Trigger point definitions and structure

Many of you are familiar with trigger points. For those of you who are not, here is a quick review of definitions.

"Myofascial Trigger Point (clinical definition of a central trigger point): A hyperirritable spot in skeletal muscle that is associated with a hypersensitive palpable nodule in a taut band. The spot is painful on compression, and can give rise to characteristic referred pain, referred tenderness, motor dysfunction, and autonomic phenomena"(1) emphasis mine. What this means is that when you, the clinician, suspect a trigger point, you can palpate for it. It will be hard. When you locate it, the patient will say "ouch."

"Myofascial Trigger Point (etiological definition of a central trigger point): A cluster of electrically active loci, each of which is associated with a contraction knot and a dysfunctional motor endplate in skeletal muscle"(1) emphasis mine. What is important is that a trigger point is electrically different from the surrounding tissue. The same is true for acupuncture points. These facts suggest a possible mechanism for the effectiveness of Tandem Point therapy, which will discussed later.

"Attachment Trigger Point: A trigger point at the musculotendinous junction and/or at the osseous attachment of the muscle that identifies the enthesopathy caused by unrelieved tension characteristic of the taut band that is produced by a central trigger point."(1)

"Key Myofascial Trigger Point: A trigger point responsible for activating one or more satellite trigger points. Clinically, a key trigger point is identified when inactivation of that trigger point also inactivates the satellite trigger point."(1)

"Satellite Myofascial Trigger Point: A central myofascial trigger point that was induced neurogenically or mechanically by the activity of a key trigger point. . . . A satellite trigger point may develop:

• in the zone of reference of the key trigger point
• in an overloaded synergist that is substituting for the muscle harboring the key trigger point (key muscle) or in an antagonist countering the increased tension of the key muscle [both previously called a secondary trigger point], or
• in a muscle linked apparently only neurogenically to the key trigger point."(1)

C. Chan Gunn, M.D., has also found a linkage between trigger points and contractures in other muscles on the same myotome, and I will discuss that linkage further later.

"Taut Band: The group of tense muscle fibers extending from a trigger point to the muscle attachments. The tension of the fibers is caused by contraction knots that are located in the region of the trigger point."(1)

"Referred (Trigger-Point) Pain: Pain that arises in a trigger point, but is felt at a distance, often entirely remote form its source. The pattern of referred pain is reproducibly related to its site of origin. The distribution of referred trigger-point pain rarely coincides entirely with the distribution of a peripheral nerve or dermatomal segment."

"Schematic of a trigger point complex of a muscle in longitudinal section. The schematic identifies three regions that can exhibit abnormal tenderness (red). It also illustrates contraction knots that most likely: make a trigger point feel nodular, cause the taut band, and mark the site of an active locus. A, the central trigger point (CTrP) which is found in the endplate zone, contains numerous electrically active loci, and contains numerous contraction knots. The local tenderness of the CTrP is identified by a red oval. A taut band of muscle fibers extends from the trigger point to the attachment at each end of the involved fibers. The sustained tension that the taut band exerts on the attachment tissues can induce a localized enthesopathy that is identified as an attachment trigger point (ATrP). The local tenderness of the enthesopathy at the ATrP is identified by a red circle with a black border. B, this enlarged view of part of the central trigger point shows the distribution of five contraction knots.... In patients, the CTrP would feel nodular as compared to the adjacent muscle tissue, because it contains numerous "swollen" contraction knots that take up additional space and are much more firm and tense than uninvolved muscle fibers."

Source: Simons DG, Travell JG, Simons LS: Travell & Simons' Myofascial Pain and Dysfunction: The Trigger Point Manual, Vol. 1, Second Edition, Williams & Wilkins, Baltimore, p. 70. Reproduced with the permission of Lippincott Williams & Wilkins

This diagram is based on photographs taken under light microscopy of canine muscle tender spots that meet trigger point criteria. The diagram shows attachment trigger points at each end of one muscle and a central trigger point. Looking within the trigger point, you can see multiple contraction knots with contracted sarcomeres. David Simons notes that oxygen is missing from a trigger point. Water and ions may also be missing.

Source: Oschman JL, Oschman NH: Readings on the Scientific Basis of Bodywork, Energetic, and Movement Therapies, N.O.R.A., Dover, NH, 1997 (p. 17). Reproduced with the kind permission of N.O.R.A.

Painful, palpable nodules may appear in tendons, especially at the periosteal attachments. During Tandem Point therapy, these nodules feel and act just like trigger points. I use them interchangeably with trigger points in muscles. [During Rolfing(TM) sessions, I have observed that the release of fascial restrictions is facilitated by pressing acupuncture points.]

Recent research reveals that trigger points are electrically different from the surrounding tissue. Electromyograph studies show that active trigger points have (a) intermittent and variable high-amplitude spike potentials, and (b) a consistently present, lower amplitude noise-like component, called by David Simons spontaneous electrical activity.(2) While Simons discusses this electrical activity as being diagnostic or characteristic of a trigger point, I would like you to consider that this electrical activity may be the most important feature of the trigger point, the feature that perpetuates the trigger point.