Part 1
Philip A.M. Rogers MRCVS, Andrew Fischer MD, PhD,
Pekka J.Pontinen MD and Luc A.A. Janssens DMV, PhD
IVAS Course, Oslo, Norway (1988)
Postgraduate Course in Veterinary AP, Sydney (1991)
(revised 1990, 1991, 1993, 1996)


Normal muscle is not painful on palpation and contains no Trigger Points (TPs). The role of TPs in maintaining myofascial pain and methods of TP therapy are outlined.

Chronic myofascial pain is most commonly associated with TPs in muscles, especially around arthritic joints. Long term therapeutic success depends on TP detection and their elimination.

Objective assessment of myofascial pain has medico-legal applications as well as facilitating an accurate monitor of the result of drug, physical or other therapies. Fischer adapted analogue force gauges to facilitate objective assessment of the location and degree of myofascial pain in human patients. The principle is more than 40 years old but has not been documented properly until recently. Repeatability of readings is excellent.

a. A pressure threshold meter (pressure range 0-11 kg/cm sq) measures pain threshold at the TPs. Pressure thresholds at TPs are 2-4 kg/cm sq lower than thresholds in healthy muscle. Threshold pressures can be used to confirm the exact locations of TPs and to quantify their sensitivity relative to healthy muscle.

b. A pressure tolerance meter (pressure range 0-17 kg/cm sq) measures pain tolerance at standard sites in muscle and bone. Pressure tolerance over muscle and is used to assess overall pain tolerance. Fit athletes and patients trained in self-hypnosis or relaxation therapy usually have higher tolerances than people who are sedentary, unfit or poorly trained in mental control. A low overall tolerance is a poor prognostic sign and may indicate generalised pain of psychosomatic origin.

c. A tissue compliance meter (a special force gauge with a sliding plate) measures penetration depth in tissue at probe pressures of 1, 2, 3, 4 and 5 kg/cm sq. Tissue compliance can be used to quantify and demonstrate the degree of muscle tension or spasm.

d. A dynamometer (force range 0-27 kg) measures contraction power of the limb muscles. Muscle dynamometry can be used to assess muscle power to flex, extend, abduct and adduct limbs and joints.

These concepts do not seem to have been documented in animal patients. They offer a unique possibility to assess myofascial pain, of great potential importance in the investigation of equine and canine lameness and poor racing performance. The pressure threshold gauge could probably be used to measure sensitivity at the diagnostic organ reflex (Shu and Mu) points of classical acupuncture.


The purpose of this article is threefold:

a. to review briefly the role of Trigger Points (TPs) in myofascial pain;

b. to discuss objective assessment of TP sensitivity in human myofascial pain and

c. to review methods of treating myofascial pain.

These concepts are important for veterinarians, especially those involved in equine or canine sports medicine.

Pain may be classed as peripheral or central. Peripheral pain may be primary or secondary.

Primary pain may arise in trauma or inflammation of a nerve, muscle, organ, bone, joint, vertebra etc. Physical lesions may or may not be present. Bones, joints and vertebral discs may cause pain if they are luxated. Muscle pain may arise due to overstretching.

Secondary pain may be referred from foci of irritation in thoracic/ abdominal organs or other body parts or may be referred from active Trigger Points (TPs) anywhere in the body. It may arise also in generalised conditions, such as rheumatoid arthritis, allergy, gout or cancer in humans or nutritional muscular dystrophy (selenium/vitamin E deficiency) and generalised myositis (azoturia) of animals.

Trigger points (TPs): TPs are defined as foci of irritation which can initiate and maintain acute or chronic myofascial or visceral pain in nearby or distant areas. Pressure on the TP or needling causes great pain locally and radiates/triggers pain to the related body segment (usually the location of the human patient's subjective pain). TPs, unless acute, are not spontaneously painful - the patient is usually unaware of their presence until the points are pressed (Travell and Simons 1984, 1985).

The AhShi point in human acupuncture (AP), is defined as a point, usually in muscle, which is tender on palpation (Anon 1980). AhShi means Ouch! or Ah Yes! There are two kinds of AhShi points:

a. those which radiate pain to the problem area (the area in which the patient complains of pain) and

b. those from which palpation elicits only local tenderness.

Type (a) is the TP of western medicine and is the most important point in AP therapy. The relevance of TPs as a sign of and a perpetuating cause of equine and canine myofascial pain will be discussed in section A.

