How should lock jaw (trismus) be evaluated and managed?

Evaluation and Management of Lock Jaw (Trismus)

Begin conservative management with exercise therapy immediately upon diagnosis, as it is the cornerstone of treatment and should start as soon as possible to prevent progression. 1, 2

Initial Assessment and Etiology Determination

The first step is identifying the underlying cause, which dictates management strategy:

• Radiation-induced trismus: Most common in head and neck cancer patients, affecting masticatory muscles with prevalence ranging 0-100% depending on tumor site and radiation dose 3, 2
• Tumor invasion: Direct infiltration into masticatory muscles, particularly the medial pterygoid 4
• Post-surgical complications: Following oral surgery, third molar extraction, or TMJ procedures 5
• Temporomandibular joint disease: Internal derangement, disc displacement, arthritis, or synovitis 3, 6
• Iatrogenic injury: From dental procedures or inferior alveolar nerve blocks 3, 5
• Tetanus: Presents with lockjaw followed by generalized rigidity; case-fatality ratio of 18% in the United States 3
• Infection: Post-operative infections, particularly with Staphylococcus aureus (53% of cases) 3

Critical red flags requiring immediate attention: Unexplained weight loss, dysphagia, oral lesions suggesting malignancy (trismus is the presenting sign in 42% of oral cavity cancers), or signs of tetanus 1, 6

Measurement and Classification

• Trismus is defined as mouth opening ≤35 mm (normal interincisal distance is >40 mm) 6, 2
• Measure maximum interincisal opening to establish baseline and track progress 1
• Document pain characteristics including onset, duration, quality, and severity 6

Primary Treatment Algorithm

First-Line Conservative Management (85-90% of patients improve with this approach) 6

Exercise therapy must begin immediately:

• Gentle stretching exercises using tongue blades held for 15 seconds, 4-5 stretches per day 3, 1, 7
• Custom mouth opening devices such as TheraBite® Jaw Motion Rehabilitation System™ for structured rehabilitation 3, 1, 7
• Maintain range of motion exercises throughout and after radiation treatment in at-risk populations 3, 1

Pharmacologic adjuncts to facilitate exercise compliance:

• Nerve-stabilizing agents: Pregabalin, gabapentin, or duloxetine to combat pain and muscle spasms 1
• Analgesics: Acetaminophen or NSAIDs (ibuprofen) for pain control 1
• Corticosteroids: Dexamethasone to reduce inflammation and associated trismus 1
• Prophylactic antibiotics: 7-10 day course following TMJ surgery due to proximity to contamination sources 3

Dental-Specific Interventions

• Treat active dental caries and periodontal disease promptly to prevent worsening trismus 1
• Manage oral candidiasis if present, as it can exacerbate symptoms 3, 1
• Pre-radiation dental evaluation: Complete extractions at least 2 weeks before radiation therapy starts 3

Imaging Strategy (Only When Conservative Management Fails)

Do not obtain imaging initially unless red flags are present 6

When imaging is indicated:

• MRI with contrast: Gold standard for detecting active TMJ inflammation, disc position/morphology, and soft tissue pathology 3, 6
• CT or CBCT: Gold standard for bone lesion assessment when condylar fracture or degenerative changes suspected 3, 6

Specialist Interventions for Refractory Cases

Refer to oral/maxillofacial surgeon or multidisciplinary TMJ clinic when:

• Symptoms persist despite 4-6 weeks of conservative management 6
• Pain significantly impacts quality of life 6

Botulinum toxin type A injections into affected muscles for refractory pain and spasm control when conservative measures fail 1

Critical Pitfalls to Avoid

• Never rush to surgical referral without exhausting conservative options first, as 85-90% improve with non-invasive treatment 6
• Do not overlook psychological factors such as depression and catastrophizing, which reduce treatment success 6
• Avoid relying solely on imaging findings, particularly minor TMJ fluid or contrast enhancement, which may be normal variations 6
• Screen for underlying malignancy if no obvious dental or TMJ cause is identified, especially with associated symptoms 1
• Consider tetanus in any patient with lockjaw and unclear vaccination history; this is a medical emergency 3

Prevention Strategies

• Maintain range of motion exercises throughout and after radiation treatment in at-risk populations 1
• Pre-operative assessment for trismus severity to determine if it will affect surgical exposure 1
• Reduce bacterial burden through antimicrobial photo-disinfection therapy and chlorhexidine gluconate body wipes before TMJ surgery 3
• Smoking cessation 4-6 weeks before surgery to reduce infection risk 3