Evidence Update- Do PEMF Devices like the Assisi Loop Work?

Introduction
Since the discovery of electricity and magnetism, these mysterious forces have been thought to have healing powers. Many fanciful electrical devices were promoted in the nineteenth and early twentieth century as cures for diverse ailments or general health tonics.1 More serious scientific research into the effects of electromagnetic fields on tissues and animals began in the 1930s, and by the 1980s there was sufficient evidence for some kinds of pulsed electromagnetic filed (PEMF) devices to be approved by the FDA for use in human patients.2

Since then, a large number of PEMF devices have been marketed for both human and veterinary medical use. The scientific evidence behind these devices, from in vitro and animal model studies to clinical trials, is complex and inconsistent. Pubmed lists about 50 systematic reviews covering nearly 200 clinical trials, and there well over 1,000 articles if one includes preclinical laboratory studies. PEMF devices use a variety of designs and treatment protocols for a wide range of medical conditions, so any generalizations about the efficacy of these devices are necessarily tenuous. However, because PEMF devices are aggressively marketed to veterinarians and animal owners, some assessment of the evidence behind them is necessary.

It’s been ten years since my first review of this subject, and there was little evidence to support claims for veterinary PEMF devices at the time. Though this is still the case, some new evidence is available.

Pre-clinical Evidence
There is a large scientific literature showing that electromagnetic fields have interesting and potentially significant biological effects on animal cells and tissues. PEMF devices can affect the levels of calcium and nitric oxide in tissues, which can influence extensive and complex pathways involved in metabolism, inflammation, pain transduction, tissue growth and repair, and many other biological activities. PEMF devices have also been shown to affect gene expression, vasomotor tone, and many other physiologic processes.2–5 These studies show the potential for clinically relevant benefits from PEMF treatment. 

Lab animal studies also show effects of PEMF treatment that may be useful to clinical patients, though there is great variation in the treatment used and the results. Some evidence suggests benefits in soft-tissue and bone healing, though not all of the research is positive.2,6–8

However, it is important to understand that such in vitro and animal model findings are not sufficient to justify clinical use. Many therapies, from pharmaceuticals to manual therapies to other high-tech treatments such as low-level laser, have demonstrable effects on tissues that often do not translate into meaningful clinical benefits for patients. Clinical trials are always necessary before making confident claims for any medical therapy.

Human Clinical Trial Evidence
Though there are hundreds of clinical studies in humans for PEMF in various indications, the results are mixed and difficult to interpret. For example, there are some studies showing meaningful improvements in post-operative pain in human patients undergoing breast augmentation surgery.9,10 However, systematic reviews of studies evaluating PEMF for pain associated with osteoarthritis of the knee are mixed, with some showing no effect,11 some inconclusive,12–15 and others suggesting some benefit.16 Strong generalizations about the efficacy of PEMF for pain aren’t justified based on a literature incorporating varied treatment protocols for different indications with mixed results.

The same inconsistency exists in studies of bone healing17–20 and other clinical uses in humans.21–23 There is evidence of benefits, but it is inconsistent, and the strength of this evidence is limited by heterogeneity in treatment protocols and indications as well as by methodological weaknesses in clinical trials. 

As always, clinical trial evidence for specific indications in veterinary patients is the most relevant type of evidence for veterinarians choosing which treatments to adopt. The clinical trial literature for PEMF is currently very sparse, but there are some studies we can evaluate.

Veterinary Clinical Trials
Though some encouraging case studies and uncontrolled studies have been published,24 there have been only a few controlled clinical trials of PEMF treatment in veterinary patients. 

A small pilot study randomly divided 16 dogs undergoing ovariohysterectomy into four groups- IV saline, IV saline and PEMF, IV morphine, and IV morphine and PEMF. For 6 hours after extubation, a variety of physiologic variables were measured, including heart and respiratory rates and blood pressure, and a validated pain scale was employed by a blinded observer. There were a couple of statistical differences in blood pressure at some time points, but no identifiable analgesic effect of PEMF. The small number of animals in each group likely made the study underpowered to detect all but the most dramatic effects.25

A 2018 study evaluated the use of a PEMF device in 16 dogs undergoing hemilaminectomy for naturally-occurring intervertebral disk disease (IVDD).26 Eight dogs were randomized to active or sham PEMF treatment and evaluated in terms of a primary outcome (gait) and numerous secondary outcomes involving neurologic status, function, and pain. There was no benefit detected in the primary outcome or in the majority of secondary outcomes. 

Placing responses and one measure of pain at the surgical site did appear improved in the PEMF group compared to the control. However, when multiple secondary outcomes are evaluated in a clinical study, it is common for some differences to appear by chance despite statistical efforts to control for this,27 and the authors state that these findings “should be interpreted with caution.”26

The most recent veterinary clinical trial also used IVDD patients as subjects.28 Fifty-three patients were randomly assigned to active or sham PEMF treatment and evaluated in the hospital and by owners at home for up to 6 weeks after surgery. There were no apparent benefits in terms of pain or function as assessed by owners or clinicians, though post-hoc power calculations indicated the study was not sufficiently powered to detect some of these differences. There were some small differences in long-term appearance of surgical wounds, though all wounds healed appropriately. Owners also gave slightly more pain medication to dogs in the control group than the PEMF group, though pain was not rated differently between the groups.

