Optimization of bone formation at cathodes

Abstract

A method including applying varying signals to a first electrode at the tissue site and a second electrode remote from the tissue site and monitoring the results to determine a distinctive transition in the current-voltage characteristics of the electrode pair. A signal is then selected and applied to the electrodes to operate beyond the transition. Periodically, a varying signal is applied to the electrodes and the monitoring process reperformed to determine a new transition and an appropriate signal is selected to operate beyond the transition.

What is claimed: 
     
       1. A method of stimulating osteogenesis or other tissue repair processes at a tissue site within a living body comprising: locating a first electrode at said tissue site within the living body;   coupling a second electrode to said living body remote from said tissue site;   applying various signal levels to said first and second electrodes and monitoring the resulting current flows between the electrodes to determine a current-voltage characteristic of said electrodes;   identifying a voltage signal level at which a distinctive transition occurs in said current-voltage characteristic; and   applying a voltage signal level to said electrodes to cause the electrodes to operate at a point on the current-voltage characteristic which is just beyond the point at which said transition occurs.   
     
     
       2. A method according to claim 1, including periodically applying said signal levels to said electrodes and monitoring the resulting current flow between the electrodes to re-determine the location along said current voltage characteristic of said transition point, and modifying said voltage signal applied to said electrodes to cause the electrodes to operate just beyond said newly determined transition point. 
     
     
       3. A method according to claim 1, wherein said electrodes are operated at a current level between 10 and 50 microamperes. 
     
     
       4. A method according to claim 1, wherein said first electrode is a cathode and said second electrode is an anode. 
     
     
       5. A method according to claim 1, wherein said second electrode is percutaneous. 
     
     
       6. A method according to claim 1, wherein said second electrode is fully implanted. 
     
     
       7. A method according to claim 1, wherein said second electrode is located transcutaneous. 
     
     
       8. A method according to claim 1, including: locating a plurality of first electrodes at said tissue site;   applying said signal levels to said plurality of first electrodes and said second electrodes and monitoring the resulting current flows to determine the voltage signal level associated with said distinctive transition for each of said first electrodes; and   applying a voltage signal level to each of said first electrodes to cause each of said electrodes to operate just beyond its respective transition point.   
     
     
       9. A method according to claim 8, wherein each of first electrodes includes a plurality of conducting ports at said tissue site; and   wherein said voltage signal level is applied to said electrodes such that each conducting port carries a current between 10 and 50 microamps.   
     
     
       10. A method according to claim 1, wherein: said first electrode includes a plurality of conducting ports at said tissue site; and   wherein said signal level is applied to said electrodes such that each conducting port carries a current between 10 and 50 microamps.   
     
     
       11. An apparatus for stimulating osteogenesis or other tissue repair processes at a tissue site in living tissue comprising: a first electrode adapted to be positioned at said tissue site within the living body;   a second electrode adapted to be positioned in electrical contact with said living body;   signal means connected to said first and second electrodes for applying various voltage signal levels to said first and second electrodes and for monitoring resulting current flows between the electrodes to determine a current-voltage characteristic of said electrodes, and for applying a voltage signal level to the electrodes to cause the electrodes to operate at a point along the current-voltage characteristic which is just beyond the point at which a distinctive transition in said characteristic occurs.   
     
     
       12. An apparatus according to claim 11, wherein said signal means further comprises: monitor means for monitoring said current-voltage characteristic and for recognizing changes in the point at which the distinctive transition occurs;   control means for causing said signal means to maintain the operation of the electrodes at a point which is just beyond the point at which the changed transition occurs.   
     
     
       13. An apparatus according to claim 12, wherein said monitor means includes timing means for periodically causing said monitor means to recognize changes in the point at which the transition occurs, and for causing said signal means to maintain the operation of the electrodes at a point which is just beyond the point at which the changed transition occurs. 
     
