Pulsed Magnetic Fields
The following summary is from a paper by DH Trock, AJ Bollet and R Markoll. The Effect of Pulsed Electromagnetic Fields in the Treatment of osteoarthritis of the Knee and Cervical Spine. Report of Randomised, Double Blind, Placebo Controlled Trials. Journal of Rheumatology 1994; 21 (10): 1903-1911:
The theory and development of pulsed magnetic fields
Pulsed electromagnetic fields (PEMF) have been used widely to treat non-healing fractures and related problems in bone healing since approval by the US Food and Drug Administration (FDA) in 1979, with a success rate averaging 70-80% in a wide variety of centres in several countries l, 2.
The original basis for the trial of this form of therapy was the observation that physical stress on bone causes the appearance of tiny electric currents (piezoelectric potentials) that are thought to be the mechanism of transduction of the physical stresses into a signal that promotes bone formation. Direct electric field stimulation was successful in treatment 0Â of non-union3, but problems with the invasive placement of electrodes led to the use of PEMF, with the expectation that these magnetic impulses would generate small induced currents (Faraday currents) in the highly conductive extracellular fluid, mimicking the piezoelectric potentials l, 2.
The piezoelectric potentials, originally thought to be due to phenomena occurring at the surface of crystals in the bone, have been shown to be due primarily to movement of fluid containing electrolytes in channels of the bone containing organic constituents with fixed charges, generating what are called ”streaming potentials”4. Studies of electrical phenomena in cartilage have demonstrated a mechanical-electrical transduction mechanism that resembles those described in bone, appearing when cartilage is mechanically compressed, causing movement of fluid and electrolytes, leaving unneutralised negative charges in the proteoglycans and collagen in the cartilage matrix 5, 6. These streaming potentials apparently serve a purpose in cartilage similar to that in bone, transducing mechanical stress to an electrical (or electromagnetic) phenomenon capable of stimulating chondrocyte synthesis of matrix components 7-9.
Richard Markoll then developed a means of delivering the PEMF to the human body and refined the constellation of variables (frequencies, pulse rates, intensities, treatment intervals, etc) by applying the fields to about 1,000 patients in Europe to determine the most effective method of treating patients with arthritis and related sports-type injuries10. The current paper gives the result of a randomised trial using that group of frequencies.
REFERENCES
1. Bassett CAL, Pilla AA, Pawluk RJ: A non-operative salvage of surgically resistant pseudarthrosis and non-unions by pulsing electromagnetic fields. A preliminary report. Clin Orthop 1977;124: 128-43.
2. Bassett CAL, Mitchell SN, Gaston SR: Pulsing electromagnetic field treatment in ununited fractures and failed arthrodeses. JAMA 1982:247:623-8.
3. Brighton CT, Pollack SR: Treatment of recalcitrant non-union with a capacitively coupled electrical field. A preliminary report. J Bone Joint Surg 1985;67A:577-85.
4. Guzelsu N, Walsh WR: Streaming potential in intact wet bone. J Biomech 1990:23: 673-85.
5. Frank EH, Grodzinsky AI: Cartilage electromechanics. 1. Electrokinetic transduction and the effects of electrolyte pH and ionic strength. J Biomech /987;20:615-27.
6. Frank EH, Grodzinsky AI: Cartilage electromechanics. 11. A continuum model of cartilage electrokinetics and correlation with experiments. J Biomech 1987;20:629-39.
7. Parkkinen JJ, Mikko IL, Helminen HI, Tammi M: Local stimulation of proteoglycan synthesis in articular cartilage explants by dynamic compression in vitro. J Orthop Res 1982:10:610-20.
8. Sah RLY, Kim Y, Doong IH, Grodzinsky AI, Plass AHK, Sandy ID: Biosynthetic response of cartilage explants to dynamic compression. J Orthop Res 1989:7:619-36.
9. Sah RLY, Grodzinsky AI, Plaas AHK, Sandy ID: Effects of static and dynamic compression on matrix metabolism in cartilage explants. In: Kuettner KE, Schleyerbach R, Peyron IG, Haseall VC, eds. Articular Cartilage and Osteoarthritis. New York: Raven Press, 1992:373-92.
10. Trock DH, Bollet AJ, Dyer RH Jr, Fielding LP, Miner WK, Markoll R: A double blind trial of the clinical effects of pulsed electromagnetic fields in osteoarthritis. J Rheumatol 1993;20:456-60.
Frequencies and Treatment duration used
A double-blind controlled trial of PEMF for persistent rotator cuff tendonitis was reported by A. Binder, G Parr, B Hazleman & S Fitton-Jackson in Lancet (31 March) 1984: 695-8. In this trial a single ovoid coil (12.2cm X 13.2 cm) was held against the affected shoulder with padding secured by two velcro straps and energised for 5-9 hours a day, with each treatment lasting at least 1 hour. This lasted 4 weeks after which the control group was given an operative coil and both groups continued for another 4 weeks.
