What is the approach to diagnose and treat trismus (lock jaw)?

Diagnosis and Management of Trismus (Lock Jaw)

Trismus, or lock jaw, is defined as a prolonged, tetanic spasm of the jaw muscles that restricts normal mouth opening and requires prompt diagnosis and appropriate management to prevent permanent functional impairment. 1

Diagnostic Approach

Clinical Evaluation

• Measure the degree of mouth opening limitation
• Assess for signs of potential causes:
  • Odontogenic infection (most common cause in clinical practice) 2
  • Trauma to masticatory muscles
  • Tumor invasion into muscles of mastication 3
  • Tetanus (characterized by generalized rigidity and painful muscle contractions) 3
  • Radiation therapy effects (radiation-induced trismus) 3
  • Temporomandibular joint disorders
  • Previous surgical procedures

Key Diagnostic Tests

• Complete oral and head/neck examination 3
• Dental radiographs to identify potential dental infections
• Forced ductions test to determine if restriction is mechanical or neurological 3
• High-resolution MRI in cases of suspected tumor involvement or complex cases 3
• Consider tetanus testing in cases with history of potential exposure and generalized symptoms 3

Management Algorithm

1. Treat the Underlying Cause

• Odontogenic infections:

  • Drainage of infection
  • Appropriate antibiotics
  • Extraction of causative tooth if indicated 2
  • Note: Extension exercises should not be undertaken during active abscess formation 4

• Post-radiation trismus:

  • Maintain range of motion with exercises
  • Tongue blades and gentle stretching
  • Custom mouth opening devices for rehabilitation 3

• Tumor-related trismus:

  • Multidisciplinary approach with oncology team
  • Careful evaluation of tumor invasion into masticatory muscles 3

• Tetanus-related trismus:

  • Immediate tetanus immunoglobulin administration
  • Antimicrobial therapy
  • Supportive care and airway management 3

2. Symptomatic Treatment

• Pain management with appropriate analgesics
• Muscle relaxants for spasm-related trismus
• Anti-inflammatory medications for inflammatory causes
• Local anesthesia techniques (modified Akinosi technique can be useful in cases of severe trismus) 2

3. Rehabilitation

• "Continuous dynamic jaw extension" therapy once acute phase has resolved 4
• Progressive stretching exercises
• Physical therapy modalities
• Custom-made mouth opening devices 3

Special Considerations

Trismus in Head and Neck Cancer Patients

• Trismus may indicate tumor invasion into the medial pterygoid muscle 3
• May contraindicate certain surgical approaches like transoral robotic surgery
• Requires careful assessment before treatment planning 3
• May be a late effect of radiation therapy requiring preventive measures 3

Surgical Management

• Intraoral management under local anesthesia can be effective for odontogenic infections even with severe trismus 2
• Early intervention shortens recovery time and may prevent permanent limitation

Prevention in High-Risk Patients

• For patients undergoing radiation therapy:
  • Pre-treatment dental evaluation
  • Maintain range of motion exercises during and after treatment
  • Regular follow-up to monitor for development of trismus 3

Common Pitfalls

• Dismissing trismus as merely stress-related without proper evaluation
• Failing to identify serious underlying causes like tumor invasion or infection
• Delaying treatment, which may lead to permanent functional impairment 5
• Not implementing preventive measures in high-risk patients (radiation therapy)
• Attempting extension exercises during active infection 4

Early diagnosis and appropriate management based on the underlying cause are essential for successful treatment of trismus and prevention of permanent functional limitations.