Therapeutic Modalities and Electrotherapy
This domain tests parameter literacy and safety. Most marks are lost not on the concept of a modality but on wrong frequency, wrong intensity, wrong duration, or a missed contraindication.
Electrical stimulation parameters
- Conventional TENS: 80–120 Hz, pulse width 50–100 microseconds, sensory-level intensity, proposed to work through segmental pain gating.
- Low-frequency or acupuncture-like TENS: 2–4 Hz, higher intensity producing visible muscle twitch, associated with opioid-mediated analgesia.
- Interferential current: two medium-frequency circuits producing a beat frequency at the intersection; four electrodes in a criss-cross arrangement.
- NMES for strengthening: 20–50 Hz with sufficient intensity for a visible contraction; Russian current uses 2500 Hz carrier delivered in 50 Hz bursts. Contraindications across electrotherapy: pacemaker or implanted electronic device, pregnancy over the abdomen and pelvis, malignancy in the treatment area, active bleeding, transcerebral or carotid sinus application, and areas of impaired sensation.
Ultrasound
1 MHz penetrates 3–5 cm and suits deeper tissue; 3 MHz penetrates 1–2 cm and suits superficial structures. Use 0.1–0.5 W/cm² pulsed (typically 20% duty cycle) for acute tissue and 0.5–2.0 W/cm² continuous for chronic tissue. Dose relates to intensity multiplied by the effective radiating area of the head, and treatment time is usually 5–10 minutes. Avoid application over growth plates, the eye, gonads, the pregnant uterus, malignancy, thrombophlebitis, infection and the heart.
Thermal and cryotherapy
Cryotherapy for 10–20 minutes produces vasoconstriction and analgesia; avoid in cold hypersensitivity, Raynaud's phenomenon and peripheral vascular disease. Superficial heat is contraindicated in acute inflammation, bleeding disorders and impaired sensation.
Worked example
Chronic Achilles tendinopathy in an adult with a 5 cm² ultrasound head. Reasoning: the tissue is deep, so choose 1 MHz. The condition is chronic, so use continuous mode at 1.0 W/cm² for about 8 minutes, keeping the head moving. If the complaint were acute paratenon inflammation, switch to 3 MHz pulsed at 0.2–0.5 W/cm² and shorten the session.
Traps that cost marks
- Reversing the 1 MHz/3 MHz depth relationship.
- Using continuous ultrasound on acute inflammation.
- Forgetting to check for a pacemaker before applying any electrical current.