Tuesday, September 16, 2008


The purpose of this following article is introduce new concepts emerging in trigger point hypothesis and describe new resulting approaches to the treatment of TrPs. Voluntary muscle is the largest human organ system. The musculotendinous contractual unit sustains posture against gravity and actuates movement against inertia. Muscular injury can occur when soft tissues are exposed to single or recurrent episodes of biomechanical overloading. Muscular pain is often attributed to a myofascial pain disorder, a condition originally described by Drs Janet Travell and David Simons.
Within each trigger point is a hyperirritable spot, the 'taut-band', which is composed of hypercontracted extrafusal muscle fibres. Two important clinical characteristics of trigger points, referred pain and local twitch response, can be elicited by mechanical stimulation (palpation or needling).
Disease epidemiology:
Among patients seeking treatment from a variety of medical specialists, myofascial pain has been reported to vary from 30% to 93% depending on the subspecialty practice and setting.
Forty-four million Americans are estimated to have myofascial pain.
Activating factors:
Palpation of this spot within the trigger point provokes radiating, aching-type pain into localised reference zones.
Acute or chronic injury to a muscle, tendon, ligament, joint, disc or nerve.
Current hypothesis on pathogenesis:
Controversy exists between medical specialists regarding the diagnostic criteria for myofascial pain disorders and their existence as a pathological entity.
1. Recent human and animal studies have suggested that the pathogenesis of either referred pain or local twitch response is related to integration in the spinal cord. Etiology include presynaptic, synaptic, and postsynaptic mechanisms of abnormal depolarization (ie, excessive release of acetycholine [ACh], defects of acetylcholinesterase, and upregulation of nicotinic ACh-receptor activity, respectively). The pathogenesis of an MTrP appears to be related to integrative mechanisms in the spinal cord in response to sensitized nerve fibers associated with abnormal endplates.
2. EPN: Recent electrophysiological studies revealed that endplate noise (EPN) could be specifically recorded from a myofascial trigger point (MTrP) region. Endplate noise was significantly more prevalent in myofascial trigger points than in sites that were outside of a trigger point but still within the endplate zone. Endplate noise seems to be characteristic of, but is not restricted to, the region of a myofascial trigger point.
EPN has been considered as the focal graded potentials due to excessive acetylcholine release in neuromuscular junction. A recent histological study has demonstrated a free nerve ending at the vicinity of the site, from where EPN could be recorded in an MTrP region. However, the sensory (afferent) and the motor (efferent) connections between an MTrP and the spinal cord still has never been fully studied.
3. It also has been proposed that there are multiple sensitive loci in a trigger point region. A sensitive locus may contain one or more sensitized nociceptive nerve endings. Mechanical stimulation of a sensitive locus can elicit a local twitch response which is frequently associated with characteristic referred pain. Theoretically, sensitive loci can be found in any site of a skeletal muscle, but is usually distributed with highest concentration near the endplate region where a trigger point is frequently found. The trigger point is a common pathogenic pathway of muscle pain from different causes.
(1) An MTrP or an MTrS contains multiple minute loci that are closely related to nerve fibers and motor endplates. (2) Both referred pain and local twitch response (characteristics of MTrPs) are related to the spinal cord mechanism. (3) The taut band of skeletal muscle fibers (which contains an MTrP or an MTrS in the endplate zone) is probably related to excessive release of acetylcholine in abnormal endplates.
Histopathological integration of pathophysiological hypothesis of mayofascial triggerpoint:
The spinal cord connections of an MTrS are basically similar to that for a normal tissue region. The motor neurons related to MTrS tended to be smaller in their diameters.
sensitive locus & the active locus:
As already mentioned there are multiple MTrP loci in an MTrP region. An MTrP locus contains a sensory component (sensitive locus) and a motor component (active locus). A sensitive locus is the site from which pain, referred pain (ReP), and local twitch response (LTR) can be elicited by needle stimulation.
Sensitive loci are probably sensitized nociceptors based on a histological study. They are widely distributed in the whole muscle, but are concentrated in the endplate zone. An active locus is the site from which spontaneous electrical activity (SEA) can be recorded. Active loci are dysfunctional endplates since SEA is essentially the same as endplate noise (EPN) recorded from an abnormal endplate as reported by neurophysiologists.
Hence the pathogenesis of MTrPs appears to be related to the integration in the spinal cord (formation of MTrP circuits) in response to the disturbance of the nerve endings and abnormal contractile mechanism at multiple dysfunctional endplates.

Concepts on which the treatment are based:
The treatment of myofascial pain disorders requires that symptomatic trigger points and muscles are identified as primary or ancillary pain generators. This working hypothesis regarding the etiology of TrPs has changed the approach to treating TrPs. As an example, Travell and Simons abandoned the application of ischemic compression to TrPs; instead the authors adopted several techniques associated with osteopathic medicine (ie, muscle-energy, myofascial, counterstrain; high-velocity low-amplitude thrusts).
Mechanical, thermal and chemical treatments, which neurophysiologically or physically denervate the neural loop of the trigger point, can result in reduced pain and temporary resolution of muscular overcontraction. Most experts believe that appropriate treatment should be directed at the trigger point to restore normal muscle length and proper biomechanical orientation of myofascial elements, followed by treatment that includes strengthening and stretching of the affected muscle. Chronic myofascial pain is usually a product of both physical and psychosocial influences that complicate convalescence.
The treatment spectrum:
Methods usually applied to treat MTrPs include stretch, massage, thermotherapy, electrotherapy, laser therapy, MTrP injection, dry needling, and acupuncture. The mechanism of acupuncture is similar to dry needling or MTrP injection. The new technique of MTrP injection can also be used to treat neurogenic spasticity.
Scientists are now proposing and reporting the results of new approaches using capsaicin, a vanilloid-receptor agonist, and ACh antagonists (eg, dimethisoquin hydrochloride, botulinum toxin, quinidine, linalool).

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