Can a daily dose of electricity ease joint pain? That’s the promise of transcutaneous electrical nerve stimulation (TENS) devices that are now sold over the counter and heavily marketed in television and magazine ads.
Doctors, physical therapists, chiropractors, and other healthcare professionals have treated muscle and joint pain with TENS for years.
The devices are now available without a prescription, starting at about $25 per unit, although some products cost significantly more. But are they worth the money, and can they truly offer a drug-free way to block pain, as their makers promise?
An old idea, renewed
Using electricity to relieve pain isn’t a new idea. Ancient healers employed its power by applying fish, such as rays, that discharge electrical current to treat gout and other painful conditions.
And following the discovery of electricity, “electrotherapy” machines were used for pain treatment in the 18th century. Interest in electrotherapy eventually waned, but returned in the mid-1960s, which led to development of TENS devices and related pain-relief tools now used in healthcare settings.
Despite the recent hype about TENS, it was actually back in 2004 when the Food and Drug Administration (FDA) approved the first over-the-counter TENS device. Since then, wearable “electrotherapy” pain-relieving products have come on the market, many of them based on the same technology as TENS.
In theory, TENS blunts pain by delivering pulses of electrical currents through the skin. These electrical signals activate nerves and trigger the release of endorphins, which are naturally-occurring chemicals that block substances in the body that produce pain. TENS may produce other physiological changes that ease pain as well.
TENS products come in a variety of sizes and styles. Some include a handheld device, similar to a remote control, with wires connected to small adhesive electrode pads, which you apply to the skin covering your sore joint or muscle. Using the handheld device, you control the intensity of the stimulation that’s applied by the pads. (Some devices allow you to regulate the frequency of pulses, too.)
Wireless TENS devices are attached to adhesive pads that are applied directly to the skin and have buttons for raising or lowering intensity. There are products designed for use on specific joints, such as the knees or shoulders.
While TENS delivers electrical current, you don’t feel a shock or zap; instead, the devices produce a tingling sensation that’s either mild or strong, depending on the intensity setting you choose. One popular TENS product has 63 different settings. Instructions typically recommend using TENS for 15 to 30 minutes, several times a day. However, some users leave the devices on longer.
Do they work?
It’s important to bear in mind that FDA approval of TENS devices sold to consumers does not require that those products undergo rigorous study to prove that they actually relieve pain.
That means much of what is known about TENS and relief of arthritis pain comes from studies of devices designed for and applied by healthcare professionals—and there’s no guarantee that over-the-counter versions produce the same results.
What’s more, studies of professional-quality TENS devices have had conflicting results, failing to yield clear answers about the therapy and its role in treating any form of arthritis.
Skeptics of TENS often point to a 2009 analysis of 18 studies in which people with osteoarthritis of the knee received the therapy. The analysis was conducted on behalf of the Cochrane Collaboration, a network of scientists and physicians that assesses the benefits of medical therapies. These studies, which included 813 patients with knee osteoarthritis, compared people who received TENS with others who received fake (or sham) versions of TENS or no additional therapy at all.
The analysis showed that, overall, TENS users fared no better than subjects in the other two groups. However, the authors remained uncertain whether TENS was beneficial for knee osteoarthritis since many of studies they evaluated were small and of poor quality.
In a more recent study, researchers in the United Kingdom wanted to learn whether TENS was a useful addition to standard care for patients with knee osteoarthritis. They recruited 224 patients and split them into three groups. One group was enrolled in a program of education and exercise designed for knee osteoarthritis. A second received the same care, plus TENS, while the third group received the same care plus a sham treatment designed to mimic TENS.
The 2014 study, published in Arthritis Care & Research, found that patients in the TENS group reduced their pain levels and were able to get around better after six weeks of treatment—but the same was true for patients in the other two groups.
Other studies have found that sham TENS works as well as the real thing, leaving researchers to suggest that any benefit the devices may confer comes from the placebo effect—that is, the belief that a therapy is working.
In defense of TENS
Still, some doctors and other healthcare professionals are convinced that there’s a role for TENS in treating arthritis. A small study in Orthopedics in 2016 found that patients with knee osteoarthritis who underwent TENS lowered their pain levels and maintained better muscle strength when compared with patients in a control group.
Some proponents argue that the reason TENS has failed in many studies is that the therapy wasn’t performed correctly. They note that researchers who found no benefit often used devices set at low intensity, which was unable to provide adequate nerve stimulation and trigger the cascade of biochemical changes that block the transmission of pain signals.
A 2007 review in BMC Musculoskeletal Disorders included only studies in which the dose of TENS was considered optimal, which by the authors’ definition was as strong as a patient could tolerate without being uncomfortable. In those studies, TENS provided significant, if modest, short-term pain relief of knee osteoarthritis.
TENS has not been well studied in patients with other forms of arthritis. A 2003 review for the Cochrane Collaboration found conflicting evidence for whether the therapy was beneficial in rheumatoid arthritis, although the analysis included just three studies involving 78 patients.
Features to look for
Ask your doctor or physical therapist about the features you should look for in a TENS device; many of them have more settings than you'll ever need. Some features to consider include:
• Batteries: You can choose from units powered by standard batteries (which can be expensive to replace), rechargeable batteries, or a rechargeable lithium battery. Some devices have an AC power adapter.
• Electrode pads: Most TENS units have either two or four electrodes. Electrode pads lose their adhesiveness over time and need replacing. Also check whether you will have to apply gel to the pads or if the gel is already applied.
• Modes: Do you want a device that can be preset or turns off automatically?
• Ease of use: Make sure you can easily control the buttons, knobs, or touchpad. Are controls easy to read and clearly labeled? Some higher-end models use screens; consider the display’s size and whether it has backlighting.
• Your budget: Consider purchasing an inexpensive model, which may be adequate for your needs, before shelling out a lot of money.
If you decide TENS might be worth a try, keep a few things in mind before you buy:
• Some research suggests that people who use TENS frequently develop tolerance to its effects, making the device less effective.
• Electrode pads lose their adhesiveness over time and need replacing, adding to the cost.
• While TENS is generally safe and free of side effects, it’s not for everyone. Don’t use these devices if you have a pacemaker or any other implanted device made of metal. Follow all instructions especially those regarding proper placement; affixing one to certain parts of the body, such as the face or upper back, can cause muscle spasms. In some cases users have developed skin irritation. Don’t place them over your eyes, on broken or irritated skin, over areas affected by nerve damage, or near a transdermal (skin) drug patch.
• Medicare reimbursement for TENS devices is very limited—for example, TENS for chronic lower back pain is not covered. You’ll need to find out from Medicare (1-800-MEDICARE) about whether a TENS prescription for your particular diagnosis is covered.
It’s always wise to check with your doctor before making any addition to your treatment regimen, so ask him or her if TENS makes sense for you.
Finally, keep your expectations in check and maintain a proper perspective. TENS might help, but it’s best thought of as an addition—not a replacement—to exercise and other well-established arthritis aids.