Chapter 7 Rehabilitation Physical Modalities 155Low‐level laser therapy (LLLT)/
photobiomodulation
LASER is an acronym for “light amplification
by stimulated emission of radiation.” Laser
application is also referred to as photobiomod
ulation. Lasers produce electromagnetic radia
tion that is monochromatic, coherent, and
collimated. These qualities allow laser light to
penetrate tissues. Photons can be reflected (not
penetrate the tissue), transmitted (pass
through the tissue), or refracted (pass through
the tissue but in an altered direction), the last
two of which result in physiological changes
at the molecular, cellular, and gross level.
Light energy is absorbed by chromophores
(light‐absorbing molecules found in the tissue)
causing a number of biological effects (Yadav
& Gupta, 2016).
Classes of lasers
Lasers are classified according to their power,
maximum permissible exposure (MPE), and
wavelength. Power, measured in watts (joules/s),
is the rate of energy production. Dosage, the
amount of energy delivered to the tissue, is
determined by multiplying power by time. The
dose required to treat the tissue is dependent
upon wavelength, power density, type of tis
sue, condition of tissue, acuity of the problem,
pigmentation, depth of target tissue, and treat
ment technique (scanning vs point‐to‐point).
Doses that are too low are not effective and
doses that are too high can be biosuppressive.
The energy provided can then be determined in
power density (W/cm^2 ) or energy density (J/cm^2 ).
The wavelength of laser light determines the
depth of penetration (Chung et al., 2012). Except
for the 970–980 nm wavelength, where there
is a peak in water absorption, longer wave
lengths provide deeper penetration (Hudson
et al., 2013). There is evidence that wavelengths
of 810–830 nm penetrate the skin most effectively
(Passarella & Karu, 2014), while 780–950 nm
wavelengths are better for deeper tissues
(Chung et al., 2012).
Other sources report that wavelengths of
600–700 nm are best for treating superficial
tissues as the photons are absorbed at this
layer rather than passing through to the
deeper tissue. A direct comparison of energy
and penetration showed 50% more penetra
tion with a 808 nm wavelength compared to
980 nm (Hudson et al., 2013).
Lasers are also categorized based on their
potential for causing harm. Therapeutic lasers
fall into class 3R, class 3B, and class 4. Class 3R
lasers have 1–5 mW of power. Class 3B lasers
have 5–500 mW of power, are commonly used
in rehabilitation, and produce nonvisible light
that is not damaging to the eye when reflected
off matte surfaces. Protective eyewear should
be used when in close proximity to these lasers.
Class 4 lasers have greater than 500 mW of
power, and include both therapy and surgical
lasers. Surgical lasers range from 15 to 40 W● TENS around L stifle (frequency: 50 Hz; pulse
duration: 75 μs; amplitude to patient tolerance
for 15 minutes). Used to improve tolerance for
manual therapies. Discontinued when patient
tolerated manual work without significant
discomfort.
● NMES, L quadriceps and hamstrings (frequency:
35 Hz; pulse duration: 100 μs; 2 s ramp; 10 s on,
30 s off; amplitude to patient tolerance for 10
min). Performed with the patient in supported
standing as tolerated. Discontinued when patient
was able to produce strong voluntary muscle
contractions.
● TUS, L sartorius—area already shaved (mode:
continuous; frequency: 3 MHz; intensity: 1.0 W/
cm^2 ; duration: 7 min), gentle stretch appliedduring the last 2 minutes. Discontinued when
muscle guarding resolved, flexibility regained.
● Cryotherapy, L stifle, 15 min at end of sessions—
patient day‐boarding at clinic. Cryotherapy used
throughout rehab course to decrease inflamma-
tion and minimize post‐exercise discomfort.
● Low‐level laser therapy (LLLT), stifle joint line, 4 J/
cm^2 , increasing to 6 J/cm^2 as therapy progressed.
Also used for muscle trigger points (R teres major,
L iliopsoas) as noted, 6 J/cm^2. LLLT used through-
out rehab course to promote healing.At 10 weeks post‐surgery, the patient had regained
full range of motion, near‐symmetrical muscle mass,
and near‐symmetrical gait mechanics at a walk and
controlled trot.