Extracorporeal Shock Wave Therapy—Application for Trigger Points
Most clinicians who practice pain management are familiar with the contributions of Drs. David Simons and Janet Travell, who are credited with pioneering the importance of trigger points (TPs) in many of the pathologies we see in the clinic.1 The emergence of TPs as both a primary and secondary form of muscle pathology has been a gradual one, culminating in today’s more complete understanding.
In preparation for this report I reviewed or, more accurately, scoured the literature for a complete historical perspective on TPs. Surprisingly, the early descriptions of TPs do not look much different than today’s versions. From a descriptive sense, TPs have been characterized rather well right from the start. What has changed over time is our understanding of the importance that TPs play in myriad conditions affecting the muscles, joints, and skeleton.
Over the last 50 years, we also have evolved more interventions to treat TPs. The problem has been that none of the interventions have enough convincing data to support widespread use. What is also surprising is that not until the 21st century were TPs actually imaged, which, logically, should then lead to a better and more lucid understanding of how to treat this entity.1 Figure 1 illustrates the concept of the TP whereby “X” indicates the location (foci) of a TP followed by the pain radiation pattern (red) that a patient describes as symptomatic.
In fact, the ultrasonic image of a TP might surprise many readers. The search for truth is a process of acquiring, validating, and discarding (when necessary) information and in the process, challenging our assumptions so we end up giving shape to a conceptual schema that is meaningful in our clinical endeavors.
For a myofascial condition that has been identified for many years, for which we have so many apparently valid treatments, and about which we also have such a complete understanding, why is it we are still debating TPs? The topic should have been relegated to old news a long time ago. Unlike infectious diseases, TPs don’t respond to vaccines, inoculation, medications, or surgery. Yet TPs are ubiquitous in North American society and occur at a much higher frequency than any old or newly emerging infectious disease. They have indeed become the focal point in many discussions surrounding musculoskeletal pathology so any treatment that demonstrates an efficacy for resolving TPs in muscle is a welcome addition to the pain practitioner’s arsenal.
Overview of TPs
In preparing this report, I gathered a fairly large amount of data—at least more than the usual amount of reports/citations. The availability of information on this subject is really quite abundant with scientific validation studies continuing to increase and far surpassing those unequivocal reports based solely on observation and opinion. The reason for the extra volume of data is that this is a report that should focus on the efficacy of a new technology (shock wave therapy); however, since it is described within the treatment context of myofascial pain, whose hallmark features are of that highly controversial entity known as the TP, we should first validate the target condition.
The existence of TPs has now been confirmed by a large and growing body of funded (including by the National Institutes of Health) research. We can now see TPs using ultrasonography; we can now measure their electrical activity and stiffness using electromyography (EMG) and acoustic elastography, respectively; we can palpate them, provoke, measure their size, and assess their tenderness (algometry); assay their biochemical environment (in vitro studies); and treat them with various interventions and watch them change shape and disappear.
Early Myofascial Work
The first edition of Travell and Simons appeared circa 1983, and was the first organized attempt to provide a detailed accounting of what TPs were and how TPs behaved, which illuminated, to some degree, how best to locate them.2 This was one of the few examples where much of the discovery work was performed, and data collected, many years before the actual publication. The authors, Janet Travell, MD, (White House physician to Presidents Kennedy and Johnson) and David Simons, MD, (National Aeronautics and Space Administration flight surgeon) described TPs in two forms: latent and active, with characteristics linked to each form. The preferred form of treatment, as recommended by these pioneers, was injection therapy and/or spray and stretch techniques using a vapo-coolant such as fluoromethane. Along the way, other forms of treatment—such as ischemic compression—became popular but eventually fell out of favor with both Travell and Simons. They preferred, instead—at least later on—to advocate for less intense digital pressure in their manual approach.2
There was much work by both Travell and Simons prior to the publication of the first manual, but they were not the only group to be studying myofascial pain. In 1957, the prolific pain physician John Bonica, MD, published a report in the Journal of the American Medical Association and made references to the existence of hypersensitive regions (referring to pain syndromes) called the “trigger area” and recognized that this area formed as part of muscle and connective tissue.3 Dr. Bonica goes on to make reference to an anatomical mapping of these trigger areas, quite possibly a similar conceptualization of pain referral zones mapped out by Travell and Simons. In his description, he also makes references to a vicious cycle that becomes self-sustaining (pain-spasm-pain) and has both a motor and sensory component.
Although the focal point of his paper is about two forms of local anesthesia as the primary intervention for treatment of trigger area pain, he does acknowledge physical therapy, specifically corrective and restorative exercises, along with psychotherapy, as being beneficial in these types of conditions. Presumably, Bonica realized early on that there was a connection between psychic stress and somatic dysfunction, thereby including psychotherapy as a treatment recommendation.