Advances and Instrumentation in Diagnosis and Treatment of Trigger Points in Human Myofascial Pain: Veterinary Implications
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)
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)
ABSTRACT
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.
INTRODUCTION
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.
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.
INTRODUCTION
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.
A.1. TRIGGER POINTS (TPs) AND MYOFASCIAL SYNDROMES IN HUMANS
Types of TPs: There are different types: active and passive, primary and secondary. All TPs are associated with dysfunction but only active TPs are associated with pain. Primary and secondary TPs may be active or passive.
Active TPs are very tender on palpation and associated with existing pain or other dysfunction. They may vary in irritability (associated with variation in symptoms) from hour to hour and day to day. The severity and extent of the referred pain depends on the irritability of the TP, not on its size or the size of the affected muscle. Active TPs can become passive after alleviation of the precipitating factors, rest or inadequate therapy (Verhaert 1985).
Passive (latent) TPs are less tender on palpation. They may be found in clinically normal patients and are associated with restricted movement (guarding) and weakness/fatigue of the affected muscles. (Muscles "learn" to avoid movements which cause pain). Passive TPs can be activated easily by many factors, especially overstretching/overuse, and can then trigger clinical pain or dysfunction. The fitter the muscle, the more difficult it is to activate its passive TPs (Verhaert 1985).
Primary TPs are those which arise as a direct result of physical injury, local irritation in virus diseases or direct environmental effects on myofascial tissue. Active primary TPs, causing pain, "guarding" and increased muscle stress elsewhere, may recruit secondary TPs in the same or other muscles.
Secondary TPs are those which arise due to foci of irritation elsewhere, such as in visceral disease or as recruits to very active primary TPs elsewhere.
Aetiology of TPs: Normal muscle, connective tissue, skin and fully healed scars are not painful on palpation and should contain no TPs. When they arise, TPs are usually located in muscle but foci of irritation in the skin, ligaments, fascia, subcutaneous connective tissue and periosteum can also act as TPs (Janssens 1984; Verhaert 1985). Scar tissue, especially that with keloid formation or areas of local tenderness, may also act a TP (Fox 1975; Khoe 1979; Rogers 1982; Verhaert 1985). Tender scars may arise after surgical incision (especially transverse), haematoma or tissue bruising, burns, local infection, abscesses, vaccination, needle-track infection and in infected tooth-sockets.
TPs are usually initiated (or latent ones activated) by acute or chronic overload or direct injury to the affected muscles (hyper-extension, strain, trauma, a fall, being cast etc). Fatigued or unfit muscles are very prone to injury and, therefore, TPs can easily arise in them (Cain and Rogers 1987).
TPs can also arise during periods of rapid growth (growing pains due to slight muscle, joint and tendon stress/strain) or as a sequel to systemic infection or fever, especially virus infection (Fox 1975; Janssens 1984).
Irritation of the thoracic or abdominal organs, of vertebral nerve-roots, joints, muscles or periosteum may refer pain to related skin and muscle and may establish TPs in the same and nearby spinal segments. Arthritis, subluxation of vertebrae, overriding of vertebral spines or facet joints, vertebral disc lesions or spinal nerve pressure (entrapment) are often associated with TPs. Over-exertion of muscle (hyper-contraction, tearing some of the weaker fibres) and chills/draughts on exposed parts of the body, especially after exercise, or if the part is hot or sweating can also activate TPs (Moss 1972; TP Therapy Symposium 1981; Janssens 1984; Verhaert 1985).
Detection/elimination of active TPs are important in the treatment of clinical pain and other disorders. Regular examination for and elimination of passive TPs (by massage and physical exercise) can restore full muscular function and can prevent many problems. This is the basis of Chinese acupressure, Shiatsu (Japanese AP massage) and Tai Chi (Chinese body exercises).
Clinical detection of TPs: TPs are located by careful palpation of the body, searching for points of exquisite tenderness. As each point is pressed, the human patient is asked: "What do you feel now ?". Unless the TPs are very active, the patient is unaware of their existence or location until they are palpated. TPs persist under general anaesthesia and post-mortem (Schade 1919).
To the palpating hand, TPs feel like nodules surrounded by a taut band of otherwise normal muscle. Occasionally the affected muscle may be hypertonic or in spasm. If the examiner pinches an active TP or snaps a finger across it, the patient may give a local or general jerk (positive "jump sign"). Pressing, pinching or needling the active TP triggers pain to the problem area (referred pain area, joint, other muscles or viscus) unless the referred area is in severe pain beforehand. Local TP tenderness can last for hours afterwards (Verhaert 1985). Passive TPs have similar characteristics but are not as painful and do not refer pain elsewhere to the same degree as active TPs.
The anatomical relationships between TPs and their area of referred pain are quite specific and a detailed knowledge of these relationships can help to predict the location of TPs in pain of specific organs or areas (Anon 1980; Travell and Simons 1984, 1985).
Histologically, TPs can show fat dusting. Severe forms may show fibrosis and dystrophic changes (swollen mitochondria, destruction of myofilaments, ruptured sarcomeres and collagen accumulation) in replacement connective tissue (Michlke et al 1960, Fassbender 1975).
Chronic myofascial syndromes typically present as an acute episode (active TPs present) but with a history of recurrent episodes over months or years. This is due to alternation of the TPs between the active and passive states with rest, time and various therapies which failed to find or eliminate the TPs (Verhaert 1985). TPs, especially those entrapping spinal nerves, may induce related sensory disorders (paraesthesia, hyperaesthesia, tinnitus, disturbed vestibular function (vision, space perception, ataxia)) and autonomic signs (Chung 1983; Travell and Simons 1984, 1985; Janssens 1984). In the early stages signs include: localised vasodilation (thermographic hot-spots) with localised muscle spasm, secretion (saliva, sweat, tears etc) and pilomotor activity. Chronic TPs may show vasoconstriction (thermographic cold-spots), hyper-irritability of motor neurons (Verhaert 1985). The are often fibrotic and quite difficult to penetrate with a needle.
Affected muscles have a restricted range of movement and resist passive or active stretching, as this causes pain. Muscle contraction against a fixed resistance is also painful. They are easily fatigued and can do less work. Muscle atrophy or neurological deficit is seldom present unless the TP or local muscle spasm entraps a nerve (Verhaert 1985).
Although TPs may arise in association with spondylosis, arthritis, disc disease in humans and animals and in canine hip dysplasia, radiography in the more common myofascial disorders is usually negative. Blood tests for muscle enzymes are usually negative unless there is extensive muscle damage, as in equine azoturia.
A.2. TRIGGER POINTS (TPs) AND MYOFASCIAL SYNDROMES IN ANIMALS
Veterinary acupuncturists have known for many years of the diagnostic and therapeutic relationships between functional disorder of internal organs and the presence of tender points in the paravertebral area (the Shu points, Kothbauer's Pain Points etc).
