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Trigger Point Injections

A trigger point is commonly referred to as a knot in the muscle. It occurs when a muscle contracts, but fails to relax. The term "trigger point" was coined by Dr. Janet Trevell in 1942, but practitioners have had a hard time agreeing on what constitutes a trigger point. Biopsy tests have shown that trigger points were hyper-irritable and electrically active muscle spindles in general muscle tissue.

According to Dr. Trevell, trigger points have the following characteristics:

  • Pain related to a discrete, irritable point in skeletal muscle or fascia, not caused by acute local trauma, inflammation, degeneration, neoplasm, or infection.

  • The painful point can be felt as a nodule or band in the muscle and a twitch response can be elicited on stimulation of the trigger point.

  • Palpation of the trigger point reproduces the patients complaint of pain, and the pain radiates in a distribution typical of the specific muscle harboring the trigger point.

  • The pain cannot be explained by findings on neurological 


Where do trigger points cause pain? 


Muscles are the only place that trigger points can form. Because the muscles are connected to ligaments and tendons, a trigger point can contract and cause pain in an adjacent joint where there are no muscles. Referred pain is a problem that is common with trigger points. Because several nerves use the same pathway, it is not uncommon for a nerve to affect tissue other than the tissue that is primarily innervated. 

How Can Trigger Point Pain Treatments Help?

Trigger points are classified by distinguishing between primary/secondary, key/satellite, and active/latent. A primary trigger point can set off other trigger points. The trigger points set off by the primary trigger point are called secondary. When a primary trigger is treated, it will not also treat the secondary. A key trigger point is basically the same as a primary trigger point; however, a satellite trigger point (key trigger points secondary) will be treated by treating the key trigger point. An active trigger point actively refers pain, either locally or to another location, whereas a latent trigger point exists, but is not actively referring pain.

Dr. Trevell also introduced the concept of myofascial pain syndrome, which is described as a focal hyperirritability in muscle that can strongly modulate central nervous system functions. There are 18 points on the body that are checked for abnormal sensitivity when diagnosing myofascial pain syndrome. It is considered myofascial pain syndrome if ten or fewer of the spots checked are considered abnormally sensitive. If 11 or more of the 18 points show abnormal sensitivity, it is considered fibromyalgia. In order to release a trigger point, a mix of saline, local anesthetics and steroids are injected directly into the affected muscle. 

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