What Is Lockjaw?

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Lockjaw (trismus) is when the jaw muscles spasm and affect jaw movement. If you develop this condition, your jaw may be "frozen" in a certain position, and you might not be able to open your mouth wide. Lockjaw can be painful and it cause complications, such as choking. Medication side effects, cancer treatment, and tetanus are a few a the possible causes.

potential causes of lockjaw

Verywell / Brianna Gilmartin

Symptoms of Lockjaw

Lockjaw affects the whole jaw and is usually equal on both sides. It can occur suddenly, reaching its peak effect over the course of a few hours.

There are a number of nerves and muscles that control jaw movement. Due to their anatomical arrangement, lockjaw is typically characterized by a jaw position that is partially open.

While an inability to open the mouth fully is the most common symptom of lockjaw, several others can occur as well.

Within just a few hours, lockjaw is associated with:

When you can't control your mouth, your speech may be difficult for others to understand and you can have trouble swallowing.

After about a day, lockjaw can affect your oral health because you can't swallow saliva. This can cause:


If you experience lockjaw for a longer than a few days, it can affect your overall health. Complications of persistent lockjaw include:

  • Tooth decay and ulcers in your mouth due to an inability to effectively brush your teeth and floss
  • Bruxism (teeth grinding), which can cause your tooth enamel to wear away and even your teeth to crack
  • Malnourishment due to difficulty eating
  • Muscle contracture: Stiffening of the muscle characterized by a change in the muscle structure, which does not respond to treatment as easily as a muscle spasm


A muscle spasm is a condition in which a muscle remains in its active position and cannot relax. This can occur due to an injury to the muscle, nerve, bone, tendon, or ligament.

Another common cause of lock jaw is hypocalcemia. This can sometime occur during thyroid surgery.

You might think of how you often get a "Charley horse" in your leg if you don't stretch before going on a run. The muscle spasm occurring with lockjaw is essentially the same thing, just in a different location and with a range of different possible causes and risk factors.

Temporomandibular Joint (TMJ) Disorders

Your temporomandibular joint is located at the sides of your face, below your eyes and towards your ears. This joint is where the muscles, bones, tendons, and ligaments that control your jaw meet.

Temporomandibular joint disorders, often called TMJ, can develop due to arthritis, inflammatory disease, or facial trauma. TMJ commonly results in lockjaw.

Because TMJ is often a chronic condition, related lockjaw can recur even after it resolves.


Infections in and around your mouth or jaw muscles, such as a peritonsillar abscess, can affect the movement of the jaw, resulting in lockjaw.

In rare instances, your nerve or muscle can become permanently damaged due to an infection, potentially predisposing to recurrent episodes of lockjaw.


Some medications can affect nerve function and may predispose or cause lockjaw. Reglan (metoclopramide) and some antipsychotic medications are the most common culprits.

Rarely, anesthetics can cause a rare complication called malignant hyperthermia, which can cause muscle spasms, including lockjaw.


Cancer and some cancer treatments (i.e., surgery or radiation) can cause injuries to the structures that control jaw movement. If you have had head or neck cancer, or have had surgery or radiation treatment for these cancers, you have about a 30% chance of developing lockjaw.


Tetanus occurs due to a life-threatening neurotoxin that is released by Clostridium tetani, a bacterium commonly present in the environment. Tetanus toxin can cause muscle spasms, which may affect the heart muscles, chest muscles (impairing breathing), or any voluntary muscles in the body—including those of the jaw.

Tetanus is a significant risk factor for lockjaw and almost always causes it. In fact, lockjaw used to be called tetanus. However, in most parts of the world, tetanus is extremely rare because immunizations and booster shots that protect against the infection are routine.

Other Medical Conditions

Sometimes, nerve or muscle diseases can cause muscle spasms. For example, stiff person syndrome, a rare autoimmune disorder, can cause spasms in any voluntary muscle.


Lockjaw is diagnosed based on your medical history and a physical examination. The effects can make it difficult for you to verbally explain your symptoms to your medical team, so most people have to describe their medical history by writing it down.

Physical Examination

Normally, most people can open their mouth between 35 to 55 millimeters (mm) or 1.4 to 2.2 inches wide. If you have lockjaw, you may only be able to open your mouth less than 35 mm (1.4 inches)—a distance that's less than three fingers in width. Your healthcare provider will measure how wide your mouth can open to see if you fall in or out of the normal range.

If you have lockjaw, you might not be able to close your mouth all the way, and you are likely to have trouble moving your jaw. Your healthcare provider may also detect stiffness and tightness of your jaw muscles, and your teeth may be clenched.


If there is a concern that you could have an injury, infection, or tumor affecting your mouth, face, or jaw, you may need to have diagnostic testing.

Imaging studies, such as X-rays, computerized tomography (CT), ultrasound, or magnetic resonance imaging (MRI) can often identify lesions in and around the jaw.

In some instances, a biopsy is needed so that your medical team can more closely examine a tumor.


Otolaryngologists (ENTs), dentists, and oral surgeons treat lockjaw, and they may suggest medication and/or physical therapy. Additional treatments to address the underlying problem (such as an infection) are typically necessary as well.

If your muscle spasm was caused by medication, then discontinuing it is typically recommended. (Never stop a medication without your healthcare provider's OK.)

Spasm Relief and Therapy

Oral and injected muscle relaxants are typically helpful. Common examples of oral medications include Flexeril (cyclobenzaprine) and Skelaxin (metaxalone). Such medications may, however, cause side effects such as drowsiness.

Targeted injections, including botulinum toxin or anti-inflammatory steroids, can relax the muscle, relieving the spasm. Injections require scheduling an interventional procedure, and they do not cause the systemic side effects seen with oral medications.

In addition to medical management, you may need physical therapy and/or speech therapy. Your therapist may also suggest at-home exercises so you can improve control of your jaw muscles. When you take part in at-home therapy, is important to avoid pushing your exercises to a painful level.

Treating the Underlying Problem

If your lockjaw is caused by a medical problem, you will need treatment for the cause of your lockjaw. For example, infections may necessitate oral or intravenous (IV) antibiotics. TMJ may require anti-inflammatory treatment. And tumors may require radiation or surgery.

If radiation therapy or surgery is the cause of your lockjaw, then physical therapy may be the most effective treatment approach. Longstanding lockjaw after radiation therapy can be very challenging to reverse.

A Word From Verywell

If you have experienced lockjaw, you may be at risk for developing it again, so it is important to discuss prevention with your healthcare provider. Preventative strategies may include avoiding medications that trigger it, getting treatment for TMJ, and maintaining regular exercise of your jaw muscles. Most importantly, if you notice the symptoms acting up, you should seek medical attention promptly to avoid contractures or other complications.

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