Journal: Am Fam Physician 2002;65:653-60
Authors: DAVID J. ALVAREZ, D.O., and PAMELA G. ROCKWELL, D.O.
Affiliation: University of Michigan Medical School, Ann Arbor, Michigan
Trigger points are discrete, focal, hyperirritable spots located in a taut band of skeletal muscle. They produce pain locally and in a referred pattern and often accompany chronic musculoskeletal disorders. Acute trauma or repetitive microtrauma may lead to the development of stress on muscle fibers and the formation of trigger points. Patients may have regional, persistent pain resulting in a decreased range of motion in the affected muscles. These include muscles used to maintain body posture, such as those in the neck, shoulders, and pelvic girdle.
Trigger points may also manifest as tension headache, tinnitus, temporomandibular joint pain, decreased range of motion in the legs, and low back pain. Palpation of a hypersensitive bundle or nodule of muscle fiber of harder than normal consistency is the physical finding typically associated with a trigger point. Palpation of the trigger point will elicit pain directly over the affected area and/or cause radiation of pain toward a zone of reference and a local twitch response. Various modalities, such as the Spray and Stretch technique, ultrasonography, manipulative therapy and injection, are used to inactivate trigger points.
Trigger-point injection has been shown to be one of the most effective treatment modalities to inactivate trigger points and provide prompt relief of symptoms.
About 23 million persons, or 10 percent of the U.S. population, have one or more chronic disorders of the musculoskeletal system.  Musculoskeletal disorders are the main cause of disability in the working-age population and are among the leading causes of disability in other age groups. 
Myofascial pain syndrome is a common painful muscle disorder caused by myofascial trigger points.  This must be differentiated from fibromyalgia syndrome, which involves multiple tender spots or tender points.  These pain syndromes are often concomitant and may interact with one another.
Trigger points are discrete, focal, hyperirritable spots located in a taut band of skeletal muscle. The spots are painful on compression and can produce referred pain, referred tenderness, motor dysfunction, and autonomic phenomena. 
Trigger points are classified as being active or latent, depending on
their clinical characteristics.  An active trigger point causes pain
at rest. It is tender to palpation with a referred pain pattern that is similar to the patient’s pain complaint. [3,5,6] This referred pain is felt not at the site of the trigger-point origin, but remote from it. The pain is often described as spreading or radiating.  Referred pain is an important characteristic of a trigger point. It differentiates a trigger point from a tender point, which is associated with pain at the site of palpation only (Table 1). 
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Am Fam Physician 2002;65:653-60.
Copyright© 2002 American Academy of Family Physicians.