They also knew that stimulation of tender points (TPs, AhShi points) in muscle or scar tissue by dry needling, procaine/Impletol (Bayer, Germany) injection, laser or electrical methods etc could resolve many disorders (see references in Rogers 1974-1988). The classical AP reflex points (paravertebral Shu and thoracoabdominal Mu points) and some diagnostic points have been described for cattle (Kothbauer and Meng 1983) and horses (Cain and Rogers 1987). However, documentation of the precise locations and related symptomatology of animal TPs is poor in comparison with that of human TPs.
Janssens (1984) was the first to document in detail the presence of muscular TPs as a cause of chronic pain in animals. Pain had been present in 21 dogs for a mean time of 6 months. TP therapy (dry needling for 5 minutes/week or injection of the TPs (0.25-2 ml 1.0% xylocaine or 0.5% procaine via 25-28 gauge needle)) gave 70% success in a mean time of 17 days (2.5 sessions). Relapse occurred in 33% and treatment of relapses gave the same result as initial treatment.
In a second paper (Janssens 1987), he reported the occurrence of TPs in 47 lame or claudicating dogs. Clinical signs had been present for a mean time of 6 months. TPs were found in the following muscles:
triceps (AP point LU 1 in animals) (52%);
adductor and pectineus (AP point LV 9 or 10) (15%);
peroneus longus (AP point GB34) (12%);
gluteus medius (AP point GB29) (10%),
iliocostalis lumborum (AP point BL26) (6%);
quadriceps (4%).
TP therapy gave successful outcome in 60% of cases in a mean time of 19 days. Results with Triceps TPs were better (79% success). Relapse occurred in 33%, usually with the original TPs recurring again. Repeat treatment gave similar results to the initial treatment.
As in humans, TPs in animals can be due to trauma, muscle overload and by reflex effects, associated with foci of irritation in internal organs or other body parts.
Fever or viral infection may initiate TPs: 'Flu is often associated with muscle pain and tenderness. The sequel to 'flu may be multiple TPs. This may explain why large racing stables may have many horses with recurrent myofascial pain and poor racing performance. There is often a history of equine viral epidemics (especially equine 'flu) preceding a period of 1-2 years of poor racing performance.
While TPs in animals have diagnostic and therapeutic implications in all species, they are of special importance in sports medicine. Animals used for competitive sports (racing, jumping, polo etc) or for active work (draught animals, hunting dogs etc) need to be at peak physical fitness. For top performance, they rely heavily on the musculoskeletal system. In particular, they need full flexion and extension of the paravertebral muscles for maximum stride and speed and to enable them to gallop around corners. TPs in the paraspinal muscles (neck to sacrum) are commonly associated with lameness or stiffness in horses and dogs. TPs are also common in the heavy muscles of the neck, shoulder and thigh. Unless TPs are "released", muscle power and flexibility is impaired and athletic performance is reduced. TPs are self- sustaining and may remain indefinitely unless detected and eliminated (Verhaert 1985).
TPs can induce abnormal muscular and autonomic nervous function. This may manifest as acute or chronic pain, spasm, tremor, incoordination, stiffness, muscle weakness (including buckling of a limb (knee in humans; shoulder, elbow, hip or stifle in horses)), paraesthesia, numbness and poor circulation. By firing spontaneously into the nervous system, TPs maintain a state of reflex muscle guarding (spasm), with consequent pain, restriction of movement and poor blood supply in affected muscles. Atrophy of disuse can arise but is rare unless nerve entrapment occurs. Weeks to years after the pain stimulus which initiated them, TPs can remain in an active or passive state. Effective TP therapy can have rapid, dramatic effects on the wellbeing of the patient. Chronic pain due to unreleased active TPs has lasted from months to several decades in human patients and TP therapy has eliminated it immediately or in a matter of days (Travell and Simons; Verhaert 1985).
B.1. DIAGNOSTIC INSTRUMENTS TO ASSESS HUMAN MYOFASCIAL PAIN
The instrumentation consists of four different analogue force spring gauges. Each probe has a discoid rubber tip 1 cm sq (diameter 1.12 cm ). Gauges 1 and 2 record the pressure (in kg/cm sq) required to elicit pain threshold and tolerance in the muscle being investigated. Gauge 3 measures depth of penetration of a probe in muscle at precise pressures applied. Gauge 4 measures the force (kg) needed to overcome muscle power. Each instrument has a maximum "hold clutch" to register the maximum force applied. It is released by pressing a zero button.
These four gauges can document the location and severity of muscle and TP pain and weakness in humans and the outcome of treatment for medico-legal purposes. Accurate, objective documentation of TP locations and pain is very relevant to clinical assessment, diagnosis and prognosis. It also has most important medico-legal implications, especially in the differentiation of genuine pain patients from malingerers in insurance/compensation claims.
If pain is bilateral, a nearby normal area can be used as a reference. A decrease of pressure threshold to 3 kg/cm sq is considered abnormal (Fischer 1988).
1. PRESSURE THRESHOLD MEASUREMENT OF MUSCLE AND TPs: The instrument (Figure 1) is a spring gauge from 0-11 kg applied force, calibrated in steps of 0.1 kg. It is used to quantify the sensitivity of tender areas, such as sprains, strains, arthritic joints or TPs located by clinical examination/ palpation and to demonstrate the difference between thresholds of tender and healthy muscle. It also can demonstrate the disappearance of TP tenderness as the case is treated successfully. A rubber-protected pressure probe, 1 cm sq is used to apply vertical pressure to the tender areas. Pressure is increased steadily at 1 kg/sec. To prevent the probe from slipping, it is steadied by the thumb and index fingers of the left hand in right-handed operators. The patient is asked to indicate the first appearance of pain/discomfort to the applied pressure, at which time, the gauge is read and the pressure recorded in kg/cm sq. The "hold clutch" is released for the next measurement. Readings at TPs can be compared with those in healthy muscle on the opposite side, which has pressure thresholds 2-4 kg/cm sq higher than those recorded at TPs.
The gauge can be used to show the immediate improvement which occurs after correct injection of TP and to prove that the whole TP has been injected. Pressure threshold values increase typically by c. 4 kg/cm sq immediately after correct TP injection (Fischer 1986). Clinical improvement in pain is associated with increased pressure threshold values in patients whose pain is caused by TPs (Fischer 1984, Jimenez 1985).
Pressure algometry is highly reproducible (Merskey et al 1962, 1964). Pressure threshold values reliably locate TPs and quantify their sensitivity. The repeatability of the measurements within and between operators was confirmed by Reeves et al (1986) and Tunks et al (1988). Makela and Pontinen (1988) confirmed the repeatability of pressure threshold measurements at latent TPs in healthy volunteers and also in pain patients. They confirmed the value of the method in demonstrating the success of TP therapy by lasers and TENS methods of point therapy (Airaksinen et al 1988; Pontinen 1987).
