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16 Articles in Volume 19, Issue #2
Analgesics of the Future: Inside the Potential of Glial Cell Modulators
APPs as Leaders in Pain Management
Cases in Urine Drug Monitoring Interpretation: How to Stay in Control (Part 1)
Complex Chronic Pain Disorders
Efficacy of Chiropractic Care for Back Pain: A Clinical Summary
Hydrodissection for the Treatment of Abdominal Pain Caused by Post-Operative Adhesions
Letters: The Word "Catastrophizing;" AIPM Ceases Operations; Patient Questions
Management of Severe Radiculopathy in a Pregnant Patient
Managing Pain in Adults with Intellectual Disabilities
Pain in the Courtroom: An Excerpt
Q&A with Howard L. Fields: How Patients’ Expectations May Control Pain
Special Report: CGRP Monoclonal Antibodies for Chronic Migraine
The Management of Chronic Overlapping Pain Conditions
Vibration for Chronic Pain
What are the dangers of loperamide abuse?
When Patient Education Fails to Improve Outcomes: A Low Back Pain Case

Vibration for Chronic Pain

The benefits of mechanical stimulation in managing chronic conditions: from a history of whole body stimulation to today's focal techniques.
Pages 60-63; 67

Vibration, or the transmission of oscillatory mechanical stimulation, may be accomplished with auditory or ultrasonic waves, pulsed electromagnetic fields, electrical stimulation, shockwaves, or mechanical devices with motor-driven shaking platforms or eccentric flywheels. Perhaps because of an association between “good vibrations” and 1960s pop-psychology, there is an inverse relationship between an oscillatory mechanical therapy’s reimbursement and the therapy containing the actual “V” word. As research on whole body vibration (WBV) literature, and more recently focal vibration (FV) expands, the evidence supports each modality for a variety of chronic pain conditions, as reviewed herein.

History

Perhaps the first patients intentionally treated with vibration were those of neurologist Jean-Martin Charcot. After associating clinical improvement of his patients with Parkinson’s disease and prolonged train rides, he described in 1892 the creation of a similarly shaking chair – and similar clinical improvement.1 Although his student Georges Gilles de la Tourette created (and published) data on a vibrating helm for migraine, little else was done with therapeutic vibration for half a century. In 1949, Whedon created an oscillating bed with physiologic and metabolic improvement of patients with whole body casts.2

The association between vibration and pain relief developed in conjunction with an understanding of sensation itself. Pain transmission travels peripherally on fast ADelta fibers, joining in the substantia gelitinosa of the dorsal column with ABeta nerves transmitting mechanical information, and C-fibers transmitting cold and pressure information. Summary information is passed via interneurons to spinal fibers to the brain, with an interplay such that stronger signals in arriving to the dorsal horn inhibit weaker ones. After Melzack and Wall3 postulated that mechanical ABeta stimulation could reduce pain and physiologists tested WBV on animals for osteogenesis, full body plates to treat humans arrived. By the early 2000s, manufacturing was capable of small intense motors that could provide high-frequency vibration focally, and research on both WBV and FV have since grown exponentially.

An understanding of the mechanics and physiology may help to frame the sometimes contradictory literature, helping to predict when a patient may benefit from vibration. An understanding of vibration’s impact on mechanoreceptors, and the role of tension and intrinsic vibration frequency on anabolic cell behavior, help to illuminate vibration’s role in pain management.

(Source: Medical Technologies Limited UK)

Physiology

Of the four principal mechanoreceptors innervated by ABeta fibers, two likely account for most of the “gate control” pain-reducing effects. Fast-adapting, light-touch Meissner corpuscles detect frequencies between 20 and 40 Hz, while fast-reacting and long-acting deep Pacinian corpuscles begin sensing vibration at 65 Hz, with maximal sensitivity at 250 Hz.4 While WBV-induced longitudinal stretching of ABeta Ruffini bulbous corpuscles may cause additional “gate control” pain relief, it is more likely that the Ia and II afferents on the muscle spindles themselves centrally mediate pain relief with larger amplitude vibration. As both Ia afferents and ABeta afferents share the anatomical path to the substantia, a shared physiology of pain inhibition is posited.

