Lasers: Applications for therapeutic use

You've seen them at conferences and heard about them in lectures. In case you missed the discussion, therapeutic lasers are taking hold in veterinary medicine. Why? Because they work.

(NICK KOUDIS/GETTY IMAGES)

But you should know some of the facts and the basic science behind this technology so you can ask the right questions before you purchase one.

Laser stands for light amplification by stimulated emission of radiation. Cold or low-level laser therapy (LLLT) is relatively new in the United States, having gained FDA approval in 2002. It has, however, been used for many years in other parts of the world, including Canada, Australia, Europe and some Asian countries. Randomized controlled trials, systematic literature reviews and meta-analyses now being conducted are supporting the effectiveness of lasers in treating pain and making recommendations regarding dosages and machine specifications.

How does laser treatment reduce patients' pain?

Lasers can reduce pain in several ways. One review paper cited the anti-inflammatory effects of laser treatment as similar to those of pharmacologic agents such as celecoxib, meloxicam, diclofenac and dexamethasone.1 Lasers also can control pain by reducing oxidative stress, improving angiogenesis and augmenting collagen synthesis and skeletal repair.2 A randomized controlled trial showed that lasers were able to inhibit transmission at the neuromuscular junction, which reduced nerve firing and pain signaling.3 In a meta-analysis of laser use in people, laser therapy was shown to decrease neck pain immediately, with positive effects that could last up to three months after the end of a treatment series.4

What other benefits can laser treatment offer patients?

Lasers also have been shown to improve tendinopathy lesions. Research validates that injured soft tissues exposed to laser light demonstrate an increase in collagen synthesis, improved metabolism of tenocytes or myocytes, increased fibroblastic activity, neovascularization, improved tensile strength, acceleration of the healing process and organization of collagen bundles. LLLT also is widely used and found to be effective in treating chronic joint disorders, enhancing biosynthesis of cartilage, stimulating microcirculation and reducing inflammation in the synovium and synovial fluid.

Bone healing is another indication for LLLT. Improvement is seen as osteoblastic proliferation, bone neoformation, bone stiffness, collagen deposition, amount of well-organized trabeculae and creation of a smaller, stronger callus. Exposure to laser light can also promote wound healing, reducing wound size and healing time. Laser therapy has also shown impressive results in remediation of peripheral nerve injuries and even spinal cord lesions.

Can laser therapy be dangerous?

The editors of a recent special edition of Physiotherapy Canada thoroughly reviewed contraindications and precautions for laser therapy.5 They determined it should not be used over the eyes or reproductive organs or in regions known or suspected of malignancy. Laser therapy is not safe to use in regions with circulatory compromise or in patients with hemorrhagic disorders with actively bleeding tissues. Only experienced practitioners should use a laser on recently irradiated tissues or over the anterior neck or carotid sinus. Caution also should be taken in patients with photosensitivity disorders, infections and a compromised immune function or active epiphyses.

What do I need to know about phototherapy?

Laser light is collimated—it does not diverge. It possesses coherence and monochromaticity, which means when it's produced, it maintains a single wavelength. Human and animal studies have shown that body tissue tends to absorb and use wavelengths within the range of 600 to 1,000 nanometers (nm).

Laser machines come with one or multiple sets of predetermined wavelengths, and wavelength determines the penetration depth. Wavelengths within the 600-nm range do not directly penetrate more than 0.5 to 2 cm, or indirectly up to 5 cm, via the dissipation of energy. Wavelengths that range from the mid-700- to low-900-nm range penetrate the deepest, directly affecting tissues up to 5 cm and indirectly up to 10.

Light energy is measured in joules (1 joule = 1 watt × 1 second). So a 500-milliwatt (mW) machine can deliver 1 joule of energy in two seconds, and a one-watt machine can deliver 1 joule of energy in one second. A 10-watt machine can deliver that same energy in 1/10th of a second. While being fast might be good if you want to deliver a large number of joules or treat a large area, it also means your laser technique must be modified to prevent superficial tissue damage.

Which laser is better—Class 3b or 4a?

Therapeutic laser machines come in a wide range of powers, anywhere from 5 mW to 10 watts. The most common therapeutic lasers fit into either Class 3b with a power range of 5 to 500 mW or Class 4a with more than 500 mW. Power has absolutely nothing to do with depth of penetration or the targeting of specific tissues—just the speed of delivery. More powerful laser machines are simply able to deliver laser energy more quickly.