2. PRESSURE TOLERANCE OF MUSCLE: The instrument (Figure 2) is a spring gauge from 0-17 kg applied force, calibrated in steps of 0.2 kg. It is used to quantify the upper level of sensitivity to pressure pain, i.e. the maximum pressure which can be tolerated when applied to standard sites (lower medial tibia (shin bone) and medial deltoid muscles), exploring non-tender areas and avoiding tender ones. (The deltoids seldom have TPs). A rubber-protected pressure probe, 1 cm sq is used to apply vertical pressure, increasing steadily at 1 kg/sec to the selected points. To prevent the probe from slipping, it is steadied by the thumb and index fingers of the left hand in right-handed operators. The patient is asked to indicate when the pressure pain becomes intolerable (very painful), at which time, the gauge is read and the pressure is recorded in kg/cm sq. The "hold clutch" is released for the next reading.
The purpose of pressure tolerance measurement is to quantify pain sensitivity and aid the diagnosis of abnormal muscle tenderness in relation to bone. In healthy subjects, muscle has higher pressure tolerance values than shinbone and values are very similar on both sides of the body. Fit athletes have higher pressure tolerance than unfit subjects. Men have slightly higher pressure tolerance than women. In patients with high pressure tolerance over muscle and bone, pressure thresholds at TPs may be higher than is usual.
Functional disorders show lower pressure tolerance values than those in organic disease.
If pressure tolerance of muscle is less than that of shinbone, generalised myopathy (a common cause of chronic pain and treatable by hormone therapy) is considered. It may arise in hypo- or hyper- thyroid disorders and in oestrogen deficiency (Fischer 1988).
If pressure tolerance is low at many measurement points over muscle and bone, it indicates an hyperalgesic syndrome, sometimes with psychiatric implications. The prognosis is poor and special therapies are needed (Fischer 1984, 1986, 1986, 1987, 1988). If there is a narrow gap between pressure threshold and pressure tolerance, hysterical personality is likely.
3. TISSUE COMPLIANCE MEASUREMENTS: The tissue compliance meter (Figure 3) is a spring gauge, force range from 0-5 kg in steps of 0.05 kg, with a special 5 cm diameter displacement head set flush at right angles to the probe. The rubber-protected pressure probe, 1 cm sq is used to apply vertical pressure. The displacement of the head (in mm) from the zero position is read off a scale at exactly 1, 2, 3, 4 and 5 kg applied pressure over the muscle being investigated. The principle is that a probe applied at a given pressure sinks deeper into healthy muscle than into tense or spastic muscle. When the displacement curves of normal and tense or spastic muscle are compared, the degree of tension can be demonstrated objectively. Especially in the range 2-5 kg/cm sq, penetration in tense or spastic muscle is 2-7 mm less than in healthy muscle. The meter can quantify displacement in other types of soft tissue pathology also: haematoma, oedema, scarring, tumours, inflammation, flaccidity etc (Fischer 1987). It can also be used to monitor the response to physical and other therapies (Fischer 1988).
4. DYNAMOMETRY OF JOINTS AND MUSCLE: The instrument (Figure 4) is a spring gauge from 0-27 kg applied force, calibrated in steps of 0.5 kg. It quantifies the current state of muscle power or weakness and the speed and extent of recovery of strength in cases treated successfully. It is used to assess the muscle power (flexion, extension, adduction, abduction) of individual joints or limbs. A rubber-protected contact plate, 14 cm sq is used to spread the force applied vertically to the part under investigation.
B.2. DIAGNOSTIC INSTRUMENTS TO ASSESS ANIMAL MYOFASCIAL PAIN
Similar instruments to those described in B.1. (above) could be adapted for
veterinary use, especially to quantify TP tenderness and muscle spasm in dogs and horses. Adapted gauges would be especially useful in the investigation of lameness or poor racing performance, where muscle pain (paravertebral, shoulder, thigh etc) is suspected as the cause.
Although pressure meters are being tested by a few veterinarians at present, this area of research is wide open, as there appears to be nothing published on the topic yet.
C. RECENT ADVANCES IN TP/MYOFASCIAL SYNDROME THERAPY IN HUMANS AND ANIMALS
Conventional treatment of lameness in athletic animals includes physiotherapy, rest, analgesic and anti-inflammatory medication, topical application of liniments, poultices, hot- or cold- packs, dressings or support bandages etc. Severe damage to fascia, tendons or muscles may need surgery. Treatment of equine back-pain may involve change of saddle or rider or the use of better saddle-pads. In spite of conventional measures, many horses and greyhounds take weeks or months to regain the potential for full athletic performance.
Direct injury, overstretching and viral diseases are the main cause of TPs. Active TPs can become passive following a period of rest or conventional treatment. Passive TPs are easy to reactivate (Verhaert 1985). Therefore, it is advisable to search for TPs in patients recovering from such incidents, even those patients which appear to be clinically normal. All TPs should be treated by first-aid or professional methods.
Animal TPs are easy to find by palpation. Finger or probe pressure or electrical stimulation of TPs is very painful: their palpation usually causes dogs to howl, snap or bite (Janssens 1984, 1987) and cattle or horses to vocalise, buck, kick, cringe, yield or go down or take definite aversive action (Kothbauer and Meng 1983; Cain and Rogers 1987). All TPs should be eliminated. Fully healthy tissue contains no TPs.
If multiple TPs are present and if pain is generalised, one must be selective in the choice of points for treatment. Treatment of many TPs in one session can be very painful. The human patient may not return for follow-up treatment and the animal patient may be much more difficult to handle in subsequent sessions. One can manage such cases as follows:
a. Humans with multiple TPs are best treated at special AP points (such as LI 4, LV03, ST36, PC06, BL23) for 1-3 sessions before TP therapy begins. In many cases, these preliminary sessions help to localise the clinical pain, making the selection of TPs easier.
b. Animals with multiple TPs: The special AP points ((a), above) are easy to locate and needle in dogs. However, in horses and cattle, LI 4 and LV 3 are difficult to locate or needle and ST36, PC06 are difficult to needle. In those species, one can use BaiHui (lumbosacral space), TH15, BL23 in the preliminary sessions.
With manageable numbers of TPs at presentation (or following preliminary AP sessions), one may start with the less painful TPs. These tend to be older, less active and associated with earlier symptoms than those of the current problem. Their palpation may refer little pain. Their elimination often eliminates the current problem also. If not, the more recent TPs are treated later on (Verhaert 1985).
Where there are few TPs to be treated, the most important ones to treat are the most painful ones. These are usually the most recent, are active and, on palpation or needling, refer pain to the patient's subjective problem area. Elimination of the more recent active TPs may shift the patient's pain pattern to that of older (less active or, now, passive) TPs. These may be treated later, if they persist.
Many methods are used to treat TPs. They include "stretch and spray", massage/vibration, TP injection, dry needling, electro-AP, TENS, laser and other methods.
TP "stretch and spray" technique: This is a method suggested by Travell and Simons. The muscle(s) containing the TPs are stretched (painful) and sprayed by an aerosol coolant (ethyl chloride or similar substances). It may be suitable for TPs in limb muscles in humans and dogs but has little practical application in horses because of the pain involved and the mass and power of the muscular system in horses.
