The effects of pulsed magnetic fields of the type used in the stimulation of bone fracture healing.

The main impression received by us whilst writing this review is the scarcity of technical data in the clinical studies and the total absence of controlled trials. The spatial patterns of the stimulus have not been measured, and no experiments have proved that there is an effect from the magnetic field itself. Control experiments using dummy stimulators must be done, since the orthopaedic management of the stimulated patients is different from conventional management and this may have significant and beneficial clinical effects. There is no clinical study at present which shows a direct therapeutic benefit due solely to the application of the magnetic field component of the overall treatment regime. The in vivo animal experiments suggest that there may be effects due to the magnetic fields used but results are very scarce compared with the accumulated data from direct current stimulation. In vitro studies are far removed from the clinical situation, but could nonetheless prove useful if the opportunity of controlling the stimulus can be taken. In the majority of experiments, approximately spatially uniform magnetic fields have been applied, but temporal changes in the magnetic field and both spatial and temporal variation in electric field lead to non-uniform stimulation. Little attempt has been made to assess or control the induced fields by defining the system geometry. Hence it is still unknown whether effects are due to the magnetic field, the induced extracellular electric field or to fields induced at cellular level by regions of different conductivity. In conclusion, we believe that, unlike steady current work, the pulsed magnetic field treatment of fractures has not been sufficiently well investigated and, although some of the animal experiments suggest significant effects, the benefit of using magnetic fields in the clinical management of non-union and delayed union has still to be proven. Double blind trials are essential and, if these do prove that there is a definite effect of the fields, the mechanisms must then be studied using a combination of theoretical, in vivo and in vitro techniques.