A secondary benefit for patients with pain may emerge from mechanoreceptor’s role in balance. In the foot, for example, 70% of the mechanoreceptors are fast-adapting Meissner and Pacinian cells, but with three times the receptive fields of the hands. When these cells are anesthetized, balance is significantly reduced. Interestingly, the activation thresholds in the sole are also much higher; in other words, patients may not need to perceive the vibration to stimulate receptors and improve balance. Subthreshold vibration training and using vibration to amplify signal in the soles has been used to improve balance in patients with neuropathies, suggesting a modality of pain improvement through improved balance and kinesthetic awareness.5

All substances vibrate at an internal resonant frequency. Strike a string, steel beam, or taut band, and the frequency of vibration is intrinsic to the material, tension, and any surrounding compression lending integrity to the structure. This “tension integrity” in the body is provided by connective tissues. Vibration transmitted to skin stimulates mechanoreceptors and can descend to muscles. By transmission to limbs through weight bearing, vibration passes through bones, tendons, muscles, and the cells that make them up. Mechanical forces themselves can deform cells to open sodium channels, allowing ions to enter and leading to action potentials; integrins on cells recognize and respond to mechanical stressors.

Growth Stimulation & Balance Stabilization

Below a mechanical strain threshold, muscles atrophy and bone is resorbed. On a cellular level, stressors that exceed the minimum strain threshold prompt growth. Single whole body vibration sessions may increase overall oxygen uptake in tissues, thereby increasing microcirculation and blood flow. Over time, WBV works to decrease osteoclast activity, change gene expression of growth factors, and increase growth hormone expression.6 As a more macro example, orthopedists do not typically immobilize humerus fractures because the microtensions from active shoulder muscles remodel bone faster than casting. Vibration acts as a mechanical signal that exceeds the threshold strain level, increasing cellular anabolic (growth) activity.

In everyday life, cells and tissues undergo growth and remodeling with mechanical vibratory forces.7 Walking, for example, generates vibratory waves with a frequency between 10 to 20 Hz.8 When vibration exceeds the threshold for a growth response, typically due to higher amplitudes or excessive duration, the inability of tissues to respond with growth can cause damage. Rather than the increased microcirculation seen with low amplitudes of 0.3 g, the amplitudes of 1 to 2 N vasoconstrict.

Whole body vibration plates are mechanically limited to frequencies between 10 and 60 Hz and displacements of < 1 mm to 10 mm.7 When standing or sitting on vibrating plates, patients may experience passive stimulation that works to improve balance and tone,9 potentially reducing pain from future minor injuries. When weight bearing, the vibration may help to directly speed remodeling of chronic or damaged tissues, reducing pain over time.10 Lower frequencies may reduce pain through gate control inhibition of Ruffini corpuscles. With this physiologic basis, it is possible for a clinician to predict when vibration will be effective, and when it is less likely to be so.

WBV for the Management of Chronic Pain

Osteoarthritis

WBV in conjunction with squats or exercise has been shown to improve pain, strength, and functioning compared to static whole body vibration, with an improved effect based on frequency. One study found significantly greater pain reduction at 3 and 4 months in 22 women with knee osteoarthritis (OA) who performed an 8-week combined exercise/WBV regimen compared to 22 women who exercised alone. Both groups had significant improvements in functioning and strength.11 For knee OA, in particular, a meta-analysis by Zafar, et al,12 noted improved pain and function, but inconsistent improvement in muscle mass. Follow-up studies in this field typically find continued pain relief benefit up to 6 months following interventions of 3 months with 2 to 5 sessions per week. These benefits likely are conferred from improved strength and balance, though a decrease in central sensitization is possible. Shorter trials have shown functional improvement, but pain relief does not always achieve statistical significance.13

