The trigger point model states that unexplained pain frequently radiates from these points of local tenderness to broader areas, sometimes distant from the trigger point itself. Practitioners claim to have identified reliable referred pain patterns, allowing practitioners to associate pain in one location with trigger points elsewhere. Many chiropractors and massage therapists find the model useful in practice, but the medical community at large has not embraced trigger point therapy. Although trigger points do appear to be an observable phenomenon with defined properties, there is a lack of a consistent methodology for diagnosing trigger points and a dearth of theory explaining how trigger points arise and why they produce specific referred pain patterns.
The term "trigger point" was coined in 1942 by Dr. Janet Travell to describe a clinical finding with the following characteristics:
One criticism of the trigger point concept is that practitioners do not necessarily agree on what constitutes a trigger point.
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:
A 2007 review of diagnostic criteria used in studies of trigger points concluded that
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. Latent trigger points can influence muscle activation patterns, which can result in poorer muscle coordination and balance.
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 completely 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, psychological distress (via systemic inflammation), 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 causative 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.
In the study by Shah and associates, they have shown the feasibility of continuous, in vivo recovery of small molecules from soft tissue without harmful effects. With this technique, they have been able to investigate the biochemical milieu of muscle in subjects with active, latent, or absent myofascial trigger points (MTrPs) and to contrast this with that of the noninvolved muscle.
Treatment of trigger points may be by manual, Myofascial Trigger Point Therapy by a trained Myofascial Trigger Point Therapist , Myotherapy (deep pressure as in Bonnie Prudden's approach, massage or tapotement as in Dr. Griner's approach), mechanical vibration, pulsed ultrasound, electrostimulation, ischemic compression, injection (see below), dry-needling, "spray-and-stretch" using a cooling (vapocoolant) spray, and stretching techniques that invoke reciprocal inhibition within the musculoskeletal system. Use of elbows, feet or various tools to direct pressure directly upon the trigger point often occurs, to save practitioner's hands.
A successful treatment protocol relies on identifying trigger points, resolving them and, if all trigger points have been deactivated, 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 neuromuscular facilitation (PNF) stretching to be effective. Fascia surrounding muscles should also be treated, possibly with myofascial release, to elongate and resolve strain patterns, otherwise muscles will simply be returned to positions where trigger points are likely to re-develop.
The results of manual therapy are related to the skill level of the therapist. If trigger points are pressed too short a time, they may activate or remain active; if pressed too long or hard, they may be irritated or the muscle may be bruised, resulting in pain in the area treated. This bruising may last for a 1-3 days after treatment, and may feel like, but is not similar to, delayed onset muscle soreness (DOMS), the pain felt days after overexerting muscles. Pain is also common after a massage if the practitioner uses pressure on unnoticed latent or active trigger points, or is not skilled in myofascial trigger point therapy. Lack of reduction of pain after one to three treatment sessions by a trigger point practitioner should be referred to a medical professional. Evidence based medicine researchers have concluded evidence for the usefulness of trigger points in the diagnosis of fibromyalgia is thin. Fibromyalgia patients generally have multiple, reoccurring trigger points, typically in a quadrant or more of the body.
Despite the concerns about long acting agents, a mixture of lidocaine and marcaine is often used. A mixture of 1 part 2% lidocaine with 3 parts 0.5% Marcaine provides 0.5% lidocaine and 0.375% Marcaine. This has the advantages of immediate anesthesia with lidocaine during injection to minimize injection pain while providing a longer duration of action with a lowered concentration of Marcaine.
Sarapin can be used for trigger point injection.
Trigger points in the male or female pelvis, such as found in chronic pelvic pain syndrome (CPPS), should be treated by physicians trained in the use of intra-rectal trigger point and myofascial release techniques.
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 & Simons). 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 proposed mechanism is that trigger points are muscle 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 occurrence of myofascial pain and trigger points.
Another idea for a trigger point mechanism is that 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 themselves may develop trigger points in a compensatory fashion.
Current hypotheses include:
A 2008 review in Arch Phys Med Rehabil. of two recent studies, concludes they present groundbreaking findings that can reduce some of the controversy surrounding myofascial trigger points (MTrPs). The integrated hypothesis is the most credible and most complete proposed etiology of MTrPs. However, the feedback loop suggested in this hypothesis has a few weak links, and studies by Shah and colleagues in particular supply a solid link for one of them. The feedback loop connects the hypothesized energy crisis with the milieu changes responsible for noxious stimulation of local nociceptors that causes the local and referred pain of MTrPs. Shah's reports quantify the presence of not just 1 noxious stimulant but 11 of them with outstanding concentrations of immune system histochemicals. The results also strongly place a solid histochemical base under the important clinical distinction between active and latent MTrPs. Subjects with active MTrPs in the muscle have a biochemical milieu of selected inflammatory mediators, neuropeptides, cytokines, and catecholamines different from subjects with latent or absent MTrPs.
Today, much treatment of trigger points and their pain complexes are handled by myofascial trigger point therapists, massage therapists, physical therapists, osteopaths, occupational therapists, myotherapists, some naturopaths, chiropractors, dentists and acupuncturists], and other hands-on somatic practitioners who have had experience or training in the field of neuromuscular therapy (NMT).
The trigger point concept remains unknown to most doctors and is not generally taught in medical school curricula. Among physicians, typically only physiatrists (physicians specializing in physical medicine and rehabilitation) are well versed in trigger point diagnosis and therapy. Other health professionals, such as myofascial trigger point therapists, physiotherapists, naturopaths, chiropractors, dentists, massage therapists and structural integrators and some veterinarians are generally more aware of these ideas and many of them make use of trigger points in their clinical work.
Travell and Simon's seminal work on the subject, Myofascial Pain and Dysfunction: The Trigger Point Manual, states the following: