David G. Simons

Pathophysiologic and electrophysiologic mechanisms of myofascial trigger points

OBJECTIVE To review recent clinical and basic science studies on myofascial trigger points (MTrPs) to facilitate a better understanding of the mechanism of an MTrP. DATA SOURCES English literature in the last 15 years regarding scientific investigations on MTrPs in either humans or animals. STUDY SELECTION Research works, especially electrophysiologic studies, related to the pathophysiology of MTrP. DATA SYNTHESIS (1) Studies on an animal model have found that a myofascial trigger spot (MTrS) in a taut band of rabbit skeletal muscle fibers is similar to a human MTrP in many aspects. (2) An MTrP or an MTrS contains multiple minute loci that are closely related to nerve fibers and motor endplates. (3) Both referred pain and local twitch response (characteristics of MTrPs) are related to the spinal cord mechanism. (4) 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. CONCLUSION 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.

Appearance of new receptive fields in rat dorsal horn neurons following noxious stimulation of skeletal muscle: a model for referral of muscle pain?

To test the hypothesis that painful stimuli to skeletal muscle lead to a widespread unmasking of synaptic connections in dorsal horn neurons, intramuscular injections of bradykinin (BKN) were made outside the receptive fields (RFs) of these cells in the rat. Following BKN injections, new RFs all of which were located in the deep tissues and had high mechanical thresholds appeared in 9 out of 21 (42.8%) nociceptive dorsal horn neurons which originally had a single RF in deep tissues or in the skin. The appearance of new RFs may lead to a mislocation of the source of pain if in fact the impulse activity of a nociceptive dorsal horn neuron contains information on the site of the stimulus.

Endplate potentials are common to midfiber myofacial trigger points.

Simons DG, Hong C-Z, Simons LS: Endplate potentials are common to midfiber myofacial trigger points. Am J Phys Med Rehabil 2002;81:212–222. ObjectiveTo compare the prevalence of motor endplate potentials (noise and spikes) in active central myofascial trigger points, endplate zones, and taut bands of skeletal muscle to assess the specificity of endplate potentials to myofascial trigger points. DesignThis nonrandomized, unblinded needle examination of myofascial trigger points compares the prevalence of three forms of endplate potentials at one test site and two control sites in 11 muscles of 10 subjects. The endplate zone was independently determined electrically. Active central myofascial trigger points were identified by spot tenderness in a palpable taut band of muscle, a local twitch response to snapping palpation, and the subject’s recognition of pain elicited by pressure on the tender spot. ResultsEndplate noise without spikes occurred in all 11 muscles at trigger-point sites, in four muscles at endplate zone sites outside of trigger points (P = 0.024), and did not occur in taut band sites outside of an endplate zone (P = 0.000034). ConclusionEndplate 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.

Myofascial origins of low back pain: 1. Principles of diagnosis and treatment

Myofascial trigger points (TPs) are frequently overlooked sources of acute and chronic low back pain. An active myofascial TP is suspected by its focal tenderness to palpation and by restricted stretch range of motion. The restricted lengthening of the muscle is due to the tense band of muscle fibers in which the TP is located. The presence of a TP is confirmed by a local twitch response and by reproduction of its known pattern of referred pain, which matches the distribution of the patients pain. Only an active TP causes a clinical pain complaint; a latent TP does not. The pain can be relieved by the stretch-and-spray procedure, ischemic compression, or precise injection of the TP with procaine solution. Relief is usually long lasting only if mechanical and systemic perpetuating factors are corrected.

New Views of Myofascial Trigger Points: Etiology and Diagnosis

Two studies appearing in Archives, one by Shah and colleagues and another one by Chen and colleagues, present groundbreaking findings that can reduce some of the controversy surrounding myofascial trigger points (MTPs). Both author groups recognize the ubiquity of this disease and the importance to patients of health care professionals becoming better acquainted with the cause and identification of MTPs. The integrated hypothesis is the most credible and most complete proposed etiology of MTPs. 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 MTPs. Shahs 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 MTPs. The study by Chen on the use of magnetic resonance elastography (MRE) imaging of the taut band of an MTP in an upper trapezius muscle may open a whole new chapter in the centuries-old search for a convincing demonstration of the cause of MTP symptoms. MRE is a modification of existing magnetic resonance imaging equipment, and it images stress produced by adjacent tissues with different degrees of tension. This report seems to present an MRE image of the taut band that shows the chevron signature of the increased tension of the taut band compared with surrounding tissues.

