Interferential Current Therapy; Mechanism, Uses, Warning

Interferential current therapy/ Interferential therapy (IFT) is a noninvasive therapy using simultaneously two or more medium-frequency currents passing through tissue. Interferential therapy (IFT) is a commonly used modality in physiotherapy practice for pain? relief. Pain relief is believed to be achieved through the production of endogenous opioids like endorphins and enkephalins. By controlling the interfered area of the current flows, selective stimulation is possible in target muscles, including deep muscles. However, controlling the interfered area or the intensity of the current precisely is still lacking. Using simulations based on a biological model of the thigh as well as electrical muscle stimulation (EMS) experiments, we investigated the influence of electrode area ratio in changing the interfered area of the currents.

Interferential current (IFC) therapy is a form of transcutaneous electrical stimulation using medium frequency current, generally at about 4 kHz^{[rx], [rx])}. The interaction of 2 slightly different medium-frequency currents generates an amplitude-modulated low-frequency current (0–250 Hz). Because the kHz-region has low skin impedance, amplitude-modulated frequency currents reach deeper tissues and relieve various musculoskeletal pains, fibromyalgia, and knee osteoarthritis^{[rx],[rx],[rx])}. These types of pain? are related to the muscle fatigue? that results from metabolic, energetic, and structural changes in muscles; these changes are due to deficiencies in oxygen and nutrients supplied by the blood vessels, or to altered efficiency of the nervous system^[rx]. A consistently fatigued muscle can develop various disorders and disturbances in the microcirculation that can lead to the sensitization of pain? receptors, discomfort, and muscle stiffness?^[rx]. Interferential therapy (IFT) is a commonly used modality in physiotherapy practice for pain? relief. Pain relief is believed to be achieved through the production of endogenous opioids like endorphins and enkephalins. ^[rx].

Mechanism of Action of Interferential Current Therapy

It is suggested that by adjusting the frequency produced in the interference zone, it is possible to influence a range of different nerves. By changing the type of nerve which is primarily stimulated, the physiological outcome of the stimulation is modified, and hence, so is the therapeutic outcome. Frequencies can be utilized which primarily activate motor nerves, resulting in a muscle stimulation ranging from LF twitching (<15 Hz) to a tetanic, sustained contraction (>40 Hz) each of which has their therapeutic uses. ^[rx]

There is at present, no evidence to suggest that muscle stimulation with electrical stimulation is anymore (or less) effective than by active exercise, but it can be utilized as a means of ensuring the muscle activity level is raised. This, in turn, will influence the local blood flow as a normal physiological response to an adjusted metabolic rate. Frequency ranges from 1-150 Hz or more can be employed in this respect, though it is suggested that clinically, the most appropriate ranges are between 10 and 20 or 25 Hz. At the lower end of this scale, a rapid muscular twitching will be produced, whilst at the upper end, partial tetany will result. Using appropriate frequencies, sensory nerve stimulation can be achieved, thereby producing a mechanism to activate the pain? gate (e.g. between 80-130 Hz) and opioid (<10 Hz) mechanisms which are associated with physiological pain relief. ^[rx]

Types of Interferential Current Therapy

• Static interference – electrodes are immobile during the treatment and affect a single spot between them
• Mobile or kinetic interference – has a greater therapeutical effect, and the physical therapist moves the electrodes manually
• Dynamic interference – the procedure is automatized

Interfering current is similar to dynamic current, but with stronger and deeper effect along with better sustainability when combined with vibrational massage. Interfering current stimulates callus creation, thus enhancing the bone tissue growth.

Indications of Interferential Current Therapy

Pain? relief

• Electrical stimulation for pain? relief has widespread clinical use, thought the direct research evidence for the use of IFT in this role is limited. Logically one could use the higher frequencies (90-130Hz) to stimulate the pain gate mechanisms & thereby mask the pain symptoms.
• Alternatively, stimulation with lower frequencies (2-5Hz) can be used to activate the opioid mechanisms, again providing a degree of relief. These two different modes of action can be explained physiologically & will have different latent periods & varying duration of effect.
• It remains possible that relief of pain? may be achieved by stimulation of the reticular formation at frequencies of 10-25Hz or by blocking C fiber transmission at >50Hz.

Muscle stimulation

• Bellew et al (2012) evaluated the stimulatory effects of IFT and various Burst Mode currents in terms of their capacity to generate significant quality muscle contraction, the results were supportive of IFT as a treatment option.
• The choice of treatment parameters will depend on the desired effect. The most effective motor nerve stimulation range with IFT appears to lie between approximately 10 and 20, maybe 10 and 25Hz. Stimulation below 10Hz results in a series of coarse twitches which may be of clinical benefit, though it has yet to be unequivocally demonstrated with IFT.
• Stimulation at higher frequencies than that needed to bring about a partial tetany (usually around 20 or 25Hz) can generate a strong tetanic contraction, which might be considered beneficial to assist patient appreciation of the required muscle work, but again, in terms of IFT intervention, it has yet to be demonstrated that this contraction level is needed over and above a partial tetany.

