6.2 Electrical Stimulation Modalities
Key Takeaways
- High-rate (conventional) Transcutaneous Electrical Nerve Stimulation (TENS) at 50-150 Hz with short phase duration produces sensory-level analgesia via gate-control; low-rate (acupuncture-like) TENS at 1-4 Hz with longer phase duration produces motor-level analgesia via endogenous opioid release.
- Neuromuscular Electrical Stimulation (NMES) for muscle re-education uses biphasic pulsed current or 2500 Hz medium-frequency burst-modulated current (Russian); typical on/off ratios are 10 seconds on / 50 seconds off to limit fatigue.
- Interferential Current (IFC) crosses two medium-frequency channels (e.g., 4000 and 4100 Hz) to produce a low-frequency beat in deep tissue with less skin sensation than direct low-frequency stimulation.
- Iontophoresis uses continuous direct current to drive ionized medications through the skin; dexamethasone phosphate is negatively charged and is delivered from the negative (cathode) electrode.
- Electrical stimulation is contraindicated over a demand-type pacemaker or implanted cardiac defibrillator, the carotid sinus, transcerebrally or transthoracically, over a pregnant uterus, on broken or insensate skin without precaution, and over active deep vein thrombosis.
Electrical Stimulation Modalities
Electrical stimulation (e-stim) items on the NPTE-PTA reward two skills: (1) selecting the correct modality and parameter set for a stated goal, and (2) recognizing contraindications. The same physical hardware can deliver pain control, muscle contraction, edema reduction, or drug delivery depending on settings.
TENS: Transcutaneous Electrical Nerve Stimulation
TENS targets pain. Two parameter families dominate the exam.
| Mode | Pulse rate | Phase duration | Intensity | Mechanism | Onset / duration of relief |
|---|---|---|---|---|---|
| High-rate (conventional) | 50-150 Hz | 50-100 µs | Sensory (strong tingle, no contraction) | Gate-control (A-beta fibers) | Fast onset, short duration after unit is off |
| Low-rate (acupuncture-like) | 1-4 Hz | 150-300 µs | Motor (visible twitch) | Endogenous opioid release | Slower onset, longer carryover |
| Brief intense | 80-150 Hz | >150 µs | Strong, near tetany | Rapid analgesia | Used for short painful procedures |
If the POC says "chronic low back pain, wearable unit for home use," low-rate TENS is a strong fit for longer carryover. If the POC says "acute postoperative pain, immediate sensory relief," high-rate TENS is the better choice.
NMES: Neuromuscular Electrical Stimulation
NMES produces a tetanic muscle contraction to address weakness, atrophy, motor re-education, or spasticity management.
- Waveform: symmetrical or asymmetrical biphasic pulsed current; alternatively, 2500 Hz medium-frequency burst-modulated current ("Russian stimulation").
- Pulse rate: 35-80 Hz to achieve fused tetanus.
- Phase duration: 200-400 µs for large muscles such as the quadriceps.
- On/off ratio: start at 1:5 (e.g., 10 sec on / 50 sec off) to limit fatigue; progress toward 1:1 with strengthening tolerance.
- Ramp: 1-3 second ramp up/down to make contractions comfortable.
- Intensity: to a strong, visible contraction the patient tolerates.
Classic NMES applications include post-operative quadriceps activation after Total Knee Arthroplasty (TKA) or Anterior Cruciate Ligament (ACL) reconstruction, shoulder subluxation after stroke, and dorsiflexor activation for foot drop.
IFC: Interferential Current
IFC crosses two medium-frequency channels to generate a therapeutic low-frequency "beat" in the tissue where the channels intersect. Because the carrier frequency is high (around 4000 Hz), skin resistance is lower and patients tolerate higher intensities than with direct low-frequency stimulation. IFC is commonly used for deep pain control and edema management, with four electrodes arranged so the target tissue lies at the intersection.
Iontophoresis
Iontophoresis uses continuous direct current to push ionized medications across the skin. The key NPTE-PTA points:
- The drug ion and the delivery electrode must share the same polarity ("like repels like").
- Dexamethasone phosphate is negatively charged and is therefore placed under the negative (cathode) electrode for delivery.
- Lidocaine is positively charged and is delivered from the positive (anode).
- Typical dose is 40 milliamp-minutes (e.g., 4 mA for 10 minutes).
- Skin irritation is more common under the cathode; inspect skin before and after treatment.
Electrode Placement Principles
- Use the largest electrodes the area allows; current density rises as electrode size falls.
- Maintain at least one electrode-width of skin between electrodes to prevent the current from concentrating at the surface.
- For NMES strengthening, place electrodes over the muscle belly and motor point, parallel to muscle fibers.
- For TENS pain control, options include over the painful area, surrounding it, on the dermatome, on the contralateral side, or at trigger points.
Contraindications
| Contraindication | Reason |
|---|---|
| Demand-type pacemaker or implanted cardioverter-defibrillator (ICD) | Risk of device interference and arrhythmia |
| Over the carotid sinus | Vagal reflex, hypotension |
| Transcerebral or transthoracic placement | Cardiac and central nervous system risks |
| Over the pregnant uterus or low back during pregnancy | Risk to fetus |
| Over active malignancy (relative for palliative TENS only) | Potential to stimulate tumor blood flow |
| Over deep vein thrombosis | Risk of embolus |
| Over broken or irritated skin (with iontophoresis especially) | Burns, irritation |
| Areas of impaired sensation without precaution | Patient cannot warn of overdose |
| Confused or non-communicative patient | Cannot give safety feedback |
A pacemaker is an absolute contraindication for most clinical settings; some current guidelines allow distal extremity TENS in selected patients with cardiology clearance, but on the NPTE-PTA, pick the option that withholds e-stim and contacts the supervising PT.
A PTA is treating a patient three weeks after a Total Knee Arthroplasty (TKA) with a 2-/5 quadriceps lag. The supervising PT's POC calls for electrical stimulation to assist quadriceps re-education. Which parameter set is most appropriate?
A patient with chronic lateral epicondylitis has a corticosteroid iontophoresis treatment ordered with dexamethasone phosphate. Where should the PTA place the dexamethasone-loaded electrode?
Which patient is the LEAST appropriate candidate for transcutaneous electrical nerve stimulation (TENS)?