Terapia electromagnetica

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ELECTROMAGNETIC FIELDS
AND MAGNETS
Investigational Treatment for Musculoskeletal
Disorders

David H. Trock, MD

In technology, men know that all the wishes and
prayers in the world will not change the nature of a
grain of sand.

AYN RAND, The Voice of Reason, Ayn Rand: Essays in
Objectivist Thought

Our generation has seen unprecedented advances in electromagnetic wave technologysuch as the microwave oven, the cellular telephone, and the magnetic resonance imager, each a creative exploitation of an invisible electromagnetic signal that was initially met with rigid skepticism. The modern bone growth stimulators that employ pulsed electromagnetic fields (PEMFs) have been available for 20 years, although they are just becoming a standard of care for delayed union fracture. Afoundation of in vitro and clinical studies has demonstrated that electric and magnetic energy may favorably affect disorders of dense connective tissue. These signals have become a fertile area of research in orthopedics and rheumatology.

¬¬¬¬¬¬
From the Yale University School of Medicine, New Haven; and the Section of Rheumatology Danbury
Hospital, Danbury, Connecticut

RHEUMATICDISEASE CLINICS OF NORTH AMERICA

VOLUME 26 NUMBER 1 FEBRUARY 2000 51


52 TROCK

BACKGROUND

The first concept of electricity was known when a static charge resulted from rubbing fur on amber; hence, the Greek name for amber, elektron, was adapted.

Accidentally, in 1820, Oersted noticed the relationship between magnetism and electricity when his compass needle was deflected bythe current of a nearby wire. Also in 1820, Ampere developed the electromagnet and postulated that tiny electric currents circulate within the molecules of magnetic material. In 1832, Michael Faraday confirmed that electric charges could be transferred by electromagnetism, later called electromagnetic induction. Approximately 150 years later, Faraday currents would become relevant in themicroenvironment of dense connective tissue, the basis of modern bone growth stimulators and other new electromagnetic devices that affect biological tissue.

In 1865, James Clerk Maxwell prophetically stated that when magnetic lines of force move sidewise, their movement results in an electric field at right angles to the magnetic lines, that is, if a magnet were pushed through a coil of wire, it couldstart an electric current going through the wire. The theory of Maxwell states that an electric field is always accompanied by a magnetic field and, conversely, a variable (i.e., pulsed) magnetic field is always accompanied by an electric field.

To explain the effect of electromagnetism on growth and repair of bone and cartilage, three physical concepts, including Wolff's Law, thepiezoelectric effect, and the concept of streaming potentials, must first be discussed.

Wolff's Law of reorganization states that the balance between bone formation and resorption is largely controlled by mechanical strain. When a long bone is compressed, bone formation occurs at the periosteal surface of the compressed side, whereas bone resorption occurs on the side of tension. It is no coincidence thata negative charge occurs on the compressed side, where bone formation occurs (Fig. 1). Indeed, the external application of such a current also results in bone growth. Wolff's Law has been explained by the electric transduction of mechanical deformation, which promotes bone differentiation.39 In dense connective tissue, the electric potential immediately generated by mechanical stress is thepiezoelectric effect, first described in 1957 by Fukada and Yasuda,16 which states that if you deform a crystalline structure (such as bone), electrons migrate to the compressed side, creating a negative potential that quickly disappears if the compression is maintained. . As compression is released, however, an equal and opposite positive pulse appears as the electrons rebound back into place....
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