Low Back Pain

A large body of literature details damage from prolonged excessive exposure to vibration in workers using power tools or driving large vibrating equipment. For example, daily exposure to 1.6 m/s2 of hand-held force or greater resulted in hand-arm vibration syndrome in 39% of metal workers (the force of focal vibration devices is 0.01 0.03 m/s2).14 Therapeutic forces of WBV approach or exceed the workplace exposure limits of 1.15 m/s2 , according to the International Organization for Standardization, but as WBV risk is calculated by cumulative daily 8-hour exposure over the course of years, short course WBV does not approach cumulative doses by orders of magnitude. On the contrary, for those who sit for office work, 30-minute sessions of WBV have demonstrated promise. Three months of 2.5 sessions per week improved pain and disability, and reduced sick leave for a cohort of 40-plus “seated working office employees” (68.3% female; mean age 45.5 ± 9.1 years; mean BMI 26.6 ± 5.2).15 (Editor’s Note: See also, Newhart, et al, in the January/February 2019 issue of PPM for an explanation of the controversial literature regarding vibration and low back pain.)

Rheumatic Conditions: Fibromyalgia and Rheumatoid Arthritis

Unlike pain conditions that result from chronic overuse, underuse, or mechanical damage, inflammatory conditions tend to have less robust responses. Meta-analyses for fibromyalgia have noted improved balance16 and slightly improved quality of life (SMD 0.49, 95% CI, 0045 – 0.981)17 but little impact on fatigue or pain. Individual studies, however, have shown support for these benefits. One study of subjects with rheumatoid arthritis (RA) who performed 15 minutes of WBV twice per week for 3 months demonstrated continued diminution of fatigue at follow-up, but there was no intervention in the control group.18 As multiple other studies support benefits such as reducing arthrogenic inhibition and improving bone density, it is possible the degree of benefit for rheumatic conditions in high-quality studies is obscured with small-sample meta-analysis techniques.

In summary, whole body vibration regimens may be most beneficial for patients whose stability impedes function and for those with low activity due to sedentary jobs or underlying rheumatic or pain conditions. Effective regimens may involve weight bearing on a plate for 30 minutes, 3 times a week or more for 3 months.

Focal Vibration (Local Vibration)

With WBV, the patient stands, sits, or exercises on a vibrating plate, thus transmitting vibration to the whole body. As with the ability to transmit focused energy with ultrasound, new small mechanical cylinder and coin motors, as well as acoustic “speaker” vibrators, may be placed directly on desired locations. Because the transmission of mechanical force decays at different rates through skin, fat, muscle, and bone, an initial frequency decays slightly to slower frequencies as the waves of mechanical energy spread. This transmission provides the opportunity for focal vibration to stimulate multiple ABeta receptors for a more robust pain inhibition.19 There is currently no consensus on whether to call the small area placement of vibration “focal,” “local,” or “segmental,” and thus, the terms are used interchangeably. For this purposes of this review, the term “focal” will be used.

Chronic Overuse Injuries

In addition to the primarily Pacinian corpuscle ABeta induced pain relief, focal vibration works to induce mechanical changes of benefit to overuse injuries. Chronic overuse injuries, such as delayed onset muscle soreness after training, exhibit microscopic muscle tears. Multiple theories of pain production, including lactic acid, muscle spasm, inflammation, connective tissue damage, and enzyme efflux, may contribute to both chronic and overused tissues. Imtiyaz, et al,20 demonstrated that 5 minutes of vibration prior to exercise was equivalent to 15 minutes of massage at reducing delayed onset muscle soreness, likely through multiple mechanisms. By mechanically reducing spasm and separating maximally coupled actin/myosin bonds, vibration facilitates initially increased muscle contraction strength.20 This separation may also facilitate subsequent movement without re-injury and subsequent increased lactic acid production. Vibration increases range of motion and blood flow, both of which may help to reduce micro-injury and facilitate removal of pain-inducing cytokines and reduction of pain.21