TP massage/vibration: This is a common form of first-aid and is used 1-2 times/ day in physiotherapy. It is very useful to prescribe Do It Yourself or First-Aid massage (by a friend, partner, animal handler etc) daily between TP therapy sessions.
Massage/vibration can be given by hand or by mechanical instruments. Because of the mass of the equine muscular system, massage is best done by "fisting" the TPs for 4-6 minutes/day. Massage can be combined with rubs or liniments containing physical stimulants/rubefacients (such as alcohol, menthol, mustard, turpentine, acetic acid, salicylate) or penetrating agents/ dispersants (DMSO: operator should wear gloves !). Moss recommended massaging in adrenalin cream in humans.
TP injection is very successful and takes little time. It was the original method used in German Neural Therapy. Melzack (1977) said that short acting local anaesthetic blocks of TPs often give prolonged, sometimes permanent, relief of some forms of myofascial or visceral pain. It is the most suitable method for busy medical and veterinary practitioners, if the patient can tolerate it. Cain and Rogers (1987) have used TP and AP point injection successfully in equine patients for many years.
The solution for injection can be saline; Impletol (Bayer, Germany); 0.5-1% procaine or xylocaine; solutions containing Vit B1, B12, salicylate, DMSO; homoeopathic preparations etc. Many different types of solution are used, with similar results. Some clinicians feel that better results are obtained with saline or slightly irritant solutions than with those containing local anaesthetics. They explain this by longer periods of TP stimulation post- injection.
It is important to "hit" the centre of the TP. Chronic, fibrotic TPs may be difficult to penetrate. This can be very painful to the patient and (in humans) usually refers pain to the patient's subjective pain area. Needle sizes vary from 10-40 mm, depending on the depth of the point. Needles are 21-25 gauge. The volume injected at each TP depends on the tissue to be injected. In dogs and humans, volumes are 0.25-5 ml; in horses 1-10 ml.
Fischer believes that vigorous needling and injection is necessary to break down the scar (fibrous) tissue in chronic myofascial TPs. However, this belief is not shared by others. For instance, Janssens (1984, 1987) treated TPs using 5 minutes simple needle insertion/session in some dogs and injection in others. He could see no clear difference between the methods. Pontinen has used TENS, Laser and simple AP successfully to release TPs in humans and Rogers has used electro AP successfully to release TPs in horses with myofascial pain.
Scars are usually injected with small volumes, 0.1-0.2 ml/point and all tender points along the scar are injected. A dental syringe and 25 gauge needle are used. Alternatively, the French Dermojet (high pressure) spray-injector can be used.
TP dry needling: This is the usual method of stimulating AhShi points and AP points. Sterile 28-34 gauge AP needles or fine hypodermic needles are inserted into the centre of the TPs. They are left in-situ for 5-20 minutes, with or without manipulation (pecking, rotation). It is suitable for relaxed, placid patients but requires a longer session time than injection. Janssens (1984, 1987) has reported good results with simple needling in dogs. The method may not be suitable for very nervous, active or dangerous patients.
TP Electro-AP: This method is similar to dry needling but the needles are stimulated by an AP electro-stimulator. It has been used successfully by Pontinen in humans and Rogers in dogs and horses. It requires a longer session time than injection.
TP TENS: Transcutaneous Electrical Nerve Stimulation can be used to treat TPs in humans (Pontinen 1987). Skin electrodes are lubricated with a saline jelly and are taped over the TPs and connected to the stimulator. Output frequency is usually set in the range 1-10 Hz. Output is increased gradually until a strong but comfortable stimulus is attained. The muscles underneath usually show a visible twitch. Session time is usually 20 minutes. Patients can be treated at the clinic 1-2 times/week or can be given a personal, portable TENS instrument and shown which points to stimulate and how to operate the instrument. In that case, TPs are treated daily for 10-60 minutes. The results are excellent.
TENS in animals poses many problems. Little has been published on the use of TENS on animal TPs. The hair may need to be clipped and electrodes are more difficult to keep in place than in humans. A variation of TENS, using AP stimulators connected to gauze bandages soaked in saline solution and applied to AP points on the limbs or painful joints/bones has been used successfully by some veterinary acupuncturists. The use of TENS in animals needs to be supervised at all times.
TP Laser: Laser is an electromagnetic energy in the visible or infrared light range. The beam but can be interrupted (modulated) at variable frequencies and intervals by mechanical or electronic means. Mid-power lasers (5-30 mW/cm sq), mainly class 3A and 3B are used.
The most common is the Gallium Arsenide (Ga-As) or diode laser, emitting invisible light (902 nM) in the infra-red range. The depth of penetration increases with wavelength (Kolari et al 1988). Thus, cold laser is most effective when the tissues to be treated are superficial and infrared laser penetrates deeper than HeNe (red) laser.
Laser is usually given 2-8 times, at intervals of 1-3 days. At each session, the laser is applied for 20-120 seconds to or around the rim of the lesion and to each of the AP points or TPs selected for the case. Irradiation time depends on output power and depth of point. High output lasers and superficial points need less irradiation time. Airaksinen et al 1988 and Pontinen 1987 reported good results in TP therapy in humans.
Although Laser has been used successfully to treat back pain in horses (Martin and Klide 1987) and many veterinary acupuncturists are using lasers, there is little published on the use of laser on animal TPs. It is possible that lasers for human use may not be powerful enough to reach deeper TPs in large animals. More powerful veterinary lasers are being tested now.
Laser irradiation of scars, especially if concentrated on tender points, keloids and areas of marked adhesion, can produce dramatic clinical improvement in these cases.
Other methods have been used to treat TPs. They include heat, cold, faradism, ultrasound and moxibustion. Ultrasound and faradism are said to give poor results (Melzack et al 1977; Melzack 1978; Brook and Stenn (1983), Janssens 1984).
CONCLUSIONS
Many syndromes in human and animal patients involve acute or chronic pain, sensory and autonomic components and may be caused by, or associated with, unreleased TPs, especially in muscle and scar tissue.
Detection of TPs by clinical palpation is relatively easy. Quantification of TP sensitivity, pain threshold and tolerance, tissue compliance and limb dynamometry is now possible in humans. Similar methods may be applicable in animals.
TP therapy is an effective, rapid method of treating these problems. Many methods are effective but TP injection and infra-red Laser offer the most convenient methods for busy practitioners and personal TENS instruments offer a useful method of self-treatment for human patients once the case is diagnosed and the TPs are located. Unsupervised TENS is unsuitable for veterinary use.
ACKNOWLEDGEMENTS
P.A.M.R. thanks the Nordic Acupuncture Society for funding his trip to their 1988 Annual Congress at Laugarvatn, Iceland, at which TP therapy, pressure algometry and thermography were discussed.
This review was prompted by the work of co-authors Fischer and Pontinen and by Janssens' documentation of TP therapy in dogs. The Thesis by Dr. J. Verhaert (Belgium) was a most helpful source of concentrated information. It is recommended reading. The paper was given at the International Veterinary Acupuncture (IVAS) Training Course, Oslo, Norway, November 1988.
