Transcutaneous Electrical Nerve Stimulation (TENS) is a non-invasive method for managing pain by delivering low-voltage electrical currents through electrodes placed on the skin. Since the device sends electrical impulses near major nerve pathways, understanding correct electrode placement is paramount for both effectiveness and safety. A primary concern for many users involves the safety of applying these electrical pads directly over the bony ridges of the spinal column.
How TENS Therapy Works
The pain-relieving effects of TENS therapy are attributed to two primary physiological mechanisms. One widely accepted explanation is the Gate Control Theory of pain, which suggests that a neurological “gate” controls which pain signals reach the brain. The electrical stimulation from the TENS unit activates large, fast-conducting sensory nerve fibers (A-beta fibers), which effectively close this gate in the spinal cord. This action interferes with and inhibits the transmission of slower, smaller pain signals (A-delta and C fibers) from reaching the brain, thereby reducing the perception of discomfort.
The second mechanism involves the body’s natural pain-relieving chemicals. The TENS unit’s electrical current stimulates the central nervous system to release endogenous opioids, such as endorphins and enkephalins. These naturally occurring substances act similarly to opioid medications by binding to specific receptors in the nervous system to produce an analgesic effect.
The Risks of Direct Spinal Column Placement
Placing TENS electrodes directly over the spinal column is strongly discouraged due to safety hazards. The vertebrae offer little soft tissue or muscle for the electrical current to pass through before reaching the underlying structures. This placement increases the risk of unpredictable electrical current flow and direct overstimulation of the spinal cord and major nerve roots.
Direct stimulation of the spinal nerves can lead to nerve irritation, which may cause increased pain or muscle spasms rather than relief. Placing electrodes in a way that allows the current to flow across the chest or directly over the heart is extremely hazardous. Stimulating the front of the neck over the carotid sinus can cause a sudden, dangerous drop in heart rate or blood pressure, or induce spasms in the laryngeal muscles.
Recommended Electrode Placement for Back Pain
Electrodes should be placed on the soft tissue that runs parallel to the spine. This placement allows the electrical current to effectively target the nerves and muscles involved in the pain without risking direct stimulation of the central nervous system.
When using a two-electrode setup, position one pad on the left side of the spine and the other on the right side, ensuring they are at least one inch apart. If using four pads, a “cross pattern” can be used, where the pads are placed diagonally to frame the pain area. Always ensure the pads are placed on healthy, non-irritated skin and are not directly over any joint, bony prominence, or area of numbness.
Critical Safety Precautions and Contraindications
There are several contraindications that make TENS therapy unsafe for certain individuals. People with implanted electronic devices should never use a TENS unit, as the electrical currents can interfere with the device’s function. Use during pregnancy should be avoided, particularly over the abdominal and lower back regions, as safety has not been definitively established.
Anyone diagnosed with epilepsy should avoid using TENS, especially with electrode placement near the head or neck, which could potentially trigger a seizure. TENS units should not be applied over areas of skin that are broken, irritated, or infected. Users must also avoid placing electrodes over areas with compromised sensation, because the inability to feel the intensity of the current increases the risk of overstimulation or electrical burns.