Therapeutic Laser is a modality used to improve quality of life and healing of tissues in animals. To understand why the therapy is beneficial, it’s first important to understand how lasers work so we can know in what situations they would be applicable.
“Laser” is actually an acronym for Light Amplification by Stimulated Emission of Radiation. The light is produced by electrical stimulation of a special material (gas, solid, or liquid). As the electrons of the material are excited from their normal position and then return to a resting state, they release specific photons that produce a concentrated, collimated light beam of one specific wavelength (nm). The resulting photon light then travels straight into tissues being absorbed by the cell’s chromophores and causing a photochemical reaction within the cells. The longer the wavelength, the deeper the light will travel. Wavelengths of about 600 nm will penetrate 0.5-2.0 cm, and waves of 700-900 nm will penetrate tissues up to 5 cm deep. Indirect affects from the light will also be seen even further into the tissues via the circulatory, immune, and nervous system.
In the US, we classify various lasers based on their safety (particularly the potential for eye damage), which also coincides with its power (Watts or Joules). One Joule (J) is the light energy delivered with 1 Watt (W) of power in one second. Higher powered lasers take less time to deliver the same amount of energy. A 1 W laser machine delivers 1 J in 1 second; a 500 mW machine delivers 1 J in 2 seconds. Several studies have shown cells need a dosage of 4-10 J/cm2 to stimulate a positive photochemical response. To deliver that dosage to the desired tissue, penetration is dependent a combination of power, wavelength, and treatment time.
Our clinic uses a Class 3B laser with an large surface applicator that delivers multiple wavelengths to treat superficial and deep conditions. Our unit also is fully adjustable and allows for dosage change (as either J or J/cm2) depending on the condition treated. In addition, the unit has various preset parameters for ease of use.
The biochemical mechanisms are currently researched, but each phase of the healing process appears to be positively influenced. To begin, the laser energy is absorbed by chromophores in the mitochondria of tissue cells to increase ATP production, DNA/RNA synthesis, and cell metabolism. In turn this leads to increased expression of various cytokines, enzymes, growth factors, and genes related to cell proliferation and migration (i.e., Nitric Oxide). The inflammatory phase of healing is accelerated and shortened, ultimately due to a reduction of inflammatory mediators (i.e., COX-2 and PGE) and inflammatory cells. There is increased vasodilatation and activation of lymphatic drainage in the initial 36 hour period due to a change in cell membrane permeability and ion exchange (Na/K pump), decreasing local swelling. The healing process then enters the proliferative phase where laser energy enhances fibroblast and cell proliferation, and macrophage activation. The final phase of the healing involves remodeling of scar tissue, where laser energy increases the organization of collagen fibers.
Studies have also shown that laser therapy is helpful in decreasing acute and chronic pain through multiple mechanisms. The laser energy promotes endogenous endorphin production, increases serotonin release, suppresses nociceptor pain receptors and blocks C fiber afferent nerve transmission. Since laser energy decreases nerve transmission of pain signals, some animals may be able to reduce or eliminate pain medications. Though laser therapy is good for decreasing the inflammation and pain associated with arthritis, it should be considered a complimentary therapy to physical rehabilitation which is geared towards changing muscle strength, tissue flexibility and long term comfort. Ideally laser therapy should be performed by a veterinarian certified in physical rehabilitation who thoroughly understands musculoskeletal disorders in conjunction with rehabilitation exercises.
What specific uses do therapy laser units have in veterinary medicine? Laser therapy is used for improved healing, such as with wound care, fracture repair, and post surgery, or for decreased pain, such as with osteoarthritis or tendonitis. Improvements can generally be seen after 1 treatment for wound care, 2-4 treatments with acute pain, and 1-7 treatments with chronic pain. For acute wounds, treatments will occur up to daily. For pain control, treatments generally start twice a week. Treatment sites include areas with obvious pain or flexibility limitations, but often includes “trigger points”, which are areas of secondary muscle tension. Once maximum improvement of chronic pain is observed, some animals are able to reduce to a treatment frequency of about once every 2 to 4 weeks. We can utilize this therapy on ANY animal and currently our clinic has treated dogs, cats, birds, turtles, and sugar gliders to name a few.
by Beth Rhyne, DVM, CCRP, Charlotte Street Animal Hospital. 208 Charlotte Street, charlottestreetanimalhospital.com