TENS Therapy: An Introduction

Strictly speaking TENS is a tool, not a therapy. One should always try to select the best tool for the job but here as elsewhere the skill of the craftsman is more important than all of the bells and the whistles.

TENS is an acronym for Trans-Cutaneous Electrical Nerve Stimulation, a tool used for neuromodulation, which is making a comeback in the field of pain management. The first modern clinical TENS units were introduced in 1974 and were put to a number of uses with mixed success. As a result TENS treatments of all types tended to fall out of favor (a case of throwing the baby out with the bath water).


The basic TENS unit comprises a pulse generator (usually square wave) and either 2 or 4 electrodes. The pulse generator usually has independent controls for adjusting the voltage applied, the pulse width and the rate of stimulation. Increasing either the voltage or the pulse width has the effect of increasing the amount of energy delivered and also the area stimulated. Adjusting the rate of stimulation will change the perception of the stimulation by favoring one group of nerves over another. Large myelinated sensory nerves are capable of responding to higher rates of stimulation. Non-myelinated sensory nerves, autonomic nerves and motor nerves usually respond better to lower rates of stimulation. All of the nerves eventually transmit signals back into the spinal cord and eventually back up to the brain, which cause changes in nerve activity and nerve chemistry. The potential uses of TENS therapy are limited to a large extent by the impedance of skin and subcutaneous tissues so that only relatively superficial structures can be effectively stimulated.


The most important thing to remember about TENS is that strictly speaking it is a tool and not a therapy. As such the degree of pain relief achieved will depend on the condition being treated as well as the skill of the therapist. A useful analogy is that using a hammer to insert a screw into a piece of wood is likely to produce unsatisfactory results not because a hammer is an unreliable tool or because screws are not good anchoring devices, but simply because a different tool would be more appropriate. TENS units were initially tested as therapies for axial back pain, joint injections, median branch ablations, physical therapy, traction and inversion devises might have been more appropriate. Conversely if the leads of the TENS unit are not placed correctly pain relief will either be diminished or nonexistent. Picking an appropriate target nerve, such as the ulnar or ilioinguinal nerve and knowing the most superficial points along its path are critical determinants of success.



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