Electrotherapy and Physical Modalities
This section tests safe selection, parameter setting, and contraindications for electrical, thermal, acoustic, and mechanical modalities.
Core rules and concepts
- TENS uses gate-control or endorphin mechanisms depending on frequency; check skin, sensation, and pacemaker status.
- Interferential current uses two medium-frequency currents producing a low-frequency beat.
- Neuromuscular electrical stimulation can recruit denervated or disuse-atrophied muscle, but denervated muscle requires long-pulse currents.
- Ultrasound: intensity × effective radiating area = power; thermal effects need continuous mode, non-thermal pulsed mode is used for healing.
- Cryotherapy reduces temperature, pain, and swelling; contraindicated in cold hypersensitivity, Raynaud phenomenon, and compromised circulation.
- Contraindications for diathermy include pacemakers, metal implants, pregnancy, and malignancy.
Worked example
Ultrasound is prescribed at 1.0 W/cm² with an effective radiating area of 5 cm². Power = 1.0 × 5 = 5 W. For a 5-minute treatment, the machine must be set to 5 W and 5 minutes, with continuous movement over the target area. Reasoning: intensity alone does not determine dose; the emitting area determines total power. Increasing intensity without checking area can overheat tissue. The physiotherapist should also screen for metal, pacemakers, pregnancy, and impaired sensation.
Traps that cost marks
- Applying ultrasound over the epiphyses in children or over the eye, heart, or pregnant uterus.
- Using diathermy near a pacemaker or metal implant.
- Confusing TENS pain relief with motor-level stimulation.
- Leaving electrodes over broken skin or applying cryotherapy to insensitive skin.