Electro-mechanical Factors Regulating Bone Architecture 



85 



osteogenesis, while regions of positivlty may be characterized by osteolysis. It was 

 interesting, therefore, to observe the effects on living bone of artificially induced, 

 continuous, direct currents (Bassett et al., 1964). These experiments involved the 



Fig. 4. Scheme of possible effects of stress-generated potentials in aiding the ebb and flow of charged molecules 



and ions about an osteocyte. Note pulse pattern — it is unequally biphasic since deforming force removed 



before signal had decayed 



implantation of small, active and inactive-control, silicone-coated battery packs in 

 canine thighs, so that two platinum electrodes projected through the lateral mid- 

 femoral cortex into the medullary canal. The active packs delivered currents ranging 

 from 0.7 to 3.4 // amps, in vivo. Control specimens developed small masses of new, 

 reactive bone around each inactive electrode where it projected into the marrow space. 

 When 2 to 3 // amps, were flowing, the mass of newly formed bone was increased 

 markedly about the cathode, but not the anode. The larger bone mass near the nega- 

 tive pole seemed to result from an increased cellularity which was most marked at 

 14 days after operation and which decreased by 21 days. From the pattern of 

 deposition, both at the cathodes and anodes, it was unlikely that the results could 

 be ascribed to an electrophoretic action of the current on precursors of osseous 

 matrix. 



There was no evidence that an anticipated increase in osteoclastic activity had 

 occurred in the anodal region. In seeking an explanation for this result, it is impor- 

 tant to note that the animals were active during the post-operative period and 

 developed, most probably, significant stress concentrations in the region of both holes 

 in the cortex. Such stress concentrations could result in increased electrical activity 

 which might have overridden the local effects of the anode. On the other hand, 

 osteoclasis may not be related to anodal activity. 



This experiment, employing unphysiologic, continuous, direct currents, demon- 

 strates that osteogenesis is increased in regions of electronegativity. Although sug- 

 gestive, it does not establish conclusively a link between stress-induced potential and 

 the activity of bone cells. For example, all of the evidence so far indicates that the 

 intermittant electrical signals measured on bone surfaces usually are biphasic, al- 



