Theoretical model for investigating the magnetic and electric fields produced during pulsed magnetic field therapy for nonunion of the tibia

Pulsed magnetic field therapy for tibial nonunion has become an established orthopaedic procedure in many centres. The field is generated by passing pulses of current through coils positioned one each side of the limb but the magnitudes of the magnetic and induced electric fields produced are not usually known. The paper describes a method of calculating the fields that gives good agreement between theory and measurement. An improved model of a bone in a limb has been developed and this model predicts that the peak induced electric field close to the fracture site is between 0·03 and 0·6 Vm⁻¹, depending on which of the many clinically tested coil systems is used. The effect of changing geometry and the contribution of the outer surface of the limb are examined, and the implications for future experimental work are discussed.