Coils (consisting of 50 turns) were energised from pulse generators set at a frequency of 73 Hz. The current and field were not stated.
More than 70% of patients improved on PEMF therapy.
A second randomised double-blind controlled trial of PEMF for osteoarthritis was reported by Trock et al in the Journal of Rheumatology 1993; 20 (3): 456-460. In this trial the coils were energised from pulse generators set at a frequency below 30 Hz with the pulsed magnetic field varying and averaging 10-20 gauss at a coil current of 2 amperes supplied from 120V AC. Pulse phase duration was 67ms, including 15 micropulses with a pause duration of 0.1 s. Treatments were given for 30 minutes. 3-5 sessions were given each week for a total of 18 treatments, extending over about 1 month.
A third randomised double-blind controlled trial of PEMF for osteoarthritis was reported by Trock et al in the Journal of Rheumatology 1994; 21 (10): 1903-1911. In this trial the same coils were used as in the second trial and were energised from pulse generators. However for this trial the field was energised in a step-wise fashion as follows:
5 Hz, 10-15 gauss for 10 minutes; 10 Hz, 15-25 gauss for 10 minutes; then 12 Hz, 15-25 Hz for 10 minutes. The coil current of up to 2 amperes was again supplied from 120V AC.
The waveform was quasirectangular with abruptly rising and deteriorating waveform, with a pulse burst duty cycle of 0.8 sec. The number of pulse/bursts is determined by frequency. The maximum was 20. The coil used for knee treatment was 11″ ID and that for the cervical spine was 22″ ID.
Treatments were given for 30 minutes. 3-5 sessions were given each week for a total of 18 treatments, extending over about 1 month.
The treatment resulted in an improvement in pain by an average of 37% and in active daily living by 35%.
The authors refer to several mechanisms to account of the healing effect, including the movement of calcium and other ions across cell membranes and the stimulation of DNA transcription with increased protein synthesis (in addition to the effects listed earlier).
The latest device, the Quantron Resonance System, is a further development of this approach. It uses even weaker fields for shorter periods. Standard treatment involves two sessions each day, each of 8 minutes with fields of typically 100 milligauss. The coils are energised by means of alternating current with a saw-tooth pattern whose frequency is about 30Hz. The saw-tooth pattern is generated by the addition of several higher frequency pulses at about 200 Hz. Because the saw-tooth waveform is polarised (ie more energy is provided during the positive half cycle than during the negative half cycle) the field is reversed every two minutes to balance the effect of the field.
This device consists of a “mat” with length ~2 metres and width ~1 metre with three pairs of coils embedded in it: The first pair (1 & 2) under the shoulder region, the second pair (3 & 4) under the buttocks region and the third pair (5 & 6) under the calf/ankle region. This is connected to a control box. Ten different programs are selectable depending on the type of problem to be treated.
The magnetic field strength measured at various locations directly above the “mat” for the different programs are shown in Figures 1 and 2 below. The variation of the field produced is shown in Figures 1(a) and 1(b). The layout of the six coils is shown in Figure 2.
Pulsating Magnetic Field – Quantron Resonance System
The following magnetic fields were measured at locations above the six coils. Readings were taken just above the centre of each coil and averaged over the two coils of a pair:
|
Magnetic |
|||
| Program/Switch No. | Above coils 1,2 | Above coils 3,4 | Above coils 5,6 |
|
1 |
0-5 |
0-18 |
0-27 |
|
2 |
0-16 |
0-42 |
0-57 |
|
3 |
0-28 |
0-55 |
0-85 |
|
4 |
0-33 |
0-75 |
0-100 |
|
5 |
0-44 |
0-85 |
0-116 |
|
6 |
0-60 |
0-90 |
0-109 |
|
7 |
0-63 |
0-110 |
0-125 |
|
8 |
0-75 |
0-118 |
0-130 |
|
9 |
0-79 |
0-110 |
0-135 |
|
10 |
0-85 |
0-125 |
0-140 |
The fluctuation of the magnetic field was such that it rose and fell in intensity four times every 12 seconds (as shown in Figure 1 below). This was repeated 10 times for each interval, ie for 120 seconds (2 minutes)
The same series of fluctuations was again repeated for another 2 minutes, presumably with reversed polarity as indicated by the left light on the control box.
The first series was repeated again for 2 minutes with the initial polarity.
Finally the second series was repeated with the reversed polarity.
The operation then switched off (after a total of 8 minutes).
Figure 2 shows the magnetic field intensity at other locations around the coils.
(a)
+ +
_ _
(b)
Figure 1. Variation in magnetic field intensity over time
The distribution of the magnetic fields around the various locations were measured during the program activated by Switch 6 for which the average field for the coils were 1,2: 70; 3,4: 95; 5,6: 120.
