Chapter 7 Rehabilitation Physical Modalities 145The mechanisms by which TUS reduces pain
are likely similar to those of superficial heat—
increased blood flow to the area may assist in
removing pain mediators in the area, nerve
conduction is impacted, and muscle spasm
decreased. In addition, the mechanical effects
of TUS may alter cell membrane permeability,
leading to decreased inflammation and related
discomfort (Kavadar et al., 2015; Rai et al., 2016).
There is evidence that TUS may have a positive
impact on the central pathways of pain process
ing as well (Hsieh, 2005).
Therapeutic effects on tissue healing
and protection
Just as with superficial heating agents, the
heating effects of TUS cause vasodilation
(Noble et al., 2007) leading to increased local
blood circulation and oxygenation (Morishita
et al., 2014a; Chang et al., 2015). This promotes
healing by delivering nutrients and removing
waste products. When specifically treating
tendons, TUS has been shown to improve the
microcirculation (Chang et al., 2015) and tensile
strength (Enwemeka, 1989; Ng, 2011) of injured
tendons as compared to nontreated controls.
Chang and colleagues then correlated these
positive indicators of healing with improved
tendon function following surgical repair of
Achilles tendon tears (Chang et al., 2017).
Similar findings with canine patients were
noted in a study by Saini and colleagues in
which TUS was employed in the treatment of
surgically severed Achilles tendons in dogs
(Saini et al., 2002). Also, Mueller and colleagues
described two canine cases of partial gastrocne
mius muscle avulsion (not surgically induced)
that were treated conservatively with ultra
sound and showed complete return to full
activity (Mueller et al., 2009).
TUS also has angiogenic effects in tissues
with compromised blood supply. Huang and
colleagues and Lu and colleagues demon
strated that TUS can reverse peripheral
ischemia in type 2 diabetic mice as evidenced
by increased blood perfusion and capillary
density (Huang et al., 2014; Lu et al., 2016a). In a
subsequent study by Lu and colleagues, TUS
was found to impart similar angiogenic bene
fits in rats with hypertensive peripheral arterial
disease (Lu et al., 2016b).
The nonthermal effects of TUS benefit tissue
healing as well, such as following tendon repair
(Geetha et al., 2014) and when treating tenosyn
ovitis (Sharma et al., 2015). In the treatment of
wounds, especially in the inflammatory and
proliferative phases of healing, pulsed TUS can
promote angiogenesis and granulation tissue
formation, and speed wound contraction
(Fantinati et al., 2016) while also helping to con
trol necrotic tissue by increasing the phagocytic
capacity of macrophages (Korelo et al., 2016).
Indeed, full‐thickness wounds such as surgically
created wounds (Mahran, 2014) and pressure
ulcers (Polak et al., 2014) demonstrate more
rapid healing when treated with pulsed ultra
sound using lower intensities (0.5 W/cm^2 ),
strongly suggesting that the mechanical
effects are involved with healing. Pulsed TUS
also accelerates wound contraction through
enhanced collagen production and density,
especially in wounds with adequate blood sup
ply (Altomare et al., 2009).
Pulsed TUS may also have protective effects
for tissues surrounding an injury. Using pulsed
TUS, Martins and colleagues demonstrated a
reduction in the oxidative stress and secondary
tissue damage often seen following a crushing
injury of muscle (Martins et al., 2016).
Additionally, the nonthermal effects of TUS
may enhance peripheral nerve regeneration.
Mourad and colleagues found a more rapid
return to full foot function when low‐intensity
ultrasound was applied 3 days per week for 30
days following sciatic nerve crush injury in rats
(Mourad et al., 2001). A 2005 study demonstrated
improved nerve fiber density and a greater num
ber of Schwann cell nuclei in treated injured rat
sciatic nerves as compared to those not treated
(Raso et al., 2005), and Akhlaghi and colleagues
showed 90% of full functional recovery after just
2 weeks of pulsed TUS following sciatic nerve
crush injury (Akhlaghi et al., 2012).
Finally, both the thermal and nonthermal
effects of TUS may promote healing and regen
eration of articular cartilage. A 2012 study dem
onstrated an increase in the cartilage thickness
in human patients with mild to moderate knee
osteoarthritis following 24 sessions of pulsed
TUS (Loyola‐Sánchez et al., 2012). Nam and
colleagues also found that both pulsed and con
tinuous TUS increased chondrogenesis in rat
tibial articular cartilage (Nam et al., 2014).