Medical knowledge is often based on animal experimentation before it is applied in human patients. Now, veterinarians may learn from human experimentation.
Types of TPs: There are different types: active and passive, primary and secondary. All TPs are associated with dysfunction but only active TPs are associated with pain. Primary and secondary TPs may be active or passive.
Active TPs are very tender on palpation and associated with existing pain or other dysfunction. They may vary in irritability (associated with variation in symptoms) from hour to hour and day to day. The severity and extent of the referred pain depends on the irritability of the TP, not on its size or the size of the affected muscle. Active TPs can become passive after alleviation of the precipitating factors, rest or inadequate therapy (Verhaert 1985).
Passive (latent) TPs are less tender on palpation. They may be found in clinically normal patients and are associated with restricted movement (guarding) and weakness/fatigue of the affected muscles. (Muscles "learn" to avoid movements which cause pain). Passive TPs can be activated easily by many factors, especially overstretching/overuse, and can then trigger clinical pain or dysfunction. The fitter the muscle, the more difficult it is to activate its passive TPs (Verhaert 1985).
Primary TPs are those which arise as a direct result of physical injury, local irritation in virus diseases or direct environmental effects on myofascial tissue. Active primary TPs, causing pain, "guarding" and increased muscle stress elsewhere, may recruit secondary TPs in the same or other muscles.
Secondary TPs are those which arise due to foci of irritation elsewhere, such as in visceral disease or as recruits to very active primary TPs elsewhere.
Aetiology of TPs: Normal muscle, connective tissue, skin and fully healed scars are not painful on palpation and should contain no TPs. When they arise, TPs are usually located in muscle but foci of irritation in the skin, ligaments, fascia, subcutaneous connective tissue and periosteum can also act as TPs (Janssens 1984; Verhaert 1985). Scar tissue, especially that with keloid formation or areas of local tenderness, may also act a TP (Fox 1975; Khoe 1979; Rogers 1982; Verhaert 1985). Tender scars may arise after surgical incision (especially transverse), haematoma or tissue bruising, burns, local infection, abscesses, vaccination, needle-track infection and in infected tooth-sockets.
TPs are usually initiated (or latent ones activated) by acute or chronic overload or direct injury to the affected muscles (hyper-extension, strain, trauma, a fall, being cast etc). Fatigued or unfit muscles are very prone to injury and, therefore, TPs can easily arise in them (Cain and Rogers 1987).
TPs can also arise during periods of rapid growth (growing pains due to slight muscle, joint and tendon stress/strain) or as a sequel to systemic infection or fever, especially virus infection (Fox 1975; Janssens 1984).
Irritation of the thoracic or abdominal organs, of vertebral nerve-roots, joints, muscles or periosteum may refer pain to related skin and muscle and may establish TPs in the same and nearby spinal segments. Arthritis, subluxation of vertebrae, overriding of vertebral spines or facet joints, vertebral disc lesions or spinal nerve pressure (entrapment) are often associated with TPs. Over-exertion of muscle (hyper-contraction, tearing some of the weaker fibres) and chills/draughts on exposed parts of the body, especially after exercise, or if the part is hot or sweating can also activate TPs (Moss 1972; TP Therapy Symposium 1981; Janssens 1984; Verhaert 1985).
Detection/elimination of active TPs are important in the treatment of clinical pain and other disorders. Regular examination for and elimination of passive TPs (by massage and physical exercise) can restore full muscular function and can prevent many problems. This is the basis of Chinese acupressure, Shiatsu (Japanese AP massage) and Tai Chi (Chinese body exercises).
Clinical detection of TPs: TPs are located by careful palpation of the body, searching for points of exquisite tenderness. As each point is pressed, the human patient is asked: "What do you feel now ?". Unless the TPs are very active, the patient is unaware of their existence or location until they are palpated. TPs persist under general anaesthesia and post-mortem (Schade 1919).
To the palpating hand, TPs feel like nodules surrounded by a taut band of otherwise normal muscle. Occasionally the affected muscle may be hypertonic or in spasm. If the examiner pinches an active TP or snaps a finger across it, the patient may give a local or general jerk (positive "jump sign"). Pressing, pinching or needling the active TP triggers pain to the problem area (referred pain area, joint, other muscles or viscus) unless the referred area is in severe pain beforehand. Local TP tenderness can last for hours afterwards (Verhaert 1985). Passive TPs have similar characteristics but are not as painful and do not refer pain elsewhere to the same degree as active TPs.
The anatomical relationships between TPs and their area of referred pain are quite specific and a detailed knowledge of these relationships can help to predict the location of TPs in pain of specific organs or areas (Anon 1980; Travell and Simons 1984, 1985).
Histologically, TPs can show fat dusting. Severe forms may show fibrosis and dystrophic changes (swollen mitochondria, destruction of myofilaments, ruptured sarcomeres and collagen accumulation) in replacement connective tissue (Michlke et al 1960, Fassbender 1975).
Chronic myofascial syndromes typically present as an acute episode (active TPs present) but with a history of recurrent episodes over months or years. This is due to alternation of the TPs between the active and passive states with rest, time and various therapies which failed to find or eliminate the TPs (Verhaert 1985). TPs, especially those entrapping spinal nerves, may induce related sensory disorders (paraesthesia, hyperaesthesia, tinnitus, disturbed vestibular function (vision, space perception, ataxia)) and autonomic signs (Chung 1983; Travell and Simons 1984, 1985; Janssens 1984). In the early stages signs include: localised vasodilation (thermographic hot-spots) with localised muscle spasm, secretion (saliva, sweat, tears etc) and pilomotor activity. Chronic TPs may show vasoconstriction (thermographic cold-spots), hyper-irritability of motor neurons (Verhaert 1985). The are often fibrotic and quite difficult to penetrate with a needle.
Affected muscles have a restricted range of movement and resist passive or active stretching, as this causes pain. Muscle contraction against a fixed resistance is also painful. They are easily fatigued and can do less work. Muscle atrophy or neurological deficit is seldom present unless the TP or local muscle spasm entraps a nerve (Verhaert 1985).
Although TPs may arise in association with spondylosis, arthritis, disc disease in humans and animals and in canine hip dysplasia, radiography in the more common myofascial disorders is usually negative. Blood tests for muscle enzymes are usually negative unless there is extensive muscle damage, as in equine azoturia.
A.2. TRIGGER POINTS (TPs) AND MYOFASCIAL SYNDROMES IN ANIMALS
Veterinary acupuncturists have known for many years of the diagnostic and therapeutic relationships between functional disorder of internal organs and the presence of tender points in the paravertebral area (the Shu points, Kothbauer's Pain Points etc).
They also knew that stimulation of tender points (TPs, AhShi points) in muscle or scar tissue by dry needling, procaine/Impletol (Bayer, Germany) injection, laser or electrical methods etc could resolve many disorders (see references in Rogers 1974-1988). The classical AP reflex points (paravertebral Shu and thoracoabdominal Mu points) and some diagnostic points have been described for cattle (Kothbauer and Meng 1983) and horses (Cain and Rogers 1987). However, documentation of the precise locations and related symptomatology of animal TPs is poor in comparison with that of human TPs.
