144 Canine Sports Medicine and Rehabilitation
Therapeutic effects of TUS: thermal
and nonthermal
TUS can provide heating benefits to tissues up
to 5 cm deep without causing thermal damage
to more superficial tissues. TUS can increase
pain thresholds, blood flow, metabolic rate, and
collagen extensibility. It can also decrease mus
cle guarding and spasm and reduce subacute
and chronic inflammation.
The nonthermal, or mechanical, effects of
TUS include microstreaming and cavitation.
Microstreaming, or acoustic streaming, refers to
small‐grade, unidirectional pressure waves cre
ated in the fluids around cells. Cavitation is the
compression and expansion of small gas bubbles
in body fluids. Both may modify cellular func
tion and membrane permeability, thus assisting
with tissue repair and swelling reduction.
Parameters of treatment
Frequency, measured in megahertz (MHz),
determines the depth of sound energy penetra
tion. Most TUS units offer two frequencies:
1 MHz and 3 MHz. The 1 MHz option provides
a deeper heating of up to 5 cm in depth; 3 MHz
is selected when heating of more superficial tis
sue is desired, within 1–2.5 cm. The 3 MHz
option is also used when TUS is applied around
a bony prominence to avoid periosteal pain.
Intensity, measured in watts per centimeter
squared (W/cm^2 ), affects the degree and rate
of temperature increase. Higher intensities will
cause greater and more rapid temperature
elevations. A typical intensity range found on
TUS units is 0.25–3.0 W/cm^2.
Two modes are generally available for provid
ing TUS: continuous and pulsed. Continuous
mode refers to a constant flow of energy. Pulsed
mode has regular breaks in energy flow and is
described by its duty cycle, the percentage of
time that ultrasound is being emitted during
one pulse period. Most TUS units provide duty
cycles from 5% to 50%. Pulsed mode is usually
chosen when only minimal heating or the non
thermal effects of TUS are desired, such as
when treating an acute injury.
The duration of TUS treatments must be suf
ficient if the goal is to achieve therapeutic levels
of tissue heating (an increase of 1 to 4 °C).
When TUS is part of a patient’s treatment
plan, all application parameters must be con
sidered in combination with the depth of the
target tissue, the size of the treatment area, the
stage of healing, and the goal of treatment
(Miller et al., 2008). Especially when deeper
heating is desired, in addition to using the cor
rect frequency, sufficient intensity and duration
is needed to achieve and then maintain the tem
perature elevation for an adequate time period
in order for therapeutic effects to occur. Even
small variations in dosage can have a large
impact on temperature change (Demchak &
Stone, 2008).Evidence supporting the use of TUSTherapeutic effects on pain
When providing thermal effects, TUS can
reduce the discomfort associated with trigger
points (Draper et al., 2010; Benjaboonyanupap
et al., 2015), muscular soreness following an
overuse injury (Aaron et al., 2017), plantar fas
ciitis (Krukowska et al., 2016), rotator cuff injury
(Yildirim et al., 2013), and myofascial pain (Ilter
et al., 2015; Rai et al., 2016), with improvments
often maintained for extended periods of time
(Kavadar et al., 2015). Furthermore, when com
bined with active therapeutic exercise, TUS
provides benefits above those seen with exer
cise alone for patients with lumbar disc disease
(Boyraz et al., 2015) and spinal stenosis, such
that use of analgesic medications is decreased
(Goren et al., 2010). TUS has also been shown to
effectively reduce the pain associated with oste
oarthritis (Zhang et al., 2016; Yeğin et al., 2017), a
condition also seen frequently in the canine
rehabilitation setting.
The nonthermal effects of TUS appear to
offer pain‐reducing benefits as well. Both a
2014 review by Zeng and colleagues and a
2015 randomized, placebo‐controlled, dou
ble‐blind study by Yildiz and colleagues
found that continuous and pulsed TUS are
effective in improving both pain status and
functional mobility in the management of
knee osteoarthritis (Zeng et al., 2014; Yildiz
et al., 2015). This information could be useful
if thermal modalities are contraindicated for
a patient.