Bottom Line
Despite the fact that there has been interest in the potential medical applications of electricity for over 150 years, and serious scientific research investigating PEMF has been going on for over 50 years, there is surprisingly little robust evidence showing meaningful clinical benefits. We know a lot about the physiologic effects of PEMF, and preclinical research suggests a number of clinical applications. There is clinical trial evidence from humans showing potential benefits for bone and soft-tissue healing, pain reduction, and other uses, but this evidence is inconsistent and complicated by the use of many different devices and treatment protocols. PEMF devices are widely used, and this creates the impression that they have been solidly validated, but the reality is more ambiguous. 

There is also preclinical research in veterinary species showing physiological effects from PEMF devices and potential clinical applications. However, there are very few clinical trials of PEMF in actual patients. The studies that have been published have not found consistent and convincing evidence of clinically meaningful benefits. Many outcome measures have shown no effect of PEMF, though a few have shown effects that might be meaningful. If additional independent trials confirm such potential benefits, it may be possible to have confidence in some clinical uses of PEMF. For now, however, the marketing claims of PEMF manufacturers and the excitement of proponents far exceed the strength of the available scientific evidence.

It is also worth noting that most studies of PEMF devices in human and veterinary patients have found few, if any, adverse effects. While this is reassuring, it also calls into question the real potency of these devices. Medical treatments with important and dramatic benefits that have no meaningful side effects and extremely rare, and it is more common to find that the absence of adverse effects indicates the absence of any meaningful clinical effects at all.

References

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2.        Gaynor JS, Hagberg S, Gurfein BT. Veterinary applications of pulsed electromagnetic field therapy. Res Vet Sci. 2018;119:1-8. doi:10.1016/j.rvsc.2018.05.005

3.        Fini M, Giavaresi G, Carpi A, Nicolini A, Setti S, Giardino R. Effects of pulsed electromagnetic fields on articular hyaline cartilage: review of experimental and clinical studies. Biomed Pharmacother. 2005;59(7):388-394. doi:10.1016/j.biopha.2005.02.002

4.        Yuan J, Xin F, Jiang W. Underlying Signaling Pathways and Therapeutic Applications of Pulsed Electromagnetic Fields in Bone Repair. Cell Physiol Biochem. 2018;46(4):1581-1594. doi:10.1159/000489206

5.        Pilla AA. Nonthermal electromagnetic fields: From first messenger to therapeutic applications. Electromagn Biol Med. 2013;32(2):123-136. doi:10.3109/15368378.2013.776335

6.        Kwan R, Lu S, Choi H, Kloth L, Cheing G. Efficacy of Biophysical Energies on Healing of Diabetic Skin Wounds in Cell Studies and Animal Experimental Models: A Systematic Review. Int J Mol Sci. 2019;20(2):368. doi:10.3390/ijms20020368

7.        Crowe MJ, Sun Z-P, Battocletti JH, Macias MY, Pintar FA, Maiman DJ. Exposure to pulsed magnetic fields enhances motor recovery in cats after spinal cord injury. Spine (Phila Pa 1976). 2003;28(24):2660-2666. doi:10.1097/01.BRS.0000099385.46102.0D

8.        Inoue N, Ohnishi I, Chen D, Deitz LW, Schwardt JD, Chao EYS. Effect of pulsed electromagnetic fields (PEMF) on late-phase osteotomy gap healing in a canine tibial model. J Orthop Res. 2002;20(5):1106-1114. doi:10.1016/S0736-0266(02)00031-1

9.        Rawe IM, Lowenstein A, Barcelo CR, Genecov DG. Control of Postoperative Pain with a Wearable Continuously Operating Pulsed Radiofrequency Energy Device: A Preliminary Study. Aesthetic Plast Surg. 2012;36(2):458-463. doi:10.1007/s00266-011-9828-3

10.      Ae H, Pilla AA. Effects of Pulsed Electromagnetic Fields on Postoperative Pain: A Double-Blind Randomized Pilot Study in Breast Augmentation Patients. doi:10.1007/s00266-008-9169-z

11.      Cao L-Y, Jiang M-J, Yang S-P, Zhao L, Wang J-M. [Pulsed electromagnetic field therapy for the treatment of knee osteoarthritis: a systematic review]. Zhongguo Gu Shang. 2012;25(5):384-388. http://www.ncbi.nlm.nih.gov/pubmed/22870682. Accessed October 18, 2019.