     
       14. An apparatus according to claim 11, wherein said signal means provides a current of between 10 to 50 microamperes. 
     
     
       15. An apparatus according to claim 11, wherein said first electrode is a cathode and said second electrode is an anode. 
     
     
       16. An apparatus according to claim 11, wherein said first electrode is a percutaneous electrode and said second electrode is a transcutaneous electrode. 
     
     
       17. An apparatus according to claim 11, wherein said first electrode is a percutaneous electrode and said second electrode is a percutaneous electrode. 
     
     
       18. An apparatus according to claim 11, wherein said first and second electrodes are totally implantable electrodes. 
     
     
       19. An apparatus according to claim 18, wherein said signal means is totally implantable. 
     
     
       20. An apparatus according to claim 11, further comprising a plurality of first electrodes adapted to be positioned at said tissue site; and   wherein said signal means applies a voltage signal level to each of said first electrodes to cause the electrodes to operate at a point along its respective current-voltage characteristic which is just beyond its distinctive transition point. .Iadd.   
     
     
       21.  A method of dynamically determining an operating point for stimulation of osteogenesis or other tissue repair processes at a tissue site within a living body comprising: locating a first electrode at said tissue site within the living body;   coupling a second electrode to said living body remote from said tissue site;   applying various signal levels to said first and second electrodes and monitoring the resulting current flows between the electrodes to determine a current-voltage characteristic of said electrodes;   identifying a voltage signal level at which a distinctive transition occurs in said current-voltage characteristic; and   periodically applying said signal levels to said electrodes and monitoring the resulting current flow between the electrodes to re-determine the location along said current voltage characteristic of said transition point..Iaddend. .Iadd.   
     
     
       22.  A method of stimulating osteogenesis or other tissue repair processes at a tissue site within a living body comprising: locating a first electrode at said tissue site within the living body;   coupling a second electrode to said living body remote from said tissue site;   applying various signal levels to said first and second electrodes and monitoring the resulting current flows between the electrodes to determine a current-voltage characteristic of said electrodes;   identifying a voltage signal level at which a distinctive transition occurs in said current-voltage characteristic;   applying a voltage signal level to said electrodes to cause the electrodes to operate about a point on the current-voltage characteristic at which said transition occurs;   periodically applying said signal levels to said electrodes and monitoring the resulting current flow between the electrodes to re-determine the location along said current voltage characteristic of said transition point; and   modifying said voltage signal applied to said electrodes to cause the electrodes to operate about said newly determined transition point..Iaddend. .Iadd.   
     
     
       23.  An apparatus for dynamically determining an operating point for stimulation of osteogenesis or other tissue repair processes at a tissue site in living tissue comprising: a first electrode adapted to be positioned at said tissue site within the living body;   a second electrode adapted to be positioned in electrical contact with said living body;   signal means connected to said first and second electrodes for applying various voltage signal levels to said first and second electrodes and for monitoring resulting current flows between the electrodes to determine a current-voltage characteristic of said electrodes, said signal means including monitor means for monitoring said current-voltage characteristic and for recognizing changes in the point at which the distinctive transition occurs..Iaddend. .Iadd.   
     
     
       24.  An apparatus for stimulating osteogenesis or other tissue repair processes at a tissue site in living tissue comprising: a first electrode adapted to be positioned at said tissue site within the living body;   a second electrode adapted to be positioned in electrical contact with said living body; and   signal means connected to said first and second electrodes for applying various voltage signal levels to said first and second electrodes and for monitoring resulting current flows between the electrodes to determine a current-voltage characteristic of said electrodes, and for applying a voltage signal level to the electrodes to cause the electrodes to operated about a point along the current-voltage characteristic at which a distinctive transition in said characteristic occurs, said signal means including monitor means for monitoring said current-voltage characteristic and for recognizing changes in the point at which the distinctive transition occurs, and control means for causing said signal means to maintain the operation of the electrodes about the point at which the changed transition occurs..Iaddend.