Clinical Question: Can treatment with high-strength magnets decrease pain associated with osteoarthritis of the knee?

Setting: Outpatient (any)

Study Design: Randomized controlled trial (double-blinded)

Synopsis: Electromagnetic therapy (i.e., using a magnet that can be turned on and off) has been shown to have a pain-relieving effect in patients with knee osteoarthritis. This study evaluated the use of static magnets—that is, magnetized metal in a sleeve worn around the knee. The investigators identified 26 patients with clinical and radiologic evidence of knee osteoarthritis requiring drug therapy or modification of daily activities.

The patients were assigned randomly (allocation concealment uncertain) to six weeks of magnet therapy or sham treatment. Treated patients received a high-strength magnetic knee sleeve with four magnets aligned with the “north” side facing the joint, whereas patients in the control group received an identical-looking knee sleeve with magnetized discs that radiated a magnetic field away from the joint (through arrangement of the magnets). This approach maintains blinding because a metal object held close to either device would be attracted to it, although the sham knee sleeve provided no magnetic field to the knee joint. The blinding procedure worked, with most patients in both groups (69 percent in the active group and 77 percent in the sham group) thinking they had the active magnets. Patients wore the knee sleeves for seven to 10 hours per day.

Despite the small number of patients in each group, pain was diminished significantly in the active magnet group after the first four hours of wearing the sleeve (79-mm versus 10-mm improvement in pain on a 5-item visual analog scale; P = .03). However, by six weeks there was no difference between the two groups regarding the degree of improvement in any of the scores on the the Western Ontario McMaster instrument, which is the standard scale for assessing arthritis therapy and focuses on pain, stiffness, physical function, and overall change. Both groups experienced improvement in all of these domains. However, the study probably was not large enough to find a small difference between the two groups, if one existed.

Bottom Line: High-strength magnet therapy acutely diminishes pain in patients who have osteoarthritis of the knee. However, after six weeks of therapy, magnet therapy has no greater impact on symptoms than sham therapy. Most of the patients in the placebo group (as well as in the active therapy group) thought they were receiving active therapy, and this attitude may have bolstered the placebo effect in both groups, making it hard to find a difference if one truly existed. (Level of Evidence: 1c)