Janssens (1984) was the first to document in detail the presence of muscular TPs as a cause of chronic pain in animals. Pain had been present in 21 dogs for a mean time of 6 months. TP therapy (dry needling for 5 minutes/week or injection of the TPs (0.25-2 ml 1.0% xylocaine or 0.5% procaine via 25-28 gauge needle)) gave 70% success in a mean time of 17 days (2.5 sessions). Relapse occurred in 33% and treatment of relapses gave the same result as initial treatment.
In a second paper (Janssens 1987), he reported the occurrence of TPs in 47 lame or claudicating dogs. Clinical signs had been present for a mean time of 6 months. TPs were found in the following muscles:
triceps (AP point LU 1 in animals) (52%);
adductor and pectineus (AP point LV 9 or 10) (15%);
peroneus longus (AP point GB34) (12%);
gluteus medius (AP point GB29) (10%),
iliocostalis lumborum (AP point BL26) (6%);
quadriceps (4%).
TP therapy gave successful outcome in 60% of cases in a mean time of 19 days. Results with Triceps TPs were better (79% success). Relapse occurred in 33%, usually with the original TPs recurring again. Repeat treatment gave similar results to the initial treatment.
As in humans, TPs in animals can be due to trauma, muscle overload and by reflex effects, associated with foci of irritation in internal organs or other body parts.
Fever or viral infection may initiate TPs: 'Flu is often associated with muscle pain and tenderness. The sequel to 'flu may be multiple TPs. This may explain why large racing stables may have many horses with recurrent myofascial pain and poor racing performance. There is often a history of equine viral epidemics (especially equine 'flu) preceding a period of 1-2 years of poor racing performance.
While TPs in animals have diagnostic and therapeutic implications in all species, they are of special importance in sports medicine. Animals used for competitive sports (racing, jumping, polo etc) or for active work (draught animals, hunting dogs etc) need to be at peak physical fitness. For top performance, they rely heavily on the musculoskeletal system. In particular, they need full flexion and extension of the paravertebral muscles for maximum stride and speed and to enable them to gallop around corners. TPs in the paraspinal muscles (neck to sacrum) are commonly associated with lameness or stiffness in horses and dogs. TPs are also common in the heavy muscles of the neck, shoulder and thigh. Unless TPs are "released", muscle power and flexibility is impaired and athletic performance is reduced. TPs are self- sustaining and may remain indefinitely unless detected and eliminated (Verhaert 1985).
TPs can induce abnormal muscular and autonomic nervous function. This may manifest as acute or chronic pain, spasm, tremor, incoordination, stiffness, muscle weakness (including buckling of a limb (knee in humans; shoulder, elbow, hip or stifle in horses)), paraesthesia, numbness and poor circulation. By firing spontaneously into the nervous system, TPs maintain a state of reflex muscle guarding (spasm), with consequent pain, restriction of movement and poor blood supply in affected muscles. Atrophy of disuse can arise but is rare unless nerve entrapment occurs. Weeks to years after the pain stimulus which initiated them, TPs can remain in an active or passive state. Effective TP therapy can have rapid, dramatic effects on the wellbeing of the patient. Chronic pain due to unreleased active TPs has lasted from months to several decades in human patients and TP therapy has eliminated it immediately or in a matter of days (Travell and Simons; Verhaert 1985).
B.1. DIAGNOSTIC INSTRUMENTS TO ASSESS HUMAN MYOFASCIAL PAIN
The instrumentation consists of four different analogue force spring gauges. Each probe has a discoid rubber tip 1 cm sq (diameter 1.12 cm ). Gauges 1 and 2 record the pressure (in kg/cm sq) required to elicit pain threshold and tolerance in the muscle being investigated. Gauge 3 measures depth of penetration of a probe in muscle at precise pressures applied. Gauge 4 measures the force (kg) needed to overcome muscle power. Each instrument has a maximum "hold clutch" to register the maximum force applied. It is released by pressing a zero button.
These four gauges can document the location and severity of muscle and TP pain and weakness in humans and the outcome of treatment for medico-legal purposes. Accurate, objective documentation of TP locations and pain is very relevant to clinical assessment, diagnosis and prognosis. It also has most important medico-legal implications, especially in the differentiation of genuine pain patients from malingerers in insurance/compensation claims.
If pain is bilateral, a nearby normal area can be used as a reference. A decrease of pressure threshold to 3 kg/cm sq is considered abnormal (Fischer 1988).
1. PRESSURE THRESHOLD MEASUREMENT OF MUSCLE AND TPs: The instrument (Figure 1) is a spring gauge from 0-11 kg applied force, calibrated in steps of 0.1 kg. It is used to quantify the sensitivity of tender areas, such as sprains, strains, arthritic joints or TPs located by clinical examination/ palpation and to demonstrate the difference between thresholds of tender and healthy muscle. It also can demonstrate the disappearance of TP tenderness as the case is treated successfully. A rubber-protected pressure probe, 1 cm sq is used to apply vertical pressure to the tender areas. Pressure is increased steadily at 1 kg/sec. To prevent the probe from slipping, it is steadied by the thumb and index fingers of the left hand in right-handed operators. The patient is asked to indicate the first appearance of pain/discomfort to the applied pressure, at which time, the gauge is read and the pressure recorded in kg/cm sq. The "hold clutch" is released for the next measurement. Readings at TPs can be compared with those in healthy muscle on the opposite side, which has pressure thresholds 2-4 kg/cm sq higher than those recorded at TPs.
The gauge can be used to show the immediate improvement which occurs after correct injection of TP and to prove that the whole TP has been injected. Pressure threshold values increase typically by c. 4 kg/cm sq immediately after correct TP injection (Fischer 1986). Clinical improvement in pain is associated with increased pressure threshold values in patients whose pain is caused by TPs (Fischer 1984, Jimenez 1985).
Pressure algometry is highly reproducible (Merskey et al 1962, 1964). Pressure threshold values reliably locate TPs and quantify their sensitivity. The repeatability of the measurements within and between operators was confirmed by Reeves et al (1986) and Tunks et al (1988). Makela and Pontinen (1988) confirmed the repeatability of pressure threshold measurements at latent TPs in healthy volunteers and also in pain patients. They confirmed the value of the method in demonstrating the success of TP therapy by lasers and TENS methods of point therapy (Airaksinen et al 1988; Pontinen 1987).
