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 a frequency of 4000Hz and Circuit B carries 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 equipment 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 a 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.

Frequency sweep
The principle of using the sweep is that the machine is set to automatically vary the stimulation frequency, it uses either pre-set or user-set sweep ranges. The sweep range should be appropriate to the desired physiological effects.

The pattern of the sweep makes a significant difference in the stimulation received by the patient. Most machines offer several sweep patterns:

• Triangular sweep pattern.
• Rectangular Sweep Pattern.
• Trapezoidal Sweep Pattern.

In the 'triangular' sweep pattern, the machine gradually changes from the base to the top frequency, for 6 seconds. Although some machines offer 1 or 3-second options.  All frequencies between the base and top frequencies are delivered in equal proportion.
Rectangular sweep is a different stimulation pattern in which the base and top frequencies are set, but the machine then 'switches' between these two specific frequencies rather than gradually changing from one to the other
One will deliver a full range of stimulation frequencies between the set frequency levels and the other will switch from one frequency to the other. The 'trapezoidal' sweep is effectively a combination of these two.

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 producing 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 reducing swelling, by washing away the chemicals that stimulate the nociceptive nerve endings.

A 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, a frequency between 5 and 20 Hz causes a partial tetany contraction and a frequency from 30 to 100 Hz causes a tetanic contraction. IFT also helps to reduce edema 100Hz frequency promotes vasodilation, thus decreasing edema. And a frequency of 10 Hz activates the musculoskeletal pump, used to promote venous and lymphatic return causing a reduction of edema. The neurons that make up 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

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 till the patient feels tingling, further as accommodation occurs the intensity is increased slowly to the point of muscle stimulation. The duration of treatment varies between 10 - 20 minutes.

Electrode placement
The patient is placed in a comfortable position and the skin is prepared for the treatment. The skin is cleaned, in case of any skin lesion, the area is insulated with petroleum jelly. Vacuum electrodes or pad electrodes are placed accurately at the treatment site 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 are as:

• Pain Relief in conditions such as causalgia, herpes zoster, and 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 motion stress incontinence
• Reduction of Edema (Condition involving the excess collection of watery fluid in the cavities or tissues)
• Muscle injuries
• Ligamentous injuries

Interferential therapy is widely used but the Physiotherapist should know how to use it depending on the condition. Interferential Therapy uses the significant physiological effects of low frequency (<250pps) electrical stimulation of nerves.

Effects of Interferential Therapy:

• Reduces pain and inflammation.
• Increases blood circulation.
• Causes vasodilation.
• Removes waste substances from the affected area.
• Increases metabolic rate.
• Decreases blood pressure.
• Treats chronic ligamentous lesions.
• Cures edema and hematoma.
• Improves restricted movements of joints.
• Increases muscle stimulation.
• Restores the lost movement of muscles.

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.
• Arterial disease.
• Febrile condition.
• Deep vein thrombosis.
• During menstruation.
• Unreliable patient.
• Fewer.