This study demonstrated the feasibility of recruiting and retaining compliant participants for an RCT to evaluate SMF therapy for CTS. We also found that 15mT and 45mT SMFs can be safely applied to the contents of the carpal canal for a 6-week period. The primary outcome measure of CTS symptoms improved after 6 weeks of treatment to a similar degree in the sham control group and two active magnet groups. At 18 weeks, 12 weeks after the treatment had ceased some but not all of the apparent treatment benefits were still observed in all three groups. The timing and magnitude of change for these variables was similar across all groups.
In order to achieve a high level of internal validity we used standardized measurements and follow-up protocols and employed a double-blind randomization with a sham control. Our population was well characterized with regard to the diagnosis of CTS. Of particular note, we restricted our enrollment to those participants with electrophysiologically-confirmed median nerve compression within the carpal tunnel and were able to precisely quantify the SMF dose delivered to the contents of the carpal tunnel. Our findings of significant pre- to post-symptomatic improvement in each of the three study groups, needs to be accounted for. A variety of explanations including natural progression of the disease, a placebo effect or regression to the mean are possible. A particularly strong placebo effect is known to be associated with the use of injections, surgery and novel medical devices and cannot be ruled out in this study.13
We took steps in our measurement protocol to minimize regression to the mean for our primary outcome; at outset we averaged two BCTQ questionnaires, administered two weeks apart, to obtain a more representative baseline SSS measure.
In addition to these oft cited explanations for why a control group improves to the same extent as the experimental group we considered the possibility that our sham device, although non-magnetic, was not inert. The aluminum disk chosen as our control may have exerted some unintended effects on a clinically relevant acupuncture point (PC 7) over which the disk was affixed. In addition, positioned as it was over the palmar aspect of the wrist the disk also prevented the extremes of wrist flexion. It is possible that the mild mechanical pressure exerted with nightly application stimulated an important acupuncture point and/or that the placement of the disk at the base of the hand simulated the effect of a simple wrist splint.
In retrospect, we believe that our efforts to maximize participant blinding may have compromised our SMF dosing regimen. Participants in our study were allowed to wear their devices only during the hours of sleep (7–9 hours per 24 hours) for six weeks, whereas participants in a previous, less well controlled study, reportedly experienced symptomatic and electrophysiologic improvement after wearing their magnets continuously 24 hours per day for 30 days.5
Within the field of magnet therapy there are few studies to guide the selection and use of SMF dosimetry and treatment regimens. Thus several other components of our SMF dosing regimen may have been less than optimal. We evaluated only two SMF strengths (15mT and 45mT). We were unable to test any alternate magnetic field strengths, durations of magnet wear, types of magnets, or magnetic polar configurations within the scope of this study.
Wrist splints are often prescribed, along with recommendations for activity modification, as a first line of treatment for CTS. The magnitude of changes on the SSS of the BCTQ that we observed in our study are similar to improvements reported in non-sham controlled studies of wrist splints for CTS.14 15 16 17
Compared to our mean SSS changes of 0.7 in the 15mT and 0.8 in the 45mT groups Mishra found a significant SSS pre to post change of .39.17
Walker et al demonstrated an improvement of 0.7 in full time splint wearers and .59 in the night time only wearers.15
Manente et al reported a SSS reduction of 1.2 in participants who wore the MANU hand brace compared to no treatment while the mean SSS improved by 0.88 in another study that compared the MANU to a wrist splint group who experienced a 0.78 improvement.14
In this study we wanted to evaluate an objective outcome measure (NCS) and explore a potential disease modifying effect of SMF by testing before and after median nerve electrophysiological parameters. Basic science researchers have reported enhanced neurite growth7
and blockade of sensory nerve potential firing8
which suggests that SMFs under certain conditions can influence neural tissue. Our participants experienced no significant within- or between- group improvements in median nerve electrophysiology. This may be because SMFs do not facilitate median nerve repair in the carpal tunnel or because our SMF dosimetry may have been suboptimal.
Success of blinding
Blinding participants in clinical trials that involve the use of a permanent magnet is challenging because magnetic properties are so easily discovered. We used a participant blinding approach (masking to study hypothesis) that is endorsed by the CONSORT group for use in non-pharmacological studies.18
We can be relatively confident that blinding was successful because the majority of participants in each group thought they had a real magnet. (). 45% of participants who had active magnets either tested or discovered the magnetic properties of their devices. Yet, only one person in the sham group deliberately tested her device and no one in that group inadvertently discovered that the device was not magnetized. However, in future long term studies the likelihood that people in the sham group will test their devices for magnetic properties is high.
This study has highlighted many challenges of conducting randomized controlled trials that involve the use of permanent magnets. A wide variety of SMF dosing parameters need to be evaluated, including the assessment of different types of permanent magnets, such as flexible magnets and ferrite magnets, as well as neodymium magnets; testing SMFs of different field strengths and polarities; and the application of magnets for different durations of time and frequencies of application. In addition SMF dosing regimens need to be optimized for each medical condition to be evaluated. Of vital importance is the need for a sham control device that is believable to participants but confirmed to have no physiological effect. Finally, as an alternative to RCTs, future consideration should be given to comparative effectiveness studies which may provide more useful information to clinicians with regard to whether one physical modality, such as wrist splints, is more likely to benefit patients than another, such as static magnetic field therapy.