Double-blind placebo-controlled trial of static magnets for the treatment of osteoarthritis of the knee: results of a pilot study.

Context: Outpatient clinical studies of magnet therapy, a complementary therapy commonly used to treat osteoarthritis (OA), have been limited by the absence of a credible placebo control.

Objective: Our objective was to assess the feasibility and promise of studying static magnetic therapy for knee OA and determine the ability of a new placebo-magnet device to provide concealment of group assignment.

Design: Randomized, double-blind, placebo-controlled clinical trial.

Setting: Academic teaching hospital in Boston.

Participants: We enrolled 29 subjects with idiopathic or post-traumatic OA of the knee.

Interventions: Subjects received either high-strength magnetic (active) or placebo-magnetic (placebo) knee sleeve treatment for 4 hours in a monitored setting and self-treatment 6 hours daily for 6 weeks.

Main Outcome Measures: Primary outcomes were change in knee pain as measured by the WOMAC Osteoarthritis Index Pain Subscale at 6 weeks and extent of group concealment at study end.

Results: At 4 hours, VAS pain scores (+/- SE) on a 5-item scale (0-500, 500 worst) decreased 79 +/- 18 mm in the active group and 10 +/- 21 mm in the placebo group (P < 0.05). There were no significant differences in any primary or secondary measure of efficacy between the treatment groups at 6 weeks. Despite widespread testing for magnetic properties, at study end, 69% of the active group and 77% of the placebo group (P > 0.2) believed that they had been assigned to the active treatment group.

Conclusion: Despite our small sample size, magnets showed statistically significant efficacy compared to placebo after 4 hours under rigorously controlled conditions. The sustained efficacy of magnetic therapy for knee osteoarthritis could be assessed in an adequately powered trial utilizing an appropriate control such our new placebo-magnet device.