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Trigger points are described as hyperirritable spots in skeletal muscle that are associated with palpable nodules in taut bands of muscle fibers. The palpable nodules are the result of small contraction knots in muscle tissue. They are considered a common cause of pain. Direct compression of a trigger point may elicit local tenderness, referred pain, and motor dysfunction.
According to proponents of the concept, a trigger point does not really cause a contraction, but rather causes a contracture. A contraction is muscular activity mediated by the nervous system, while a contracture is said to be a mechanical "sticking" of the muscle fibers with no involvement from the nervous system. The hypothesis is that usually an event of muscular overload causes a prolonged release of Ca2+ ion from the sarcoplasmic reticulum (storage unit for the muscle cell) which results in a sticking of the untrained or overloaded cells. This leads to a compression of capillaries and results in an increased local energy demand and local ischemia (loss of blood circulation) to the area. This "energy crisis" (as it is termed in the seminal work on trigger points) causes the release of chemicals that augment pain activity. Since an involved muscle is weakened by this theorised sustained shortening, surrounding muscles can be made to pick up the slack and develop trigger points themselves.Simons, D.G. Cardiology and Myofascial Trigger Points: Janet G. Travell's Contribution . Tex Heart Inst J. 2003; 30(1): 3–7.*
The theory of trigger points is not accepted by all of mainstream medicine. Evidence based medicine researchers have concluded evidence for the usefulness of trigger points in the diagnosis of fibromyalgia is thin. Another study on lower back pain for example concluded usefulness of examining for the presence of trigger points in patients with LBP should be questioned.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=1307701&query_hl=2&itool=pubmed_docsum
History
Trigger points have been a subject of study by a small number of doctors for several decades although this has not become part of mainstream medicine. The existence of tender areas and zones of induration in muscles has been recognized in medicine for many years and was described as muscular rheumatism or fibrositis in English; German terms included myogelose and myalgie. However, there was little agreement about what they meant. Important work was carried out by J. H. Kellgren at University College Hospital, London, in the 1930s and, independently, by Michael Gutstein in Berlin and Michael Kelly in Australia (the latter two workers continued to publish into the 1950s and 1960s). Kellgren conducted experiments in which he injected saline into healthy volunteers and showed that this gave rise to zones of referred pain lower down the limbs.
Today, much treatment of trigger points and their pain complexes are handled by massage therapists, physical therapists, occupational therapists, some chiropractors and other hands-on somatic practitioners who have had experience in training in the field of neuromuscular therapy (NMT).
Janet G. Travell, MD
It was, however, an American physician, Janet G. Travell, who was responsible for the most detailed and important work. Her work treating US President John F. Kennedy's back pain was so successful that she was asked to be the first female Personal Physician to the President.Bagg J,(2003),The President's Physician,Texas Heart Institute,Houston* She published more than 40 papers between 1942 and 1990 and in 1983 the first volume of The Trigger Point Manual appeared; this was followed by the second volume in 1992. A second edition of this work has now been published. In her later years Travell collaborated extensively with her colleague David Simons. A third edition is soon to be published by Simons and his wife, both of whom have survived Travell.
The trigger point concept remains unknown to most doctors and is not generally taught in medical school curricula. Other health professionals, such as physiotherapists, osteopaths, naturopaths, chiropractors, physiatrists and (some) veterinarians are generally more aware of these ideas and many of them make use of trigger points in their clinical workSwedish Medical CenterAmerican Academy of Family PhysiciansDynamic Chiropractic.
Travell and Simon's seminal work on the subject, Myofascial Pain and Dysfunction: The Trigger Point Manual, states the following:
- around 75% of pain clinic patients have a trigger point as the sole source of their pain.
- The following conditions are often diagnosed (incorrectly) when trigger points are the true cause of pain: carpal tunnel syndrome, bursitis, tendinitis, angina pectoris, sciatic symptoms, along with many other pain problems.
- Arthritis is often cited as the cause for pain even though pain is not always concomitant with arthritis. The real culprit may be a trigger point, normally activated by a certain activity involving the muscles used in the motion, by chronically bad posture, bad mechanics, repetitive motion, structural deficiencies such as a lower limb length inequality or a small hemipelvis, or nutritional deficiencies.
Myofascial pain syndrome
The main innovation of Travell's work was the introduction of the myofascial pain syndrome concept. This is described as a focal hyperritability in muscle that can strongly modulate central nervous system functions. Travell and followers distinguish this from fibromyalgia, which is characterized by widespread pain and tenderness and is described as a central augmentation of nociception giving rise to deep tissue tenderness that includes muscles. It is said to be considerably more difficult to treat.
In order for a medical sign to be diagnostically useful, independent examiners must be able to agree on its presence (see intersubjective verifiability). A study by Gerwin et. al. found that independent examiners were generally able to identify myofascial trigger points (MTrP), but only with sufficient training and agreement on the definition and features of MTrP's. Gerwin et. al. said:
- Three previous studies (Nice et al., 1992; Wolfe et al., 1992; Njoo and Van der Does, 1994) have examined this problem, and none of them could establish the reliability of MTrP examination in all of its major manifestations. ... The present study shows that four examiners can achieve statistically significant agreement, at times almost perfect agreement, about the presence or absence of five major features of the MTrP and on the presence or absence of the TrP, whether it be latent or active. This establishes the MTrP as a reliable clinical sign. The present study also shows that these features are identified with greater or lesser reliability depending on the specific feature and the specific muscle being examined. ... A training period was found to be essential in order to achieve these results.Gerwin RD, Shannon S, Hong CZ, Hubbard D, Gevirtz R. Interrater reliability in myofascial trigger point examination. Pain. 1997 Jan;69(1-2):65-73.
