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 the joint. These changes may mimic arthritic changes, and may be accompanied by inflammation and pain. If left untreated, degenerative processes may continue, ultimately becoming permanent. Degenerative changes in the muscle are also highly likely. Disuse atrophy, as seen by reduction in muscle mass and strength, as well as shortening of muscle fibers is observed within days of immobilization.


Early treatment of trismus can prevent or minimize many of the conditions described above. Passive motion, applied several times per day has been shown to be more effective than static stretching. Recent research at the University of Pittsburgh has shown that passive motion provides significant reduction in inflammation and pain.

When does trismus ‘start’?, What are the risk factors?

Not every person who receives radiation to the head and neck will develop trismus. While there are few published studies, the range of prevalence of the condition is between 10 and 40 percent. The severity of the condition also varies widely, with some patients reporting no limitation to opening, while others are restricted to four or five millimeters. In rare cases, persons with trismus must be intubated due to severe limitation to opening. The severity of the condition varies with the placement of the radiation, the amount of radiation received, and the patient’s own ability to tolerate the treatment. In some cases, there is anecdotal evidence that certain chemotherapy agents may exacerbate the condition.

Radiation that affects the temporomandibular joint, the pterygoid muscles, or the masseter muscle, is most likely to result in trismus. The tumors related to this type of radiation include nasopharyngeal, base of tongue, salivary gland, and cancers of the maxilla or mandible. Radiation in excess of 60 Gr. is more likely to cause trismus, than is radiation at levels below that amount. Patients who have been previously irradiated, and who are being treated for a recurrence, appear to be at higher risk of trismus than those who are receiving their first treatment. This would seem to indicate the effects of radiation are cumulative, even over many years.

Radiation induced trismus may begin toward the end of radiation treatment, or at any time during the subsequent 12 months. Most often, we observe tightening that increases slowly over several weeks or months. On occasion, however, we see cases where the condition suddenly worsens with no apparent instigating factor. The condition may worsen over time, remain the same, or the symptoms may reduce over time, even in the absence of treatment. However, the condition is most likely to worsen if not treated.

Some patients who have not received radiation treatment may develop trismus secondary to scarring and edema after surgery. In spite of the difference in the cause of the condition, it appears that diagnosis and treatment is similar for both types of patients. Experience suggests the combination of surgery and radiation to treat cancers of the head and neck places patients at an increased risk to develop trismus.

What’s happening to cause this?

The primary factor in limiting jaw motion in the irradiated patient or surgery patient is the rapid formation of collagen secondary to radiation damage or surgery. In planning treatment, it is important to recall that immobile joints also suffer degenerative changes. Thus, while the initial cause of limited motion lies with the connective tissue, degradation of the joint can compound the problem. Joints which are immobilized show very rapid degenerative changes which can make remobilization difficult. Treatment that incorporates motion to the joint in addition to simple stretching has been shown to be more efficacious than treatment that simply stretches connective tissue.

It should be noted that trismus is frequently overlooked. Patients may assume that the reduction in jaw mobility is ‘normal’, or that it will resolve on its own. It is also easy for radiation oncologists, surgeons and their nurses to overlook the condition. Patients receiving radiation therapy or combined radiation and chemotherapy often require feeding tubes or limit their intake to mostly liquids during treatment. Thus they may not realize the slow progressive onset of trismus, until they attempt to resume intake of soft or solid foods. In its mild form, it is not life threatening and easy to ignore. If left untreated, however it has the potential of making recovery more difficult, as well as increasing problems associated with speech, oral hygiene and swallowing.

A simple test for trismus

Trismus tends to develop slowly. In some patients, it progresses so slowly that they may not notice it until they can only open their mouth to 20mm or less. Treatment that begins early in the progression of the condition is likely to be more effective, and easier on the patient. Because of this, it is important to be proactive in looking for early signs of trismus. One simple test is the ‘three finger test’. Ask the patient to insert three fingers into the mouth. If all three fingers fit between the central incisors, mouth opening is considered functional. If less than three fingers can be inserted, restriction is likely.

Treatment options

If the examination reveals the presence of limited mouth opening, and diagnosis determines the condition to be trismus, treatment should begin as soon as is practical. As restriction becomes more severe, the need for treatment becomes more urgent. If treatment is delayed, the difficulty in reversing the condition increases.

Over the years, there have been a wide array of apparatus that have attempted to treat limited movement of the jaw. These devices range from a variety of cages that fit over the head, to heavy springs that fit between the teeth, screws that are placed between the central incisors, and hydraulic bulbs placed between the teeth. The most commonly used treatment appears to be tongue depressors. These are stacked, forced and held between the teeth in an attempt to push the mouth open over time.

Devices range widely in cost. Many devices must be custom made for each patient, thus increasing the cost of treatment. Others, such as continuous passive motion devices are rented on a daily or weekly basis, at rates of up to several hundred dollars per week. The least expensive option is the use of tongue depressors. This low-cost alternative has been used for many years to attempt to mobilize the jaw. However, low cost should not be confused with cost effective. In order to be cost effective, a treatment must be effective. A search of the literature failed to reveal any studies that could demonstrate significant improvement in treating trismus with tongue depressors.