Class 3b lasers (and low-powered Class 4a lasers) are used in direct contact with the skin. Many manufacturers and laser therapy textbooks recommend pressing the probe firmly against or into the skin to improve penetration depth. High-powered Class 4a lasers, on the other hand, cannot be held motionless against the skin because of the potential for cutaneous thermal damage. This makes accurate dosage calculation impossible. Even with direct contact, a substantial amount of laser light is reflected and refracted by the skin and subcutaneous tissues. A sweeping technique is commonly recommended with high-powered lasers, but there's still a tremendous amount of light reflection, so there's no way of knowing exactly how much energy is reaching the target tissues.

Manufacturers and clinicians say they see benefits with their high-powered Class 4a lasers. That's not in dispute. Light energy has the potential to heal. However, the effectiveness of high-powered Class 4a lasers cannot be validated in research because of this dosage-delivery dilemma. For this reason, some companies have elected to produce 750-mW and 1-watt Class 4a lasers that can be placed directly on the skin, improving upon speed but maintaining the ability to accurately calculate the joules delivered.

Which is better—continuous or pulsed wave?

It's important to understand how pulsing the light (frequency or hertz [Hz]) comes into play. It's been proposed that low frequencies (10 to 100 Hz) are more effective in treating pain, while higher frequencies (2,500 to 5,000 Hz) impact inflammation. At least for now, no research has shown discernable correlation between any particular frequency and a clinical outcome.

Pulsing light can make dosage calculation more difficult, because it breaks up the laser beam, impacting the overall joules of energy delivered. Clinically, pulsation frequency can be adjusted to diminish the energy delivered and reduce the superficial heating properties, for example, in animals with dark hair and people with dark skin who may experience a thermal reaction because of greater absorption of the light.

What is a super pulsed laser?

Super pulsed lasers use a 904/905-nm wavelength and deliver light in a different way. The beam is flashed for only a brief fraction of a second. Within that time, a burst of 25 to 60 watts of light energy (depending on the unit being used) is emitted. Afterward, the light shuts off until the next timed burst. The premise behind this delivery model is that the superficial cells are photo-bleached by the light, allowing easier penetration by the subsequent bursts of light. Super pulsed lasers are reported to be beneficial for treating pain.

What's the bottom line?

Laser machines can be an effective tool in veterinary rehabilitation, but practitioners need to have a good understanding of this modality before using it to treat their patients. Knowing the most appropriate dosages for each condition is critical, as is the anatomical location where laser should be applied, how often and for how long. Training in rehabilitation is the best way to acquire the skills needed to use laser therapy safely and effectively.

Ms. Hughes is co-owner of The Canine Fitness Centre Ltd., Calgary, Canada. She also is on the faculty of the Canine Rehabilitation Institute, Wellington, Fla.

References

1. Chow RT, Johnson MI, Lopes-Martins RA, et al. Efficacy of low-level laser therapy in the management of neck pain: a systemic review and meta-analysis of randomised placebo or active-treatment controlled trials. Lancet 2009;374(9705):1897-1908.

2. Bjordal JM, Johnson MI, Iversen V, et al. Low-level laser therapy in acute pain: a systematic review of possible mechanisms of action and clinical effects in randomized placebo-controlled trials. Photomed Laser Surg 2006;24(2):158-168.

3. Chow RT, David MA, Armati PJ. 830 nm laser irradiation induces varicosity formation, reduces mitochondrial membrane potential and blocks fast axonal flow in small and medium diameter rat dorsal root ganglion neurons: implications for the analgesic effects of 830 nm laser. J Peripher Nerv Syst 2007;12(1):28-39.

4. Chow RT, Heller GZ, Barnsley L. The effect of 300mW, 830 nm laser on chronic neck pain: a double-blinded, randomized, placebo-controlled study. Pain 2006;124(1-2):201-210.

5. Houghton PE, Nussbaum EL, Hoens AM. Electrophysical Agents. Contraindications and precautions: an evidence-based approach to clinical decision making in physical therapy. Physiotherapy Canada 2010;62(5 Special Issue):1-80.

Suggested reading

Tuner J, Hode L. The new laser therapy handbook. Grängesberg, Sweden: Prima Books, 2010.