Randomised controlled clinical trial of magnet use in chronic low back pain; a pilot study

Abstract

Introduction:

Chronic low back pain (CLBP) is one of the most common pain states seen in general medicine today. However, there are currently few, if any, reliable modalities that can be used in its treatment. Magnets are in common use as a therapeutic modality in the relief of a number of pain states. However, the validity of this use is relatively untested, with the effects of magnets on CLBP having not been studied previously.

Objective:

To investigate the potential usefulness of static magnetic field therapy in the relief of CLBP.

Design:

A prospective, blinded, randomised, controlled clinical trial.

Settings/location:

Welsh Institute of Chiropractic, University of Glamorgan.

Subjects:

Twelve CLBP patients (symptoms for more than 3 months) who were participating in a spinal rehabilitation clinic at the Welsh Institute of Chiropractic (WIOC). None of the subjects had any neurological deficit, or any known underlying pathological problems.

Interventions:

A belt containing two small ‘Neomax’ disc magnets (either 1.20 ± 0.05 T in the active or 0.5 ± 0.05 T in the inactive group) was given to each patient. This was applied continually for the 4 weeks of the trial.

Outcome measures:

Oswestry disability questionnaire, a visual analogue pain scale (VAS), as well as left and right lateral lumbar flexion.

Results:

Ten subjects completed the study. VAS scores showed a strong trend (p = 0.05) towards a decrease in pain in the active magnet group. However, no significant change was seen in either the Oswestry or lumbar flexion results.

Conclusions:

Although the numbers in this study were small, they illustrate the possibility that VAS could be decreased in these patients. This suggests that there may be some worth in using magnets to symptomatically relieve CLBP.

The results support a larger scale study of static magnetic field application in chronic low back pain.

Introduction

Magnetotherapy has always been viewed with an air of skepticism since the physician Franz Anton Mesmer (1734–1815) re-discovered its therapeutic effects with respect to pain relief (for review, see Ramey¹). The earliest published reports indicated that pain relief and restoration of function occurred within a few days of the treatment.² Some elements of magnetism have been used by chiropractors since the early days of the profession.

There are two types of magnetic fields (static and pulsating) that have been shown to potentially promote the relief of pain.3, 4, 5 A further potentially important consideration is that of the magnetic strength being applied to the patient. There are two different forms of expressing the strength of a magnet:

• The unit of magnetic flux density is the Tesla (T), which is the standard unit for the SI system (kg/s/A).

• The unit of magnetic flux intensity is the Gauss (G) which should always be converted to the Tesla (1 T is the equivalent to 1000 G).

The World Health Organization (WHO) consider that those magnets in common therapeutic use do not have any detrimental effect on the human body.⁶ As a result, magnets have become a popular alternative for pain relief, without a complete understanding of their mechanism of action or physiological effects.

A recent study of post-polio pain patients clearly demonstrated a potential use for static magnets.⁵ The treatment consisted of a single application of a static magnet on a painful trigger point for 45 min and reported a significant and rapid relief of pain. However, although there have been reports of the effective treatment of pain by magnets, the mechanisms underlying this phenomenon are not clear.

Early studies attempted to describe the effect that a static magnetic field had on neural function, usually with respect to the effect on pain perception. It has been suggested that the pain relief produced by a static magnetic field is related to changes (decreases) in the proximal nerve conduction time.⁷ However, it has since been concluded that it may not be alterations in nerve conductivity that result in pain relief, but rather a change in the nerve excitability.⁸ In respect of therapy, however, there are two parameters that still need to be clarified: the duration of the application, magnetic field strength and orientation. With respect to orientation, the negative (north) side of the magnet apparently should be directed towards the patient's skin in order to have an increased ability to achieve pain relief.⁹

Although there appear to have been no definitive studies that have considered the duration of application, this element most probably has therapeutic implications. Results from various studies have suggested that increasing either the duration of magnet therapy or the frequency of the treatment might lead to an increased therapeutic effect.5, 8, 9 Therefore, it is considered that long periods of use per day would be appropriate in order to optimize the effectiveness of the magnets.

The field strength required for therapeutic activity appears to be open to some debate. The type of magnet appears to affect its activity in that multipolar rather than unipolar magnets may be more effective in reducing sensory afferent activity (nociceptor pain), ostensibly due to their greater field penetration.¹⁰ With respect to the actual field strength, use of magnetic fields close to axons in vitro indicates that approximately 10 mT is required to effect changes.¹⁰ However, when taking the body into account, both distance and the potential of body tissues to dampen the field strength must be considered. Therefore, with respect to the use of static bipolar magnets, 0.5 T appears to produce minimal, if any, activity in low back pain,⁹ whereas 1 T was reported as being capable of affecting proximal axonal action potential conduction time.7, 8 On the basis of this, it was decided to use the higher value (greater than or equal to 1 T) for the active treatment magnets. In addition, due to the public awareness of magnets, it was deemed appropriate and necessary to use a magnetised placebo. However, the choice was made to use a placebo which, although being magnetic, had shown minimal therapeutic activity in a previous study of a similar condition (approximately 0.5 T⁹).

Chronic low back pain (CLBP) is considered to be one of the most common and more difficult problems encountered by health care practitioners.11, 12 With respect to treatment, active exercise appears to have a benefit, providing increased mobility, muscle strength and work conditioning.¹³ In addition, there is little evidence to suggest that activity could be harmful to chronic low back pain sufferers.¹² Rehabilitation reduces patient dependency on passive care treatments and teaches patient the importance of self-treatment techniques needed to control their own pain. It gives the patient control of their treatment and disease. It is common knowledge that these patients also use other alternative “cures”, one of which is the use of magnets. It is, therefore, appropriate that one tests this use of magnets in conjunction with other more usual methods of treatment. This condition can be assessed in three ways: with respect to the current pain perceived by the patient (using a visual analogue pain scale; VAS). Alternatively, it can be assessed with respect to the degree of impact it has on the patient's life, or “disability” of the patient (using the Oswestry disability questionnaire). The final form of assessment is that of physical movement or impairment of this parameter. For this, lumbar flexion, extension or lateral flexion can be of use, dependent on the muscles being assessed.