Trismus
Treatment of and for trismus can be largely divided into treatment that is specific to the underlying cause which will then alleviate the trismus (for example, discontinuing a drug causing it, or draining an abscess responsible for spasm in the muscles of mastication), or treatments that address the trismus when the primary cause has been alleviated or its only effect is trismus (for example, ankylosis of the temporomandibular joint).
Extra-articular (external to the jaw joint) causes for trismus
Of the many different extra-articular causes of trismus, some are very common and mainly cause short-term temporary difficulties with opening of the mouth and/or movements of the jaw in general.
Infection
A range of abscesses afflicting the parotid gland or the base of the skull, as well as infections of the jaw bones (for example, acute osteomyelitis) can cause trismus and the treatment, generally is a combination of drainage, débridement and antibacterial agents.
Trauma
Fractures of the mandible (lower jaw) and the zygomatic arch (cheek bone) are common causes of trismus. Inability to open the mouth in order to enable safe anaesthesia for elevation of a depressed fracture of the zygomatic arch is a rare but interesting conundrum. In reality the bone reduces when the mouth is forced open under anaesthesia then allowing a ‘proper’ reduction and fixation. It is vanishingly rare to attempt this procedure under local anaesthesia.
Essentially treatment for trismus of this origin is open reduction and internal fixation of the fractures with early mobilisation (minimal or no intermaxillary traction or fixation).
Rare traumatic conditions causing scarring of the oral mucosa (lining of the mouth) such as caustic or electrical burns may cause trismus. Excision of scar tissue and reorientation by Z-plasty or formal replacement by grafts or flaps may be required.
Dental and surgical treatment
The two most common causes of trismus related to dental treatments are the extraction of teeth (in particular the extraction of mandibular third molars (wisdom teeth)) and local anaesthetic injections (which may sometimes cause a minor bleed and give rise to a haematoma). These are managed essentially by masterly inactivity; any infection should be treated by appropriate antibacterial agents. Self-manual opening up to the point of using a trismus screw speeds nature along.
Temporomandibular (jaw) joint disorders
These are common conditions that may be caused by trauma to the jaw joint (for example, prolonged and particularly wide opening of the mouth) or by painful spasms of the muscles that move the jaws (myofascial pain dysfunction syndrome). In both cases, the treatment of the underlying cause of a jaw-joint disorder, or of facial pain address the resulting trismus.
Tumours
These are managed as appropriate to that particular tumour. There may then be iatrogenic (caused by treatment) trismus (see below).
The fibrotic scars of soft tissue radionecrosis can significantly limit mouth opening and the consequences of grade 3 (severe) osteoradionecrosis can do the same. In both cases conservative and self-help measures (such as physiotherapy exercises) may be limited in benefit and radical excision of necrotic and scar tissue and replacement with viable vascularised tissue is an essential surgical intervention.
Radiodermatitis at the end of a course of radiotherapy has been shown to be a strong predictor for late-onset fibrosis (true for all parts of the body after irradiation), with radical neck dissection an additional risk factor in the head and neck region. Radiation-induced fibrosis results from specific, misguided wound healing mechanisms, caused by tissue injuries from high-energy radiation. In particular, and in response to the inflammatory reactions to radiation exposure, this wound healing is driven by overactive recruitment of myofibroblasts to the site of injury. These are mediators in the wound-healing process and are mainly responsible for the contraction of a wound and for the deposition of collagen (connective tissue) fibres for tissue repair. In the healing process of radiation damage, both wound contraction and deposition of fibrous collagen are excessive, and thus are responsible for the stiff, fibrotic tissue causing trismus.
Given this mechanism of fibrosis development and the common development of radiation-induced fibrosis (not just following irradiation in the head & neck region), there have been attempts to find medications to prevent or at least reduce the formation of fibrotic tissue, all targeting the various roles of myofibroblasts (inhibition of factors that activate myofibroblasts or their differentiation, stimulation of myofibroblast-inhibiting factors, stimulating apoptosis (death) of myofibroblasts, and other ways of impairing the function of myofibroblasts). Unfortunately, none of these attempts have so far been successful, so that for the time being the best options remain conservative and selfhelp measures (patience and perseverance required) and radical surgical intervention (see above).
Drugs
Stopping the drug, using an alternative or similar is the obvious solution.
Congenital (inborn) causes
These all require staged forms of surgical reconstruction.
Other causes
Anxiety-induced hyperventilation (breathing too fast), producing apparent tetanic spasm can, seriously, be treated by breathing into a paper bag to prevent the biochemical changes causing the spasm created by blowing off CO2.
Intra-articular (internal to the jaw joint) causes for trismus
Direct surgical intervention of the temporomandibular joint addresses these trismus issues.