Extracorporeal Shock Wave Therapy: Applications in Tendon-related Injuries
Most pain clinicians will agree that there is a certain class of musculoskeletal (MSK) disorders that have historically been very challenging to treat and too often result in patients being labeled as non-genuine in their representation of the problem. A seemingly simple diagnosis—such as tendonitis, bursitis, fasciitis, or epicondylitis—can become chronic without warning, eventually leading to disability and significant lost time from work.
This is part two of a three-part series: read part one.
This is particularly relevant in the field of occupational medicine or work-related injuries, where both indemnity payments and medical bills for diagnosis and treatments add cost to the care scenario. The ultimate goal of return to work is difficult when clinicians are confronted with a recalcitrant condition that demonstrates resistance to our best medical, surgical, and rehabilitation efforts.
Although we have no way of predicting which cases will go on to become chronic, biological evidence is mounting that what starts as an uncomplicated tendon strain, can steadily morph into a much more complex disorder (tendinosis) with time.1 These difficult MSK cases often reveal that the tendon-bone attachment or enthesis is the focal point of pathological changes.
A Growing Problem
Tendon injuries are ubiquitous in our industrialized society. This is partly due to the repetitive nature of many jobs, and partly to a lack of individual fitness, which encompasses a number of factors including gradual age-related deconditioning. It can be argued that as individuals we need to take better care of our human frames including ongoing maintenance in the form of stress, nutrition, and exercise management versus the “fix it only when it breaks” mentality, which arguably defines much of our current tertiary approach to care.
Whether one agrees with this assessment or not, we should still recognize that primary prevention is predicted to be an important policy pillar of our healthcare system in the United States today. When resources are finite, society must find a way to effectively treat patients without as much reliance on expensive pharmacotherapies, invasive procedures (injections), surgeries, postsurgical rehabilitation, etc. It is clear that patients will play a greater role in determining their ultimate health status. Physicians will need to engage patients with alternative strategies for improving health and fitness including guiding, supporting, and directing patients to make better lifestyle choices in nutrition, activity, stress, leisure, and medication management.2 One of the results might be a society with less dependence on medication and medical tests/procedures and greater affinity for regular exercise and improved nutrition status.
The situation is obviously much more complicated than that, but these might be a few of the changes we notice in the next few years as we divert resources to focus on prevention. We are on the cusp of a medical revolution of sorts, with the advent of regenerative medicine becoming the new model for healing and standard for medical care. It is within the context of this powerful new paradigm that we present part two of this three-part series focusing on myotripsy, or shockwave therapy. At the very core of regenerative medicine is signal transduction occurring at the cellular level, also known as mechanotransduction.3
Cellular Signaling in Mechanical Transduction
Cellular intelligence is an evolutionary process and there is evidence to suggest that our cells have evolved through genetic pressure or the preferential selection of advantageous genetic mutations. Cells with a greater ability to produce, recognize, interpret and respond to signals in the environment would be better prepared to survive. The “signaling” aspect in cellular communication is thought to be both a function of chemical messengers or molecules combined with an underlying electro-magnetic energy acting as the driving force to the system.4 Chemical molecules are made available by one cell and specifically combine with receptor mechanisms on another cell’s surface, and so the transduction process begins.
This relatively new conceptual framework in molecular biology research has medical scientists excited because of the enormous implications behind it. Many of the leading diseases that public health professionals are most concerned with today are the result of a breakdown in any one of these three steps:
- Cell signaling, or the release of an organic or inorganic chemical molecule (protein, peptide, gas, amino acid, nucleotide, or steroid)
- Signal recognition, usually occurring at the receiving cell surface via specific receptor binding
- Internal signaling, where molecules convert the original signal into internal behavior5
This is a very simplified multi-step summary of signal transduction. This background information will become an important segue into how myotripsy, or extracorporeal shock wave therapy (ESWT), can effectively interact with damaged tissue.
The extracellular matrix (ECM) forms the fundamental environment through which all cellular activity can take place since it is the conduit from extra- to intracellular activities. Every cell in the body is immersed in and surrounded by an ECM component that allows cell-to-cell communication along with other vital cell functions such as transport, metabolism, and drug interactions. Figure 1 depicts the ECM of the subdermal region, while Figure 2 depicts the ECM of muscle fibers. The ECM is really the basis for the fascial network that surrounds all cells of the body and provides an inter-connectedness that goes well beyond that described by conventional anatomy books. We now know that functional anatomy has so much more relevance in clinical practice and can provide, not only better insights into disease pathophysiology, but also hints at how to prevent and/or rehabilitate it.
Tendon/Ligament Attachment Sites
Insertional irritations are difficult to treat at best, and can be an exercise in frustration for both patient and practitioner at worst. These osteotendinous and/or osteoligamentous junctures represent a morphologically unique area in the anatomy of soft/bony tissue. This interface between soft tissue and bone can be divided into two primary types—fibrous (F) and fibrocartilaginous (FC)— according to the type of tissue present at the attachment site. The FC enthesis, or attachment site, does not have a periosteum and is referred to as a direct attachment.6 In either case, there is a postulated enthesis organ whose function at or near the enthesis serves a common function of stress dissipation. We will not provide a detailed analysis of the enthesis organ but suffice it to say that this structure is of particular importance to clinicians because it helps explain the patterns of injury and the diffuse nature of symptoms.7