Trismus is defined in Taber’s Cyclopedic Medical Dictionary as a tonic contraction of the muscles of mastication. In the past, this word was often used to describe the effects of tetanus, also called ‘lock-jaw’. More recently, the term ‘trismus’ has been used to describe any restriction to mouth opening, including restrictions caused by trauma, surgery or radiation. This limitation in the ability to open the mouth can have serious health implications, including reduced nutrition due to impaired mastication, difficulty in speaking, and compromised oral hygiene. In persons who have received radiation to the head and neck, the condition is often observed in conjunction with difficulty in swallowing.

Quality of life

Trismus can dramatically affect quality of life in a variety of ways. Communication is more difficult when one is suffering from trismus. Not only is it difficult to speak with the mouth partly closed, thus impairing articulation, but trismus can decrease the size of the resonating oral cavity and thus diminish vocal quality. Severe trismus makes it difficult or impossible to insert dentures. It may make physical re-examination difficult, if limited mouth opening precludes adequate visualization of the site. Oral hygiene is compromised, chewing and swallowing is more difficult, and there is an increased risk of aspiration.

Some causes of trismus

Limited jaw mobility can result from trauma, surgery, radiation treatment, or even TMJ problems. The limitation in opening may be a result of muscle damage, joint damage, rapid growth of connective tissue (i.e. scarring) or a combination of these factors. Limitations caused by factors external to the joint include neoplasms, acute infection, myositis, systemic diseases (lupus, scleroderma, and others) pseudoankylosis, burn injuries or other trauma to the musculature surrounding the joint.

Limitations caused by factors internal to the joint include bony ankylosis (bony in growth within the joint), fibrous ankylosis, arthritis, infections, trauma and (perhaps) micro-trauma that may include brusixm.

Central Nervous System disorders can also cause limitations to mouth opening. Tetanus, lesions that affect the trigeminal nerve and drug toxicity may all be suspects in this condition.

Finally, there are iatrogenic causes, such as third molar extraction (in which the muscles of mastication may be torn, or the joint hyperextended) hematomas secondary to dental injection and late effects of intermaxillary fixation after mandibular fracture or other trauma.

The muscles of mastication (also called the ‘elevator muscles’) consist of the Temporalis, Masseter, Medial pterygoid and Lateral pterygoid. Each muscle plays an important role in mastication, and when damaged, each can cause limitations in opening. When any muscle is damaged, a pain reflex may be stimulated. This condition, called “muscle guarding” results when muscle fibers engender pain when they are stretched. This pain causes the muscles to contract, resulting in loss or range of motion. This contraction is truly a reflex; it cannot be controlled by the patient. Thus, in treating this condition it is important to recall that rapid motion, or the use of powerful forces may be self-defeating. Rapid motion may create the reflex that causes muscles to contract, thereby making stretching of connective tissue difficult or even impossible. Gentle, passive motion has been shown to be efficacious in treating the condition.

Muscles and joints are both affected

Regardless of the immediate cause, mandibular hypomobility will ultimately result in both muscle and joint degeneration. Studies have shown that muscles that fail to move through their range of motion for as little as three days begin to show signs of atrophy. Similarly, joints which are immobilized quickly begin to show degenerative changes in the joint, including thickening of synovial fluid and thinning of cartilage. In the case of patients receiving radiation treatment of the head and neck, trismus may progress slowly, even unnoticed for months, causing secondary changes to both muscles and joints. Thus treatment, consisting of gentle passive motion, should begin as soon as practicable.

Signs of trismus

The most obvious effect of trismus is difficulty in opening the mouth. As discussed above, in cancer patients this frequently results from scar tissue from radiation or surgery, nerve damage, or a combination of factors. In stroke patients, the general cause is central nervous system dysfunction. Difficulty in speech and swallowing often accompany the limitation in mouth opening, and create a combination of symptoms that may be difficult to treat.

In cases of trismus caused by radiation treatment, patients also frequently present with Xerostomia, mucusitis, and pain as a result of radiation burns. There may also be associated symptoms such as headache, jaw pain, ear ache, deafness, or pain on moving the jaw. In cases of Temporomandibular tightness, the joint itself may become fibrotic, or even (in rare cases) ankylotic. Each of these factors may affect the treatment provided to the patient.

Problems caused by trismus

Eating issues

Limited mouth opening frequently results in reduced nutrition. The inability to open the mouth to receive more than a very small amount of food makes eating quite difficult. Patients with this condition may experience significant weight loss, and may have significant nutritional deficits. This is of particular importance at a time when the patient is attempting to recover from surgery, chemotherapy, or radiation treatment. It is generally accepted that weight loss of more than 10% of initial body weight is considered significant, and indicates inadequate nutritional intake.

Limited mouth opening may also result in compromised airway clearance. Limited mouth opening may make proper mastication of food more difficult. A normal swallow requires an individual to manipulate the food into a cohesive bolus prior to propulsion. If the tongue cannot move properly due to limited mouth opening, the bolus may not be formed properly leading to post-swallow excess residue. The combination of compromised mastication, poor bolus organization and increased residue has the potential to lead to aspiration of part or all of the bolus.

Oral hygiene issues

Limited mouth opening can result in compromised oral hygiene. In cancer patients who have received radiation to the mandible, oral hygiene is of particular importance. While rare, osteoradionecrosis can be severely debilitating, or even fatal. Poor oral hygiene can result in dental caries (cavities) which can lead to infection. Infection of the mandible can lead to further complications, including osteoradionecrosis. This condition, in which the bone of the mandible dies from radiation or infection can be quite serious. In the best cases, the treatment entails hyperbaric oxygen, and is time consuming and expensive.

Swallowing and speech issues

Many persons with limited mouth opening also present with difficulty in swallowing and speech. Speech is compromised when the mouth is unable to open sufficiently to create normal sounds. Swallowing is compromised when, due to muscle damage, surgery or radiation, the larynx is unable to be properly elevated, or when the timing of the elevation does not coincide with the passage of the bolus.

Joint Immobilization

Although the most apparent signs of trismus involve the ability to open the mouth, it is important to realize that there are likely to be problems within the joint, as well. When a joint is immobilized, degenerative changes occur within