Mechanical Stress on Suspended Cortical Bone Sample by Low Frequency Magnetic Field

Low-frequency (LF), low-amplitude alternating current (ac) magnetic fields are approved by the U.S. Food and Drug Administration as an adjunct to the orthopedic surgery procedure (spinal fusion surgery) and for the treatment of selected bone healing complications (fracture non-union). The biological effects are understood to rely on a contact-less induction of electric currents in the electrically conducting compartments of the bone. Here, we investigate another potential mechanism of the LF magnetic field effect on bone by measuring mechanical force on bone due to its diamagnetic susceptibility. The biological rationale is the bone's exquisite sensitivity to local mechanical stresses that determine its structure and physiology. Thus, the periodic magnetic microstress effects on bone over an extended period of the typical clinical LF magnetic field application (hours daily over a period of a few months) could contribute to bone regeneration. The aim was to demonstrate the diamagnetic field effect on thin, human cortical bone slice preparations (from commercial tissue repository) suspended in the vicinity of a rotating cylindrical, diametrically magnetized permanent magnet. The data provide a basis for the calculation of diamagnetic microstresses generated by the clinical LF magnetic field stimulation devices and their significance as potential contributing factors to the biological mechanism of action of LF ac magnetic fields.