Comparison of asymmetrical and symmetrical pulse waveforms in electromagnetic stimulation.

Pulsing electromagnetic field (PEMF) stimulation is a noninvasive therapeutic modality that has been successfully used to stimulate healing of surgically resistant human bone fracture nonunions. Asymmetry of the stimulus pulse waveform was thought to be necessary for therapeutic effectiveness, but asymmetrical pulses require significant electrical energy that constrains clinical delivery systems to suboptimal designs. Development of low-energy consuming stimuli will enable clinical device improvements and may provide additional information about the interaction of electromagnetic fields with tissues. The objectives of this study were (a) to determine if asymmetry of the stimulus pulse waveform is needed for efficacy and (b) to determine if symmetrical pulse waveform stimuli also can produce a beneficial therapeutic response. The rabbit fibular osteotomy model was used to answer these questions and to identify which components of the clinically used asymmetrical PEMF produce the therapeutic response. The results suggest that asymmetry is not necessary and that a narrow pulse width, symmetrical square wave signal can also stimulate stiffness increases in this model. The data also suggest that the high-amplitude, narrow-pulse portion of the asymmetrical PEMF is the principal component of the signal pulse that is responsible for the clinical therapeutic effect.