Moss (1972) noted that the locations of TPs in patients with musculoskeletal pain were very similar to the locations of classic AP points used to treat the affected body areas. Melzack (1979) reported 71% agreement between TP and AP point locations. Similar correspondence was confirmed by Pontinen (1982), Chung (1983) and Dung (1987) in humans and by Janssens (1987) in dogs.

TPs in human muscle have been called reactive points, Tender Points, fibrositic nodules, AhShi points and rheumatic spots. TPs may be identical to rheumatic spots but are not the same as local AhShi points (Type B) or tender points in fibromyalgia or fibromyositis, nor are they the same as zones of referred pain.

A myofascial TP is a hyperirritable locus within a taut band of skeletal muscle. It is located in the muscular tissue and/or its associated fascia.

Myofascial pain is defined as pain in the myofascial areas of the body. X-ray findings are usually negative (Brook and Stenn (1983). The pain is associated with local or distant foci of irritation in muscle, fascia, skin and subcutaneous tissue, viscera, joints and bones. It is a most common type of pain in man and animals. It may occur in any part of the body, may be acute or chronic and may appear to be superficial or deep, localised or diffuse.

Myofascial pain may be referred from and to nearby or distant structures. For instance, cardiac hypoxia may refer pain and establish TPs near thoracic spines T4-T6 (AP points BL14,15,16). Uterine or ovarian irritation may refer pain and establish TPs in the muscles between L5-S1 or L2-L3 respectively (AP points BL26 and 23) and in the low abdomen (AP points CV03, ST30). A TP in the long muscles of the back, just caudal to the scapula, may refer pain to the buttock area.

Myofascial pain occurs frequently, but not always, in the same dermatome or sclerotome as the TP but does not include the entire segment. It may refer to other segments also (Janssens 1984; Verhaert 1985).

Assessment of human myofascial pain: Pressure gauges have been used since the 1940's to assess pain objectively (Steinbrocker (1949), Keele (1954), McCarthy et al (1965), Lansbury (1966)) but little use has been made of them in human algometry/dolorimetry. Apart from those methods there was no way available to enable general practitioners to quantify pain objectively. At present, two basic criteria, both subjective, are used:

a. Questionnaires as to the subjective nature of pain: location (localised, generalised, superficial, deep, shifting etc); duration (recent, chronic, relapse of old pain); type (dull, nagging, sharp, fiery etc) and severity (various scales, such as a 0 to 10 visual analogue scale (VAS)).

b. Observation of posture, movement (flexibility/lameness/stiffness/ guarding), joint flexion, muscle spasm and autonomic changes (vascular, neurodermatitic).

Dung (1987) described a method of quantifying human pain by the number and sequence of appearance of tender AP points (TPs), especially between the dorsal spinal processes and in the paravertebral area (Dung 1986). Patients with >72 pairs of TPs on the body were likely to have severe, non-specific, poorly responsive pain, with poor prognosis even after AP/TP therapy. Those with 48-72 pairs (tertiary pain degree) were likely to be difficult cases. Those with <48 or 24 pairs were likely to have less severe pain (secondary or primary pain degree respectively) and a much better prognosis. Although it was claimed to be objective, Dung's localisation of TPs and his quantification of pain depended on the patient's verbal response to TP palpation. Therefore, it was not objective.

Infrared thermography: Measurement of skin temperature is very useful in the objective diagnosis and evaluation of myofascial pain (Fischer 1986, 1988). IR thermography can detect hot (vasodilation, muscle spasm) and cold (vasoconstriction) spots in tissues. Acute pain-points, as in myositis or an active TP, usually show as areas hotter than nearby areas. Fibrositic nodules (chronic, fibrosed TPs) and sensory root and nerve dysfunction show as cold spots. Areas of referred pain may also show up as cold areas.

The method is useful in pinpointing the site of acute vertebral or joint pain (hot areas) but the instrumentation is very expensive and is unlikely to be found in the family physician's surgery.

Fischer (1984) proposed an objective, practical and relatively cheap method of quantifying myofascial pain after the TPs and problem areas are located by careful clinical examination and palpation. His methods are based on adapted force gauges to quantify pressure pain thresholds at TPs, pressure tolerance of muscle and bone, tissue compliance measurements and dynamometry of muscle, especially of limb muscle. Each of these concepts will be discussed in section B. Advances in treating TPs and myofascial syndromes are discussed briefly in section C.