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11 Articles in Volume 10, Issue #8
A Neuro-geometric Basis for Pain Management
Brain Reorganization with Severe Pain: New Understanding and Challenges
Chronic Migraine: An Interactive Case History, Part 2
Diagnosing and Managing Chronic Ankle Instability
High Potency Ultrasound for the Treatment of Connective Tissue Disorders
Intranasal Naloxone for At-home Opioid Rescue
Misuse of ‘Hyperalgesia’ to Limit Care
Neurological Effects of Therapeutic Laser
Preventive Medications For Headache
Psychological Wounds of Trauma and Motor Vehicle Accidents
Treat the Pain... Save a Heart

High Potency Ultrasound for the Treatment of Connective Tissue Disorders

The clinical value of ESWT appears to be growing with an increasing number of practitioners turning to this technology for the treatment of typically unresponsive conditions.
Editor's Note: An electric current can be turned into electro-magnetic energy by passing the current through a crystal or other transformer. The energy is transmitted in waves, and the waves can be of various lengths. Accumulating clinical evidence indicates that the various energy waves preferentially treat different conditions. Four energy waves are now being used in clinical pain practice: (1) radio, (2) ultrasound, (3) infrared, and (4) laser. Practical Pain Management firmly believes that all pain practitioners should investigate these four therapeutic energy waves and determine which best fits their practice. Practical Pain Management will publish, without preferential bias, articles on the clinical experience of these four energy waves. We encourage all readers to give us their experience.

Extracorporeal shockwave therapy (ESWT) is a form of ultrasound energy waves that was first introduced in the United States in 2000. It was called “extracorporeal,” since it was administered outside the body. “Shockwave” referred to the high potency energy wave that produces a number of therapeutic benefits. Over the years since introduction of this high energy device, many practitioners consider ESWT to be the premier treatment for chronic tendon and ligament disorders often referred to as enthesopathic conditions. These conditions have challenged clinicians over the years and no universal “best” therapy has emerged from the various interventions available.

Mechanical Properties of Ultrasound

Figure 1. Treating plantar fasciitis with shockwave therapy.

Ultrasound waves, which are the basis for ESWT, have found numerous therapeutic medical applications over the years including kidney stone ablation (litho-tripsy), bone growth stimulation, as a sclerosing and anti-inflammatory agent in physical therapy and, most recently, as a treatment for recalcitrant enthesopathies including plantar fasciitis (see Figure 1), achilles tendonopathy and chronic epicondylitis (see Figure 2). Conventional ultrasound physical therapy consists of applying high frequency sound waves (acoustic radiation) to a target area for the reduction of pain and inflammation. There is a certain amount of heat generated (thermal effects) as ultrasonic waves collide with tissue interfaces of varying densities. The practitioner can adjust the frequency of the sound waves emitted from the transducer, or sound head, to target superficial or deeper structures with higher and lower frequency adjustments, respectively. There is a piezoelectric crystal that vibrates within the casing of a transducer or sound head causing a conversion from electrical to mechanical energy. The ultrasound waves usually require a couplant gel that acts as an energy transfer medium from the sound head to the target tissue.

 

Figure 2. Treating chronic epicondylitis with shockwave therapy.

In physiotherapeutic applications, the “piezoelectric effect” caused by the crystal creates a “micro-massaging effect” in the tissue that can facilitate fluid re-absorption in inflamed areas and help to physically break down tissue in arthrofibrosis or cheloid scarring. Ultrasound is primarily a mechanical wave and secondarily a form of thermal energy. Heat is a byproduct of sound wave interaction with tissues of varying densities and not inherent in the wave itself.

ESWT is different than conventional ultrasound in that it is delivered as a more focused and intense beam of energy usually to a small area considered the focal point of the problem. ESWT is a shock wave or high-pressure acoustic wave with very high amplitude, rapid rise time, and short pulse duration. In the early days of this technology, patients were anesthetized prior to having high energy ESWT performed on them. Today these treatments are performed by a number of different practitioners with no anesthesia. In fact, localized pain during the treatment can act as a guide to where the most effective irradiation should occur. Often, the more pain elicited during the treatment may mean better post treatment outcomes.

Mechanism of Action

A precise mechanism of action with respect to ESWT has not been identified with certainty but a couple of competing hypothesis have been put forth. One theory suggests that chronic pain is simply a function of the central nervous system “forgetting” that there is a physiological problem somewhere in the body and so healing efforts are no longer directed to that area—hence, persistent pain and symptoms. It is difficult to reconcile this notion with a condition such as phantom limb pain where the body part in question has been removed yet symptoms persist.

There is some evidence to suggest that pre-amputation anesthesia to abolish pain well in advance of the surgery can abate and/or minimize the chance of developing phantom limb disorder. This would support the idea that there is a hardwiring element to pain and that both central and peripheral mechanisms need to be considered. Proponents of this theory might consider that ESWT works by reminding the brain that there continues to be a problem and thereby reactivating the healing mechanism of the body. There is little evidence that ESWT works in this manner, in fact, the scientific literature supports the likelihood of a true “mechanical effect” as being the most obvious and measurable tissue response.

