Transcutaneous Electric Nerve Stimulation (TENS)
TENS variations are often described by their technical characteristics: high frequency, low intensity (conventional TENS) or low frequency, high intensity (acupuncture-like TENS, AL-TENS) (Walsh et al., 2009).
How TENS Addresses Pain:
- Gate control theory, established in 1965, proposes a gate consisting of excitatory and inhibitory synapses that exist in the dorsal horn of the spinal cord (Walsh et al., 2009). This gate can regulate the amount of nociceptive traffic (painful stimuli) transmitted to the brain. This gate could be closed by non-noxious stimuli (e.g. touch, pressure and electrical currents), and block potential nociceptive stimuli.
- Increased release of endorphins through heat transmission, possibly more localized to the area of the pain
- Physiologically, conventional TENS selectively activates non-noxious low threshold afferent nerve fibers in the skin (Aβ-fibers). When administering TENS, Aβ nerve fiber activity is reported by the client to feel like a strong electrical paresthesia (pins and needles) beneath the electrodes (Walsh et al., 2009). AL-TENS is intended to generate a muscle twitch to activate small diameter afferent nerve fibers in muscles (Aδ) and descending pain inhibitory pathways. AL-TENS is administered at low frequency and high intensity currents over muscles, without pain.
Placement for TENS (Borst, n.d.)
- Can either be placed directly over the area of pain, or pads can “sandwich” the pain
- Pad placement effects the depth of the
- Close placement=superficial current
- Further placement= deep current
Inferential current (IFC)
Developed in the 1950s, IFC is most commonly used for pain relief (Kitchen, 2001). IFC is also claimed to reduce inflammation, and assist tissue repair (including bone fractures), and reeducate muscle (especially with incontinence).
How IFC Addresses Pain:
- IFC delivers current to deep-seated structures through an amplitude-modulated interference wave typically with the use of four electrodes (Kitchen, 2001).
- The wave is created by two out of phase currents that collide with each other to generate an interference with a frequency that can penetrate through the skin to deeper structures and even excite neurons.
- Use of IFC should generate a strong but comfortable electrical paranesthesia at the site of the pain, to generate Aβ activity (Kitchen, 2001).
Image 1. Interference Wave (Kitchen, 2001)
Evidence to Support Use of Electrical Stimulation (TENS and IFC) for Pain
- A Cochrane systematic review found preliminary evidence that TENS reduces pain intensity over and above that seen with no treatment for acute pain (Walsh et al., 2009). Definitive conclusions were limited by the high risk of bias, inadequate sample sizes, and unsuccessful blinding of treatment interventions. Although the use of TENS as a potential treatment option for managing acute pain is debatable based on these results, it can be self-administered, is safe, and can be inexpensive (Walsh et al., 2009).
- Current evidence suggests that overall TENS and IFC have similar effects on pain and improvements in functional outcome measures (de Almeida et al., 2018). There is a need for larger, well-designed and standardized studies to establish the best parameters for pain management due to limitations in current literature.
General Contraindications for Using Electric Stimulation: cardiac pacemakers (in areas close to device), near the carotid sinus, near, central venous and peripheral intravenous central catheter lines, metal implants, pregnancy, severe obesity, active bleeding, cancer, over the spine (Borst, n.d.)
General Precautions for Using Electric Stimulation: muscle fatigue, peripheral nerve pathology, cognitive impairment, allergic reactions, decreased sensation, open wounds, tendon or nerve repair surgery (need to wait 4-6 weeks typically to not displace tendon or nerve repair) (Borst, n.d.)
Borst, M. (n.d.). Test prep for the CHT exam (3rd ed.). American Society of Hand Therapist.
de Almeida, C. C., da Silva, V. Z. M., Júnior, G. C., Liebano, R. E., & Durigan, J. L. Q. (2018). Transcutaneous electrical nerve stimulation and interferential current demonstrate similar effects in relieving acute and chronic pain: a systematic review with meta-analysis. Brazilian journal of physical therapy, 22(5), 347-354.
Kitchen, S. (Ed.). (2001). Electrotherapy E-Book: evidence-based practice (11th ed.). Elsevier Health Sciences.
Snyder, A. R., Perotti, A. L., Lam, K. C., & Bay, R. C. (2010). The influence of high-voltage electrical stimulation on edema formation after acute injury: a systematic review. Journal of sport rehabilitation, 19(4), 436-451.
Walsh, D. M., Howe, T. E., Johnson, M. I., Moran, F., & Sluka, K. A. (2009). Transcutaneous electrical nerve stimulation for acute pain. Cochrane Database of Systematic Reviews, (2).
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