Qualities of trigger points
Trigger points have a number of qualities. They may be classified as active/latent and also as key/satellites and primary/secondary.
An active trigger point is one that actively refers pain either locally or to another location (most trigger points refer pain elsewhere in the body along nerve pathways). A latent trigger point is one that exists, but does not yet refer pain actively, but may do so when pressure or strain is applied to the myoskeletal structure containing the trigger point.
A key trigger point is one that has a pain referral pattern along a nerve pathway that activates a latent trigger point on the pathway, or creates it. A satellite trigger point is one which is activated by a key trigger point. Successfully treating the key trigger point often will resolve the satellite and return it from being active to latent, or completing treating it too.
In contrast, a primary trigger point in many cases will biomechanically activate a secondary trigger point in another structure. Treating the primary trigger point does not treat the secondary trigger point.
Activation of trigger points may be caused by a number of factors, including acute or chronic muscle overload, activation by other trigger points (key/satellite, primary/secondary), disease, psycho-emotional disorders, homeostatic imbalances, direct trauma to the region, radiculopathy, infections and health choices such as smoking.
Trigger points can appear in many myofascial structures including muscles, tendons, ligaments, skin, joint capsule, periosteal, and scar tissue. When present in muscles there is often pain and weakness in the associated structures. These pain patterns in muscles follow specific nerve pathways and have been readily mapped to allow for identification of the causitive pain factor. Many trigger points have pain patterns that overlap, and some create reciprocal cyclic relationships that need to be treated extensively to remove them.
Diagnosis of trigger points is by examing signs, symptoms, pain patterns and manual palpation. Usually there is a taught band in muscles containing trigger points, and a hard nodule can be felt. Often a twitch response can be felt in the muscle by running your finger perpendicular to the muscle's direction; this twitch response often activates the "all or nothing" response in a muscle that causes it to contract. Pressing on an affected muscle can offer refer pain. Clusters of trigger points are not uncommon in some of the larger muscles, such as the Gluteus group (Gluteus Maximus, Gluteus Medius, Gluteus Minimus). Often there is a heat differential in the local area of a trigger point, and many practitioners can sense that.
Theories
There have been several theories about trigger points. It was once believed that trigger points were scars or inflammation in the muscle. This was disproved when biopsies showed no abnormalities. (looking for citation)
More recently it has been proposed that trigger points are spasms or contractures of voluntary muscle, possibly caused by an abnormality at the neuromuscular junction where the nerves controlling muscles connect to the muscle fibers (Travell & Simon). This theory seems unlikely because no contractions of voluntary muscle have been identified by traditional EMG and because the trigger points are often not in the location of the neuromuscular junction.
The most recent theory is that trigger points are spindles, made over-active by adrenalin stimulation. These very short muscle fibers, only about 1 cm in length, are called intrafusal muscle fibers to distinguish them from the voluntary muscle fibers which are called extrafusal muscle fibers. Only the intrafusal muscle fibers inside the spindle are activated by adrenalin via the sympathetic nervous system which also controls heart rate, blood pressure and other internal regulatory functions. The “sympathetic spindle spasm” theory of trigger points proposes that when spindles are over-activated by adrenalin they become painful. A clinical research trial is being conducted and should be completed by the end on 2006 by Dr. David Hubbard in San Diego, California. Paul Svacina, Engineer and bodyworker also in California, believes that this theory supports the idea that stress and decrease of moderate physical activity in modern lives has increased the occurence of myofascial pain and trigger points.
Current theories include:
- Travell’s Initial Trauma Theory
- Integrated Trigger Point Hypothesis
- Pain-Spasm-Pain Cycle
- Muscle Spindle Hypothesis
- Neuropathic Hypothesis
- Fibrotic Scar Tissue Hypothesis
Treatment
Treatment of trigger points may be by massage (petrissage, effleurage, tapotement), mechanical vibration, pulsed ultrasound, electrostimulation *, ischemic compression, trigger point release technique, injection of saline, CO2 or local anesthetic such as procaine hydrocloride (novocain), dry-needling without anesthetic or saline, "spray-and-stretch" using a cooling (vapocoolant) spray, and stretching techniques that invoke reciprocal inhibition within the musculoskeletal system. Use of various tools to direct pressure directly upon the trigger point often occurs, to save practitioner's hands as well as to better direct treatment. Practitioners of medical acupuncture often use trigger points as the basis for their treatment and studies have shown a considerable similarity between the locations of trigger points and classic acupuncture points.
A successful treatment protocol relies on identifying trigger points, resolving them and elongating the structures affected along their natural range of motion and length. In the case of muscles, which is where most treatment occurs, this involves stretching the muscle using combinations of passive, active, active isolated (AIS), muscle energy techniques (MET), and proprioceptive neuromuscule facilitation (PNF) stretching to be effective. Fascia surrounding muscles should also be treated to elongate and resolve strain patterns, otherwise muscles will simply be returned to positions where trigger points are likely to re-develop.
Often after treatment, clients/patients may encountered some limited pain in the area treated in the form of delayed onset muscle soreness (DOMS). This is similar to the pain some athletes get when over-exerting muscles and may last for a 1-3 days after treatment. Further pain after this period of treatment should be examined by a medical professional.
Self-treatment
There are a number of ways to self-treat trigger points and these methods are described in numerous texts. It should be noted that due to the controversy related to this field, as well as its relative newness, that no single guide should be taken as the sole or final truth. Underlying any attempts at self-treatment should be a working knowledge of the area to be treated, especially with regard to the musculature.
Footnotes
"Trigger point"