A number of studies have demonstrated the efficacy of one particular product; the Therabite Jaw Motion Rehabilitation System. Buchbinder studied a population of patients with radiation-induced trismus. Over a ten-week period, the researchers compared the effectiveness of three different protocols to improve mandibular mobility. At the end of ten weeks, the group using the Therabite System had improved an average of more than 13mm, while the group using tongue depressors improved less than 5mm. A third group, using their fingers to force their mouth open, showed even less improvement.

In another study, researchers at NYU found significant improvement in persons suffering from trismus. This study, which lasted 16 weeks, also found that the use of tongue depressors was not helpful in improving the condition.

One of the benefits of the Therabite System is that it not only stretches the connective tissue that causes trismus, but also allows for proper mobilization of the temporomandibular joint, thus addressing a secondary cause of pain and tightness. This device is generally covered by medical insurance and Medicare, and is well tolerated by the patients. We have found that early use of this device helps to improve mobility of the mandible and also to improve speech and swallowing in a patient population that is at risk of having difficulties with these functions.


It is important to measure initial opening (central incisor to central incisor) before beginning therapy and to record this opening. Also, record the opening after each session, and note any pain or discomfort, as well as the number of exercises performed. The Therabite device comes with patented range of motion scales and a patient log-book that is specifically designed for this purpose.

A good starting regimen for most patients is ‘7-7-7’. Open and close the mouth with assisted opening seven times. Hold the open position to the maximum opening that can be sustained without pain for seven seconds. They should perform these exercises seven times per day.

If the patient is capable of performing more than seven sessions, this can only add to the benefit. Patients who are extremely motivated may hold the stretch for more than seven seconds, or perform more than seven stretches per session. In all cases, be alert for signs of pain and muscle soreness, and advise against following the ‘no pain-no gain’ philosophy.

Pain should be avoided, as it will result in muscle guarding that may reduce the effectiveness of the therapy and reduce compliance.

The total time needed to complete this protocol is less than 10 min/day.

Over time, the regimens may be reduced. At first, it is better to reduce the number of stretches per session, rather than reducing the number of sessions. Later, as the patient continues to make progress, the number of sessions may be reduced.

Expected Results

A typical patient will gain from 1-4 mm of opening in the first session (about one minute). However, most, if not all, of this gain will be lost within the next two hours. Only by continuing to stretch and mobilize for many sessions per day will any lasting benefit be achieved.

In most studies, patients using the Therabite system gain between 1-1.5mm of sustainable gains per week. Thus, to gain 10 mm of ‘permanent gain’, a patient may need to exercise from six to ten weeks.

Most patients will continue to need to mobilize and stretch at least once per day for the rest of their lives.

Insurance Coverage/Payment

For most persons who have undergone radiation treatment, the Therabite System® will be covered by most major medical carriers and Medicare. Therabite Corporation has trained personnel who handle all aspects of the insurance process, and can take assignment of many insurance policies.

More details about joints and muscles

Over the past several years, the knowledge of the effects of inactivity, and passive motion on various joint structures and capacity have increased significantly. We now know that even short durations of immobilization of a joint can result in degenerative activity within the joint. Troyer (The effect of short term immobilization on the rabbit knee joint cartilage, a histochemical study; clinical orthopedics and related research; num. 107 Mar.-Apr. 1975 249-256) found in rabbit knees that had been immobilized, there was a depolymerization of glycosaminoglycans, and other pathologic changes that appear similar to degenerative joint disease. Hall (Cartilage changes after experimental immobilization of the knee joint of the young rat, J. bone joint surg. Vol. 45-A no. 1, 1963 36-44) had similar findings when studying immobilized rats. Both researchers found that degenerative changes began after only a few days of immobilization.

Immobilization and joint pathology can also have deliterious effects on muscle function and protein composition. Young (Young, A, Stokes, M. and Ilesm J, Effects of joint pathology on muscle; Clinical orth. and related res. Num. 219, June 1997, 21-27) found that flexion contractures were common in the muscles acting across a damaged joint. He found further that the process is self-perpetuating because ‘flexion contracture and extensor weakness alter joint biomechanics, predisposing to further joint damage.’ Thus muscle atrophy, which was originally caused by joint pathology, causes more joint pathology, which becomes self-perpetuating. Booth (Booth, F.: Physiologic and biochemical effects of immobilization on muscle; Clin Orth. and rel. res. No. 219 June 1987; 15-20) describes reduction in strength and increase in fatigability as two effects of immobilization. He found a rapid increase in atrophy after as little as five days of immobilization

Muscles and joints respond quite quickly to the demands made of them. In response to increased function, hypertophy develops. In response to decreased function, atrophy develops. Patients who have developed trismus are at risk for joint degeneration, as well as tightening of connective tissue.

Studies have shown that passive motion can reverse the effects of immobility on the joint, while stretching can make connective tissue more flexible. The combination of stretching and motion has been shown to be more efficacious than stretching alone in populations of persons with trismus. However, motion per se is not sufficient to show improvement. Studies have shown that passive motion is much more efficacious than active motion in the rehabilitation of joints and connective tissue. Active motion is motion that is driven by the musculature around the joint, causing movement of the joint. Passive motion, on the other hand occurs when an external force is applied causing movement of the joint in the absence of activity of the muscles around the joint. One example of a device which allows for the use of passive motion is the Therabite Jaw Motion Rehabilitation System.

This background provides a theoretical basis for the application of gentle passive motion in the treatment of trismus patients. Early intervention reduces the chances of complications, is easier for the patient to tolerate, and increases the speed of recovery.