The trend in laser therapy over the past 10 years has been to increase power density and dose, since this has been shown to improve therapeutic outcomes considerably.1 The first therapeutic laser in the U.S. was cleared by the FDA in 2002 and had an output of 5 mW of power.2 Now, only four years later, several manufacturers have entered the marketplace and the power of FDA-cleared, therapeutic lasers can range up to 7,500 mW.3 That represents an increase in power of 150,000 percent (Figure 1).
Despite more than 35 years of experience with therapeutic laser devices, concerns remain as to the effectiveness of laser therapy as a treatment modality. Controlled clinical studies have demonstrated that while laser therapy is effective for some specific applications, the most common reason for poor clinical outcomes is related to low power or dosage.1 The expansion of the health care provider's armamentarium to include laser therapy for pain management, inflammatory reduction and accelerated healing has "pointed to the need for higher output levels and, similarly, led to implementation of higher wavelengths with deeper penetration in tissue."4
Key words: Class IV laser therapy, high-power laser therapy, LLLT, low-level laser therapy.
A great deal of misunderstanding exists among practitioners relating to the selection of a therapeutic laser device that will provide the deepest penetration and the greatest amount of stimulation for conditions seen routinely in practice. Given the parallels of X-ray and infrared (laser) physics, both of which are continuums of energy within the electromagnetic spectrum, it is a wonder why many practitioners remained confused about the three important parameters of therapeutic laser devices: power, wavelength and power density. Although these are not the only parameters, they are outlined in this article because of their frequent association in the literature, due to their influence on clinical outcomes.
The Importance of Power and Penetration
Cells and tissues that are ischemic and poorly perfused as a result of inflammation, edema and injury have been shown to have a significantly higher response to laser therapy irradiation than normal healthy structures.5 Tina Karu, PhD, of the Laser Technology Center in Russia and affiliated with the University of California, Berkley, has researched the effects of light on the cell since the 1980s. She found there are photoreceptors at the molecular level that, when triggered, activate a number of biological reactions such as DNA/RNA synthesis, increased cAMP levels, protein and collagen synthesis and cellular proliferation. The result is rapid regeneration, normalization and healing of damaged cellular tissue. Thus, light is a trigger for the rearrangement of cellular metabolism.6
Bjordal places the range of laser energy absorption (joules) by the skin and subcutaneous tissue to be in the range of 50 percent to 90 percent.7 The amount of laser energy absorption increases as the wavelength decreases (Figure 2), thereby making higher wavelengths preferable for deeper stimulation of the physiological processes necessary for pain/inflammation reduction and accelerated tissue healing.
Tuner and Hode state: "There is no point in increasing the dose if the wavelength has a low penetration factor; the penetration of the particular wavelength must be taken into account."1 The laws of laser physics have demonstrated that the higher the wavelength, the deeper the penetration. Penetration is paramount in order to stimulate deep musculoskeletal, vascular, lymphatic and neurological structures.
Given the in-depth nature of X-ray physics and utilization as taught in most school curricula, we can draw several parallels to further our understanding of laser physics. The mAs setting governs the quantity of X-ray photons produced in a given period of time. This quantity is also referred to as the dose. Therapeutic lasers deliver their dose by the amount of photons emitted secondary to the milliWatt setting over a given period of time. The higher the setting in both instances, the higher the dose.
X-ray penetration is governed by the kVp setting. In laser therapy, penetration is governed by the wavelength which is measured in nanometers (nm).7 Both kVp and wavelength are affected by tissue density.
The most common musculoskeletal conditions that initiate a health care provider's intervention are neck pain and low-back pain. Leading researchers published in the world's most respected, peer-reviewed journals have identified the most common generators of pain in the cervical and lumbar regions. Bogduk, et al., have reported that the zygapophyseal joints of the neck were implicated most frequently in acute (traumatic) and chronic neck pain conditions.8-11 Several authors have reported the most common tissue of pain origin in the low back to be the outer layer of the annulus fibrosis and PLL.12,13 Given that the depth of these documented structures lies below multiple layers of muscle and fascia in the aforementioned spinal regions, successful clinical outcomes in chiropractic necessitate that a therapeutic laser device has the ability to penetrate multiple layers of biological tissue, while simultaneously providing sufficient power to stimulate photoreceptors responsible for triggering positive physiological events for pain/inflammation reduction and accelerated tissue healing.
Class III or "low-level" lasers have a limited power output of up to 500 mW. As mentioned previously, therapeutic laser devices are now being manufactured to meet the needs of deeply seated conditions. These devices are referred to as class IV, or "high-power" therapeutic lasers, and have been cleared for use by the FDA up to 7,500 mW.