Do endplate noise and spikes arise from normal motor endplates

The concept that the endplate noise and endplate spike components of motor endplate potentials represent normal endplate potentials seems to be flawed. The morphology of the normal miniature endplate potentials described in the physiology literature is different from the morphology of the noise-like component of endplate potentials. This noise-like component is identified as normal in current electromyographic literature. There is strong experimental evidence that one source of the endplate noise component is grossly increased release (up to three orders of magnitude) of acetylcholine from the nerve terminal of that neuromuscular junction. The spikes can be accounted for by release of additional acetylcholine in response to mechanical stimulation by the electromyographic needle. Other possibilities exist.

Myofascial origins of low back pain. 3. Pelvic and lower extremity muscles.

Gluteal, pelvic, and lower extremity muscles are common sites of origin of myofascial low back pain. Trigger points (TPs) in the gluteus maximus and medius muscles refer pain locally to the gluteal and sacral regions, while those in the gluteus minimus are likely to refer pain down the lower extremity as far as the ankle on the same side. TPs in intrapelvic muscles refer pain chiefly to the pelvic region. Besides producing referred myofascial pain, TPs in the piriformis muscle can cause symptoms of entrapment of the peroneal portion or all of the sciatic nerve. TPs in the soleus muscle may refer pain to the sacroiliac joint.

New Aspects of Myofascial Trigger Points: Etiological and Clinical

SUMMARY Objectives: To identify important new developments in our understanding of the nature and clinical characteristics of myofascial trigger points [TrPs]. Findings: Recent research studies reinforce the credibility of three key features of an integrated hypothesis that is designed to explain the pathophysiology of TrPs: increased acetylcholine effect, increased muscle-fiber tension, and local release of sensitizing substances. Electromyographic studies of TrPs support an increased acetylcholine effect that produces endplate noise. Nine histological studies of animal and human subjects identify features that indicate abnormally increased muscle-fiber tension and help to account for the taut bands observed clinically. Microdialysis studies by Jay Shah, MD and colleagues at the National Institutes of Health compared, in nine subjects, the findings in active TrPs to findings in latent TrPs and in normal muscles [nine examinations]. They found a significantly reduced pressure pain threshold and pH at the three active TrPs. In active TrPs, seven pain-related substances were significantly increased: substance P, calcitonin gene-related peptide, bradykinin, serotonin, norepinephrine, tumor necrosis factor, and interleukin-1β. Using shockwave generators, Wolfgang Bauermeister, MD located active TrPs in the gluteus medius and/or gluteus minimus muscles in all of 114 patients with sciatica. In another study, treatment of idiopathic low back pain with piezoelectric generated shockwaves resulted in 80 percent reduction of pain in 15 of 20 patients after 10 treatments. Treatment with electrohydraulic shockwaves reduced the pain 85 percent in 18 of 20 patients after six treatments. Conclusions: The microdialysis findings in TrPs help to validate the integrated hypothesis and to explain the painfulness of TrPs. Either an electrohydraulic or piezoelectric shockwave device can be used to locate and treat TrPs. Clinically, the electrohydraulic method seems preferable.

Myofascial origins of low back pain. 2. Torso muscles.

Trigger points (TPs) in muscles of the lower torso associated with the spine are an important cause of low back pain. The quadratus lumborum is the muscle most commonly involved, but TPs located there are often overlooked because of inadequate physical examination techniques. TPs in the lower rectus abdominis refer pain horizontally across the low back, and those in the iliopsoas refer pain in a vertical pattern, parallel to the lumbosacral spine. The pain pattern of TPs in the serratus posterior inferior is noted in the region of the muscle itself.

Myofascial Pain Syndromes-Trigger Points

Four articles this quarter present major progress in new experimental data. Hou et al. demonstrated in rabbits that motor endplate potentials [spontaneous electrical activity] of trigger spots are partially dependent on increased calcium channel permeability. Delaney et al. report an elegant way to measure the effect of myofascial trigger point [TrP] massage on autonomic nervous system activity. This opens a new research window through which to explore the close relation between TrP activity and autonomic nervous system activity. Esenyel et al. present a randomized, controlled, unblinded comparison of the results of ultrasound application and injection of TrPs and found that both were equally and significantly effective. This is one of the very few scientific papers that address the effectiveness of treating TrPs with ultrasound. Pongratz reported a noteworthy histological study specifically of TrPs. In addition, the efficacy of needling TrPs is becoming firmly established, and one review article presents in detail the importance of considering TrPs in patients with symptoms of radiculopathy.