Low-frequency electromagnetic radiation has been used for centuries since the time of Paracelsus to control pain and treat a number of disorders, but proper scientific investigations into its putative properties have been conducted only over the last decades. Broadly speaking, there are two main types of treatment that exploit electromagnetic radiation: static magnetic fields and low-frequency pulsed electromagnetic fields (PEMF). PEMF is the most popular type of treatment and employs unipolar or bipolar magnets. Unipolar magnet therapy uses several discrete magnets aligned with the same magnetic pole towards the skin; usually the pole facing the patient is the negative one, hence the term unipolar. In contrast, bipolar magnet therapy uses magnetic material arranged in an alternating pattern, so that both positive and negative poles face the skin. Experimental observations have documented a significant impact of PEMF on a number of biological processes. In particular, PEMF have been demonstrated to enhance fibroblast, chondrocyte and osteoblast metabolism, as well as to modulate the effects of hormones and neurotransmitters on the receptors of different cell types. However, despite the wealth of data on the in vitro effects of PEMF, it is unclear to what extent such mechanisms of action may have clinical relevance. Beneficial effects following PEMF treatment have been claimed in a whole array of different conditions. More specifically, PEMF have been used for the treatment of avascular necrosis of the hips, Legg-Perthes’ disease, osteoporosis, tendinitis, chronic pain due to musculoskeletal disorders and delayed bone fractures. So far, the latter is the only indication that has received approval by the Food and Drug Administration[17]. Conclusive proof for the clinical efficacy of PEMF beyond the licensed indication is still lacking, and the American College of Rheumatology currently does not recommend PEMF treatment for osteoarthritis of the hips and knees because of inadequate scientific documentation. Nevertheless, PEMF therapy continues to enjoy a vast popularity, which has translated into worldwide sales of $5 billion.
Pulsed Electromagnetic Field Therapy, PEMT. How does it work?
Lecture abstract Dr. D. Laycock, Ph.D. Med. Eng. MBES, MIPEM, B.Ed.
All living cells within the body possess potentials between the inner and outer membrane of the cell, which, under normal healthy circumstances, are fixed. Different cells, e.g. Muscle cells and Nerve cells, have different potentials of about -70 mV respectively. When cells are damaged, these potentials change such that the balance across the membrane changes, causing the attraction of positive sodium ions into the cell and negative trace elements and proteins out of the cell. The net result is that liquid is attracted into the interstitial area and swelling or oedema ensues. The application of pulsed magnetic fields has, through research findings, been shown to help the body to restore normal potentials at an accelerated rate, thus aiding the healing of most wounds and reducing swelling faster. The most effective frequencies found by researchers so far, are very low frequency pulses of a 50 Hz base. These, if gradually increased to 25 pulses per second for time periods of 600 seconds (10 minutes), condition the damaged tissue to aid the natural healing process.
Pain reduction is another area in which pulsed electromagnetic therapy has been shown to be very effective. Pain signals are transmitted along nerve cells to pre-synaptic terminals. At these terminals, channels in the cell alter due to a movement of ions. The membrane potential changes, causing the release of a chemical transmitter from a synaptic vesicle contained within the membrane. The pain signal is chemically transferred across the synaptic gap to chemical receptors on the post-synaptic nerve cell. This all happens in about 1/2000th of a second, as the synaptic gap is only 20 to 50 nm wide. As the pain signal, in chemical form, approaches the post-synaptic cell, the membrane changes and the signal is transferred. If we look at the voltages across the synaptic membrane then, under no pain conditions, the level is about -70 mV. When the pain signal approaches, the membrane potential increases to approximately +30 mV, allowing a sodium flow. This in turn triggers the synaptic vesicle to release the chemical transmitter and so transfer the pain signal across the synaptic gap or cleft. After the transmission, the voltage reduces back to its normal quiescent level until the next pain signal arrives.
The application of pulsed magnetism to painful sites causes the membrane to be lowered to a hyper-polarization level of about -90 mV. When a pain signal is detected, the voltage must now be raised to a relatively higher level in order to fire the synaptic vesicles. Since the average change of potential required to reach the trigger voltage of nearly +30 mV is +100 mV, the required change is too great and only +10 mV is attained. This voltage is generally too low to cause the synaptic vesicle to release the chemical transmitter and hence the pain signal is blocked. The most effective frequencies that have been observed from research in order to cause the above changes to membrane potentials, are a base frequency of around 100 Hz and pulse rate settings of between 5 and 25 Hz