Trismus and Restricted Mouth Opening



  • Trismus classically refers to reduced opening of the jaws caused by spasm of the muscles of mastication (temporalis, masseter, medial pterygoid and lateral pterygoid)
  • Trismus may also be used to refer to restricted mouth opening in general
  • In the past “lockjaw” has been used as a synonym for both trismus and tetanus
  • Trismus is derived from the Greek word trismos meaning “a scream; a grinding, rasping or gnashing”

Trismus may be part of the presenting complaint or an incidental finding complicating management of comorbidity


Muscular spasm

  • Tetanus
  • Seizure
  • Upper motor neuron lesions e.g. stroke, traumatic brain injury
  • Stiff person syndrome
  • hypocalcemic tetany
  • Giant cell arteritis
  • Drugs and poisons
    • Suxamthonium-induced masseter spasm
    • Malignant hyperthermia
    • Strychnine poisoning
  • Myositis
  • Trigeminal neuralgia

Intra-articular causes of restricted mouth opening

  • Temporo-mandibular joint (TMJ) dysfunction
  • TMJ ankylosis (fibrous or bony)
  • TMJ arthritis (infective or non-infective)
  • TMJ synovitis
  • TMJ meniscal disease
  • TMJ foreign body

Other extra-articular causes of restricted mouth opening

  • Congenital
    • Congenital deformities
    • Gaucher disease
  • Psychogenic
  • Iatrogenic
    • Radiation therapy to head and neck
  • Neoplastic
    • Oral submucous fibrosis
    • Nasopharyngeal or infratemporal tumors/ fibrosis of temporalis tendon
  • Infection
    • Orodental infection
    • Malignant otitis externa
    • Peritonsilar abscess
    • Retropharyngeal or parapharyngeal abscess
    • Osteomyelitis
    • Meningitis
    • Cerebral abscess
    • Parotid abscess
  • Trauma
    • Severe soft tissue swelling and haematomas
    • Fractures e.g. mandibular condyle, zygomatic arch
  • Iatrogenic
    • post-surgical deformity (e.g. temporalis scarring after craniotomy)
    • Wired jaw
    • needle injury to medial pterygoid, local anaesthetic injection in infrapterygoind space)
    • Cervical spine collar preventing mouth opening
  • Other
    • Scleroderma
    • Acquired deformity e.g. burns
    • Neck flexion deformity


Restricted mouth opening

  • “3 finger test” — functionally normal mouth opening can be assumed if the patient can fit 3 fingers side-by-side between the top and bottom incisors
  • <4 cm inter-incisor gap — associated with difficult direct laryngoscopy and orotracheal intubation

Features of underlying cause

  • Muscular spasm: pain, tenderness, affected muscles firm to palpation


  • Difficult airway management
  • Impaired oral intake, mastication and nutrition
  • Poor oral hygiene and increased risk of orodental infection
  • Impaired speech
  • Aspiration


  • Depend on suspected underlying cause e.g. X-ray/ CT of TMJ +/- facial bones


Trismus can be acutely life-threatening in patients with airway compromise

  • May be associated with other space restricting deformities (e.g. protruding teeth, other facial or cervical spine abnormalities)
  • May prevent insertion of
    • Oropharyngeal airways
    • Suprglottic airway devices
    • Laryngoscopes and endotracheal tubes

Neuromuscular blockade

  • Relieves trismus caused by muscular spasm
  • Suxamethonium should be avoided
    • can cause transient trismus/ masseter spasm
    • Can cause hyperkalaemia in neuromuscular disorders (e.g. tetanus)

Options for restricted mouth opening not amenable to neuromuscular blockade

  • Mouth opening appliances to allow orotracheal intubation
  • Bowen-Jackson laryngoscope (narrow profile blade)
  • Video laryngoscopy and bougie (e.g. McGrath Mac blade, C-Mac, Glidescope) (if >20 mm mouth opening)
  • Lighted stylet or Bonfils (if available and user familiarity)
  • Flexiscope-assisted nasal intubation (f <20mm mouth opening)
  • Blind nasal intubation (risk of bleeding and failure)
  • Submental intubation
  • Tracheostomy or (in an emergency) cricothyroidotomy

Seek and treat underlying cause and complications

  • Depending on the cause, muscular spasm may respond to heat packs, massage, physiotherapy and mouth opening appliances
  • Refractory chronic trismus may require physiotherapy interventions

Supportive care and monitoring


  • Depends on underlying cause and presence or absence of complications

CCC Airway Series

Journal articles

  • Dhanrajani PJ, Jonaidel O. Trismus: aetiology, differential diagnosis and treatment. Dent Update. 2002 Mar;29(2):88-92, 94. [pubmed]
  • O’leary MR. Trismus: modern pathophysiological correlates. Am J Emerg Med. 1990;8(3):220-7. [pubmed]
  • Santiago-Rosado LM, Lewison CS. Trismus. 2018 Mar 29. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2018 Jan-. Available from http://www.ncbi.nlm.nih.gov/books/NBK493203/ [pubmed]
  • van der Spek AF, Reynolds PI, Fang WB, et al. Changes in resistance to mouth opening induced by depolarizing and non-depolarizing neuromuscular relaxants. Br J Anaesth 1990;64:21–7. [article]

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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