Interferential therapy (IFT)

What is IF current?

IF Current

• IF (Interferential) current = interference of 2 medium-frequency currents → produces a low-frequency current.

• Usually uses a base current of 4000 Hz.

• Why medium frequency?

  • More comfortable than low-frequency current.

  • Interference in tissues is theorised to allow greater depth penetration.

How IF is generated

Generating IF

• AMF (Amplitude Modulated Frequency) = the effective component of IF.

• AMF = difference between the 2 frequencies.

• Example:

  • 4000 Hz − 4100 Hz = 100 Hz AMF.

How/when to modulate IF machines

Modulating IF

• Most IF machines can sweep/alter the AMF over time → frequency sweep.

• Different sweep patterns:

  • 6:6 → slow increase + decrease over 6 sec

  • 1:1 → 1 sec at one dose, then 1 sec at another

  • 6:6 → 6 sec at one dose, then 6 sec at another

• Clinical value/effectiveness of frequency sweeps is questionable.

How many electrodes and where?

IF — Electrodes

• 2 or 4 electrodes can be used.

• With 4 electrodes, position them so the 2 currents interfere.

• Suction electrodes don’t add to the treatment → they only facilitate application.

IFT — Electrode Placement

• Place electrodes to stimulate:

  • Nerve root → if treating pain

  • Motor point

• 4 channels can be used to achieve greater depth/joint penetration.

IF — Evidence & Clinical Use

• Moderate-quality evidence supports IFT for:

  • Knee OA → significant short-term pain reduction (Chen et al., 2022).

  • Chronic non-specific low back pain → 1.57-point pain reduction vs placebo (Rampazo et al., 2023).

• IFT appears to work through conventional nerve stimulation, similar to TENS.

• Most effective as an adjunct, not standalone treatment.

• No evidence for unique “interferential” effects.

• Limited evidence for:

  • Muscle strengthening

  • Increased circulation

  • Wound healing

• Cost-effectiveness vs TENS is questionable (NICE, 2022).

• Best used as part of multimodal therapy.

IFT & Modern Pain Science

Pain mechanisms:

• Gate control theory → main explanation.

• Activates A-beta fibres → inhibits nociception at the spinal level.

• May influence descending pain modulation.

Biopsychosocial model:

• Patient expectations influence outcomes.

• Therapeutic relationship can enhance treatment effects.

• Consider central sensitisation in chronic pain.

Evidence-based approach:

• No research specifically examines IFT pain-relief mechanisms.

• Current understanding is extrapolated from TENS research.

• Set realistic expectations about outcomes.

IFT — Evidence-Based Parameters

• Carrier frequency: 4000 Hz

• AMF for pain: 100 Hz constant → most evidence

• Duration: 20–30 min

• Frequency: 3–5×/week for 2–4 weeks

• Intensity: Strong but comfortable, just below pain threshold

• Key finding: Exact parameters may be less important than previously thought.

• Focus on patient comfort + treatment adherence.

• 2 vs 4 electrodes: similar effectiveness.

IF treatment dosages

IFT — When to Use

Consider IFT for:

• Chronic musculoskeletal pain

• As an adjunct to exercise/manual therapy

• Patient preference after education

• When TENS unavailable/not tolerated

Do NOT use IFT:

• As the primary treatment for complex pain

• Expecting unique “interferential” effects

• Conditions with poor evidence: fibromyalgia, wound healing, incontinence

Patient selection:

• Realistic expectations → modest benefits

• Commitment to multimodal treatment

• No contraindications

IFT — Tissue Healing

• Limited evidence for tissue-healing effects:

  • No strong evidence for enhanced bone healing

  • Wound healing benefits not established

  • Circulation improvements not consistently demonstrated

Modern approach:

• Focus on optimal loading + movement

• Address nutrition, sleep + stress

• IFT may help patients participate in active treatment

Clinical application:

• Use IFT to reduce pain barriers to rehabilitation

• Combine with evidence-based interventions

• Monitor functional outcomes, not just pain.

IFT — Hazards & Detrimental Effects

• Burns

• Increased pain

• Nausea + vomiting

• Dizziness

• Headaches / migraine

• Neurological effects

IFT — Recent Safety Concerns

• Reported adverse effects:

  • Unusual neurological effects lasting 4–5 hrs post-treatment

  • Possible interaction with opioids (tramadol case report)

  • Balance disturbances in elderly patients

Extra precautions:

• Elderly with cognitive/balance deficits

• Patients taking opioid medication

• Patients with pre-existing neurological conditions

Safety:

• IFT included in NHS adverse-event surveillance

• Importance of standardised reporting.

Precautions and contraindications

Precautions:

• Perform sharp/blunt skin test.

• Check skin integrity → allergies, eczema, skin lesions.

• DO NOT place electrodes over the anterior neck.

• Set all parameters before switching on/connecting electrodes to the patient.

Contraindications

Absolute contraindications:

• Pregnancy → around foetus / 1st trimester

• Active implants → e.g. pacemakers

• Epilepsy → do not apply around the neck

• Actively bleeding tissue

Local contraindications:

• Malignancy

• Eyes

• Testes

• Active epiphysis

Use caution with:

• Local circulatory insufficiency

• Devitalised tissue