Pain Referral Patterns

Myofascial Referred Pain

Referred Pain is pain that is caused by a trigger point but is experienced at a distance. It is quite often can be entirely remote from the source TrP. The pattern of this pain is every time reproducible and connected to its locus of origin. However, its distribution seldom coincides completely with the distribution of a relevant dermatomal segment or peripheral nerve.

Referred Pain and Referred Autonomic Responses

Referred pain is part of more generic Referred (Trigger-Point) Phenomena.

Apart from pain, the latter include Referred Autonomic Phenomena:

• tenderness;
• increased motor unit activity (spasm)*;
• vasoconstriction – blanching;
• vasodilatation – the widening of blood vessels;
• coldness;
• sweating;
• pilomotor response – “goose flesh”;
• ptosis - the upper eyelid droops over the eye;
• hypersecretion.

* There is an example in research literature (Headley BJ) when pressure on a trigger point in a right soleus gave rise to a strong spasm response in the right lumbar paraspinal muscles.

These phenomena also usually appear at a remote distance from the trigger point, in the same general zone to which a certain trigger point refers pain.
The intensity and expanse of the referred pain depends on the level of irritability of the trigger point, and not on the size of the harboring muscle. Trigger points in small muscles can be as upsetting to the patient as those in large muscles.

Essential Zone of Reference

The region of the body, where phenomena caused by the myofascial TrP are observed is called Essential Zone of Reference. The essential referred pain area is indicated by solid red in pain charts.

Spillover Pain Zone

The area where certain, but not all, patients feel referred pain outside the essential pain area, due to greater irritability (hyperirritability) of a trigger point is called Spillover Pain Zone. In the pain-pattern trigger point charts it is indicated by red stippling or solid pink to be distinguished from an essential referred pain area (solid red).

The pain referral pattern is characteristic for each muscle. Some patients feel numbness or paresthesia (‘pins and needles’) rather than pain.

Satellite Trigger Points

Satellite Myofascial Trigger Points

A key trigger point can mechanically or neurogenically give rise to a so-called satellite trigger points.

It’s difficult to distinguish the mechanism responsible for the key-satellite relationship by examination only. The association normally is confirmed by simultaneous deactivation of the satellite TrP when the key TrP is deactivated.

Common locations of satellite trigger points may include:

• site of reference of the key trigger point;
• overloaded synergist substituting for the key muscle – the muscle harboring the key trigger point;
• antagonist of the key muscle, because it counters the increased tension of the latter;
• a muscle associated only neurogenically with the key TrP.

Earlier, only a TrP that developed in the referred pain zone of another TrP was considered as a satellite trigger point.
A term “secondary trigger points” was used previously for the TrPs which developed in an antagonist or a synergist of the muscle harboring the key trigger point. This is earlier term for a “satellite trigger point”.

Central and Attachment Trigger Points

Central Trigger Points

Central TrPs are in the middle portion of the muscle belly, near the center of muscle fibers. They are strongly associated with dysfunctional endplates, contain many electrically active points, and many contraction knots.

Central Trigger Points can be found near midfiber (not necessarily in the middle of a muscle) in various portions of the muscle.

Attachment Trigger Points

Trigger Points which are in a region of muscle attachment (at the musculotendinous junction or/and at the osseous attachment of the muscle) are called attachment trigger points. They are believed to be caused by unrelieved tension of the taut band that is associated with a central TrP.

Taut Band

Taut Band - Tense Muscle Fibers

A palpable nodule and associated taut band (tense muscle fibers) are characteristics of a trigger point.

The first step in identifying a trigger point is learning how to recognize the nodule and taut band of muscle fibers by palpation.

A taut band restricts range of motion and increases muscle tension.

It extends from a trigger point to muscle attachments.

The cause of the tension of the muscle fibers is contraction knots ("micro-cramps") which are in the site of the trigger point. Reflex contraction of the fibers in the taut band gives rise to the local twitch response (LTR).

The taut band always respond with a twitch response when the trigger point is penetrated by a needle.

The taut band can be identified by gently rubbing across the muscle fibers of a superficial muscle. If it is present, one can feel a nodule at the trigger point and a rope-like thickening that runs from this nodule to the attachment of the taut muscle fibers at each end of the muscle.

It can be snapped or rolled under the finger in palpated muscles. When the TrP is deactivated, the taut band becomes less tense, often (but not necessarily) disappears, sometimes instantaneously, and range of motion returns to normal.

However, the presence of a palpable taut band alone, by itself, cannot be a reliable sign of the TrP because it can occasionally be observed in pain-free individuals without evidence of trigger point phenomena.*

*Simons, D. G., Travell, J. G., & Simons, L. S. (1999). Travell & Simons' myofascial pain and dysfunction: The trigger point manual. Baltimore: Lippincott Williams & Wilkins. Volume 1. P.34

Latent Myofascial Trigger Point

Latent Trigger Point

A myofascial TrP that is clinically dormant with respect to spontaneous pain (doesn’t hurt if undisturbed).

It is painful only when palpated. A latent trigger point may have all the other clinical characteristics of an active trigger point (weakens the muscle, shortens the muscle length, etc.) and also has a taut band increasing muscle tension and restricting ROM (range of motion).

Key Myofascial Trigger Point

Key Trigger Point

This type of TrP is responsible for activating one or group of so-called "satellite" trigger points.
It is identified when deactivation of that trigger point also deactivates the satellite trigger point.

Active Myofascial Trigger Point

Active Trigger Point

This type of a trigger point causes a clinical pain complaint.

Characteristics of an active trigger point:

• tenderness;
• it prevents full lengthening and weakens the muscle;
• refers a patient-recognized pain on direct compression;
• mediates a local twitch response of muscle fibers when adequately stimulated;
• when compressed within the patient's pain tolerance, produces referred motor phenomena and often autonomic phenomena, generally in its pain reference zone;
• causes tenderness in the pain reference zone.

To be distinguished from a latent myofascial trigger point.

Associated Trigger Point

Associated Myofascial Trigger Point

A TrP in one muscle that arises concurrently with a TrP in another muscle. One of them may have stimulated the other, or both may be brought about by the same mechanical or neurogenic cause.

Examples:

The synergistic teres minor and teres major, latissimus dorsi muscles often develop associated trigger points.

In the presence of interosseous muscles trigger points, associated trigger points may develop in the intrinsic thumb muscles.

When upper trapezius is involved, associated trigger points are likely to develop in the functionally similar levator scapulae muscles and the opposite side trapezius muscles, and also in the same side rhomboid and supraspinatus muscles.

See also key trigger points, satellite trigger points.

Primary Trigger Point

Primary Myofascial Trigger Point

It’s a central myofascial trigger point which was activated directly by repetitive overuse, or chronic/acute overload of the muscle, in which it developed. It was not activated as a result of TrP activity in another muscle and this is its main characteristic.

When we say "primary" we distinguish it from "satellite" but primary trigger point is not necessarily key trigger point in the absence of its satellites.

See also key trigger point and satellite trigger point.