Recently published systematic reviews of the literature have concluded there is a lack of adequate evidence of effectiveness of class III "low-level" laser therapy for treatment of musculoskeletal disorders,14 arthritis15-18 and pain.19-25 Recently, reviews also have concluded that low-energy laser therapy is ineffective in treating carpal tunnel syndrome.26,27 This should be of particular concern to the physical medicine and rehabilitation professions, which commonly encounter these conditions. Tuner and Hode have performed an analysis of a number of frequently cited studies on the effects of class III, "low-power" laser therapy. The authors state: "In many of these studies, analysis uncovered one or more reasons for the negative findings reported, the most common being the use of extremely low doses."1
How Much Is too Much?
Manufacturers and proponents of class III "low-level" laser devices often express concerns regarding inhibition of the healing process due to "overstimulation" from increased treatment times or higher powered devices. However, reports of therapeutic laser devices having an inhibitory effect on cells have only occurred on thin-tissue cultures in petri dishes (in vitro), and lack validation in human studies (in vivo), with the exception for inhibition and suppression of depolarization of C-fibers resulting in a reduction in pain.28-33
As the interest level surrounding laser therapy continues to grow in the physical medicine and rehabilitation professions, one class IV "high-power" manufacturer3 now includes the use of Gold Standard outcome assessment tools with its product, including an algometer34-36 to measure changes in tissue sensitivity pre- and posttreatment, and patient questionnaires that quantitatively assess patient improvement in a variety of areas, including pain, function and quality of life. This class IV manufacturer promotes the utilization of a core set of measures published in Spine to validate the efficacy of laser therapy treatment. These outcome assessment instruments measure the following five domains: back-specific function, generic health status, pain, work disability and patient satisfaction. Perhaps in the future, more therapeutic laser manufacturers will follow suit and expose their technology to scrutiny of scientific rigor for the benefit of those who would choose laser therapy as an adjunct to chiropractic care.
Dr. Jan Tuner, president of the Swedish Laser Medical Society and renowned lecturer and author on the topic, states: "I can see two alternatives for myself: to speak up and start a conflict within the laser community, maybe discrediting the therapy itself in the eyes of the general public, or to keep quiet and let U.S. practitioners pay a lot of money for very low-powered lasers, leaving us with dissatisfied customers and discredit from those who are supposed to use laser therapy in medicine."1
A Look to the Future
Tuner and Hodes' position on class IV "high-power" lasers is reported as: "For the moment, we must rely on our own clinical experience. That experience, however, is so encouraging that it cannot be ignored, even with lack of scientific support. It would appear that 'high-powered' therapeutic lasers will be able to further expand the scope of laser therapy."1 Given that the number one reason for poor clinical outcomes is low power and poor penetration, most health care providers utilizing low-powered devices agree with these pioneers in the field.
- Erchonia Medical, Inc., home page. Accessed 22 March 2006. www.erchonia.com.
- Avicenna Laser Technology home page. Accessed 22 March 2006. www.avicennalaser.com.
- Prochazka M. "Class IV Laser in Non-Invasive Laser Therapy." Laser Partner, 22 March 2006. www.laserpartner.org/lasp/web/en/2003/0069.htm.
- Almeida-Lopes L. Human gingival fibroblast proliferation enhanced by LLLT. Analysis in vitro of the cellular proliferation of human gingival fibroblasts with low level laser. Dissertation at Universidade do Vale do Paraíba, São Paulo, Brazil. 1999.
- Karu T. The Science of Low Power Laser Therapy. Amsterdan, the Netherlands: Gordon and Beach Science Publishers; 1998.
- Bjordal J, Couppe C, Chow R, Tuner J, Ljunggren E. A systematic review of low level laser therapy with location-specific doses for pain from chronic joint disorders. Aust J Physiother 2003;49(2):107-16.
- Bogduk N, Marsland A. The cervical zygapophyseal joints as a source of neck pain. Spine 1988;13:610-7.
- Bogduk N, Aprill C. On the nature of neck pain, discography and cervical zygapophyseal joint blocks. Pain 1993; 54:213-7.
- Barnsley L, Lord SM, Wallis BJ, Bogduk N. The prevalence of chronic cervical zygapophyseal joint pain after whiplash. Spine 1995;20(1):20-6.
- Lord SM, Barnsley L, Wallis BJ, Bogduk N. Chronic cervical zygapophyseal joint pain after whiplash: a placebo-controlled prevalence study. Spine 1996;21(15):1737-45.
- Smythe M, Wright V. Sciatica and the intervertebral disc. An experimental study. J Bone Joint Surg 1958; 40:1401-18.
- Kuslich AD, Ulstrom CL, Michael CJ. The tissue origin of low back pain and sciatica. Ortho Clin North Am 1991;22:181-187.