12.      Chen L, Duan X, Xing F, et al. Effects of pulsed electromagnetic field therapy on pain, stiffness and physical function in patients with knee osteoarthritis: a systematic review and meta-analysis of randomized controlled trials. J Rehabil Med. October 2019:0. doi:10.2340/16501977-2613

13.      Ryang We S, Koog YH, Jeong K-I, Wi H. Effects of pulsed electromagnetic field on knee osteoarthritis: a systematic review. Rheumatology. 2013;52(5):815-824. doi:10.1093/rheumatology/kes063

14.      Hulme JM, Welch V, de Bie R, Judd M, Tugwell P, Tugwell P. Electromagnetic fields for the treatment of osteoarthritis. In: Hulme JM, ed. Cochrane Database of Systematic Reviews. Chichester, UK: John Wiley & Sons, Ltd; 2002:CD003523. doi:10.1002/14651858.CD003523

15.      Negm A, Lorbergs A, MacIntyre NJ. Efficacy of low frequency pulsed subsensory threshold electrical stimulation vs placebo on pain and physical function in people with knee osteoarthritis: systematic review with meta-analysis. Osteoarthr Cartil. 2013;21(9):1281-1289. doi:10.1016/j.joca.2013.06.015

16.      Bjordal JM, Johnson MI, Lopes-Martins RA, Bogen B, Chow R, Ljunggren AE. Short-term efficacy of physical interventions in osteoarthritic knee pain. A systematic review and meta-analysis of randomised placebo-controlled trials. BMC Musculoskelet Disord. 2007;8(1):51. doi:10.1186/1471-2474-8-51

17.      Griffin XL, Costa ML, Parsons N, Smith N. Electromagnetic field stimulation for treating delayed union or non-union of long bone fractures in adults. Cochrane Database Syst Rev. April 2011. doi:10.1002/14651858.CD008471.pub2

18.      Al-Jabri T, Tan JYQ, Tong GY, et al. The role of electrical stimulation in the management of avascular necrosis of the femoral head in adults: a systematic review. BMC Musculoskelet Disord. 2017;18(1):319. doi:10.1186/s12891-017-1663-5

19.      Walker NA, Denegar CR, Preische J. Low-intensity pulsed ultrasound and pulsed electromagnetic field in the treatment of tibial fractures: a systematic review. J Athl Train. 42(4):530-535. http://www.ncbi.nlm.nih.gov/pubmed/18174942. Accessed October 18, 2019.

20.      Hannemann PFW, Mommers EHH, Schots JPM, Brink PRG, Poeze M. The effects of low-intensity pulsed ultrasound and pulsed electromagnetic fields bone growth stimulation in acute fractures: a systematic review and meta-analysis of randomized controlled trials. Arch Orthop Trauma Surg. 2014;134(8):1093-1106. doi:10.1007/s00402-014-2014-8

21.      Page MJ, Green S, Kramer S, Johnston R V, McBain B, Buchbinder R. Electrotherapy modalities for adhesive capsulitis (frozen shoulder). Cochrane Database Syst Rev. 2014;(10):CD011324. doi:10.1002/14651858.CD011324

22.      Page MJ, Green S, Mrocki MA, et al. Electrotherapy modalities for rotator cuff disease. Cochrane Database Syst Rev. 2016;(6):CD012225. doi:10.1002/14651858.CD012225

23.      Hug K, Röösli M. Therapeutic effects of whole-body devices applying pulsed electromagnetic fields (PEMF): A systematic literature review. Bioelectromagnetics. 2012;33(2):95-105. doi:10.1002/bem.20703

24.      Gaynor JS, Hagberg S, Gurfein BT. Veterinary applications of pulsed electromagnetic field therapy. Res Vet Sci. 2018;119:1-8. doi:10.1016/j.rvsc.2018.05.005

25.      Shafford HL, Hellyer PW, Crump KT, Wagner AE, Mama KR, Gaynor JS. Use of a pulsed electromagnetic field for treatment of post–operative pain in dogs: a pilot study. Vet Anaesth Analg. 2002;29(1):43-48. doi:10.1046/j.1467-2987.2001.00072.x

26.      Zidan N, Fenn J, Griffith E, et al. The Effect of Electromagnetic Fields on Post-Operative Pain and Locomotor Recovery in Dogs with Acute, Severe Thoracolumbar Intervertebral Disc Extrusion: A Randomized Placebo-Controlled, Prospective Clinical Trial. J Neurotrauma. 2018;35(15):1726-1736. doi:10.1089/neu.2017.5485

27.      Heneghan C, Goldacre B, Mahtani KR. Why clinical trial outcomes fail to translate into benefits for patients. Trials. 2017;18(1):122. doi:10.1186/s13063-017-1870-2

28.      Alvarez LX, McCue J, Lam NK, Askin G, Fox PR. Effect of Targeted Pulsed Electromagnetic Field Therapy on Canine Postoperative Hemilaminectomy: A Double-Blind, Randomized, Placebo-Controlled Clinical Trial. J Am Anim Hosp Assoc. 2019;55(2):83-91. doi:10.5326/JAAHA-MS-6798

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