In vivo studies done in rabbits supports the second and more plausible explanation for positive effects, namely that of neo-vascularization or increased local blood supply along with concomitant tissue regeneration, as the primary mechanism by which tendon-bone junction enthesopathies actually heal.1 A recent European study examined the use of shock wave therapy to stimulate hypertrophic long bone non-unions and concluded that not only is ESWT as effective as surgery in stimulating union of long bones but that it has better short-term outcomes than surgery.2 Another similar study published a short time later supports this same premise when applied to non-union fractures of the metaphyseal-diaphyseal region of the fifth metatarsal. The investigators found that screw fixation has more associated complications and these often lead to additional surgeries and further complications. These authors conclude that ESWT is the preferred method of treatment for non-union fractures of the fifth metatarsal bone.3

“ESWT is currently being used primarily in chronic cases of tendonopathy such as plantar fasciitis and lateral epicondylitis where suspected changes in tissue morphology—via injury or disease—have occurred.”

Tendinopathy

The pathophysiology of tendinopathy is not fully understood but there is strong evidence to suggest that both tissue hypoxia and apoptosis are involved in the process.4 Immunohistological techniques have identified certain proteins associated with both hypoxia and apoptosis and there appears to be a spectrum of pathology (mild to severe) that has protein specific correlation. This means that the greater the tendon breakdown, the greater the concentration of these proteins. Other studies support this inflammation-degeneration cascade in the pathogenesis of tendonopathy but also make a distinction between gliding and non-gliding tendons. Gliding tendons, such as the posterior tibialis tendon (PTT), change direction by turning around a bony protrusion. In this region, it is postulated that the tendon is subjected to intermittent compressive and shear forces and that the area of extracellular matrix that consists of avascular fibrocartilage is the most vulnerable. This avascularity is considered to a prime factor in tendon disease.5 Repetitive micro-trauma such as in the case of overuse can test the limited repair capability that is inherent in avascular tissue such as that found in the extracellular matrix of gliding tendons. The role of vascularity in tendonopathy is a complex one, with both an increase and decrease of vascularity being involved in the pathogenesis of degenerative tendon disease. Several factors have been identified to upregulate the very important angiogenic factor called vascular endothelial growth factor (VEGF). These factors include hypoxia, inflammatory cytokines and mechanical load.

In cases where neo-vascularization might be beneficial, the use of ESWT could have advantages over more traditional and/or invasive treatments and therapies. In one study performed by Rompe et al,6 the investigators compared corticosteroid injections to the greater trochanter of the hip with shockwave therapy in the treatment of greater trochanteric pain syndrome. The authors concluded that corticosteroid injection was significantly less successful than was either home training or shockwave therapy in the treatment of hip pain.

Shockwave Therapy in the Clinic

ESWT is currently being used primarily in chronic cases of tendonopathy such as plantar fasciitis and lateral epicondylitis where suspected changes in tissue morphology—via injury or disease—have occurred. The region of attachment between tendon and bone (enthuses) has long been recognized as potentially vulnerable to stress-strain forces due to the inherently avascular nature of the region. It is generally accepted that with limited circulation comes a limited ability to heal after trauma. With enthesopathy, pain develops in the free nerve endings of the entheses (enthesalgia) with concomitant inflammation that may not be cleared effectively. This may then lead to consolidation and calcification that is often verified with diagnostic ultrasonography. Enthesopathy is associated with inflammatory diseases and the risk is highest in those persons having rheumatoid inflammatory conditions or spondyloarthro-pathies and arthritides in general.

It is also associated with direct or indirect trauma to the tendon, ligament or joint capsule and represents a time-dependent process—manifesting as enthesopathy in later stages. It stands to reason that sound waves might be an ideal medium to address both the calcification and poor vascularity issues that characterize this condition. It is plausible that ESWT can have the effect of breaking up calcific areas in a specific location—after all, lithotripsy does just that with calcified gall and kidney stones. We also know from physiotherapy-related research that therapeutic doses of ultrasound can have a thermal effect that causes an improved perfusion capacity in a defined area.

Both these two effects form the basis of the primary mechanism of action ascribed to ESWT by practitioners who use this technology today. ESWT has also found a place in veterinary medicine with this modality being used with greater frequency in equine disorders similar to those described in our human patients. The condition of proximal suspensory desmitis—a condition that can cause lameness in horses and disrupt lucrative racing careers—is often treated using shockwave therapy. Veterinarians cite the many advantages of this conservative modality over the disadvantages of the surgical alternatives as driving factors in the use of ESWT for equine problems.

Summary

Despite a growing anecdotal tidal wave of empirical data (over 1,600 citations) that investigates the use of ESWT in chronic, recalcitrant enthesopathic conditions—in both clinical and equine patients—the research and academic communities remain skeptical of ESWT and steadfast in their belief that research does not yet validate the cost-effectiveness of this modality. The Cochrane collaboration concludes that it finds little to no benefit in improving pain or function in lateral epicondylitis.

Despite the seemingly thumbs down verdict by some of the research and insurance companies, the clinical value of ESWT appears to be growing with an increasing number of practitioners turning to this technology for the treatment of typically unresponsive conditions. This is not the only therapy that demonstrates the chasm that often exists between the clinical and research communities. As the number of shockwave manufacturers grows and actual working units increase, there is expected to be a corresponding increase in available scientific evidence and our collective clinical experience so that the question of efficacy can be answered more definitively through comparative effectiveness research.

Last updated on: April 28, 2016
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