaw pain region — diagnostic algorithm (coming soon)
• Ear and TMJ diagnostic algorithm
• TMJ Screening Examination protocol
• Sternocleidomastoid — key TrP driving satellite activation in the zygomaticus major
• Masseter — primary masticatory muscle; trismus activates zygomaticus major TrPs
• Orbicularis oculi — co-involved facial muscle; referred pain to the nose
• Platysma — co-involved facial muscle; prickling jaw pain
• Buccinator — co-involved; subzygomatic jaw pain, swallowing symptoms

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 13.
• Travell J. Identification of myofascial trigger point syndromes: a case of atypical facial neuralgia. Arch Phys Med Rehabil 62:100–106, 1981.