Transcutaneous Electrical Nerve Stimulation (TENS) uses a small, battery-operated device to deliver low-voltage electrical impulses through electrodes placed on the skin. This non-invasive, drug-free method is used to manage chronic pain. The primary function of a TENS unit is to temporarily interfere with pain signals traveling to the brain, offering a customizable approach to discomfort. This article examines the underlying science and clinical evidence regarding the effectiveness of TENS for managing the long-term pain associated with arthritis.
The Science Behind TENS Therapy
The pain-relieving effects of TENS are attributed to two distinct physiological mechanisms that modify how the nervous system processes discomfort. The most widely accepted model is the “Pain Gate Theory,” which suggests a mechanism exists within the spinal cord that controls the flow of pain signals. TENS operates by stimulating large, non-pain-carrying nerve fibers (A-beta fibers). This sensory input is faster than the pain signals traveling along smaller fibers, effectively “closing the gate” and inhibiting the transmission of the pain message to the brain.
A secondary mechanism involves the release of the body’s natural pain-dampening chemicals, known as endogenous opioids. The electrical impulses from the TENS unit stimulate the production and release of substances like endorphins and enkephalins. These naturally occurring compounds bind to specific receptors, producing an analgesic effect similar to certain medications. This dual action allows TENS to offer a temporary reduction in the perception of pain.
TENS Efficacy for Specific Types of Arthritis
Clinical research has investigated the effectiveness of TENS as an adjunctive treatment for both major types of joint inflammation. The most substantial body of evidence focuses on Osteoarthritis (OA), particularly in the knee. Several systematic reviews suggest that TENS provides a moderate, short-term reduction in pain intensity for those with knee OA, especially when the device is used at an adequate intensity during activity.
However, the clinical guidelines remain mixed, with some groups, such as the American College of Rheumatology, recommending against its use for OA due to inconsistent results across trials. The effectiveness appears highly dependent on the correct use of intensity and frequency settings. When trials use sub-therapeutic settings, they frequently conclude that TENS offers no significant benefit over a placebo device.
Evidence for TENS use in Rheumatoid Arthritis (RA) is far more limited and generally less conclusive than for OA. While TENS is used as an option for RA patients, the scarcity of rigorous randomized controlled trials makes it difficult to draw firm conclusions. For both OA and RA, the general consensus is that TENS can be a beneficial, non-harmful adjunct for some individuals who have not found sufficient relief from other pain management strategies.
Guidelines for Unit Placement and Settings
For maximum effect, the electrodes must be placed correctly, typically surrounding the painful joint area rather than directly over the joint itself. A common technique involves placing the pads so that the electrical current runs parallel to the nerve pathways or across the site of pain, ensuring the pads are at least one inch apart. Avoid placing electrodes directly over bony prominences, as this can increase discomfort and reduce the effectiveness of the current.
TENS units offer two primary modes of stimulation, corresponding to the two pain-relieving mechanisms. Conventional, or high-frequency, TENS uses a pulse rate between 80 and 120 Hertz (Hz) and a short pulse width to activate the Pain Gate Theory, providing immediate, short-lived relief. This setting should produce a strong, comfortable tingling sensation without causing muscle contraction.
Acupuncture-like, or low-frequency, TENS uses a lower pulse rate, typically between 2 and 10 Hz, with a longer pulse width. This mode stimulates the release of endorphins, offering pain relief that may take longer to onset but can last for a longer period after the stimulation ends. The intensity must be sufficient to cause a small, visible muscle twitch or contraction, which is necessary to trigger the endorphin response.
Important Safety and Usage Restrictions
TENS is considered a low-risk pain management tool, but several absolute contraindications and precautions must be observed before use. The electrical impulses can interfere with the function of implanted electronic devices. TENS must not be used by individuals with a cardiac pacemaker, defibrillator, or any other implanted electronic device.
The safety of TENS has not been established for use during pregnancy, and it is typically advised against unless specifically recommended by a healthcare provider. Potential minor side effects include skin irritation or burns at the electrode site, often due to a poor connection or sensitivity to the adhesive. Using TENS near metal implants, such as joint replacements, requires caution, as the metal may distort the current flow.
Electrodes should never be placed over specific sensitive body areas. Any unusual sensation should prompt immediate cessation of use.
Restricted Electrode Placement Areas
- The front of the neck where the carotid sinus is located.
- The eyes.
- Near any open wounds, irritated skin, or cancerous lesions.
- Placement that would cause the current to flow transcranially (across the head).