Digastric Muscle Trigger Points and Referred Pain Patterns

Before you read about digastric trigger points and its pain you may want to find out more about the digastric muscle itself.

The digastric muscle, together with the pterygoid muscles and its synergists, the other suprahyoid muscles, is primarily responsible for opening the jaw. Therefore, overload can occur in this muscle during habitual open mouth breathing. However, an overworked masseter, together with open mouth breathing, causes the most problems.

See the Trigger Point Therapy Workbook

Digastric Trigger Points Causes and Symptoms

Trigger points in the digastric commonly occur secondary to trigger points in the antagonistic masseter muscle, which is the workhorse jaw muscle responsible for most of the closing force of the jaw and chewing. Problems occur in the digastric because of habitual mouth breathing, which often occurs from chronic sinus problems, nasal blockage such as from nasal polyps, or a deviated septum. This puts added stress on the digastric and the pain they cause is likely to be compounded by referred pain from the lateral pterygoid, its synergist in opening the jaw. Both the masseter and temporalis are far more powerful than the digastric and lateral pterygoid so when these muscles are overactive the mandible depressors easily become strained.

Bruxism is a major cause of problems in the masseter as well as the other jaw muscles, including the digastric.

Retrusion of the mandible can also give rise to trigger points in the digastric. Retrusion means that the lower jaw is placed in a position posterior to its normal one. This is often hereditary, due to a Class 2 malocclusion.  A class 2 malocclusion, called retrognathism or overbite, occurs when the upper jaw and teeth severely overlap the bottom jaw and teeth. ¹ “Malocclusion of Teeth: MedlinePlus Medical Encyclopedia.” National Library of Medicine – National Institutes of Health. Web. 04 Jan. 2011. <:http://www.nlm.nih.gov/medlineplus/ency/article/001058.htm>.This may also occur when woodwind instruments are played as the mandible is often brought back to form the embouchure. However, it should be noted that playing woodwind and brass includes muscles of the mouth, face, jaw, and tongue and the actions of these muscles are very complex. The actions used to form the mouth into the embouchure are not natural and musicians often report a host of problems. TMJ is often blamed for these problems but may be a misdiagnosis. Some common symptoms that woodwind and brass musicians have are called “embouchure dystonia”, dystonia is a movement disorder that causes the muscles to contract and spasm involuntarily. ²Dystonia Medical Research Foundation. Web. 04 Jan. 2011. <http://www.dystonia-foundation.org/pages/embouchure_dystonia/58.php>.,³”What Is Dystonia.” Dystonia Medical Research Foundation. Web. 04 Jan. 2011. <http://www.dystonia-foundation.org/pages/what_is_dystonia_/26.php>.

Each belly of the digastric has its own referred pain patterns. The most widespread and common pain is referred from the posterior belly and this causes pain in the upper part of the sternocleidomastoid, under the chin, and upward to the occipital portion of the occipitofrontalis muscle. This pain may become apparent only after trigger points in the sternocleidomastoid are resolved. Pain may then be left in the upper part of the SCM muscle. This SCM pain that is caused by TrP’s in the posterior belly of the digastric is sometimes called ‘pseudo-sternocleidomastoid pain’. The superior SCM may still be tender to touch but will itself be free of trigger points or twitch responses.

The stylohyoid muscle has also been associated with head and neck pain but the digastric and stylohyoid are difficult to differentiate. Trigger points in the anterior belly sometimes refer pain the lower front teeth and together with TrP’s in the mylohyoid muscle can cause throat pain and difficulty when swallowing. Associated trigger points in the masseter and temporalis are likely to occur with digastric TrP’s.

Anterior Digastric Trigger Points

As stated above, trigger points in the anterior belly of the digastric refer pain to the lower front teeth. The trigger points will be located underneath the point of the chin just lateral to the midline. Massage this area freely with long even strokes.

Posterior Digastric Trigger Points

Trigger points of the posterior belly are located under the corner of the jaw. Start with your fingers in the soft part of the flesh underneath the jaw and in front of its corner, just anterior to the upper part of the sternocleidomastoid. From here run your fingers along the front border of the SCM up toward your earlobe, feeling for the very tender spots. Sustained pressure may reproduce the referred pain symptoms. ⁴Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 12: Digastric Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: the Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 273-280. Print.,⁵Davies, Clair. The Trigger Point Therapy Workbook: Your Self-treatment Guide for Pain Relief. Oakland, CA: New Harbinger Publications, 2004. 72. Print.