- de Bie RA, de Vet HC, Lenssen AF, et al. Low-level laser therapy in ankle sprains: a randomized clinical trial Arch Phys Med Rehabil 1998;79(11):1415-1420.
- Brosseau L, Welch V, Wells G, et al. Low level laser therapy (classes I, II and III) for treating osteoarthritis (Cochrane Review). The Cochrane Library, Issue 3, 2002. Oxford, UK: Update Software; 2002a.
- Brosseau L, Welch V, Wells G, et al. Low level laser therapy (classes I, II and III) for treating rheumatoid arthritis (Cochrane Review). The Cochrane Library, Issue 3, 2002. Oxford, UK: Update Software; 2002b.
- Marks R, de Palma F. Clinical efficacy of low power laser therapy in osteoarthritis. Physiother Res Int 1999;4(2):141-157.
- Puett DW, Griffin MR. Published trials of nonmedicinal and noninvasive therapies for hip and knee osteoarthritis. Ann Intern Med 1994;121(2):133-140.
- Crawford F, Atkins D, Edwards J. Interventions for treating plantar heel pain (Cochrane Review). The Cochrane Library, Issue 3, 2002. Oxford, UK: Update Software.
- Gross AR, Aker PD, Goldsmith CH, et al. Physical medicine modalities for mechanical neck disorders (Cochrane Review). The Cochrane Library, Issue 3, 2002. Oxford, UK: Update Software.
- van der Heijden GJ, van der Windt DA, de Winter AF. Physiotherapy for patients with soft tissue shoulder disorders: a systematic review of randomised clinical trials. Br Med J 1997;315:25-30.
- Binder A. Neck pain. Clinical Evidence, Issue 7. Tavistock Square, UK; BMJ Publishing Group; June 2002.
- Crawford F. Plantar heel pain (including plantar fasciitis). Clinical Evidence, Issue 7. Tavistock Square, UK: BMJ Publishing Group; June 2002.
- Speed C, Hazleman B. Shoulder pain. Clinical Evidence, Issue 7. Tavistock Square, UK: BMJ Publishing Group; June 2002.
- Cullum N, Nelson EA, Nixon J. Pressure Sores. Clinical Evidence, Issue 7. Tavistock Square, UK: BMJ Publishing Group; June 2002.
- Gerritsen AA, de Krom MC, Struijs MA, et al. Conservative treatment options for carpal tunnel syndrome: A systematic review of randomised controlled trials. J Neurol 2002;249(3):272-280.
- O'Connor D, Marshall S, Massy-Westropp N. Non-surgical treatment (other than steroid injection) for carpal tunnel syndrome. Cochrane Database Syst Rev 2003;(1):CD003219.
- Nussbaum E, Lilge L, Mazzulli T. Effects of low-level laser therapy (LLLT) of 810 nm upon in vitro growth of bacteria: relevance of irradiance and radiant exposure. J Clin Laser Med Surg 2003 Oct;21(5):283-90.
- Nussbaum EL, Lilge L, Mazzulli T. Effects of 630-, 660-, 810-, and 905-nm laser irradiation delivering radiant exposure of 1-50 J/cm2 on three species of bacteria in vitro J Clin Laser Med Surg 2002 Dec;20(6):325-33.
- Karu T. "Low-Intensity Laser Light Action Upon Fibroblasts and Lymphocytes." Progress in Laser Therapy. Ed. by T. Ohshiro, R.G. Calderhead; J. Wiley and Sons: Chichester, New York, Brisbane, Toronto, Singapore, 1991, pp.175-180.
- Smith K. The photobiological basis of low level laser radiation therapy. Laser Therapy 1991 Jan;3(1).
- Ohno T. Pain suppressive effect of low power laser irradiation. A quantitative analysis of substance P in the rat spinal dorsal root ganglion J Nippon Med Sch 1997;64 (5):395-400. (In Japanese with English abstract.)
- Tsuchiya K, et al. Diode laser irradiation selectively diminishes slow component of axonal volleys to dorsal roots from the saphenous nerve. Neuroscience Letters 1993;161:65-68.
- Fischer AA. Pressure threshold meter: its use for classification of tender spots. Phys Med & Rehab 1986;67(11):836-8.
- Fischer AA. Pressure algometry over normal muscles. Standard values, validity and reproducibility of pressure threshold. Pain 1987;30(1):115-26.
- Antonaci F, Lucas GA, Sand T. Pressure algometry in healthy subjects: inter-examiner variability. Scand J Rehab Med 1998;30(1):3-8.
- Bombardier C. Outcome assessments in the evaluation of treatment of spinal disorders. Spine 2000;25:3100-3.