Increased local blood flow

• Most of the work that has been done involves laboratory experimentation on asymptomatic subjects, and most blood flow measurements are superficial i.e. skin blood flow. Whether IFT is actually capable of generating a change (increase) in blood flow at depth remains questionable.
• The elegant experimentation by Noble et al (2000) demonstrated vascular changes at 10–20Hz, though was unable to clearly identify the mechanism for this change. The stimulation was applied via suction electrodes, and the outcome could, therefore, be as a result of the suction rather than the stimulation, though this is largely negated by virtue of the fact that other stimulation frequencies were also delivered with the suction electrodes without the blood flow changes.
• The most likely mechanism is via muscle stimulation effects (IFT causing muscle contraction which brings about a local metabolic and thus vascular change). The possibility that the IFT is acting as an inhibitor or sympathetic activity remains a theoretical possibility rather than an established mechanism.
• Based on currently available evidence, the most likely option for IFT use as a means to increase local blood flow remains via the muscle stimulation mode, and thus the 10-20 or 10-25Hz frequency sweep options appears to be the most likely beneficial option.

Reduction of edema?

• IFT has been claimed to be effective as a treatment to promote the reabsorption of edema? in the tissues. Again, the evidence is very limited in this respect and the physiological mechanism by which it could be achieved as a direct effect of the IFT remains to be established.
• The preferable clinical option in the light of the available evidence is to use the IFT to bring about local muscle contraction(s) which combined with the local vascular changes that will result could be effective in encouraging the reabsorption of tissue fluid. The use of suction electrodes may be beneficial but also remains unproven in this respect.
• Relaxing muscles spasms –  From sciatic nerve pain? to impinged nerves in the shoulder, IFT can help relax and reduce muscle spasms.
• Preventing or slowing tissue atrophy? due to disuse – Since IFT is able to produce contractions that mimic the body’s movements, this helps prevent atrophy? such as stroke? patients recovering the use of their limb(s).
• Increasing blood circulation – By activating the muscles, IFT enhances blood flow and can be used in post-recovery for athletes and the typical patient population.
• Re-educating muscles, such as in situations where a muscle injury limited its use – IFT can be used to initiate muscle recruitment, for example, research has shown that the use of IFT helps patients regain strength following a total knee arthroplasty (TKA).
• Maintaining or increasing the range of motion – Electrotherapy can be used to aid in increasing a patient’s range of motion. Research has shown that IFT is helpful in improving motor recovery and range of motion in patients with hemiplegia.
• Reducing symptomatic, chronic?, intractable pain?
• Lowering acute? pain? related to trauma
• Lessening acute? pain? related to surgery
• Hematoma
• Chronic? ligamentous ulcer?. সহজ বাংলা: শরীরের অস্বাভাবিক দাগ, ক্ষত বা ফোলা অংশ।" data-rx-term="lesion" data-rx-definition="A lesion is an abnormal area of tissue such as a spot, wound, patch, lump, or ulcer. সহজ বাংলা: শরীরের অস্বাভাবিক দাগ, ক্ষত বা ফোলা অংশ।">lesion?
• Trigger spot
• Stress incontinence – contraction of pelvic floor muscle
• Delayed union – in case of fracture? to stimulate the union
• Helping with blood flow and improving circulation
• Facilitating the repair of muscle and other body tissues
• Improving the effectiveness of delivering prescription? drugs – electromotive drug administration (EMDA)

Contraindications of Interferential Current Therapy

As with any rehabilitative modality, electrical stimulation has a list of contraindications. The IFT as described here should be used subject to these contraindications:

• It should not be used to treat symptomatic local pain? unless the cause of the pain has been clearly diagnosed.
• IFT should not be used in areas of the body where cancerous lesions exist.
• The treatment should not be applied in areas of the skin that are swollen, infected, or inflamed (e.g. varicose veins)
• Patients suspected of having serious infectious diseases or diseases that require heat or fevers to be suppressed should not be treated with IFT.
• IFT current should not be applied to the anterior neck (carotid sinus) or through the head.
• Women who are pregnant should avoid IFT treatment, as safe use has not been established for pregnancy.
• Patients with cardiac demand pacemakers should not be treated using powered muscle stimulators.
• IFT waveforms should not be used on patients who have cardiac demand pacemakers.
• Patients who have an allergic response to the electrodes, gel or tape
• Application over the anterior aspect of the neck or carotid sinus
• Deep vein thrombosis?
• Pregnant uterus
• Danger of hemorrhage

References