Chronic Pain Conditions

In chronic pain management, focal vibration has been limited by the availability of home use devices; however, there is interesting historical research support for other use. In 1983, after Ottoson, et al,22 noted “remarkable efficiency” of focal vibration for orofacial pain, Lundeberg published a sprawling thesis covering multiple placebo-controlled clinical trials in 135 acute pain and 596 chronic pain patients.23 After extensive trials building on work by Melzack,3 he concluded that, for patients with chronic pain, FV was most effective in the 100 to 200 Hz frequency range, and best when directly on the locus of pain, followed by placement proximal to pain, followed by placement at the paraspinous location enervating the dermatome with pain. Most patients experienced greatest relief with moderate rather than light pressure. Of the 68% of chronic patients who responded to the first trial, maximal relief was experienced by 88% of chronic pain patients in 20 minutes, and in 30 minutes by the remainder. An additional 73 patients responded to a second trial, for overall efficacy of 80%. The duration of relief correlated with the degree of response (approximately 6 hours). Of note, patients were able to prolong the benefits of vibration by following treatment with 10-minute ice sessions. Approximately 265 chronic pain patients were followed for 18 months, with 59% reporting improvement or elimination of pain. No products resulted from the trials, and the use of focal vibration and ice for home pain relief fell away. As home-care and self-care vibration devices come on the market, there is a growing buildup of registered studies evaluating focal vibration for the treatment of chronic pain conditions, including those reviewed below.

Knee Osteoarthritis: In a study by Rabini, et al,24 After at least 6 months of pain, 50 patients were randomized to 100 Hz focal vibration or placebo for approximately 30 minutes on three consecutive days. Amplitude was adjustable, with most patients using 0.2 – 0.5 mm. Those using FV demonstrated improved pain and mobility, with WOMAC scores most significantly improved at 24-week follow-up.

Mastectomy Pain: For patients with post-mastectomy pain, FV with exercise improved outcomes and reduced pain more than exercise alone.25 Focal vibration has shown similar balance benefits as WBV,26 implying a utility for home therapies.

Overuse Pain (Epicondylitis and Plantar Fasciitis): Lundeberg23 reported that 87 of 118 patients with epicondylitis of greater than 6 months duration experienced pain relief with a first application of focal vibration. After three months of daily home use, 6 of 27 continued to use vibration, with approximately one-third reporting resolution of pain, and one-half finding the ongoing treatment to be ineffective. In a case series of 10 patients with plantar fasciitis not responding to typical methods, ice and 160-Hz vibration relieved pain for 8 of 10, with two sessions twice a day for 1 week reducing pain by half, and increasing pain-free days by 30%.27

Upper Extremity Contracture Pain: Focal vibration has an extensive history in neurorehabilitation due to its recruitment of Ia and II afferents, and potential central reorganization. For patients with pain resulting from contractures and underuse of extremities after stroke, focal vibration has also been found to reduce pain. In 32 post-stroke patients with pain, 300 Hz for 30 minutes on the affected triceps three times a week reduced pain and improved function significantly compared to placebo after 4 weeks of therapy.28

Overall, through different physiologic mechanisms, vibration above mechanical stress threshold for durations 15 to 45 minutes seems to play a role in mitigating chronic pain conditions. Most studies find maximal benefit with 30-minute sessions for whole body, or up to 45 minutes of focal treatment.23 Placement directly on the painful location seems most effective, with compression or coverage of the entire area preferable to trigger point stimulation. Pain relief may be improved with more sessions per week or even per day, up to a maximum of four per day.

Summary

Future directions imply that thermal combinations, certainly with ice but possibly with heat for spasm reduction and decreasing central sensitization, are likely new tools in the armamentarium against chronic pain. The ability of home use and self-care to reduce catastrophizing and improve convenience for chronic pain patients may enhance the potential of focal vibration modalities. Overall, the time may have come to support vibration therapy as a useful modality in reducing the impact of pain.

Last updated on: March 20, 2019
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New Device Combines Acupuncture With Four Other Technologies to Alleviate Pain
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