2. PRESSURE TOLERANCE OF MUSCLE: The instrument (Figure 2) is a spring gauge from 0-17 kg applied force, calibrated in steps of 0.2 kg. It is used to quantify the upper level of sensitivity to pressure pain, i.e. the maximum pressure which can be tolerated when applied to standard sites (lower medial tibia (shin bone) and medial deltoid muscles), exploring non-tender areas and avoiding tender ones. (The deltoids seldom have TPs). A rubber-protected pressure probe, 1 cm sq is used to apply vertical pressure, increasing steadily at 1 kg/sec to the selected points. To prevent the probe from slipping, it is steadied by the thumb and index fingers of the left hand in right-handed operators. The patient is asked to indicate when the pressure pain becomes intolerable (very painful), at which time, the gauge is read and the pressure is recorded in kg/cm sq. The "hold clutch" is released for the next reading.
The purpose of pressure tolerance measurement is to quantify pain sensitivity and aid the diagnosis of abnormal muscle tenderness in relation to bone. In healthy subjects, muscle has higher pressure tolerance values than shinbone and values are very similar on both sides of the body. Fit athletes have higher pressure tolerance than unfit subjects. Men have slightly higher pressure tolerance than women. In patients with high pressure tolerance over muscle and bone, pressure thresholds at TPs may be higher than is usual.
Functional disorders show lower pressure tolerance values than those in organic disease.
If pressure tolerance of muscle is less than that of shinbone, generalised myopathy (a common cause of chronic pain and treatable by hormone therapy) is considered. It may arise in hypo- or hyper- thyroid disorders and in oestrogen deficiency (Fischer 1988).
If pressure tolerance is low at many measurement points over muscle and bone, it indicates an hyperalgesic syndrome, sometimes with psychiatric implications. The prognosis is poor and special therapies are needed (Fischer 1984, 1986, 1986, 1987, 1988). If there is a narrow gap between pressure threshold and pressure tolerance, hysterical personality is likely.
3. TISSUE COMPLIANCE MEASUREMENTS: The tissue compliance meter (Figure 3) is a spring gauge, force range from 0-5 kg in steps of 0.05 kg, with a special 5 cm diameter displacement head set flush at right angles to the probe. The rubber-protected pressure probe, 1 cm sq is used to apply vertical pressure. The displacement of the head (in mm) from the zero position is read off a scale at exactly 1, 2, 3, 4 and 5 kg applied pressure over the muscle being investigated. The principle is that a probe applied at a given pressure sinks deeper into healthy muscle than into tense or spastic muscle. When the displacement curves of normal and tense or spastic muscle are compared, the degree of tension can be demonstrated objectively. Especially in the range 2-5 kg/cm sq, penetration in tense or spastic muscle is 2-7 mm less than in healthy muscle. The meter can quantify displacement in other types of soft tissue pathology also: haematoma, oedema, scarring, tumours, inflammation, flaccidity etc (Fischer 1987). It can also be used to monitor the response to physical and other therapies (Fischer 1988).
4. DYNAMOMETRY OF JOINTS AND MUSCLE: The instrument (Figure 4) is a spring gauge from 0-27 kg applied force, calibrated in steps of 0.5 kg. It quantifies the current state of muscle power or weakness and the speed and extent of recovery of strength in cases treated successfully. It is used to assess the muscle power (flexion, extension, adduction, abduction) of individual joints or limbs. A rubber-protected contact plate, 14 cm sq is used to spread the force applied vertically to the part under investigation.
B.2. DIAGNOSTIC INSTRUMENTS TO ASSESS ANIMAL MYOFASCIAL PAIN
Similar instruments to those described in B.1. (above) could be adapted for
veterinary use, especially to quantify TP tenderness and muscle spasm in dogs and horses. Adapted gauges would be especially useful in the investigation of lameness or poor racing performance, where muscle pain (paravertebral, shoulder, thigh etc) is suspected as the cause.
Although pressure meters are being tested by a few veterinarians at present, this area of research is wide open, as there appears to be nothing published on the topic yet.
C. RECENT ADVANCES IN TP/MYOFASCIAL SYNDROME THERAPY IN HUMANS AND ANIMALS
Conventional treatment of lameness in athletic animals includes physiotherapy, rest, analgesic and anti-inflammatory medication, topical application of liniments, poultices, hot- or cold- packs, dressings or support bandages etc. Severe damage to fascia, tendons or muscles may need surgery. Treatment of equine back-pain may involve change of saddle or rider or the use of better saddle-pads. In spite of conventional measures, many horses and greyhounds take weeks or months to regain the potential for full athletic performance.
Direct injury, overstretching and viral diseases are the main cause of TPs. Active TPs can become passive following a period of rest or conventional treatment. Passive TPs are easy to reactivate (Verhaert 1985). Therefore, it is advisable to search for TPs in patients recovering from such incidents, even those patients which appear to be clinically normal. All TPs should be treated by first-aid or professional methods.
Animal TPs are easy to find by palpation. Finger or probe pressure or electrical stimulation of TPs is very painful: their palpation usually causes dogs to howl, snap or bite (Janssens 1984, 1987) and cattle or horses to vocalise, buck, kick, cringe, yield or go down or take definite aversive action (Kothbauer and Meng 1983; Cain and Rogers 1987). All TPs should be eliminated. Fully healthy tissue contains no TPs.
If multiple TPs are present and if pain is generalised, one must be selective in the choice of points for treatment. Treatment of many TPs in one session can be very painful. The human patient may not return for follow-up treatment and the animal patient may be much more difficult to handle in subsequent sessions. One can manage such cases as follows:
a. Humans with multiple TPs are best treated at special AP points (such as LI 4, LV03, ST36, PC06, BL23) for 1-3 sessions before TP therapy begins. In many cases, these preliminary sessions help to localise the clinical pain, making the selection of TPs easier.
b. Animals with multiple TPs: The special AP points ((a), above) are easy to locate and needle in dogs. However, in horses and cattle, LI 4 and LV 3 are difficult to locate or needle and ST36, PC06 are difficult to needle. In those species, one can use BaiHui (lumbosacral space), TH15, BL23 in the preliminary sessions.
With manageable numbers of TPs at presentation (or following preliminary AP sessions), one may start with the less painful TPs. These tend to be older, less active and associated with earlier symptoms than those of the current problem. Their palpation may refer little pain. Their elimination often eliminates the current problem also. If not, the more recent TPs are treated later on (Verhaert 1985).
Where there are few TPs to be treated, the most important ones to treat are the most painful ones. These are usually the most recent, are active and, on palpation or needling, refer pain to the patient's subjective problem area. Elimination of the more recent active TPs may shift the patient's pain pattern to that of older (less active or, now, passive) TPs. These may be treated later, if they persist.
Many methods are used to treat TPs. They include "stretch and spray", massage/vibration, TP injection, dry needling, electro-AP, TENS, laser and other methods.
TP "stretch and spray" technique: This is a method suggested by Travell and Simons. The muscle(s) containing the TPs are stretched (painful) and sprayed by an aerosol coolant (ethyl chloride or similar substances). It may be suitable for TPs in limb muscles in humans and dogs but has little practical application in horses because of the pain involved and the mass and power of the muscular system in horses.
TP massage/vibration: This is a common form of first-aid and is used 1-2 times/ day in physiotherapy. It is very useful to prescribe Do It Yourself or First-Aid massage (by a friend, partner, animal handler etc) daily between TP therapy sessions.
