In general terms, combination therapy involves the simultaneous application of ultrasound (US)
with an electrical stimulation therapy. In Europe, Diadynamic Currents are frequently utilised,
but in the UK, US is most often combined with
bipolar Interferential Therapy (IF).
There is a significant lack of published material in
this area. And much of the information herein is
anecdotal or based on the experience of those who
use the modality frequently. Broadly, the effects of
the combined treatment are those of the individual
modalities. There is no evidence at present for any
additional effects which can only be achieved when
the modalities are used in this particular way.
It is suggested that:
• by combining US with IF, the advantages/effects
of each treatment modality can be realised, but lower intensities are used to achieve the
• the accommodation effects that accompany IF treatment are reduced (or even eliminated)
The main advantages on such a combination are said to be:
• in localising lesions (especially chronic) ie.diagnostic use
• in ensuring accurate localisation of US treatment- to provide increased
accuracy/effectiveness in treating
deeper lesions
• in treating trigger points
Possible Explanation:
Exposure of a peripheral nerve to US
reduces the membrane resting potential by
increasing its permeability to various ions
(especially Sodium (Na+) and Calcium
(Ca++). By virtue of this adjusted
permeability, the nerve membrane is taken
closer to its threshold (the point where it
depolarises, though doesn’t usually make
the nerve fire. The simultaneous
application of the Interferential current
through the nerve induces the
depolarisation potential, though it will take
a smaller current than usual to achieve this due to the potentiation effect of the ultrasound.

This can easily be demonstrated. If both the US and IF are applied, and during the application,
the US is turned down to zero, the sensation produced by the IF will diminish even though the IF
intensity has not been changed. The intensity of the IF sensation returns when the US is turned
up again.
The combination of US with IF appears to give rise to less adverse treatment effects than are
associated with the combination of US with Diadynamic Currents, or other electrical
stimulations. It has also been suggested that a greater effective treatment depth can be achieved
with the US - IF combination though there is no direct evidence for such a claim..
In summary, it would appear that by combining the two treatment modalities, none of the
individual effects of the treatments are lost, but the benefit is that lower treatment intensities can
be used to achieve the same results, & there are additional benefits in terms of diagnosis &
treatment times.
A) Diagnostic Use of Combined Therapy
It is suggested that a continuous US output of 0.5W/cm2 should be used for this procedure,
though numerous practitioners do claim to have achieved significant results with lower
intensities. A frequency of 1MHz is preferable if available as it gives more effective penetration
into the tissues.. The IF output is most commonly set to 100Hz (with no sweep) using a bipolar
Place the indifferent electrode (the normal IF pad electrode) in a position so that the current can
pass through the tissue in question. As a general guide, it can be placed on the same aspect of the
limb (more usual for superficial lesions) or on the opposite side of the limb (for deeper lesions).
Turn on the US first, followed by the IF
Starting with the US head distant from the lesion, gradually increase the IF output intensity until
the `normal' tingling is encountered by the patient.
Move towards the lesion site, noting any areas of increased sensitivity, local or referred pain.
The point of maximal sensitivity is assumed to be the focal point of the lesion, though it will not
provide information as to the precise tissue in question, nor to depth – only a ‘geographical’
location. This position is usually consistent and reproducible.
B) Treatment with Combined Therapy
Diagnostic and therapeutic uses of Combination Therapy need not be used together. As a
treatment, it is appropriate when the therapeutic effects of US and those of IF are both justified.

At the present time, and in the absence of any specific evidence of additional effect when used in
combination, this would seem to be the sole justification for the modality.
The individual doses for the US and IF should be those which are appropriate for the lesion and
the required effects. There is no evidence that ‘special’ treatment doses are required. It should be
noted however, that the intensity of the IF required to achieve the usual effect is likely to be
lower than normal.
Some manufacturers suggest that it is not necessary to incorporate a swing in the IF dose as the
effect of accommodation is minimised. There does not appear to be any reason why an
appropriate frequency swing should not be used if it is appropriate to the effect required..
If the treatment times are dissimilar, there is a potential problem in that the US component will
usually finish first, leaving the IF element to continue in isolation. When the required treatment
times are similar, the combination of the modalities can save time and effort (even without
additional effect). When they are dissimilar, it may be as effective to apply two separate
It is important to observe the safe & effective U/S treatment technique during combined
treatment i.e. always using a moving treatment head, maintain effective contact, & maintain the
perpendicular relationship between the treatment head & the patients skin whenever possible.
Treatment Example :
Patient with an acute lesion/tear of the lateral ligament of the ankle. Ultrasound is justified on the
basis that it will promote the inflammatory/repair process and interferential is used for its effect
in reducing acute pain.
US dose (based on normal dose calculations)
3MHz, 0.2 W/cm2, Pulse 1:4, 10 minutes
Interferential dose (for acute pain)
90 – 130Hz, bipolar, 10 minutes
Interferential pad electrode placed medially at the ankle, US treatment head applied over the torn
component(s) of the lateral ligament.
The treatment could be more effective than either one modality in isolation, though there is no
evidence that by using them simultaneously, there is any advantage over using them sequentially.
There do not appear to be any specific contraindications for combination therapy other than
those for the individual modalities.