By Sharon L. Kolasinski, MD, FACP, FACR, Assistant Professor of Medicine; Director, Rheumatology Fellowship Program; and Chief of Clinical Service, Division of Rheumatology at the University of Pennsylvania School of Medicine in Philadelphia.
Naturally occurring magnetized stone has been used in traditional medical practice for hundreds of years.1 More recent uses of magnets in medicine include nuclear magnetic resonance imaging and the use of bone stimulators to enhance the healing of nonunion fractures. Currently, considerable interest exists in the use of magnets for the treatment of arthritis and musculoskeletal pain, and many devices are commercially available through retail outlets and web sites. In fact, magnet sales approached $5 billion in 1999 according to U.S. News and World Report.2
Although theoretical arguments can be made as to why pulsed electromagnetic fields may have a beneficial effect in ununited fractures, a rationale for the use of static magnets in painful conditions is less clear. Laboratory work, largely from the orthopedic realm, provides a relevant physiologic framework for discussion of therapeutic magnet use, but clinical trials are lacking.
Mechanism of Action
Pulsed electromagnetic fields (PEMFs) of 1-10 mTesla have been in use as bone-growth stimulators for more than two decades. Their success rests on certain physiologic concepts in the functioning of normal bone and cartilage. First, compression of bone during normal activities results in the generation of negative charge along the compressed surface. In other words, mechanical compression leads to the formation of an electrical potential via a piezoelectric effect.1 Hydroxyapatite and collagen are known to be piezoelectric in nature and contribute to this generated potential. The electric potential, in turn, affects cell functioning. Bone differentiates and chondrocytes synthesize proteoglycan in response to compressive forces via this electrical transduction.
Externally applied electric fields can alter the electrical environment of bone and cartilage as well. Exogenous electromagnetic fields can induce currents through ionic solutions, influencing cell behavior in ways similar to that seen with the normal response to mechanical compression. Stimulation of chondrogenesis and enhancement of glycosaminoglycan production are among the effects that have been demonstrated in response to PEMFs, suggesting a mechanism through which PEMFs may lead to fracture union. Others have suggested that anti-inflammatory effects may be possible with PEMF because DNA synthesis can be modulated in certain immune cells.3
Externally applied static magnets would not be expected to induce an electric current in a stationary conducting medium. However, it has been hypothesized that the movement of ions associated with blood flow could induce an electric current in soft tissues and joints when exposed to a static magnet. This could lead to effects on chondrocytes and cells within the soft tissues. Some investigators have suggested that application of permanent magnets could, therefore, alter the course of osteoarthritis (OA).
Recently, investigators reported on a canine model of OA.4 Dogs underwent transection of the anterior cruciate ligament and were then cared for in pens with floors covered with: no mattress and no foam; a foam floor mattress with nonmagnetized ceramic pieces between two layers of foam; or a foam floor mattress with magnetized pieces. The magnetized floor mattress delivered 45-50 mTesla at the surface of the mattress. At the end of 12 weeks, the investigators histologically examined the cartilage of each dog. They reported that magnet-treated dogs had qualitatively less severe cartilage surface changes than did the other groups, as well as lower levels of matrix metalloproteinases. These findings led the investigators to suggest that further studies are warranted to delineate how magnetic fields might be used to reduce the severity of OA.
Static magnets may have additional effects. Constant magnetic stimulation may desensitize sensory neurons by modifying cell membrane potentials. This could lead to an analgesic benefit suggested in clinical trials.
Clinical Studies
Although early reports suggested that static magnets may be of benefit for diabetic neuropathy and postpolio syndrome, it was not until recently that well-designed trials appeared in the literature reporting more rigorous evaluations of the efficacy of static magnets in painful conditions. One of the earlier well-designed trials was carried out with patients with low back pain.5 In this randomized, double-blind, placebo-controlled, crossover pilot study, participants were enrolled at a Veterans Affairs hospital through the primary care and rehabilitation services. Only 24 subjects enrolled with a mean age of 60 years and a mean pain duration of 19 years. Patients had spondylosis confirmed radiographically, with three subjects having had prior laminectomies. The primary outcome measure was a visual analog score (VAS) for pain. Subjects wore a device made of a flexible rubber-like material impregnated with active magnetic material that either remained magnetized or was demagnetized to provide a sham device. The magnetic strength of the active device was 30 mTesla. No statistically significant differences between the active and sham treatments were seen in VAS for pain, nor using the McGill Pain Questionnaire.
Mattress pads embedded with ceramic magnets were used with subjects enrolled in a trial to assess the effectiveness of magnets on fibromyalgia symptoms.6 The investigators used two "functional" pads, one rated by the manufacturer to have a magnetic strength of 395 mTesla, which was placed between the mattress and box spring, and the other 75 mTesla within an eggcrate foam pad, placed on top of the mattress. Two identical sham pads were used and a usual care group received no active intervention. A total of 119 subjects were spread among the five groups and were assessed after three and six months of use. Over the six-month time period, all subjects improved in terms of quality of life, measured by the Fibromyalgia Impact Questionnaire (FIQ), and in the number of tender points. No statistically significant differences were noted between any of the groups, although the group that was exposed to the strongest magnetic field had a reduction in pain intensity levels (measured by one question of the 19-question FIQ).