Massage/vibration can be given by hand or by mechanical instruments. Because of the mass of the equine muscular system, massage is best done by "fisting" the TPs for 4-6 minutes/day. Massage can be combined with rubs or liniments containing physical stimulants/rubefacients (such as alcohol, menthol, mustard, turpentine, acetic acid, salicylate) or penetrating agents/ dispersants (DMSO: operator should wear gloves !). Moss recommended massaging in adrenalin cream in humans.
TP injection is very successful and takes little time. It was the original method used in German Neural Therapy. Melzack (1977) said that short acting local anaesthetic blocks of TPs often give prolonged, sometimes permanent, relief of some forms of myofascial or visceral pain. It is the most suitable method for busy medical and veterinary practitioners, if the patient can tolerate it. Cain and Rogers (1987) have used TP and AP point injection successfully in equine patients for many years.
The solution for injection can be saline; Impletol (Bayer, Germany); 0.5-1% procaine or xylocaine; solutions containing Vit B1, B12, salicylate, DMSO; homoeopathic preparations etc. Many different types of solution are used, with similar results. Some clinicians feel that better results are obtained with saline or slightly irritant solutions than with those containing local anaesthetics. They explain this by longer periods of TP stimulation post- injection.
It is important to "hit" the centre of the TP. Chronic, fibrotic TPs may be difficult to penetrate. This can be very painful to the patient and (in humans) usually refers pain to the patient's subjective pain area. Needle sizes vary from 10-40 mm, depending on the depth of the point. Needles are 21-25 gauge. The volume injected at each TP depends on the tissue to be injected. In dogs and humans, volumes are 0.25-5 ml; in horses 1-10 ml.
Fischer believes that vigorous needling and injection is necessary to break down the scar (fibrous) tissue in chronic myofascial TPs. However, this belief is not shared by others. For instance, Janssens (1984, 1987) treated TPs using 5 minutes simple needle insertion/session in some dogs and injection in others. He could see no clear difference between the methods. Pontinen has used TENS, Laser and simple AP successfully to release TPs in humans and Rogers has used electro AP successfully to release TPs in horses with myofascial pain.
Scars are usually injected with small volumes, 0.1-0.2 ml/point and all tender points along the scar are injected. A dental syringe and 25 gauge needle are used. Alternatively, the French Dermojet (high pressure) spray-injector can be used.
TP dry needling: This is the usual method of stimulating AhShi points and AP points. Sterile 28-34 gauge AP needles or fine hypodermic needles are inserted into the centre of the TPs. They are left in-situ for 5-20 minutes, with or without manipulation (pecking, rotation). It is suitable for relaxed, placid patients but requires a longer session time than injection. Janssens (1984, 1987) has reported good results with simple needling in dogs. The method may not be suitable for very nervous, active or dangerous patients.
TP Electro-AP: This method is similar to dry needling but the needles are stimulated by an AP electro-stimulator. It has been used successfully by Pontinen in humans and Rogers in dogs and horses. It requires a longer session time than injection.
TP TENS: Transcutaneous Electrical Nerve Stimulation can be used to treat TPs in humans (Pontinen 1987). Skin electrodes are lubricated with a saline jelly and are taped over the TPs and connected to the stimulator. Output frequency is usually set in the range 1-10 Hz. Output is increased gradually until a strong but comfortable stimulus is attained. The muscles underneath usually show a visible twitch. Session time is usually 20 minutes. Patients can be treated at the clinic 1-2 times/week or can be given a personal, portable TENS instrument and shown which points to stimulate and how to operate the instrument. In that case, TPs are treated daily for 10-60 minutes. The results are excellent.
TENS in animals poses many problems. Little has been published on the use of TENS on animal TPs. The hair may need to be clipped and electrodes are more difficult to keep in place than in humans. A variation of TENS, using AP stimulators connected to gauze bandages soaked in saline solution and applied to AP points on the limbs or painful joints/bones has been used successfully by some veterinary acupuncturists. The use of TENS in animals needs to be supervised at all times.
TP Laser: Laser is an electromagnetic energy in the visible or infrared light range. The beam but can be interrupted (modulated) at variable frequencies and intervals by mechanical or electronic means. Mid-power lasers (5-30 mW/cm sq), mainly class 3A and 3B are used.
The most common is the Gallium Arsenide (Ga-As) or diode laser, emitting invisible light (902 nM) in the infra-red range. The depth of penetration increases with wavelength (Kolari et al 1988). Thus, cold laser is most effective when the tissues to be treated are superficial and infrared laser penetrates deeper than HeNe (red) laser.
Laser is usually given 2-8 times, at intervals of 1-3 days. At each session, the laser is applied for 20-120 seconds to or around the rim of the lesion and to each of the AP points or TPs selected for the case. Irradiation time depends on output power and depth of point. High output lasers and superficial points need less irradiation time. Airaksinen et al 1988 and Pontinen 1987 reported good results in TP therapy in humans.
Although Laser has been used successfully to treat back pain in horses (Martin and Klide 1987) and many veterinary acupuncturists are using lasers, there is little published on the use of laser on animal TPs. It is possible that lasers for human use may not be powerful enough to reach deeper TPs in large animals. More powerful veterinary lasers are being tested now.
Laser irradiation of scars, especially if concentrated on tender points, keloids and areas of marked adhesion, can produce dramatic clinical improvement in these cases.
Other methods have been used to treat TPs. They include heat, cold, faradism, ultrasound and moxibustion. Ultrasound and faradism are said to give poor results (Melzack et al 1977; Melzack 1978; Brook and Stenn (1983), Janssens 1984).
CONCLUSIONS
Many syndromes in human and animal patients involve acute or chronic pain, sensory and autonomic components and may be caused by, or associated with, unreleased TPs, especially in muscle and scar tissue.
Detection of TPs by clinical palpation is relatively easy. Quantification of TP sensitivity, pain threshold and tolerance, tissue compliance and limb dynamometry is now possible in humans. Similar methods may be applicable in animals.
TP therapy is an effective, rapid method of treating these problems. Many methods are effective but TP injection and infra-red Laser offer the most convenient methods for busy practitioners and personal TENS instruments offer a useful method of self-treatment for human patients once the case is diagnosed and the TPs are located. Unsupervised TENS is unsuitable for veterinary use.
ACKNOWLEDGEMENTS
P.A.M.R. thanks the Nordic Acupuncture Society for funding his trip to their 1988 Annual Congress at Laugarvatn, Iceland, at which TP therapy, pressure algometry and thermography were discussed.
This review was prompted by the work of co-authors Fischer and Pontinen and by Janssens' documentation of TP therapy in dogs. The Thesis by Dr. J. Verhaert (Belgium) was a most helpful source of concentrated information. It is recommended reading. The paper was given at the International Veterinary Acupuncture (IVAS) Training Course, Oslo, Norway, November 1988.
Medical knowledge is often based on animal experimentation before it is applied in human patients. Now, veterinarians may learn from human experimentation.
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