Therapeutic Ultrasound
If you've had physio before it’s quite likely that you will
have encountered therapeutic ultrasound. It’s the machine with the gel on the
end. People sometimes say “Am I pregnant then?”. Well Ultrasound can be used
for imaging too, but not the machine used by physiotherapists for treatment of
injuries. So there is diagnostic ultrasound and there is therapeutic
ultrasound.
So what exactly is it?
Therapeutic ultrasound has been used in clinical practice
since the 1950’s and during this time its popularity has fluctuated but it has
always remained the most utilised electrotherapy modality in physiotherapy. So
basically it is a small machine that generates sound waves that are at high
frequency. It is higher than what can be heard by the human ear, hence the name
‘Ultra’ sound. We can hear from 16Hz to 20,000 Hz in children and young adults,
as we get older we can’t hear the higher frequencies (Hz is the frequency per
second). But ultrasound is used at either 1MHz or 3MHz, which is 1 million or 3
million frequencies per second! So these sound waves when applied to tissues of
the body have a therapeutic effect.
How does it work then?
Sound is a form of energy and when it is passed into things
the energy is absorbed. Air doesn’t transmit hardly any ultrasound and this is
why the gel is used to transmit the energy in the tissues of the body. Also
some tissues absorb Ultrasound better than others and this is vital in what
ultrasound is effective for.
Basically increased protein content of the structures
increases the absorption amounts. Generally blood absorbs very little, fat in
slightly more but still not a lot. Nerve is not a great absorber either but
better then fat. Muscle does absorb quite well but not as well as ligament and
tendon (Watson 2008).
So this means ultrasound is excellent for ligament and
tendons, okay for muscle and not good for much else.
What does it actually do to you?
Basically speeds up the rate of healing & enhances the
quality of the repair (Watson 2006).
The specific effects of Ultrasound are considered thermal
and non-thermal.
Thermal:
Basically this effect is simply heat, which is proven to
have a therapeutic effect. At 40‑45°C, increased blood flow will
result, which will aid healing and this temperature is found to initiate the resolution
of chronic inflammation (Dyson & Suckling 1978).
Ultrasound is most effective in heating dense collagenous
tissues such as periosteum, collagenous tissues (ligament, tendon & fascia)
& fibrotic muscle (Dyson 1981). It also requires a high intensity in
continuous mode.
The issue is not that ultrasound doesn’t have thermal
therapeutic effect but that other cheaper and easier modes of heat work just as
well if not better, for example a wheat bag! The non-thermal effects are more
about what Ultrasound is all about rather than the thermal effects.
Non-Thermal:
These effects are cavitation and acoustic streaming (Baker
et al 2001). Another effect that I remember being taught at university was micro
massage. It sounds impressive but there is no good evidence showing this
actually occurs.
Acoustic streaming:
This is when the tissue fluids move in a swirling circular
motion near the vibrating structure. These structures can be cell membranes
& the surfaces of stable cavitation gas bubbles (Dyson & Suckling
1978). Sounds interesting but what this actually does is to affect diffusion
rates & membrane permeability. Sodium ion permeability is altered resulting
in changes in the cell membrane potential. Calcium ion transport is modified,
which alters enzyme control mechanisms of various metabolic processes,
especially concerning protein synthesis & cellular secretions.
Cavitation:
Formation of gas filled voids within the tissues & body
fluids. There is stable and unstable cavitation. Stable is the effect of therapeutic ultrasound, which enhances acoustic streaming. Unstable cavitation is when the bubbles collapse
very quickly which releases large amount of energy, this is detrimental to the
soft tissues and doesn't occur if good technique is used.
Overall these effects excites the cell membranes in tissue,
which increases cellular activity. This basically increases metabolic activities
such as healing increase (Watson 2008).
So when should I have ultrasound?
Ultrasound is effective at all phases of healing (except the
bleeding phase):
Inflammation Phase:
This stimulates the mast cells, platelets, white cells with
phagocytic roles and the macrophages (Nussbaum 1997, ter Haar 1999, Fyfe &
Cahal 1982, Maxwell 1992, Watson 2008; Li et al 2003). The increased activity
of these cells means the overall influence of therapeutic ultrasound is
pro-inflammatory rather than anti-inflammatory. Remember inflammation is good
and we need it to heal so the harder it works the faster we heal! (Dyson et al
1999).
