Electrical effects in bone

This paper presents a review of the work carried out on the electromechanical properties of bone over the the past three decades. Research in this field has established the piezoelectric nature of bone and identified collagen as the generating source in dry bone. Some of the characteristics of the strain generated potential (SGP) signal from dry and hydrated bone were found to be unaccountable in terms of a classical piezoelectric theory. Modifications of the theory were suggested and in the case of fully hydrated bone, a new mechanism (streaming potential) has emerged. The paper also reports on recent developments in the field and presents results from microstructural (osteonic) studies and from fluid-filled bone. The review indicates the need for actual in vivo work because most of the reported data were obtained, in the last decade, from in vitro work and were considered valid in vivo. Modelling of the mechanism which produces the SGP has been considered to explain the characteristics of these potentials. A representative model recently developed by the present authors and co-workers is reported. This model relates the generated potential to reorientation of spontaneous dipoles and differentiates between the generated and recorded signal, thus identifying effects from the measuring circuitry. The clinical aspects of electricity of bone in assisting fracture healing and the different techniques employed are mentioned briefly. Emphasis on new techniques of piezoelectric implants and their future development is also reported.