Clinically the effects of PEMF in the treatment of osteoarthritis have been shown to include decreased pain and increased functional capacity, as well as decreased pain on passive motion and joint tenderness. There are many possible mechanisms which could be underlying these clinical effects, since PEMF have been shown to have several biological effects in laboratory experiments which could be relevant to the pathogenesis of osteoarthritis. Therefore, in this document, we will first summarize known relevant biological effects; second, we will mention known bioelectric phenomena which occur in dense connective tissues which are relevant to the normal physiology of joint tissues, and third, we will put these points in the perspective of possible reasons for the clinical benefits of PEMF observed in patients with osteoarthritis.

I. Relevant biological effects of electrical fields and PEMF

Direct electrical stimulation has been shown to increase cartilage repair (induced epicondylar defects) in rabbits as well as increasing repair of experimental tendon defects (using chick tendon explants maintained in tissue culture media). The first studies of this physical modality demonstrated increased bone formation. PEMF have been used to induce electrical currents in tissues, producing similar results. This has been most extensively studied for bone; the device generating such pulses was approved by the FDA in 1979 as the "Bone Growth Stimulator."

Among the tissues which are responsive to PEMF in the laboratory, the dense connective tissues have been studied most extensively. Fibroblasts from tendons of various species, fibroblasts from skin, chondrocytes from epiphyseal and articular cartilage of several species (especially chick, rabbit and bovine) and osteocytes have all been shown to increase collagen and/or glycosaminoglycan synthesis. Other tissues have been shown to increase protein synthesis, as well as mRNA synthesis (the precursor step which leads to protein synthesis). In each instance the nature of the proteins made by a given cell line was unchanged; whatever they were making before, they made more of it when stimulated by PEMF This statement is most important regarding collagen; specifically, chondrocytes, which make type II collagen, made more type II, which make type I collagen made more of that type of collagen.