Interferential Therapy (I...

IFT which stands for Interferential Therapy is one of the types of electrotherapy used for the management of pain. The principle of interferential therapy is to cause two medium frequency currents of slightly different frequencies to interfere with one another. For example, if circuit A carries a current with the frequency of 4000Hz and Circuit B carry a current with a frequency of 3980 Hz, then the low frequency produced will be 20 Hz and this frequency is very useful in pain modulation. A new low-frequency current known as the beat  frequency  is equal to the difference in frequencies between the two medium frequency currents produced in the tissues at the point where the two currents cross.

It is basically used for the treatment of Chronic, Post Traumatic, and Post-surgical pains. The basic principle involves the utilization of effects of low frequencies (<250pps) without painful or unpleasant side effects. The major advantage of IFT is that it produces effects in the tissue, exactly where required without unnecessary and uncomfortable skin stimulation. This technique is widely used to elicit muscle contraction, promote healing and reduce edema.

Vector effect

The interference field is rotated to an angle of 45⁰ in each direction, the field thus covers a wider area. This is useful in diffuse pathology or if the site of the lesion cannot be accurately localized.

Frequency swings

Some equipments allows a variation in the speed of the frequency swing. A rhythmic mode may be a continuous swing from 0 to 100 Hz in 5-10s and back in similar time or it may hold for 1-6s at one frequency followed by 1-6s at another frequency with a variable time to swing between the two.

Constant frequency

Some treatments may be carried out with the interference fixed at a certain frequency. Rhythmic frequency is useful if several types of tissues are to be treated at once. A variation in the frequency also overcomes the problem of tissue accommodation where the response of a particular tissue decreases with time.

Interferential current therapy works by sending small amounts of electrical stimulation to damaged tissues in the body. The therapy is meant to boost the body's natural process of responding to pain, by increasing circulation thus produces hormones that promote healing. IFT delivers intermittent pulses to stimulate surface nerves and block the pain signal, by delivering continuous deep stimulation into the affected tissue. IFT relieves pain, increases circulation, decreases edema, and stimulates the muscles. A frequency of 100Hz may stimulate the large diameter A-beta fibers, which have an effect on the pain gate, and inhibit the transmission of small-diameter nociceptive traffic ( C and A-delta fiber), which effectively closes the gait to painful impulses. Interferential current Increases the circulation of blood thus reduces swelling, by washing away the chemicals that stimulate the nociceptive nerve endings.

The frequency between 1 and 100 Hz is used to contract the normal innervated muscles. Different types of frequencies cause different contractions, a low frequency, causes a twitch, frequency between 5 and 20 Hz causes a partial tetany contraction and frequency from 30 to 100 Hz causes a tetanic contraction. IFT also helps to reduce edema 100Hz frequency promotes vasodilation, thus decreases edema. And a frequency of 10 Hz activates the musculoskeletal pump, used to promote venous and lymphatic return causing reduction of edema. The neurons that make the autonomic nervous system, are small and poorly myelinated like the Aδ and C fibers of the peripheral nervous system and to stimulate the autonomic nervous system, lower frequencies are utilized to increase the blood flow.

The effect of IFT depends upon

·         Frequency

·         Intensity of current

·         Electrode placement

·         Localization of the lesion

Frequency

• 100-150Hz constant or 90-100Hz rhythmic: These frequencies are useful for pain relief, IFT acts on large myelinated fibers in the dorsal horn, blocking off small pain fibers. The higher frequencies have a triggering effect on the endogenous opiates in the mid-brain which inhibit pain.

• 0-10Hz rhythmic or 10- 50Hz rhythmic: These frequencies are useful for muscle stimulation. They produce stimulation of deep, normally innervated muscle tissue with little sensory stimulation. As the frequency increases the contraction changes from a twitch to a tetanic contraction.

• 0-100Hz rhythmic: The range of frequencies produces vasodilatation. This is stimulation and relaxation of vessel walls, giving a sinusoidal effect.

Intensity of current

• The current is increased until the patient feels tingling. As accommodation occurs the intensity is increased to the point of muscle stimulation. The duration of treatment varies between 10 - 20 minutes.

Electrode placement

• The patient is positioned comfortably and the skin is prepared for the treatment. It is cleaned and in case of any skin lesion, the area is insulated with petroleum jelly. Vacuum electrodes or pad electrodes are positioned such that the site for the treatment is accurately located and the two pairs of electrodes are positioned so that the crossing point of the two currents is over or within the lesion.

IFT works in a special way as it uses interferential rather than normal stimulation. The main clinical applications for which IFT appears to be used ar

• Pain Relief in conditions such as causalgia, herpes zoster, neuralgia.
• Cervical spondylosis.
• Osteoarthritis of the knee.
• Ankylosing spondylitis
• Rheumatoid arthritis.
• Frozen shoulder.
• Disc herniation.
• Spinal canal stenosis.
• Muscle Stimulation - prevent muscle wastage, re-education, maintain range of motionStress incontinence
• Reduction of Edema (Condition involving the excess collection of watery fluid in the cavities or tissues)
• Muscle injuries
• Ligamentous injuries

IFT is a common pain-relieving modality without side effects that oral painkillers and anti-inflammatory medications have. Like any other therapeutic modality, it also has some limitations like,

·         Infective condition

·         Malignancy

·         Pacemakers

·         Loss of sensation.

·         Danger of Hemorrhage

·         Large open wounds

·         Dermatological Conditions

·         Pregnant Uterus