What is LockJaw?

Trismus (or lock jaw) is a condition in which someone has severely restricted mouth opening. It is a problem commonly encountered by dental practitioners, and responds well in the hands of a trained physical therapist. Trismus has a number of potential causes which range from simple and non-progressive to those that can be potentially life threatening. Knowledge of the normal range of mouth opening is essential in the diagnosis and treatment of trismus. It varies from patient to patient within a range of 40-60mm. 2 finger (~40mm) to 3 finger breadth (~54-57mm) is the usual width of opening.

Trismus is often defined as a mouth opening of less than 20mm. Other classifications include:
Mouth opening of > 30mm but < 40 mm indicated light trismus
Mouth opening of 15-30mm indicated moderate trismus
Mouth opening of < 15 mm indicated severe trismus (less than 1 finger breadth)

Limited mouth opening often poses challenges in the following areas:

  • Dental examination and treatment
  • Oral care including cleaning your mouth and teeth. This may lead to bad breath, cavities, and infections
  • Eating, drinking, chewing and swallowing
  • Talking
  • Kissing
  • Medical care if a breathing tube is necessary (emergency or surgery)

Lockjaw Causes

  1. Infection
    • Odontogenic (tooth related)
      • Pulpal
      • Periodontal
    • Non odonogenic
      • Tonsillitis
      • Tetanus
      • Meningitis
      • Parotid gland abscess
      • Brain abscess
  2. Trauma:
    • Surgical extraction of the mandibular molars
    • Post anesthetic injections; inferior alveolar nerve block, posterior superior alveolar nerve blocks (this is the more common reason we see clients with trismus due to trauma to the Medial Pterygoid muscle)
    • Direct trauma involving facial and mandibular fractures
  3. Dental treatment
  4. Temporomandibular Joint (TMJ) disorders
  5. Tumors including benign and malignant lesions involving oral cavity and submucosal areas
  6. Drug induced: Some drugs are capable of causing trismus as a secondary effect, phenothiazine, succinyl choline and tricyclic antidepressants being more among the most common. Trismus can be seen as extra pyramidal side effects of metaclopromide, Phenothiazine and other medications.
  7. Radiotherapy and chemotherapy: Fibrosis (scarring) may build up years after therapy
  8. Congenital disorders
  9. Miscellaneous disorders include Hysteria and Lupus erythematosus
  10. Fibrosis as a result of local surgery


How to Diagnose lock jaw / Trismus

The spatula test is a simple way to diagnose trismus. The posterior pharyngeal wall is touched with spatula and a reflexive spasm of the masseter occurs (positive) instead of the normal gag reflex (negative).

Once trismus develops, it is very hard to treat. That is why prevention and early recognition are essential to patient outcomes. It is important to see a physical therapist specializing in Temporomandibular Dysfunction (TMD) as soon as possible. They will provide manual treatment to the muscles restricting jaw motion and home exercises to restore opening. It is also very important to see a physical therapist with skill and specialized training in the area of TMD to prevent the possibility of developing a TMJ disc disorder.

Lockjaw Treatment – Physical Therapy Examples

  1. Sustained stretching with tongue depressors, with or without heat related modalitiesimage3
  2. Manual soft tissue mobilization to the involved muscles, as well as teaching the patient self-massage, particularly to the medial pterygoidimage4
  3. Teaching the Finger Spread technique for home stretching.image5
  4. If capsular tightness develops, graded and gentle joint mobilizationsimage6

Physical therapy treatment objectives include removing edema, softening and stretching fibrous tissue, restoring circulatory efficiency, increasing muscular length and strength, and ultimately recovering full functional range of motion. The earlier patients with trismus receive physical therapy, the faster they will recover normal opening. Some more challenging patients, post radiation cases and others who are undiagnosed for months may take several months to recover.

Do you have lock jaw? Do you have more questions on lockjaw symptoms, causes and treatment? Comment below and let me know.

Michael Karegeannes
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