Proliferation Phase:
This is the scar production phase. Ultrasound has a
stimulative effect on the fibroblasts, endothelial cells and myofibroblasts
(Ramirez et al 1997, Mortimer and Dyson 1988, Young & Dyson 1990, Young
& Dyson 1990b, Nussbaum 1997, 1998, Dyson & Smalley 1983, Maxwell 1992,
Watson and Young 2008, Watson 2007, 2008, Ng 2011). Is that enough references?! So ultrasound is
also pro-proliferative in the same way that it is pro-inflammatory.
Remodelling Phase:
This phase is when the generic scar that was produced in the
initial stages of healing is refined to adopt the functional characteristics of
the tissue that it is repairing. So a scar in a tendon be adapted to behave
more like a tendon. This phase is not a short one, research has shown that it
can last for a year or more and it is vital for a quality repair (El Batouty et
al 1986, ter Haar 1987). So you could argue this phase is the most important, especially
to prevent future reoccurrences.
Ultrasound has been found to enhance the appropriate
orientation of the newly formed collagen fibres and also to the collagen
profile change from mainly Type III to a more dominant Type I construction,
thus increasing tensile strength and enhancing scar mobility (Nussbaum 1998,
Wang 1998).
So what settings do I use then?
The depth of the target tissue is important as the energy
needed (Intensity setting). If it is a deep tissue then use of 1MHz is best and
if it is superficial then 3MHz is best. The reason for this is that each
frequency has a different half-life depth.
See table below:
|
Depth (cm)
|
3 MHz
|
1 MHz
|
|
2
|
50%
|
|
|
4
|
25%
|
50%
|
|
6
|
|
|
|
8
|
|
25%
|
So what settings are best for what conditions?
(This chart explains this best: (Watson 2002))
What reasons mean that you can’t have Ultrasound?
Don’t ultrasound over the uterus during pregnancy.
Don’t ultrasound over malignancy.
Don’t ultrasound over active bleeding, which usually is 4-6
hours of post injury.
Don’t ultrasound over significant vascular abnormalities:
e.g.: deep vein thrombosis, emboli and severe atherosclerosis.
Don’t ultrasound Haemophiliacs not covered by factor
replacement.
Don’t ultrasound over:
The eyes.
The stellate ganglion (nerves located on either side of the
voice box, at the base of the neck).
The cardiac area in advanced heart disease & where
pacemakers in situ.
The gonads.
Active epiphyses in children (debatable).
Precautions of ultrasound use:
Ensure that the applicator is moved throughout the
treatment. Treatment with a stationary treatment head is considered bad
practice
Continuous ultrasound is not recommended over metal implants
as they may heat up.
So what does the evidence say about the effectiveness for various conditions?
Low Back Pain:
No quality evidence was found supporting ultrasound for pain
or quality of life in non-specific chronic Low Back Pain (Ebadi et al 2014).
Shoulder:
Ultrasound was found beneficial for sub acromial impingement
in the shoulder (Yildirim et al 2013).
Elbow:
Progressive exercise therapy is more effective than
ultrasound when treating chronic tennis elbow (Pienimaki et al 1996).
Systematic review finds potential effectiveness of
ultrasound for tennis elbow (Dingemanse et al 2013).
Hand:
Continuous ultrasound to the hand benefits grip strength in
people with rheumatoid arthritis (RA) (Casimiro et al 2012).
Oral steroids, splinting, ultrasound, yoga & wrist
mobilisation provide short-term relief from carpal tunnel syndrome (O'Connor et
al 2003).
There is poor quality evidence stating: therapeutic
ultrasound is more effective than placebo for carpal tunnel syndrome (Page et
al 2013).
Muscle:
The recovery rate of muscle is 50% greater with therapeutic
ultrasound (Dyson et al 1999).
Bone:
Low intensity pulsed ultrasound reduced fracture healing
time (mean difference in healing time was 64 days to controls) (Busse et al
2002).
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