Magnetic insoles were studied at the Mayo Clinic for use in a group of subjects suffering for at least 30 days from foot pain with maximal tenderness on physical examination over the medial plantar fascia.7 All participants wore an insole made of magnetic foil embedded in foam under the proximal arch of the foot. The active treatment group wore insoles with a magnetic strength of 245 mTesla and the placebo group wore identical demagnetized insoles for 4 hrs/d, 4 d/wk for eight weeks. The investigators could not demonstrate any benefit attributable to the magnetic insoles. Both treatment and placebo groups reported improvements in morning foot pain and over a third in each group had virtually complete symptom resolution at week 8.
The largest trial published to date assessed the effectiveness of a magnetic bracelet commercially available in Great Britain for control of symptoms of hip and knee OA.8 Patients with radiographically confirmed OA were randomly assigned to wear one of three identical appearing bracelets: one with a magnetic field strength of 170-200 mTesla; one with a strength of 21-30 mTesla (intended to be an undetectable placebo); and one nonmagnetic. A manufacturing defect led to the use of weak-strength magnetic bracelets that were considerably more magnetized than intended; most had a magnetic field strength of 69-196 mTesla when tested at the end of the trial. Participants wore the bracelets for 12 weeks and their responses to questionnaires assessing their pain and functioning were cataloged; differences were minimal. Although positive effects were noted with the standard magnetic bracelet on both WOMAC A and WOMAC B scales, only the difference in VAS for pain between the standard magnetic bracelet and the dummy bracelet reached statistical significance. Furthermore, about a third of patients in the standard and dummy groups were able to correctly identify whether they wore a magnetized bracelet and the authors did not directly calculate the effect of this unblinding. Two participants in each group reported dizziness, increased pain, or increased stiffness.
Adverse Effects
Concern has been expressed in the popular press about a possible link between exposure to magnetic fields from high currency wires and cancer based on scattered reports of increases in leukemia and childhood cancers. No clear body of data has emerged, since confounding environmental and socioeconomic variables have made interpretation of these observations difficult. Nonetheless, the American Physical Society has gone on record with the opinion that there is no evidence that power lines cause cancer.9
Contraindications and Precautions
No systematic survey of the long-term safety of PEMFs or locally applied static magnets exists. It has been recommended that PEMFs not be used by those with cancer or pacemakers, or by pregnant women.
Within the pediatric literature, there are reports of ingestion of steel beads from magnetic bracelets by children causing intestinal obstruction, perforation, and fistula formation.10
Product Specifications
Thousands of web sites sell hundreds of products that are magnetized, including bracelets, rings, mattress pads, face masks, neck collars, and supports for knees, elbows, and ankles. Product prices range from $10-$20 for a bracelet to $250-$500 for a mattress pad. Magnetized materials may include gold, silver, copper, neodymium, or ceramic ferrite.
Conclusion
Although pulsed electromagnetic fields are commonly used in orthopedics to help heal nonunion fractures, the wider medical use of pulsed or static magnets in the prevention or treatment of arthritis or musculoskeletal pain syndromes is not well substantiated. What little clinical evidence exists is largely anecdotal and the few well-designed trials show scant benefit.
Recommendation
Patients and physicians are concerned about side effects associated with nonsteroidal anti-inflammatory drugs, including COX-2 inhibitors, and continue to search for treatment options for a variety of musculoskeletal complaints and arthritis. Pulsed electromagnetic fields have important beneficial effects on cartilage and bone, but the benefits of static magnets are less clearly defined. Static magnet use may be associated with analgesia in some patients and appears to be safe based on short-term studies.
References
1. Trock DH. Electromagnetic fields and magnets. Investigational treatment for musculoskeletal disorders. Rheum Dis Clin North Am 2000;26:51-62.
2. Hobson K. Bracelet power. Can you zap arthritis pain with magnets? U.S. New & World Report. Available at: www.usnews.com/usnews/health/briefs/arthritis/hb041217c.htm. Accessed April 4, 2005.
3. Johnson MT, et al. Noninvasive treatment of inflammation using electromagnetic fields: Current and emerging therapeutic potential. Biomed Sci Instrum 2004;40:469-474.
4. Rogachefsky RA, et al. Use of a permanent magnetic field to inhibit the development of canine osteoarthritis. Bioelectromagnetics 2004;25:260-270.
5. Collacott EA, et al. Bipolar permanent magnets for the treatment of chronic low back pain: A pilot study. JAMA 2000; 283:1322-1325.
6. Alfano AP, et al. Static magnetic fields for treatment of fibromyalgia: A randomized controlled trial. J Altern Complement Med 2001;7:53-64.
7. Winemiller MH, et al. Effect of magnetic vs sham-magnetic insoles on plantar heel pain: A randomized, controlled trial. JAMA 2003;290:1474-1478.
8. Harlow T, et al. Randomised controlled trial of magnetic bracelets for relieving pain in osteoarthritis of the hip and knee. BMJ 2004;329:1450-1454.
9. Broad WJ. Cancer fear is unfounded, physicists say: Power line concern is called needless. NY Times May 14, 1995.
10. Lee SK, et al. Mischievous magnets: Unexpected health hazard in children. J Pediatr Surg 1996;31:1694-1695.
Kolasinski SL. Magnets for musculoskeletal symptoms. Altern Med Alert 2005;8(5):53-55.
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